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Sample records for affecting actin dynamics

  1. Actin dynamics shape microglia effector functions.

    Science.gov (United States)

    Uhlemann, Ria; Gertz, Karen; Boehmerle, Wolfgang; Schwarz, Tobias; Nolte, Christiane; Freyer, Dorette; Kettenmann, Helmut; Endres, Matthias; Kronenberg, Golo

    2016-06-01

    Impaired actin filament dynamics have been associated with cellular senescence. Microglia, the resident immune cells of the brain, are emerging as a central pathophysiological player in neurodegeneration. Microglia activation, which ranges on a continuum between classical and alternative, may be of critical importance to brain disease. Using genetic and pharmacological manipulations, we studied the effects of alterations in actin dynamics on microglia effector functions. Disruption of actin dynamics did not affect transcription of genes involved in the LPS-triggered classical inflammatory response. By contrast, in consequence of impaired nuclear translocation of phospho-STAT6, genes involved in IL-4 induced alternative activation were strongly downregulated. Functionally, impaired actin dynamics resulted in reduced NO secretion and reduced release of TNFalpha and IL-6 from LPS-stimulated microglia and of IGF-1 from IL-4 stimulated microglia. However, pathological stabilization of the actin cytoskeleton increased LPS-induced release of IL-1beta and IL-18, which belong to an unconventional secretory pathway. Reduced NO release was associated with decreased cytoplasmic iNOS protein expression and decreased intracellular arginine uptake. Furthermore, disruption of actin dynamics resulted in reduced microglia migration, proliferation and phagocytosis. Finally, baseline and ATP-induced [Ca(2+)]int levels were significantly increased in microglia lacking gelsolin, a key actin-severing protein. Together, the dynamic state of the actin cytoskeleton profoundly and distinctly affects microglia behaviours. Disruption of actin dynamics attenuates M2 polarization by inhibiting transcription of alternative activation genes. In classical activation, the role of actin remodelling is complex, does not relate to gene transcription and shows a major divergence between cytokines following conventional and unconventional secretion.

  2. Cofilin-mediated actin dynamics promotes actin bundle formation during Drosophila bristle development.

    Science.gov (United States)

    Wu, Jing; Wang, Heng; Guo, Xuan; Chen, Jiong

    2016-08-15

    The actin bundle is an array of linear actin filaments cross-linked by actin-bundling proteins, but its assembly and dynamics are not as well understood as those of the branched actin network. Here we used the Drosophila bristle as a model system to study actin bundle formation. We found that cofilin, a major actin disassembly factor of the branched actin network, promotes the formation and positioning of actin bundles in the developing bristles. Loss of function of cofilin or AIP1, a cofactor of cofilin, each resulted in increased F-actin levels and severe defects in actin bundle organization, with the defects from cofilin deficiency being more severe. Further analyses revealed that cofilin likely regulates actin bundle formation and positioning by the following means. First, cofilin promotes a large G-actin pool both locally and globally, likely ensuring rapid actin polymerization for bundle initiation and growth. Second, cofilin limits the size of a nonbundled actin-myosin network to regulate the positioning of actin bundles. Third, cofilin prevents incorrect assembly of branched and myosin-associated actin filament into bundles. Together these results demonstrate that the interaction between the dynamic dendritic actin network and the assembling actin bundles is critical for actin bundle formation and needs to be closely regulated.

  3. Regulation of Actin Dynamics in Pollen Tubes: Control of Actin Polymer Level

    Institute of Scientific and Technical Information of China (English)

    Naizhi Chen; Xiaolu Qu; Youjun Wu; Shanjin Huang

    2009-01-01

    Actin cytoskeleton undergoes rapid reorganization In response to internal and external cues. How the dynamics of actin cytoskeleton are regulated, and how its dynamics relate to its function are fundamental questions inplant cell biology. The pollen tube is a well characterized actin-based call morphogenesis in plants. One of the striking features of actin cytoskeleton characterized in the pollen tube is its surprisingly low level of actin polymer. This special phenomenon might relate to the function of actin cytoskeleton in pollen tubes. Understanding the molecular mechanism underlying this special phenomenon requires careful analysis of actin-binding proteins that modulate actin dynamics directly. Recent biochemical and biophysical analyses of several highly conserved plant actin-binding proteins reveal unusual and un-expected properties, which emphasizes the importance of carefully analyzing their action mechanism and cellular activity. In this review, we highlight an actin monomer sequestering protein, a barbed end capping protein and an F-actin severing and dynamizing protein in plant. We propose that these proteins function in harmony to regulate actin dynamics and maintain the low level of actin polymer in pollen tubes.

  4. The pros and cons of common actin labeling tools for visualizing actin dynamics during Drosophila oogenesis

    OpenAIRE

    Spracklen, Andrew J.; Fagan, Tiffany N.; Lovander, Kaylee E.; Tootle, Tina L.

    2014-01-01

    Dynamic remodeling of the actin cytoskeleton is required for both development and tissue homeostasis. While fixed image analysis has provided significant insight into such events, a complete understanding of cytoskeletal dynamics requires live imaging. Numerous tools for the live imaging of actin have been generated by fusing the actin-binding domain from an actin-interacting protein to a fluorescent protein. Here we comparatively assess the utility of three such tools – Utrophin, Lifeact, an...

  5. The pros and cons of common actin labeling tools for visualizing actin dynamics during Drosophila oogenesis.

    Science.gov (United States)

    Spracklen, Andrew J; Fagan, Tiffany N; Lovander, Kaylee E; Tootle, Tina L

    2014-09-15

    Dynamic remodeling of the actin cytoskeleton is required for both development and tissue homeostasis. While fixed image analysis has provided significant insight into such events, a complete understanding of cytoskeletal dynamics requires live imaging. Numerous tools for the live imaging of actin have been generated by fusing the actin-binding domain from an actin-interacting protein to a fluorescent protein. Here we comparatively assess the utility of three such tools--Utrophin, Lifeact, and F-tractin--for characterizing the actin remodeling events occurring within the germline-derived nurse cells during Drosophila mid-oogenesis or follicle development. Specifically, we used the UAS/GAL4 system to express these tools at different levels and in different cells, and analyzed these tools for effects on fertility, alterations in the actin cytoskeleton, and ability to label filamentous actin (F-actin) structures by both fixed and live imaging. While both Utrophin and Lifeact robustly label F-actin structures within the Drosophila germline, when strongly expressed they cause sterility and severe actin defects including cortical actin breakdown resulting in multi-nucleate nurse cells, early F-actin filament and aggregate formation during stage 9 (S9), and disorganized parallel actin filament bundles during stage 10B (S10B). However, by using a weaker germline GAL4 driver in combination with a higher temperature, Utrophin can label F-actin with minimal defects. Additionally, strong Utrophin expression within the germline causes F-actin formation in the nurse cell nuclei and germinal vesicle during mid-oogenesis. Similarly, Lifeact expression results in nuclear F-actin only within the germinal vesicle. F-tractin expresses at a lower level than the other two labeling tools, but labels cytoplasmic F-actin structures well without causing sterility or striking actin defects. Together these studies reveal how critical it is to evaluate the utility of each actin labeling tool

  6. Actin dynamics and the elasticity of cytoskeletal networks

    Directory of Open Access Journals (Sweden)

    2009-09-01

    Full Text Available The structural integrity of a cell depends on its cytoskeleton, which includes an actin network. This network is transient and depends upon the continual polymerization and depolymerization of actin. The degradation of an actin network, and a corresponding reduction in cell stiffness, can indicate the presence of disease. Numerical simulations will be invaluable for understanding the physics of these systems and the correlation between actin dynamics and elasticity. Here we develop a model that is capable of generating actin network structures. In particular, we develop a model of actin dynamics which considers the polymerization, depolymerization, nucleation, severing, and capping of actin filaments. The structures obtained are then fed directly into a mechanical model. This allows us to qualitatively assess the effects of changing various parameters associated with actin dynamics on the elasticity of the material.

  7. The unusual dynamics of parasite actin result from isodesmic polymerization.

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    Skillman, Kristen M; Ma, Christopher I; Fremont, Daved H; Diraviyam, Karthikeyan; Cooper, John A; Sept, David; Sibley, L David

    2013-01-01

    Previous reports have indicated that parasite actins are short and inherently unstable, despite being required for motility. Here we re-examine the polymerization properties of actin in Toxoplasma gondii, unexpectedly finding that it exhibits isodesmic polymerization in contrast to the conventional nucleation-elongation process of all previously studied actins from both eukaryotes and bacteria. Polymerization kinetics of actin in T. gondii lacks both a lag phase and critical concentration, normally characteristic of actins. Unique among actins, the kinetics of assembly can be fit with a single set of rate constants for all subunit interactions, without need for separate nucleation and elongation rates. This isodesmic model accurately predicts the assembly, disassembly and the size distribution of actin filaments in T. gondii in vitro, providing a mechanistic explanation for actin dynamics in vivo. Our findings expand the repertoire of mechanisms by which actin polymerization is governed and offer clues about the evolution of self-assembling, stabilized protein polymers.

  8. Dynamic buckling of actin within filopodia

    DEFF Research Database (Denmark)

    Leijnse, Natascha; Oddershede, Lene B; Bendix, Pól Martin

    2015-01-01

    Filopodia are active tubular structures protruding from the cell surface which allow the cell to sense and interact with the surrounding environment through repetitive elongation-retraction cycles. The mechanical behavior of filopodia has been studied by measuring the traction forces exerted...... in conjunction with rotation enables the cell to explore a much larger 3-dimensional space and allows for more complex, and possibly stronger, interactions with the external environment.(2) Here we focus on how bending of the filopodial actin dynamically correlates with pulling on an optically trapped...

  9. Dynamics of actin evolution in dinoflagellates.

    Science.gov (United States)

    Kim, Sunju; Bachvaroff, Tsvetan R; Handy, Sara M; Delwiche, Charles F

    2011-04-01

    Dinoflagellates have unique nuclei and intriguing genome characteristics with very high DNA content making complete genome sequencing difficult. In dinoflagellates, many genes are found in multicopy gene families, but the processes involved in the establishment and maintenance of these gene families are poorly understood. Understanding the dynamics of gene family evolution in dinoflagellates requires comparisons at different evolutionary scales. Studies of closely related species provide fine-scale information relative to species divergence, whereas comparisons of more distantly related species provides broad context. We selected the actin gene family as a highly expressed conserved gene previously studied in dinoflagellates. Of the 142 sequences determined in this study, 103 were from the two closely related species, Dinophysis acuminata and D. caudata, including full length and partial cDNA sequences as well as partial genomic amplicons. For these two Dinophysis species, at least three types of sequences could be identified. Most copies (79%) were relatively similar and in nucleotide trees, the sequences formed two bushy clades corresponding to the two species. In comparisons within species, only eight to ten nucleotide differences were found between these copies. The two remaining types formed clades containing sequences from both species. One type included the most similar sequences in between-species comparisons with as few as 12 nucleotide differences between species. The second type included the most divergent sequences in comparisons between and within species with up to 93 nucleotide differences between sequences. In all the sequences, most variation occurred in synonymous sites or the 5' UnTranslated Region (UTR), although there was still limited amino acid variation between most sequences. Several potential pseudogenes were found (approximately 10% of all sequences depending on species) with incomplete open reading frames due to frameshifts or early stop

  10. Dynamic Actin Gene Family Evolution in Primates

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    Liucun Zhu

    2013-01-01

    Full Text Available Actin is one of the most highly conserved proteins and plays crucial roles in many vital cellular functions. In most eukaryotes, it is encoded by a multigene family. Although the actin gene family has been studied a lot, few investigators focus on the comparison of actin gene family in relative species. Here, the purpose of our study is to systematically investigate characteristics and evolutionary pattern of actin gene family in primates. We identified 233 actin genes in human, chimpanzee, gorilla, orangutan, gibbon, rhesus monkey, and marmoset genomes. Phylogenetic analysis showed that actin genes in the seven species could be divided into two major types of clades: orthologous group versus complex group. Codon usages and gene expression patterns of actin gene copies were highly consistent among the groups because of basic functions needed by the organisms, but much diverged within species due to functional diversification. Besides, many great potential pseudogenes were found with incomplete open reading frames due to frameshifts or early stop codons. These results implied that actin gene family in primates went through “birth and death” model of evolution process. Under this model, actin genes experienced strong negative selection and increased the functional complexity by reproducing themselves.

  11. Sensing actin dynamics: Structural basis for G-actin-sensitive nuclear import of MAL

    Energy Technology Data Exchange (ETDEWEB)

    Hirano, Hidemi; Matsuura, Yoshiyuki, E-mail: matsuura.yoshiyuki@d.mbox.nagoya-u.ac.jp

    2011-10-22

    Highlights: {yields} MAL has a bipartite NLS that binds to Imp{alpha} in an extended conformation. {yields} Mutational analyses verified the functional significance of MAL-Imp{alpha} interactions. {yields} Induced folding and NLS-masking by G-actins inhibit nuclear import of MAL. -- Abstract: The coordination of cytoskeletal actin dynamics with gene expression reprogramming is emerging as a crucial mechanism to control diverse cellular processes, including cell migration, differentiation and neuronal circuit assembly. The actin-binding transcriptional coactivator MAL (also known as MRTF-A/MKL1/BSAC) senses G-actin concentration and transduces Rho GTPase signals to serum response factor (SRF). MAL rapidly shuttles between the cytoplasm and the nucleus in unstimulated cells but Rho-induced depletion of G-actin leads to MAL nuclear accumulation and activation of transcription of SRF:MAL-target genes. Although the molecular and structural basis of actin-regulated nucleocytoplasmic shuttling of MAL is not understood fully, it is proposed that nuclear import of MAL is mediated by importin {alpha}/{beta} heterodimer, and that G-actin competes with importin {alpha}/{beta} for the binding to MAL. Here we present structural, biochemical and cell biological evidence that MAL has a classical bipartite nuclear localization signal (NLS) in the N-terminal 'RPEL' domain containing Arg-Pro-X-X-X-Glu-Leu (RPEL) motifs. The NLS residues of MAL adopt an extended conformation and bind along the surface groove of importin-{alpha}, interacting with the major- and minor-NLS binding sites. We also present a crystal structure of wild-type MAL RPEL domain in complex with five G-actins. Comparison of the importin-{alpha}- and actin-complexes revealed that the binding of G-actins to MAL is associated with folding of NLS residues into a helical conformation that is inappropriate for importin-{alpha} recognition.

  12. Dynamic buckling of actin within filopodia

    DEFF Research Database (Denmark)

    Leijnse, Natascha; Oddershede, Lene B; Bendix, Pól Martin

    2015-01-01

    on external substrates.(1) These studies have revealed that internal actin flow can transduce a force across the cell surface through transmembrane linkers like integrins. In addition to the elongation-retraction behavior filopodia also exhibit a buckling and rotational behavior. Filopodial buckling...... a filopodium and holding it while measuring the cellular response, we also monitor and analyze the waiting times for the first buckle observed in the fluorescently labeled actin shaft....

  13. Actin organization, bristle morphology, and viability are affected by actin capping protein mutations in Drosophila

    OpenAIRE

    1996-01-01

    Regulation of actin filament length and orientation is important in many actin-based cellular processes. This regulation is postulated to occur through the action of actin-binding proteins. Many actin-binding proteins that modify actin in vitro have been identified, but in many cases, it is not known if this activity is physiologically relevant. Capping protein (CP) is an actin-binding protein that has been demonstrated to control filament length in vitro by binding to the barbed ends and pre...

  14. LL-37 induces polymerization and bundling of actin and affects actin structure.

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    Asaf Sol

    Full Text Available Actin exists as a monomer (G-actin which can be polymerized to filaments F-actin that under the influence of actin-binding proteins and polycations bundle and contribute to the formation of the cytoskeleton. Bundled actin from lysed cells increases the viscosity of sputum in lungs of cystic fibrosis patients. The human host defense peptide LL-37 was previously shown to induce actin bundling and was thus hypothesized to contribute to the pathogenicity of this disease. In this work, interactions between actin and the cationic LL-37 were studied by optical, proteolytic and surface plasmon resonance methods and compared to those obtained with scrambled LL-37 and with the cationic protein lysozyme. We show that LL-37 binds strongly to CaATP-G-actin while scrambled LL-37 does not. While LL-37, at superstoichiometric LL-37/actin concentrations polymerizes MgATP-G-actin, at lower non-polymerizing concentrations LL-37 inhibits actin polymerization by MgCl(2 or NaCl. LL-37 bundles Mg-F-actin filaments both at low and physiological ionic strength when in equimolar or higher concentrations than those of actin. The LL-37 induced bundles are significantly less sensitive to increase in ionic strength than those induced by scrambled LL-37 and lysozyme. LL-37 in concentrations lower than those needed for actin polymerization or bundling, accelerates cleavage of both monomer and polymer actin by subtilisin. Our results indicate that the LL-37-actin interaction is partially electrostatic and partially hydrophobic and that a specific actin binding sequence in the peptide is responsible for the hydrophobic interaction. LL-37-induced bundles, which may contribute to the accumulation of sputum in cystic fibrosis, are dissociated very efficiently by DNase-1 and also by cofilin.

  15. Structural Modeling and Molecular Dynamics Simulation of the Actin Filament

    Energy Technology Data Exchange (ETDEWEB)

    Splettstoesser, Thomas [University of Heidelberg; Holmes, Kenneth [Max Planck Institute, Heidelberg, Germany; Noe, Frank [DFG Research Center Matheon, FU Berlin, Germany; Smith, Jeremy C [ORNL

    2011-01-01

    Actin is a major structural protein of the eukaryotic cytoskeleton and enables cell motility. Here, we present a model of the actin filament (F-actin) that not only incorporates the global structure of the recently published model by Oda et al. but also conserves internal stereochemistry. A comparison is made using molecular dynamics simulation of the model with other recent F-actin models. A number of structural determents such as the protomer propeller angle, the number of hydrogen bonds, and the structural variation among the protomers are analyzed. The MD comparison is found to reflect the evolution in quality of actin models over the last 6 years. In addition, simulations of the model are carried out in states with both ADP or ATP bound and local hydrogen-bonding differences characterized.

  16. Actin-based dynamics during spermatogenesis and its significance

    Institute of Scientific and Technical Information of China (English)

    XIAO Xiang; YANG Wan-xi

    2007-01-01

    Actin can be found in all kinds ofeukaryotic cells, maintaining their shapes and motilities, while its dynamics in sperm cells is understood less than their nonmuscle somatic cell counterparts. Spermatogenesis is a complicated process, resulting in the production of mature sperm from primordial germ cell. Significant structural and biochemical changes take place in the seminiferous epithelium of the adult testis during spermatogenesis. It was proved that all mammalian sperm contain actin, and that F-actin may play an important role during spermatogenesis, especially in nuclear shaping. Recently a new model for sperm head elongation based on the acrosome-acroplaxome-manchette complex has been proposed. In Drosophila, F-actin assembly is supposed to be very crucial during individualization. In this mini-review, we provide an overview of the structure, function, and regulation characteristics of actin cytoskeleton, and a summary of the current status of research of actin-based structure and movement is also provided, with emphasis on the role of actins in sperm head shaping during spermiogenesis and the cell junction dynamics in the testis. Research of the Sertoli ectoplasmic specialization is in the spotlight, which is a testis-specific actin-based junction very important for the movement of germ cells across the epithelium. Study of the molecular architecture and the regulating mechanism of the Sertoli ectoplasmic specialization has become an intriguing field. All this may lead to a new strategy for male infertility and,at the same time, a novel idea may result in devising much safer contraception with high efficiency. It is hoped that the advances listed in this review would give developmental and morphological researchers a favorable investigating outline and could help to enlarge the view of new strategies and models for actin dynamics during spermatogenesis.

  17. Visualization of Actin Cytoskeletal Dynamics in Fixed and Live Drosophila Egg Chambers.

    Science.gov (United States)

    Groen, Christopher M; Tootle, Tina L

    2015-01-01

    Visualization of actin cytoskeletal dynamics is critical for understanding the spatial and temporal regulation of actin remodeling. Drosophila oogenesis provides an excellent model system for visualizing the actin cytoskeleton. Here, we present methods for imaging the actin cytoskeleton in Drosophila egg chambers in both fixed samples by phalloidin staining and in live egg chambers using transgenic actin labeling tools.

  18. Arabidopsis AtADF1 is Functionally Affected by Mutations on Actin Binding Sites

    Institute of Scientific and Technical Information of China (English)

    Chun-Hai Dong; Wei-Ping Tang; Jia-Yao Liu

    2013-01-01

    The plant actin depolymerizing factor (ADF) binds to both monomeric and filamentous actin,and is directly involved in the depolymerization of actin filaments.To better understand the actin binding sites of the Arabidopsis thaliana L.AtADF1,we generated mutants of AtADF1 and investigated their functions in vitro and in vivo.Analysis of mutants harboring amino acid substitutions revealed that charged residues (Arg98 and Lys100) located at the α-helix 3 and forming an actin binding site together with the N-terminus are essential for both G-and F-actin binding.The basic residues on the β-strand 5 (K82/A) and the α-helix 4 (R135/A,R137/A) form another actin binding site that is important for F-actin binding.Using transient expression of CFP-tagged AtADF1 mutant proteins in onion (Allium cepa) peel epidermal cells and transgenic Arabidopsis thaliana L.plants overexpressing these mutants,we analyzed how these mutant proteins regulate actin organization and affect seedling growth.Our results show that the ADF mutants with a lower affinity for actin filament binding can still be functional,unless the affinity foractin monomers is also affected.The G-actin binding activity of the ADF plays an essential role in actin binding,depolymerization of actin polymers,and therefore in the control of actin organization.

  19. PI(3,5)P2 controls endosomal branched actin dynamics by regulating cortactin-actin interactions.

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    Hong, Nan Hyung; Qi, Aidong; Weaver, Alissa M

    2015-08-31

    Branched actin critically contributes to membrane trafficking by regulating membrane curvature, dynamics, fission, and transport. However, how actin dynamics are controlled at membranes is poorly understood. Here, we identify the branched actin regulator cortactin as a direct binding partner of phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2) and demonstrate that their interaction promotes turnover of late endosomal actin. In vitro biochemical studies indicated that cortactin binds PI(3,5)P2 via its actin filament-binding region. Furthermore, PI(3,5)P2 competed with actin filaments for binding to cortactin, thereby antagonizing cortactin activity. These findings suggest that PI(3,5)P2 formation on endosomes may remove cortactin from endosome-associated branched actin. Indeed, inhibition of PI(3,5)P2 production led to cortactin accumulation and actin stabilization on Rab7(+) endosomes. Conversely, inhibition of Arp2/3 complex activity greatly reduced cortactin localization to late endosomes. Knockdown of cortactin reversed PI(3,5)P2-inhibitor-induced actin accumulation and stabilization on endosomes. These data suggest a model in which PI(3,5)P2 binding removes cortactin from late endosomal branched actin networks and thereby promotes net actin turnover.

  20. Dendritic cell podosome dynamics does not depend on the F-actin regulator SWAP-70.

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    Anne Götz

    Full Text Available In addition to classical adhesion structures like filopodia or focal adhesions, dendritic cells similar to macrophages and osteoclasts assemble highly dynamic F-actin structures called podosomes. They are involved in cellular processes such as extracellular matrix degradation, bone resorption by osteoclasts, and trans-cellular diapedesis of lymphocytes. Besides adhesion and migration, podosomes enable dendritic cells to degrade connective tissue by matrix metalloproteinases. SWAP-70 interacts with RhoGTPases and F-actin and regulates migration of dendritic cells. SWAP-70 deficient osteoclasts are impaired in F-actin-ring formation and bone resorption. In the present study, we demonstrate that SWAP-70 is not required for podosome formation and F-actin turnover in dendritic cells. Furthermore, we found that toll-like receptor 4 ligand induced podosome disassembly and podosome-mediated matrix degradation is not affected by SWAP-70 in dendritic cells. Thus, podosome formation and function in dendritic cells is independent of SWAP-70.

  1. AIP1 acts with cofilin to control actin dynamics during epithelial morphogenesis.

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    Chu, Dandan; Pan, Hanshuang; Wan, Ping; Wu, Jing; Luo, Jun; Zhu, Hong; Chen, Jiong

    2012-10-01

    During epithelial morphogenesis, cells not only maintain tight adhesion for epithelial integrity but also allow dynamic intercellular movement to take place within cell sheets. How these seemingly opposing processes are coordinated is not well understood. Here, we report that the actin disassembly factors AIP1 and cofilin are required for remodeling of adherens junctions (AJs) during ommatidial precluster formation in Drosophila eye epithelium, a highly stereotyped cell rearrangement process which we describe in detail in our live imaging study. AIP1 is enriched together with F-actin in the apical region of preclusters, whereas cofilin displays a diffuse and uniform localization pattern. Cofilin overexpression completely rescues AJ remodeling defects caused by AIP1 loss of function, and cofilin physically interacts with AIP1. Pharmacological reduction of actin turnover results in similar AJ remodeling defects and decreased turnover of E-cadherin, which also results from AIP1 deficiency, whereas an F-actin-destabilizing drug affects AJ maintenance and epithelial integrity. Together with other data on actin polymerization, our results suggest that AIP1 enhances cofilin-mediated actin disassembly in the apical region of precluster cells to promote remodeling of AJs and thus intercellular movement, but also that robust actin polymerization promotes AJ general adhesion and integrity during the remodeling process.

  2. Lifeact-mEGFP reveals a dynamic apical F-actin network in tip growing plant cells.

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    Luis Vidali

    Full Text Available BACKGROUND: Actin is essential for tip growth in plants. However, imaging actin in live plant cells has heretofore presented challenges. In previous studies, fluorescent probes derived from actin-binding proteins often alter growth, cause actin bundling and fail to resolve actin microfilaments. METHODOLOGY/PRINCIPAL FINDINGS: In this report we use Lifeact-mEGFP, an actin probe that does not affect the dynamics of actin, to visualize actin in the moss Physcomitrella patens and pollen tubes from Lilium formosanum and Nicotiana tobaccum. Lifeact-mEGFP robustly labels actin microfilaments, particularly in the apex, in both moss protonemata and pollen tubes. Lifeact-mEGFP also labels filamentous actin structures in other moss cell types, including cells of the gametophore. CONCLUSIONS/SIGNIFICANCE: Lifeact-mEGFP, when expressed at optimal levels does not alter moss protonemal or pollen tube growth. We suggest that Lifeact-mEGFP represents an exciting new versatile probe for further studies of actin's role in tip growing plant cells.

  3. Actin-Dynamics in Plant Cells: The Function of Actin Perturbing Substances Jasplakinolide, Chondramides, Phalloidin, Cytochalasins, and Latrunculins

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    Holzinger, Andreas; Blaas, Kathrin

    2016-01-01

    This chapter will give an overview of the most common F-actin perturbing substances, that are used to study actin dynamics in living plant cells in studies on morphogenesis, motility, organelle movement or when apoptosis has to be induced. These substances can be divided into two major subclasses – F-actin stabilizing and polymerizing substances like jasplakinolide, chondramides and F-actin severing compounds like chytochalasins and latrunculins. Jasplakinolide was originally isolated form a marine sponge, and can now be synthesized and has become commercially available, which is responsible for its wide distribution as membrane permeable F-actin stabilizing and polymerizing agent, which may even have anti-cancer activities. Cytochalasins, derived from fungi show an F-actin severing function and many derivatives are commercially available (A, B, C, D, E, H, J), also making it a widely used compound for F-actin disruption. The same can be stated for latrunculins (A, B), derived from red sea sponges, however the mode of action is different by binding to G-actin and inhibiting incorporation into the filament. In the case of swinholide a stable complex with actin dimers is formed resulting also in severing of F-actin. For influencing F-actin dynamics in plant cells only membrane permeable drugs are useful in a broad range. We however introduce also the phallotoxins and synthetic derivatives, as they are widely used to visualize F-actin in fixed cells. A particular uptake mechanism has been shown for hepatocytes, but has also been described in siphonal giant algae. In the present chapter the focus is set on F-actin dynamics in plant cells where alterations in cytoplasmic streaming can be particularly well studied; however methods by fluorescence applications including phalloidin- and antibody staining as well as immunofluorescence-localization of the inhibitor drugs are given. PMID:26498789

  4. ALKBH4-dependent demethylation of actin regulates actomyosin dynamics

    DEFF Research Database (Denmark)

    Li, M.-M.; Shi, Y.; Niu, Y.

    2013-01-01

    and midbody via association with methylated actin. ALKBH4-mediated regulation of actomyosin dynamics is completely dependent on its catalytic activity. Disorganization of cleavage furrow components and multinucleation associated with ALKBH4 deficiency can all be restored by reconstitution with wild...

  5. Simiate is an Actin binding protein involved in filopodia dynamics and arborisation of neurons.

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    Kristin eDerlig

    2014-04-01

    Full Text Available The Actin cytoskeleton constitutes the functional base for a multitude of cellular processes extending from motility and migration to cell mechanics and morphogenesis. The latter is particularly important to neuronal cells since the accurate functioning of the brain crucially depends on the correct arborisation of neurons, a process that requires the formation of several dozens to hundreds of dendritic branches. Recently, a model was proposed where different transcription factors are detailed to distinct facets and phases of dendritogenesis and exert their function by acting on the Actin cytoskeleton, however, the proteins involved as well as the underlying molecular mechanisms are largely unknown.Here, we demonstrate that Simiate, a protein previously indicated to activate transcription, directly associates with both, G- and F-Actin and in doing so, affects Actin polymerisation and Actin turnover in living cells. Imaging studies illustrate that Simiate particularly influences filopodia dynamics and specifically increases the branching of proximal, but not distal dendrites of developing neurons. The data suggests that Simiate functions as a direct molecular link between transcription regulation on one side, and dendritogenesis on the other, wherein Simiate serves to coordinate the development of proximal and distal dendrites by acting on the Actin cytoskeleton of filopodia and on transcription regulation, hence supporting the novel model.

  6. Dynamic actin controls polarity induction de novo in protoplasts.

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    Zaban, Beatrix; Maisch, Jan; Nick, Peter

    2013-02-01

    Cell polarity and axes are central for plant morphogenesis. To study how polarity and axes are induced de novo, we investigated protoplasts of tobacco Nicotiana tabacum cv. BY-2 expressing fluorescently-tagged cytoskeletal markers. We standardized the system to such a degree that we were able to generate quantitative data on the temporal patterns of regeneration stages. The synthesis of a new cell wall marks the transition to the first stage of regeneration, and proceeds after a long preparatory phase within a few minutes. During this preparatory phase, the nucleus migrates actively, and cytoplasmic strands remodel vigorously. We probed this system for the effect of anti-cytoskeletal compounds, inducible bundling of actin, RGD-peptides, and temperature. Suppression of actin dynamics at an early stage leads to aberrant tripolar cells, whereas suppression of microtubule dynamics produces aberrant sausage-like cells with asymmetric cell walls. We integrated these data into a model, where the microtubular cytoskeleton conveys positional information between the nucleus and the membrane controlling the release or activation of components required for cell wall synthesis. Cell wall formation is followed by the induction of a new cell pole requiring dynamic actin filaments, and the new cell axis is manifested as elongation growth perpendicular to the orientation of the aligned cortical microtubules.

  7. Dynamics of Actin Filament Ends in a Network

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    Yang, Le; Sept, David; Carlsson, Anders

    2004-03-01

    The formation of filopodia-like bundles in vitro from a dendritic actin network has been observed(D. Vignjevic et al, J. Cell Biol. 160, 951 (2003)) to occur as a result of a nucleation process. We study the dynamics of the actin filament ends in such a network in order to evaluate the dynamics of the bundle nucleation process. Our model treats two semiflexible actin filaments fixed at one end and free at the other, moving according to Brownian dynamics. The initial filament positions are chosen according to a thermal distribution, and we evaluate the time for the filaments to come close enough to each other to interact and bind. The capture criterion is based either on the distance between filaments, or on a combination of distance and relative orientation. We evaluate the dependence of the capture time on the filament length and radius, and the distance between the filament bases. Since treating the movement of the individual monomers in filaments is computationally unwieldy, we treat the filament motion using a normal mode analysis which permits use of a much longer timestep. We find that this method yields rapid convergence even when only the few longest-wavelength modes are included.

  8. Dynamic Actin Controls Polarity Induction de novo in Protoplasts

    Institute of Scientific and Technical Information of China (English)

    Beatrix Zaban; Jan Maisch; Peter Nick

    2013-01-01

    Cell polarity and axes are central for plant morphogenesis.To study how polarity and axes are induced de novo,we investigated protoplasts of tobacco Nicotiana tabacum cv.BY-2 expressing fluorescentlytagged cytoskeletal markers.We standardized the system to such a degree that we were able to generate quantitative data on the temporal patterns of regeneration stages.The synthesis of a new cell wall marks the transition to the first stage of regeneration,and proceeds after a long preparatory phase within a few minutes.During this preparatory phase,the nucleus migrates actively,and cytoplasmic strands remodel vigorously.We probed this system for the effect of anti-cytoskeletal compounds,inducible bundling of actin,RGD-peptides,and temperature.Suppression of actin dynamics at an early stage leads to aberrant tripolar cells,whereas suppression of microtubule dynamics produces aberrant sausagelike cells with asymmetric cell walls.We integrated these data into a model,where the microtubular cytoskeleton conveys positional information between the nucleus and the membrane controlling the release or activation of components required for cell wall synthesis.Cell wall formation is followed by the induction of a new cell pole requiring dynamic actin filaments,and the new cell axis is manifested as elongation growth perpendicular to the orientation of the aligned cortical microtubules.

  9. Dynamic organization of actin cytoskeleton during the polarity formation and germination of pollen protoplasts

    Institute of Scientific and Technical Information of China (English)

    XU Xia; Zl Huijun; SUN Yina; REN Haiyun

    2004-01-01

    The formation of the polarity of pollen protoplast and the dynamics of actin cytoskeleton were observed by non-fixation, Alexa-Phalloidin probing and confocal laser scanning microscopy. Our results showed that the protoplast obtained from stored pollen contained numerous crystalline fusiform bodies to constitute a storage form of actin. When dormant pollen was hydrated, the actin cytoskeleton forms a fine network spreading uniformly in the protoplast. In the process of polarity formation and germination of pollen protoplast, actin filaments marshaled slowly to the brim, and then formed multilayer continuous actin filament bundles surrounding the cortical of the protoplast. When the protoplast was exposed to actin filament-disrupting drugs, such as Latrunculin A and Cytochalasin D, continuously arranged actin bundles were disturbed and in this condition, the protoplast could not germinate. But when exposed to actin filament stabiling drug-phalliodin, the dynamics of actin filaments in the protoplasts behaved normally and the protoplasts could germinate normally. These results were also confirmed by the pharmacology experiments on pollen grains. And when Latrunculin A or Cytochalasin D was washed off, the ratio of pollen germination was resumed partly. All the results above show that the dynamic organization of the actin cytoskeleton are critical in the cell polarity formation and germination of pollen protoplast, and that the reorganization of actin cytoskeleton is mainly due to the rearrangement of actin filament arrays.

  10. Dynamics of actin cables in polarized growth of the filamentous fungus Aspergillus nidulans

    Directory of Open Access Journals (Sweden)

    Anna eBergs

    2016-05-01

    Full Text Available Highly polarized growth of filamentous fungi requires a continuous supply of proteins and lipids to the hyphal tip. This transport is managed by vesicle trafficking via the actin and microtubule cytoskeletons and their associated motor proteins. Particularly, actin cables originating from the hyphal tip are essential for hyphal growth. Although specific marker proteins to visualize actin cables have been developed in filamentous fungi, the exact organization and dynamics of actin cables has remained elusive. Here we visualized actin cables using tropomyosin (TpmA and Lifeact fused to fluorescent proteins in Aspergillus nidulans and studied the dynamics and regulation. GFP tagged TpmA visualized dynamic actin cables formed from the hyphal tip with cycles of elongation and shrinkage. The elongation and shrinkage rates of actin cables were similar and approximately 0.6 μm/s. Comparison of actin markers revealed that high concentrations of Lifeact reduced actin dynamics. Simultaneous visualization of actin cables and microtubules suggests temporally and spatially coordinated polymerization and depolymerization between the two cytoskeletons. Our results provide new insights into the molecular mechanism of ordered polarized growth regulated by actin cables and microtubules.

  11. Emergence of large-scale cell morphology and movement from local actin filament growth dynamics.

    Directory of Open Access Journals (Sweden)

    Catherine I Lacayo

    2007-09-01

    Full Text Available Variations in cell migration and morphology are consequences of changes in underlying cytoskeletal organization and dynamics. We investigated how these large-scale cellular events emerge as direct consequences of small-scale cytoskeletal molecular activities. Because the properties of the actin cytoskeleton can be modulated by actin-remodeling proteins, we quantitatively examined how one such family of proteins, enabled/vasodilator-stimulated phosphoprotein (Ena/VASP, affects the migration and morphology of epithelial fish keratocytes. Keratocytes generally migrate persistently while exhibiting a characteristic smooth-edged "canoe" shape, but may also exhibit less regular morphologies and less persistent movement. When we observed that the smooth-edged canoe keratocyte morphology correlated with enrichment of Ena/VASP at the leading edge, we mislocalized and overexpressed Ena/VASP proteins and found that this led to changes in the morphology and movement persistence of cells within a population. Thus, local changes in actin filament dynamics due to Ena/VASP activity directly caused changes in cell morphology, which is coupled to the motile behavior of keratocytes. We also characterized the range of natural cell-to-cell variation within a population by using measurable morphological and behavioral features--cell shape, leading-edge shape, filamentous actin (F-actin distribution, cell speed, and directional persistence--that we have found to correlate with each other to describe a spectrum of coordinated phenotypes based on Ena/VASP enrichment at the leading edge. This spectrum stretched from smooth-edged, canoe-shaped keratocytes--which had VASP highly enriched at their leading edges and migrated fast with straight trajectories--to more irregular, rounder cells migrating slower with less directional persistence and low levels of VASP at their leading edges. We developed a mathematical model that accounts for these coordinated cell-shape and

  12. Persistent nuclear actin filaments inhibit transcription by RNA polymerase II.

    Science.gov (United States)

    Serebryannyy, Leonid A; Parilla, Megan; Annibale, Paolo; Cruz, Christina M; Laster, Kyle; Gratton, Enrico; Kudryashov, Dmitri; Kosak, Steven T; Gottardi, Cara J; de Lanerolle, Primal

    2016-09-15

    Actin is abundant in the nucleus and it is clear that nuclear actin has important functions. However, mystery surrounds the absence of classical actin filaments in the nucleus. To address this question, we investigated how polymerizing nuclear actin into persistent nuclear actin filaments affected transcription by RNA polymerase II. Nuclear filaments impaired nuclear actin dynamics by polymerizing and sequestering nuclear actin. Polymerizing actin into stable nuclear filaments disrupted the interaction of actin with RNA polymerase II and correlated with impaired RNA polymerase II localization, dynamics, gene recruitment, and reduced global transcription and cell proliferation. Polymerizing and crosslinking nuclear actin in vitro similarly disrupted the actin-RNA-polymerase-II interaction and inhibited transcription. These data rationalize the general absence of stable actin filaments in mammalian somatic nuclei. They also suggest a dynamic pool of nuclear actin is required for the proper localization and activity of RNA polymerase II.

  13. Stochastic dynamics of actin filaments in guard cells regulating chloroplast localization during stomatal movement.

    Science.gov (United States)

    Wang, Xiu-Ling; Gao, Xin-Qi; Wang, Xue-Chen

    2011-08-01

    Actin filaments and chloroplasts in guard cells play roles in stomatal function. However, detailed actin dynamics vary, and the roles that they play in chloroplast localization during stomatal movement remain to be determined. We examined the dynamics of actin filaments and chloroplast localization in transgenic tobacco expressing green fluorescent protein (GFP)-mouse talin in guard cells by time-lapse imaging. Actin filaments showed sliding, bundling and branching dynamics in moving guard cells. During stomatal movement, long filaments can be severed into small fragments, which can form longer filaments by end-joining activities. With chloroplast movement, actin filaments near chloroplasts showed severing and elongation activity in guard cells during stomatal movement. Cytochalasin B treatment abolished elongation, bundling and branching activities of actin filaments in guard cells, and these changes of actin filaments, and as a result, more chloroplasts were localized at the centre of guard cells. However, chloroplast turning to avoid high light, and sliding of actin fragments near the chloroplast, was unaffected following cytochalasin B treatment in guard cells. We suggest that the sliding dynamics of actin may play roles in chloroplast turning in guard cells. Our results indicate that the stochastic dynamics of actin filaments in guard cells regulate chloroplast localization during stomatal movement.

  14. Desmosome dynamics in migrating epithelial cells requires the actin cytoskeleton

    Science.gov (United States)

    Roberts, Brett J.; Pashaj, Anjeza; Johnson, Keith R.; Wahl, James K.

    2011-01-01

    Re-modeling of epithelial tissues requires that the cells in the tissue rearrange their adhesive contacts in order to allow cells to migrate relative to neighboring cells. Desmosomes are prominent adhesive structures found in a variety of epithelial tissues that are believed to inhibit cell migration and invasion. Mechanisms regulating desmosome assembly and stability in migrating cells are largely unknown. In this study we established a cell culture model to examine the fate of desmosomal components during scratch wound migration. Desmosomes are rapidly assembled between epithelial cells at the lateral edges of migrating cells and structures are transported in a retrograde fashion while the structures become larger and mature. Desmosome assembly and dynamics in this system are dependent on the actin cytoskeleton prior to being associated with the keratin intermediate filament cytoskeleton. These studies extend our understanding of desmosome assembly and provide a system to examine desmosome assembly and dynamics during epithelial cell migration. PMID:21945137

  15. The role of cyclase-associated protein in regulating actin filament dynamics – more than a monomer-sequestration factor

    OpenAIRE

    Ono, Shoichiro

    2013-01-01

    Dynamic reorganization of the actin cytoskeleton is fundamental to a number of cell biological events. A variety of actin-regulatory proteins modulate polymerization and depolymerization of actin and contribute to actin cytoskeletal reorganization. Cyclase-associated protein (CAP) is a conserved actin-monomer-binding protein that has been studied for over 20 years. Early studies have shown that CAP sequesters actin monomers; recent studies, however, have revealed more active roles of CAP in a...

  16. Dynamics and Regulation of Actin Cytoskeleton in Plant Cells

    Institute of Scientific and Technical Information of China (English)

    Ren Haiyun

    2007-01-01

    @@ The actin cytoskeleton constituted of globular actin (G-actin) is a ubiquitous component of eukaryotic cells and plays crucial roles in diverse physiological processes in plant cells, such as cytoplasmic streaming, organelle and nucleus positioning, cell morphogenesis, cell division, tip growth, etc.

  17. Polarized actin structural dynamics in response to cyclic uniaxial stretch

    Science.gov (United States)

    Huang, Lawrence; Helmke, Brian P.

    2014-01-01

    Endothelial cell (EC) alignment to directional flow or stretch supports anti-inflammatory functions, but mechanisms controlling polarized structural adaptation in response to physical cues remain unclear. This study aimed to determine whether factors associated with early actin edge ruffling implicated in cell polarization are prerequisite for stress fiber (SF) reorientation in response to cyclic uniaxial stretch. Time-lapse analysis of EGFP-actin in confluent ECs showed that onset of either cyclic uniaxial or equibiaxial stretch caused a non-directional increase in edge ruffling. Edge activity was concentrated in a direction perpendicular to the stretch axis after 60 min, consistent with the direction of SF alignment. Rho-kinase inhibition caused reorientation of both stretch-induced edge ruffling and SF alignment parallel to the stretch axis. Arp2/3 inhibition attenuated stretch-induced cell elongation and disrupted polarized edge dynamics and microtubule organizing center reorientation, but it had no effect on the extent of SF reorientation. Disrupting localization of p21-activated kinase (PAK) did not prevent stretch-induced SF reorientation, suggesting that this Rac effector is not critical in regulating stretch-induced cytoskeletal remodeling. Overall, these results suggest that directional edge ruffling is not a primary mechanism that guides SF reorientation in response to stretch; the two events are coincident but not causal. PMID:25821527

  18. Lamin A/C and emerin regulate MKL1/SRF activity by modulating actin dynamics

    Science.gov (United States)

    Ho, Chin Yee; Jaalouk, Diana E.; Vartiainen, Maria K.; Lammerding, Jan

    2013-01-01

    Laminopathies, caused by mutations in the LMNA gene encoding the nuclear envelope proteins lamins A and C, represent a diverse group of diseases that include Emery-Dreifuss Muscular Dystrophy (EDMD), dilated cardiomyopathy (DCM), limb-girdle muscular dystrophy, and Hutchison-Gilford progeria syndrome (HGPS).1 The majority of LMNA mutations affect skeletal and cardiac muscle by mechanisms that remain incompletely understood. Loss of structural function and disturbed interaction of mutant lamins with (tissue-specific) transcription factors have been proposed to explain the tissue-specific phenotypes.1 We report here that lamin A/C-deficient (Lmna−/−) and Lmna N195K mutant cells have impaired nuclear translocation and downstream signaling of the mechanosensitive transcription factor megakaryoblastic leukaemia 1 (MKL1), a myocardin family member that is pivotal in cardiac development and function.2 Disturbed nucleo-cytoplasmic shuttling of MKL1 was caused by altered actin dynamics in Lmna−/− and N195K mutant cells. Ectopic expression of the nuclear envelope protein emerin, which is mislocalized in Lmna mutant cells and also linked to EDMD and DCM, restored MKL1 nuclear translocation and rescued actin dynamics in mutant cells. These findings present a novel mechanism that could provide insight into the disease etiology for the cardiac phenotype in many laminopathies, whereby lamins A/C and emerin regulate gene expression through modulation of nuclear and cytoskeletal actin polymerization. PMID:23644458

  19. Lamin A/C and emerin regulate MKL1-SRF activity by modulating actin dynamics.

    Science.gov (United States)

    Ho, Chin Yee; Jaalouk, Diana E; Vartiainen, Maria K; Lammerding, Jan

    2013-05-23

    Laminopathies, caused by mutations in the LMNA gene encoding the nuclear envelope proteins lamins A and C, represent a diverse group of diseases that include Emery-Dreifuss muscular dystrophy (EDMD), dilated cardiomyopathy (DCM), limb-girdle muscular dystrophy, and Hutchison-Gilford progeria syndrome. Most LMNA mutations affect skeletal and cardiac muscle by mechanisms that remain incompletely understood. Loss of structural function and altered interaction of mutant lamins with (tissue-specific) transcription factors have been proposed to explain the tissue-specific phenotypes. Here we report in mice that lamin-A/C-deficient (Lmna(-/-)) and Lmna(N195K/N195K) mutant cells have impaired nuclear translocation and downstream signalling of the mechanosensitive transcription factor megakaryoblastic leukaemia 1 (MKL1), a myocardin family member that is pivotal in cardiac development and function. Altered nucleo-cytoplasmic shuttling of MKL1 was caused by altered actin dynamics in Lmna(-/-) and Lmna(N195K/N195K) mutant cells. Ectopic expression of the nuclear envelope protein emerin, which is mislocalized in Lmna mutant cells and also linked to EDMD and DCM, restored MKL1 nuclear translocation and rescued actin dynamics in mutant cells. These findings present a novel mechanism that could provide insight into the disease aetiology for the cardiac phenotype in many laminopathies, whereby lamin A/C and emerin regulate gene expression through modulation of nuclear and cytoskeletal actin polymerization.

  20. Investigating sub-spine actin dynamics in rat hippocampal neurons with super-resolution optical imaging.

    Directory of Open Access Journals (Sweden)

    Vedakumar Tatavarty

    Full Text Available Morphological changes in dendritic spines represent an important mechanism for synaptic plasticity which is postulated to underlie the vital cognitive phenomena of learning and memory. These morphological changes are driven by the dynamic actin cytoskeleton that is present in dendritic spines. The study of actin dynamics in these spines traditionally has been hindered by the small size of the spine. In this study, we utilize a photo-activation localization microscopy (PALM-based single-molecule tracking technique to analyze F-actin movements with approximately 30-nm resolution in cultured hippocampal neurons. We were able to observe the kinematic (physical motion of actin filaments, i.e., retrograde flow and kinetic (F-actin turn-over dynamics of F-actin at the single-filament level in dendritic spines. We found that F-actin in dendritic spines exhibits highly heterogeneous kinematic dynamics at the individual filament level, with simultaneous actin flows in both retrograde and anterograde directions. At the ensemble level, movements of filaments integrate into a net retrograde flow of approximately 138 nm/min. These results suggest a weakly polarized F-actin network that consists of mostly short filaments in dendritic spines.

  1. Depletion of the actin bundling protein SM22/transgelin increases actin dynamics and enhances the tumourigenic phenotypes of cells

    Directory of Open Access Journals (Sweden)

    Thompson Oliver

    2012-01-01

    Full Text Available Abstract Background SM22 has long been studied as an actin-associated protein. Interestingly, levels of SM22 are often reduced in tumour cell lines, while they are increased during senescence possibly indicating a role for SM22 in cell fate decisions via its interaction with actin. In this study we aimed to determine whether reducing levels of SM22 could actively contribute to a tumourigenic phenotype. Results We demonstrate that in REF52 fibroblasts, decreased levels of SM22 disrupt normal actin organization leading to changes in the motile behaviour of cells. Interestingly, SM22 depletion also led to an increase in the capacity of cells to spontaneously form podosomes with a concomitant increase in the ability to invade Matrigel. In PC3 prostate epithelial cancer cells by contrast, where SM22 is undetectable, re-expression of SM22 reduced the ability to invade Matrigel. Furthermore SM22 depleted cells also had reduced levels of reactive oxygen species when under serum starvation stress. Conclusions These findings suggest that depletion of SM22 could contribute to tumourigenic properties of cells. Reduction in SM22 levels would tend to promote cell survival when cells are under stress, such as in a hypoxic tumour environment, and may also contribute to increases in actin dynamics that favour metastatic potential.

  2. STK16 regulates actin dynamics to control Golgi organization and cell cycle

    Science.gov (United States)

    Liu, Juanjuan; Yang, Xingxing; Li, Binhua; Wang, Junjun; Wang, Wenchao; Liu, Jing; Liu, Qingsong; Zhang, Xin

    2017-01-01

    STK16 is a ubiquitously expressed, myristoylated, and palmitoylated serine/threonine protein kinase with underexplored functions. Recently, it was shown to be involved in cell division but the mechanism remains unclear. Here we found that human STK16 localizes to the Golgi complex throughout the cell cycle and plays important roles in Golgi structure regulation. STK16 knockdown or kinase inhibition disrupts actin polymers and causes fragmented Golgi in cells. In vitro assays show that STK16 directly binds to actin and regulates actin dynamics in a concentration- and kinase activity-dependent way. In addition, STK16 knockdown or kinase inhibition not only delays mitotic entry and prolongs mitosis, but also causes prometaphase and cytokinesis arrest. Therefore, we revealed STK16 as a novel actin binding protein that resides in the Golgi, which regulates actin dynamics to control Golgi structure and participate in cell cycle progression. PMID:28294156

  3. New insights into dynamic actin-based chloroplast photorelocation movement.

    Science.gov (United States)

    Kong, Sam-Geun; Wada, Masamitsu

    2011-09-01

    Chloroplast movement is essential for plants to survive under various environmental light conditions. Phototropins-plant-specific blue-light-activated receptor kinases-mediate the response by perceiving light intensity and direction. Recently, novel chloroplast actin (cp-actin) filaments have been identified as playing a pivotal role in the directional chloroplast photorelocation movement. Encouraging progress has recently been made in this field of research through molecular genetics and cell biological analyses. This review describes factors that have been identified as being involved in chloroplast movement and their roles in the regulation of cp-actin filaments, thus providing a basis for reflection on their biochemical activities and functions.

  4. An Arabidopsis Class Ⅱ Formin, AtFH19, Nucleates Actin Assembly, Binds to the Barbed End of Actin Filaments, and Antagonizes the Effect of AtFH1 on Actin Dynamics

    Institute of Scientific and Technical Information of China (English)

    Yiyan Zheng; Haibo Xin; Jinxing Lin; Chun-Ming Liu; Shanjin Huang

    2012-01-01

    Formin is a major protein responsible for regulating the nucleation of actin filaments,and as such,it permits the cell to control where and when to assemble actin arrays.It is encoded by a multigene family comprising 21 members in Arabidopsis thaliana.The Arabidopsis formins can be separated into two phylogenetically-distinct classes:there are 11 class Ⅰ formins and 10 class Ⅱ formins.Significant questions remain unanswered regarding the molecular mechanism of actin nucleation and elongation stimulated by each formin isovariant,and how the different isovariants coordinate to regulate actin dynamics in cells.Here,we characterize a class Ⅱ formin,AtFH19,biochemically.We found that AtFH19 retains all general properties of the formin family,including nucleation and barbed end capping activity.It can also generate actin filaments from a pool of actin monomers bound to profilin.However,both the nucleation and barbed end capping activities of AtFH19 are less efficient compared to those of another well-characterized formin,AtFH1.Interestingly,AtFH19 FH1FH2 competes with AtFH1 FH1FH2 in binding actin filament barbed ends,and inhibits the effect of AtFH1 FH1FH2 on actin.We thus propose a mechanism in which two quantitatively different formins coordinate to regulate actin dynamics by competing for actin filament barbed ends.

  5. Changes in actin dynamics are involved in salicylic acid signaling pathway.

    Science.gov (United States)

    Matoušková, Jindřiška; Janda, Martin; Fišer, Radovan; Sašek, Vladimír; Kocourková, Daniela; Burketová, Lenka; Dušková, Jiřina; Martinec, Jan; Valentová, Olga

    2014-06-01

    Changes in actin cytoskeleton dynamics are one of the crucial players in many physiological as well as non-physiological processes in plant cells. Positioning of actin filament arrays is necessary for successful establishment of primary lines of defense toward pathogen attack, depolymerization leads very often to the enhanced susceptibility to the invading pathogen. On the other hand it was also shown that the disruption of actin cytoskeleton leads to the induction of defense response leading to the expression of PATHOGENESIS RELATED proteins (PR). In this study we show that pharmacological actin depolymerization leads to the specific induction of genes in salicylic acid pathway but not that involved in jasmonic acid signaling. Life imaging of leafs of Arabidopsis thaliana with GFP-tagged fimbrin (GFP-fABD2) treated with 1 mM salicylic acid revealed rapid disruption of actin filaments resembling the pattern viewed after treatment with 200 nM latrunculin B. The effect of salicylic acid on actin filament fragmentation was prevented by exogenous addition of phosphatidic acid, which binds to the capping protein and thus promotes actin polymerization. The quantitative evaluation of actin filament dynamics is also presented.

  6. Real-time dynamics of emerging actin networks in cell-mimicking compartments.

    Directory of Open Access Journals (Sweden)

    Siddharth Deshpande

    Full Text Available Understanding the cytoskeletal functionality and its relation to other cellular components and properties is a prominent question in biophysics. The dynamics of actin cytoskeleton and its polymorphic nature are indispensable for the proper functioning of living cells. Actin bundles are involved in cell motility, environmental exploration, intracellular transport and mechanical stability. Though the viscoelastic properties of actin-based structures have been extensively probed, the underlying microstructure dynamics, especially their disassembly, is not fully understood. In this article, we explore the rich dynamics and emergent properties exhibited by actin bundles within flow-free confinements using a microfluidic set-up and epifluorescence microscopy. After forming entangled actin filaments within cell-sized quasi two-dimensional confinements, we induce their bundling using three different fundamental mechanisms: counterion condensation, depletion interactions and specific protein-protein interactions. Intriguingly, long actin filaments form emerging networks of actin bundles via percolation leading to remarkable properties such as stress generation and spindle-like intermediate structures. Simultaneous sharing of filaments in different links of the network is an important parameter, as short filaments do not form networks but segregated clusters of bundles instead. We encounter a hierarchical process of bundling and its subsequent disassembly. Additionally, our study suggests that such percolated networks are likely to exist within living cells in a dynamic fashion. These observations render a perspective about differential cytoskeletal responses towards numerous stimuli.

  7. Formins: Actin nucleators that regulate cytoskeletal dynamics during spermatogenesis.

    Science.gov (United States)

    Li, Nan; Mruk, Dolores D; Tang, Elizabeth I; Wong, Chris Kc; Lee, Will M; Silvestrini, Bruno; Cheng, C Yan

    2015-01-01

    Formins are a growing class of actin nucleation proteins that promote the polymerization of actin microfilaments, forming long stretches of actin microfilaments to confer actin filament bundling in mammalian cells. As such, microfilament bundles can be formed in specific cellular domains, in particular in motile mammalian cells, such as filopodia. Since ectoplasmic specialization (ES), a testis-specific adherens junction (AJ), at the Sertoli cell-cell and Sertoli-spermatid interface is constituted by arrays of actin microfilament bundles, it is likely that formins are playing a significant physiological role on the homeostasis of ES during the epithelial cycle of spermatogenesis. In this Commentary, we provide a timely discussion on formin 1 which was recently shown to be a crucial regulator of actin microfilaments at the ES in the rat testis (Li N et al. Endocrinology, 2015, in press; DOI: 10.1210/en.2015-1161, PMID:25901598). We also highlight research that is needed to unravel the functional significance of formins in spermatogenesis.

  8. Actin filament dynamics are dominated by rapid growth and severing activity in the Arabidopsis cortical array

    OpenAIRE

    Staiger, Christopher J.; Sheahan, Michael B.; Khurana, Parul; Wang,Xia; McCurdy, David W.; Blanchoin, Laurent

    2009-01-01

    Metazoan cells harness the power of actin dynamics to create cytoskeletal arrays that stimulate protrusions and drive intracellular organelle movements. In plant cells, the actin cytoskeleton is understood to participate in cell elongation; however, a detailed description and molecular mechanism(s) underpinning filament nucleation, growth, and turnover are lacking. Here, we use variable-angle epifluorescence microscopy (VAEM) to examine the organization and dynamics of the cortical cytoskelet...

  9. New Insights into Dynamic Actin-Based Chloroplast Photorelocation Movement

    Institute of Scientific and Technical Information of China (English)

    Sam-Geun Kong; Masamitsu Wada

    2011-01-01

    Chloroplast movement is essential for plants to survive under various environmental light conditions.Phototropins-plant-specific blue-light-activated receptor kinases-mediate the response by perceiving light intensity and direction.Recently,novel chloroplast actin (cp-actin) filaments have been identified as playing a pivotal role in the directional chloroplast photorelocation movement.Encouraging progress has recently been made in this field of research through molecular genetics and cell biological analyses.This review describes factors that have been identified as being involved in chloroplast movement and their roles in the regulation of cp-actin filaments,thus providing a basis for reflection on their biochemical activities and functions.

  10. Modulating F-actin organization induces organ growth by affecting the Hippo pathway

    OpenAIRE

    Sansores-Garcia, Leticia; Bossuyt, Wouter; Wada, Ken-Ichi; Yonemura, Shigenobu; Tao, Chunyao; Sasaki, Hiroshi; Halder, Georg

    2011-01-01

    This study identifies actin organization as an upstream regulator of the Hippo pathway: F-actin accumulation promotes Yorkie-dependent transcriptional activation. This modulation of Hippo signalling by actin regulators controls organ growth in Drosophila.

  11. Filament attachment dynamics in actin-based propulsion

    CERN Document Server

    Katz, J I

    2005-01-01

    Theory and experiment have established that F-actin filaments are strongly attached to the intracellular parasites (such as Listeria) they propel with ``comet tails''. We consider the implications of these observations for propulsion. By calculating the motion produced in various models of attachment and comparing to experiment we demonstrate that the attachment must be sliding rather than hinged. By modeling experiments on ActA-coated spheres we draw conclusions regarding the interaction between F-actin and their surfaces that may also be applicable to living systems.

  12. Neuronal actin dynamics, spine density and neuronal dendritic complexity are regulated by CAP2

    Directory of Open Access Journals (Sweden)

    Atul Kumar

    2016-07-01

    Full Text Available Actin remodeling is crucial for dendritic spine development, morphology and density. CAP2 is a regulator of actin dynamics through sequestering G-actin and severing F-actin. In a mouse model, ablation of CAP2 leads to cardiovascular defects and delayed wound healing. This report investigates the role of CAP2 in the brain using Cap2gt/gt mice. Dendritic complexity, the number and morphology of dendritic spines were altered in Cap2gt/gt with increased number of excitatory synapse. This was accompanied by increased F-actin content and F-actin accumulation in cultured Cap2gt/gt neurons. Moreover, reduced surface GluA1 was observed in mutant neurons under basal condition and after induction of chemical LTP. Additionally, we show an interaction between CAP2 and n-cofilin, presumably mediated through the C-terminal domain of CAP2 and dependent on cofilin ser3 phosphorylation. In vivo, the consequences of this interaction were altered phosphorylated cofilin levels and formation of cofilin aggregates in the neurons. Thus, our studies identify a novel role of CAP2 in neuronal development and neuronal actin dynamics.

  13. The interplay between neuronal activity and actin dynamics mimic the setting of an LTD synaptic tag

    OpenAIRE

    Szabó, Eszter C.; Manguinhas, Rita; Fonseca, Rosalina

    2016-01-01

    Persistent forms of plasticity, such as long-term depression (LTD), are dependent on the interplay between activity-dependent synaptic tags and the capture of plasticity-related proteins. We propose that the synaptic tag represents a structural alteration that turns synapses permissive to change. We found that modulation of actin dynamics has different roles in the induction and maintenance of LTD. Inhibition of either actin depolymerisation or polymerization blocks LTD induction whereas only...

  14. The interplay between neuronal activity and actin dynamics mimic the setting of an LTD synaptic tag.

    Science.gov (United States)

    Szabó, Eszter C; Manguinhas, Rita; Fonseca, Rosalina

    2016-09-21

    Persistent forms of plasticity, such as long-term depression (LTD), are dependent on the interplay between activity-dependent synaptic tags and the capture of plasticity-related proteins. We propose that the synaptic tag represents a structural alteration that turns synapses permissive to change. We found that modulation of actin dynamics has different roles in the induction and maintenance of LTD. Inhibition of either actin depolymerisation or polymerization blocks LTD induction whereas only the inhibition of actin depolymerisation blocks LTD maintenance. Interestingly, we found that actin depolymerisation and CaMKII activation are involved in LTD synaptic-tagging and capture. Moreover, inhibition of actin polymerisation mimics the setting of a synaptic tag, in an activity-dependent manner, allowing the expression of LTD in non-stimulated synapses. Suspending synaptic activation also restricts the time window of synaptic capture, which can be restored by inhibiting actin polymerization. Our results support our hypothesis that modulation of the actin cytoskeleton provides an input-specific signal for synaptic protein capture.

  15. Structure and mechanism of mouse cyclase-associated protein (CAP1) in regulating actin dynamics.

    Science.gov (United States)

    Jansen, Silvia; Collins, Agnieszka; Golden, Leslie; Sokolova, Olga; Goode, Bruce L

    2014-10-31

    Srv2/CAP is a conserved actin-binding protein with important roles in driving cellular actin dynamics in diverse animal, fungal, and plant species. However, there have been conflicting reports about whether the activities of Srv2/CAP are conserved, particularly between yeast and mammalian homologs. Yeast Srv2 has two distinct functions in actin turnover: its hexameric N-terminal-half enhances cofilin-mediated severing of filaments, while its C-terminal-half catalyzes dissociation of cofilin from ADP-actin monomers and stimulates nucleotide exchange. Here, we dissected the structure and function of mouse CAP1 to better understand its mechanistic relationship to yeast Srv2. Although CAP1 has a shorter N-terminal oligomerization sequence compared with Srv2, we find that the N-terminal-half of CAP1 (N-CAP1) forms hexameric structures with six protrusions, similar to N-Srv2. Further, N-CAP1 autonomously binds to F-actin and decorates the sides and ends of filaments, altering F-actin structure and enhancing cofilin-mediated severing. These activities depend on conserved surface residues on the helical-folded domain. Moreover, N-CAP1 enhances yeast cofilin-mediated severing, and conversely, yeast N-Srv2 enhances human cofilin-mediated severing, highlighting the mechanistic conservation between yeast and mammals. Further, we demonstrate that the C-terminal actin-binding β-sheet domain of CAP1 is sufficient to catalyze nucleotide-exchange of ADP-actin monomers, while in the presence of cofilin this activity additionally requires the WH2 domain. Thus, the structures, activities, and mechanisms of mouse and yeast Srv2/CAP homologs are remarkably well conserved, suggesting that the same activities and mechanisms underlie many of the diverse actin-based functions ascribed to Srv2/CAP homologs in different organisms.

  16. Mammalian CAP (Cyclase-associated protein) in the world of cell migration: Roles in actin filament dynamics and beyond.

    Science.gov (United States)

    Zhou, Guo-Lei; Zhang, Haitao; Field, Jeffrey

    2014-01-01

    Cell migration is essential for a variety of fundamental biological processes such as embryonic development, wound healing, and immune response. Aberrant cell migration also underlies pathological conditions such as cancer metastasis, in which morphological transformation promotes spreading of cancer to new sites. Cell migration is driven by actin dynamics, which is the repeated cycling of monomeric actin (G-actin) into and out of filamentous actin (F-actin). CAP (Cyclase-associated protein, also called Srv2) is a conserved actin-regulatory protein, which is implicated in cell motility and the invasiveness of human cancers. It cooperates with another actin regulatory protein, cofilin, to accelerate actin dynamics. Hence, knockdown of CAP1 slows down actin filament turnover, which in most cells leads to reduced cell motility. However, depletion of CAP1 in HeLa cells, while causing reduction in dynamics, actually led to increased cell motility. The increases in motility are likely through activation of cell adhesion signals through an inside-out signaling. The potential to activate adhesion signaling competes with the negative effect of CAP1 depletion on actin dynamics, which would reduce cell migration. In this commentary, we provide a brief overview of the roles of mammalian CAP1 in cell migration, and highlight a likely mechanism underlying the activation of cell adhesion signaling and elevated motility caused by depletion of CAP1.

  17. The DCR protein TTC3 affects differentiation and Golgi compactness in neurons through specific actin-regulating pathways.

    Directory of Open Access Journals (Sweden)

    Gaia Elena Berto

    Full Text Available In neuronal cells, actin remodeling plays a well known role in neurite extension but is also deeply involved in the organization of intracellular structures, such as the Golgi apparatus. However, it is still not very clear which mechanisms may regulate actin dynamics at the different sites. In this report we show that high levels of the TTC3 protein, encoded by one of the genes of the Down Syndrome Critical Region (DCR, prevent neurite extension and disrupt Golgi compactness in differentiating primary neurons. These effects largely depend on the capability of TTC3 to promote actin polymerization through signaling pathways involving RhoA, ROCK, CIT-N and PIIa. However, the functional relationships between these molecules differ significantly if considering the TTC3 activity on neurite extension or on Golgi organization. Finally, our results reveal an unexpected stage-dependent requirement for F-actin in Golgi organization at different stages of neuronal differentiation.

  18. Maternal effect mutations of the sponge locus affect actin cytoskeletal rearrangements in Drosophila melanogaster embryos

    OpenAIRE

    1992-01-01

    In the syncytial blastoderm stage of Drosophila embryogenesis, dome- shaped actin "caps" are observed above the interphase nuclei. During mitosis, this actin rearranges to participate in the formation of pseudocleavage furrows, transient membranous invaginations between dividing nuclei. Embryos laid by homozygous sponge mothers lack these characteristic actin structures, but retain other actin associated structures and processes. Our results indicate that the sponge product is specifically re...

  19. The role of cyclase-associated protein in regulating actin filament dynamics - more than a monomer-sequestration factor.

    Science.gov (United States)

    Ono, Shoichiro

    2013-08-01

    Dynamic reorganization of the actin cytoskeleton is fundamental to a number of cell biological events. A variety of actin-regulatory proteins modulate polymerization and depolymerization of actin and contribute to actin cytoskeletal reorganization. Cyclase-associated protein (CAP) is a conserved actin-monomer-binding protein that has been studied for over 20 years. Early studies have shown that CAP sequesters actin monomers; recent studies, however, have revealed more active roles of CAP in actin filament dynamics. CAP enhances the recharging of actin monomers with ATP antagonistically to ADF/cofilin, and also promotes the severing of actin filaments in cooperation with ADF/cofilin. Self-oligomerization and binding to other proteins regulate activities and localization of CAP. CAP has crucial roles in cell signaling, development, vesicle trafficking, cell migration and muscle sarcomere assembly. This Commentary discusses the recent advances in our understanding of the functions of CAP and its implications as an important regulator of actin cytoskeletal dynamics, which are involved in various cellular activities.

  20. Cdc42-dependent actin dynamics controls maturation and secretory activity of dendritic cells

    DEFF Research Database (Denmark)

    Schulz, Anna M; Stutte, Susanne; Hogl, Sebastian

    2015-01-01

    Cell division cycle 42 (Cdc42) is a member of the Rho guanosine triphosphatase family and has pivotal functions in actin organization, cell migration, and proliferation. To further study the molecular mechanisms of dendritic cell (DC) regulation by Cdc42, we used Cdc42-deficient DCs. Cdc42...... disruption, our results propose that Cdc42 control of actin dynamics keeps DCs in an immature state, and cessation of Cdc42 activity during DC maturation facilitates secretion as well as rapid up-regulation of intracellular molecules to the cell surface....

  1. The Role of Structural Dynamics of Actin in Class-Specific Myosin Motility

    Science.gov (United States)

    Noguchi, Taro Q. P.; Morimatsu, Masatoshi; Iwane, Atsuko H.; Yanagida, Toshio; Uyeda, Taro Q. P.

    2015-01-01

    The structural dynamics of actin, including the tilting motion between the small and large domains, are essential for proper interactions with actin-binding proteins. Gly146 is situated at the hinge between the two domains, and we previously showed that a G146V mutation leads to severe motility defects in skeletal myosin but has no effect on motility of myosin V. The present study tested the hypothesis that G146V mutation impaired rotation between the two domains, leading to such functional defects. First, our study showed that depolymerization of G146V filaments was slower than that of wild-type filaments. This result is consistent with the distinction of structural states of G146V filaments from those of the wild type, considering the recent report that stabilization of actin filaments involves rotation of the two domains. Next, we measured intramolecular FRET efficiencies between two fluorophores in the two domains with or without skeletal muscle heavy meromyosin or the heavy meromyosin equivalent of myosin V in the presence of ATP. Single-molecule FRET measurements showed that the conformations of actin subunits of control and G146V actin filaments were different in the presence of skeletal muscle heavy meromyosin. This altered conformation of G146V subunits may lead to motility defects in myosin II. In contrast, distributions of FRET efficiencies of control and G146V subunits were similar in the presence of myosin V, consistent with the lack of motility defects in G146V actin with myosin V. The distribution of FRET efficiencies in the presence of myosin V was different from that in the presence of skeletal muscle heavy meromyosin, implying that the roles of actin conformation in myosin motility depend on the type of myosin. PMID:25945499

  2. The role of structural dynamics of actin in class-specific myosin motility.

    Directory of Open Access Journals (Sweden)

    Taro Q P Noguchi

    Full Text Available The structural dynamics of actin, including the tilting motion between the small and large domains, are essential for proper interactions with actin-binding proteins. Gly146 is situated at the hinge between the two domains, and we previously showed that a G146V mutation leads to severe motility defects in skeletal myosin but has no effect on motility of myosin V. The present study tested the hypothesis that G146V mutation impaired rotation between the two domains, leading to such functional defects. First, our study showed that depolymerization of G146V filaments was slower than that of wild-type filaments. This result is consistent with the distinction of structural states of G146V filaments from those of the wild type, considering the recent report that stabilization of actin filaments involves rotation of the two domains. Next, we measured intramolecular FRET efficiencies between two fluorophores in the two domains with or without skeletal muscle heavy meromyosin or the heavy meromyosin equivalent of myosin V in the presence of ATP. Single-molecule FRET measurements showed that the conformations of actin subunits of control and G146V actin filaments were different in the presence of skeletal muscle heavy meromyosin. This altered conformation of G146V subunits may lead to motility defects in myosin II. In contrast, distributions of FRET efficiencies of control and G146V subunits were similar in the presence of myosin V, consistent with the lack of motility defects in G146V actin with myosin V. The distribution of FRET efficiencies in the presence of myosin V was different from that in the presence of skeletal muscle heavy meromyosin, implying that the roles of actin conformation in myosin motility depend on the type of myosin.

  3. Signaling and Dynamic Actin Responses of B Cells on Topographical Substrates

    Science.gov (United States)

    Ketchum, Christina; Sun, Xiaoyu; Fourkas, John; Song, Wenxia; Upadhyaya, Arpita

    B cells become activated upon physical contact with antigen on the surface of antigen presenting cells, such as dendritic cells. Binding of the B cell receptor with antigen initiates actin-mediated spreading of B cells, signaling cascades and eventually infection fighting antibodies. Lymphocytes, including B cells and T cells, have been shown to be responsive to the physical parameters of the contact surface, such as antigen mobility and substrate stiffness. However the roll of surface topography on lymphocyte function is unknown. Here we investigate the degree to which substrate topography controls actin-mediated spreading and B cell activation using nano-fabricated surfaces and live cell imaging. The model topographical system consists of 600 nanometer tall ridges with spacing varying between 800 nanometers and 5 micrometers. Using TIRF imaging we observe actin dynamics, B cell receptor motion and calcium signaling of B cells as they spread on the ridged substrates. We show that the spacing between ridges had a strong effect on the dynamics of actin and calcium influx on B cells. Our results indicate that B cells are highly sensitive to surface topography during cell spreading and signaling activation.

  4. The F-actin modifier villin regulates insulin granule dynamics and exocytosis downstream of islet cell autoantigen 512

    Directory of Open Access Journals (Sweden)

    Hassan Mziaut

    2016-08-01

    Conclusion: Our findings show that villin controls the size of the F-actin cages restricting SGs and, thus, regulates their dynamics and availability for exocytosis. Evidence that villin acts downstream of Ica512 also indicates that SGs directly influence the remodeling properties of the cortical actin cytoskeleton for tight control of insulin secretion.

  5. The Dynamic Pollen Tube Cytoskeleton: Live Cell Studies Using Actin-Binding and Microtubule-Binding Reporter Proteins

    Institute of Scientific and Technical Information of China (English)

    Alice Y. Cheung; Qiao-hong Duan; Silvia Santos Costa; Barend H.J.de Graaf; Veronica S.Di Stilio; Jose Feijo; Hen-Ming Wu

    2008-01-01

    Pollen tubes elongate within the pistil to transport sperm cells to the embryo sac for fertilization.Growth occurs exclusively at the tube apex,rendering pollen tube elongation a most dramatic polar cell growth process.A hall-mark pollen tube feature is its cytoskeleton,which comprises elaborately organized and dynamic actin microfilaments and microtubules.Pollen tube growth is dependent on the actin cytoskeleton;its organization and regulation have been exalined extensively by various approaches.including fluorescent protein labeled actin-binding proteins in live cell studies.Using the previously described GFP-NtADF1 and GFP-LIADF1, and a new actin reporter protein NtPLIM2b-GFP,we re-affirm that the predominant actin structures in elongating tobacco and lily pollen tubes are long,streaming actin cables along the pollen tube shank,and a subapical structure comprising shorter actin cables.The subapical collection of actin microfilaments undergoes dynamic changes,giving rise to the appearance of structures that range from basket-or funnel-shaped,mesh-like to a subtle ring.NtPLIM2b-GFP is used in combination with a guanine nucleotide exchange factor for the Rho GTPases,AtROP-GEF1,to illustrate the use of these actin reporter proteins to explore the linkage between the polar cell growth process and its actin cytoskeleton.Contrary to the actin cytoskeleton,microtubules appear not to play a direct role in supporting the polar cell growth process in angiosperm pollen tubes.Using a microtubule reporter protein based on the microtubule end-binding protein from Arabidopsis AtEB1,GFP-AtEB1,we show that the extensive microtubule network in elongating pollen tubes displays varying degrees of dynamics.These reporter proteins provide versatile tools to explore the functional connection between major structural and signaling components of the polar pollen tube growth process.

  6. Dynamics of actin waves on patterned substrates: a quantitative analysis of circular dorsal ruffles.

    Directory of Open Access Journals (Sweden)

    Erik Bernitt

    Full Text Available Circular Dorsal Ruffles (CDRs have been known for decades, but the mechanism that organizes these actin waves remains unclear. In this article we systematically analyze the dynamics of CDRs on fibroblasts with respect to characteristics of current models of actin waves. We studied CDRs on heterogeneously shaped cells and on cells that we forced into disk-like morphology. We show that CDRs exhibit phenomena such as periodic cycles of formation, spiral patterns, and mutual wave annihilations that are in accord with an active medium description of CDRs. On cells of controlled morphologies, CDRs exhibit extremely regular patterns of repeated wave formation and propagation, whereas on random-shaped cells the dynamics seem to be dominated by the limited availability of a reactive species. We show that theoretical models of reaction-diffusion type incorporating conserved species capture partially the behavior we observe in our data.

  7. Novel regulation of Ski protein stability and endosomal sorting by actin cytoskeleton dynamics in hepatocytes.

    Science.gov (United States)

    Vázquez-Victorio, Genaro; Caligaris, Cassandre; Del Valle-Espinosa, Eugenio; Sosa-Garrocho, Marcela; González-Arenas, Nelly R; Reyes-Cruz, Guadalupe; Briones-Orta, Marco A; Macías-Silva, Marina

    2015-02-13

    TGF-β-induced antimitotic signals are highly regulated during cell proliferation under normal and pathological conditions, such as liver regeneration and cancer. Up-regulation of the transcriptional cofactors Ski and SnoN during liver regeneration may favor hepatocyte proliferation by inhibiting TGF-β signals. In this study, we found a novel mechanism that regulates Ski protein stability through TGF-β and G protein-coupled receptor (GPCR) signaling. Ski protein is distributed between the nucleus and cytoplasm of normal hepatocytes, and the molecular mechanisms controlling Ski protein stability involve the participation of actin cytoskeleton dynamics. Cytoplasmic Ski is partially associated with actin and localized in cholesterol-rich vesicles. Ski protein stability is decreased by TGF-β/Smads, GPCR/Rho signals, and actin polymerization, whereas GPCR/cAMP signals and actin depolymerization promote Ski protein stability. In conclusion, TGF-β and GPCR signals differentially regulate Ski protein stability and sorting in hepatocytes, and this cross-talk may occur during liver regeneration.

  8. The actin-interacting protein AIP1 is essential for actin organization and plant development

    NARCIS (Netherlands)

    Ketelaar, T.; Anthony, R.G.; Voigt, B.; Menzel, D.; Hussey, P.J.

    2004-01-01

    Cell division, growth, and cytoplasmic organization require a dynamic actin cytoskeleton. The filamentous actin (F-actin) network is regulated by actin binding proteins that modulate actin dynamics. These actin binding proteins often have cooperative interactions [1 and 2]. In particular, actin inte

  9. mDia2 regulates actin and focal adhesion dynamics and organization in the lamella for efficient epithelial cell migration.

    Science.gov (United States)

    Gupton, Stephanie L; Eisenmann, Kathryn; Alberts, Arthur S; Waterman-Storer, Clare M

    2007-10-01

    Cell migration requires spatial and temporal regulation of filamentous actin (F-actin) dynamics. This regulation is achieved by distinct actin-associated proteins, which mediate polymerization, depolymerization, severing, contraction, bundling or engagement to the membrane. Mammalian Diaphanous-related (mDia) formins, which nucleate, processively elongate, and in some cases bundle actin filaments, have been extensively studied in vitro, but their function in the cell has been less well characterized. Here we study the role of mDia2 activity in the dynamic organization of F-actin in migrating epithelial cells. We find that mDia2 localizes in the lamella of migrating epithelial cells, where it is involved in the formation of a stable pool of cortical actin and in maintenance of polymerization-competent free filament barbed ends at focal adhesions. Specific inhibition of mDia2 alters focal adhesion turnover and reduces migration velocity. We suggest that the regulation of filament assembly dynamics at focal adhesions may be necessary for the formation of a stable pool of cortical lamella actin and the proper assembly and disassembly dynamics of focal adhesions, making mDia2 an important factor in epithelial cell migration.

  10. Modulation of actin dynamics as potential macrophage subtype-targeting anti-tumour strategy

    Science.gov (United States)

    Pergola, Carlo; Schubert, Katrin; Pace, Simona; Ziereisen, Jana; Nikels, Felix; Scherer, Olga; Hüttel, Stephan; Zahler, Stefan; Vollmar, Angelika M.; Weinigel, Christina; Rummler, Silke; Müller, Rolf; Raasch, Martin; Mosig, Alexander; Koeberle, Andreas; Werz, Oliver

    2017-01-01

    Tumour-associated macrophages mainly comprise immunosuppressive M2 phenotypes that promote tumour progression besides anti-tumoural M1 subsets. Selective depletion or reprogramming of M2 may represent an innovative anti-cancer strategy. The actin cytoskeleton is central for cellular homeostasis and is targeted for anti-cancer chemotherapy. Here, we show that targeting G-actin nucleation using chondramide A (ChA) predominantly depletes human M2 while promoting the tumour-suppressive M1 phenotype. ChA reduced the viability of M2, with minor effects on M1, but increased tumour necrosis factor (TNF)α release from M1. Interestingly, ChA caused rapid disruption of dynamic F-actin filaments and polymerization of G-actin, followed by reduction of cell size, binucleation and cell division, without cellular collapse. In M1, but not in M2, ChA caused marked activation of SAPK/JNK and NFκB, with slight or no effects on Akt, STAT-1/-3, ERK-1/2, and p38 MAPK, seemingly accounting for the better survival of M1 and TNFα secretion. In a microfluidically-supported human tumour biochip model, circulating ChA-treated M1 markedly reduced tumour cell viability through enhanced release of TNFα. Together, ChA may cause an anti-tumoural microenvironment by depletion of M2 and activation of M1, suggesting induction of G-actin nucleation as potential strategy to target tumour-associated macrophages in addition to neoplastic cells. PMID:28134280

  11. Planar Cell Polarity (PCP) Protein Vangl2 Regulates Ectoplasmic Specialization Dynamics via Its Effects on Actin Microfilaments in the Testes of Male Rats.

    Science.gov (United States)

    Chen, Haiqi; Mruk, Dolores D; Lee, Will M; Cheng, C Yan

    2016-05-01

    Planar cell polarity (PCP) proteins confer polarization of a field of cells (eg, elongating/elongated spermatids) within the plane of an epithelium such as the seminiferous epithelium of the tubule during spermatogenesis. In adult rat testes, Sertoli and germ cells were found to express PCP core proteins (eg, Van Gogh-like 2 [Vangl2]), effectors, ligands, and signaling proteins. Vangl2 expressed predominantly by Sertoli cells was localized at the testis-specific, actin-rich ectoplasmic specialization (ES) at the Sertoli-spermatid interface in the adluminal compartment and also Sertoli-Sertoli interface at the blood-testis barrier (BTB) and structurally interacted with actin, N-cadherin, and another PCP/polarity protein Scribble. Vangl2 knockdown (KD) by RNA interference in Sertoli cells cultured in vitro with an established tight junction-permeability barrier led to BTB tightening, whereas its overexpression using a full-length cDNA construct perturbed the barrier function. These changes were mediated through an alteration on the organization actin microfilaments at the ES in Sertoli cells, involving actin-regulatory proteins, epidermal growth factor receptor pathway substrate 8, actin-related protein 3, and Scribble, which in turn affected the function of adhesion protein complexes at the ES during the epithelial cycle of spermatogenesis. Using Polyplus in vivo-jetPEI reagent as a transfection medium to silence Vangl2 in the testis in vivo by RNA interference with high efficacy, Vangl2 KD led to changes in F-actin organization at the ES in the epithelium, impeding spermatid and phagosome transport and spermatid polarity, meiosis, and BTB dynamics. For instance, step 19 spermatids remained embedded in the epithelium alongside with step 9 and 10 spermatids in stages IX-X tubules. In summary, the PCP protein Vangl2 is an ES regulator through its effects on actin microfilaments in the testis.

  12. Nuclear Actin in Development and Transcriptional Reprogramming.

    Science.gov (United States)

    Misu, Shinji; Takebayashi, Marina; Miyamoto, Kei

    2017-01-01

    Actin is a highly abundant protein in eukaryotic cells and dynamically changes its polymerized states with the help of actin-binding proteins. Its critical function as a constituent of cytoskeleton has been well-documented. Growing evidence demonstrates that actin is also present in nuclei, referred to as nuclear actin, and is involved in a number of nuclear processes, including transcriptional regulation and chromatin remodeling. The contribution of nuclear actin to transcriptional regulation can be explained by its direct interaction with transcription machineries and chromatin remodeling factors and by controlling the activities of transcription factors. In both cases, polymerized states of nuclear actin affect the transcriptional outcome. Nuclear actin also plays an important role in activating strongly silenced genes in somatic cells for transcriptional reprogramming. When these nuclear functions of actin are considered, it is plausible to speculate that nuclear actin is also implicated in embryonic development, in which numerous genes need to be activated in a well-coordinated manner. In this review, we especially focus on nuclear actin's roles in transcriptional activation, reprogramming and development, including stem cell differentiation and we discuss how nuclear actin can be an important player in development and cell differentiation.

  13. Dynamic Synchronization of Teacher-Students Affection in Affective Instruction

    Science.gov (United States)

    Zhang, Wenhai; Lu, Jiamei

    2011-01-01

    Based on Bower's affective network theory, the article links the dynamic analysis of affective factors in affective instruction, and presents affective instruction strategic of dynamic synchronization between teacher and students to implement the best ideal mood that promotes students' cognition and affection together. In the process of teaching,…

  14. Live imaging provides new insights on dynamic F-actin filopodia and differential endocytosis during myoblast fusion in Drosophila.

    Directory of Open Access Journals (Sweden)

    Shruti Haralalka

    Full Text Available The process of myogenesis includes the recognition, adhesion, and fusion of committed myoblasts into multinucleate syncytia. In the larval body wall muscles of Drosophila, this elaborate process is initiated by Founder Cells and Fusion-Competent Myoblasts (FCMs, and cell adhesion molecules Kin-of-IrreC (Kirre and Sticks-and-stones (Sns on their respective surfaces. The FCMs appear to provide the driving force for fusion, via the assembly of protrusions associated with branched F-actin and the WASp, SCAR and Arp2/3 pathways. In the present study, we utilize the dorsal pharyngeal musculature that forms in the Drosophila embryo as a model to explore myoblast fusion and visualize the fusion process in live embryos. These muscles rely on the same cell types and genes as the body wall muscles, but are amenable to live imaging since they do not undergo extensive morphogenetic movement during formation. Time-lapse imaging with F-actin and membrane markers revealed dynamic FCM-associated actin-enriched protrusions that rapidly extend and retract into the myotube from different sites within the actin focus. Ultrastructural analysis of this actin-enriched area showed that they have two morphologically distinct structures: wider invasions and/or narrow filopodia that contain long linear filaments. Consistent with this, formin Diaphanous (Dia and branched actin nucleator, Arp3, are found decorating the filopodia or enriched at the actin focus, respectively, indicating that linear actin is present along with branched actin at sites of fusion in the FCM. Gain-of-function Dia and loss-of-function Arp3 both lead to fusion defects, a decrease of F-actin foci and prominent filopodia from the FCMs. We also observed differential endocytosis of cell surface components at sites of fusion, with actin reorganizing factors, WASp and SCAR, and Kirre remaining on the myotube surface and Sns preferentially taken up with other membrane proteins into early endosomes and

  15. Live imaging provides new insights on dynamic F-actin filopodia and differential endocytosis during myoblast fusion in Drosophila.

    Science.gov (United States)

    Haralalka, Shruti; Shelton, Claude; Cartwright, Heather N; Guo, Fengli; Trimble, Rhonda; Kumar, Ram P; Abmayr, Susan M

    2014-01-01

    The process of myogenesis includes the recognition, adhesion, and fusion of committed myoblasts into multinucleate syncytia. In the larval body wall muscles of Drosophila, this elaborate process is initiated by Founder Cells and Fusion-Competent Myoblasts (FCMs), and cell adhesion molecules Kin-of-IrreC (Kirre) and Sticks-and-stones (Sns) on their respective surfaces. The FCMs appear to provide the driving force for fusion, via the assembly of protrusions associated with branched F-actin and the WASp, SCAR and Arp2/3 pathways. In the present study, we utilize the dorsal pharyngeal musculature that forms in the Drosophila embryo as a model to explore myoblast fusion and visualize the fusion process in live embryos. These muscles rely on the same cell types and genes as the body wall muscles, but are amenable to live imaging since they do not undergo extensive morphogenetic movement during formation. Time-lapse imaging with F-actin and membrane markers revealed dynamic FCM-associated actin-enriched protrusions that rapidly extend and retract into the myotube from different sites within the actin focus. Ultrastructural analysis of this actin-enriched area showed that they have two morphologically distinct structures: wider invasions and/or narrow filopodia that contain long linear filaments. Consistent with this, formin Diaphanous (Dia) and branched actin nucleator, Arp3, are found decorating the filopodia or enriched at the actin focus, respectively, indicating that linear actin is present along with branched actin at sites of fusion in the FCM. Gain-of-function Dia and loss-of-function Arp3 both lead to fusion defects, a decrease of F-actin foci and prominent filopodia from the FCMs. We also observed differential endocytosis of cell surface components at sites of fusion, with actin reorganizing factors, WASp and SCAR, and Kirre remaining on the myotube surface and Sns preferentially taken up with other membrane proteins into early endosomes and lysosomes in the

  16. A kinome RNAi screen identified AMPK as promoting poxvirus entry through the control of actin dynamics.

    Directory of Open Access Journals (Sweden)

    Theresa S Moser

    Full Text Available Poxviruses include medically important human pathogens, yet little is known about the specific cellular factors essential for their replication. To identify genes essential for poxvirus infection, we used high-throughput RNA interference to screen the Drosophila kinome for factors required for vaccinia infection. We identified seven genes including the three subunits of AMPK as promoting vaccinia infection. AMPK not only facilitated infection in insect cells, but also in mammalian cells. Moreover, we found that AMPK is required for macropinocytosis, a major endocytic entry pathway for vaccinia. Furthermore, we show that AMPK contributes to other virus-independent actin-dependent processes including lamellipodia formation and wound healing, independent of the known AMPK activators LKB1 and CaMKK. Therefore, AMPK plays a highly conserved role in poxvirus infection and actin dynamics independent of its role as an energy regulator.

  17. Structural Dynamics of Actin during Active Interaction with Myosin Depends on the Isoform of the Essential Light Chain

    Science.gov (United States)

    Prochniewicz, Ewa; Guhathakurta, Piyali; Thomas, David D.

    2013-01-01

    We have used time-resolved phosphorescence anisotropy (TPA) to investigate the effects of essential light chain (ELC) isoforms (A1 and A2) on the interaction of skeletal muscle myosin with actin, in order to relate structural dynamics to previously reported functional effects. Actin was labeled with a phosphorescent probe at C374, and the myosin head (S1) was separated into isoenzymes S1A1 and S1A2 by ion-exchange chromatography. As previously reported, S1A1 exhibited substantially lower ATPase activity at saturating actin but substantially higher apparent actin affinity, resulting in higher catalytic efficiency. In the absence of ATP, each isoenzyme increased actin’s final anisotropy cooperatively and to a similar extent, indicating similar restriction of the amplitude of intrafilament rotational motions in the strong-binding (S) state of actomyosin. In contrast, in the presence of saturating ATP, S1A1 increased actin anisotropy much more than S1A2 and with greater cooperativity, indicating that S1A1 was more effective in restricting actin dynamics during the active interaction of actin and myosin. We conclude that during the active interaction of actin and ATP with myosin, S1A1 is more effective at stabilizing the S state (probably the force-generating state) of actomyosin, while S1A2 tends to stabilize the weak-binding (non-force-generating) W state. When a mixture of isoenzymes is present, S1A1 is dominant in its effects on actin dynamics. We conclude that ELC of skeletal muscle myosin modulates strong-to-weak structural transitions during the actomyosin ATPase cycle in an isoform-dependent manner, with significant implications for the contractile function of actomyosin. PMID:23339370

  18. Cdc42-dependent actin dynamics controls maturation and secretory activity of dendritic cells

    Science.gov (United States)

    Schulz, Anna M.; Stutte, Susanne; Hogl, Sebastian; Luckashenak, Nancy; Dudziak, Diana; Leroy, Céline; Forné, Ignasi; Imhof, Axel; Müller, Stephan A.; Brakebusch, Cord H.; Lichtenthaler, Stefan F.

    2015-01-01

    Cell division cycle 42 (Cdc42) is a member of the Rho guanosine triphosphatase family and has pivotal functions in actin organization, cell migration, and proliferation. To further study the molecular mechanisms of dendritic cell (DC) regulation by Cdc42, we used Cdc42-deficient DCs. Cdc42 deficiency renders DCs phenotypically mature as they up-regulate the co-stimulatory molecule CD86 from intracellular storages to the cell surface. Cdc42 knockout DCs also accumulate high amounts of invariant chain–major histocompatibility complex (MHC) class II complexes at the cell surface, which cannot efficiently present peptide antigens (Ag’s) for priming of Ag-specific CD4 T cells. Proteome analyses showed a significant reduction in lysosomal MHC class II–processing proteins, such as cathepsins, which are lost from DCs by enhanced secretion. As these effects on DCs can be mimicked by chemical actin disruption, our results propose that Cdc42 control of actin dynamics keeps DCs in an immature state, and cessation of Cdc42 activity during DC maturation facilitates secretion as well as rapid up-regulation of intracellular molecules to the cell surface. PMID:26553928

  19. Cyclase-associated Protein 1 (CAP1) Promotes Cofilin-induced Actin Dynamics in Mammalian Nonmuscle CellsV⃞

    OpenAIRE

    Bertling, Enni; Hotulainen, Pirta; Mattila, Pieta K.; Matilainen, Tanja; Salminen, Marjo; Lappalainen, Pekka

    2004-01-01

    Cyclase-associated proteins (CAPs) are highly conserved actin monomer binding proteins present in all eukaryotes. However, the mechanism by which CAPs contribute to actin dynamics has been elusive. In mammals, the situation is further complicated by the presence of two CAP isoforms whose differences have not been characterized. Here, we show that CAP1 is widely expressed in mouse nonmuscle cells, whereas CAP2 is the predominant isoform in developing striated muscles. In cultured NIH3T3 and B1...

  20. Activation of 5-HT7 receptor stimulates neurite elongation through mTOR, Cdc42 and actin filaments dynamics.

    Science.gov (United States)

    Speranza, Luisa; Giuliano, Teresa; Volpicelli, Floriana; De Stefano, M Egle; Lombardi, Loredana; Chambery, Angela; Lacivita, Enza; Leopoldo, Marcello; Bellenchi, Gian C; di Porzio, Umberto; Crispino, Marianna; Perrone-Capano, Carla

    2015-01-01

    Recent studies have indicated that the serotonin receptor subtype 7 (5-HT7R) plays a crucial role in shaping neuronal morphology during embryonic and early postnatal life. Here we show that pharmacological stimulation of 5-HT7R using a highly selective agonist, LP-211, enhances neurite outgrowth in neuronal primary cultures from the cortex, hippocampus and striatal complex of embryonic mouse brain, through multiple signal transduction pathways. All these signaling systems, involving mTOR, the Rho GTPase Cdc42, Cdk5, and ERK, are known to converge on the reorganization of cytoskeletal proteins that subserve neurite outgrowth. Indeed, our data indicate that neurite elongation stimulated by 5-HT7R is modulated by drugs affecting actin polymerization. In addition, we show, by 2D Western blot analyses, that treatment of neuronal cultures with LP-211 alters the expression profile of cofilin, an actin binding protein involved in microfilaments dynamics. Furthermore, by using microfluidic chambers that physically separate axons from the soma and dendrites, we demonstrate that agonist-dependent activation of 5-HT7R stimulates axonal elongation. Our results identify for the first time several signal transduction pathways, activated by stimulation of 5-HT7R, that converge to promote cytoskeleton reorganization and consequent modulation of axonal elongation. Therefore, the activation of 5-HT7R might represent one of the key elements regulating CNS connectivity and plasticity during development.

  1. Activation of 5-HT7 receptor stimulates neurite elongation through mTOR, Cdc42 and actin filaments dynamics

    Directory of Open Access Journals (Sweden)

    Luisa eSperanza

    2015-03-01

    Full Text Available Recent studies have indicated that the serotonin receptor subtype 7 (5-HT7R plays a crucial role in shaping neuronal morphology during embryonic and early postnatal life. Here we show that pharmacological stimulation of 5-HT7R using a highly selective agonist, LP-211, enhances neurite outgrowth in neuronal primary cultures from the cortex, hippocampus and striatal complex of embryonic mouse brain, through multiple signal transduction pathways. All these signaling systems, involving mTOR, the Rho GTPase Cdc42, Cdk5 and ERK, are known to converge on the reorganization of cytoskeletal proteins that subserve neurite outgrowth. Indeed, our data indicate that neurite elongation stimulated by 5-HT7R is modulated by drugs affecting actin polymerization.In addition, we show, by 2D western blot analyses, that treatment of neuronal cultures with LP-211 alters the expression profile of cofilin, an actin binding protein involved in microfilaments dynamics. Furthermore, by using microfluidic chambers that physically separate axons from the soma and dendrites, we demonstrate that agonist-dependent activation of 5-HT7R stimulates axonal elongation. Our results identify for the first time several signal transduction pathways, activated by stimulation of 5-HT7R, that converge to promote cytoskeleton reorganization and consequent modulation of axonal elongation. Therefore, the activation of 5-HT7R might represent one of the key elements regulating CNS connectivity and plasticity during development.

  2. Filopodial retraction force is generated by cortical actin dynamics and controlled by reversible tethering at the tip

    DEFF Research Database (Denmark)

    Bornschlögl, Thomas; Romero, Stéphane; Vestergaard, Christian L.

    2013-01-01

    Filopodia are dynamic, finger-like plasma membrane protrusions that sense the mechanical and chemical surroundings of the cell. Here, we show in epithelial cells that the dynamics of filopodial extension and retraction are determined by the difference between the actin polymerization rate at the ...

  3. A variational approach to the growth dynamics of pre-stressed actin filament networks

    Science.gov (United States)

    John, Karin; Stöter, Thomas; Misbah, Chaouqi

    2016-09-01

    In order to model the growth dynamics of elastic bodies with residual stresses a thermodynamically consistent approach is needed such that the cross-coupling between growth and mechanics can be correctly described. In the present work we apply a variational principle to the formulation of the interfacial growth dynamics of dendritic actin filament networks growing from biomimetic beads, an experimentally well studied system, where the buildup of residual stresses governs the network growth. We first introduce the material model for the network via a strain energy density for an isotropic weakly nonlinear elastic material and then derive consistently from this model the dynamic equations for the interfaces, i.e. for a polymerizing internal interface in contact with the bead and a depolymerizing external interface directed towards the solvent. We show that (i) this approach automatically preserves thermodynamic symmetry-properties, which is not the case for the often cited ‘rubber-band-model’ (Sekimoto et al 2004 Eur. Phys. J. E 13 247-59, Plastino et al 2004 Eur. Biophys. J. 33 310-20) and (ii) leads to a robust morphological instability of the treadmilling network interfaces. The nature of the instability depends on the interplay of the two dynamic interfaces. Depending on the biochemical conditions the network envelope evolves into a comet-like shape (i.e. the actin envelope thins out at one side and thickens on the opposite side of the bead) via a varicose instability or it breaks the symmetry via higher order zigzag modes. We conclude that morphological instabilities due to mechano-chemical coupling mechanisms and the presences of mechancial pre-stresses can play a major role in locally organizing the cytoskeleton of living cells.

  4. Fimbrin phosphorylation by metaphase Cdk1 regulates actin cable dynamics in budding yeast.

    Science.gov (United States)

    Miao, Yansong; Han, Xuemei; Zheng, Liangzhen; Xie, Ying; Mu, Yuguang; Yates, John R; Drubin, David G

    2016-01-01

    Actin cables, composed of actin filament bundles nucleated by formins, mediate intracellular transport for cell polarity establishment and maintenance. We previously observed that metaphase cells preferentially promote actin cable assembly through cyclin-dependent kinase 1 (Cdk1) activity. However, the relevant metaphase Cdk1 targets were not known. Here we show that the highly conserved actin filament crosslinking protein fimbrin is a critical Cdk1 target for actin cable assembly regulation in budding yeast. Fimbrin is specifically phosphorylated on threonine 103 by the metaphase cyclin-Cdk1 complex, in vivo and in vitro. On the basis of conformational simulations, we suggest that this phosphorylation stabilizes fimbrin's N-terminal domain, and modulates actin filament binding to regulate actin cable assembly and stability in cells. Overall, this work identifies fimbrin as a key target for cell cycle regulation of actin cable assembly in budding yeast, and suggests an underlying mechanism.

  5. Cyclase-associated protein 1 (CAP1) promotes cofilin-induced actin dynamics in mammalian nonmuscle cells.

    Science.gov (United States)

    Bertling, Enni; Hotulainen, Pirta; Mattila, Pieta K; Matilainen, Tanja; Salminen, Marjo; Lappalainen, Pekka

    2004-05-01

    Cyclase-associated proteins (CAPs) are highly conserved actin monomer binding proteins present in all eukaryotes. However, the mechanism by which CAPs contribute to actin dynamics has been elusive. In mammals, the situation is further complicated by the presence of two CAP isoforms whose differences have not been characterized. Here, we show that CAP1 is widely expressed in mouse nonmuscle cells, whereas CAP2 is the predominant isoform in developing striated muscles. In cultured NIH3T3 and B16F1 cells, CAP1 is a highly abundant protein that colocalizes with cofilin-1 to dynamic regions of the cortical actin cytoskeleton. Analysis of CAP1 knockdown cells demonstrated that this protein promotes rapid actin filament depolymerization and is important for cell morphology, migration, and endocytosis. Interestingly, depletion of CAP1 leads to an accumulation of cofilin-1 into abnormal cytoplasmic aggregates and to similar cytoskeletal defects to those seen in cofilin-1 knockdown cells, demonstrating that CAP1 is required for proper subcellular localization and function of ADF/cofilin. Together, these data provide the first direct in vivo evidence that CAP promotes rapid actin dynamics in conjunction with ADF/cofilin and is required for several central cellular processes in mammals.

  6. A family of ROP proteins that suppresses actin dynamics, and is essential for polarized growth and cell adhesion.

    Science.gov (United States)

    Burkart, Graham M; Baskin, Tobias I; Bezanilla, Magdalena

    2015-07-15

    In plants, the ROP family of small GTPases has been implicated in the polarized growth of tip-growing cells, such as root hairs and pollen tubes; however, most of the data derive from overexpressing ROP genes or constitutively active and dominant-negative isoforms, whereas confirmation by using loss-of-function studies has generally been lacking. Here, in the model moss Physcomitrella patens, we study ROP signaling during tip growth by using a loss-of-function approach based on RNA interference (RNAi) to silence the entire moss ROP family. We find that plants with reduced expression of ROP genes, in addition to failing to initiate tip growth, have perturbed cell wall staining, reduced cell adhesion and have increased actin-filament dynamics. Although plants subjected to RNAi against the ROP family also have reduced microtubule dynamics, this reduction is not specific to loss of ROP genes, as it occurs when actin function is compromised chemically or genetically. Our data suggest that ROP proteins polarize the actin cytoskeleton by suppressing actin-filament dynamics, leading to an increase in actin filaments at the site of polarized secretion.

  7. Immunological responses and actin dynamics in macrophages are controlled by N-cofilin but are independent from ADF.

    Directory of Open Access Journals (Sweden)

    Friederike Jönsson

    Full Text Available Dynamic changes in the actin cytoskeleton are essential for immune cell function and a number of immune deficiencies have been linked to mutations, which disturb the actin cytoskeleton. In macrophages and dendritic cells, actin remodelling is critical for motility, phagocytosis and antigen presentation, however the actin binding proteins, which control antigen presentation have been poorly characterized. Here we dissect the specific roles of the family of ADF/cofilin F-actin depolymerizing factors in macrophages and in local immune responses. Macrophage migration, cell polarization and antigen presentation to T-cells require n-cofilin mediated F-actin remodelling. Using a conditional mouse model, we show that n-cofilin also controls MHC class II-dependent antigen presentation. Other cellular processes such as phagocytosis and antigen processing were found to be independent of n-cofilin. Our data identify n-cofilin as a novel regulator of antigen presentation, while ADF on the other hand is dispensable for macrophage motility and antigen presentation.

  8. Regimes of wave type patterning driven by refractory actin feedback: transition from static polarization to dynamic wave behaviour

    Science.gov (United States)

    Holmes, W. R.; Carlsson, A. E.; Edelstein-Keshet, L.

    2012-08-01

    Patterns of waves, patches, and peaks of actin are observed experimentally in many living cells. Models of this phenomenon have been based on the interplay between filamentous actin (F-actin) and its nucleation promoting factors (NPFs) that activate the Arp2/3 complex. Here we present an alternative biologically-motivated model for F-actin-NPF interaction based on properties of GTPases acting as NPFs. GTPases (such as Cdc42, Rac) are known to promote actin nucleation, and to have active membrane-bound and inactive cytosolic forms. The model is a natural extension of a previous mathematical mini-model of small GTPases that generates static cell polarization. Like other modellers, we assume that F-actin negative feedback shapes the observed patterns by suppressing the trailing edge of NPF-generated wave-fronts, hence localizing the activity spatially. We find that our NPF-actin model generates a rich set of behaviours, spanning a transition from static polarization to single pulses, reflecting waves, wave trains, and oscillations localized at the cell edge. The model is developed with simplicity in mind to investigate the interaction between nucleation promoting factor kinetics and negative feedback. It explains distinct types of pattern initiation mechanisms, and identifies parameter regimes corresponding to distinct behaviours. We show that weak actin feedback yields static patterning, moderate feedback yields dynamical behaviour such as travelling waves, and strong feedback can lead to wave trains or total suppression of patterning. We use a recently introduced nonlinear bifurcation analysis to explore the parameter space of this model and predict its behaviour with simulations validating those results.

  9. Actin dynamics and competition for myosin monomer govern the sequential amplification of myosin filaments.

    Science.gov (United States)

    Beach, Jordan R; Bruun, Kyle S; Shao, Lin; Li, Dong; Swider, Zac; Remmert, Kirsten; Zhang, Yingfan; Conti, Mary A; Adelstein, Robert S; Rusan, Nasser M; Betzig, Eric; Hammer, John A

    2017-02-01

    The cellular mechanisms governing non-muscle myosin II (NM2) filament assembly are largely unknown. Using EGFP-NM2A knock-in fibroblasts and multiple super-resolution imaging modalities, we characterized and quantified the sequential amplification of NM2 filaments within lamellae, wherein filaments emanating from single nucleation events continuously partition, forming filament clusters that populate large-scale actomyosin structures deeper in the cell. Individual partitioning events coincide spatially and temporally with the movements of diverging actin fibres, suppression of which inhibits partitioning. These and other data indicate that NM2A filaments are partitioned by the dynamic movements of actin fibres to which they are bound. Finally, we showed that partition frequency and filament growth rate in the lamella depend on MLCK, and that MLCK is competing with centrally active ROCK for a limiting pool of monomer with which to drive lamellar filament assembly. Together, our results provide new insights into the mechanism and spatio-temporal regulation of NM2 filament assembly in cells.

  10. Exploring the possible role of lysine acetylation on Entamoeba histolytica virulence: a focus on the dynamics of the actin cytoskeleton.

    Science.gov (United States)

    López-Contreras, L; Hernández-Ramírez, V I; Lagunes-Guillén, A E; Montaño, Sarita; Chávez-Munguía, B; Sánchez-Ramírez, B; Talamás-Rohana, P

    2013-01-01

    Cytoskeleton remodeling can be regulated, among other mechanisms, by lysine acetylation. The role of acetylation on cytoskeletal and other proteins of Entamoeba histolytica has been poorly studied. Dynamic rearrangements of the actin cytoskeleton are crucial for amebic motility and capping formation, processes that may be effective means of evading the host immune response. Here we report the possible effect of acetylation on the actin cytoskeleton dynamics and in vivo virulence of E. histolytica. Using western blot, immunoprecipitation, microscopy assays, and in silico analysis, we show results that strongly suggest that the increase in Aspirin-induced cytoplasm proteins acetylation reduced cell movement and capping formation, likely as a consequence of alterations in the structuration of the actin cytoskeleton. Additionally, intrahepatic inoculation of Aspirin-treated trophozoites in hamsters resulted in severe impairment of the amebic virulence. Taken together, these results suggest an important role for lysine acetylation in amebic invasiveness and virulence.

  11. Exploring the Possible Role of Lysine Acetylation on Entamoeba histolytica Virulence: A Focus on the Dynamics of the Actin Cytoskeleton

    Directory of Open Access Journals (Sweden)

    L. López-Contreras

    2013-01-01

    Full Text Available Cytoskeleton remodeling can be regulated, among other mechanisms, by lysine acetylation. The role of acetylation on cytoskeletal and other proteins of Entamoeba histolytica has been poorly studied. Dynamic rearrangements of the actin cytoskeleton are crucial for amebic motility and capping formation, processes that may be effective means of evading the host immune response. Here we report the possible effect of acetylation on the actin cytoskeleton dynamics and in vivo virulence of E. histolytica. Using western blot, immunoprecipitation, microscopy assays, and in silico analysis, we show results that strongly suggest that the increase in Aspirin-induced cytoplasm proteins acetylation reduced cell movement and capping formation, likely as a consequence of alterations in the structuration of the actin cytoskeleton. Additionally, intrahepatic inoculation of Aspirin-treated trophozoites in hamsters resulted in severe impairment of the amebic virulence. Taken together, these results suggest an important role for lysine acetylation in amebic invasiveness and virulence.

  12. Phosphatidylinositol 5-phosphatase oculocerebrorenal syndrome of Lowe protein (OCRL) controls actin dynamics during early steps of Listeria monocytogenes infection.

    Science.gov (United States)

    Kühbacher, Andreas; Dambournet, Daphné; Echard, Arnaud; Cossart, Pascale; Pizarro-Cerdá, Javier

    2012-04-13

    Listeria monocytogenes is a bacterial pathogen that induces its own entry into a broad range of mammalian cells through interaction of the bacterial surface protein InlB with the cellular receptor Met, promoting an actin polymerization/depolymerization process that leads to pathogen engulfment. Phosphatidylinositol bisphosphate (PI[4,5]P(2)) and trisphosphate (PI[3,4,5]P(3)) are two major phosphoinositide species that function as molecular scaffolds, recruiting cellular effectors that regulate actin dynamics during L. monocytogenes infection. Because the phosphatidylinositol 5'-phosphatase OCRL dephosphorylates PI(4,5)P(2) and to a lesser extent PI(3,4,5)P(3), we investigated whether this phosphatase modulates cell invasion by L. monocytogenes. Inactivation of OCRL by small interfering RNA (siRNA) leads to an increase in the internalization levels of L. monocytogenes in HeLa cells. Interestingly, OCRL depletion does not increase but rather decreases the surface expression of the receptor Met, suggesting that OCRL controls bacterial internalization by modulating signaling cascades downstream of Met. Immuno-fluorescence microscopy reveals that endogenous and overexpressed OCRL are present at L. monocytogenes invasion foci; live-cell imaging additionally shows that actin depolymerization coincides with EGFP-OCRL-a accumulation around invading bacteria. Together, these observations suggest that OCRL promotes actin depolymerization during L. monocytogenes infection; in agreement with this hypothesis, OCRL depletion leads to an increase in actin, PI(4,5)P(2), and PI(3,4,5)P(3) levels at bacterial internalization foci. Furthermore, in cells knocked down for OCRL, transfection of enzymatically active EGFP-OCRL-a (but not of a phosphatase-dead enzyme) decreases the levels of intracellular L. monocytogenes and of actin associated with invading bacteria. These results demonstrate that through its phosphatase activity, OCRL restricts L. monocytogenes invasion by modulating

  13. Cyclase-associated protein (CAP) acts directly on F-actin to accelerate cofilin-mediated actin severing across the range of physiological pH.

    Science.gov (United States)

    Normoyle, Kieran P M; Brieher, William M

    2012-10-12

    Fast actin depolymerization is necessary for cells to rapidly reorganize actin filament networks. Utilizing a Listeria fluorescent actin comet tail assay to monitor actin disassembly rates, we observed that although a mixture of actin disassembly factors (cofilin, coronin, and actin-interacting protein 1 is sufficient to disassemble actin comet tails in the presence of physiological G-actin concentrations this mixture was insufficient to disassemble actin comet tails in the presence of physiological F-actin concentrations. Using biochemical complementation, we purified cyclase-associated protein (CAP) from thymus extracts as a factor that protects against the inhibition of excess F-actin. CAP has been shown to participate in actin dynamics but has been thought to act by liberating cofilin from ADP·G-actin monomers to restore cofilin activity. However, we found that CAP augments cofilin-mediated disassembly by accelerating the rate of cofilin-mediated severing. We also demonstrated that CAP acts directly on F-actin and severs actin filaments at acidic, but not neutral, pH. At the neutral pH characteristic of cytosol in most mammalian cells, we demonstrated that neither CAP nor cofilin are capable of severing actin filaments. However, the combination of CAP and cofilin rapidly severed actin at all pH values across the physiological range. Therefore, our results reveal a new function for CAP in accelerating cofilin-mediated actin filament severing and provide a mechanism through which cells can maintain high actin turnover rates without having to alkalinize cytosol, which would affect many biochemical reactions beyond actin depolymerization.

  14. The kinesin-like proteins, KAC1/2, regulate actin dynamics underlying chloroplast light-avoidance in Physcomitrella patens

    Institute of Scientific and Technical Information of China (English)

    Zhiyuan Shen; Yen-Chen Liu; Jeffrey P Bibeau; Kyle P Lemoi; Erkan Tzel; Luis Vidali

    2015-01-01

    In plants, light determines chloroplast position;these organelles show avoidance and accumulation re-sponses in high and low fluence-rate light, respectively. Chloroplast motility in response to light is driven by cytoskeletal elements. The actin cytoskeleton mediates chloroplast photorelocation responses in Arabidopsis thali-ana. In contrast, in the moss Physcomitrella patens, both, actin filaments and microtubules can transport chloroplasts. Because of the surprising evidence that two kinesin-like proteins (called KACs) are important for actin-dependent chloroplast photorelocation in vascular plants, we wanted to determine the cytoskeletal system responsible for the function of these proteins in moss. We performed gene-specific silencing using RNA interference in P. patens. We confirmed existing reports using gene knockouts, that PpKAC1 and PpKAC2 are required for chloroplast dispersion under uniform white light conditions, and that the two proteins are functionally equivalent. To address the specific cytoskeletal elements responsible for motility, this loss-of-function approach was combined with cytoskeleton-targeted drug studies. We found that, in P. patens, these KACs mediate the chloroplast light-avoidance response in an actin filament-dependent, rather than a microtubule-dependent manner. Using correlation-decay analysis of cytoskeletal dynamics, we found that PpKAC stabilizes cortical actin filaments, but has no effect on microtubule dynamics.

  15. Rho/Rho-dependent kinase affects locomotion and actin-myosin II activity of Amoeba proteus.

    Science.gov (United States)

    Kłopocka, W; Redowicz, M J

    2004-10-01

    The highly motile free-living unicellular organism Amoeba proteus has been widely used as a model to study cell motility. However, the molecular mechanisms underlying its unique locomotion are still scarcely known. Recently, we have shown that blocking the amoebae's endogenous Rac- and Rho-like proteins led to distinct and irreversible changes in the appearance of these large migrating cells as well as to a significant inhibition of their locomotion. In order to elucidate the mechanism of the Rho pathway, we tested the effects of blocking the endogenous Rho-dependent kinase (ROCK) by anti-ROCK antibodies and Y-27632, (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl)cyclohexanecarboxamide dihydrochloride, a specific inhibitor of ROCK, on migrating amoebae and the effect of the Rho and ROCK inhibition on the actin-activated Mg-ATPase of the cytosolic fraction of the amoebae. Amoebae microinjected with anti-ROCK inhibitors remained contracted and strongly attached to the glass surface and exhibited an atypical locomotion. Despite protruding many pseudopodia that were advancing in various directions, the amoebae could not effectively move. Immunofluorescence studies showed that ROCK-like protein was dispersed throughout the cytoplasm and was also found in the regions of actin-myosin II interaction during both isotonic and isometric contraction. The Mg-ATPase activity was about two- to threefold enhanced, indicating that blocking the Rho/Rho-dependent kinase activated myosin. It is possible then that in contrast to the vertebrate cells, the inactivation of Rho/Rho-dependent kinase in amoebae leads to the activation of myosin II and to the observed hypercontracted cells which cannot exert effective locomotion.

  16. Effect of Flumorph on F-Actin Dynamics in the Potato Late Blight Pathogen Phytophthora infestans.

    Science.gov (United States)

    Hua, Chenlei; Kots, Kiki; Ketelaar, Tijs; Govers, Francine; Meijer, Harold J G

    2015-04-01

    Oomycetes are fungal-like pathogens that cause notorious diseases. Protecting crops against oomycetes requires regular spraying with chemicals, many with an unknown mode of action. In the 1990s, flumorph was identified as a novel crop protection agent. It was shown to inhibit the growth of oomycete pathogens including Phytophthora spp., presumably by targeting actin. We recently generated transgenic Phytophthora infestans strains that express Lifeact-enhanced green fluorescent protein (eGFP), which enabled us to monitor the actin cytoskeleton during hyphal growth. For analyzing effects of oomicides on the actin cytoskeleton in vivo, the P. infestans Lifeact-eGFP strain is an excellent tool. Here, we confirm that flumorph is an oomicide with growth inhibitory activity. Microscopic analyses showed that low flumorph concentrations provoked hyphal tip swellings accompanied by accumulation of actin plaques in the apex, a feature reminiscent of tips of nongrowing hyphae. At higher concentrations, swelling was more pronounced and accompanied by an increase in hyphal bursting events. However, in hyphae that remained intact, actin filaments were indistinguishable from those in nontreated, nongrowing hyphae. In contrast, in hyphae treated with the actin depolymerizing drug latrunculin B, no hyphal bursting was observed but the actin filaments were completely disrupted. This difference demonstrates that actin is not the primary target of flumorph.

  17. In vitro reconstitution of dynamic microtubules interacting with actin filament networks

    NARCIS (Netherlands)

    Preciado Lopez, M.; Huber, F.; Grigoriev, Ilya; Steinmetz, M.O.; Akhmanova, Anna; Dogterom, M.; Koenderink, G.H.

    2014-01-01

    Interactions between microtubules and actin filaments (F-actin) are essential for eukaryotic cell migration, polarization, growth, and division. Although the importance of these interactions has been long recognized, the inherent complexity of the cell interior hampers a detailed mechanistic study o

  18. Electrostatics control actin filament nucleation and elongation kinetics.

    Science.gov (United States)

    Crevenna, Alvaro H; Naredi-Rainer, Nikolaus; Schönichen, André; Dzubiella, Joachim; Barber, Diane L; Lamb, Don C; Wedlich-Söldner, Roland

    2013-04-26

    The actin cytoskeleton is a central mediator of cellular morphogenesis, and rapid actin reorganization drives essential processes such as cell migration and cell division. Whereas several actin-binding proteins are known to be regulated by changes in intracellular pH, detailed information regarding the effect of pH on the actin dynamics itself is still lacking. Here, we combine bulk assays, total internal reflection fluorescence microscopy, fluorescence fluctuation spectroscopy techniques, and theory to comprehensively characterize the effect of pH on actin polymerization. We show that both nucleation and elongation are strongly enhanced at acidic pH, with a maximum close to the pI of actin. Monomer association rates are similarly affected by pH at both ends, although dissociation rates are differentially affected. This indicates that electrostatics control the diffusional encounter but not the dissociation rate, which is critical for the establishment of actin filament asymmetry. A generic model of protein-protein interaction, including electrostatics, explains the observed pH sensitivity as a consequence of charge repulsion. The observed pH effect on actin in vitro agrees with measurements of Listeria propulsion in pH-controlled cells. pH regulation should therefore be considered as a modulator of actin dynamics in a cellular environment.

  19. The structural dynamics of α-tropomyosin on F-actin shape the overlap complex between adjacent tropomyosin molecules

    Science.gov (United States)

    Lehman, William; Li, Xiaochuan (Edward); Orzechowski, Marek; Fischer, Stefan

    2013-01-01

    Coiled-coil tropomyosin, localized on actin filaments in virtually all eukaryotic cells, serves as a gatekeeper regulating access of the motor protein myosin and other actin-binding proteins onto the thin filament surface. Tropomyosin's modular pseudo-repeating pattern of approximately 39 amino acid residues is designed to allow binding of the coiled-coil to successive actin subunits along thin filaments. Even though different tropomyosin isoforms contain varying numbers of repeat modules, the pseudo-repeat length, in all cases, matches that of a single actin subunit. Thus, the seven pseudo-repeats of 42 nm long muscle tropomyosin bind to seven successive actin subunits along thin filaments, while simultaneously bending into a super-helical conformation that is preshaped to the actin filament helix. In order to form a continuous cable on thin filaments that is free of gaps, adjacent tropomyosin molecules polymerize head-to-tail by means of a short (∼9 residue) overlap. Several laboratories have engineered peptides to mimic the N- and C-terminal tropomyosin association and to characterize the overlap structure. All overlapping domains examined show a compact N-terminal coiled-coil inserting into a partially opened C-terminal partner, where the opposing coiled-coils at the overlap junction face each other at up to ∼90° twist angles. Here, Molecular Dynamics (MD) simulations were carried out to determine constraints on the formation of the tropomyosin overlap complex and to assess the amount of twisting exhibited by full-length tropomyosin when bound to actin. With the exception of the last 20 to 40 C- and N-terminal residues, we find that the average tropomyosin structure closely resembles a “canonical” model proposed in the classic work of McLachlan and Stewart, displaying perfectly symmetrical supercoil geometry matching the F-actin helix with an integral number of coiled-coil turns, a coiled-coil helical pitch of 137 Å, a superhelical pitch of 770

  20. Rac1 at the crossroad of actin dynamics and neuroinflammation in Amyotrophic Lateral Sclerosis

    Directory of Open Access Journals (Sweden)

    Nadia eD'Ambrosi

    2014-09-01

    Full Text Available Rac1 is a major player of the Rho family of small GTPases that controls multiple cell signaling pathways, such as the organization of cytoskeleton (including adhesion and motility, cell proliferation, apoptosis and activation of immune cells. In the nervous system, in particular, Rac1 GTPase plays a key regulatory function of both actin and microtubule cytoskeletal dynamics and thus it is central to axonal growth and stability, as well as dendrite and spine structural plasticity. Rac1 is also a crucial regulator of NADPH-dependent membrane oxidase (NOX, a prominent source of ROS, thus having a central role in the inflammatory response and neurotoxicity mediated by microglia cells in the nervous system. As such, alterations in Rac1 activity might well be involved in the processes that give rise to Amyotrophic Lateral Sclerosis (ALS, a complex syndrome where cytoskeletal disturbances in motor neurons and redox alterations in the inflammatory compartment play pivotal and synergic roles in the final disease outcomes. Here we will discuss the genetic and mechanistic evidence indicating the relevance of Rac1 dysregulation in the pathogenesis of ALS.

  1. Directed actin assembly and motility.

    Science.gov (United States)

    Boujemaa-Paterski, Rajaa; Galland, Rémi; Suarez, Cristian; Guérin, Christophe; Théry, Manuel; Blanchoin, Laurent

    2014-01-01

    The actin cytoskeleton is a key component of the cellular architecture. However, understanding actin organization and dynamics in vivo is a complex challenge. Reconstitution of actin structures in vitro, in simplified media, allows one to pinpoint the cellular biochemical components and their molecular interactions underlying the architecture and dynamics of the actin network. Previously, little was known about the extent to which geometrical constraints influence the dynamic ultrastructure of these networks. Therefore, in order to study the balance between biochemical and geometrical control of complex actin organization, we used the innovative methodologies of UV and laser patterning to design a wide repertoire of nucleation geometries from which we assembled branched actin networks. Using these methods, we were able to reconstitute complex actin network organizations, closely related to cellular architecture, to precisely direct and control their 3D connections. This methodology mimics the actin networks encountered in cells and can serve in the fabrication of innovative bioinspired systems.

  2. Vault-poly-ADP-ribose polymerase in the Octopus vulgaris brain: a regulatory factor of actin polymerization dynamic.

    Science.gov (United States)

    De Maio, Anna; Natale, Emiliana; Rotondo, Sergio; Di Cosmo, Anna; Faraone-Mennella, Maria Rosaria

    2013-09-01

    Our previous behavioural, biochemical and immunohistochemical analyses conducted in selected regions (supra/sub oesophageal masses) of the Octopus vulgaris brain detected a cytoplasmic poly-ADP-ribose polymerase (more than 90% of total enzyme activity). The protein was identified as the vault-free form of vault-poly-ADP-ribose polymerase. The present research extends and integrates the biochemical characterization of poly-ADP-ribosylation system, namely, reaction product, i.e., poly-ADP-ribose, and acceptor proteins, in the O. vulgaris brain. Immunochemical analyses evidenced that the sole poly-ADP-ribose acceptor was the octopus cytoskeleton 50-kDa actin. It was present in both free, endogenously poly-ADP-ribosylated form (70kDa) and in complex with V-poly-ADP-ribose polymerase and poly-ADP-ribose (260kDa). The components of this complex, alkali and high salt sensitive, were purified and characterized. The kind and the length of poly-ADP-ribose corresponded to linear chains of 30-35 ADP-ribose units, in accordance with the features of the polymer synthesized by the known vault-poly-ADP-ribose polymerase. In vitro experiments showed that V-poly-ADP-ribose polymerase activity of brain cytoplasmic fraction containing endogenous actin increased upon the addition of commercial actin and was highly reduced by ATP. Anti-actin immunoblot of the mixture in the presence and absence of ATP showed that the poly-ADP-ribosylation of octopus actin is a dynamic process balanced by the ATP-dependent polymerization of the cytoskeleton protein, a fundamental mechanism for synaptic plasticity.

  3. Dynamic Musical Communication of Core Affect

    Directory of Open Access Journals (Sweden)

    Nicole eFlaig

    2014-03-01

    Full Text Available Is there something special about the way music communicates feelings? Theorists since Meyer (1956 have attempted to explain how music could stimulate varied and subtle affective experiences by violating learned expectancies, or by mimicking other forms of social interaction. Our proposal is that music speaks to the brain in its own language; it need not imitate any other form of communication. We review recent theoretical and empirical literature, which suggests that all conscious processes consist of dynamic neural events, produced by spatially dispersed processes in the physical brain. Intentional thought and affective experience arise as dynamical aspects of neural events taking place in multiple brain areas simultaneously. At any given moment, this content comprises a unified scene that is integrated into a dynamic core through synchrony of neuronal oscillations. We propose that 1 neurodynamic synchrony with musical stimuli gives rise to musical qualia including tonal and temporal expectancies, and that 2 music-synchronous responses couple into core neurodynamics, enabling music to directly modulate core affect. Expressive music performance, for example, may recruit rhythm-synchronous neural responses to support affective communication. We suggest that the dynamic relationship between musical expression and the experience of affect presents a unique opportunity for the study of emotional experience. This may help elucidate the neural mechanisms underlying arousal and valence, and offer a new approach to exploring the complex dynamics of the how and why of emotional experience.

  4. Dynamic musical communication of core affect.

    Science.gov (United States)

    Flaig, Nicole K; Large, Edward W

    2014-01-01

    Is there something special about the way music communicates feelings? Theorists since Meyer (1956) have attempted to explain how music could stimulate varied and subtle affective experiences by violating learned expectancies, or by mimicking other forms of social interaction. Our proposal is that music speaks to the brain in its own language; it need not imitate any other form of communication. We review recent theoretical and empirical literature, which suggests that all conscious processes consist of dynamic neural events, produced by spatially dispersed processes in the physical brain. Intentional thought and affective experience arise as dynamical aspects of neural events taking place in multiple brain areas simultaneously. At any given moment, this content comprises a unified "scene" that is integrated into a dynamic core through synchrony of neuronal oscillations. We propose that (1) neurodynamic synchrony with musical stimuli gives rise to musical qualia including tonal and temporal expectancies, and that (2) music-synchronous responses couple into core neurodynamics, enabling music to directly modulate core affect. Expressive music performance, for example, may recruit rhythm-synchronous neural responses to support affective communication. We suggest that the dynamic relationship between musical expression and the experience of affect presents a unique opportunity for the study of emotional experience. This may help elucidate the neural mechanisms underlying arousal and valence, and offer a new approach to exploring the complex dynamics of the how and why of emotional experience.

  5. Actin Dynamics Regulates Voltage-Dependent Calcium-Permeable Channels of the Vicia faba Guard Cell Plasma Membrane

    Institute of Scientific and Technical Information of China (English)

    Wei Zhang; Liu-Min Fan

    2009-01-01

    Free cytosolic Ca~(2+) ([Ca~(2+)]_(cyt)) is an ubiquitous second messenger in plant cell signaling, and [Ca~(2+)]_(cyt) elevation is associated with Ca~(2+)-permeable channels in the plasma membrane and endomembranes regulated by a wide range of stimuli. However, knowledge regarding Ca~(2+) channels and their regulation remains limited in planta. A type of voltage-dependent Ca~(2+)-permeable channel was identified and characterized for the Vicia faba L. guard cell plasma membrane by using patch-clamp techniques. These channels are permeable to both Ba~(2+) and Ca~(2+), and their activities can be inhibited by micromolar Gd~(3+). The unitary conductance and the reversal potential of the channels depend on the Ca~(2+) or Ba~(2+) gradients across the plasma membrane. The inward whole-cell Ca~(2+) (Ba~(2+)) current, as well as the unitary current amplitude and NP. of the single Ca~(2+) channel, increase along with the membrane hyperpolarization. Pharmacological experiments suggest that actin dynamics may serve as an upstream regulator of this type of calcium channel of the guard cell plasma membrane. Cytochalasin D, an actin polymerization blocker, activated the NP_o of these channels at the single channel level and increased the current amplitude at the whole-cell level. But these channel activations and current increments could be restrained by pretreatment with an F-actin stabilizer, phalloidin. The potential physiological significance of this regulatory mechanism is also discussed.

  6. Shank-cortactin interactions control actin dynamics to maintain flexibility of neuronal spines and synapses

    NARCIS (Netherlands)

    Mac Gillavry, H.D.; Kerr, JM; Kassner, J; Frost, NA; Blanpied, TA

    2016-01-01

    The family of Shank scaffolding molecules (comprising Shank1, 2 and 3) are core components of the postsynaptic density (PSD) in neuronal synapses. Shanks link surface receptors to other scaffolding molecules within the PSD, as well as to the actin cytoskeleton. However, determining the function of S

  7. Dynamic interaction between actin and nesprin2 maintain the cell nucleus in a prestressed state

    Science.gov (United States)

    Kumar, Abhishek; Shivashankar, G. V.

    2016-12-01

    Mechanical coupling between the nucleus and the cytoskeleton is indispensable for direct force transduction from the extra cellular matrix (ECM) to the chromatin. Although this physical coupling has been shown to be crucial for nuclear positioning and its function, the quantification of nuclear-cytoskeleton interaction has been lacking. In this paper, using various quantitative fluorescence spectroscopy techniques, we investigate the nature of this connection. High-resolution 3D imaging shows that nesprin2G forms short linear structures along actin stress fibers (ASFs) in the apical region of the nucleus. Fluorescence recovery after photobleaching (FRAP) revealed that the alignment of nesprin2G becomes heterogeneous when cell shape is engineered from elongated rectangular shape to square using micropatterned substrates. Further, fluorescence cross-correlation spectroscopy (FCCS) revealed that actin interacts transiently with outer nuclear membrane protein nesprin2G with a time scale of 12 ms. In addition, fluorescence resonance energy transfer (FRET) experiments show that the apical ASFs and nesprin2G are in close physical proximity. This interaction is spatially heterogeneous with high FRET along the ASFs. Lastly, we show that the disruption of actin to nuclear connection by over-expression of Dominant Negative Klarsicht, ANC-1, Syne Homology (DNKASH) leads to an increase in nuclear height. These results not only reveal the characteristics of actin-nesprin2G interaction and its significance in regulating nuclear morphology, but also validate the utility of quantitative fluorescence techniques in deciphering physical connections that are essential for mechanotransduction.

  8. The role of actin turnover in retrograde actin network flow in neuronal growth cones.

    Directory of Open Access Journals (Sweden)

    David Van Goor

    Full Text Available The balance of actin filament polymerization and depolymerization maintains a steady state network treadmill in neuronal growth cones essential for motility and guidance. Here we have investigated the connection between depolymerization and treadmilling dynamics. We show that polymerization-competent barbed ends are concentrated at the leading edge and depolymerization is distributed throughout the peripheral domain. We found a high-to-low G-actin gradient between peripheral and central domains. Inhibiting turnover with jasplakinolide collapsed this gradient and lowered leading edge barbed end density. Ultrastructural analysis showed dramatic reduction of leading edge actin filament density and filament accumulation in central regions. Live cell imaging revealed that the leading edge retracted even as retrograde actin flow rate decreased exponentially. Inhibition of myosin II activity before jasplakinolide treatment lowered baseline retrograde flow rates and prevented leading edge retraction. Myosin II activity preferentially affected filopodial bundle disassembly distinct from the global effects of jasplakinolide on network turnover. We propose that growth cone retraction following turnover inhibition resulted from the persistence of myosin II contractility even as leading edge assembly rates decreased. The buildup of actin filaments in central regions combined with monomer depletion and reduced polymerization from barbed ends suggests a mechanism for the observed exponential decay in actin retrograde flow. Our results show that growth cone motility is critically dependent on continuous disassembly of the peripheral actin network.

  9. Role of cyclic nucleotide-dependent actin cytoskeletal dynamics:Ca(2+](i and force suppression in forskolin-pretreated porcine coronary arteries.

    Directory of Open Access Journals (Sweden)

    Kyle M Hocking

    Full Text Available Initiation of force generation during vascular smooth muscle contraction involves a rise in intracellular calcium ([Ca(2+]i and phosphorylation of myosin light chains (MLC. However, reversal of these two processes alone does not account for the force inhibition that occurs during relaxation or inhibition of contraction, implicating that other mechanisms, such as actin cytoskeletal rearrangement, play a role in the suppression of force. In this study, we hypothesize that forskolin-induced force suppression is dependent upon changes in actin cytoskeletal dynamics. To focus on the actin cytoskeletal changes, a physiological model was developed in which forskolin treatment of intact porcine coronary arteries (PCA prior to treatment with a contractile agonist resulted in complete suppression of force. Pretreatment of PCA with forskolin suppressed histamine-induced force generation but did not abolish [Ca(2+]i rise or MLC phosphorylation. Additionally, forskolin pretreatment reduced filamentous actin in histamine-treated tissues, and prevented histamine-induced changes in the phosphorylation of the actin-regulatory proteins HSP20, VASP, cofilin, and paxillin. Taken together, these results suggest that forskolin-induced complete force suppression is dependent upon the actin cytoskeletal regulation initiated by the phosphorylation changes of the actin regulatory proteins and not on the MLC dephosphorylation. This model of complete force suppression can be employed to further elucidate the mechanisms responsible for smooth muscle tone, and may offer cues to pathological situations, such as hypertension and vasospasm.

  10. Expression of a dynamin 2 mutant associated with Charcot-Marie-Tooth disease leads to aberrant actin dynamics and lamellipodia formation.

    Science.gov (United States)

    Yamada, Hiroshi; Kobayashi, Kinue; Zhang, Yubai; Takeda, Tetsuya; Takei, Kohji

    2016-08-15

    Specific mutations in dynamin 2 are linked to Charcot-Marie-Tooth disease (CMT), an inherited peripheral neuropathy. However, the effects of these mutations on dynamin function, particularly in relation to the regulation of the actin cytoskeleton remain unclear. Here, selected CMT-associated dynamin mutants were expressed to examine their role in the pathogenesis of CMT in U2OS cells. Ectopic expression of the dynamin CMT mutants 555Δ3 and K562E caused an approximately 50% decrease in serum stimulation-dependent lamellipodia formation; however, only K562E caused aberrations in the actin cytoskeleton. Immunofluorescence analysis showed that the K562E mutation resulted in the disappearance of radially aligned actin bundles and the simultaneous appearance of F-actin clusters. Live-cell imaging analyses showed F-actin polymers of decreased length assembled into immobile clusters in K562E-expressing cells. The K562E dynamin mutant colocalized with the F-actin clusters, whereas its colocalization with clathrin-coated pit marker proteins was decreased. Essentially the same results were obtained using another cell line, HeLa and NG108-15 cells. The present study is the first to show the association of dynamin CMT mutations with aberrant actin dynamics and lamellipodia, which may contribute to defective endocytosis and myelination in Schwann cells in CMT.

  11. RhoA-mediated MLC2 regulates actin dynamics for cytokinesis in meiosis.

    Science.gov (United States)

    Duan, Xing; Liu, Jun; Zhu, Cheng-Cheng; Wang, Qiao-Chu; Cui, Xiang-Shun; Kim, Nam-Hyung; Xiong, Bo; Sun, Shao-Chen

    2016-01-01

    During oocyte meiosis, the bipolar spindle forms in the central cytoplasm and then migrates to the cortex. Subsequently, the oocyte extrudes the polar body through two successive asymmetric divisions, which are regulated primarily by actin filaments. Myosin light chain2 (MLC2) phosphorylation plays pivotal roles in smooth muscle contraction, stress fiber formation, cell motility and cytokinesis. However, whether MLC2 phosphorylation participates in the oocyte polarization and asymmetric division has not been clarified. The present study investigated the expression and functions of MLC2 during mouse oocyte meiosis. Our result showed that p-MLC2 was localized in the oocyte cortex, with a thickened cap above the chromosomes. Meanwhile, p-MLC2 was also localized in the poles of spindle. Disruption of MLC2 activity by MLC2 knock down (KD) caused the failure of polar body extrusion. Immunofluorescent staining showed that a large proportion of oocytes arrested in telophase stage and failed to undergo cytokinesis after culturing for 12 hours. In the meantime, actin filament staining at oocyte membrane and cytoplasm were reduced in MLC2 KD oocytes. Finally, we found that the phosphorylation of MLC2 protein levels was decreased after disruption of RhoA activity. Above all, our data indicated that the RhoA-mediated MLC2 regulates the actin organization for cytokinesis during mouse oocyte maturation.

  12. Nuclear envelope lamin-A couples actin dynamics with immunological synapse architecture and T cell activation.

    Science.gov (United States)

    González-Granado, José M; Silvestre-Roig, Carlos; Rocha-Perugini, Vera; Trigueros-Motos, Laia; Cibrián, Danay; Morlino, Giulia; Blanco-Berrocal, Marta; Osorio, Fernando G; Freije, José M P; López-Otín, Carlos; Sánchez-Madrid, Francisco; Andrés, Vicente

    2014-04-22

    In many cell types, nuclear A-type lamins regulate multiple cellular functions, including higher-order genome organization, DNA replication and repair, gene transcription, and signal transduction; however, their role in specialized immune cells remains largely unexplored. We showed that the abundance of A-type lamins was almost negligible in resting naïve T lymphocytes, but was increased upon activation of the T cell receptor (TCR). The increase in lamin-A was an early event that accelerated formation of the immunological synapse between T cells and antigen-presenting cells. Polymerization of F-actin in T cells is a critical step for immunological synapse formation, and lamin-A interacted with the linker of nucleoskeleton and cytoskeleton (LINC) complex to promote F-actin polymerization. We also showed that lamin-A expression accelerated TCR clustering and led to enhanced downstream signaling, including extracellular signal-regulated kinase 1/2 (ERK1/2) signaling, as well as increased target gene expression. Pharmacological inhibition of the ERK pathway reduced lamin-A-dependent T cell activation. Moreover, mice lacking lamin-A in immune cells exhibited impaired T cell responses in vivo. These findings underscore the importance of A-type lamins for TCR activation and identify lamin-A as a previously unappreciated regulator of the immune response.

  13. Effects of F/G-actin ratio and actin turn-over rate on NADPH oxidase activity in microglia

    DEFF Research Database (Denmark)

    Rasmussen, Izabela; Pedersen, Line Hjortshøj; Byg, Luise;

    2010-01-01

    Most in vivo studies that have addressed the role of actin dynamics in NADPH oxidase function in phagocytes have used toxins to modulate the polymerization state of actin and mostly effects on actin has been evaluated by end point measurements of filamentous actin, which says little about actin d...

  14. Drebrin attenuates the interaction between actin and myosin-V.

    Science.gov (United States)

    Ishikawa, Ryoki; Katoh, Kaoru; Takahashi, Ayumi; Xie, Ce; Oseki, Koushi; Watanabe, Michitoshi; Igarashi, Michihiro; Nakamura, Akio; Kohama, Kazuhiro

    2007-07-27

    Drebrin-A is an actin-binding protein localized in the dendritic spines of mature neurons, and has been suggested to affect spine morphology [K. Hayashi, T. Shirao, Change in the shape of dendritic spines caused by overexpression of drebrin in cultured cortical neurons, J. Neurosci. 19 (1999) 3918-3925]. However, no biochemical analysis of drebrin-A has yet been reported. In this study, we purified drebrin-A using a bacterial expression system, and characterized it in vitro. Drebrin-A bound to actin filaments with a stoichiometry of one drebrin molecule to 5-6 actin molecules. Furthermore, drebrin-A decreased the Mg-ATPase activity of myosin V. In vitro motility assay revealed that the attachment of F-actin to glass surface coated with myosin-V was decreased by drebrin-A, but once F-actin attached to the surface, the sliding speed of F-actin was unaffected by the presence of drebrin A. These findings suggest that drebrin-A may affect spine dynamics, vesicle transport, and other myosin-V-driven motility in neurons through attenuating the interaction between actin and myosin-V.

  15. Energetic modeling and single-molecule verification of dynamic regulation on receptor complexes by actin corrals and lipid raft domains

    Science.gov (United States)

    Lin, Chien Y.; Huang, Jung Y.; Lo, Leu-Wei

    2014-12-01

    We developed an energetic model by integrating the generalized Langevin equation with the Cahn-Hilliard equation to simulate the diffusive behaviors of receptor proteins in the plasma membrane of a living cell. Simulation results are presented to elaborate the confinement effects from actin corrals and protein-induced lipid domains. Single-molecule tracking data of epidermal growth factor receptors (EGFR) acquired on live HeLa cells agree with the simulation results and the mechanism that controls the diffusion of single-molecule receptors is clarified. We discovered that after ligand binding, EGFR molecules move into lipid nanodomains. The transition rates between different diffusion states of liganded EGFR molecules are regulated by the lipid domains. Our method successfully captures dynamic interactions of receptors at the single-molecule level and provides insight into the functional architecture of both the diffusing EGFR molecules and their local cellular environment.

  16. Yersinia outer protein YopE affects the actin cytoskeleton in Dictyostelium discoideum through targeting of multiple Rho family GTPases

    LENUS (Irish Health Repository)

    Vlahou, Georgia

    2009-07-14

    Abstract Background All human pathogenic Yersinia species share a virulence-associated type III secretion system that translocates Yersinia effector proteins into host cells to counteract infection-induced signaling responses and prevent phagocytosis. Dictyostelium discoideum has been recently used to study the effects of bacterial virulence factors produced by internalized pathogens. In this study we explored the potential of Dictyostelium as model organism for analyzing the effects of ectopically expressed Yersinia outer proteins (Yops). Results The Yersinia pseudotuberculosis virulence factors YopE, YopH, YopM and YopJ were expressed de novo within Dictyostelium and their effects on growth in axenic medium and on bacterial lawns were analyzed. No severe effect was observed for YopH, YopJ and YopM, but expression of YopE, which is a GTPase activating protein for Rho GTPases, was found to be highly detrimental. GFP-tagged YopE expressing cells had less conspicuous cortical actin accumulation and decreased amounts of F-actin. The actin polymerization response upon cAMP stimulation was impaired, although chemotaxis was unaffected. YopE also caused reduced uptake of yeast particles. These alterations are probably due to impaired Rac1 activation. We also found that YopE predominantly associates with intracellular membranes including the Golgi apparatus and inhibits the function of moderately overexpressed RacH. Conclusion The phenotype elicited by YopE in Dictyostelium can be explained, at least in part, by inactivation of one or more Rho family GTPases. It further demonstrates that the social amoeba Dictyostelium discoideum can be used as an efficient and easy-to-handle model organism in order to analyze the function of a translocated GAP protein of a human pathogen.

  17. Technical advance: identification of plant actin-binding proteins by F-actin affinity chromatography

    Science.gov (United States)

    Hu, S.; Brady, S. R.; Kovar, D. R.; Staiger, C. J.; Clark, G. B.; Roux, S. J.; Muday, G. K.

    2000-01-01

    Proteins that interact with the actin cytoskeleton often modulate the dynamics or organization of the cytoskeleton or use the cytoskeleton to control their localization. In plants, very few actin-binding proteins have been identified and most are thought to modulate cytoskeleton function. To identify actin-binding proteins that are unique to plants, the development of new biochemical procedures will be critical. Affinity columns using actin monomers (globular actin, G-actin) or actin filaments (filamentous actin, F-actin) have been used to identify actin-binding proteins from a wide variety of organisms. Monomeric actin from zucchini (Cucurbita pepo L.) hypocotyl tissue was purified to electrophoretic homogeneity and shown to be native and competent for polymerization to actin filaments. G-actin, F-actin and bovine serum albumin affinity columns were prepared and used to separate samples enriched in either soluble or membrane-associated actin-binding proteins. Extracts of soluble actin-binding proteins yield distinct patterns when eluted from the G-actin and F-actin columns, respectively, leading to the identification of a putative F-actin-binding protein of approximately 40 kDa. When plasma membrane-associated proteins were applied to these columns, two abundant polypeptides eluted selectively from the F-actin column and cross-reacted with antiserum against pea annexins. Additionally, a protein that binds auxin transport inhibitors, the naphthylphthalamic acid binding protein, which has been previously suggested to associate with the actin cytoskeleton, was eluted in a single peak from the F-actin column. These experiments provide a new approach that may help to identify novel actin-binding proteins from plants.

  18. Requirements for F-BAR proteins TOCA-1 and TOCA-2 in actin dynamics and membrane trafficking during Caenorhabditis elegans oocyte growth and embryonic epidermal morphogenesis.

    Directory of Open Access Journals (Sweden)

    Chiara Giuliani

    2009-10-01

    Full Text Available The TOCA family of F-BAR-containing proteins bind to and remodel lipid bilayers via their conserved F-BAR domains, and regulate actin dynamics via their N-Wasp binding SH3 domains. Thus, these proteins are predicted to play a pivotal role in coordinating membrane traffic with actin dynamics during cell migration and tissue morphogenesis. By combining genetic analysis in Caenorhabditis elegans with cellular biochemical experiments in mammalian cells, we showed that: i loss of CeTOCA proteins reduced the efficiency of Clathrin-mediated endocytosis (CME in oocytes. Genetic interference with CeTOCAs interacting proteins WSP-1 and WVE-1, and other components of the WVE-1 complex, produced a similar effect. Oocyte endocytosis defects correlated well with reduced egg production in these mutants. ii CeTOCA proteins localize to cell-cell junctions and are required for proper embryonic morphogenesis, to position hypodermal cells and to organize junctional actin and the junction-associated protein AJM-1. iii Double mutant analysis indicated that the toca genes act in the same pathway as the nematode homologue of N-WASP/WASP, wsp-1. Furthermore, mammalian TOCA-1 and C. elegans CeTOCAs physically associated with N-WASP and WSP-1 directly, or WAVE2 indirectly via ABI-1. Thus, we propose that TOCA proteins control tissues morphogenesis by coordinating Clathrin-dependent membrane trafficking with WAVE and N-WASP-dependent actin-dynamics.

  19. Loss of cofilin 1 disturbs actin dynamics, adhesion between enveloping and deep cell layers and cell movements during gastrulation in zebrafish.

    Directory of Open Access Journals (Sweden)

    Chun-Wei Lin

    Full Text Available During gastrulation, cohesive migration drives associated cell layers to the completion of epiboly in zebrafish. The association of different layers relies on E-cadherin based cellular junctions, whose stability can be affected by actin turnover. Here, we examined the effect of malfunctioning actin turnover on the epibolic movement by knocking down an actin depolymerizing factor, cofilin 1, using antisense morpholino oligos (MO. Knockdown of cfl1 interfered with epibolic movement of deep cell layer (DEL but not in the enveloping layer (EVL and the defect could be specifically rescued by overexpression of cfl1. It appeared that the uncoordinated movements of DEL and EVL were regulated by the differential expression of cfl1 in the DEL, but not EVL as shown by in situ hybridization. The dissociation of DEL and EVL was further evident by the loss of adhesion between layers by using transmission electronic and confocal microscopy analyses. cfl1 morphants also exhibited abnormal convergent extension, cellular migration and actin filaments, but not involution of hypoblast. The cfl1 MO-induced cell migration defect was found to be cell-autonomous in cell transplantation assays. These results suggest that proper actin turnover mediated by Cfl1 is essential for adhesion between DEL and EVL and cell movements during gastrulation in zebrafish.

  20. Dynamics of actin monomers assembled into long filaments%肌动蛋白纤维的组装动力学∗

    Institute of Scientific and Technical Information of China (English)

    郭坤琨; 谢仪

    2016-01-01

    We investigate the dynamics of actin monomers that are assembled into long filaments via the particle-based Brownian dynamics simulations. In order to study the dynamics of long filaments containing up to several hundred protomers, a coarse-grained model for actin polymerization involving several simplifications is used. In order to overcome the large separation of time scales between the diffusive motion of the free monomers and the relatively slow polymerized and depolymerized processes at the two ends of the filaments, all polymerized and depolymerized rates are rescaled by a dimensionless parameter. Actin protomers within a filament generally possess three nucleotide states corresponding to a bound adenosine triphosphate (ATP), adenosine diphosphate with inorganic phosphate (ADP. Pi), and ADP molecules in the presence of ATP hydrolysis. Here in this paper, single nucleotide state and two nucleotide states of actin protomers are described by the simplified theoretical model, giving the dependence of the growth rate on actin concentration. The simplest case where all protomers are identical, is provided by the assembly of ADP-actins. In the simulations, the growth rate is found to increase linearly with free monomer concentration, which agrees quantitatively with in vitro experimental result. These surprised phenomena observed in the experiments, such as treadmilling processes and length diffusion of actin filaments at the steady state, are presented in detail by Brownian dynamics simulations. For free actin concentrations close to the critical concentration, cT≈ccr,T, the filaments undergo treadmilling, that is, they grow at the barbed end and shrink at the pointed end, leading to the directed translational motion of the filament. In the absence of ATP hydrolysis, the functional dependence of a length diffusion constant on ADP-actin monomer concentration implies that a length diffusion constant is found to increase linearly with ADP-actin monomer concentration

  1. An actin cytoskeleton with evolutionarily conserved functions in the absence of canonical actin-binding proteins.

    Science.gov (United States)

    Paredez, Alexander R; Assaf, Zoe June; Sept, David; Timofejeva, Ljudmilla; Dawson, Scott C; Wang, Chung-Ju Rachel; Cande, W Z

    2011-04-12

    Giardia intestinalis, a human intestinal parasite and member of what is perhaps the earliest-diverging eukaryotic lineage, contains the most divergent eukaryotic actin identified to date and is the first eukaryote known to lack all canonical actin-binding proteins (ABPs). We sought to investigate the properties and functions of the actin cytoskeleton in Giardia to determine whether Giardia actin (giActin) has reduced or conserved roles in core cellular processes. In vitro polymerization of giActin produced filaments, indicating that this divergent actin is a true filament-forming actin. We generated an anti-giActin antibody to localize giActin throughout the cell cycle. GiActin localized to the cortex, nuclei, internal axonemes, and formed C-shaped filaments along the anterior of the cell and a flagella-bundling helix. These structures were regulated with the cell cycle and in encysting cells giActin was recruited to the Golgi-like cyst wall processing vesicles. Knockdown of giActin demonstrated that giActin functions in cell morphogenesis, membrane trafficking, and cytokinesis. Additionally, Giardia contains a single G protein, giRac, which affects the Giardia actin cytoskeleton independently of known target ABPs. These results imply that there exist ancestral and perhaps conserved roles for actin in core cellular processes that are independent of canonical ABPs. Of medical significance, the divergent giActin cytoskeleton is essential and commonly used actin-disrupting drugs do not depolymerize giActin structures. Therefore, the giActin cytoskeleton is a promising drug target for treating giardiasis, as we predict drugs that interfere with the Giardia actin cytoskeleton will not affect the mammalian host.

  2. Actin-based propulsion of functionalized hard versus fluid spherical objects

    Science.gov (United States)

    Delatour, Vincent; Shekhar, Shashank; Reymann, Anne-Cécile; Didry, Dominique; Diêp Lê, Kim Hô; Romet-Lemonne, Guillaume; Helfer, Emmanuèle; Carlier, Marie-France

    2008-02-01

    The directed polymerization of a branched actin network against a functionalized surface drives cell protrusions and organelle propulsion in living cells. Solid microspheres or giant unilamellar vesicles, functionalized with neural Wiskott-Aldrich syndrome protein (N-WASP), initiate the formation of a branched actin array using actin-related protein 2/3 (Arp2/3) complex, when placed in a motility assay reconstituted with pure proteins. These systems are useful biomimetic models of actin-based propulsion that allow to address how the interplay between the physical properties of the functionalized surface and the dynamics of the actin cytoskeleton determines motile behavior. Both solid beads and deformable vesicles display either continuous or saltatory propulsive motions, which are analyzed comparatively; we show that the deformability of liposomes and the mobility of N-WASP at the lipid surface affect the dynamic and structural parameters of the actin meshwork. Our results indicate that beads and vesicles use different mechanisms to translate insertional polymerization of actin at their surface into directed movement: stress relaxation within the actin gel prevents the accumulation of filaments at the front of moving beads, while segregation of nucleators reduces actin polymerization at the front of moving vesicles.

  3. Bistability in the Rac1, PAK, and RhoA Signaling Network Drives Actin Cytoskeleton Dynamics and Cell Motility Switches

    Science.gov (United States)

    Byrne, Kate M.; Monsefi, Naser; Dawson, John C.; Degasperi, Andrea; Bukowski-Wills, Jimi-Carlo; Volinsky, Natalia; Dobrzyński, Maciej; Birtwistle, Marc R.; Tsyganov, Mikhail A.; Kiyatkin, Anatoly; Kida, Katarzyna; Finch, Andrew J.; Carragher, Neil O.; Kolch, Walter; Nguyen, Lan K.; von Kriegsheim, Alex; Kholodenko, Boris N.

    2016-01-01

    Summary Dynamic interactions between RhoA and Rac1, members of the Rho small GTPase family, play a vital role in the control of cell migration. Using predictive mathematical modeling, mass spectrometry-based quantitation of network components, and experimental validation in MDA-MB-231 mesenchymal breast cancer cells, we show that a network containing Rac1, RhoA, and PAK family kinases can produce bistable, switch-like responses to a graded PAK inhibition. Using a small chemical inhibitor of PAK, we demonstrate that cellular RhoA and Rac1 activation levels respond in a history-dependent, bistable manner to PAK inhibition. Consequently, we show that downstream signaling, actin dynamics, and cell migration also behave in a bistable fashion, displaying switches and hysteresis in response to PAK inhibition. Our results demonstrate that PAK is a critical component in the Rac1-RhoA inhibitory crosstalk that governs bistable GTPase activity, cell morphology, and cell migration switches. PMID:27136688

  4. Actinic reticuloid

    Energy Technology Data Exchange (ETDEWEB)

    Marx, J.L.; Vale, M.; Dermer, P.; Ragaz, A.; Michaelides, P.; Gladstein, A.H.

    1982-09-01

    A 58-year-old man has his condition diagnosed as actinic reticuloid on the basis of clinical and histologic findings and phototesting data. He had clinical features resembling mycosis fungoides in light-exposed areas. Histologic findings disclosed a bandlike infiltrate with atypical mononuclear cells in the dermis and scattered atypical cells in the epidermis. Electron microscopy disclosed mononuclear cells with bizarre, convoluted nuclei, resembling cerebriform cells of Lutzner. Phototesting disclosed a diminished minimal erythemal threshold to UV-B and UV-A. Microscopic changes resembling actinic reticuloid were reproduced in this patient 24 and 72 hours after exposure to 15 minimal erythemal doses of UV-B.

  5. Nucleus-associated actin in Amoeba proteus.

    Science.gov (United States)

    Berdieva, Mariia; Bogolyubov, Dmitry; Podlipaeva, Yuliya; Goodkov, Andrew

    2016-10-01

    The presence, spatial distribution and forms of intranuclear and nucleus-associated cytoplasmic actin were studied in Amoeba proteus with immunocytochemical approaches. Labeling with different anti-actin antibodies and staining with TRITC-phalloidin and fluorescent deoxyribonuclease I were used. We showed that actin is abundant within the nucleus as well as in the cytoplasm of A. proteus cells. According to DNase I experiments, the predominant form of intranuclear actin is G-actin which is associated with chromatin strands. Besides, unpolymerized actin was shown to participate in organization of a prominent actin layer adjacent to the outer surface of nuclear envelope. No significant amount of F-actin was found in the nucleus. At the same time, the amoeba nucleus is enclosed in a basket-like structure formed by circumnuclear actin filaments and bundles connected with global cytoplasmic actin cytoskeleton. A supposed architectural function of actin filaments was studied by treatment with actin-depolymerizing agent latrunculin A. It disassembled the circumnuclear actin system, but did not affect the intranuclear chromatin structure. The results obtained for amoeba cells support the modern concept that actin is involved in fundamental nuclear processes that have evolved in the cells of multicellular organisms.

  6. Crosslink dynamics in a model of two filaments of actin under shear

    Science.gov (United States)

    Boerma, Arjan; van der Giessen, Erik; Papanikolaou, Stefanos

    2015-03-01

    We seek to elucidate the dynamic mechanisms underlying the stress dependent effects of the cellular cytoskeleton, as they are observed in the storage and loss modulus as a function of frequency and cross-linker concentration. We report on the statistical behavior of the effects originating from cross-linker dynamics in the basic constituent of a cytoskeleton network: two mutually cross-linked filaments. We model each of the filaments and the cross-linkers in terms of elastic finite elements. Unbinding of individual cross-linkers takes place through a realistic constitutive model and re-binding may occur to maintain the average cross-linker density. Our approach provides a direct analysis of the athermal interplay of the elastic filament interactions with the dynamics of the cross-linking molecules.

  7. A dynamical systems approach to actin-based motility in Listeria monocytogenes

    Science.gov (United States)

    Hotton, S.

    2010-11-01

    A simple kinematic model for the trajectories of Listeria monocytogenes is generalized to a dynamical system rich enough to exhibit the resonant Hopf bifurcation structure of excitable media and simple enough to be studied geometrically. It is shown how L. monocytogenes trajectories and meandering spiral waves are organized by the same type of attracting set.

  8. KSHV Entry and Trafficking in Target Cells—Hijacking of Cell Signal Pathways, Actin and Membrane Dynamics

    Directory of Open Access Journals (Sweden)

    Binod Kumar

    2016-11-01

    Full Text Available Kaposi’s sarcoma associated herpesvirus (KSHV is etiologically associated with human endothelial cell hyperplastic Kaposi’s sarcoma and B-cell primary effusion lymphoma. KSHV infection of adherent endothelial and fibroblast cells are used as in vitro models for infection and KSHV enters these cells by host membrane bleb and actin mediated macropinocytosis or clathrin endocytosis pathways, respectively. Infection in endothelial and fibroblast cells is initiated by the interactions between multiple viral envelope glycoproteins and cell surface associated heparan sulfate (HS, integrins (α3β1, αVβ3 and αVβ5, and EphA2 receptor tyrosine kinase (EphA2R. This review summarizes the accumulated studies demonstrating that KSHV manipulates the host signal pathways to enter and traffic in the cytoplasm of the target cells, to deliver the viral genome into the nucleus, and initiate viral gene expression. KSHV interactions with the cell surface receptors is the key platform for the manipulations of host signal pathways which results in the simultaneous induction of FAK, Src, PI3-K, Rho-GTPase, ROS, Dia-2, PKC ζ, c-Cbl, CIB1, Crk, p130Cas and GEF-C3G signal and adaptor molecules that play critical roles in the modulation of membrane and actin dynamics, and in the various steps of the early stages of infection such as entry and trafficking towards the nucleus. The Endosomal Sorting Complexes Required for Transport (ESCRT proteins are also recruited to assist in viral entry and trafficking. In addition, KSHV interactions with the cell surface receptors also induces the host transcription factors NF-κB, ERK1/2, and Nrf2 early during infection to initiate and modulate viral and host gene expression. Nuclear delivery of the viral dsDNA genome is immediately followed by the host innate responses such as the DNA damage response (DDR, inflammasome and interferon responses. Overall, these studies form the initial framework for further studies of

  9. KSHV Entry and Trafficking in Target Cells—Hijacking of Cell Signal Pathways, Actin and Membrane Dynamics

    Science.gov (United States)

    Kumar, Binod; Chandran, Bala

    2016-01-01

    Kaposi’s sarcoma associated herpesvirus (KSHV) is etiologically associated with human endothelial cell hyperplastic Kaposi’s sarcoma and B-cell primary effusion lymphoma. KSHV infection of adherent endothelial and fibroblast cells are used as in vitro models for infection and KSHV enters these cells by host membrane bleb and actin mediated macropinocytosis or clathrin endocytosis pathways, respectively. Infection in endothelial and fibroblast cells is initiated by the interactions between multiple viral envelope glycoproteins and cell surface associated heparan sulfate (HS), integrins (α3β1, αVβ3 and αVβ5), and EphA2 receptor tyrosine kinase (EphA2R). This review summarizes the accumulated studies demonstrating that KSHV manipulates the host signal pathways to enter and traffic in the cytoplasm of the target cells, to deliver the viral genome into the nucleus, and initiate viral gene expression. KSHV interactions with the cell surface receptors is the key platform for the manipulations of host signal pathways which results in the simultaneous induction of FAK, Src, PI3-K, Rho-GTPase, ROS, Dia-2, PKC ζ, c-Cbl, CIB1, Crk, p130Cas and GEF-C3G signal and adaptor molecules that play critical roles in the modulation of membrane and actin dynamics, and in the various steps of the early stages of infection such as entry and trafficking towards the nucleus. The Endosomal Sorting Complexes Required for Transport (ESCRT) proteins are also recruited to assist in viral entry and trafficking. In addition, KSHV interactions with the cell surface receptors also induces the host transcription factors NF-κB, ERK1/2, and Nrf2 early during infection to initiate and modulate viral and host gene expression. Nuclear delivery of the viral dsDNA genome is immediately followed by the host innate responses such as the DNA damage response (DDR), inflammasome and interferon responses. Overall, these studies form the initial framework for further studies of simultaneous targeting of

  10. Antiepileptic teratogen valproic acid (VPA) modulates organisation and dynamics of the actin cytoskeleton

    DEFF Research Database (Denmark)

    Walmod, P S; Skladchikova, G; Kawa, A;

    1999-01-01

    The antiepileptic drug valproic acid (VPA) and teratogenic VPA analogues have been demonstrated to inhibit cell motility and affect cell morphology. We here show that disruption of microtubules or of microfilaments by exposure to nocodazole or cytochalasin D had different effects on morphology of...

  11. G-actin regulates rapid induction of actin nucleation by mDia1 to restore cellular actin polymers.

    Science.gov (United States)

    Higashida, Chiharu; Suetsugu, Shiro; Tsuji, Takahiro; Monypenny, James; Narumiya, Shuh; Watanabe, Naoki

    2008-10-15

    mDia1 belongs to the formin family of proteins that share FH1 and FH2 domains. Although formins play a critical role in the formation of many actin-based cellular structures, the physiological regulation of formin-mediated actin assembly within the cell is still unknown. Here we show that cells possess an acute actin polymer restoration mechanism involving mDia1. By using single-molecule live-cell imaging, we found that several treatments including low-dose G-actin-sequestering drugs and unpolymerizable actin mutants activate mDia1 to initiate fast directional movement. The FH2 region, the core domain for actin nucleation, is sufficient to respond to latrunculin B (LatB) to increase its actin nucleation frequency. Simulation analysis revealed an unexpected paradoxical effect of LatB that leads to a several fold increase in free G-actin along with an increase in total G-actin. These results indicate that in cells, the actin nucleation frequency of mDia1 is enhanced not only by Rho, but also strongly through increased catalytic efficiency of the FH2 domain. Consistently, frequent actin nucleation by mDia1 was found around sites of vigorous actin disassembly. Another major actin nucleator, the Arp2/3 complex, was not affected by the G-actin increase induced by LatB. Taken together, we propose that transient accumulation of G-actin works as a cue to promote mDia1-catalyzed actin nucleation to execute rapid reassembly of actin filaments.

  12. Lamin A/C and emerin regulate MKL1/SRF activity by modulating actin dynamics

    OpenAIRE

    Ho, Chin Yee; Jaalouk, Diana E.; Maria K. Vartiainen; Lammerding, Jan

    2013-01-01

    Laminopathies, caused by mutations in the LMNA gene encoding the nuclear envelope proteins lamins A and C, represent a diverse group of diseases that include Emery-Dreifuss Muscular Dystrophy (EDMD), dilated cardiomyopathy (DCM), limb-girdle muscular dystrophy, and Hutchison-Gilford progeria syndrome (HGPS). 1 The majority of LMNA mutations affect skeletal and cardiac muscle by mechanisms that remain incompletely understood. Loss of structural function and disturbed interaction of mutant lami...

  13. Dynamic artificial neural networks with affective systems.

    Science.gov (United States)

    Schuman, Catherine D; Birdwell, J Douglas

    2013-01-01

    Artificial neural networks (ANNs) are processors that are trained to perform particular tasks. We couple a computational ANN with a simulated affective system in order to explore the interaction between the two. In particular, we design a simple affective system that adjusts the threshold values in the neurons of our ANN. The aim of this paper is to demonstrate that this simple affective system can control the firing rate of the ensemble of neurons in the ANN, as well as to explore the coupling between the affective system and the processes of long term potentiation (LTP) and long term depression (LTD), and the effect of the parameters of the affective system on its performance. We apply our networks with affective systems to a simple pole balancing example and briefly discuss the effect of affective systems on network performance.

  14. Keratin 8/18 Regulation of Cell Stiffness-Extracellular Matrix Interplay through Modulation of Rho-Mediated Actin Cytoskeleton Dynamics

    Science.gov (United States)

    Bordeleau, François; Myrand Lapierre, Marie-Eve; Sheng, Yunlong; Marceau, Normand

    2012-01-01

    Cell mechanical activity generated from the interplay between the extracellular matrix (ECM) and the actin cytoskeleton is essential for the regulation of cell adhesion, spreading and migration during normal and cancer development. Keratins are the intermediate filament (IF) proteins of epithelial cells, expressed as pairs in a lineage/differentiation manner. Hepatic epithelial cell IFs are made solely of keratins 8/18 (K8/K18), hallmarks of all simple epithelia. Notably, our recent work on these epithelial cells has revealed a key regulatory function for K8/K18 IFs in adhesion/migration, through modulation of integrin interactions with ECM, actin adaptors and signaling molecules at focal adhesions. Here, using K8-knockdown rat H4 hepatoma cells and their K8/K18-containing counterparts seeded on fibronectin-coated substrata of different rigidities, we show that the K8/K18 IF-lacking cells lose their ability to spread and exhibit an altered actin fiber organization, upon seeding on a low-rigidity substratum. We also demonstrate a concomitant reduction in local cell stiffness at focal adhesions generated by fibronectin-coated microbeads attached to the dorsal cell surface. In addition, we find that this K8/K18 IF modulation of cell stiffness and actin fiber organization occurs through RhoA-ROCK signaling. Together, the results uncover a K8/K18 IF contribution to the cell stiffness-ECM rigidity interplay through a modulation of Rho-dependent actin organization and dynamics in simple epithelial cells. PMID:22685604

  15. Keratin 8/18 regulation of cell stiffness-extracellular matrix interplay through modulation of Rho-mediated actin cytoskeleton dynamics.

    Directory of Open Access Journals (Sweden)

    François Bordeleau

    Full Text Available Cell mechanical activity generated from the interplay between the extracellular matrix (ECM and the actin cytoskeleton is essential for the regulation of cell adhesion, spreading and migration during normal and cancer development. Keratins are the intermediate filament (IF proteins of epithelial cells, expressed as pairs in a lineage/differentiation manner. Hepatic epithelial cell IFs are made solely of keratins 8/18 (K8/K18, hallmarks of all simple epithelia. Notably, our recent work on these epithelial cells has revealed a key regulatory function for K8/K18 IFs in adhesion/migration, through modulation of integrin interactions with ECM, actin adaptors and signaling molecules at focal adhesions. Here, using K8-knockdown rat H4 hepatoma cells and their K8/K18-containing counterparts seeded on fibronectin-coated substrata of different rigidities, we show that the K8/K18 IF-lacking cells lose their ability to spread and exhibit an altered actin fiber organization, upon seeding on a low-rigidity substratum. We also demonstrate a concomitant reduction in local cell stiffness at focal adhesions generated by fibronectin-coated microbeads attached to the dorsal cell surface. In addition, we find that this K8/K18 IF modulation of cell stiffness and actin fiber organization occurs through RhoA-ROCK signaling. Together, the results uncover a K8/K18 IF contribution to the cell stiffness-ECM rigidity interplay through a modulation of Rho-dependent actin organization and dynamics in simple epithelial cells.

  16. How Resource Phenology Affects Consumer Population Dynamics.

    Science.gov (United States)

    Bewick, Sharon; Cantrell, R Stephen; Cosner, Chris; Fagan, William F

    2016-02-01

    Climate change drives uneven phenology shifts across taxa, and this can result in changes to the phenological match between interacting species. Shifts in the relative phenology of partner species are well documented, but few studies have addressed the effects of such changes on population dynamics. To explore this, we develop a phenologically explicit model describing consumer-resource interactions. Focusing on scenarios for univoltine insects, we show how changes in resource phenology can be reinterpreted as transformations in the year-to-year recursion relationships defining consumer population dynamics. This perspective provides a straightforward path for interpreting the long-term population consequences of phenology change. Specifically, by relating the outcome of phenological shifts to species traits governing recursion relationships (e.g., consumer fecundity or competitive scenario), we demonstrate how changes in relative phenology can force systems into different dynamical regimes, with major implications for resource management, conservation, and other areas of applied dynamics.

  17. Mechanics of Biomimetic Liposomes Encapsulating an Actin Shell.

    Science.gov (United States)

    Guevorkian, Karine; Manzi, John; Pontani, Léa-Lætitia; Brochard-Wyart, Françoise; Sykes, Cécile

    2015-12-15

    Cell-shape changes are insured by a thin, dynamic, cortical layer of cytoskeleton underneath the plasma membrane. How this thin cortical structure impacts the mechanical properties of the whole cell is not fully understood. Here, we study the mechanics of liposomes or giant unilamellar vesicles, when a biomimetic actin cortex is grown at the inner layer of the lipid membrane via actin-nucleation-promoting factors. Using a hydrodynamic tube-pulling technique, we show that tube dynamics is clearly affected by the presence of an actin shell anchored to the lipid bilayer. The same force pulls much shorter tubes in the presence of the actin shell compared to bare membranes. However, in both cases, we observe that the dynamics of tube extrusion has two distinct features characteristic of viscoelastic materials: rapid elastic elongation, followed by a slower elongation phase at a constant rate. We interpret the initial elastic regime by an increase of membrane tension due to the loss of lipids into the tube. Tube length is considerably shorter for cortex liposomes at comparable pulling forces, resulting in a higher spring constant. The presence of the actin shell seems to restrict lipid mobility, as is observed in the corral effect in cells. The viscous regime for bare liposomes corresponds to a leakout of the internal liquid at constant membrane tension. The presence of the actin shell leads to a larger friction coefficient. As the tube is pulled from a patchy surface, membrane tension increases locally, leading to a Marangoni flow of lipids. As a conclusion, the presence of an actin shell is revealed by its action that alters membrane mechanics.

  18. Platelet adhesion: structural and functional diversity of short dystrophin and utrophins in the formation of dystrophin-associated-protein complexes related to actin dynamics.

    Science.gov (United States)

    Cerecedo, Doris; Martínez-Rojas, Dalila; Chávez, Oscar; Martínez-Pérez, Francisco; García-Sierra, Francisco; Rendon, Alvaro; Mornet, Dominique; Mondragón, Ricardo

    2005-12-01

    Platelets are dynamic cell fragments that modify their shape during activation. Utrophin and dystrophins are minor actin-binding proteins present in muscle and non-muscle cytoskeleton. In the present study, we characterised the pattern of Dp71 isoforms and utrophin gene products by immunoblot in human platelets. Two new dystrophin isoforms were found, Dp71f and Dp71 d, as well as the Up71 isoform and the dystrophin-associated proteins, alpha and beta -dystrobrevins. Distribution of Dp71d/Dp71delta110m, Up400/Up71 and dystrophin-associated proteins in relation to the actin cytoskeleton was evaluated by confocal microscopy in both resting and platelets adhered on glass. Formation of two dystrophin-associated protein complexes (Dp71d/Dp71delta110m approximately DAPC and Up400/Up71 approximately DAPC) was demonstrated by co-immunoprecipitation and their distribution in relation to the actin cytoskeleton was characterised during platelet adhesion. The Dp71d/Dp71delta100m approximately DAPC is maintained mainly at the granulomere and is associated with dynamic structures during activation by adhesion to thrombin-coated surfaces. Participation of both Dp71d/Dp71delta110m approximately DAPC and Up400/Up71 approximately DAPC in the biological roles of the platelets is discussed.

  19. Actinic cheilitis: A review

    Directory of Open Access Journals (Sweden)

    Elangovan Somasundaram

    2015-01-01

    Full Text Available Actinic cheilitis (AC is a chronic inflammatory disorder of the lips that is caused by prolonged exposure to sunlight in susceptible individuals. It affects the vermilion region of the lower lip almost exclusively. UV-B rays with a wavelength of 290-320 nm are held responsible for the sunlight-induced damage. The exact mechanism of the development of AC is unclear. It is considered to be potentially malignant.

  20. Prostaglandins temporally regulate cytoplasmic actin bundle formation during Drosophila oogenesis

    OpenAIRE

    Spracklen, Andrew J.; Kelpsch, Daniel J.; Chen, Xiang; Spracklen, Cassandra N.; Tootle, Tina L.

    2014-01-01

    Prostaglandins (PGs)—lipid signals produced downstream of cyclooxygenase (COX) enzymes—regulate actin dynamics in cell culture and platelets, but their roles during development are largely unknown. Here we define a new role for Pxt, the Drosophila COX-like enzyme, in regulating the actin cytoskeleton—temporal restriction of actin remodeling during oogenesis. PGs are required for actin filament bundle formation during stage 10B (S10B). In addition, loss of Pxt results in extensive early actin ...

  1. Actin-dependent mechanisms in AMPA receptor trafficking

    Directory of Open Access Journals (Sweden)

    Jonathan G Hanley

    2014-11-01

    Full Text Available The precise regulation of AMPA receptor (AMPAR number and subtype at the synapse is crucial for the regulation of excitatory neurotransmission, synaptic plasticity and the consequent formation of appropriate neural circuits during learning and memory. AMPAR trafficking involves the dynamic processes of exocytosis, endocytosis and endosomal recycling, all of which involve the actin cytoskeleton. The actin cytoskeleton is highly dynamic and highly regulated by an abundance of actin-binding proteins and upstream signalling pathways that modulate actin polymerization and depolymerisation. Actin dynamics generate forces that manipulate membranes in the process of vesicle biogenesis, and also for propelling vesicles through the cytoplasm to reach their destination. In addition, trafficking mechanisms exploit more stable aspects of the actin cytoskeleton by using actin-based motor proteins to traffic vesicular cargo along actin filaments. Numerous studies have shown that actin dynamics are critical for AMPAR localization and function. The identification of actin-binding proteins that physically interact with AMPAR subunits, and research into their mode of action is starting to shed light on the mechanisms involved. Such proteins either regulate actin dynamics to modulate mechanical forces exerted on AMPAR-containing membranes, or associate with actin filaments to target or transport AMPAR-containing vesicles to specific subcellular regions. In addition, actin-regulatory proteins that do not physically interact with AMPARs may influence AMPAR trafficking by regulating the local actin environment in the dendritic spine.

  2. Dynamin2 organizes lamellipodial actin networks to orchestrate lamellar actomyosin.

    Directory of Open Access Journals (Sweden)

    Manisha Menon

    Full Text Available Actin networks in migrating cells exist as several interdependent structures: sheet-like networks of branched actin filaments in lamellipodia; arrays of bundled actin filaments co-assembled with myosin II in lamellae; and actin filaments that engage focal adhesions. How these dynamic networks are integrated and coordinated to maintain a coherent actin cytoskeleton in migrating cells is not known. We show that the large GTPase dynamin2 is enriched in the distal lamellipod where it regulates lamellipodial actin networks as they form and flow in U2-OS cells. Within lamellipodia, dynamin2 regulated the spatiotemporal distributions of α-actinin and cortactin, two actin-binding proteins that specify actin network architecture. Dynamin2's action on lamellipodial F-actin influenced the formation and retrograde flow of lamellar actomyosin via direct and indirect interactions with actin filaments and a finely tuned GTP hydrolysis activity. Expression in dynamin2-depleted cells of a mutant dynamin2 protein that restores endocytic activity, but not activities that remodel actin filaments, demonstrated that actin filament remodeling by dynamin2 did not depend of its functions in endocytosis. Thus, dynamin2 acts within lamellipodia to organize actin filaments and regulate assembly and flow of lamellar actomyosin. We hypothesize that through its actions on lamellipodial F-actin, dynamin2 generates F-actin structures that give rise to lamellar actomyosin and for efficient coupling of F-actin at focal adhesions. In this way, dynamin2 orchestrates the global actin cytoskeleton.

  3. Dynamics of Actin Stress Fibers and Focal Adhesions during Slow Migration in Swiss 3T3 Fibroblasts: Intracellular Mechanism of Cell Turning

    Directory of Open Access Journals (Sweden)

    Michiko Sugawara

    2016-01-01

    Full Text Available To understand the mechanism regulating the spontaneous change in polarity that leads to cell turning, we quantitatively analyzed the dynamics of focal adhesions (FAs coupling with the self-assembling actin cytoskeletal structure in Swiss 3T3 fibroblasts. Fluorescent images were acquired from cells expressing GFP-actin and RFP-zyxin by laser confocal microscopy. On the basis of the maximum area, duration, and relocation distance of FAs extracted from the RFP-zyxin images, the cells could be divided into 3 regions: the front region, intermediate lateral region, and rear region. In the intermediate lateral region, FAs appeared close to the leading edge and were stabilized gradually as its area increased. Simultaneously, bundled actin stress fibers (SFs were observed vertically from the positions of these FAs, and they connected to the other SFs parallel to the leading edge. Finally, these connecting SFs fused to form a single SF with matured FAs at both ends. This change in SF organization with cell retraction in the first cycle of migration followed by a newly formed protrusion in the next cycle is assumed to lead to cell turning in migrating Swiss 3T3 fibroblasts.

  4. Yeast RAD2, a homolog of human XPG, plays a key role in the regulation of the cell cycle and actin dynamics

    Directory of Open Access Journals (Sweden)

    Mi-Sun Kang

    2013-12-01

    Mutations in the human XPG gene cause Cockayne syndrome (CS and xeroderma pigmentosum (XP. Transcription defects have been suggested as the fundamental cause of CS; however, defining CS as a transcription syndrome is inconclusive. In particular, the function of XPG in transcription has not been clearly demonstrated. Here, we provide evidence for the involvement of RAD2, the Saccharomyces cerevisiae counterpart of XPG, in cell cycle regulation and efficient actin assembly following ultraviolet irradiation. RAD2 C-terminal deletion, which resembles the XPG mutation found in XPG/CS cells, caused cell growth arrest, the cell cycle stalling, a defective α-factor response, shortened lifespan, cell polarity defect, and misregulated actin-dynamics after DNA damage. Overexpression of the C-terminal 65 amino acids of Rad2p was sufficient to induce hyper-cell polarization. In addition, RAD2 genetically interacts with TPM1 during cell polarization. These results provide insights into the role of RAD2 in post-UV irradiation cell cycle regulation and actin assembly, which may be an underlying cause of XPG/CS.

  5. Keeping it all together: auxin-actin crosstalk in plant development.

    Science.gov (United States)

    Zhu, Jinsheng; Geisler, Markus

    2015-08-01

    Polar auxin transport and the action of the actin cytoskeleton are tightly interconnected, which is documented by the finding that auxin transporters reach their final destination by active movement of secretory vesicles along F-actin tracks. Moreover, auxin transporter polarity and flexibility is thought to depend on transporter cycling that requires endocytosis and exocytosis of vesicles. In this context, we have reviewed the current literature on an involvement of the actin cytoskeleton in polar auxin transport and identify known similarities and differences in its structure, function and dynamics in comparison to non-plant organisms. By describing how auxin modulates actin expression and actin organization and how actin and its stability affects auxin-transporter endocytosis and recycling, we discuss the current knowledge on regulatory auxin-actin feedback loops. We focus on known effects of auxin and of auxin transport inhibitors on the stability and organization of actin and examine the functionality of auxin and/or auxin transport inhibitor-binding proteins with respect to their suitability to integrate auxin/auxin transport inhibitor action. Finally, we indicate current difficulties in the interpretation of organ, time and concentration-dependent auxin/auxin transport inhibitor treatments and formulate simple future experimental guidelines.

  6. Multiple actin binding domains of Ena/VASP proteins determine actin network stiffening.

    Science.gov (United States)

    Gentry, Brian S; van der Meulen, Stef; Noguera, Philippe; Alonso-Latorre, Baldomero; Plastino, Julie; Koenderink, Gijsje H

    2012-11-01

    Vasodilator-stimulated phosphoprotein (Ena/VASP) is an actin binding protein, important for actin dynamics in motile cells and developing organisms. Though VASP's main activity is the promotion of barbed end growth, it has an F-actin binding site and can form tetramers, and so could additionally play a role in actin crosslinking and bundling in the cell. To test this activity, we performed rheology of reconstituted actin networks in the presence of wild-type VASP or mutants lacking the ability to tetramerize or to bind G-actin and/or F-actin. We show that increasing amounts of wild-type VASP increase network stiffness up to a certain point, beyond which stiffness actually decreases with increasing VASP concentration. The maximum stiffness is 10-fold higher than for pure actin networks. Confocal microscopy shows that VASP forms clustered actin filament bundles, explaining the reduction in network elasticity at high VASP concentration. Removal of the tetramerization site results in significantly reduced bundling and bundle clustering, indicating that VASP's flexible tetrameric structure causes clustering. Removing either the F-actin or the G-actin binding site diminishes VASP's effect on elasticity, but does not eliminate it. Mutating the F-actin and G-actin binding site together, or mutating the F-actin binding site and saturating the G-actin binding site with monomeric actin, eliminates VASP's ability to increase network stiffness. We propose that, in the cell, VASP crosslinking confers only moderate increases in linear network elasticity, and unlike other crosslinkers, VASP's network stiffening activity may be tuned by the local concentration of monomeric actin.

  7. [Photodynamic therapy for actinic cheilitis].

    Science.gov (United States)

    Castaño, E; Comunión, A; Arias, D; Miñano, R; Romero, A; Borbujo, J

    2009-12-01

    Actinic cheilitis is a subtype of actinic keratosis that mainly affects the lower lip and has a higher risk of malignant transformation. Its location on the labial mucosa influences the therapeutic approach. Vermilionectomy requires local or general anesthetic and is associated with a risk of an unsightly scar, and the treatment with 5-fluorouracil or imiquimod lasts for several weeks and the inflammatory reaction can be very intense. A number of authors have used photodynamic therapy as an alternative to the usual treatments. We present 3 patients with histologically confirmed actinic cheilitis treated using photodynamic therapy with methyl aminolevulinic acid as the photosensitizer and red light at 630 nm. The clinical response was good, with no recurrences after 3 to 6 months of follow-up. Our experience supports the use of photodynamic therapy as a good alternative for the treatment of actinic cheilitis.

  8. Studies of dynamical processes affecting global climate

    Energy Technology Data Exchange (ETDEWEB)

    Keller, C.; Cooper, D.; Eichinger, W. [and others

    1998-12-31

    This is the final report of a three-year, Laboratory Directed Research and Development project at the Los Alamos National Laboratory (LANL). The main objective was, by a combined theoretical and observational approach, to develop improved models of dynamic processes in the oceans and atmosphere and to incorporate them into large climate codes, chiefly in four main areas: numerical physics, chemistry, water vapor, and ocean-atmosphere interactions. Main areas of investigation included studies of: cloud parameterizations for global climate codes, Lidar and the planetary boundary layer, chemistry, climate variability using coupled ocean-atmospheric models, and numerical physical methods. This project employed a unique approach that included participation of a number of University of California faculty, postdoctoral fellows and graduate students who collaborated with Los Alamos research staff on specific tasks, thus greatly enhancing the research output. Overall accomplishments during the sensing of the atmospheric planetary were: (1) first two- and three-dimensional remote sensing of the atmospheric planetary boundary layer using Lidars, (2) modeling of 20-year cycle in both pressure and sea surface temperatures in North Pacific, (3) modeling of low frequency internal variability, (4) addition of aerosols to stratosphere to simulate Pinatubo effect on ozone, (5) development of fast, comprehensive chemistry in the troposphere for urban pollution studies, (6) new prognostic cloud parameterization in global atmospheric code remedied problems with North Pacific atmospheric circulation and excessive equatorial precipitation, (7) development of a unique aerosol analysis technique, the aerosol time-of-flight mass spectrometer (ATOFMS), which allows real-time analysis of the size and chemical composition of individual aerosol particles, and (8) numerical physics applying Approximate Inertial Manifolds to ocean circulation. 14 refs., 6 figs.

  9. Micro-Level Affect Dynamics in Psychopathology Viewed From Complex Dynamical System Theory

    NARCIS (Netherlands)

    Wichers, M.; Wigman, J. T. W.; Myin-Germeys, I.

    2015-01-01

    This article discusses the role of moment-to-moment affect dynamics in mental disorder and aims to integrate recent literature on this topic in the context of complex dynamical system theory. First, we will review the relevance of temporal and contextual aspects of affect dynamics in relation to psy

  10. From pollen actin to crop male sterility

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Actin plays an important role in the life activity of animal and plant cells. Pollen cells have plenty of actin whose structure and characteristics are very similar to the animal actin. The nucleotide sequence and amino acid sequence of plant actin gene are very similar to those of the animal gene. The content of pollen actin from male sterile plants is much more lower than that from its maintainer plants. The expression of actin gene is organ-specific during the plant development. The expression quantity of actin gene in pollen is much more higher than those from root, stem and leaf. The expression plasmid of the anti-sense actin gene was constructed, transferred to the protoplasts of wheat and tomato to inhibit the expression of actin gene in pollen and thus the male sterile plants of wheat and tomato were obtained. The actin in pollens from the transgenic plants was reduced significantly, whereas the pistil was not affected. This study might pave a new way to breeding male sterile lines for the application of hybrid vigor of wheat and tomato.

  11. Implications of oxidovanadium(IV) binding to actin.

    Science.gov (United States)

    Ramos, Susana; Almeida, Rui M; Moura, José J G; Aureliano, Manuel

    2011-06-01

    Oxidovanadium(IV), a cationic species (VO(2+)) of vanadium(IV), binds to several proteins, including actin. Upon titration with oxidovanadium(IV), approximately 100% quenching of the intrinsic fluorescence of monomeric actin purified from rabbit skeletal muscle (G-actin) was observed, with a V(50) of 131 μM, whereas for the polymerized form of actin (F-actin) 75% of quenching was obtained and a V(50) value of 320 μM. Stern-Volmer plots were used to estimate an oxidovanadium(IV)-actin dissociation constant, with K(d) of 8.2 μM and 64.1 μM VOSO(4), for G-actin and F-actin, respectively. These studies reveal the presence of a high affinity binding site for oxidovanadium(IV) in actin, producing local conformational changes near the tryptophans most accessible to water in the three-dimensional structure of actin. The actin conformational changes, also confirmed by (1)H NMR, are accompanied by changes in G-actin hydrophobic surface, but not in F-actin. The (1)H NMR spectra of G-actin treated with oxidovanadium(IV) clearly indicates changes in the resonances ascribed to methyl group and aliphatic regions as well as to aromatics and peptide-bond amide region. In parallel, it was verified that oxidovanadium(IV) prevents the G-actin polymerization into F-actin. In the 0-200 μM range, VOSO(4) inhibits 40% of the extent of polymerization with an IC(50) of 15.1 μM, whereas 500 μM VOSO(4) totally suppresses actin polymerization. The data strongly suggest that oxidovanadium(IV) binds to actin at specific binding sites preventing actin polymerization. By affecting actin structure and function, oxidovanadium(IV) might be responsible for many cellular effects described for vanadium.

  12. Relations between affective music and speech: Evidence from dynamics of affective piano performance and speech production

    Directory of Open Access Journals (Sweden)

    Xiaoluan eLiu

    2015-07-01

    Full Text Available This study compares affective piano performance with speech production from the perspective of dynamics: unlike previous research, this study uses finger force and articulatory effort as indexes reflecting the dynamics of affective piano performance and speech production respectively. Moreover, for the first time physical constraints such as piano fingerings and speech articulatory distance are included due to their potential contribution to different patterns of dynamics. A piano performance experiment and speech production experiment were conducted in four emotions: anger, fear, happiness and sadness. The results show that in both piano performance and speech production, anger and happiness generally have high dynamics while sadness has the lowest dynamics, with fear in the middle. Fingerings interact with fear in the piano experiment and articulatory distance interacts with anger in the speech experiment, i.e., large physical constraints produce significantly higher dynamics than small physical constraints in piano performance under the condition of fear and in speech production under the condition of anger. Using production experiments, this study firstly supports previous perception studies on relations between affective music and speech. Moreover, this is the first study to show quantitative evidence for the importance of considering motor aspects such as dynamics in comparing music performance and speech production in which motor mechanisms play a crucial role.

  13. Relations between affective music and speech: evidence from dynamics of affective piano performance and speech production.

    Science.gov (United States)

    Liu, Xiaoluan; Xu, Yi

    2015-01-01

    This study compares affective piano performance with speech production from the perspective of dynamics: unlike previous research, this study uses finger force and articulatory effort as indexes reflecting the dynamics of affective piano performance and speech production respectively. Moreover, for the first time physical constraints such as piano fingerings and speech articulatory constraints are included due to their potential contribution to different patterns of dynamics. A piano performance experiment and speech production experiment were conducted in four emotions: anger, fear, happiness and sadness. The results show that in both piano performance and speech production, anger and happiness generally have high dynamics while sadness has the lowest dynamics. Fingerings interact with fear in the piano experiment and articulatory constraints interact with anger in the speech experiment, i.e., large physical constraints produce significantly higher dynamics than small physical constraints in piano performance under the condition of fear and in speech production under the condition of anger. Using production experiments, this study firstly supports previous perception studies on relations between affective music and speech. Moreover, this is the first study to show quantitative evidence for the importance of considering motor aspects such as dynamics in comparing music performance and speech production in which motor mechanisms play a crucial role.

  14. Actin Cytoskeleton Manipulation by Effector Proteins Secreted by Diarrheagenic Escherichia coli Pathotypes

    Directory of Open Access Journals (Sweden)

    Fernando Navarro-Garcia

    2013-01-01

    Full Text Available The actin cytoskeleton is a dynamic structure necessary for cell and tissue organization, including the maintenance of epithelial barriers. Disruption of the epithelial barrier coincides with alterations of the actin cytoskeleton in several disease states. These disruptions primarily affect the paracellular space, which is normally regulated by tight junctions. Thereby, the actin cytoskeleton is a common and recurring target of bacterial virulence factors. In order to manipulate the actin cytoskeleton, bacteria secrete and inject toxins and effectors to hijack the host cell machinery, which interferes with host-cell pathways and with a number of actin binding proteins. An interesting model to study actin manipulation by bacterial effectors is Escherichia coli since due to its genome plasticity it has acquired diverse genetic mobile elements, which allow having different E. coli varieties in one bacterial species. These E. coli pathotypes, including intracellular and extracellular bacteria, interact with epithelial cells, and their interactions depend on a specific combination of virulence factors. In this paper we focus on E. coli effectors that mimic host cell proteins to manipulate the actin cytoskeleton. The study of bacterial effector-cytoskeleton interaction will contribute not only to the comprehension of the molecular causes of infectious diseases but also to increase our knowledge of cell biology.

  15. Disrupted dynamics of F-actin and insulin granule fusion in INS-1 832/13 beta-cells exposed to glucotoxicity: partial restoration by glucagon-like peptide 1.

    Science.gov (United States)

    Quinault, Aurore; Gausseres, Blandine; Bailbe, Danielle; Chebbah, Nella; Portha, Bernard; Movassat, Jamileh; Tourrel-Cuzin, Cecile

    2016-08-01

    Actin dynamics in pancreatic β-cells is involved in insulin exocytosis but the molecular mechanisms of this dynamics and its role in biphasic insulin secretion in pancreatic β-cells is largely unknown. Moreover, the impact of a glucotoxic environment on the sub-cortical actin network dynamics is poorly studied. In this study, we investigate the behavior of insulin granules and the subcortical actin network dynamics in INS-1 832/13 β-cells submitted to a normal or glucotoxic environment. Our results show that glucose stimulation leads to a reorganization of the subcortical actin network with a rupture of its interactions with t-SNARE proteins (Syntaxin 1A and SNAP-25), promoting insulin secretion in INS-1 832/13 β-cells. Prolonged exposure of INS-1 832/13 β-cells to high-glucose levels (glucotoxicity) leads to the densification of the cortical actin network, which prevents its reorganization under acute glucose, and diminishes the glucose-stimulated insulin secretion, as shown by the decreased number of fusion events. The most interesting in our results is the partial restoration by GLP-1 of the insulin secretion ability from high-glucose treated INS-1 832/13 cells. This improved insulin exocytosis is associated with partial restored actin dynamics and fusion events during the two phases of the secretion, with a preferential involvement of Epac2 signaling in the first phase and a rather involvement of PKA signaling in the second phase of insulin exocytosis. All these data provide some new insights into the mechanism by which current therapeutics may be improving insulin secretion.

  16. Characterizing mouse male germ cell-specific actin capping protein α3 (CPα3): dynamic patterns of expression in testicular and epididymal sperm

    Institute of Scientific and Technical Information of China (English)

    Keizo Tokuhiro; Yasushi Miyagawa; Hiromitsu Tanaka

    2008-01-01

    Aim: To characterize mouse capping protein α3 (CPα3) during spermatogenesis and sperm maturation. Methods: We produced rat anti-CPα3 antiserum and examined the expression of CPα3 in various mouse tissues using Western blot analysis and the localization of CPα3 in testicular and epididymal sperm using immunohistochemical analyses. We also examined how the localization of CPα3 and β-actin (ACTB) in sperm changed after the acrosomal reaction by performing immunohistochemical analyses using anti-CPα3 antiserum and anti-actin antibody. Results: Western blot analysis using specific antiserum revealed that CPα3 was expressed specifically in testes. Interestingly, the molecular weight of CPα3 changed during sperm maturation in the epididymis. Furthermore, the subcellular localization of CPα3 in sperm changed dynamically from the flagellum to the post-acrosomal region of the head during epididymal maturation. The distribution of ACTB was in the post-acrosomal region of the head and the flagellum. After inducing the acrosomal reaction, the CPα3 and ACTB localization was virtually identical to the localization before the acrosomal reaction.Conclusion: CPα3 might play an important role in sperm morphogenesis and/or sperm function.

  17. Xenopus egg cytoplasm with intact actin.

    Science.gov (United States)

    Field, Christine M; Nguyen, Phuong A; Ishihara, Keisuke; Groen, Aaron C; Mitchison, Timothy J

    2014-01-01

    We report optimized methods for preparing Xenopus egg extracts without cytochalasin D, that we term "actin-intact egg extract." These are undiluted egg cytoplasm that contains abundant organelles, and glycogen which supplies energy, and represents the least perturbed cell-free cytoplasm preparation we know of. We used this system to probe cell cycle regulation of actin and myosin-II dynamics (Field et al., 2011), and to reconstitute the large, interphase asters that organize early Xenopus embryos (Mitchison et al., 2012; Wühr, Tan, Parker, Detrich, & Mitchison, 2010). Actin-intact Xenopus egg extracts are useful for analysis of actin dynamics, and interaction of actin with other cytoplasmic systems, in a cell-free system that closely mimics egg physiology, and more generally for probing the biochemistry and biophysics of the egg, zygote, and early embryo. Detailed protocols are provided along with assays used to check cell cycle state and tips for handling and storing undiluted egg extracts.

  18. The actinome of Dictyostelium discoideum in comparison to actins and actin-related proteins from other organisms.

    Directory of Open Access Journals (Sweden)

    Jayabalan M Joseph

    Full Text Available Actin belongs to the most abundant proteins in eukaryotic cells which harbor usually many conventional actin isoforms as well as actin-related proteins (Arps. To get an overview over the sometimes confusing multitude of actins and Arps, we analyzed the Dictyostelium discoideum actinome in detail and compared it with the genomes from other model organisms. The D. discoideum actinome comprises 41 actins and actin-related proteins. The genome contains 17 actin genes which most likely arose from consecutive gene duplications, are all active, in some cases developmentally regulated and coding for identical proteins (Act8-group. According to published data, the actin fraction in a D. discoideum cell consists of more than 95% of these Act8-type proteins. The other 16 actin isoforms contain a conventional actin motif profile as well but differ in their protein sequences. Seven actin genes are potential pseudogenes. A homology search of the human genome using the most typical D. discoideum actin (Act8 as query sequence finds the major actin isoforms such as cytoplasmic beta-actin as best hit. This suggests that the Act8-group represents a nearly perfect actin throughout evolution. Interestingly, limited data from D. fasciculatum, a more ancient member among the social amoebae, show different relationships between conventional actins. The Act8-type isoform is most conserved throughout evolution. Modeling of the putative structures suggests that the majority of the actin-related proteins is functionally unrelated to canonical actin. The data suggest that the other actin variants are not necessary for the cytoskeleton itself but rather regulators of its dynamical features or subunits in larger protein complexes.

  19. Dynamic modelling of processes in rivers affected by precipitation runoff

    DEFF Research Database (Denmark)

    Jacobsen, Judith L.

    1997-01-01

    In this thesis, models for the dynamics of oxygen and organic matter in receiving waters (such as rivers and creeks), which are affected by rain, are developed. A time series analysis framework is used, but presented with special emphasis on continuous time state space models. Also, the concept...

  20. Dynamics of learner affective development in early FLL

    Directory of Open Access Journals (Sweden)

    Jelena Mihaljević Djigunović

    2012-10-01

    Full Text Available Affective learner factors were first considered as a cause of success in language learning. This was followed by a change in approach and recently authors (e.g., Edelenbos, Johnstone, & Kubanek, 2006 have considered them an important outcome, especially in early foreign language learning (FLL. Current research into affective learner factors in early FLL tries to catch the developmental aspects too, and studies are emerging that take a contextual view as well. This paper describes a study on affective characteristics of young FL learners that combines the developmental and contextual perspectives. Using the case study methodology the author analyses the affective profiles of three young learners of English as a foreign language who were followed for 4 years. The analyses are done taking into account their immediate language learning environment, home support, out-of-school exposure to English and language achievement. The findings suggest that affective learner factors contribute to the dynamic complexity of early FLL.

  1. Network Diversity and Affect Dynamics: The Role of Personality Traits

    Science.gov (United States)

    Alshamsi, Aamena; Pianesi, Fabio; Lepri, Bruno; Pentland, Alex; Rahwan, Iyad

    2016-01-01

    People divide their time unequally among their social contacts due to time constraints and varying strength of relationships. It was found that high diversity of social communication, dividing time more evenly among social contacts, is correlated with economic well-being both at macro and micro levels. Besides economic well-being, it is not clear how the diversity of social communication is also associated with the two components of individuals’ subjective well-being, positive and negative affect. Specifically, positive affect and negative affect are two independent dimensions representing the experience (feeling) of emotions. In this paper, we investigate the relationship between the daily diversity of social communication and dynamic affect states that people experience in their daily lives. We collected two high-resolution datasets that capture affect scores via daily experience sampling surveys and social interaction through wearable sensing technologies: sociometric badges for face-to-face interaction and smart phones for mobile phone calls. We found that communication diversity correlates with desirable affect states–e.g. an increase in the positive affect state or a decrease in the negative affect state–for some personality types, but correlates with undesirable affect states for others. For example, diversity in phone calls is experienced as good by introverts, but bad by extroverts; diversity in face-to-face interaction is experienced as good by people who tend to be positive by nature (trait) but bad for people who tend to be not positive by nature. More broadly, the moderating effect of personality type on the relationship between diversity and affect was detected without any knowledge of the type of social tie or the content of communication. This provides further support for the power of unobtrusive sensing in understanding social dynamics, and in measuring the effect of potential interventions designed to improve well-being. PMID:27035904

  2. Network Diversity and Affect Dynamics: The Role of Personality Traits.

    Science.gov (United States)

    Alshamsi, Aamena; Pianesi, Fabio; Lepri, Bruno; Pentland, Alex; Rahwan, Iyad

    2016-01-01

    People divide their time unequally among their social contacts due to time constraints and varying strength of relationships. It was found that high diversity of social communication, dividing time more evenly among social contacts, is correlated with economic well-being both at macro and micro levels. Besides economic well-being, it is not clear how the diversity of social communication is also associated with the two components of individuals' subjective well-being, positive and negative affect. Specifically, positive affect and negative affect are two independent dimensions representing the experience (feeling) of emotions. In this paper, we investigate the relationship between the daily diversity of social communication and dynamic affect states that people experience in their daily lives. We collected two high-resolution datasets that capture affect scores via daily experience sampling surveys and social interaction through wearable sensing technologies: sociometric badges for face-to-face interaction and smart phones for mobile phone calls. We found that communication diversity correlates with desirable affect states--e.g. an increase in the positive affect state or a decrease in the negative affect state--for some personality types, but correlates with undesirable affect states for others. For example, diversity in phone calls is experienced as good by introverts, but bad by extroverts; diversity in face-to-face interaction is experienced as good by people who tend to be positive by nature (trait) but bad for people who tend to be not positive by nature. More broadly, the moderating effect of personality type on the relationship between diversity and affect was detected without any knowledge of the type of social tie or the content of communication. This provides further support for the power of unobtrusive sensing in understanding social dynamics, and in measuring the effect of potential interventions designed to improve well-being.

  3. Network Diversity and Affect Dynamics: The Role of Personality Traits.

    Directory of Open Access Journals (Sweden)

    Aamena Alshamsi

    Full Text Available People divide their time unequally among their social contacts due to time constraints and varying strength of relationships. It was found that high diversity of social communication, dividing time more evenly among social contacts, is correlated with economic well-being both at macro and micro levels. Besides economic well-being, it is not clear how the diversity of social communication is also associated with the two components of individuals' subjective well-being, positive and negative affect. Specifically, positive affect and negative affect are two independent dimensions representing the experience (feeling of emotions. In this paper, we investigate the relationship between the daily diversity of social communication and dynamic affect states that people experience in their daily lives. We collected two high-resolution datasets that capture affect scores via daily experience sampling surveys and social interaction through wearable sensing technologies: sociometric badges for face-to-face interaction and smart phones for mobile phone calls. We found that communication diversity correlates with desirable affect states--e.g. an increase in the positive affect state or a decrease in the negative affect state--for some personality types, but correlates with undesirable affect states for others. For example, diversity in phone calls is experienced as good by introverts, but bad by extroverts; diversity in face-to-face interaction is experienced as good by people who tend to be positive by nature (trait but bad for people who tend to be not positive by nature. More broadly, the moderating effect of personality type on the relationship between diversity and affect was detected without any knowledge of the type of social tie or the content of communication. This provides further support for the power of unobtrusive sensing in understanding social dynamics, and in measuring the effect of potential interventions designed to improve well-being.

  4. Drosophila pupal macrophages--a versatile tool for combined ex vivo and in vivo imaging of actin dynamics at high resolution.

    Science.gov (United States)

    Sander, Moritz; Squarr, Anna Julia; Risse, Benjamin; Jiang, Xiaoyi; Bogdan, Sven

    2013-01-01

    Molecular understanding of actin dynamics requires a genetically traceable model system that allows live cell imaging together with high-resolution microscopy techniques. Here, we used Drosophila pupal macrophages that combine many advantages of cultured cells with a genetic in vivo model system. Using structured illumination microscopy together with advanced spinning disk confocal microscopy we show that these cells provide a powerful system for single gene analysis. It allows forward genetic screens to characterize the regulatory network controlling cell shape and directed cell migration in a physiological context. We knocked down components regulating lamellipodia formation, including WAVE, single subunits of Arp2/3 complex and CPA, one of the two capping protein subunits and demonstrate the advantages of this model system by imaging mutant macrophages ex vivo as well as in vivo upon laser-induced wounding.

  5. Cellular prion protein is required for neuritogenesis: fine-tuning of multiple signaling pathways involved in focal adhesions and actin cytoskeleton dynamics

    Directory of Open Access Journals (Sweden)

    Alleaume-Butaux A

    2013-07-01

    Full Text Available Aurélie Alleaume-Butaux,1,2 Caroline Dakowski,1,2 Mathéa Pietri,1,2 Sophie Mouillet-Richard,1,2 Jean-Marie Launay,3,4 Odile Kellermann,1,2 Benoit Schneider1,2 1INSERM, UMR-S 747, 2Paris Descartes University, Sorbonne Paris Cité, UMR-S 747, 3Public Hospital of Paris, Department of Biochemistry, INSERM UMR-S 942, Lariboisière Hospital, Paris, France; 4Pharma Research Department, Hoffmann La Roche Ltd, Basel, Switzerland Abstract: Neuritogenesis is a dynamic phenomenon associated with neuronal differentiation that allows a rather spherical neuronal stem cell to develop dendrites and axon, a prerequisite for the integration and transmission of signals. The acquisition of neuronal polarity occurs in three steps: (1 neurite sprouting, which consists of the formation of buds emerging from the postmitotic neuronal soma; (2 neurite outgrowth, which represents the conversion of buds into neurites, their elongation and evolution into axon or dendrites; and (3 the stability and plasticity of neuronal polarity. In neuronal stem cells, remodeling and activation of focal adhesions (FAs associated with deep modifications of the actin cytoskeleton is a prerequisite for neurite sprouting and subsequent neurite outgrowth. A multiple set of growth factors and interactors located in the extracellular matrix and the plasma membrane orchestrate neuritogenesis by acting on intracellular signaling effectors, notably small G proteins such as RhoA, Rac, and Cdc42, which are involved in actin turnover and the dynamics of FAs. The cellular prion protein (PrPC, a glycosylphosphatidylinositol (GPI-anchored membrane protein mainly known for its role in a group of fatal neurodegenerative diseases, has emerged as a central player in neuritogenesis. Here, we review the contribution of PrPC to neuronal polarization and detail the current knowledge on the signaling pathways fine-tuned by PrPC to promote neurite sprouting, outgrowth, and maintenance. We emphasize that Pr

  6. Separation of actin-dependent and actin-independent lipid rafts

    NARCIS (Netherlands)

    Klappe, Karin; Hummel, Ina; Kok, Jan Willem

    2013-01-01

    Lipid rafts have been isolated on the basis of their resistance to various detergents and more recently by using detergent-free procedures. The actin cytoskeleton is now recognized as a dynamic regulator of lipid raft stability. We carefully analyzed the effects of the cortical actin-disrupting agen

  7. Bundling Actin Filaments From Membranes: Some Novel Players

    Directory of Open Access Journals (Sweden)

    Clément eThomas

    2012-08-01

    Full Text Available Progress in live-cell imaging of the cytoskeleton has significantly extended our knowledge about the organization and dynamics of actin filaments near the plasma membrane of plant cells. Noticeably, two populations of filamentous structures can be distinguished. On the one hand, fine actin filaments which exhibit an extremely dynamic behavior basically characterized by fast polymerization and prolific severing events, a process referred to as actin stochastic dynamics. On the other hand, thick actin bundles which are composed of several filaments and which are comparatively more stable although they constantly remodel as well. There is evidence that the actin cytoskeleton plays critical roles in trafficking and signaling at both the cell cortex and organelle periphery but the exact contribution of actin bundles remains unclear. A common view is that actin bundles provide the long-distance tracks used by myosin motors to deliver their cargo to growing regions and accordingly play a particularly important role in cell polarization. However, several studies support that actin bundles are more than simple passive highways and display multiple and dynamic roles in the regulation of many processes, such as cell elongation, polar auxin transport, stomatal and chloroplast movement, and defense against pathogens. The list of identified plant actin-bundling proteins is ever expanding, supporting that plant cells shape structurally and functionally different actin bundles. Here I review the most recently characterized actin-bundling proteins, with a particular focus on those potentially relevant to membrane trafficking and/or signaling.

  8. LATS1 tumor suppressor is a novel actin-binding protein and negative regulator of actin polymerization

    Institute of Scientific and Technical Information of China (English)

    Stacy Visser-Grieve; Zhonghua Zhou; Yi-Min She; He Huang; Terry D Cyr; Tian Xu; Xiaolong Yang

    2011-01-01

    Dear Editor,The LATS tumor suppressor,conserved from Drosophila (dlats) to humans (LATS1,LATS2),plays a vital role in maintaining cellular homeostasis in humans since loss of either LATS1 or LATS2 leads to the development of numerous cancer types such as breast cancer and leukemia [1].Apart from its roles as a Ser/Thr kinase within the emerging Hippo pathway regulating cell proliferation and apoptosis,ultimately leading to the control of organ size and tumorigenesis [2],LATS is also implicated in a broad range of functions including regulation of genetic stability,transcription,and protein stability [1 ].Recently,tumor suppressors have also been shown to affect the later stages of tumorigenesis,including metastasis.Among this group of metastasis regulators are genes that can directly affect actin dynamics by binding to F-actin,such as the tumor suppressors p53 [3],NF2 [4] and APC [5].

  9. CNS myelin wrapping is driven by actin disassembly.

    Science.gov (United States)

    Zuchero, J Bradley; Fu, Meng-Meng; Sloan, Steven A; Ibrahim, Adiljan; Olson, Andrew; Zaremba, Anita; Dugas, Jason C; Wienbar, Sophia; Caprariello, Andrew V; Kantor, Christopher; Leonoudakis, Dmitri; Leonoudakus, Dmitri; Lariosa-Willingham, Karen; Kronenberg, Golo; Gertz, Karen; Soderling, Scott H; Miller, Robert H; Barres, Ben A

    2015-07-27

    Myelin is essential in vertebrates for the rapid propagation of action potentials, but the molecular mechanisms driving its formation remain largely unknown. Here we show that the initial stage of process extension and axon ensheathment by oligodendrocytes requires dynamic actin filament assembly by the Arp2/3 complex. Unexpectedly, subsequent myelin wrapping coincides with the upregulation of actin disassembly proteins and rapid disassembly of the oligodendrocyte actin cytoskeleton and does not require Arp2/3. Inducing loss of actin filaments drives oligodendrocyte membrane spreading and myelin wrapping in vivo, and the actin disassembly factor gelsolin is required for normal wrapping. We show that myelin basic protein, a protein essential for CNS myelin wrapping whose role has been unclear, is required for actin disassembly, and its loss phenocopies loss of actin disassembly proteins. Together, these findings provide insight into the molecular mechanism of myelin wrapping and identify it as an actin-independent form of mammalian cell motility.

  10. Interactive affective sharing versus non-interactive affective sharing in work groups : Comparative effects of group affect on work group performance and dynamics

    NARCIS (Netherlands)

    Klep, Annefloor; Wisse, Barbara; Van Der Flier, Henk

    2011-01-01

    This study explores whether the dynamic path to group affect, which is characterized by interactive affective sharing processes, yields different effects on task performance and group dynamics than the static path to group affect, which arises from non-interactive affective sharing. The results of o

  11. The core and conserved role of MAL is homeostatic regulation of actin levels.

    Science.gov (United States)

    Salvany, Lara; Muller, Julius; Guccione, Ernesto; Rørth, Pernille

    2014-05-15

    The transcription cofactor MAL is regulated by free actin levels and thus by actin dynamics. MAL, together with its DNA-binding partner, SRF, is required for invasive cell migration and in experimental metastasis. Although MAL/SRF has many targets, we provide genetic evidence in both Drosophila and human cellular models that actin is the key target that must be regulated by MAL/SRF for invasive cell migration. By regulating MAL/SRF activity, actin protein feeds back on production of actin mRNA to ensure sufficient supply of actin. This constitutes a dedicated homeostatic feedback system that provides a foundation for cellular actin dynamics.

  12. Modelling phagosomal lipid networks that regulate actin assembly

    Directory of Open Access Journals (Sweden)

    Schwarz Roland

    2008-12-01

    Full Text Available Abstract Background When purified phagosomes are incubated in the presence of actin under appropriate conditions, microfilaments start growing from the membrane in a process that is affected by ATP and the lipid composition of the membrane. Isolated phagosomes are metabolically active organelles that contain enzymes and metabolites necessary for lipid interconversion. Hence, addition of ATP, lipids, and actin to the system alter the steady-state composition of the phagosomal membrane at the same time that the actin nucleation is initiated. Our aim was to model all these processes in parallel. Results We compiled detailed experimental data on the effects of different lipids and ATP on actin nucleation and we investigated experimentally lipid interconversion and ATP metabolism in phagosomes by using suitable radioactive compounds. In a first step, a complex lipid network interconnected by chemical reactions catalyzed by known enzymes was modelled in COPASI (Complex Pathway Simulator. However, several lines of experimental evidence indicated that only the phosphatidylinositol branch of the network was active, an observation that dramatically reduced the number of parameters in the model. The results also indicated that a lipid network-independent ATP-consuming activity should be included in the model. When this activity was introduced, the set of differential equations satisfactorily reproduced the experimental data. On the other hand, a molecular mechanism connecting membrane lipids, ATP, and the actin nucleation process is still missing. We therefore adopted a phenomenological (black-box approach to represent the empirical observations. We proposed that lipids and ATP influence the dynamic interconversion between active and inactive actin nucleation sites. With this simple model, all the experimental data were satisfactorily fitted with a single positive parameter per lipid and ATP. Conclusion By establishing an active 'dialogue' between an

  13. Alendronate affects calcium dynamics in cardiomyocytes in vitro.

    Science.gov (United States)

    Kemeny-Suss, Naomi; Kasneci, Amanda; Rivas, Daniel; Afilalo, Jonathan; Komarova, Svetlana V; Chalifour, Lorraine E; Duque, Gustavo

    2009-01-01

    Therapy with bisphosphonates, including alendronate (ALN), is considered a safe and effective treatment for osteoporosis. However, recent studies have reported an unexpected increase in serious atrial fibrillation (AF) in patients treated with bisphosphonates. The mechanism that explains this side effect remains unknown. Since AF is associated with an altered sarcoendoplasmic reticulum calcium load, we studied how ALN affects cardiomyocyte calcium homeostasis and protein isoprenylation in vitro. Acute and long-term (48h) treatment of atrial and ventricular cardiomyocytes with ALN (10(-8)-10(-6)M) was performed. Changes in calcium dynamics were determined by both fluorescence measurement of cytosolic free Ca(2+) concentration and western blot analysis of calcium-regulating proteins. Finally, effect of ALN on protein farnesylation was also identified. In both atrial and ventricular cardiomyocytes, ALN treatment delayed and diminished calcium responses to caffeine. Only in atrial cells, long-term exposure to ALN-induced transitory calcium oscillations and led to the development of oscillatory component in calcium responses to caffeine. Changes in calcium dynamics were accompanied by changes in expression of proteins controlling sarcoendoplasmic reticulum calcium. In contrast, ALN minimally affected protein isoprenylation in these cells. In summary, treatment of atrial cardiomyocytes with ALN-induced abnormalities in calcium dynamics consistent with induction of a self-stimulatory, pacemaker-like behavior, which may contribute to the development of cardiac side effects associated with these drugs.

  14. Prostaglandins temporally regulate cytoplasmic actin bundle formation during Drosophila oogenesis.

    Science.gov (United States)

    Spracklen, Andrew J; Kelpsch, Daniel J; Chen, Xiang; Spracklen, Cassandra N; Tootle, Tina L

    2014-02-01

    Prostaglandins (PGs)--lipid signals produced downstream of cyclooxygenase (COX) enzymes--regulate actin dynamics in cell culture and platelets, but their roles during development are largely unknown. Here we define a new role for Pxt, the Drosophila COX-like enzyme, in regulating the actin cytoskeleton--temporal restriction of actin remodeling during oogenesis. PGs are required for actin filament bundle formation during stage 10B (S10B). In addition, loss of Pxt results in extensive early actin remodeling, including actin filaments and aggregates, within the posterior nurse cells of S9 follicles; wild-type follicles exhibit similar structures at a low frequency. Hu li tai shao (Hts-RC) and Villin (Quail), an actin bundler, localize to all early actin structures, whereas Enabled (Ena), an actin elongation factor, preferentially localizes to those in pxt mutants. Reduced Ena levels strongly suppress early actin remodeling in pxt mutants. Furthermore, loss of Pxt results in reduced Ena localization to the sites of bundle formation during S10B. Together these data lead to a model in which PGs temporally regulate actin remodeling during Drosophila oogenesis by controlling Ena localization/activity, such that in S9, PG signaling inhibits, whereas at S10B, it promotes Ena-dependent actin remodeling.

  15. A potential yeast actin allosteric conduit dependent on hydrophobic core residues val-76 and trp-79.

    Science.gov (United States)

    Wen, Kuo-Kuang; McKane, Melissa; Stokasimov, Ema; Fields, Jonathon; Rubenstein, Peter A

    2010-07-02

    Intramolecular allosteric interactions responsible for actin conformational regulation are largely unknown. Previous work demonstrated that replacing yeast actin Val-76 with muscle actin Ile caused decreased nucleotide exchange. Residue 76 abuts Trp-79 in a six-residue linear array beginning with Lys-118 on the surface and ending with His-73 in the nucleotide cleft. To test if altering the degree of packing of these two residues would affect actin dynamics, we constructed V76I, W79F, and W79Y single mutants as well as the Ile-76/Phe-79 and Ile-76/Tyr-79 double mutants. Tyr or Phe should decrease crowding and increase protein flexibility. Subsequent introduction of Ile should restore packing and dampen changes. All mutants showed decreased growth in liquid medium. W79Y alone was severely osmosensitive and exhibited vacuole abnormalities. Both properties were rescued by Ile-76. Phe-79 or Tyr decreased the thermostability of actin and increased its nucleotide exchange rate. These effects, generally greater for Tyr than for Phe, were reversed by introduction of Ile-76. HD exchange showed that the mutations caused propagated conformational changes to all four subdomains. Based on results from phosphate release and light-scattering assays, single mutations affected polymerization in the order of Ile, Phe, and Tyr from least to most. Introduction of Ile-76 partially rescued the polymerization defects caused by either Tyr-79 or Phe-79. Thus, alterations in crowding of the 76-79 residue pair can strongly affect actin conformation and behavior, and these results support the theory that the amino acid array in which they are located may play a central role in actin regulation.

  16. SYP73 Anchors the ER to the Actin Cytoskeleton for Maintenance of ER Integrity and Streaming in Arabidopsis.

    Science.gov (United States)

    Cao, Pengfei; Renna, Luciana; Stefano, Giovanni; Brandizzi, Federica

    2016-12-05

    The endoplasmic reticulum (ER) is an essential organelle that spreads throughout the cytoplasm as one interconnected network of narrow tubules and dilated cisternae that enclose a single lumen. The ER network undergoes extensive remodeling, which critically depends on membrane-cytoskeleton interactions [1]. In plants, the ER is also highly mobile, and its streaming contributes significantly to the movement of other organelles [2, 3]. The remodeling and motility of the plant ER rely mainly on actin [4] and to a minor extent on microtubules [5]. Although a three-way interaction between the ER, cytosolic myosin-XI, and F-actin mediates the plant ER streaming [6], the mechanisms underlying stable interaction of the ER membrane with actin are unknown. Early electron microscopy studies suggested a direct attachment of the plant ER with actin filaments [7, 8], but it is plausible that yet-unknown proteins facilitate anchoring of the ER membrane with the cytoskeleton. We demonstrate here that SYP73, a member of the plant Syp7 subgroup of SNARE proteins [9] containing actin-binding domains, is a novel ER membrane-associated actin-binding protein. We show that overexpression of SYP73 causes a striking rearrangement of the ER over actin and that, similar to mutations of myosin-XI [4, 10, 11], loss of SYP73 reduces ER streaming and affects overall ER network morphology and plant growth. We propose a model for plant ER remodeling whereby the dynamic rearrangement and streaming of the ER network depend on the propelling action of myosin-XI over actin coupled with a SYP73-mediated bridging, which dynamically anchors the ER membrane with actin filaments.

  17. Increased actin polymerization and stabilization interferes with neuronal function and survival in the AMPKγ mutant Loechrig.

    Directory of Open Access Journals (Sweden)

    Mandy Cook

    Full Text Available loechrig (loe mutant flies are characterized by progressive neuronal degeneration, behavioral deficits, and early death. The mutation is due to a P-element insertion in the gene for the γ-subunit of the trimeric AMP-activated protein kinase (AMPK complex, whereby the insertion affects only one of several alternative transcripts encoding a unique neuronal isoform. AMPK is a cellular energy sensor that regulates a plethora of signaling pathways, including cholesterol and isoprenoid synthesis via its downstream target hydroxy-methylglutaryl (HMG-CoA reductase. We recently showed that loe interferes with isoprenoid synthesis and increases the prenylation and thereby activation of RhoA. During development, RhoA plays an important role in neuronal outgrowth by activating a signaling cascade that regulates actin dynamics. Here we show that the effect of loe/AMPKγ on RhoA prenylation leads to a hyperactivation of this signaling pathway, causing increased phosphorylation of the actin depolymerizating factor cofilin and accumulation of filamentous actin. Furthermore, our results show that the resulting cytoskeletal changes in loe interfere with neuronal growth and disrupt axonal integrity. Surprisingly, these phenotypes were enhanced by expressing the Slingshot (SSH phosphatase, which during development promotes actin depolymerization by dephosphorylating cofilin. However, our studies suggest that in the adult SSH promotes actin polymerization, supporting in vitro studies using human SSH1 that suggested that SSH can also stabilize and bundle filamentous actin. Together with the observed increase in SSH levels in the loe mutant, our experiments suggest that in mature neurons SSH may function as a stabilization factor for filamentous actin instead of promoting actin depolymerization.

  18. Actin Rings of Power.

    Science.gov (United States)

    Schwayer, Cornelia; Sikora, Mateusz; Slováková, Jana; Kardos, Roland; Heisenberg, Carl-Philipp

    2016-06-20

    Circular or ring-like actin structures play important roles in various developmental and physiological processes. Commonly, these rings are composed of actin filaments and myosin motors (actomyosin) that, upon activation, trigger ring constriction. Actomyosin ring constriction, in turn, has been implicated in key cellular processes ranging from cytokinesis to wound closure. Non-constricting actin ring-like structures also form at cell-cell contacts, where they exert a stabilizing function. Here, we review recent studies on the formation and function of actin ring-like structures in various morphogenetic processes, shedding light on how those different rings have been adapted to fulfill their specific roles.

  19. Computational Study of the Binding Mechanism of Actin-Depolymerizing Factor 1 with Actin in Arabidopsis thaliana.

    Directory of Open Access Journals (Sweden)

    Juan Du

    Full Text Available Actin is a highly conserved protein. It plays important roles in cellular function and exists either in the monomeric (G-actin or polymeric form (F-actin. Members of the actin-depolymerizing factor (ADF/cofilin protein family bind to both G-actin and F-actin and play vital roles in actin dynamics by manipulating the rates of filament polymerization and depolymerization. It has been reported that the S6D and R98A/K100A mutants of actin-depolymerizing factor 1 (ADF1 in Arabidopsis thaliana decreased the binding affinity of ADF for the actin monomer. To investigate the binding mechanism and dynamic behavior of the ADF1-actin complex, we constructed a homology model of the AtADF1-actin complex based on the crystal structure of AtADF1 and the twinfilin C-terminal ADF-H domain in a complex with a mouse actin monomer. The model was then refined for subsequent molecular dynamics simulations. Increased binding energy of the mutated system was observed using the Molecular Mechanics Generalized Born Surface Area and Poisson-Boltzmann Surface Area (MM-GB/PBSA methods. To determine the residues that make decisive contributions to the ADF1 actin-binding affinity, per-residue decomposition and computational alanine scanning analyses were performed, which provided more detailed information on the binding mechanism. Root-mean-square fluctuation and principal component analyses confirmed that the S6D and R98A/K100A mutants induced an increased conformational flexibility. The comprehensive molecular insight gained from this study is of great importance for understanding the binding mechanism of ADF1 and G-actin.

  20. Energetic modeling and single-molecule verification of dynamic regulation on receptor protein diffusion by actin corrals and lipid raft domains receptor

    Science.gov (United States)

    Lin, Chien Yu; Huang, Jung Y.; Lo, Leu-Wei

    2015-03-01

    To faithfully estimate a signal that varies in both space and time, the optimization strategy used by a live cell is to organize a collection of distributed and mobile receptors into a mobile active clustering. However, living eukaryotic cells are highly heterogeneous and stochastically dynamic. It is therefore important to develop an energetic model based on fundamental laws to verify that the underlying processes are energetically favorable. We developed an energetic model based on the generalized Langevin equation and the Cahn-Hilliard equation to simulate the diffusive behaviors of receptor proteins in the plasma membrane with a hierarchical structure of actin corrals, lipid domains, and receptor proteins. Single-molecule tracking data of EGFR acquired on live HeLa cells agrees with the simulation results. We discovered that after ligand binding, EGFR molecules move into lipid nanodomains. The transition rates between different diffusion states of liganded EGFR molecules are regulated by the lipid domains. Our method captures both the sensitivity of single-molecule processes, statistic accuracy of data analysis, and the hierarchical structure of plasma membranes.

  1. Resemblance of actin-binding protein/actin gels to covalently crosslinked networks

    Science.gov (United States)

    Janmey, Paul A.; Hvidt, Søren; Lamb, Jennifer; Stossel, Thomas P.

    1990-05-01

    THE maintainance of the shape of cells is often due to their surface elasticity, which arises mainly from an actin-rich cytoplasmic cortex1,2. On locomotion, phagocytosis or fission, however, these cells become partially fluid-like. The finding of proteins that can bind to actin and control the assembly of, or crosslink, actin filaments, and of intracellular messages that regulate the activities of some of these actin-binding proteins, indicates that such 'gel sol' transformations result from the rearrangement of cortical actin-rich networks3. Alternatively, on the basis of a study of the mechanical properties of mixtures of actin filaments and an Acanthamoeba actin-binding protein, α-actinin, it has been proposed that these transformations can be accounted for by rapid exchange of crosslinks between actin filaments4: the cortical network would be solid when the deformation rate is greater than the rate of crosslink exchange, but would deform or 'creep' when deformation is slow enough to permit crosslinker molecules to rearrange. Here we report, however, that mixtures of actin filaments and actin-binding protein (ABP), an actin crosslinking protein of many higher eukaryotes, form gels Theologically equivalent to covalently crosslinked networks. These gels do not creep in response to applied stress on a time scale compatible with most cell-surface movements. These findings support a more complex and controlled mechanism underlying the dynamic mechanical properties of cortical cytoplasm, and can explain why cells do not collapse under the constant shear forces that often exist in tissues.

  2. Distributed actin turnover in the lamellipodium and FRAP kinetics.

    Science.gov (United States)

    Smith, Matthew B; Kiuchi, Tai; Watanabe, Naoki; Vavylonis, Dimitrios

    2013-01-08

    Studies of actin dynamics at the leading edge of motile cells with single-molecule speckle (SiMS) microscopy have shown a broad distribution of EGFP-actin speckle lifetimes and indicated actin polymerization and depolymerization over an extended region. Other experiments using FRAP with the same EGFP-actin as a probe have suggested, by contrast, that polymerization occurs exclusively at the leading edge. We performed FRAP experiments on XTC cells to compare SiMS to FRAP on the same cell type. We used speckle statistics obtained by SiMS to model the steady-state distribution and kinetics of actin in the lamellipodium. We demonstrate that a model with a single diffuse actin species is in good agreement with FRAP experiments. A model including two species of diffuse actin provides an even better agreement. The second species consists of slowly diffusing oligomers that associate to the F-actin network throughout the lamellipodium or break up into monomers after a characteristic time. Our work motivates studies to test the presence and composition of slowly diffusing actin species that may contribute to local remodeling of the actin network and increase the amount of soluble actin.

  3. Actin as a potential target for decavanadate.

    Science.gov (United States)

    Ramos, Susana; Moura, José J G; Aureliano, Manuel

    2010-12-01

    ATP prevents G-actin cysteine oxidation and vanadyl formation specifically induced by decavanadate, suggesting that the oxometalate-protein interaction is affected by the nucleotide. The ATP exchange rate is increased by 2-fold due to the presence of decavanadate when compared with control actin (3.1×10(-3) s(-1)), and an apparent dissociation constant (k(dapp)) of 227.4±25.7 μM and 112.3±8.7 μM was obtained in absence or presence of 20 μM V(10), respectively. Moreover, concentrations as low as 50 μM of decameric vanadate species (V(10)) increases the relative G-actin intrinsic fluorescence intensity by approximately 80% whereas for a 10-fold concentration of monomeric vanadate (V(1)) no effects were observed. Upon decavanadate titration, it was observed a linear increase in G-actin hydrophobic surface (2.6-fold), while no changes were detected for V(1) (0-200 μM). Taken together, three major ideas arise: i) ATP prevents decavanadate-induced G-actin cysteine oxidation and vanadate reduction; ii) decavanadate promotes actin conformational changes resulting on its inactivation, iii) decavanadate has an effect on actin ATP binding site. Once it is demonstrated that actin is a new potential target for decavanadate, being the ATP binding site a suitable site for decavanadate binding, it is proposed that some of the biological effects of vanadate can be, at least in part, explained by decavanadate interactions with actin.

  4. Plant villins:Versatile actin regulatory proteins

    Institute of Scientific and Technical Information of China (English)

    Shanjin Huang; Xiaolu Qu; Ruihui Zhang

    2015-01-01

    Regulation of actin dynamics is a central theme in cel biology that is important for different aspects of cel physiology. Vil in, a member of the vil in/gelsolin/fragmin superfamily of proteins, is an important regulator of actin. Vil ins contain six gelsolin homology domains (G1–G6) and an extra headpiece domain. In contrast to their mammalian counterparts, plant vil ins are expressed widely, implying that plant vil ins play a more general role in regulating actin dynamics. Some plant vil ins have a defined role in modifying actin dynamics in the pol en tube;most of their in vivo activities remain to be ascertained. Recently, our understanding of the functions and mechanisms of action for plant vil ins has progressed rapidly, primarily due to the advent of Arabidopsis thaliana genetic approaches and imaging capabilities that can visualize actin dynamics at the single filament level in vitro and in living plant cel s. In this review, we focus on discussing the biochemical activities and modes of regulation of plant vil ins. Here, we present current understand-ing of the functions of plant vil ins. Final y, we highlight some of the key unanswered questions regarding the functions and regulation of plant vil ins for future research.

  5. The model of fungal population dynamics affected by nystatin

    Science.gov (United States)

    Voychuk, Sergei I.; Gromozova, Elena N.; Sadovskiy, Mikhail G.

    Fungal diseases are acute problems of the up-to-day medicine. Significant increase of resistance of microorganisms to the medically used antibiotics and a lack of new effective drugs follows in a growth of dosage of existing chemicals to solve the problem. Quite often such approach results in side effects on humans. Detailed study of fungi-antibiotic dynamics can identify new mechanisms and bring new ideas to overcome the microbial resistance with a lower dosage of antibiotics. In this study, the dynamics of the microbial population under antibiotic treatment was investigated. The effects of nystatin on the population of Saccharomyces cerevisiae yeasts were used as a model system. Nystatin effects were investigated both in liquid and solid media by viability tests. Dependence of nystatin action on osmotic gradient was evaluated in NaCl solutions. Influences of glucose and yeast extract were additionally analyzed. A "stepwise" pattern of the cell death caused by nystatin was the most intriguing. This pattern manifested in periodical changes of the stages of cell death against stages of resistance to the antibiotic. The mathematical model was proposed to describe cell-antibiotic interactions and nystatin viability effects in the liquid medium. The model implies that antibiotic ability to cause a cells death is significantly affected by the intracellular compounds, which came out of cells after their osmotic barriers were damaged

  6. Cytoskeletal remodeling in differentiated vascular smooth muscle is actin isoform dependent and stimulus dependent.

    Science.gov (United States)

    Kim, Hak Rim; Gallant, Cynthia; Leavis, Paul C; Gunst, Susan J; Morgan, Kathleen G

    2008-09-01

    Dynamic remodeling of the actin cytoskeleton plays an essential role in the migration and proliferation of vascular smooth muscle cells. It has been suggested that actin remodeling may also play an important functional role in nonmigrating, nonproliferating differentiated vascular smooth muscle (dVSM). In the present study, we show that contractile agonists increase the net polymerization of actin in dVSM, as measured by the differential ultracentrifugation of vascular smooth muscle tissue and the costaining of single freshly dissociated cells with fluorescent probes specific for globular and filamentous actin. Furthermore, induced alterations of the actin polymerization state, as well as actin decoy peptides, inhibit contractility in a stimulus-dependent manner. Latrunculin pretreatment or actin decoy peptides significantly inhibit contractility induced by a phorbol ester or an alpha-agonist, but these procedures have no effect on contractions induced by KCl. Aorta dVSM expresses alpha-smooth muscle actin, beta-actin, nonmuscle gamma-actin, and smooth muscle gamma-actin. The incorporation of isoform-specific cell-permeant synthetic actin decoy peptides, as well as isoform-specific probing of cell fractions and two-dimensional gels, demonstrates that actin remodeling during alpha-agonist contractions involves the remodeling of primarily gamma-actin and, to a lesser extent, beta-actin. Taken together, these results show that net isoform- and agonist-dependent increases in actin polymerization regulate vascular contractility.

  7. CAS-1, a C. elegans cyclase-associated protein, is required for sarcomeric actin assembly in striated muscle

    OpenAIRE

    Nomura, Kazumi; Ono, Kanako; Ono, Shoichiro

    2012-01-01

    Assembly of contractile apparatuses in striated muscle requires precisely regulated reorganization of the actin cytoskeletal proteins into sarcomeric organization. Regulation of actin filament dynamics is one of the essential processes of myofibril assembly, but the mechanism of actin regulation in striated muscle is not clearly understood. Actin depolymerizing factor (ADF)/cofilin is a key enhancer of actin filament dynamics in striated muscle in both vertebrates and nematodes. Here, we repo...

  8. Distinct functional interactions between actin isoforms and nonsarcomeric myosins.

    Directory of Open Access Journals (Sweden)

    Mirco Müller

    Full Text Available Despite their near sequence identity, actin isoforms cannot completely replace each other in vivo and show marked differences in their tissue-specific and subcellular localization. Little is known about isoform-specific differences in their interactions with myosin motors and other actin-binding proteins. Mammalian cytoplasmic β- and γ-actin interact with nonsarcomeric conventional myosins such as the members of the nonmuscle myosin-2 family and myosin-7A. These interactions support a wide range of cellular processes including cytokinesis, maintenance of cell polarity, cell adhesion, migration, and mechano-electrical transduction. To elucidate differences in the ability of isoactins to bind and stimulate the enzymatic activity of individual myosin isoforms, we characterized the interactions of human skeletal muscle α-actin, cytoplasmic β-actin, and cytoplasmic γ-actin with human myosin-7A and nonmuscle myosins-2A, -2B and -2C1. In the case of nonmuscle myosins-2A and -2B, the interaction with either cytoplasmic actin isoform results in 4-fold greater stimulation of myosin ATPase activity than was observed in the presence of α-skeletal muscle actin. Nonmuscle myosin-2C1 is most potently activated by β-actin and myosin-7A by γ-actin. Our results indicate that β- and γ-actin isoforms contribute to the modulation of nonmuscle myosin-2 and myosin-7A activity and thereby to the spatial and temporal regulation of cytoskeletal dynamics. FRET-based analyses show efficient copolymerization abilities for the actin isoforms in vitro. Experiments with hybrid actin filaments show that the extent of actomyosin coupling efficiency can be regulated by the isoform composition of actin filaments.

  9. Actinic lichen nitidus

    Directory of Open Access Journals (Sweden)

    Loretta Davis

    2010-01-01

    Full Text Available We present the case of a 29-year-old black female with an initial clinical and histopathologic diagnosis of actinic lichen nitidus. Three years later, she presented with scattered hyperpigmented macules with oval pink/viol­aceous plaques bilaterally on her forearms and on her neck, clinically consistent with actinic lichen planus. She was treated with topical steroids at each visit, with subsequent resolution of her lesions. In this report, we discuss the spectrum of actinic lichenoid dermatoses and of disease that presents even in the same patient.

  10. Glutamyl phosphate is an activated intermediate in actin crosslinking by actin crosslinking domain (ACD toxin.

    Directory of Open Access Journals (Sweden)

    Elena Kudryashova

    Full Text Available Actin Crosslinking Domain (ACD is produced by several life-threatening Gram-negative pathogenic bacteria as part of larger toxins and delivered into the cytoplasm of eukaryotic host cells via Type I or Type VI secretion systems. Upon delivery, ACD disrupts the actin cytoskeleton by catalyzing intermolecular amide bond formation between E270 and K50 residues of actin, leading to the formation of polymerization-deficient actin oligomers. Ultimately, accumulation of the crosslinked oligomers results in structural and functional failure of the actin cytoskeleton in affected cells. In the present work, we advanced in our understanding of the ACD catalytic mechanism by discovering that the enzyme transfers the gamma-phosphoryl group of ATP to the E270 actin residue, resulting in the formation of an activated acyl phosphate intermediate. This intermediate is further hydrolyzed and the energy of hydrolysis is utilized for the formation of the amide bond between actin subunits. We also determined the pH optimum for the reaction and the kinetic parameters of ACD catalysis for its substrates, ATP and actin. ACD showed sigmoidal, non-Michaelis-Menten kinetics for actin (K(0.5 = 30 µM reflecting involvement of two actin molecules in a single crosslinking event. We established that ACD can also utilize Mg(2+-GTP to support crosslinking, but the kinetic parameters (K(M = 8 µM and 50 µM for ATP and GTP, respectively suggest that ATP is the primary substrate of ACD in vivo. The optimal pH for ACD activity was in the range of 7.0-9.0. The elucidated kinetic mechanism of ACD toxicity adds to understanding of complex network of host-pathogen interactions.

  11. Cryptococcus neoformans Is Internalized by Receptor-Mediated or ‘Triggered’ Phagocytosis, Dependent on Actin Recruitment

    Science.gov (United States)

    Guerra, Caroline Rezende; Seabra, Sergio Henrique; de Souza, Wanderley; Rozental, Sonia

    2014-01-01

    Cryptococcosis by the encapsulated yeast Cryptococcus neoformans affects mostly immunocompromised individuals and is a frequent neurological complication in AIDS patients. Recent studies support the idea that intracellular survival of Cryptococcus yeast cells is important for the pathogenesis of cryptococcosis. However, the initial steps of Cryptococcus internalization by host cells remain poorly understood. Here, we investigate the mechanism of Cryptococcus neoformans phagocytosis by peritoneal macrophages using confocal and electron microscopy techniques, as well as flow cytometry quantification, evaluating the importance of fungal capsule production and of host cell cytoskeletal elements for fungal phagocytosis. Electron microscopy analyses revealed that capsular and acapsular strains of C. neoformans are internalized by macrophages via both ‘zipper’ (receptor-mediated) and ‘trigger’ (membrane ruffle-dependent) phagocytosis mechanisms. Actin filaments surrounded phagosomes of capsular and acapsular yeasts, and the actin depolymerizing drugs cytochalasin D and latrunculin B inhibited yeast internalization and actin recruitment to the phagosome area. In contrast, nocodazole and paclitaxel, inhibitors of microtubule dynamics decreased internalization but did not prevent actin recruitment to the site of phagocytosis. Our results show that different uptake mechanisms, dependent on both actin and tubulin dynamics occur during yeast internalization by macrophages, and that capsule production does not affect the mode of Cryptococcus uptake by host cells. PMID:24586631

  12. Analysis of cytoskeleton dynamics and cell migration in drosophila ovaries using GFP-actin and E-cadherin-GFP fusion molecules

    Science.gov (United States)

    Verkhusha, Vladyslav V.; Tsukita, Shoichiro; Oda, Hiroki

    1999-06-01

    Coordination of cell migration and adhesion is essential for movement of tissues during morphogenesis. During Drosophila oogenesis so called border cells (BCs) break from an anterior epithelium of egg chamber, acquire a mesenchymal-like morphology, and migrate posteriorly between nurse cells to oocyte. The confocal microscopic observation of BCs has revealed well-developed forepart lamellipodium stained with Drosophila E-cadherin (DE-cadherin), PS2 integrin, cytoplasmic myosin and F-actin. To investigate mechanism of BC migration in vivo we have constructed a DE-cadherin-GFP and a GFP-actin fusion proteins and induced their expression BCs utilizing the UAS/GAL4 system. The DE-cadherin-GFP signal as well as immunostaining of PS2 integrin visualized a track of migrating BCs providing an evidence that adhesive molecules are pulled out and left behind on the surface of nurse cells. Our data suggest that two distinct adhesive systems, DE-cadherins and PS2 integrins simultaneously mediate the migration of BCs. Release of adhesive contacts in the tail region is a rate- limited event in BC migration. The spatial-temporal sequence of actin-based events visualized by the GFP-actin suggest a treadmilling model for actin behavior in BC lamellipodium. BC migration can be considered as simultaneous reiterating processes of lamellipodium extension and adhesive attachment, cytoskeletal contraction, and rear detachment.

  13. Actin is required for IFT regulation in Chlamydomonas reinhardtii.

    Science.gov (United States)

    Avasthi, Prachee; Onishi, Masayuki; Karpiak, Joel; Yamamoto, Ryosuke; Mackinder, Luke; Jonikas, Martin C; Sale, Winfield S; Shoichet, Brian; Pringle, John R; Marshall, Wallace F

    2014-09-01

    Assembly of cilia and flagella requires intraflagellar transport (IFT), a highly regulated kinesin-based transport system that moves cargo from the basal body to the tip of flagella [1]. The recruitment of IFT components to basal bodies is a function of flagellar length, with increased recruitment in rapidly growing short flagella [2]. The molecular pathways regulating IFT are largely a mystery. Because actin network disruption leads to changes in ciliary length and number, actin has been proposed to have a role in ciliary assembly. However, the mechanisms involved are unknown. In Chlamydomonas reinhardtii, conventional actin is found in both the cell body and the inner dynein arm complexes within flagella [3, 4]. Previous work showed that treating Chlamydomonas cells with the actin-depolymerizing compound cytochalasin D resulted in reversible flagellar shortening [5], but how actin is related to flagellar length or assembly remains unknown. Here we utilize small-molecule inhibitors and genetic mutants to analyze the role of actin dynamics in flagellar assembly in Chlamydomonas reinhardtii. We demonstrate that actin plays a role in IFT recruitment to basal bodies during flagellar elongation and that when actin is perturbed, the normal dependence of IFT recruitment on flagellar length is lost. We also find that actin is required for sufficient entry of IFT material into flagella during assembly. These same effects are recapitulated with a myosin inhibitor, suggesting that actin may act via myosin in a pathway by which flagellar assembly is regulated by flagellar length.

  14. The neuronal and actin commitment: Why do neurons need rings?

    Science.gov (United States)

    Leite, Sérgio Carvalho; Sousa, Mónica Mendes

    2016-09-01

    The role of the actin cytoskeleton in neurons has been extensively studied in actin-enriched compartments such as the growth cone and dendritic spines. The recent discovery of actin rings in the axon shaft and in dendrites, together with the identification of axon actin trails, has advanced our understanding on actin organization and dynamics in neurons. However, specifically in the case of actin rings, the mechanisms regulating their nucleation and assembly, and the functions that they may exert in axons and dendrites remain largely unexplored. Here we discuss the possible structural, mechanistic and functional properties of the subcortical neuronal cytoskeleton putting the current knowledge in perspective with the information available on actin rings formed in other biological contexts, and with the organization of actin-spectrin lattices in other cell types. The detailed analysis of these novel neuronal actin ring structures, together with the elucidation of the function of actin-binding proteins in neuron biology, has a large potential to uncover new mechanisms of neuronal function under normal conditions that may have impact in our understanding of axon degeneration and regeneration. © 2016 Wiley Periodicals, Inc.

  15. Steric effects induce geometric remodeling of actin bundles in filopodia

    CERN Document Server

    Dobramysl, Ulrich; Erban, Radek

    2016-01-01

    Filopodia are ubiquitous fingerlike protrusions, spawned by many eukaryotic cells, to probe and interact with their environments. Polymerization dynamics of actin filaments, comprising the structural core of filopodia, largely determine their instantaneous lengths and overall lifetimes. The polymerization reactions at the filopodial tip require transport of G-actin, which enter the filopodial tube from the filopodial base and diffuse toward the filament barbed ends near the tip. Actin filaments are mechanically coupled into a tight bundle by cross-linker proteins. Interestingly, many of these proteins are relatively short, restricting the free diffusion of cytosolic G-actin throughout the bundle and, in particular, its penetration into the bundle core. To investigate the effect of steric restrictions on G-actin diffusion by the porous structure of filopodial actin filament bundle, we used a particle-based stochastic simulation approach. We discovered that excluded volume interactions result in partial and the...

  16. Characterization of affective states by pupillary dynamics and autonomic correlates.

    Science.gov (United States)

    Onorati, Francesco; Barbieri, Riccardo; Mauri, Maurizio; Russo, Vincenzo; Mainardi, Luca

    2013-01-01

    With the recent advent of new recording devices and an easier access to signal processing tools, researchers are increasingly exploring and studying the Pupil Dilation (PD) signal. Recently, numerous studies pointed out the relations between PD dynamics and psychophysiological states. Although it is well known that PD is controlled by the Autonomic Nervous System (ANS), and ANS responses are related to emotional events/stimuli, the relationship between emotional states and PD is still an open issue. The aim of this study is to define the statistical properties of the PD signal, to understand its relation with ANS correlates such as Heart Rate Variability (HRV) and respiration (RESP), and to explore if PD could provide information for the evaluation of the psychophysiological response of ANS to affective triggering events. ECG, RESP, and PD data from 13 normal subjects were recorded during a memory recall paradigm, and processed with spectral and cross-spectral analysis. Our results demonstrate that variability indices extracted from fast PD oscillations, not observable through standard cardiorespiratory identification in the frequency domain, would be able to discern psychophysiological responses elicited by basic emotional stimuli. A strong linear coupling was found between the variables, due to the influence of RESP on both PD and HRV within the High Frequency (HF) band, from 0.15 to 0.45 Hz. Most importantly, our results point at PD features as possible candidates for characterizing basic emotional stimuli.

  17. The human Arp2/3 complex is composed of evolutionarily conserved subunits and is localized to cellular regions of dynamic actin filament assembly.

    Science.gov (United States)

    Welch, M D; DePace, A H; Verma, S; Iwamatsu, A; Mitchison, T J

    1997-07-28

    The Arp2/3 protein complex has been implicated in the control of actin polymerization in cells. The human complex consists of seven subunits which include the actin related proteins Arp2 and Arp3, and five others referred to as p41-Arc, p34-Arc, p21-Arc, p20-Arc, and p16-Arc (p omplex). We have determined the predicted amino acid sequence of all seven subunits. Each has homologues in diverse eukaryotes, implying that the structure and function of the complex has been conserved through evolution. Human Arp2 and Arp3 are very similar to family members from other species. p41-Arc is a new member of the Sop2 family of WD (tryptophan and aspartate) repeat-containing proteins and may be posttranslationally modified, suggesting that it may be involved in regulating the activity and/or localization of the complex. p34-Arc, p21-Arc, p20-Arc, and p16-Arc define novel protein families. We sought to evaluate the function of the Arp2/3 complex in cells by determining its intracellular distribution. Arp3, p34-Arc, and p21-Arc were localized to the lamellipodia of stationary and locomoting fibroblasts, as well to Listeria monocytogenes assembled actin tails. They were not detected in cellular bundles of actin filaments. Taken together with the ability of the Arp2/3 complex to induce actin polymerization, these observations suggest that the complex promotes actin assembly in lamellipodia and may participate in lamellipodial protrusion.

  18. Histamine activates p38 MAP kinase and alters local lamellipodia dynamics, reducing endothelial barrier integrity and eliciting central movement of actin fibers.

    Science.gov (United States)

    Adderley, Shaquria P; Lawrence, Curtis; Madonia, Eyong; Olubadewo, Joseph O; Breslin, Jerome W

    2015-07-01

    The role of the actin cytoskeleton in endothelial barrier function has been debated for nearly four decades. Our previous investigation revealed spontaneous local lamellipodia in confluent endothelial monolayers that appear to increase overlap at intercellular junctions. We tested the hypothesis that the barrier-disrupting agent histamine would reduce local lamellipodia protrusions and investigated the potential involvement of p38 mitogen-activated protein (MAP) kinase activation and actin stress fiber formation. Confluent monolayers of human umbilical vein endothelial cells (HUVEC) expressing green fluorescent protein-actin were studied using time-lapse fluorescence microscopy. The protrusion and withdrawal characteristics of local lamellipodia were assessed before and after addition of histamine. Changes in barrier function were determined using electrical cell-substrate impedance sensing. Histamine initially decreased barrier function, lamellipodia protrusion frequency, and lamellipodia protrusion distance. A longer time for lamellipodia withdrawal and reduced withdrawal distance and velocity accompanied barrier recovery. After barrier recovery, a significant number of cortical fibers migrated centrally, eventually resembling actin stress fibers. The p38 MAP kinase inhibitor SB203580 attenuated the histamine-induced decreases in barrier function and lamellipodia protrusion frequency. SB203580 also inhibited the histamine-induced decreases in withdrawal distance and velocity, and the subsequent actin fiber migration. These data suggest that histamine can reduce local lamellipodia protrusion activity through activation of p38 MAP kinase. The findings also suggest that local lamellipodia have a role in maintaining endothelial barrier integrity. Furthermore, we provide evidence that actin stress fiber formation may be a reaction to, rather than a cause of, reduced endothelial barrier integrity.

  19. The Human Arp2/3 Complex Is Composed of Evolutionarily Conserved Subunits and Is Localized to Cellular Regions of Dynamic Actin Filament Assembly

    OpenAIRE

    Welch, Matthew D.; Angela H. DePace; Verma, Suzie; Iwamatsu, Akihiro; Mitchison, Timothy J.

    1997-01-01

    The Arp2/3 protein complex has been implicated in the control of actin polymerization in cells. The human complex consists of seven subunits which include the actin related proteins Arp2 and Arp3, and five others referred to as p41-Arc, p34-Arc, p21-Arc, p20-Arc, and p16-Arc (Arp complex). We have determined the predicted amino acid sequence of all seven subunits. Each has homologues in diverse eukaryotes, implying that the structure and function of the complex has been conserved through evol...

  20. Effects of latrunculin B on the actin cytoskeleton and hyphal growth in Phytophthora infestans.

    Science.gov (United States)

    Ketelaar, Tijs; Meijer, Harold J G; Spiekerman, Marjolein; Weide, Rob; Govers, Francine

    2012-12-01

    The actin cytoskeleton is conserved in all eukaryotes, but its functions vary among different organisms. In oomycetes, the function of the actin cytoskeleton has received relatively little attention. We have performed a bioinformatics study and show that oomycete actin genes fall within a distinct clade that is divergent from plant, fungal and vertebrate actin genes. To obtain a better understanding of the functions of the actin cytoskeleton in hyphal growth of oomycetes, we studied the actin organization in Phytophthora infestans hyphae and the consequences of treatment with the actin depolymerising drug latrunculin B (latB). This revealed that latB treatment causes a concentration dependent inhibition of colony expansion and aberrant hyphal growth. The most obvious aberrations observed upon treatment with 0.1 μM latB were increased hyphal branching and irregular tube diameters whereas at higher concentrations latB (0.5 and 1 μM) tips of expanding hyphae changed into balloon-like shapes. This aberrant growth correlated with changes in the organization of the actin cytoskeleton. In untreated hyphae, staining with fluorescently tagged phalloidin revealed two populations of actin filaments: long, axially oriented actin filament cables and cortical actin filament plaques. Two hyphal subtypes were recognized, one containing only plaques and the other containing both cables and plaques. In the latter, some hyphae had an apical zone without actin filament plaques. Upon latB treatment, the proportion of hyphae without actin filament cables increased and there were more hyphae with a short apical zone without actin filament plaques. In general, actin filament plaques were more resilient against actin depolymerisation than actin filament cables. Besides disturbing hyphal growth and actin organization, actin depolymerisation also affected the positioning of nuclei. In the presence of latB, the distance between nuclei and the hyphal tip decreased, suggesting that the actin

  1. Design and evaluation of Actichip, a thematic microarray for the study of the actin cytoskeleton

    Directory of Open Access Journals (Sweden)

    Chalmel Frédéric

    2007-08-01

    Full Text Available Abstract Background The actin cytoskeleton plays a crucial role in supporting and regulating numerous cellular processes. Mutations or alterations in the expression levels affecting the actin cytoskeleton system or related regulatory mechanisms are often associated with complex diseases such as cancer. Understanding how qualitative or quantitative changes in expression of the set of actin cytoskeleton genes are integrated to control actin dynamics and organisation is currently a challenge and should provide insights in identifying potential targets for drug discovery. Here we report the development of a dedicated microarray, the Actichip, containing 60-mer oligonucleotide probes for 327 genes selected for transcriptome analysis of the human actin cytoskeleton. Results Genomic data and sequence analysis features were retrieved from GenBank and stored in an integrative database called Actinome. From these data, probes were designed using a home-made program (CADO4MI allowing sequence refinement and improved probe specificity by combining the complementary information recovered from the UniGene and RefSeq databases. Actichip performance was analysed by hybridisation with RNAs extracted from epithelial MCF-7 cells and human skeletal muscle. Using thoroughly standardised procedures, we obtained microarray images with excellent quality resulting in high data reproducibility. Actichip displayed a large dynamic range extending over three logs with a limit of sensitivity between one and ten copies of transcript per cell. The array allowed accurate detection of small changes in gene expression and reliable classification of samples based on the expression profiles of tissue-specific genes. When compared to two other oligonucleotide microarray platforms, Actichip showed similar sensitivity and concordant expression ratios. Moreover, Actichip was able to discriminate the highly similar actin isoforms whereas the two other platforms did not. Conclusion Our

  2. Photodynamic therapy for the treatment of actinic cheilitis.

    Science.gov (United States)

    Kodama, Makiko; Watanabe, Daisuke; Akita, Yoichi; Tamada, Yasuhiko; Matsumoto, Yoshinari

    2007-10-01

    Although actinic cheilitis is a common disease, it should be treated carefully because it can undergo malignant transformation. We report a case of actinic cheilitis treated with photodynamic therapy (PDT) using 5-aminolevulinic acid (ALA), with satisfactory outcome in both clinical and pathological aspects. Actinic cheilitis is a pathologic condition affecting mainly the lower lip caused by long-term exposure of the lips to the UV radiation in sunlight. Analogous to actinic keratosis of the skin, actinic cheilitis is considered as a precancerous lesion and it may develop into squamous cell carcinoma. We report a case of actinic cheilitis treated with PDT using ALA, with satisfactory outcome in both clinical and pathological aspects.

  3. The ubiquitin C-terminal hydrolase UCH-L1 promotes bacterial invasion by altering the dynamics of the actin cytoskeleton

    DEFF Research Database (Denmark)

    Basseres, Eugene; Coppotelli, Giuseppe; Pfirrmann, Thorsten;

    2010-01-01

    Invasion of eukaryotic target cells by pathogenic bacteria requires extensive remodelling of the membrane and actin cytoskeleton. Here we show that the remodelling process is regulated by the ubiquitin C-terminal hydrolase UCH-L1 that promotes the invasion of epithelial cells by Listeria monocyto...

  4. The reversible increase in tight junction permeability induced by capsaicin is mediated via cofilin-actin cytoskeletal dynamics and decreased level of occludin.

    Directory of Open Access Journals (Sweden)

    Tomoko Shiobara

    Full Text Available Previous results demonstrated that capsaicin induces the reversible tight junctions (TJ opening via cofilin activation. The present study investigated the mechanisms underlying the reversible TJ opening and compared the effect to the irreversible opening induced by actin inhibitors. Capsaicin treatment induced the F-actin alteration unique to capsaicin compared to actin-interacting agents such as latrunculin A, which opens TJ irreversibly. Along with TJ opening, capsaicin decreased the level of F-actin at bicellular junctions but increased it at tricellular junctions accompanied with its concentration on the apical side of the lateral membrane. No change in TJ protein localization was observed upon exposure to capsaicin, but the amount of occludin was decreased significantly. In addition, cosedimentation analyses suggested a decrease in the interactions forming TJ, thereby weakening TJ tightness. Introduction of cofilin, LIMK and occludin into the cell monolayers confirmed their contribution to the transepithelial electrical resistance decrease. Finally, exposure of monolayers to capsaicin augmented the paracellular passage of both charged and uncharged compounds, as well as of insulin, indicating that capsaicin can be employed to modulate epithelial permeability. Our results demonstrate that capsaicin induces TJ opening through a unique mechanism, and suggest that it is a new type of paracellular permeability enhancer.

  5. Dynamics of Affective Experience and Behavior in Depressed Adolescents

    Science.gov (United States)

    Sheeber, Lisa B.; Allen, Nicholas B.; Leve, Craig; Davis, Betsy; Shortt, Joann Wu; Katz, Lynn Fainsilber

    2009-01-01

    Background: Depression is often characterized as a disorder of affect regulation. However, research focused on delineating the key dimensions of affective experience (other than valence) that are abnormal in depressive disorder has been scarce, especially in child and adolescent samples. As definitions of affect regulation center around processes…

  6. A Hierarchical Latent Stochastic Differential Equation Model for Affective Dynamics

    Science.gov (United States)

    Oravecz, Zita; Tuerlinckx, Francis; Vandekerckhove, Joachim

    2011-01-01

    In this article a continuous-time stochastic model (the Ornstein-Uhlenbeck process) is presented to model the perpetually altering states of the core affect, which is a 2-dimensional concept underlying all our affective experiences. The process model that we propose can account for the temporal changes in core affect on the latent level. The key…

  7. Actin-filament disassembly: it takes two to shrink them fast.

    Science.gov (United States)

    Winterhoff, Moritz; Faix, Jan

    2015-06-01

    Actin-filament disassembly is indispensable for replenishing the pool of polymerizable actin and allows continuous dynamic remodelling of the actin cytoskeleton. A new study now reveals that ADF/cofilin preferentially dismantles branched networks and provides new insights into the collaborative work of ADF/cofilin and Aip1 on filament disassembly at the molecular level.

  8. Phototropin-dependent biased relocalization of cp-actin filaments can be induced even when chloroplast movement is inhibited

    OpenAIRE

    Yamada, Noboru; Suetsugu, Noriyuki; Wada, Masamitsu; Kadota, Akeo

    2011-01-01

    In a recent publication using an actin-visualized line of Arabidopsis (Ichikawa et al. 2011, ref. 11), we reported a detailed analysis with higher time resolution on the dynamics of chloroplast actin filaments (cp-actin filaments) during chloroplast avoidance movement and demonstrated a good correlation between the biased configuration of cp-actin filaments and chloroplast movement. However, we could not conclusively determine whether the reorganization of cp-actin filaments into a biased con...

  9. WH2 domain: a small, versatile adapter for actin monomers.

    Science.gov (United States)

    Paunola, Eija; Mattila, Pieta K; Lappalainen, Pekka

    2002-02-20

    The actin cytoskeleton plays a central role in many cell biological processes. The structure and dynamics of the actin cytoskeleton are regulated by numerous actin-binding proteins that usually contain one of the few known actin-binding motifs. WH2 domain (WASP homology domain-2) is a approximately 35 residue actin monomer-binding motif, that is found in many different regulators of the actin cytoskeleton, including the beta-thymosins, ciboulot, WASP (Wiskott Aldrich syndrome protein), verprolin/WIP (WASP-interacting protein), Srv2/CAP (adenylyl cyclase-associated protein) and several uncharacterized proteins. The most highly conserved residues in the WH2 domain are important in beta-thymosin's interactions with actin monomers, suggesting that all WH2 domains may interact with actin monomers through similar interfaces. Our sequence database searches did not reveal any WH2 domain-containing proteins in plants. However, we found three classes of these proteins: WASP, Srv2/CAP and verprolin/WIP in yeast and animals. This suggests that the WH2 domain is an ancient actin monomer-binding motif that existed before the divergence of fungal and animal lineages.

  10. Correlative nanoscale imaging of actin filaments and their complexes.

    Science.gov (United States)

    Sharma, Shivani; Zhu, Huanqi; Grintsevich, Elena E; Reisler, Emil; Gimzewski, James K

    2013-07-01

    Actin remodeling is an area of interest in biology in which correlative microscopy can bring a new way to analyze protein complexes at the nanoscale. Advances in EM, X-ray diffraction, fluorescence, and single molecule techniques have provided a wealth of information about the modulation of the F-actin structure and its regulation by actin binding proteins (ABPs). Yet, there are technological limitations of these approaches to achieving quantitative molecular level information on the structural and biophysical changes resulting from ABPs interaction with F-actin. Fundamental questions about the actin structure and dynamics and how these determine the function of ABPs remain unanswered. Specifically, how local and long-range structural and conformational changes result in ABPs induced remodeling of F-actin needs to be addressed at the single filament level. Advanced, sensitive and accurate experimental tools for detailed understanding of ABP-actin interactions are much needed. This article discusses the current understanding of nanoscale structural and mechanical modulation of F-actin by ABPs at the single filament level using several correlative microscopic techniques, focusing mainly on results obtained by Atomic Force Microscopy (AFM) analysis of ABP-actin complexes.

  11. Drosophila Fascin is a novel downstream target of prostaglandin signaling during actin remodeling

    OpenAIRE

    Groen, Christopher M.; Spracklen, Andrew J.; Fagan, Tiffany N.; Tootle, Tina L.

    2012-01-01

    Although prostaglandins (PGs)—lipid signals produced downstream of cyclooxygenase (COX) enzymes—regulate actin cytoskeletal dynamics, their mechanisms of action are unknown. We previously established Drosophila oogenesis, in particular nurse cell dumping, as a new model to determine how PGs regulate actin remodeling. PGs, and thus the Drosophila COX-like enzyme Pxt, are required for both the parallel actin filament bundle formation and the cortical actin strengthening required for dumping. He...

  12. Chloroplast actin filaments organize meshwork on the photorelocated chloroplasts in the moss Physcomitrella patens.

    Science.gov (United States)

    Yamashita, Hiroko; Sato, Yoshikatsu; Kanegae, Takeshi; Kagawa, Takatoshi; Wada, Masamitsu; Kadota, Akeo

    2011-02-01

    Cytoskeleton dynamics during phototropin-dependent chloroplast photorelocation movement was analyzed in protonemal cells of actin- and microtubule-visualized lines of Physcomitrella patens expressing GFP- or tdTomato-talin and GFP-tubulin. Using newly developed epi- and trans-microbeam irradiation systems that permit fluorescence observation of the cell under blue microbeam irradiation inducing chloroplast relocation, it was revealed that meshwork of actin filaments formed at the chloroplast-accumulating area both in the avoidance and accumulation movements. The structure disappeared soon when blue microbeam was turned off, and it was not induced under red microbeam irradiation that did not evoke chloroplast relocation movement. In contrast, no apparent change in microtubule organization was detected during the movements. The actin meshwork was composed of short actin filaments distinct from the cytoplasmic long actin cables and was present between the chloroplasts and plasma membrane. The short actin filaments emerged from around the chloroplast periphery towards the center of chloroplast. Showing highly dynamic behavior, the chloroplast actin filaments (cp-actin filaments) were rapidly organized into meshwork on the chloroplast surface facing plasma membrane. The actin filament configuration on a chloroplast led to the formation of actin meshwork area in the cell as the chloroplasts arrived at and occupied the area. After establishment of the meshwork, cp-actin filaments were still highly dynamic, showing appearance, disappearance, severing and bundling of filaments. These results indicate that the cp-actin filaments have significant roles in the chloroplast movement and positioning in the cell.

  13. Impact of actin filament stabilization on adult hippocampal and olfactory bulb neurogenesis.

    Science.gov (United States)

    Kronenberg, Golo; Gertz, Karen; Baldinger, Tina; Kirste, Imke; Eckart, Sarah; Yildirim, Ferah; Ji, Shengbo; Heuser, Isabella; Schröck, Helmut; Hörtnagl, Heide; Sohr, Reinhard; Djoufack, Pierre Chryso; Jüttner, René; Glass, Rainer; Przesdzing, Ingo; Kumar, Jitender; Freyer, Dorette; Hellweg, Rainer; Kettenmann, Helmut; Fink, Klaus Benno; Endres, Matthias

    2010-03-03

    Rearrangement of the actin cytoskeleton is essential for dynamic cellular processes. Decreased actin turnover and rigidity of cytoskeletal structures have been associated with aging and cell death. Gelsolin is a Ca(2+)-activated actin-severing protein that is widely expressed throughout the adult mammalian brain. Here, we used gelsolin-deficient (Gsn(-/-)) mice as a model system for actin filament stabilization. In Gsn(-/-) mice, emigration of newly generated cells from the subventricular zone into the olfactory bulb was slowed. In vitro, gelsolin deficiency did not affect proliferation or neuronal differentiation of adult neural progenitors cells (NPCs) but resulted in retarded migration. Surprisingly, hippocampal neurogenesis was robustly induced by gelsolin deficiency. The ability of NPCs to intrinsically sense excitatory activity and thereby implement coupling between network activity and neurogenesis has recently been established. Depolarization-induced [Ca(2+)](i) increases and exocytotic neurotransmitter release were enhanced in Gsn(-/-) synaptosomes. Importantly, treatment of Gsn(-/-) synaptosomes with mycotoxin cytochalasin D, which, like gelsolin, produces actin disassembly, decreased enhanced Ca(2+) influx and subsequent exocytotic norepinephrine release to wild-type levels. Similarly, depolarization-induced glutamate release from Gsn(-/-) brain slices was increased. Furthermore, increased hippocampal neurogenesis in Gsn(-/-) mice was associated with a special microenvironment characterized by enhanced density of perfused vessels, increased regional cerebral blood flow, and increased endothelial nitric oxide synthase (NOS-III) expression in hippocampus. Together, reduced filamentous actin turnover in presynaptic terminals causes increased Ca(2+) influx and, subsequently, elevated exocytotic neurotransmitter release acting on neural progenitors. Increased neurogenesis in Gsn(-/-) hippocampus is associated with a special vascular niche for neurogenesis.

  14. Actin filaments growing against a barrier with fluctuating shape

    CERN Document Server

    Sadhu, Raj Kumar

    2016-01-01

    We study force generation by a set of parallel actin filaments growing against a non-rigid obstacle, in presence of an external load. The filaments polymerize by either moving the whole obstacle, with a large energy cost, or by causing local distortion in its shape which costs much less energy. The non-rigid obstacle also has local thermal fluctuations due to which its shape can change with time and we describe this using fluctuations in the height profile of a one dimensional interface with Kardar-Parisi-Zhang dynamics. We find the shape fluctuations of the barrier strongly affects the force generation mechanism. The qualitative nature of the force-velocity curve is crucially determined by the relative time-scale of filament and barrier dynamics. The height profile of the barrier also shows interesting variation with the external load. Our analytical calculation within mean-field theory shows reasonable agreement with our simulation results.

  15. Actin-binding proteins implicated in the formation of the punctate actin foci stimulated by the self-incompatibility response in Papaver.

    Science.gov (United States)

    Poulter, Natalie S; Staiger, Christopher J; Rappoport, Joshua Z; Franklin-Tong, Vernonica E

    2010-03-01

    The actin cytoskeleton is a key target for signaling networks and plays a central role in translating signals into cellular responses in eukaryotic cells. Self-incompatibility (SI) is an important mechanism responsible for preventing self-fertilization. The SI system of Papaver rhoeas pollen involves a Ca(2+)-dependent signaling network, including massive actin depolymerization as one of the earliest cellular responses, followed by the formation of large actin foci. However, no analysis of these structures, which appear to be aggregates of filamentous (F-)actin based on phalloidin staining, has been carried out to date. Here, we characterize and quantify the formation of F-actin foci in incompatible Papaver pollen tubes over time. The F-actin foci increase in size over time, and we provide evidence that their formation requires actin polymerization. Once formed, these SI-induced structures are unusually stable, being resistant to treatments with latrunculin B. Furthermore, their formation is associated with changes in the intracellular localization of two actin-binding proteins, cyclase-associated protein and actin-depolymerizing factor. Two other regulators of actin dynamics, profilin and fimbrin, do not associate with the F-actin foci. This study provides, to our knowledge, the first insights into the actin-binding proteins and mechanisms involved in the formation of these intriguing structures, which appear to be actively formed during the SI response.

  16. Viscoelastic properties of actin-coated membranes

    Science.gov (United States)

    Helfer, E.; Harlepp, S.; Bourdieu, L.; Robert, J.; Mackintosh, F. C.; Chatenay, D.

    2001-02-01

    In living cells, cytoskeletal filaments interact with the plasma membrane to form structures that play a key role in cell shape and mechanical properties. To study the interaction between these basic components, we designed an in vitro self-assembled network of actin filaments attached to the outer surface of giant unilamellar vesicles. Optical tweezers and single-particle tracking experiments are used to study the rich dynamics of these actin-coated membranes (ACM). We show that microrheology studies can be carried out on such an individual microscopic object. The principle of the experiment consists in measuring the thermally excited position fluctuations of a probe bead attached biochemically to the membrane. We propose a model that relates the power spectrum of these thermal fluctuations to the viscoelastic properties of the membrane. The presence of the actin network modifies strongly the membrane dynamics with respect to a fluid, lipid bilayer one. It induces first a finite (ω=0) two-dimensional (2D) shear modulus G02D~0.5 to 5 μN/m in the membrane plane. Moreover, the frequency dependence at high frequency of the shear modulus [G'2D(f )~f0.85+/-0.07] and of the bending modulus (κACM(f)~f0.55+/-0.21) demonstrate the viscoelastic behavior of the composite membrane. These results are consistent with a common exponent of 0.75 for both moduli as expected from our model and from prior measurements on actin solutions.

  17. Interconnection between actin cytoskeleton and plant defense signaling.

    Science.gov (United States)

    Janda, Martin; Matoušková, Jindřiška; Burketová, Lenka; Valentová, Olga

    2014-01-01

    Actin cytoskeleton is the fundamental structural component of eukaryotic cells. It has a role in numerous elementary cellular processes such as reproduction, development and also in response to abiotic and biotic stimuli. Remarkably, the role of actin cytoskeleton in plant response to pathogens is getting to be under magnifying glass. Based on microscopic studies, most of the data showed, that actin plays an important role in formation of physiological barrier in the site of infection. Actin dynamics is involved in the transport of antimicrobial compounds and cell wall fortifying components (e.g. callose) to the site of infection. Also the role in PTI (pathogen triggered immunity) and ETI (effector triggered immunity) was recently indicated. On the other hand much less is known about the transcriptome reprogramming upon changes in actin dynamics. Our recently published results showed that drugs inhibiting actin polymerization (latrunculin B, cytochalasin E) cause the induction of genes which are involved in salicylic acid (SA) signaling pathway. In this addendum we would like to highlight in more details current state of knowledge concerning the involvement of actin dynamics in plant defense signaling.

  18. Pattern formation in polymerising actin flocks: spirals, spots and waves without nonlinear chemistry

    CERN Document Server

    Goff, Thomas Le; Marenduzzo, Davide

    2016-01-01

    We propose a model solely based on actin treadmilling and polymerisation which describes many characteristic states of actin wave formation: spots, spirals and travelling waves. In our model, as in experiments on cell recovering motility following actin depolymerisation, we choose an isotropic low density initial condition; polymerisation of actin filaments then raises the density towards the Onsager threshold where they align. We show that this alignment, in turn, destabilizes the isotropic phase and generically induces transient actin spots or spirals as part of the dynamical pathway towards a polarized phase which can either be uniform or consist of a series of actin-wave trains (flocks). Our results uncover a universal route to actin wave formation in the absence of any system specific nonlinear biochemistry, and it may help understand the mechanism underlying the observation of actin spots and waves in vivo. They also suggest a minimal setup to design similar patterns in vitro.

  19. Sclerotium rolfsii dynamics in soil as affected by crop sequences

    NARCIS (Netherlands)

    Leoni, C.; Braak, ter C.J.F.; Gilsanz, J.C.; Dogliotti, S.; Rossing, W.A.H.; Bruggen, van A.H.C.

    2014-01-01

    Crop rotation has been used for the management of soilborne diseases for centuries, but has not often been planned based on scientific knowledge. Our objective was to generate information on Sclerotium rolfsii dynamics under different crop or intercrop activities, and design and test a research appr

  20. Aging affects attunement in perceiving length by dynamic touch

    NARCIS (Netherlands)

    Withagen, Rob; Caljouw, Simone R.

    2011-01-01

    Earlier studies have revealed age-dependent differences in perception by dynamic touch. In the present study, we examined whether the capacity to learn deteriorates with aging. Adopting an ecological approach to learning, the authors examined the process of attunement-that is, the changes in what in

  1. Space charges can significantly affect the dynamics of accelerator maps

    Science.gov (United States)

    Bountis, Tassos; Skokos, Charalampos

    2006-10-01

    Space charge effects can be very important for the dynamics of intense particle beams, as they repeatedly pass through nonlinear focusing elements, aiming to maximize the beam's luminosity properties in the storage rings of a high energy accelerator. In the case of hadron beams, whose charge distribution can be considered as “frozen” within a cylindrical core of small radius compared to the beam's dynamical aperture, analytical formulas have been recently derived [C. Benedetti, G. Turchetti, Phys. Lett. A 340 (2005) 461] for the contribution of space charges within first order Hamiltonian perturbation theory. These formulas involve distribution functions which, in general, do not lead to expressions that can be evaluated in closed form. In this Letter, we apply this theory to an example of a charge distribution, whose effect on the dynamics can be derived explicitly and in closed form, both in the case of 2-dimensional as well as 4-dimensional mapping models of hadron beams. We find that, even for very small values of the “perveance” (strength of the space charge effect) the long term stability of the dynamics changes considerably. In the flat beam case, the outer invariant “tori” surrounding the origin disappear, decreasing the size of the beam's dynamical aperture, while beyond a certain threshold the beam is almost entirely lost. Analogous results in mapping models of beams with 2-dimensional cross section demonstrate that in that case also, even for weak tune depressions, orbital diffusion is enhanced and many particles whose motion was bounded now escape to infinity, indicating that space charges can impose significant limitations on the beam's luminosity.

  2. Space charges can significantly affect the dynamics of accelerator maps

    Energy Technology Data Exchange (ETDEWEB)

    Bountis, Tassos [Department of Mathematics, University of Patras, GR-26500 Patras (Greece) and Center for Research and Applications of Nonlinear Systems (CRANS), University of Patras, GR-26500 Patras (Greece)]. E-mail: tassos50@otenet.gr; Skokos, Charalampos [Center for Research and Applications of Nonlinear Systems (CRANS), University of Patras, GR-26500 Patras (Greece)

    2006-10-09

    Space charge effects can be very important for the dynamics of intense particle beams, as they repeatedly pass through nonlinear focusing elements, aiming to maximize the beam's luminosity properties in the storage rings of a high energy accelerator. In the case of hadron beams, whose charge distribution can be considered as 'frozen' within a cylindrical core of small radius compared to the beam's dynamical aperture, analytical formulas have been recently derived [C. Benedetti, G. Turchetti, Phys. Lett. A 340 (2005) 461] for the contribution of space charges within first order Hamiltonian perturbation theory. These formulas involve distribution functions which, in general, do not lead to expressions that can be evaluated in closed form. In this Letter, we apply this theory to an example of a charge distribution, whose effect on the dynamics can be derived explicitly and in closed form, both in the case of 2-dimensional as well as 4-dimensional mapping models of hadron beams. We find that, even for very small values of the 'perveance' (strength of the space charge effect) the long term stability of the dynamics changes considerably. In the flat beam case, the outer invariant 'tori' surrounding the origin disappear, decreasing the size of the beam's dynamical aperture, while beyond a certain threshold the beam is almost entirely lost. Analogous results in mapping models of beams with 2-dimensional cross section demonstrate that in that case also, even for weak tune depressions, orbital diffusion is enhanced and many particles whose motion was bounded now escape to infinity, indicating that space charges can impose significant limitations on the beam's luminosity.

  3. Spectrin-dependent and -independent association of F-actin with the erythrocyte membrane.

    Science.gov (United States)

    Cohen, C M; Foley, S F

    1980-08-01

    Binding of F-actin to spectrin-actin-depleted erythrocyte membrane inside-out vesicles was measured using [3H]F-actin. F-actin binding to vesicles at 25 degrees C was stimulated 5-10 fold by addition of spectrin dimers or tetramers to vesicles. Spectrin tetramer was twice as effective as dimer in stimulating actin binding, but neither tetramer nor dimer stimulated binding at 4 degrees C. The addition of purified erythrocyte membrane protein band 4.1 to spectrin-reconstituted vesicles doubled their actin-binding capacity. Trypsinization of unreconstituted vesicles that contain ghosts, decreased their F-actin-binding capacity by 70%. Whereas little or none of the residual spectrin was affected by trypsinization, band 4.1 was significantly degraded. Our results show that spectrin can anchor actin filaments to the cytoplasmic surface of erythrocyte membranes and suggest that band 4.1 may be importantly involved in the association.

  4. Predicting when climate-driven phenotypic change affects population dynamics

    NARCIS (Netherlands)

    McLean, Nina; Lawson, C.R.; Leech, David; Van de Pol, M.

    2016-01-01

    Species' responses to climate change are variable and diverse, yet our understanding of how different responses (e.g. physiological, behavioural, demographic) relate and how they affect the parameters most relevant for conservation (e.g. population persistence) is lacking. Despite this, studies that

  5. Recent advances into vanadyl, vanadate and decavanadate interactions with actin.

    Science.gov (United States)

    Ramos, S; Moura, J J G; Aureliano, M

    2012-01-01

    Although the number of papers about "vanadium" has doubled in the last decade, the studies about "vanadium and actin" are scarce. In the present review, the effects of vanadyl, vanadate and decavanadate on actin structure and function are compared. Decavanadate (51)V NMR signals, at -516 ppm, broadened and decreased in intensity upon actin titration, whereas no effects were observed for vanadate monomers, at -560 ppm. Decavanadate is the only species inducing actin cysteine oxidation and vanadyl formation, both processes being prevented by the natural ligand of the protein, ATP. Vanadyl titration with monomeric actin (G-actin), analysed by EPR spectroscopy, reveals a 1:1 binding stoichiometry and a K(d) of 7.5 μM(-1). Both decavanadate and vanadyl inhibited G-actin polymerization into actin filaments (F-actin), with a IC(50) of 68 and 300 μM, respectively, as analysed by light scattering assays, whereas no effects were detected for vanadate up to 2 mM. However, only vanadyl (up to 200 μM) induces 100% of G-actin intrinsic fluorescence quenching, whereas decavanadate shows an opposite effect, which suggests the presence of vanadyl high affinity actin binding sites. Decavanadate increases (2.6-fold) the actin hydrophobic surface, evaluated using the ANSA probe, whereas vanadyl decreases it (15%). Both vanadium species increased the ε-ATP exchange rate (k = 6.5 × 10(-3) s(-1) and 4.47 × 10(-3) s(-1) for decavanadate and vanadyl, respectively). Finally, (1)H NMR spectra of G-actin treated with 0.1 mM decavanadate clearly indicate that major alterations occur in protein structure, which are much less visible in the presence of ATP, confirming the preventive effect of the nucleotide on the decavanadate interaction with the protein. Putting it all together, it is suggested that actin, which is involved in many cellular processes, might be a potential target not only for decavanadate but above all for vanadyl. By affecting actin structure and function, vanadium can

  6. Preliminarily Investigating the Polymorphism of Self-organized Actin Filament in Vitro by Atomic Force Microscope

    Institute of Scientific and Technical Information of China (English)

    Jun ZHANG; Yuan-Liang WANG; Xin-Yong Chen; Chuang-Long HE; Chao CHENG; Yang CAO

    2004-01-01

    With the atomic force microscope (AFM), we preliminarily investigated the large-scale structure of actin filaments formed in low concentration protein solution (5 μg/ml) via self-organization without the presence of any F-actin dynamic interfering factors (such as phalloidin) in vitro. It was found that the G-actin could be polymerized into ordered filamentous structures with different diameter from the slimmest filament of single F-actin to giant filament in tree-like branched aggregates. The observed polymerized actin filaments, to which our most intense attention was attracted, was discretely distributed and showed obvious polymorphism distinctly different from those in the presence of phalloidin or actin binding proteins (fimbrin, gelsolin, etc.) in previous experiments. Latter structures were mainly composed of single F-actin and/or multifilaments clearly consisting of several single F-actin. The experimental results clearly demonstrated that non-interference with the F-actin intrinsic dynamics in self-organizing could lead to the polymorphism of actin filamentous structures, and further analysis implied that the disturbance of normal F-actin dynamics by many factors could prevent the emergence of structural polymorphism, more often than not, give rise to formation of specific structures instead and different interference would bring about various particular structures under certain conditions.

  7. Affective Dynamics of Leadership: An Experimental Test of Affect Control Theory

    Science.gov (United States)

    Schroder, Tobias; Scholl, Wolfgang

    2009-01-01

    Affect Control Theory (ACT; Heise 1979, 2007) states that people control social interactions by striving to maintain culturally shared feelings about the situation. The theory is based on mathematical models of language-based impression formation. In a laboratory experiment, we tested the predictive power of a new German-language ACT model with…

  8. Dynamically Tracking Anxious Individuals' Affective Response to Valenced Information.

    Science.gov (United States)

    Fua, Karl C; Teachman, Bethany A

    2017-03-30

    Past research has shown that an individual's feelings at any given moment reflect currently experienced stimuli as well as internal representations of similar past experiences. However, anxious individuals' affective reactions to streams of interrelated valenced information (vs. reactions to static stimuli that are arguably less ecologically valid) are rarely tracked. The present study provided a first examination of the newly developed Tracking Affect Ratings Over Time (TAROT) task to continuously assess anxious individuals' affective reactions to streams of information that systematically change valence. Undergraduate participants (N = 141) completed the TAROT task in which they listened to narratives containing positive, negative, and neutral physically- or socially-relevant events, and indicated how positive or negative they felt about the information they heard as each narrative unfolded. The present study provided preliminary evidence for the validity and reliability of the task. Within scenarios, participants higher (vs. lower) in anxiety showed many expected negative biases, reporting more negative mean ratings and overall summary ratings, changing their pattern of responding more quickly to negative events, and responding more negatively to neutral events. Furthermore, individuals higher (vs. lower) in anxiety tended to report more negative minimums during and after positive events, and less positive maximums after negative events. Together, findings indicate that positive events were less impactful for anxious individuals, whereas negative experiences had a particularly lasting impact on future affective responses. The TAROT task is able to efficiently capture a number of different cognitive biases, and may help clarify the mechanisms that underlie anxious individuals' biased negative processing. (PsycINFO Database Record

  9. Incorporating Affect in an Engineering Student's Epistemological Dynamics

    CERN Document Server

    Danielak, Brian A; Elby, Andrew

    2010-01-01

    Research has linked a student's affect to her epistemology (Boaler & Greeno, 2000), but those constructs often apply broadly to a discipline and/or classroom culture. Independently, an emerging line of research shows that a student in a given classroom and discipline can shift between multiple locally coherent epistemological stances (Hammer, Elby, Scherr, & Redish, 2005). Our case study of Judy, an undergraduate engineering major, begins our long-term effort at uniting these two bodies of literature.

  10. Holding back the microfilament--structural insights into actin and the actin-monomer-binding proteins of apicomplexan parasites.

    Science.gov (United States)

    Olshina, Maya A; Wong, Wilson; Baum, Jake

    2012-05-01

    Parasites from the phylum Apicomplexa are responsible for several major diseases of man, including malaria and toxoplasmosis. These highly motile protozoa use a conserved actomyosin-based mode of movement to power tissue traversal and host cell invasion. The mode termed as 'gliding motility' relies on the dynamic turnover of actin, whose polymerisation state is controlled by a markedly limited number of identifiable regulators when compared with other eukaryotic cells. Recent studies of apicomplexan actin regulator structure-in particular those of the core triad of monomer-binding proteins, actin-depolymerising factor/cofilin, cyclase-associated protein/Srv2, and profilin-have provided new insights into possible mechanisms of actin regulation in parasite cells, highlighting divergent structural features and functions to regulators from other cellular systems. Furthermore, the unusual nature of apicomplexan actin itself is increasingly coming into the spotlight. Here, we review recent advances in understanding of the structure and function of actin and its regulators in apicomplexan parasites. In particular we explore the paradox between there being an abundance of unpolymerised actin, its having a seemingly increased potential to form filaments relative to vertebrate actin, and the apparent lack of visible, stable filaments in parasite cells.

  11. Actin-Capping Protein and the Hippo pathway regulate F-actin and tissue growth in Drosophila.

    Science.gov (United States)

    Fernández, Beatriz García; Gaspar, Pedro; Brás-Pereira, Catarina; Jezowska, Barbara; Rebelo, Sofia Raquel; Janody, Florence

    2011-06-01

    The conserved Hippo tumor suppressor pathway is a key kinase cascade that controls tissue growth by regulating the nuclear import and activity of the transcription co-activator Yorkie. Here, we report that the actin-Capping Protein αβ heterodimer, which regulates actin polymerization, also functions to suppress inappropriate tissue growth by inhibiting Yorkie activity. Loss of Capping Protein activity results in abnormal accumulation of apical F-actin, reduced Hippo pathway activity and the ectopic expression of several Yorkie target genes that promote cell survival and proliferation. Reduction of two other actin-regulatory proteins, Cofilin and the cyclase-associated protein Capulet, cause abnormal F-actin accumulation, but only the loss of Capulet, like that of Capping Protein, induces ectopic Yorkie activity. Interestingly, F-actin also accumulates abnormally when Hippo pathway activity is reduced or abolished, independently of Yorkie activity, whereas overexpression of the Hippo pathway component expanded can partially reverse the abnormal accumulation of F-actin in cells depleted for Capping Protein. Taken together, these findings indicate a novel interplay between Hippo pathway activity and actin filament dynamics that is essential for normal growth control.

  12. Toxoplasma gondii profilin acts primarily to sequester G-actin while formins efficiently nucleate actin filament formation in vitro.

    Science.gov (United States)

    Skillman, Kristen M; Daher, Wassim; Ma, Christopher I; Soldati-Favre, Dominique; Sibley, L David

    2012-03-27

    Apicomplexan parasites employ gliding motility that depends on the polymerization of parasite actin filaments for host cell entry. Despite this requirement, parasite actin remains almost entirely unpolymerized at steady state; formation of filaments required for motility relies on a small repertoire of actin-binding proteins. Previous studies have shown that apicomplexan formins and profilin exhibit canonical functions on heterologous actins from higher eukaryotes; however, their biochemical properties on parasite actins are unknown. We therefore analyzed the impact of T. gondii profilin (TgPRF) and FH1-FH2 domains of two formin isoforms in T. gondii (TgFRM1 and TgFRM2) on the polymerization of T. gondii actin (TgACTI). Our findings based on in vitro assays demonstrate that TgFRM1-FH1-FH2 and TgFRM2-FH1-FH2 dramatically enhanced TgACTI polymerization in the absence of profilin, making them the sole protein factors known to initiate polymerization of this normally unstable actin. In addition, T. gondii formin domains were shown to both initiate polymerization and induce bundling of TgACTI filaments; however, they did not rely on TgPRF for these activities. In contrast, TgPRF sequestered TgACTI monomers, thus inhibiting polymerization even in the presence of formins. Collectively, these findings provide insight into the unusual control mechanisms of actin dynamics within the parasite.

  13. Agulhas leakage dynamics affects decadal variability in Atlantic overturning circulation.

    Science.gov (United States)

    Biastoch, A; Böning, C W; Lutjeharms, J R E

    2008-11-27

    Predicting the evolution of climate over decadal timescales requires a quantitative understanding of the dynamics that govern the meridional overturning circulation (MOC). Comprehensive ocean measurement programmes aiming to monitor MOC variations have been established in the subtropical North Atlantic (RAPID, at latitude 26.5 degrees N, and MOVE, at latitude 16 degrees N) and show strong variability on intraseasonal to interannual timescales. Observational evidence of longer-term changes in MOC transport remains scarce, owing to infrequent sampling of transoceanic sections over past decades. Inferences based on long-term sea surface temperature records, however, supported by model simulations, suggest a variability with an amplitude of +/-1.5-3 Sv (1 Sv = 10(6) m(3) s(-1)) on decadal timescales in the subtropics. Such variability has been attributed to variations of deep water formation in the sub-arctic Atlantic, particularly the renewal rate of Labrador Sea Water. Here we present results from a model simulation that suggest an additional influence on decadal MOC variability having a Southern Hemisphere origin: dynamic signals originating in the Agulhas leakage region at the southern tip of Africa. These contribute a MOC signal in the tropical and subtropical North Atlantic that is of the same order of magnitude as the northern source. A complete rationalization of observed MOC changes therefore also requires consideration of signals arriving from the south.

  14. CAS-1, a C. elegans cyclase-associated protein, is required for sarcomeric actin assembly in striated muscle.

    Science.gov (United States)

    Nomura, Kazumi; Ono, Kanako; Ono, Shoichiro

    2012-09-01

    Assembly of contractile apparatuses in striated muscle requires precisely regulated reorganization of the actin cytoskeletal proteins into sarcomeric organization. Regulation of actin filament dynamics is one of the essential processes of myofibril assembly, but the mechanism of actin regulation in striated muscle is not clearly understood. Actin depolymerizing factor (ADF)/cofilin is a key enhancer of actin filament dynamics in striated muscle in both vertebrates and nematodes. Here, we report that CAS-1, a cyclase-associated protein in Caenorhabditis elegans, promotes ADF/cofilin-dependent actin filament turnover in vitro and is required for sarcomeric actin organization in striated muscle. CAS-1 is predominantly expressed in striated muscle from embryos to adults. In vitro, CAS-1 binds to actin monomers and enhances exchange of actin-bound ATP/ADP even in the presence of UNC-60B, a muscle-specific ADF/cofilin that inhibits the nucleotide exchange. As a result, CAS-1 and UNC-60B cooperatively enhance actin filament turnover. The two proteins also cooperate to shorten actin filaments. A cas-1 mutation is homozygous lethal with defects in sarcomeric actin organization. cas-1-mutant embryos and worms have aggregates of actin in muscle cells, and UNC-60B is mislocalized to the aggregates. These results provide genetic and biochemical evidence that cyclase-associated protein is a critical regulator of sarcomeric actin organization in striated muscle.

  15. How Predation and Landscape Fragmentation Affect Vole Population Dynamics

    DEFF Research Database (Denmark)

    Dalkvist, Trine; Sibly, Richard M.; Topping, Chris J.

    2011-01-01

    population cycles. Because these factors covary along the gradient it is difficult to distinguish their effects experimentally in the field. The distinction is here attempted using realistic agent-based modelling. Methodology/Principal Findings: By using a spatially explicit computer simulation model based...... on behavioural and ecological data from the field vole (Microtus agrestis), we generated a number of repeated time series of vole densities whose mean population size and amplitude were measured. Subsequently, these time series were subjected to statistical autoregressive modelling, to investigate the effects...... on vole population dynamics of making predators more specialised, of altering the breeding season, and increasing the level of habitat fragmentation. We found that fragmentation as well as the presence of specialist predators are necessary for the occurrence of population cycles. Habitat fragmentation...

  16. Lubricated wrinkles: imposed constraints affect the dynamics of wrinkle coarsening

    CERN Document Server

    Kodio, Ousmane; Vella, Dominic

    2016-01-01

    We study the dynamic coarsening of wrinkles in an elastic sheet that is compressed while lying on a thin layer of viscous liquid. When the ends of the sheet are instantaneously brought together by a small distance, viscous resistance initially prevents the sheet from adopting a globally buckled shape. Instead, the sheet accommodates the compression by wrinkling. Previous scaling arguments suggested that a balance between the sheet's bending stiffness and viscous effects lead to a wrinkle wavelength $\\lambda$ that increases with time $t$ according to $\\lambda\\propto t^{1/6}$. We show that taking proper account of the compression constraint leads to a logarithmic correction of this result, $\\lambda\\propto (t/\\log t)^{1/6}$. This correction is significant over experimentally observable time spans, and leads us to reassess previously published experimental data.

  17. Lubricated wrinkles: Imposed constraints affect the dynamics of wrinkle coarsening

    Science.gov (United States)

    Kodio, Ousmane; Griffiths, Ian M.; Vella, Dominic

    2017-01-01

    We study the dynamic coarsening of wrinkles in an elastic sheet that is compressed while lying on a thin layer of viscous liquid. When the ends of the sheet are instantaneously brought together by a small distance, viscous resistance initially prevents the sheet from adopting a globally buckled shape. Instead, the sheet accommodates the compression by wrinkling. Previous scaling arguments suggested that a balance between the sheet's bending stiffness and viscous effects lead to a wrinkle wavelength λ that increases with time t according to λ ∝t1 /6 . We show that taking proper account of the compression constraint leads to a logarithmic correction of this result, λ ∝(t/logt ) 1 /6 . This correction is significant over experimentally observable time spans and leads us to reassess previously published experimental data.

  18. Dynamic touch is affected in children with cerebral palsy.

    Science.gov (United States)

    Ocarino, Juliana M; Fonseca, Sergio T; Silva, Paula L P; Gonçalves, Gabriela G P; Souza, Thales R; Mancini, Marisa C

    2014-02-01

    Children with developmental disorders such as cerebral palsy have limited opportunities for effortful interactions with objects and tools. The goal of the study was to investigate whether children with cerebral palsy have deficits in their ability to perceive object length by dynamic touch when compared to typically developing children. Fourteen children with typical development and 12 children with cerebral palsy were asked to report the length of hand-held rods after wielding them out of sight. Multilevel regression models indicated that I1 (maximum principal moment of inertia) was a significant predictor of perceived length - LP (pcerebral palsy (group factor) partially explained such variance (p=.002). In addition, accuracy and reliability of the length judgments made by children with cerebral palsy were significantly lower than the typically developing children (p<.05). Theoretical and clinical implications of these results were identified and discussed.

  19. Evolutionarily divergent, unstable filamentous actin is essential for gliding motility in apicomplexan parasites.

    Science.gov (United States)

    Skillman, Kristen M; Diraviyam, Karthikeyan; Khan, Asis; Tang, Keliang; Sept, David; Sibley, L David

    2011-10-01

    Apicomplexan parasites rely on a novel form of actin-based motility called gliding, which depends on parasite actin polymerization, to migrate through their hosts and invade cells. However, parasite actins are divergent both in sequence and function and only form short, unstable filaments in contrast to the stability of conventional actin filaments. The molecular basis for parasite actin filament instability and its relationship to gliding motility remain unresolved. We demonstrate that recombinant Toxoplasma (TgACTI) and Plasmodium (PfACTI and PfACTII) actins polymerized into very short filaments in vitro but were induced to form long, stable filaments by addition of equimolar levels of phalloidin. Parasite actins contain a conserved phalloidin-binding site as determined by molecular modeling and computational docking, yet vary in several residues that are predicted to impact filament stability. In particular, two residues were identified that form intermolecular contacts between different protomers in conventional actin filaments and these residues showed non-conservative differences in apicomplexan parasites. Substitution of divergent residues found in TgACTI with those from mammalian actin resulted in formation of longer, more stable filaments in vitro. Expression of these stabilized actins in T. gondii increased sensitivity to the actin-stabilizing compound jasplakinolide and disrupted normal gliding motility in the absence of treatment. These results identify the molecular basis for short, dynamic filaments in apicomplexan parasites and demonstrate that inherent instability of parasite actin filaments is a critical adaptation for gliding motility.

  20. Evolutionarily divergent, unstable filamentous actin is essential for gliding motility in apicomplexan parasites.

    Directory of Open Access Journals (Sweden)

    Kristen M Skillman

    2011-10-01

    Full Text Available Apicomplexan parasites rely on a novel form of actin-based motility called gliding, which depends on parasite actin polymerization, to migrate through their hosts and invade cells. However, parasite actins are divergent both in sequence and function and only form short, unstable filaments in contrast to the stability of conventional actin filaments. The molecular basis for parasite actin filament instability and its relationship to gliding motility remain unresolved. We demonstrate that recombinant Toxoplasma (TgACTI and Plasmodium (PfACTI and PfACTII actins polymerized into very short filaments in vitro but were induced to form long, stable filaments by addition of equimolar levels of phalloidin. Parasite actins contain a conserved phalloidin-binding site as determined by molecular modeling and computational docking, yet vary in several residues that are predicted to impact filament stability. In particular, two residues were identified that form intermolecular contacts between different protomers in conventional actin filaments and these residues showed non-conservative differences in apicomplexan parasites. Substitution of divergent residues found in TgACTI with those from mammalian actin resulted in formation of longer, more stable filaments in vitro. Expression of these stabilized actins in T. gondii increased sensitivity to the actin-stabilizing compound jasplakinolide and disrupted normal gliding motility in the absence of treatment. These results identify the molecular basis for short, dynamic filaments in apicomplexan parasites and demonstrate that inherent instability of parasite actin filaments is a critical adaptation for gliding motility.

  1. Social decisions affect neural activity to perceived dynamic gaze.

    Science.gov (United States)

    Latinus, Marianne; Love, Scott A; Rossi, Alejandra; Parada, Francisco J; Huang, Lisa; Conty, Laurence; George, Nathalie; James, Karin; Puce, Aina

    2015-11-01

    Gaze direction, a cue of both social and spatial attention, is known to modulate early neural responses to faces e.g. N170. However, findings in the literature have been inconsistent, likely reflecting differences in stimulus characteristics and task requirements. Here, we investigated the effect of task on neural responses to dynamic gaze changes: away and toward transitions (resulting or not in eye contact). Subjects performed, in random order, social (away/toward them) and non-social (left/right) judgment tasks on these stimuli. Overall, in the non-social task, results showed a larger N170 to gaze aversion than gaze motion toward the observer. In the social task, however, this difference was no longer present in the right hemisphere, likely reflecting an enhanced N170 to gaze motion toward the observer. Our behavioral and event-related potential data indicate that performing social judgments enhances saliency of gaze motion toward the observer, even those that did not result in gaze contact. These data and that of previous studies suggest two modes of processing visual information: a 'default mode' that may focus on spatial information; a 'socially aware mode' that might be activated when subjects are required to make social judgments. The exact mechanism that allows switching from one mode to the other remains to be clarified.

  2. Bidirectional Interplay between Vimentin Intermediate Filaments and Contractile Actin Stress Fibers

    Directory of Open Access Journals (Sweden)

    Yaming Jiu

    2015-06-01

    Full Text Available The actin cytoskeleton and cytoplasmic intermediate filaments contribute to cell migration and morphogenesis, but the interplay between these two central cytoskeletal elements has remained elusive. Here, we find that specific actin stress fiber structures, transverse arcs, interact with vimentin intermediate filaments and promote their retrograde flow. Consequently, myosin-II-containing arcs are important for perinuclear localization of the vimentin network in cells. The vimentin network reciprocally restricts retrograde movement of arcs and hence controls the width of flat lamellum at the leading edge of the cell. Depletion of plectin recapitulates the vimentin organization phenotype of arc-deficient cells without affecting the integrity of vimentin filaments or stress fibers, demonstrating that this cytoskeletal cross-linker is required for productive interactions between vimentin and arcs. Collectively, our results reveal that plectin-mediated interplay between contractile actomyosin arcs and vimentin intermediate filaments controls the localization and dynamics of these two cytoskeletal systems and is consequently important for cell morphogenesis.

  3. Virulent Burkholderia species mimic host actin polymerases to drive actin-based motility

    Science.gov (United States)

    Benanti, Erin L.; Nguyen, Catherine M.; Welch, Matthew D.

    2015-01-01

    Summary Burkholderia pseudomallei and B. mallei are bacterial pathogens that cause melioidosis and glanders, while their close relative B. thailandensis is nonpathogenic. All use the trimeric autotransporter BimA to facilitate actin-based motility, host cell fusion and dissemination. Here, we show that BimA orthologs mimic different host actin-polymerizing proteins. B. thailandensis BimA activates the host Arp2/3 complex. In contrast, B. pseudomallei and B. mallei BimA mimic host Ena/VASP actin polymerases in their ability to nucleate, elongate and bundle filaments by associating with barbed ends, as well as in their use of WH2 motifs and oligomerization for activity. Mechanistic differences among BimA orthologs resulted in distinct actin filament organization and motility parameters, which affected the efficiency of cell fusion during infection. Our results identify bacterial Ena/VASP mimics and reveal that pathogens imitate the full spectrum of host actin-polymerizing pathways, suggesting that mimicry of different polymerization mechanisms influences key parameters of infection. PMID:25860613

  4. How Fear of Future Outcomes Affects Social Dynamics

    Science.gov (United States)

    Podobnik, Boris; Jusup, Marko; Wang, Zhen; Stanley, H. Eugene

    2016-11-01

    Mutualistic relationships among the different species are ubiquitous in nature. To prevent mutualism from slipping into antagonism, a host often invokes a "carrot and stick" approach towards symbionts with a stabilizing effect on their symbiosis. In open human societies, a mutualistic relationship arises when a native insider population attracts outsiders with benevolent incentives in hope that the additional labor will improve the standard of all. A lingering question, however, is the extent to which insiders are willing to tolerate outsiders before mutualism slips into antagonism. To test the assertion by Karl Popper that unlimited tolerance leads to the demise of tolerance, we model a society under a growing incursion from the outside. Guided by their traditions of maintaining the social fabric and prizing tolerance, the insiders reduce their benevolence toward the growing subpopulation of outsiders but do not invoke punishment. This reduction of benevolence intensifies as less tolerant insiders (e.g., "radicals") openly renounce benevolence. Although more tolerant insiders maintain some level of benevolence, they may also tacitly support radicals out of fear for the future. If radicals and their tacit supporters achieve a critical majority, herd behavior ensues and the relation between the insider and outsider subpopulations turns antagonistic. To control the risk of unwanted social dynamics, we map the parameter space within which the tolerance of insiders is in balance with the assimilation of outsiders, the tolerant insiders maintain a sustainable majority, and any reduction in benevolence occurs smoothly. We also identify the circumstances that cause the relations between insiders and outsiders to collapse or that lead to the dominance of the outsiders.

  5. In vivo imaging and characterization of actin microridges.

    Directory of Open Access Journals (Sweden)

    Pui-ying Lam

    Full Text Available Actin microridges form labyrinth like patterns on superficial epithelial cells across animal species. This highly organized assembly has been implicated in mucus retention and in the mechanical structure of mucosal surfaces, however the mechanisms that regulate actin microridges remain largely unknown. Here we characterize the composition and dynamics of actin microridges on the surface of zebrafish larvae using live imaging. Microridges contain phospho-tyrosine, cortactin and VASP, but not focal adhesion kinase. Time-lapse imaging reveals dynamic changes in the length and branching of microridges in intact animals. Transient perturbation of the microridge pattern occurs before cell division with rapid re-assembly during and after cytokinesis. Microridge assembly is maintained with constitutive activation of Rho or inhibition of myosin II activity. However, expression of dominant negative RhoA or Rac alters microridge organization, with an increase in distance between microridges. Latrunculin A treatment and photoconversion experiments suggest that the F-actin filaments are actively treadmilling in microridges. Accordingly, inhibition of Arp2/3 or PI3K signaling impairs microridge structure and length. Taken together, actin microridges in zebrafish represent a tractable in vivo model to probe pattern formation and dissect Arp2/3-mediated actin dynamics in vivo.

  6. Inactivation of Tor proteins affects the dynamics of endocytic proteins in early stage of endocytosis

    Indian Academy of Sciences (India)

    Brandon Tenay; Evin Kimberlin; Michelle Williams; Juliette Denise; Joshua Fakilahyel; Kyoungtae Kim

    2013-06-01

    Tor2 is an activator of the Rom2/Rho1 pathway that regulates -factor internalization. Since the recruitment of endocytic proteins such as actin-binding proteins and the amphiphysins precedes the internalization of -factor, we hypothesized that loss of Tor function leads to an alteration in the dynamics of the endocytic proteins. We report here that endocytic proteins, Abp1 and Rvs167, are less recruited to endocytic sites not only in tor2 but also tor1 mutants. Furthermore, we found that the endocytic proteins Rvs167 and Sjl2 are completely mistargeted to the cytoplasm in tor1tor2ts double mutant cells. We also demonstrate here that the efficiency of endocytic internalization or scission in all tor mutants was drastically decreased. In agreement with the Sjl2 mislocalization, we found that in tor1tor2ts double mutant cells, as well as other tor mutant cells, the overall PIP2 level was dramatically increased. Finally, the cell wall chitin content in tor2ts and tor1tor2ts mutant cells was also significantly increased. Taken together, both functional Tor proteins, Tor1 and Tor2, are essentially required for proper endocytic protein dynamics at the early stage of endocytosis.

  7. Region-Specific Involvement of Actin Rearrangement-Related Synaptic Structure Alterations in Conditioned Taste Aversion Memory

    Science.gov (United States)

    Bi, Ai-Ling; Wang, Yue; Li, Bo-Qin; Wang, Qian-Qian; Ma, Ling; Yu, Hui; Zhao, Ling; Chen, Zhe-Yu

    2010-01-01

    Actin rearrangement plays an essential role in learning and memory; however, the spatial and temporal regulation of actin dynamics in different phases of associative memory has not been fully understood. Here, using the conditioned taste aversion (CTA) paradigm, we investigated the region-specific involvement of actin rearrangement-related…

  8. Form of an evolutionary tradeoff affects eco-evolutionary dynamics in a predator-prey system.

    Science.gov (United States)

    Kasada, Minoru; Yamamichi, Masato; Yoshida, Takehito

    2014-11-11

    Evolution on a time scale similar to ecological dynamics has been increasingly recognized for the last three decades. Selection mediated by ecological interactions can change heritable phenotypic variation (i.e., evolution), and evolution of traits, in turn, can affect ecological interactions. Hence, ecological and evolutionary dynamics can be tightly linked and important to predict future dynamics, but our understanding of eco-evolutionary dynamics is still in its infancy and there is a significant gap between theoretical predictions and empirical tests. Empirical studies have demonstrated that the presence of genetic variation can dramatically change ecological dynamics, whereas theoretical studies predict that eco-evolutionary dynamics depend on the details of the genetic variation, such as the form of a tradeoff among genotypes, which can be more important than the presence or absence of the genetic variation. Using a predator-prey (rotifer-algal) experimental system in laboratory microcosms, we studied how different forms of a tradeoff between prey defense and growth affect eco-evolutionary dynamics. Our experimental results show for the first time to our knowledge that different forms of the tradeoff produce remarkably divergent eco-evolutionary dynamics, including near fixation, near extinction, and coexistence of algal genotypes, with quantitatively different population dynamics. A mathematical model, parameterized from completely independent experiments, explains the observed dynamics. The results suggest that knowing the details of heritable trait variation and covariation within a population is essential for understanding how evolution and ecology will interact and what form of eco-evolutionary dynamics will result.

  9. Nitrogen Additions Affect Root Dynamics in a Boreal Forest Ecosystem

    Science.gov (United States)

    Turner, K. M.; Treseder, K. K.

    2004-12-01

    As with many ecosystems, North American boreal forests are increasingly subjected to anthropogenic nitrogen deposition. To examine potential effects on plant growth, we created nitrogen fertilization plots in three sites along an Alaskan fire chronosequence composed of forests aged 5, 17, and 80 years. Each site had been exposed to two years of nitrogen fertilization, with four control plots and four nitrogen plots per site. General observations indicate that aboveground net primary productivity appears to be nitrogen limited in each site. We hypothesized that nitrogen fertilization would positively influence root dynamics as well, with nitrogen additions resulting in an increase in standing root biomass and length. To test our hypothesis, we used a minirhizotron camera to collect sequential images of roots in the top 10 cm of soil in both nitrogen fertilized and control plots in each site. Images were collected monthly during the growing season, with a total of five sampling times between May 2003 and May 2004. We then analyzed the images with WinRhizotron root measurement software. Nitrogen fertilization had varying effects on root biomass among the three sites, with a significant site by N interaction (P = 0.039). A decrease in root biomass was observed in the 5 and 80 year old sites, dropping from 207 g/m2 to 79 g/m2 and from 230 g/m2 to 129 g/m2 for the youngest and oldest sites, respectively. In contrast, root biomass increased from 52 g/m2 to 107 g/m2 in the 17 year old site. (Values are for the top 10 cm of soil only, and likely underestimate total root stocks.) Patterns in standing root lengths diverged from those of root biomass, with a 2.5-fold overall increase under nitrogen fertilization across all sites (P = 0.004). There were no significant differences among sites in nitrogen response. Standing root biomass and length differed from one another in their responses to nitrogen fertilization because nitrogen additions decreased specific root weight (as g

  10. Endocytosis-dependent coordination of multiple actin regulators is required for wound healing.

    Science.gov (United States)

    Matsubayashi, Yutaka; Coulson-Gilmer, Camilla; Millard, Tom H

    2015-08-01

    The ability to heal wounds efficiently is essential for life. After wounding of an epithelium, the cells bordering the wound form dynamic actin protrusions and/or a contractile actomyosin cable, and these actin structures drive wound closure. Despite their importance in wound healing, the molecular mechanisms that regulate the assembly of these actin structures at wound edges are not well understood. In this paper, using Drosophila melanogaster embryos, we demonstrate that Diaphanous, SCAR, and WASp play distinct but overlapping roles in regulating actin assembly during wound healing. Moreover, we show that endocytosis is essential for wound edge actin assembly and wound closure. We identify adherens junctions (AJs) as a key target of endocytosis during wound healing and propose that endocytic remodeling of AJs is required to form "signaling centers" along the wound edge that control actin assembly. We conclude that coordination of actin assembly, AJ remodeling, and membrane traffic is required for the construction of a motile leading edge during wound healing.

  11. The temporal dynamics of cortisol and affective states in depressed and non-depressed individuals

    NARCIS (Netherlands)

    Booij, Sanne H.; Bos, Elisabeth H.; de Jonge, Peter; Oldehinkel, Albertine J.

    2016-01-01

    Objectives: Cortisol levels have been related to mood disorders at the group level, but not much is known about how cortisol relates to affective states within individuals over time. We examined the temporal dynamics of cortisol and affective states in depressed and non-depressed individuals in dail

  12. Magnetic manipulation of actin orientation, polymerization, and gliding on myosin using superparamagnetic iron oxide particles.

    Science.gov (United States)

    Chen, Yun; Guzik, Stephanie; Sumner, James P; Moreland, John; Koretsky, Alan P

    2011-02-11

    The actin cytoskeleton controls cell shape, motility, as well as intracellular molecular trafficking. The ability to remotely manipulate actin is therefore highly desirable as a tool to probe and manipulate biological processes at the molecular level. We demonstrate actin manipulation by labeling actin filaments with superparamagnetic iron oxide particles (IOPs) and applying a uniform magnetic field to affect actin orientation, polymerization and gliding on myosin. We show for the first time magnetic manipulation of magnetizable actin filaments at the molecular level while gliding on a bed of myosin molecules and during polymerization. A model for the magnetic alignment and guiding mechanism is proposed based on the torque from the induced molecular anisotropy due to interactions between neighboring IOPs distributed along magnetically labeled actin molecules.

  13. Ring closure in actin polymers

    Science.gov (United States)

    Sinha, Supurna; Chattopadhyay, Sebanti

    2017-03-01

    We present an analysis for the ring closure probability of semiflexible polymers within the pure bend Worm Like Chain (WLC) model. The ring closure probability predicted from our analysis can be tested against fluorescent actin cyclization experiments. We also discuss the effect of ring closure on bend angle fluctuations in actin polymers.

  14. Antenna mechanism of length control of actin cables

    CERN Document Server

    Mohapatra, Lishibanya; Kondev, Jane

    2014-01-01

    Actin cables are linear cytoskeletal structures that serve as tracks for myosin-based intracellular transport of vesicles and organelles in both yeast and mammalian cells. In a yeast cell undergoing budding, cables are in constant dynamic turnover yet some cables grow from the bud neck toward the back of the mother cell until their length roughly equals the diameter of the mother cell. This raises the question: how is the length of these cables controlled? Here we describe a novel molecular mechanism for cable length control inspired by recent experimental observations in cells. This antenna mechanism involves three key proteins: formins, which polymerize actin, Smy1 proteins, which bind formins and inhibit actin polymerization, and myosin motors, which deliver Smy1 to formins, leading to a length-dependent actin polymerization rate. We compute the probability distribution of cable lengths as a function of several experimentally tuneable parameters such as the formin-binding affinity of Smy1 and the concentra...

  15. Tracing myoblast fusion in Drosophila embryos by fluorescent actin probes.

    Science.gov (United States)

    Haralalka, Shruti; Abmayr, Susan M

    2015-01-01

    Myoblast fusion in the Drosophila embryo is a highly elaborate process that is initiated by Founder Cells and Fusion-Competent Myoblasts (FCMs). It occurs through an asymmetric event in which actin foci assemble in the FCMs at points of cell-cell contact and direct the formation of membrane protrusions that drive fusion. Herein, we describe the approach that we have used to image in living embryos the highly dynamic actin foci and actin-rich projections that precede myoblast fusion. We discuss resources currently available for imaging actin and myogenesis, and our experience with these resources if available. This technical report is not intended to be comprehensive on providing instruction on standard microscopy practices or software utilization. However, we discuss microscope parameters that we have used in data collection, and our experience with image processing tools in data analysis.

  16. Roles of Cortactin, an Actin Polymerization Mediator, in Cell Endocytosis

    Institute of Scientific and Technical Information of China (English)

    Li CHEN; Zhi-Wei WANG; Jian-wei ZHU; Xi ZHAN

    2006-01-01

    Cortactin, an actin-binding protein and a substrate of Src, is encoded by the EMS 1 oncogene.Cortactin is known to activate Arp2/3 complex-mediated actin polymerization and interact with dynamin, a large GTPase and proline rich domain-containing protein. Transferrin endocytosis was significantly reduced in cells by knock-down of cortactin expression as well as in vivo introduction of cortactin immunoreagents.Cortactin-dynamin interaction displayed morphologically dynamic co-distribution with a change in the endocytosis level in cells treated with an actin depolymerization reagent, cytochalasin D. In an in vitro beads assay, a branched actin network was recruited onto dynamin-coated beads in a cortactin Src homology domain 3 (SH3)-dependent manner. In addition, cortactin was found to function in the late stage of clathrin coated vesicle formation.Taken together, cortactin is required for optimal clathrin mediated endocytosis in a dynamin directed manner.

  17. Role of actin in auxin transport and transduction of gravity

    Science.gov (United States)

    Hu, S.; Basu, S.; Brady, S.; Muday, G.

    Transport of the plant hormone auxin is polar and the direction of the hormone movement appears to be controlled by asymmetric distribution of auxin transport protein complexes. Changes in the direction of auxin transport are believed to drive asymmetric growth in response to changes in the gravity vector. To test the possibility that asymmetric distribution of the auxin transport protein complex is mediated by attachment to the actin cytoskeleton, a variety of experimental approaches have been used. The most direct demonstration of the role of the actin cytoskeleton in localization of the protein complex is the ability of one protein in this complex to bind to affinity columns containing actin filaments. Additionally, treatments of plant tissues with drugs that fragment the actin c toskeleton reducey polar transport. In order to explore this actin interaction and the affect of gravity on auxin transport and developmental polarity, embryos of the brown alga, Fucus have been examined. Fucus zygotes are initially symmetrical, but develop asymmetry in response to environmental gradients, with light gradients being the best- characterized signal. Gravity will polarize these embryos and gravity-induced polarity is randomized by clinorotation. Auxin transport also appears necessary for environmental controls of polarity, since auxin efflux inhibitors perturb both photo- and gravity-polarization at a very discrete temporal window within six hours after fertilization. The actin cytoskeleton has previously been shown to reorganize after fertilization of Fucus embryos leading to formation of an actin patch at the site of polar outgrowth. These actin patches still form in Fucus embryos treated with auxin efflux inhibitors, yet the position of these patches is randomized. Together, these results suggest that there are connections between the actin cytoskeleton, auxin transport, and gravity oriented growth and development. (Supported by NASA Grant: NAG2-1203)

  18. The Cannabinoid Receptor CB1 Interacts with the WAVE1 Complex and Plays a Role in Actin Dynamics and Structural Plasticity in Neurons.

    Science.gov (United States)

    Njoo, Christian; Agarwal, Nitin; Lutz, Beat; Kuner, Rohini

    2015-10-01

    The molecular composition of the cannabinoid type 1 (CB1) receptor complex beyond the classical G-protein signaling components is not known. Using proteomics on mouse cortex in vivo, we pulled down proteins interacting with CB1 in neurons and show that the CB1 receptor assembles with multiple members of the WAVE1 complex and the RhoGTPase Rac1 and modulates their activity. Activation levels of CB1 receptor directly impacted on actin polymerization and stability via WAVE1 in growth cones of developing neurons, leading to their collapse, as well as in synaptic spines of mature neurons, leading to their retraction. In adult mice, CB1 receptor agonists attenuated activity-dependent remodeling of dendritic spines in spinal cord neurons in vivo and suppressed inflammatory pain by regulating the WAVE1 complex. This study reports novel signaling mechanisms for cannabinoidergic modulation of the nervous system and demonstrates a previously unreported role for the WAVE1 complex in therapeutic applications of cannabinoids.

  19. Regulation of actin catch-slip bonds with a RhoA-formin module

    Science.gov (United States)

    Lee, Cho-Yin; Lou, Jizhong; Wen, Kuo-Kuang; McKane, Melissa; Eskin, Suzanne G.; Rubenstein, Peter A.; Chien, Shu; Ono, Shoichiro; Zhu, Cheng; McIntire, Larry V.

    2016-10-01

    The dynamic turnover of the actin cytoskeleton is regulated cooperatively by force and biochemical signaling. We previously demonstrated that actin depolymerization under force is governed by catch-slip bonds mediated by force-induced K113:E195 salt-bridges. Yet, the biochemical regulation as well as the functional significance of actin catch bonds has not been elucidated. Using AFM force-clamp experiments, we show that formin controlled by RhoA switches the actin catch-slip bonds to slip-only bonds. SMD simulations reveal that the force does not induce the K113:E195 interaction when formin binds to actin K118 and E117 residues located at the helical segment extending to K113. Actin catch-slip bonds are suppressed by single residue replacements K113E and E195K that interrupt the force-induced K113:E195 interaction; and this suppression is rescued by a K113E/E195K double mutant (E/K) restoring the interaction in the opposite orientation. These results support the biological significance of actin catch bonds, as they corroborate reported observations that RhoA and formin switch force-induced actin cytoskeleton alignment and that either K113E or E195K induces yeast cell growth defects rescued by E/K. Our study demonstrates how the mechano-regulation of actin dynamics is modulated by biochemical signaling molecules, and suggests that actin catch bonds may be important in cell functions.

  20. Actinic cheilitis with a familial pattern: An unusual case

    Directory of Open Access Journals (Sweden)

    Surekha Murthi

    2014-01-01

    Full Text Available Actinic cheilitis is a chronic inflammatory disorder of the lip, affecting the lower lip mainly, caused by cumulative long-term effects of ultraviolet (UV radiation in sunlight. It is a premalignant condition with a malignancy potential of 6-10%. It is reported that it almost exclusively occurs in fair-skinned people and those who work outdoors. However, it has recently been reported that actinic cheilitis is not exclusive to fair-skinned people. It is most common in middle-aged or older male patients. Diagnosis of actinic cheilitis is mainly based on demographical, clinical, and histopathological findings. Factors such as socioeconomic status, smoking, dietary habits, and genetic predisposition are also associated with lip cancer. Here, we present a case of actinic cheilitis in two siblings and in their mother, showing a familial pattern. An incisional biopsy of the lower lip in the mother showed severe dysplastic changes indicating transformation to squamous cell carcinoma.

  1. Two distinct mechanisms for actin capping protein regulation--steric and allosteric inhibition.

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    Shuichi Takeda

    Full Text Available The actin capping protein (CP tightly binds to the barbed end of actin filaments, thus playing a key role in actin-based lamellipodial dynamics. V-1 and CARMIL proteins directly bind to CP and inhibit the filament capping activity of CP. V-1 completely inhibits CP from interacting with the barbed end, whereas CARMIL proteins act on the barbed end-bound CP and facilitate its dissociation from the filament (called uncapping activity. Previous studies have revealed the striking functional differences between the two regulators. However, the molecular mechanisms describing how these proteins inhibit CP remains poorly understood. Here we present the crystal structures of CP complexed with V-1 and with peptides derived from the CP-binding motif of CARMIL proteins (CARMIL, CD2AP, and CKIP-1. V-1 directly interacts with the primary actin binding surface of CP, the C-terminal region of the alpha-subunit. Unexpectedly, the structures clearly revealed the conformational flexibility of CP, which can be attributed to a twisting movement between the two domains. CARMIL peptides in an extended conformation interact simultaneously with the two CP domains. In contrast to V-1, the peptides do not directly compete with the barbed end for the binding surface on CP. Biochemical assays revealed that the peptides suppress the interaction between CP and V-1, despite the two inhibitors not competing for the same binding site on CP. Furthermore, a computational analysis using the elastic network model indicates that the interaction of the peptides alters the intrinsic fluctuations of CP. Our results demonstrate that V-1 completely sequesters CP from the barbed end by simple steric hindrance. By contrast, CARMIL proteins allosterically inhibit CP, which appears to be a prerequisite for the uncapping activity. Our data suggest that CARMIL proteins down-regulate CP by affecting its conformational dynamics. This conceptually new mechanism of CP inhibition provides a

  2. The role of actin networks in cellular mechanosensing

    Science.gov (United States)

    Azatov, Mikheil

    Physical processes play an important role in many biological phenomena, such as wound healing, organ development, and tumor metastasis. During these processes, cells constantly interact with and adapt to their environment by exerting forces to mechanically probe the features of their surroundings and generating appropriate biochemical responses. The mechanisms underlying how cells sense the physical properties of their environment are not well understood. In this thesis, I present my studies to investigate cellular responses to the stiffness and topography of the environment. In order to sense the physical properties of their environment, cells dynamically reorganize the structure of their actin cytoskeleton, a dynamic network of biopolymers, altering the shape and spatial distribution of protein assemblies. Several observations suggest that proteins that crosslink actin filaments may play an important role in cellular mechanosensitivity. Palladin is an actin-crosslinking protein that is found in the lamellar actin network, stress fibers and focal adhesions, cellular structures that are critical for mechanosensing of the physical environment. By virtue of its close interactions with these structures in the cell, palladin may play an important role in cell mechanics. However, the role of actin crosslinkers in general, and palladin in particular, in cellular force generation and mechanosensing is not well known. I have investigated the role of palladin in regulating the plasticity of the actin cytoskeleton and cellular force generation in response to alterations in substrate stiffness. I have shown that the expression levels of palladin modulate the forces exerted by cells and their ability to sense substrate stiffness. Perturbation experiments also suggest that palladin levels in cells altered myosin motor activity. These results suggest that the actin crosslinkers, such as palladin, and myosin motors coordinate for optimal cell function and to prevent aberrant

  3. The Formin Diaphanous Regulates Myoblast Fusion through Actin Polymerization and Arp2/3 Regulation.

    Science.gov (United States)

    Deng, Su; Bothe, Ingo; Baylies, Mary K

    2015-08-01

    The formation of multinucleated muscle cells through cell-cell fusion is a conserved process from fruit flies to humans. Numerous studies have shown the importance of Arp2/3, its regulators, and branched actin for the formation of an actin structure, the F-actin focus, at the fusion site. This F-actin focus forms the core of an invasive podosome-like structure that is required for myoblast fusion. In this study, we find that the formin Diaphanous (Dia), which nucleates and facilitates the elongation of actin filaments, is essential for Drosophila myoblast fusion. Following cell recognition and adhesion, Dia is enriched at the myoblast fusion site, concomitant with, and having the same dynamics as, the F-actin focus. Through analysis of Dia loss-of-function conditions using mutant alleles but particularly a dominant negative Dia transgene, we demonstrate that reduction in Dia activity in myoblasts leads to a fusion block. Significantly, no actin focus is detected, and neither branched actin regulators, SCAR or WASp, accumulate at the fusion site when Dia levels are reduced. Expression of constitutively active Dia also causes a fusion block that is associated with an increase in highly dynamic filopodia, altered actin turnover rates and F-actin distribution, and mislocalization of SCAR and WASp at the fusion site. Together our data indicate that Dia plays two roles during invasive podosome formation at the fusion site: it dictates the level of linear F-actin polymerization, and it is required for appropriate branched actin polymerization via localization of SCAR and WASp. These studies provide new insight to the mechanisms of cell-cell fusion, the relationship between different regulators of actin polymerization, and invasive podosome formation that occurs in normal development and in disease.

  4. The Formin Diaphanous Regulates Myoblast Fusion through Actin Polymerization and Arp2/3 Regulation.

    Directory of Open Access Journals (Sweden)

    Su Deng

    2015-08-01

    Full Text Available The formation of multinucleated muscle cells through cell-cell fusion is a conserved process from fruit flies to humans. Numerous studies have shown the importance of Arp2/3, its regulators, and branched actin for the formation of an actin structure, the F-actin focus, at the fusion site. This F-actin focus forms the core of an invasive podosome-like structure that is required for myoblast fusion. In this study, we find that the formin Diaphanous (Dia, which nucleates and facilitates the elongation of actin filaments, is essential for Drosophila myoblast fusion. Following cell recognition and adhesion, Dia is enriched at the myoblast fusion site, concomitant with, and having the same dynamics as, the F-actin focus. Through analysis of Dia loss-of-function conditions using mutant alleles but particularly a dominant negative Dia transgene, we demonstrate that reduction in Dia activity in myoblasts leads to a fusion block. Significantly, no actin focus is detected, and neither branched actin regulators, SCAR or WASp, accumulate at the fusion site when Dia levels are reduced. Expression of constitutively active Dia also causes a fusion block that is associated with an increase in highly dynamic filopodia, altered actin turnover rates and F-actin distribution, and mislocalization of SCAR and WASp at the fusion site. Together our data indicate that Dia plays two roles during invasive podosome formation at the fusion site: it dictates the level of linear F-actin polymerization, and it is required for appropriate branched actin polymerization via localization of SCAR and WASp. These studies provide new insight to the mechanisms of cell-cell fusion, the relationship between different regulators of actin polymerization, and invasive podosome formation that occurs in normal development and in disease.

  5. Actin cytoskeleton: putting a CAP on actin polymerization.

    Science.gov (United States)

    Stevenson, V A; Theurkauf, W E

    2000-10-05

    Two recent studies have identified a Drosophila homolog of cyclase-associated protein (CAP) as a developmentally important negative regulator of actin polymerization that may also directly mediate signal transduction.

  6. Identification of Arabidopsis cyclase-associated protein 1 as the first nucleotide exchange factor for plant actin.

    Science.gov (United States)

    Chaudhry, Faisal; Guérin, Christophe; von Witsch, Matthias; Blanchoin, Laurent; Staiger, Christopher J

    2007-08-01

    The actin cytoskeleton powers organelle movements, orchestrates responses to abiotic stresses, and generates an amazing array of cell shapes. Underpinning these diverse functions of the actin cytoskeleton are several dozen accessory proteins that coordinate actin filament dynamics and construct higher-order assemblies. Many actin-binding proteins from the plant kingdom have been characterized and their function is often surprisingly distinct from mammalian and fungal counterparts. The adenylyl cyclase-associated protein (CAP) has recently been shown to be an important regulator of actin dynamics in vivo and in vitro. The disruption of actin organization in cap mutant plants indicates defects in actin dynamics or the regulated assembly and disassembly of actin subunits into filaments. Current models for actin dynamics maintain that actin-depolymerizing factor (ADF)/cofilin removes ADP-actin subunits from filament ends and that profilin recharges these monomers with ATP by enhancing nucleotide exchange and delivery of subunits onto filament barbed ends. Plant profilins, however, lack the essential ability to stimulate nucleotide exchange on actin, suggesting that there might be a missing link yet to be discovered from plants. Here, we show that Arabidopsis thaliana CAP1 (AtCAP1) is an abundant cytoplasmic protein; it is present at a 1:3 M ratio with total actin in suspension cells. AtCAP1 has equivalent affinities for ADP- and ATP-monomeric actin (Kd approximately 1.3 microM). Binding of AtCAP1 to ATP-actin monomers inhibits polymerization, consistent with AtCAP1 being an actin sequestering protein. However, we demonstrate that AtCAP1 is the first plant protein to increase the rate of nucleotide exchange on actin. Even in the presence of ADF/cofilin, AtCAP1 can recharge actin monomers and presumably provide a polymerizable pool of subunits to profilin for addition onto filament ends. In turnover assays, plant profilin, ADF, and CAP act cooperatively to promote flux

  7. Differences in the dynamics of affective and cognitive processing - An ERP study.

    Science.gov (United States)

    Mueller, Christina J; Fritsch, Nathalie; Hofmann, Markus J; Kuchinke, Lars

    2017-01-15

    A controversy in emotion research concerns the question of whether affective or cognitive primacy are evident in processing affective stimuli and the factors contributing to each alternative. Using electrophysiological recordings in an adapted visual oddball paradigm allowed tracking the dynamics of affective and cognitive effects. Stimuli consisted of face pictures displaying affective expressions with rare oddballs differing from frequent stimuli in either affective expression, structure (while frequent stimuli were shown frontally these deviants were turned sideways) or they differed on both dimensions, i.e. in affective expression and structure. Results revealed a defined sequence of differences in ERP amplitudes: For stimuli deviating in their affective expression only, P1 modulations ~100ms were evident, while affective differences of structure deviants were not evident before the N170 time window. All three types of deviants differed in P300 amplitudes, indicating integration of affective and structural information. These results encompass evidence for both, cognitive and affective primacy depending on stimulus properties. Specifically affective primacy is only visible when the respective facial features can be extracted with ease. When structural differences make face processing harder, however, cognitive primacy is brought forward.

  8. State transitions of actin cortices in vitro and in vivo

    Science.gov (United States)

    Tan, Tzer Han; Keren, Kinneret; Mackintosh, Fred; Schmidt, Christoph; Fakhri, Nikta

    Most animal cells are enveloped by a thin layer of actin cortex which governs the cell mechanics. A functional cortex must be rigid to provide mechanical support while being flexible to allow for rapid restructuring events such as cell division. To satisfy these requirements, the actin cortex is highly dynamic with fast actin turnover and myosin-driven contractility. The regulatory mechanism responsible for the transition between a mechanically stable state and a restructuring state is not well understood. Here, we develop a technique to map the dynamics of reconstituted actin cortices in emulsion droplets using IR fluorescent single-walled carbon nanotubes (SWNTs). By increasing crosslinker concentration, we find that a homogeneous cortex transitions to an intermediate state with broken rotational symmetry and a globally contractile state which further breaks translational symmetry. We apply this new dynamic mapping technique to cortices of live starfish oocytes in various developmental stages. To identify the regulatory mechanism for steady state transitions, we subject the oocytes to actin and myosin disrupting drugs.

  9. Hippocampal Dendritic Spines Are Segregated Depending on Their Actin Polymerization

    Directory of Open Access Journals (Sweden)

    Nuria Domínguez-Iturza

    2016-01-01

    Full Text Available Dendritic spines are mushroom-shaped protrusions of the postsynaptic membrane. Spines receive the majority of glutamatergic synaptic inputs. Their morphology, dynamics, and density have been related to synaptic plasticity and learning. The main determinant of spine shape is filamentous actin. Using FRAP, we have reexamined the actin dynamics of individual spines from pyramidal hippocampal neurons, both in cultures and in hippocampal organotypic slices. Our results indicate that, in cultures, the actin mobile fraction is independently regulated at the individual spine level, and mobile fraction values do not correlate with either age or distance from the soma. The most significant factor regulating actin mobile fraction was the presence of astrocytes in the culture substrate. Spines from neurons growing in the virtual absence of astrocytes have a more stable actin cytoskeleton, while spines from neurons growing in close contact with astrocytes show a more dynamic cytoskeleton. According to their recovery time, spines were distributed into two populations with slower and faster recovery times, while spines from slice cultures were grouped into one population. Finally, employing fast lineal acquisition protocols, we confirmed the existence of loci with high polymerization rates within the spine.

  10. Multiscale modeling and mechanics of filamentous actin cytoskeleton.

    Science.gov (United States)

    Yamaoka, Hidetaka; Matsushita, Shinji; Shimada, Yoshitaka; Adachi, Taiji

    2012-03-01

    The adaptive structure and functional changes of the actin cytoskeleton are induced by its mechanical behavior at various temporal and spatial scales. In particular, the mechanical behaviors at different scales play important roles in the mechanical functions of various cells, and these multiscale phenomena require clarification. To establish a milestone toward achieving multiscale modeling and simulation, this paper reviews mathematical analyses and simulation methods applied to the mechanics of the filamentous actin cytoskeleton. The actin cytoskeleton demonstrates characteristic behaviors at every temporal and spatial scale, and mathematical models and simulation methods can be applied to each level of actin cytoskeletal structure ranging from the molecular to the network level. This paper considers studies on mathematical models and simulation methods based on the molecular dynamics, coarse-graining, and continuum dynamics approaches. Every temporal and spatial scale of actin cytoskeletal structure is considered, and it is expected that discrete and continuum dynamics ranging from functional expression at the molecular level to macroscopic functional expression at the whole cell level will be developed and applied to multiscale modeling and simulation.

  11. Allosteric regulation by cooperative conformational changes of actin filaments drives mutually exclusive binding with cofilin and myosin.

    Science.gov (United States)

    Ngo, Kien Xuan; Umeki, Nobuhisa; Kijima, Saku T; Kodera, Noriyuki; Ueno, Hiroaki; Furutani-Umezu, Nozomi; Nakajima, Jun; Noguchi, Taro Q P; Nagasaki, Akira; Tokuraku, Kiyotaka; Uyeda, Taro Q P

    2016-10-20

    Heavy meromyosin (HMM) of myosin II and cofilin each binds to actin filaments cooperatively and forms clusters along the filaments, but it is unknown whether the two cooperative bindings are correlated and what physiological roles they have. Fluorescence microscopy demonstrated that HMM-GFP and cofilin-mCherry each bound cooperatively to different parts of actin filaments when they were added simultaneously in 0.2 μM ATP, indicating that the two cooperative bindings are mutually exclusive. In 0.1 mM ATP, the motor domain of myosin (S1) strongly inhibited the formation of cofilin clusters along actin filaments. Under this condition, most actin protomers were unoccupied by S1 at any given moment, suggesting that transiently bound S1 alters the structure of actin filaments cooperatively and/or persistently to inhibit cofilin binding. Consistently, cosedimentation experiments using copolymers of actin and actin-S1 fusion protein demonstrated that the fusion protein affects the neighboring actin protomers, reducing their affinity for cofilin. In reciprocal experiments, cofilin-actin fusion protein reduced the affinity of neighboring actin protomers for S1. Thus, allosteric regulation by cooperative conformational changes of actin filaments contributes to mutually exclusive cooperative binding of myosin II and cofilin to actin filaments, and presumably to the differential localization of both proteins in cells.

  12. Srv2/cyclase-associated protein forms hexameric shurikens that directly catalyze actin filament severing by cofilin.

    Science.gov (United States)

    Chaudhry, Faisal; Breitsprecher, Dennis; Little, Kristin; Sharov, Grigory; Sokolova, Olga; Goode, Bruce L

    2013-01-01

    Actin filament severing is critical for the dynamic turnover of cellular actin networks. Cofilin severs filaments, but additional factors may be required to increase severing efficiency in vivo. Srv2/cyclase-associated protein (CAP) is a widely expressed protein with a role in binding and recycling actin monomers ascribed to domains in its C-terminus (C-Srv2). In this paper, we report a new biochemical and cellular function for Srv2/CAP in directly catalyzing cofilin-mediated severing of filaments. This function is mediated by its N-terminal half (N-Srv2), and is physically and genetically separable from C-Srv2 activities. Using dual-color total internal reflection fluorescence microscopy, we determined that N-Srv2 stimulates filament disassembly by increasing the frequency of cofilin-mediated severing without affecting cofilin binding to filaments. Structural analysis shows that N-Srv2 forms novel hexameric star-shaped structures, and disrupting oligomerization impairs N-Srv2 activities and in vivo function. Further, genetic analysis shows that the combined activities of N-Srv2 and Aip1 are essential in vivo. These observations define a novel mechanism by which the combined activities of cofilin and Srv2/CAP lead to enhanced filament severing and support an emerging view that actin disassembly is controlled not by cofilin alone, but by a more complex set of factors working in concert.

  13. The Role of Actin Cytoskeleton in Memory Formation in Amygdala

    Directory of Open Access Journals (Sweden)

    Raphael eLamprecht

    2016-03-01

    Full Text Available The central, lateral and basolateral amygdala nuclei are essential for the formation of long-term memories including emotional and drug-related memories. The study of cellular and molecular mechanisms underpinning memory in amygdala may shed light on the formation of memory and on fear and addiction-related disorders. A challenge is to identify molecules activated by learning that subserve cellular changes needed for memory formation and maintenance in amygdala. Recent studies show that activation of synaptic receptors during fear and drug-related learning leads to alteration in actin cytoskeleton dynamics and structure in amygdala. Such changes in actin cytoskeleton in amygdala are essential for fear and drug-related memories formation. Moreover, the actin cytoskeleton subserves, after learning, changes in neuronal morphogenesis and glutamate receptors trafficking in amygdala. These cellular events are involved in fear and drug-related memories formation. Actin polymerization is also needed for the maintenance of drug-associated memories in amygdala. Thus, the actin cytoskeleton is a key mediator between receptor activation during learning and cellular changes subserving long-term memory in amygdala. The actin cytoskeleton may serve as a target for pharmacological treatment of fear memory associated with fear and anxiety disorders and drug addiction to prevent the debilitating consequences of these diseases.

  14. C-terminal fragment of amebin promotes actin filament bundling, inhibits acto-myosin ATPase activity and is essential for amoeba migration.

    Science.gov (United States)

    Jóźwiak, Jolanta; Rzhepetskyy, Yuriy; Sobczak, Magdalena; Kocik, Elżbieta; Skórzewski, Radosław; Kłopocka, Wanda; Rędowicz, Maria Jolanta

    2011-02-01

    Amebin [formerly termed as ApABP-FI; Sobczak et al. (2007) Biochem. Cell Biol. 85] is encoded in Amoeba proteus by two transcripts, 2672-nt and 1125-nt. A product of the shorter transcript (termed as C-amebin), comprising C-terminal 375 amino-acid-residue fragment of amebin, has been expressed and purified as the recombinant GST-fusion protein. GST-C-amebin bound both to monomeric and filamentous actin. The binding was Ca(2+)-independent and promoted filament bundling, as revealed with the transmission electron microscopy. GST-C-amebin significantly decreased MgATPase activity of rabbit skeletal muscle acto-S1. Removal with endoproteinase ArgC of a positively charged C-terminal region of GST-amebin containing KLASMWEQ sequence abolished actin-binding and bundling as well as the ATPase-inhibitory effect of C-amebin, indicating that this protein region was involved in the interaction with actin. Microinjection of amoebae with antibody against C-terminus of amebin significantly affected amoebae morphology, disturbed cell polarization and transport of cytoplasmic granules as well as blocked migration. These data indicate that amebin may be one of key regulators of the actin-cytoskeleton dynamics and actin-dependent motility in A. proteus.

  15. Progresses in studies of nuclear actin

    Institute of Scientific and Technical Information of China (English)

    ZHU Xiaojuan; ZENG Xianlu; SONG Zhaoxia; HAO Shui

    2004-01-01

    Actin is a protein abundant in cells. Recently, it has been proved to be universally existent in the nuclei of many cell types. Actin and actin-binding proteins, as well as actin-related proteins, are necessary for the mediation of the conformation and function of nuclear actin, including the transformation of actin between unpolymerized and polymerized, chroinatin remodeling, regulation of gene expression and RNA processing as well as RNA transportation. In this paper, we summarized the progresses in the research of nu clear actin.

  16. Altered Cell Mechanics from the Inside: Dispersed Single Wall Carbon Nanotubes Integrate with and Restructure Actin

    Directory of Open Access Journals (Sweden)

    Mohammad F. Islam

    2012-05-01

    Full Text Available With a range of desirable mechanical and optical properties, single wall carbon nanotubes (SWCNTs are a promising material for nanobiotechnologies. SWCNTs also have potential as biomaterials for modulation of cellular structures. Previously, we showed that highly purified, dispersed SWCNTs grossly alter F-actin inside cells. F-actin plays critical roles in the maintenance of cell structure, force transduction, transport and cytokinesis. Thus, quantification of SWCNT-actin interactions ranging from molecular, sub-cellular and cellular levels with both structure and function is critical for developing SWCNT-based biotechnologies. Further, this interaction can be exploited, using SWCNTs as a unique actin-altering material. Here, we utilized molecular dynamics simulations to explore the interactions of SWCNTs with actin filaments. Fluorescence lifetime imaging microscopy confirmed that SWCNTs were located within ~5 nm of F-actin in cells but did not interact with G-actin. SWCNTs did not alter myosin II sub-cellular localization, and SWCNT treatment in cells led to significantly shorter actin filaments. Functionally, cells with internalized SWCNTs had greatly reduced cell traction force. Combined, these results demonstrate direct, specific SWCNT alteration of F-actin structures which can be exploited for SWCNT-based biotechnologies and utilized as a new method to probe fundamental actin-related cellular processes and biophysics.

  17. Genome-wide RNAi screen for nuclear actin reveals a network of cofilin regulators.

    Science.gov (United States)

    Dopie, Joseph; Rajakylä, Eeva K; Joensuu, Merja S; Huet, Guillaume; Ferrantelli, Evelina; Xie, Tiao; Jäälinoja, Harri; Jokitalo, Eija; Vartiainen, Maria K

    2015-07-01

    Nuclear actin plays an important role in many processes that regulate gene expression. Cytoplasmic actin dynamics are tightly controlled by numerous actin-binding proteins, but regulation of nuclear actin has remained unclear. Here, we performed a genome-wide RNA interference (RNAi) screen in Drosophila cells to identify proteins that influence either nuclear polymerization or import of actin. We validate 19 factors as specific hits, and show that Chinmo (known as Bach2 in mammals), SNF4Aγ (Prkag1 in mammals) and Rab18 play a role in nuclear localization of actin in both fly and mammalian cells. We identify several new regulators of cofilin activity, and characterize modulators of both cofilin kinases and phosphatase. For example, Chinmo/Bach2, which regulates nuclear actin levels also in vivo, maintains active cofilin by repressing the expression of the kinase Cdi (Tesk in mammals). Finally, we show that Nup98 and lamin are candidates for regulating nuclear actin polymerization. Our screen therefore reveals new aspects of actin regulation and links nuclear actin to many cellular processes.

  18. AFAP-1L1-mediated actin filaments crosslinks hinder Trypanosoma cruzi cell invasion and intracellular multiplication.

    Science.gov (United States)

    de Araújo, Karine Canuto Loureiro; Teixeira, Thaise Lara; Machado, Fabrício Castro; da Silva, Aline Alves; Quintal, Amanda Pifano Neto; da Silva, Claudio Vieira

    2016-10-01

    Host actin cytoskeleton polymerization has been shown to play an important role during Trypanosoma cruzi internalization into mammalian cell. The structure and dynamics of the actin cytoskeleton in cells are regulated by a vast number of actin-binding proteins. Here we aimed to verify the impact of AFAP-1L1, during invasion and multiplication of T. cruzi. Knocking-down AFAP-1L1 increased parasite cell invasion and intracellular multiplication. Thus, we have shown that the integrity of the machinery formed by AFAP-1L1 in actin cytoskeleton polymerization is important to hinder parasite infection.

  19. Factors affecting the haptic filled-space illusion for dynamic touch

    NARCIS (Netherlands)

    Sanders, A.F.J.; Kappers, A.M.L.

    2009-01-01

    In the haptic filled-space illusion for active dynamic touch, observers move their fingertip across an unfilled extent or an extent filled with intermediate stimulations. Previous researchers have reported lengths of filled extents to be overestimated, but the parameters affecting the strength of th

  20. Dynamic Effects of Craving and Negative Affect on Adolescent Smoking Relapse

    NARCIS (Netherlands)

    Zundert, R.M.P. van; Ferguson, S.G.; Shiffman, S.; Engels, R.C.M.E.

    2012-01-01

    Objective: This study examined dynamic effects of daily variations in craving and negative affect on the next-day risk of the first lapse and relapse among 149 adolescent daily smokers who achieved at least 24 hr of abstinence. Method: Participants completed real-time assessments of their smoking, c

  1. Environmental Factors Affecting Computer Assisted Language Learning Success: A Complex Dynamic Systems Conceptual Model

    Science.gov (United States)

    Marek, Michael W.; Wu, Wen-Chi Vivian

    2014-01-01

    This conceptual, interdisciplinary inquiry explores Complex Dynamic Systems as the concept relates to the internal and external environmental factors affecting computer assisted language learning (CALL). Based on the results obtained by de Rosnay ["World Futures: The Journal of General Evolution", 67(4/5), 304-315 (2011)], who observed…

  2. School Factors Explaining Achievement on Cognitive and Affective Outcomes : Establishing a Dynamic Model of Educational Effectiveness

    NARCIS (Netherlands)

    Creemers, Bert; Kyriakides, Leonidas

    2010-01-01

    The dynamic model of educational effectiveness defines school level factors associated with student outcomes. Emphasis is given to the two main aspects of policy, evaluation, and improvement in schools which affect quality of teaching and learning at both the level of teachers and students: a) teach

  3. Modeling affect dynamics : State-of-the-art and future challenges

    NARCIS (Netherlands)

    Hamaker, E.L.; Ceulemans, Eva; Grasman, R.P.P.P.; Tuerlinckx, Francis

    2015-01-01

    The current article aims to provide an up-to-date synopsis of available techniques to study affect dynamics using intensive longitudinal data (ILD). We do so by introducing the following eight dichotomies that help elucidate what kind of data one has, what process aspects are of interest, and what r

  4. Imperfect or Perfect Dynamic Bipolarity? The Case of Antonymous Affective Judgments

    Science.gov (United States)

    Vautier, Stephane; Steyer, Rolf; Jmel, Said; Raufaste, Eric

    2005-01-01

    How is affective change rated with positive adjectives such as good related to change rated with negative adjectives such as bad? Two nested perfect and imperfect forms of dynamic bipolarity are defined using latent change structural equation models based on tetrads of items. Perfect bipolarity means that latent change scores correlate -1.…

  5. Profilin as a regulator of the membrane-actin cytoskeleton interface in plant cells

    Directory of Open Access Journals (Sweden)

    Tiantian eSun

    2013-12-01

    Full Text Available Membrane structures and cytoskeleton dynamics are intimately inter-connected in the eukaryotic cell. Recently, the molecular mechanisms operating at this interface have been progressively addressed. Many experiments have revealed that the actin cytoskeleton can interact with membranes through various discrete membrane domains. The actin-binding protein, profilin has been proven to inhibit actin polymerization and to promote F-actin elongation. This is dependent on many factors, such as the profilin/G-actin ratio and the ionic environment of the cell. Additionally, profilin has specific domains that interact with phosphoinositides and poly-L-proline rich proteins; theoretically, this gives profilin the opportunity to interact with membranes, and a large number of experiments have confirmed this possibility. In this article, we summarize recent findings in plant cells, and discuss the evidence of the connections among actin cytoskeleton, profilin and biomembranes through direct or indirect relationships.

  6. Xenopus oocyte wound healing as a model system for analysis of microtubule-actin interactions.

    Science.gov (United States)

    Zhang, Tong; Mandato, Craig A

    2007-01-01

    Microtubule-actin interactions are fundamental to many cellular processes such as cytokinesis and cellular locomotion. Investigating the mechanism of microtubule-actin interactions is the key to understand the cellular morphogenesis and related pathological processes. The abundance and highly dynamic nature of microtubules and F-actin raise a serious challenge when trying to distinguish between the real and fortuitous interactions within a cell. Xenopus oocyte wound model represents an ideal system to study microtubule-actin interactions as well as microtubule-dependent control of the actin polymerization. Here, we describe a series of cytoskeleton specific treatments in Xenopus oocyte wound healing experiments and use confocal fluorescence microscopy to analyze fixed oocytes to examine microtubule-actin interactions.

  7. Patient affect experiencing following therapist interventions in short-term dynamic psychotherapy.

    Science.gov (United States)

    Town, Joel M; Hardy, Gillian E; McCullough, Leigh; Stride, Chris

    2012-01-01

    The aim of this research was to examine the relationship between therapist interventions and patient affect responses in Short-Term Dynamic Psychotherapy (STDP). The Affect Experiencing subscale from the Achievement of Therapeutic Objectives Scale (ATOS) was adapted to measure individual immediate affect experiencing (I-AES) responses in relation to therapist interventions coded within the preceding speaking turn, using the Psychotherapy Interaction Coding (PIC) system. A hierarchical linear modelling procedure was used to assess the change in affect experiencing and the relationship between affect experiencing and therapist interventions within and across segments of therapy. Process data was taken from six STDP cases; in total 24 hours of video-taped sessions were examined. Therapist interventions were found to account for a statistically significant amount of variance in immediate affect experiencing. Higher levels of immediate affect experiencing followed the therapist's use of Confrontation, Clarification and Support compared to Questions, Self-disclosure and Information interventions. Therapist Confrontation interventions that attempted to direct pressure towards either the visceral experience of affect or a patient's defences against feelings led to the highest levels of immediate affect experiencing. The type of therapist intervention accounts for a small but significant amount of the variation observed in a patient's immediate emotional arousal. Empirical findings support clinical theory in STDP that suggests strategic verbal responses promote the achievement of this specific therapeutic objective.

  8. Factors affecting the dynamic response of pre-stressed anchors after transient excitation

    Institute of Scientific and Technical Information of China (English)

    Xu Huijun; Li Qingfeng

    2011-01-01

    The wide application of pre-stressed bolting technology in coal mine tunnels has made the nondestructive stress wave reflection method of determining bolting quality an important one.The effect of the support plate on the dynamic response of the pre-stressed anchor is of particular interest.A theoreticalanalysis and numerical simulations are used to identify the factors affecting the contact stress between the support plate and the rock wall.A formula allowing the calculation of contact stress is presented.Stress wave propagation through the nut,support plate,and rock wall are predicted.The dynamic response signals were measured in the field using prestressed anchors pre-tightened to different torques.The effects from the support plate on the dynamic response were recorded and the results compared to the predictions of pre-stressed anchor.This work provides a theoretical reference for the signal processing of dynamic reflected wave signals in anchor bolts.

  9. An Investigation of Factors Affecting Elementary School Students’ BMI Values Based on the System Dynamics Modeling

    Directory of Open Access Journals (Sweden)

    Tian-Syung Lan

    2014-01-01

    Full Text Available This study used system dynamics method to investigate the factors affecting elementary school students’ BMI values. The construction of the dynamic model is divided into the qualitative causal loop and the quantitative system dynamics modeling. According to the system dynamics modeling, this study consisted of research on the four dimensions: student’s personal life style, diet-relevant parenting behaviors, advocacy and implementation of school nutrition education, and students’ peer interaction. The results of this study showed that students with more adequate health concepts usually have better eating behaviors and consequently have less chance of becoming obese. In addition, this study also verified that educational attainment and socioeconomic status of parents have a positive correlation with students’ amounts of physical activity, and nutrition education has a prominent influence on changing students’ high-calorie diets.

  10. Structural Analysis of Human Cofilin 2/Filamentous Actin Assemblies: Atomic-Resolution Insights from Magic Angle Spinning NMR Spectroscopy

    Science.gov (United States)

    Yehl, Jenna; Kudryashova, Elena; Reisler, Emil; Kudryashov, Dmitri; Polenova, Tatyana

    2017-01-01

    Cellular actin dynamics is an essential element of numerous cellular processes, such as cell motility, cell division and endocytosis. Actin’s involvement in these processes is mediated by many actin-binding proteins, among which the cofilin family plays unique and essential role in accelerating actin treadmilling in filamentous actin (F-actin) in a nucleotide-state dependent manner. Cofilin preferentially interacts with older filaments by recognizing time-dependent changes in F-actin structure associated with the hydrolysis of ATP and release of inorganic phosphate (Pi) from the nucleotide cleft of actin. The structure of cofilin on F-actin and the details of the intermolecular interface remain poorly understood at atomic resolution. Here we report atomic-level characterization by magic angle spinning (MAS) NMR of the muscle isoform of human cofilin 2 (CFL2) bound to F-actin. We demonstrate that resonance assignments for the majority of atoms are readily accomplished and we derive the intermolecular interface between CFL2 and F-actin. The MAS NMR approach reported here establishes the foundation for atomic-resolution characterization of a broad range of actin-associated proteins bound to F-actin. PMID:28303963

  11. Identifying Core Affect in Individuals from fMRI Responses to Dynamic Naturalistic Audiovisual Stimuli.

    Science.gov (United States)

    Kim, Jongwan; Wang, Jing; Wedell, Douglas H; Shinkareva, Svetlana V

    2016-01-01

    Recent research has demonstrated that affective states elicited by viewing pictures varying in valence and arousal are identifiable from whole brain activation patterns observed with functional magnetic resonance imaging (fMRI). Identification of affective states from more naturalistic stimuli has clinical relevance, but the feasibility of identifying these states on an individual trial basis from fMRI data elicited by dynamic multimodal stimuli is unclear. The goal of this study was to determine whether affective states can be similarly identified when participants view dynamic naturalistic audiovisual stimuli. Eleven participants viewed 5s audiovisual clips in a passive viewing task in the scanner. Valence and arousal for individual trials were identified both within and across participants based on distributed patterns of activity in areas selectively responsive to audiovisual naturalistic stimuli while controlling for lower level features of the stimuli. In addition, the brain regions identified by searchlight analyses to represent valence and arousal were consistent with previously identified regions associated with emotion processing. These findings extend previous results on the distributed representation of affect to multimodal dynamic stimuli.

  12. Identifying Core Affect in Individuals from fMRI Responses to Dynamic Naturalistic Audiovisual Stimuli

    Science.gov (United States)

    Kim, Jongwan; Wang, Jing; Wedell, Douglas H.

    2016-01-01

    Recent research has demonstrated that affective states elicited by viewing pictures varying in valence and arousal are identifiable from whole brain activation patterns observed with functional magnetic resonance imaging (fMRI). Identification of affective states from more naturalistic stimuli has clinical relevance, but the feasibility of identifying these states on an individual trial basis from fMRI data elicited by dynamic multimodal stimuli is unclear. The goal of this study was to determine whether affective states can be similarly identified when participants view dynamic naturalistic audiovisual stimuli. Eleven participants viewed 5s audiovisual clips in a passive viewing task in the scanner. Valence and arousal for individual trials were identified both within and across participants based on distributed patterns of activity in areas selectively responsive to audiovisual naturalistic stimuli while controlling for lower level features of the stimuli. In addition, the brain regions identified by searchlight analyses to represent valence and arousal were consistent with previously identified regions associated with emotion processing. These findings extend previous results on the distributed representation of affect to multimodal dynamic stimuli. PMID:27598534

  13. On the dynamic covariation between interpersonal behavior and affect: prediction from neuroticism, extraversion, and agreeableness.

    Science.gov (United States)

    Côté, S; Moskowitz, D S

    1998-10-01

    It was posited that the traits of Neuroticism, Extraversion, and Agreeableness are predictors of dynamic intraindividual processes involving interpersonal behavior and affect. Hypotheses derived from the behavioral concordance model that individuals with high scores on a trait would experience more positively valenced affect when engaging in behavior concordant with that trait than individuals with low scores on the trait were tested. Participants completed a questionnaire measure of the traits and reported on behavior and affect during interpersonal interactions using event-contingent sampling forms approximately 6 times a day for 20 days. Trait scores were related to indexes of the association between each dimension of interpersonal behavior and affect calculated for each individual. Previous findings concerning the trait of Agreeableness were replicated, and results strongly supported the behavioral concordance model for the trait of Neuroticism. Thus, at least some traits can provide information about intraindividual processes that vary over time.

  14. EhCoactosin stabilizes actin filaments in the protist parasite Entamoeba histolytica.

    Directory of Open Access Journals (Sweden)

    Nitesh Kumar

    2014-09-01

    Full Text Available Entamoeba histolytica is a protist parasite that is the causative agent of amoebiasis, and is a highly motile organism. The motility is essential for its survival and pathogenesis, and a dynamic actin cytoskeleton is required for this process. EhCoactosin, an actin-binding protein of the ADF/cofilin family, participates in actin dynamics, and here we report our studies of this protein using both structural and functional approaches. The X-ray crystal structure of EhCoactosin resembles that of human coactosin-like protein, with major differences in the distribution of surface charges and the orientation of terminal regions. According to in vitro binding assays, full-length EhCoactosin binds both F- and G-actin. Instead of acting to depolymerize or severe F-actin, EhCoactosin directly stabilizes the polymer. When EhCoactosin was visualized in E. histolytica cells using either confocal imaging or total internal reflectance microscopy, it was found to colocalize with F-actin at phagocytic cups. Over-expression of this protein stabilized F-actin and inhibited the phagocytic process. EhCoactosin appears to be an unusual type of coactosin involved in E. histolytica actin dynamics.

  15. Boolean gates on actin filaments

    Science.gov (United States)

    Siccardi, Stefano; Tuszynski, Jack A.; Adamatzky, Andrew

    2016-01-01

    Actin is a globular protein which forms long polar filaments in the eukaryotic cytoskeleton. Actin networks play a key role in cell mechanics and cell motility. They have also been implicated in information transmission and processing, memory and learning in neuronal cells. The actin filaments have been shown to support propagation of voltage pulses. Here we apply a coupled nonlinear transmission line model of actin filaments to study interactions between voltage pulses. To represent digital information we assign a logical TRUTH value to the presence of a voltage pulse in a given location of the actin filament, and FALSE to the pulse's absence, so that information flows along the filament with pulse transmission. When two pulses, representing Boolean values of input variables, interact, then they can facilitate or inhibit further propagation of each other. We explore this phenomenon to construct Boolean logical gates and a one-bit half-adder with interacting voltage pulses. We discuss implications of these findings on cellular process and technological applications.

  16. Optogenetics to target actin-mediated synaptic loss in Alzheimer's

    Science.gov (United States)

    Zahedi, Atena; DeFea, Kathryn; Ethell, Iryna

    2013-03-01

    Numerous studies in Alzheimer's Disease (AD) animal models show that overproduction of Aβ peptides and their oligomerization can distort dendrites, damage synapses, and decrease the number of dendritic spines and synapses. Aβ may trigger synapse loss by modulating activity of actin-regulating proteins, such as Rac1 and cofilin. Indeed, Aβ1-42 oligomers can activate actin severing protein cofilin through calcineurin-mediated activation of phosphatase slingshot and inhibit an opposing pathway that suppresses cofilin phosphorylation through Rac-mediated activation of LIMK1. Excessive activation of actin-severing protein cofilin triggers the formation of a non-dynamic actin bundles, called rods that are found in AD brains and cause loss of synapses. Hence, regulation of these actin-regulating proteins in dendritic spines could potentially provide useful tools for preventing the synapse/spine loss associated with earlier stages of AD neuropathology. However, lack of spatiotemporal control over their activity is a key limitation. Recently, optogenetic advancements have provided researchers with convenient light-activating proteins such as photoactivatable Rac (PARac). Here, we transfected cultured primary hippocampal neurons and human embryonic kidney (HEK) cells with a PARac/ mCherry-containing plasmid and the mCherry-positive cells were identified and imaged using an inverted fluorescence microscope. Rac1 activation was achieved by irradiation with blue light (480nm) and live changes in dendritic spine morphology were observed using mCherry (587nm). Rac activation was confirmed by immunostaining for phosphorylated form of effector proteinP21 protein-activated kinase 1 (PAK1) and reorganization of actin. Thus, our studies confirm the feasibility of using the PA-Rac construct to trigger actin re-organization in the dendritic spines.

  17. Toward affect-inclusive models of cognitive dynamics: Coupling epistemological resources and emotions

    CERN Document Server

    Gupta, Ayush; Elby, Andrew

    2013-01-01

    Many prominent lines of research on student's reasoning and conceptual change within learning sciences and physics education research have not attended to the role of learners' affect or emotions in the dynamics of their conceptual reasoning. This is despite evidence from psychology and cognitive- and neuro- sciences that emotions are deeply integrated with cognition and documented associations in education research between emotions and academic performance. The few studies that have aimed to integrate emotions within models of learners' cognition, have mostly done so at a coarse grain size. In this manuscript, toward the long-term goal of incorporating emotions into fine-grained models of in-themoment cognitive dynamics, we present a case study of Judy, an undergraduate electrical engineering and physics major. We argue that a fine-grained aspect of Judy's affect, her annoyance at a particular kind of homework problem, stabilizes a context-dependent epistemological stance she displays, about an unbridgeable ...

  18. Dynamic cerebral autoregulatory capacity is affected early in Type 2 diabetes

    DEFF Research Database (Denmark)

    Kim, Y.S.; Immink, R.V.; Stok, W.J.;

    2008-01-01

    ) and impaired in subjects with DM+ (30+/-5 degrees ; Pblood pressure oscillations by affected dynamic cerebral autoregulation. The steady-state response of MCA V(mean) to postural change was comparable for all groups (-12+/-6% in CTRL subjects......, -15+/-6% in subjects with DM- and -15+/-7% in subjects with DM+). HbA(1c) (glycated haemoglobin) and the duration of diabetes, but not blood pressure, were determinants of transfer function phase. In conclusion, dysfunction of dynamic cerebral autoregulation in subjects with Type 2 diabetes appears......Type 2 diabetes is associated with an increased risk of endothelial dysfunction and microvascular complications with impaired autoregulation of tissue perfusion. Both microvascular disease and cardiovascular autonomic neuropathy may affect cerebral autoregulation. In the present study, we tested...

  19. Types and concentrations of metal ions affect local structure and dynamics of RNA

    Science.gov (United States)

    Wang, Jun; Xiao, Yi

    2016-10-01

    The roles that metal ions play in the structure and dynamics of RNA molecules are long-standing problems that have been studied extensively but are still not well understood. Here we show that metal ions have distributions around RNA molecules that strongly depend on the types and concentrations of the metal ions and also the electrostatic surface of the molecule. In particular, the ion distributions may not balance all the local electronegativity of the molecule. These ion distributions do not only greatly affect local structures but also lead to different local dynamics of RNA. We studied the effects of different ion solutions on the structure and dynamics of RNA by taking the pre Q1 riboswitch aptamer domain as an illustrative example and using molecular dynamics simulations. Since the local structures and dynamics of RNAs are important to their functions, our results also indicate that the selection of proper ion conditions is necessary to model them correctly, in contrast to the use of diverse ion solutions in current molecular dynamics simulations.

  20. Fertilization in Torenia fournieri: actin organization and nuclear behavior in the central cell and primary endosperm

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Studies of the living embryo sacs of Torenia fournieri reveal that the actin cytoskeleton undergoes dramatic changes that correlate with nuclear migration within the central cell and the primary endosperm. Before pollination, actin filaments appear as short bundles randomly distributed in the cortex of the central cell. Two days after anthesis, they become organized into a distinct actin network. At this stage the secondary nucleus, which is located in the central region of the central cell, possesses an associated array of short actin filaments. Soon after pollination, the actin filaments become fragmented in the micropylar end and the secondary nucleus is located next to the egg apparatus. After fertilization, the primary endosperm nucleus moves away from the egg cell and actin filaments reorganize into a prominent network in the cytoplasm of the primary endosperm. Disruption of the actin cytoskeleton with latrunculin A and cytochalasin B indicates that actin is involved in the migration of the nucleus in the central cell. Our data also suggest that the dynamics of actin cytoskeleton may be responsible for the reorganization of the central cell and primary endosperm cytoplasm during fertilization.

  1. Actin-myosin network is required for proper assembly of influenza virus particles

    Energy Technology Data Exchange (ETDEWEB)

    Kumakura, Michiko; Kawaguchi, Atsushi, E-mail: ats-kawaguchi@md.tsukuba.ac.jp; Nagata, Kyosuke, E-mail: knagata@md.tsukuba.ac.jp

    2015-02-15

    Actin filaments are known to play a central role in cellular dynamics. After polymerization of actin, various actin-crosslinking proteins including non-muscle myosin II facilitate the formation of spatially organized actin filament networks. The actin-myosin network is highly expanded beneath plasma membrane. The genome of influenza virus (vRNA) replicates in the cell nucleus. Then, newly synthesized vRNAs are nuclear-exported to the cytoplasm as ribonucleoprotein complexes (vRNPs), followed by transport to the beneath plasma membrane where virus particles assemble. Here, we found that, by inhibiting actin-myosin network formation, the virus titer tends to be reduced and HA viral spike protein is aggregated on the plasma membrane. These results indicate that the actin-myosin network plays an important role in the virus formation. - Highlights: • Actin-myosin network is important for the influenza virus production. • HA forms aggregations at the plasma membrane in the presence of blebbistatin. • M1 is recruited to the budding site through the actin-myosin network.

  2. Cell elasticity is regulated by the tropomyosin isoform composition of the actin cytoskeleton.

    Science.gov (United States)

    Jalilian, Iman; Heu, Celine; Cheng, Hong; Freittag, Hannah; Desouza, Melissa; Stehn, Justine R; Bryce, Nicole S; Whan, Renee M; Hardeman, Edna C; Fath, Thomas; Schevzov, Galina; Gunning, Peter W

    2015-01-01

    The actin cytoskeleton is the primary polymer system within cells responsible for regulating cellular stiffness. While various actin binding proteins regulate the organization and dynamics of the actin cytoskeleton, the proteins responsible for regulating the mechanical properties of cells are still not fully understood. In the present study, we have addressed the significance of the actin associated protein, tropomyosin (Tpm), in influencing the mechanical properties of cells. Tpms belong to a multi-gene family that form a co-polymer with actin filaments and differentially regulate actin filament stability, function and organization. Tpm isoform expression is highly regulated and together with the ability to sort to specific intracellular sites, result in the generation of distinct Tpm isoform-containing actin filament populations. Nanomechanical measurements conducted with an Atomic Force Microscope using indentation in Peak Force Tapping in indentation/ramping mode, demonstrated that Tpm impacts on cell stiffness and the observed effect occurred in a Tpm isoform-specific manner. Quantitative analysis of the cellular filamentous actin (F-actin) pool conducted both biochemically and with the use of a linear detection algorithm to evaluate actin structures revealed that an altered F-actin pool does not absolutely predict changes in cell stiffness. Inhibition of non-muscle myosin II revealed that intracellular tension generated by myosin II is required for the observed increase in cell stiffness. Lastly, we show that the observed increase in cell stiffness is partially recapitulated in vivo as detected in epididymal fat pads isolated from a Tpm3.1 transgenic mouse line. Together these data are consistent with a role for Tpm in regulating cell stiffness via the generation of specific populations of Tpm isoform-containing actin filaments.

  3. Cell stress promotes the association of phosphorylated HspB1 with F-actin.

    Directory of Open Access Journals (Sweden)

    Joseph P Clarke

    Full Text Available Previous studies have suggested that the small heat shock protein, HspB1, has a direct influence on the dynamics of cytoskeletal elements, in particular, filamentous actin (F-actin polymerization. In this study we have assessed the influence of HspB1 phosphorylation on its interaction(s with F-actin. We first determined the distribution of endogenous non-phosphorylated HspB1, phosphorylated HspB1 and F-actin in neuroendocrine PC12 cells by immunocytochemistry and confocal microscopy. We then investigated a potential direct interaction between HspB1 with F-actin by precipitating F-actin directly with biotinylated phalloidin followed by Western analyses; the reverse immunoprecipitation of HspB1 was also carried out. The phosphorylation influence of HspB1 in this interaction was investigated by using pharmacologic inhibition of p38 MAPK. In control cells, HspB1 interacts with F-actin as a predominantly non-phosphorylated protein, but subsequent to stress there is a redistribution of HspB1 to the cytoskeletal fraction and a significantly increased association of pHspB1 with F-actin. Our data demonstrate HspB1 is found in a complex with F-actin both in phosphorylated and non-phosphorylated forms, with an increased association of pHspB1 with F-actin after heat stress. Overall, our study combines both cellular and biochemical approaches to show cellular localization and direct demonstration of an interaction between endogenous HspB1 and F-actin using methodolgy that specifically isolates F-actin.

  4. Phosphorylation of the actin binding protein Drebrin at S647 is regulated by neuronal activity and PTEN.

    Directory of Open Access Journals (Sweden)

    Patricia Kreis

    Full Text Available Defects in actin dynamics affect activity-dependent modulation of synaptic transmission and neuronal plasticity, and can cause cognitive impairment. A salient candidate actin-binding protein linking synaptic dysfunction to cognitive deficits is Drebrin (DBN. However, the specific mode of how DBN is regulated at the central synapse is largely unknown. In this study we identify and characterize the interaction of the PTEN tumor suppressor with DBN. Our results demonstrate that PTEN binds DBN and that this interaction results in the dephosphorylation of a site present in the DBN C-terminus--serine 647. PTEN and pS647-DBN segregate into distinct and complimentary compartments in neurons, supporting the idea that PTEN negatively regulates DBN phosphorylation at this site. We further demonstrate that neuronal activity increases phosphorylation of DBN at S647 in hippocampal neurons in vitro and in ex vivo hippocampus slices exhibiting seizure activity, potentially by inducing rapid dissociation of the PTEN:DBN complex. Our results identify a novel mechanism by which PTEN is required to maintain DBN phosphorylation at dynamic range and signifies an unusual regulation of an actin-binding protein linked to cognitive decline and degenerative conditions at the CNS synapse.

  5. Dissecting principles governing actin assembly using yeast extracts.

    Science.gov (United States)

    Michelot, Alphée; Drubin, David G

    2014-01-01

    In this chapter, we describe recent protocols that we have developed to trigger actin assembly and actin-based motility in yeast cell extracts. Our method allows for the fast preparation of yeast extracts that are competent in dynamic assembly of distinct actin filament structures of biologically appropriate protein composition. Compared to previous extract-based systems using other eukaryotic cell types, yeast provides a unique advantage for combining reconstituted assays with the preparation of extracts from genetically modified yeast strains. We present a global strategy for dissecting the functions of individual proteins, where the activities of the proteins are analyzed in systems of variable complexity, ranging from simple mixtures of pure proteins to the full complexity of a cell's cytoplasm.

  6. Fascin regulates nuclear actin during Drosophila oogenesis.

    Science.gov (United States)

    Kelpsch, Daniel J; Groen, Christopher M; Fagan, Tiffany N; Sudhir, Sweta; Tootle, Tina L

    2016-10-01

    Drosophila oogenesis provides a developmental system with which to study nuclear actin. During Stages 5-9, nuclear actin levels are high in the oocyte and exhibit variation within the nurse cells. Cofilin and Profilin, which regulate the nuclear import and export of actin, also localize to the nuclei. Expression of GFP-tagged Actin results in nuclear actin rod formation. These findings indicate that nuclear actin must be tightly regulated during oogenesis. One factor mediating this regulation is Fascin. Overexpression of Fascin enhances nuclear GFP-Actin rod formation, and Fascin colocalizes with the rods. Loss of Fascin reduces, whereas overexpression of Fascin increases, the frequency of nurse cells with high levels of nuclear actin, but neither alters the overall nuclear level of actin within the ovary. These data suggest that Fascin regulates the ability of specific cells to accumulate nuclear actin. Evidence indicates that Fascin positively regulates nuclear actin through Cofilin. Loss of Fascin results in decreased nuclear Cofilin. In addition, Fascin and Cofilin genetically interact, as double heterozygotes exhibit a reduction in the number of nurse cells with high nuclear actin levels. These findings are likely applicable beyond Drosophila follicle development, as the localization and functions of Fascin and the mechanisms regulating nuclear actin are widely conserved.

  7. Cortactin Adopts a Globular Conformation and Bundles Actin into Sheets

    Energy Technology Data Exchange (ETDEWEB)

    Cowieson, Nathan P.; King, Gordon; Cookson, David; Ross, Ian; Huber, Thomas; Hume, David A.; Kobe, Bostjan; Martin, Jennifer L. (Queensland); (Aust. Synch.)

    2008-08-21

    Cortactin is a filamentous actin-binding protein that plays a pivotal role in translating environmental signals into coordinated rearrangement of the cytoskeleton. The dynamic reorganization of actin in the cytoskeleton drives processes including changes in cell morphology, cell migration, and phagocytosis. In general, structural proteins of the cytoskeleton bind in the N-terminal region of cortactin and regulatory proteins in the C-terminal region. Previous structural studies have reported an extended conformation for cortactin. It is therefore unclear how cortactin facilitates cross-talk between structural proteins and their regulators. In the study presented here, circular dichroism, chemical cross-linking, and small angle x-ray scattering are used to demonstrate that cortactin adopts a globular conformation, thereby bringing distant parts of the molecule into close proximity. In addition, the actin bundling activity of cortactin is characterized, showing that fully polymerized actin filaments are bundled into sheet-like structures. We present a low resolution structure that suggests how the various domains of cortactin interact to coordinate its array of binding partners at sites of actin branching.

  8. Antenna Mechanism of Length Control of Actin Cables.

    Directory of Open Access Journals (Sweden)

    Lishibanya Mohapatra

    2015-06-01

    Full Text Available Actin cables are linear cytoskeletal structures that serve as tracks for myosin-based intracellular transport of vesicles and organelles in both yeast and mammalian cells. In a yeast cell undergoing budding, cables are in constant dynamic turnover yet some cables grow from the bud neck toward the back of the mother cell until their length roughly equals the diameter of the mother cell. This raises the question: how is the length of these cables controlled? Here we describe a novel molecular mechanism for cable length control inspired by recent experimental observations in cells. This "antenna mechanism" involves three key proteins: formins, which polymerize actin, Smy1 proteins, which bind formins and inhibit actin polymerization, and myosin motors, which deliver Smy1 to formins, leading to a length-dependent actin polymerization rate. We compute the probability distribution of cable lengths as a function of several experimentally tuneable parameters such as the formin-binding affinity of Smy1 and the concentration of myosin motors delivering Smy1. These results provide testable predictions of the antenna mechanism of actin-cable length control.

  9. Novel actin-like filament structure from Clostridium tetani.

    Science.gov (United States)

    Popp, David; Narita, Akihiro; Lee, Lin Jie; Ghoshdastider, Umesh; Xue, Bo; Srinivasan, Ramanujam; Balasubramanian, Mohan K; Tanaka, Toshitsugu; Robinson, Robert C

    2012-06-15

    Eukaryotic F-actin is constructed from two protofilaments that gently wind around each other to form a helical polymer. Several bacterial actin-like proteins (Alps) are also known to form F-actin-like helical arrangements from two protofilaments, yet with varied helical geometries. Here, we report a unique filament architecture of Alp12 from Clostridium tetani that is constructed from four protofilaments. Through fitting of an Alp12 monomer homology model into the electron microscopy data, the filament was determined to be constructed from two antiparallel strands, each composed of two parallel protofilaments. These four protofilaments form an open helical cylinder separated by a wide cleft. The molecular interactions within single protofilaments are similar to F-actin, yet interactions between protofilaments differ from those in F-actin. The filament structure and assembly and disassembly kinetics suggest Alp12 to be a dynamically unstable force-generating motor involved in segregating the pE88 plasmid, which encodes the lethal tetanus toxin, and thus a potential target for drug design. Alp12 can be repeatedly cycled between states of polymerization and dissociation, making it a novel candidate for incorporation into fuel-propelled nanobiopolymer machines.

  10. Cellular Levels of Signaling Factors Are Sensed by β-actin Alleles to Modulate Transcriptional Pulse Intensity

    Directory of Open Access Journals (Sweden)

    Alon Kalo

    2015-04-01

    Full Text Available The transcriptional response of β-actin to extra-cellular stimuli is a paradigm for transcription factor complex assembly and regulation. Serum induction leads to a precisely timed pulse of β-actin transcription in the cell population. Actin protein is proposed to be involved in this response, but it is not known whether cellular actin levels affect nuclear β-actin transcription. We perturbed the levels of key signaling factors and examined the effect on the induced transcriptional pulse by following endogenous β-actin alleles in single living cells. Lowering serum response factor (SRF protein levels leads to loss of pulse integrity, whereas reducing actin protein levels reveals positive feedback regulation, resulting in elevated gene activation and a prolonged transcriptional response. Thus, transcriptional pulse fidelity requires regulated amounts of signaling proteins, and perturbations in factor levels eliminate the physiological response, resulting in either tuning down or exaggeration of the transcriptional pulse.

  11. Identification of Actin-Binding Proteins from Maize Pollen

    Energy Technology Data Exchange (ETDEWEB)

    Staiger, C.J.

    2004-01-13

    Specific Aims--The goal of this project was to gain an understanding of how actin filament organization and dynamics are controlled in flowering plants. Specifically, we proposed to identify unique proteins with novel functions by investigating biochemical strategies for the isolation and characterization of actin-binding proteins (ABPs). In particular, our hunt was designed to identify capping proteins and nucleation factors. The specific aims included: (1) to use F-actin affinity chromatography (FAAC) as a general strategy to isolate pollen ABPs (2) to produce polyclonal antisera and perform subcellular localization in pollen tubes (3) to isolate cDNA clones for the most promising ABPs (4) to further purify and characterize ABP interactions with actin in vitro. Summary of Progress By employing affinity chromatography on F-actin or DNase I columns, we have identified at least two novel ABPs from pollen, PrABP80 (gelsolin-like) and ZmABP30, We have also cloned and expressed recombinant protein, as well as generated polyclonal antisera, for 6 interesting ABPs from Arabidopsis (fimbrin AtFIM1, capping protein a/b (AtCP), adenylyl cyclase-associated protein (AtCAP), AtCapG & AtVLN1). We performed quantitative analyses of the biochemical properties for two of these previously uncharacterized ABPs (fimbrin and capping protein). Our studies provide the first evidence for fimbrin activity in plants, demonstrate the existence of barbed-end capping factors and a gelsolin-like severing activity, and provide the quantitative data necessary to establish and test models of F-actin organization and dynamics in plant cells.

  12. Three-dimensional structure of actin filaments and of an actin gel made with actin-binding protein.

    Science.gov (United States)

    Niederman, R; Amrein, P C; Hartwig, J

    1983-05-01

    Purified muscle actin and mixtures of actin and actin-binding protein were examined in the transmission electron microscope after fixation, critical point drying, and rotary shadowing. The three-dimensional structure of the protein assemblies was analyzed by a computer-assisted graphic analysis applicable to generalized filament networks. This analysis yielded information concerning the frequency of filament intersections, the filament length between these intersections, the angle at which filaments branch at these intersections, and the concentration of filaments within a defined volume. Purified actin at a concentration of 1 mg/ml assembled into a uniform mass of long filaments which overlap at random angles between 0 degrees and 90 degrees. Actin in the presence of macrophage actin-binding protein assembled into short, straight filaments, organized in a perpendicular branching network. The distance between branch points was inversely related to the molar ratio of actin-binding protein to actin. This distance was what would be predicted if actin filaments grew at right angles off of nucleation sites on the two ends of actin-binding protein dimers, and then annealed. The results suggest that actin in combination with actin-binding protein self-assembles to form a three-dimensional network resembling the peripheral cytoskeleton of motile cells.

  13. Phosphorylation of the cytoskeletal protein CAP1 controls its association with cofilin and actin.

    Science.gov (United States)

    Zhou, Guo-Lei; Zhang, Haitao; Wu, Huhehasi; Ghai, Pooja; Field, Jeffrey

    2014-12-01

    Cell signaling can control the dynamic balance between filamentous and monomeric actin by modulating actin regulatory proteins. One family of actin regulating proteins that controls actin dynamics comprises cyclase-associated proteins 1 and 2 (CAP1 and 2, respectively). However, cell signals that regulate CAPs remained unknown. We mapped phosphorylation sites on mouse CAP1 and found S307 and S309 to be regulatory sites. We further identified glycogen synthase kinase 3 as a kinase phosphorylating S309. The phosphomimetic mutant S307D/S309D lost binding to its partner cofilin and, when expressed in cells, caused accumulation of actin stress fibers similar to that in cells with reduced CAP expression. In contrast, the non-phosphorylatable S307A/S309A mutant showed drastically increased cofilin binding and reduced binding to actin. These results suggest that the phosphorylation serves to facilitate release of cofilin for a subsequent cycle of actin filament severing. Moreover, our results suggest that S307 and S309 function in tandem; neither the alterations in binding cofilin and/or actin, nor the defects in rescuing the phenotype of the enlarged cell size in CAP1 knockdown cells was observed in point mutants of either S307 or S309. In summary, we identify a novel regulatory mechanism of CAP1 through phosphorylation.

  14. Srv2/CAP is required for polarized actin cable assembly and patch internalization during clathrin-mediated endocytosis.

    Science.gov (United States)

    Toshima, Junko Y; Horikomi, Chika; Okada, Asuka; Hatori, Makiko N; Nagano, Makoto; Masuda, Atsushi; Yamamoto, Wataru; Siekhaus, Daria Elisabeth; Toshima, Jiro

    2016-01-15

    The dynamic assembly and disassembly of actin filaments is essential for the formation and transport of vesicles during endocytosis. In yeast, two types of actin structures, namely cortical patches and cytoplasmic cables, play a direct role in endocytosis, but how their interaction is regulated remains unclear. Here, we show that Srv2/CAP, an evolutionarily conserved actin regulator, is required for efficient endocytosis owing to its role in the formation of the actin patches that aid initial vesicle invagination and of the actin cables that these move along. Deletion of the SRV2 gene resulted in the appearance of aberrant fragmented actin cables that frequently moved past actin patches, the sites of endocytosis. We find that the C-terminal CARP domain of Srv2p is vitally important for the proper assembly of actin patches and cables; we also demonstrate that the N-terminal helical folded domain of Srv2 is required for its localization to actin patches, specifically to the ADP-actin rich region through an interaction with cofilin. These results demonstrate the in vivo roles of Srv2p in the regulation of the actin cytoskeleton during clathrin-mediated endocytosis.

  15. Actinic cheilitis in dental practice.

    Science.gov (United States)

    Savage, N W; McKay, C; Faulkner, C

    2010-06-01

    Actinic cheilitis is a potentially premalignant condition involving predominantly the vermilion of the lower lip. The aim of the current paper was to review the clinical presentation of actinic cheilitis and demonstrate the development of management plans using a series of cases. These are designed to provide immediate treatment where required but also to address the medium and long-term requirements of the patient. The authors suggest that the clinical examination of lips and the assessment of actinic cheilitis and other lip pathology become a regular part of the routine soft tissue examination undertaken as a part of the periodic examination of dental patients. Early recognition of actinic cheilitis can allow the development of strategies for individual patients that prevent progression. These are based on past sun exposure, future lifestyle changes and the daily use of emollient sunscreens, broad-brimmed hats and avoidance of sun exposure during the middle of the day. This is a service that is not undertaken as a matter of routine in general medical practice as patients are not seen with the regularity of dental patients and generally not under the ideal examination conditions available in the dental surgery.

  16. Rapid severing and motility of chloroplast-actin filaments are required for the chloroplast avoidance response in Arabidopsis.

    Science.gov (United States)

    Kong, Sam-Geun; Arai, Yoshiyuki; Suetsugu, Noriyuki; Yanagida, Toshio; Wada, Masamitsu

    2013-02-01

    Phototropins (phot1 and phot2 in Arabidopsis thaliana) relay blue light intensity information to the chloroplasts, which move toward weak light (the accumulation response) and away from strong light (the avoidance response). Chloroplast-actin (cp-actin) filaments are vital for mediating these chloroplast photorelocation movements. In this report, we examine in detail the cp-actin filament dynamics by which the chloroplast avoidance response is regulated. Although stochastic dynamics of cortical actin fragments are observed on the chloroplasts, the basic mechanisms underlying the disappearance (including severing and turnover) of the cp-actin filaments are regulated differently from those of cortical actin filaments. phot2 plays a pivotal role in the strong blue light-induced severing and random motility of cp-actin filaments, processes that are therefore essential for asymmetric cp-actin formation for the avoidance response. In addition, phot2 functions in the bundling of cp-actin filaments that is induced by dark incubation. By contrast, the function of phot1 is dispensable for these responses. Our findings suggest that phot2 is the primary photoreceptor involved in the rapid reorganization of cp-actin filaments that allows chloroplasts to change direction rapidly and control the velocity of the avoidance movement according to the light's intensity and position.

  17. The dynamic interplay between appraisal and core affect in daily life

    Directory of Open Access Journals (Sweden)

    Peter eKuppens

    2012-10-01

    Full Text Available Appraisals and core affect are both considered central to the experience of emotion. In this study we examine the bidirectional relationships between these two components of emotional experience by examining how core affect changes following how people appraise events and how appraisals in turn change following how they feel in daily life. In an experience sampling study, participants recorded their core affect and appraisals of ongoing events; data were analyzed using cross-lagged multilevel modeling. Valence-appraisal relationships were found to be characterized by congruency: The same appraisals that were associated with a change in pleasure-displeasure (motivational congruency, other-agency, coping potential, and future expectancy, changed themselves as a function of pleasure-displeasure. In turn, mainly secondary appraisals of who is responsible and how one is able to cope with events were associated with changes in arousal, which itself is followed by changes in the future appraised relevance of events. These results integrate core affect and appraisal approaches to emotion by demonstrating the dynamic interplay of how appraisals are followed by changes in core affect which in turn change our basis for judging future events.

  18. How volatilities nonlocal in time affect the price dynamics in complex financial systems.

    Science.gov (United States)

    Tan, Lei; Zheng, Bo; Chen, Jun-Jie; Jiang, Xiong-Fei

    2015-01-01

    What is the dominating mechanism of the price dynamics in financial systems is of great interest to scientists. The problem whether and how volatilities affect the price movement draws much attention. Although many efforts have been made, it remains challenging. Physicists usually apply the concepts and methods in statistical physics, such as temporal correlation functions, to study financial dynamics. However, the usual volatility-return correlation function, which is local in time, typically fluctuates around zero. Here we construct dynamic observables nonlocal in time to explore the volatility-return correlation, based on the empirical data of hundreds of individual stocks and 25 stock market indices in different countries. Strikingly, the correlation is discovered to be non-zero, with an amplitude of a few percent and a duration of over two weeks. This result provides compelling evidence that past volatilities nonlocal in time affect future returns. Further, we introduce an agent-based model with a novel mechanism, that is, the asymmetric trading preference in volatile and stable markets, to understand the microscopic origin of the volatility-return correlation nonlocal in time.

  19. How volatilities nonlocal in time affect the price dynamics in complex financial systems.

    Directory of Open Access Journals (Sweden)

    Lei Tan

    Full Text Available What is the dominating mechanism of the price dynamics in financial systems is of great interest to scientists. The problem whether and how volatilities affect the price movement draws much attention. Although many efforts have been made, it remains challenging. Physicists usually apply the concepts and methods in statistical physics, such as temporal correlation functions, to study financial dynamics. However, the usual volatility-return correlation function, which is local in time, typically fluctuates around zero. Here we construct dynamic observables nonlocal in time to explore the volatility-return correlation, based on the empirical data of hundreds of individual stocks and 25 stock market indices in different countries. Strikingly, the correlation is discovered to be non-zero, with an amplitude of a few percent and a duration of over two weeks. This result provides compelling evidence that past volatilities nonlocal in time affect future returns. Further, we introduce an agent-based model with a novel mechanism, that is, the asymmetric trading preference in volatile and stable markets, to understand the microscopic origin of the volatility-return correlation nonlocal in time.

  20. Spatial and spatiotemporal variation in metapopulation structure affects population dynamics in a passively dispersing arthropod.

    Science.gov (United States)

    De Roissart, Annelies; Wang, Shaopeng; Bonte, Dries

    2015-11-01

    The spatial and temporal variation in the availability of suitable habitat within metapopulations determines colonization-extinction events, regulates local population sizes and eventually affects local population and metapopulation stability. Insights into the impact of such a spatiotemporal variation on the local population and metapopulation dynamics are principally derived from classical metapopulation theory and have not been experimentally validated. By manipulating spatial structure in artificial metapopulations of the spider mite Tetranychus urticae, we test to which degree spatial (mainland-island metapopulations) and spatiotemporal variation (classical metapopulations) in habitat availability affects the dynamics of the metapopulations relative to systems where habitat is constantly available in time and space (patchy metapopulations). Our experiment demonstrates that (i) spatial variation in habitat availability decreases variance in metapopulation size and decreases density-dependent dispersal at the metapopulation level, while (ii) spatiotemporal variation in habitat availability increases patch extinction rates, decreases local population and metapopulation sizes and decreases density dependence in population growth rates. We found dispersal to be negatively density dependent and overall low in the spatial variable mainland-island metapopulation. This demographic variation subsequently impacts local and regional population dynamics and determines patterns of metapopulation stability. Both local and metapopulation-level variabilities are minimized in mainland-island metapopulations relative to classical and patchy ones.

  1. A new cable truss support system for coal roadways affected by dynamic pressure

    Institute of Scientific and Technical Information of China (English)

    Hong Yan; Fulian He

    2012-01-01

    The support of coal roadways is seriously affected by intense dynamic pressures.This can lead to problems with large deformation of the roof and the two side walls of coal roadways.Rapid convergence of the walls and roof,a high damage rate to the bolts and cables,or even abrupt roof collapse or rib spalling can occur during the service period of these coal roadways.Analyzing the main support measures used in China leads to a proposed new cable truss supporting system.Thorough study of the entire structure shows the superiority of this design for roadways suffering under dynamic pressure.A corresponding mechanical model of the rock surrounding the cable truss system is described in this paper and formulas for calculating pre-tightening forces of the truss cable,and the minimum anchoring forces,were deduced.The new support system was applied to a typical roadway affected by intensive dynamic pressure that is located in the Xinyuan Coal Mine.The results show that the largest subsidence of the roof was 97 mm,the convergence of the two sides was less than 248 mm,and the average depth of the loose,fractured layer was only 6.12 mm.This proves that the new support system is feasible and effective.

  2. Self-assembly of Artificial Actin Filaments

    Science.gov (United States)

    Grosenick, Christopher; Cheng, Shengfeng

    Actin Filaments are long, double-helical biopolymers that make up the cytoskeleton along with microtubules and intermediate filaments. In order to further understand the self-assembly process of these biopolymers, a model to recreate actin filament geometry was developed. A monomer in the shape of a bent rod with vertical and lateral binding sites was designed to assemble into single or double helices. With Molecular Dynamics simulations, a variety of phases were observed to form by varying the strength of the binding sites. Ignoring lateral binding sites, we have found a narrow range of binding strengths that lead to long single helices via various growth pathways. When lateral binding strength is introduced, double helices begin to form. These double helices self-assemble into substantially more stable structures than their single helix counterparts. We have found double helices to form long filaments at about half the vertical binding strength of single helices. Surprisingly, we have found that triple helices occasionally form, indicating the importance of structural regulation in the self-assembly of biopolymers.

  3. Yersinia effector YopO uses actin as bait to phosphorylate proteins that regulate actin polymerization.

    Science.gov (United States)

    Lee, Wei Lin; Grimes, Jonathan M; Robinson, Robert C

    2015-03-01

    Pathogenic Yersinia species evade host immune systems through the injection of Yersinia outer proteins (Yops) into phagocytic cells. One Yop, YopO, also known as YpkA, induces actin-filament disruption, impairing phagocytosis. Here we describe the X-ray structure of Yersinia enterocolitica YopO in complex with actin, which reveals that YopO binds to an actin monomer in a manner that blocks polymerization yet allows the bound actin to interact with host actin-regulating proteins. SILAC-MS and biochemical analyses confirm that actin-polymerization regulators such as VASP, EVL, WASP, gelsolin and the formin diaphanous 1 are directly sequestered and phosphorylated by YopO through formation of ternary complexes with actin. This leads to a model in which YopO at the membrane sequesters actin from polymerization while using the bound actin as bait to recruit, phosphorylate and misregulate host actin-regulating proteins to disrupt phagocytosis.

  4. A modified dynamic evolving neural-fuzzy approach to modeling customer satisfaction for affective design.

    Science.gov (United States)

    Kwong, C K; Fung, K Y; Jiang, Huimin; Chan, K Y; Siu, Kin Wai Michael

    2013-01-01

    Affective design is an important aspect of product development to achieve a competitive edge in the marketplace. A neural-fuzzy network approach has been attempted recently to model customer satisfaction for affective design and it has been proved to be an effective one to deal with the fuzziness and non-linearity of the modeling as well as generate explicit customer satisfaction models. However, such an approach to modeling customer satisfaction has two limitations. First, it is not suitable for the modeling problems which involve a large number of inputs. Second, it cannot adapt to new data sets, given that its structure is fixed once it has been developed. In this paper, a modified dynamic evolving neural-fuzzy approach is proposed to address the above mentioned limitations. A case study on the affective design of mobile phones was conducted to illustrate the effectiveness of the proposed methodology. Validation tests were conducted and the test results indicated that: (1) the conventional Adaptive Neuro-Fuzzy Inference System (ANFIS) failed to run due to a large number of inputs; (2) the proposed dynamic neural-fuzzy model outperforms the subtractive clustering-based ANFIS model and fuzzy c-means clustering-based ANFIS model in terms of their modeling accuracy and computational effort.

  5. A shift from exploitation to interference competition with increasing density affects population and community dynamics.

    Science.gov (United States)

    Holdridge, Erica M; Cuellar-Gempeler, Catalina; terHorst, Casey P

    2016-08-01

    Intraspecific competition influences population and community dynamics and occurs via two mechanisms. Exploitative competition is an indirect effect that occurs through use of a shared resource and depends on resource availability. Interference competition occurs by obstructing access to a resource and may not depend on resource availability. Our study tested whether the strength of interference competition changes with protozoa population density. We grew experimental microcosms of protozoa and bacteria under different combinations of protozoan density and basal resource availability. We then solved a dynamic predator-prey model for parameters of the functional response using population growth rates measured in our experiment. As population density increased, competition shifted from exploitation to interference, and competition was less dependent on resource levels. Surprisingly, the effect of resources was weakest when competition was the most intense. We found that at low population densities, competition was largely exploitative and resource availability had a large effect on population growth rates, but the effect of resources was much weaker at high densities. This shift in competitive mechanism could have implications for interspecific competition, trophic interactions, community diversity, and natural selection. We also tested whether this shift in the mechanism of competition with protozoa density affected the structure of the bacterial prey community. We found that both resources and protozoa density affected the structure of the bacterial prey community, suggesting that competitive mechanism may also affect trophic interactions.

  6. Mechanical Response of Single Filamin A (ABP-280) Molecules and Its Role in the Actin/Filamin A Gel

    Science.gov (United States)

    Sano, Ryoko; Furuike, Shou; Ito, Tadanao; Ohashi, Kazuyo; Yamazaki, Masahito

    2004-04-01

    Actin/filamin A gel plays important roles in mechanical response of cells. We found a force (50 to 220 pN)-induced unfolding of single filamin A molecules using AFM, and have proposed a hypothesis on the role of single filamin A in the novel property of viscoelasticity of actin/filamin A gel. We also investigated structure and its dynamics of actin/filamin A gel formed in a giant liposome using fluorescence microscopy.

  7. An actin cytoskeleton with evolutionarily conserved functions in the absence of canonical actin-binding proteins

    OpenAIRE

    Paredez, Alexander R.; Assaf, Zoe June; Sept, David; Timofejeva, Ljudmilla; Dawson, Scott C.; Wang, Chung-Ju Rachel; Cande, W. Z.

    2011-01-01

    Giardia intestinalis, a human intestinal parasite and member of what is perhaps the earliest-diverging eukaryotic lineage, contains the most divergent eukaryotic actin identified to date and is the first eukaryote known to lack all canonical actin-binding proteins (ABPs). We sought to investigate the properties and functions of the actin cytoskeleton in Giardia to determine whether Giardia actin (giActin) has reduced or conserved roles in core cellular processes. In vitro polymerization of gi...

  8. Actin-Dependent Alterations of Dendritic Spine Morphology in Shankopathies

    Science.gov (United States)

    Sarowar, Tasnuva

    2016-01-01

    Shank proteins (Shank1, Shank2, and Shank3) act as scaffolding molecules in the postsynaptic density of many excitatory neurons. Mutations in SHANK genes, in particular SHANK2 and SHANK3, lead to autism spectrum disorders (ASD) in both human and mouse models. Shank3 proteins are made of several domains—the Shank/ProSAP N-terminal (SPN) domain, ankyrin repeats, SH3 domain, PDZ domain, a proline-rich region, and the sterile alpha motif (SAM) domain. Via various binding partners of these domains, Shank3 is able to bind and interact with a wide range of proteins including modulators of small GTPases such as RICH2, a RhoGAP protein, and βPIX, a RhoGEF protein for Rac1 and Cdc42, actin binding proteins and actin modulators. Dysregulation of all isoforms of Shank proteins, but especially Shank3, leads to alterations in spine morphogenesis, shape, and activity of the synapse via altering actin dynamics. Therefore, here, we highlight the role of Shank proteins as modulators of small GTPases and, ultimately, actin dynamics, as found in multiple in vitro and in vivo models. The failure to mediate this regulatory role might present a shared mechanism in the pathophysiology of autism-associated mutations, which leads to dysregulation of spine morphogenesis and synaptic signaling.

  9. Rab11 and Actin Cytoskeleton Participate in Giardia lamblia Encystation, Guiding the Specific Vesicles to the Cyst Wall

    Science.gov (United States)

    Castillo-Romero, Araceli; Leon-Avila, Gloria; Wang, Ching C.; Perez Rangel, Armando; Camacho Nuez, Minerva; Garcia Tovar, Carlos; Ayala-Sumuano, Jorge Tonatiuh; Luna-Arias, Juan Pedro; Hernandez, Jose Manuel

    2010-01-01

    Background Giardia passes through two stages during its life cycle, the trophozoite and the cyst. Cyst formation involves the synthesis of cyst wall proteins (CWPs) and the transport of CWPs into encystation-specific vesicles (ESVs). Active vesicular trafficking is essential for encystation, but the molecular machinery driving vesicular trafficking remains unknown. The Rab proteins are involved in the targeting of vesicles to several intracellular compartments through their association with cytoskeletal motor proteins. Methodology and Principal Findings In this study, we found a relationship between Rab11 and the actin cytoskeleton in CWP1 transport. Confocal microscopy showed Rab11 was distributed throughout the entire trophozoite, while in cysts it was translocated to the periphery of the cell, where it colocalized with ESVs and microfilaments. Encystation was also accompanied by changes in rab11 mRNA expression. To evaluate the role of microfilaments in encystation, the cells were treated with latrunculin A. Scanning electron microscopy showed this treatment resulted in morphological damages to encysted parasites. The intensity of fluorescence-labeled Rab11 and CWP1 in ESVs and cyst walls was reduced, and rab11 and cwp1 mRNA levels were down-regulated. Furthermore, knocking down Rab11 with a hammerhead ribozyme resulted in an up to 80% down-regulation of rab11 mRNA. Although this knockdown did not appear lethal for trophozoites and did not affect cwp1 expression during the encystation, confocal images showed CWP1 was redistributed throughout the cytosol. Conclusions and Significance Our results indicate that Rab11 participates in the early and late encystation stages by regulating CWP1 localization and the actin-mediated transport of ESVs towards the periphery. In addition, alterations in the dynamics of actin affected rab11 and cwp1 expression. Our results provide new information about the molecules involved in Giardia encystation and suggest that Rab11 and

  10. Rab11 and actin cytoskeleton participate in Giardia lamblia encystation, guiding the specific vesicles to the cyst wall.

    Directory of Open Access Journals (Sweden)

    Araceli Castillo-Romero

    Full Text Available BACKGROUND: Giardia passes through two stages during its life cycle, the trophozoite and the cyst. Cyst formation involves the synthesis of cyst wall proteins (CWPs and the transport of CWPs into encystation-specific vesicles (ESVs. Active vesicular trafficking is essential for encystation, but the molecular machinery driving vesicular trafficking remains unknown. The Rab proteins are involved in the targeting of vesicles to several intracellular compartments through their association with cytoskeletal motor proteins. METHODOLOGY AND PRINCIPAL FINDINGS: In this study, we found a relationship between Rab11 and the actin cytoskeleton in CWP1 transport. Confocal microscopy showed Rab11 was distributed throughout the entire trophozoite, while in cysts it was translocated to the periphery of the cell, where it colocalized with ESVs and microfilaments. Encystation was also accompanied by changes in rab11 mRNA expression. To evaluate the role of microfilaments in encystation, the cells were treated with latrunculin A. Scanning electron microscopy showed this treatment resulted in morphological damages to encysted parasites. The intensity of fluorescence-labeled Rab11 and CWP1 in ESVs and cyst walls was reduced, and rab11 and cwp1 mRNA levels were down-regulated. Furthermore, knocking down Rab11 with a hammerhead ribozyme resulted in an up to 80% down-regulation of rab11 mRNA. Although this knockdown did not appear lethal for trophozoites and did not affect cwp1 expression during the encystation, confocal images showed CWP1 was redistributed throughout the cytosol. CONCLUSIONS AND SIGNIFICANCE: Our results indicate that Rab11 participates in the early and late encystation stages by regulating CWP1 localization and the actin-mediated transport of ESVs towards the periphery. In addition, alterations in the dynamics of actin affected rab11 and cwp1 expression. Our results provide new information about the molecules involved in Giardia encystation and

  11. Inertial forces affect fluid front displacement dynamics in a pore-throat network model.

    Science.gov (United States)

    Moebius, Franziska; Or, Dani

    2014-08-01

    The seemingly regular and continuous motion of fluid displacement fronts in porous media at the macroscopic scale is propelled by numerous (largely invisible) pore-scale abrupt interfacial jumps and pressure bursts. Fluid fronts in porous media are characterized by sharp phase discontinuities and by rapid pore-scale dynamics that underlie their motion; both attributes challenge standard continuum theories of these flow processes. Moreover, details of pore-scale dynamics affect front morphology and subsequent phase entrapment behind a front and thereby shape key macroscopic transport properties of the unsaturated zone. The study presents a pore-throat network model that focuses on quantifying interfacial dynamics and interactions along fluid displacement fronts. The porous medium is represented by a lattice of connected pore throats capable of detaining menisci and giving rise to fluid-fluid interfacial jumps (the study focuses on flow rate controlled drainage). For each meniscus along the displacement front we formulate a local inertial, capillary, viscous, and hydrostatic force balance that is then solved simultaneously for the entire front. The model enables systematic evaluation of the role of inertia and boundary conditions. Results show that while displacement patterns are affected by inertial forces mainly by invasion of throats with higher capillary resistance, phase entrapment (residual saturation) is largely unaffected by inertia, limiting inertial effects on hydrological properties behind a front. Interfacial jump velocities are often an order of magnitude larger than mean front velocity, are strongly dependent on geometrical throat dimensions, and become less predictable (more scattered) when inertia is considered. Model simulations of the distributions of capillary pressure fluctuations and waiting times between invasion events follow an exponential distribution and are in good agreement with experimental results. The modeling approach provides insights

  12. Salt—Water Dynamics in Highly Salinized Topsoil of Salt—Affected Soil During Water Infiltration

    Institute of Scientific and Technical Information of China (English)

    WANGXUE-FENG; YOUWEN-RUI; 等

    1991-01-01

    Continuous monitoring of salt and water movement in the soil profile of highly salinized topsoil under steadystate infiltration was conducted.It gives that salt and water dynamics during convection-diffusion period can be divided into three stages:1.formation of a salt peak,2.the salt peak moving downwards till the appearance of the summit of the salt peak,3.the salt peak moving further downwards with the peak value decreasing.Results show that the maximum salt peak appears at the same depth if soil texture and outflow condition are the same.Factors affecting salt and water movement and ion components in the outflow solution underinfiltration are discussed.

  13. Factors affecting the haptic filled-space illusion for dynamic touch.

    Science.gov (United States)

    Sanders, Abram F J; Kappers, Astrid M L

    2009-02-01

    In the haptic filled-space illusion for active dynamic touch, observers move their fingertip across an unfilled extent or an extent filled with intermediate stimulations. Previous researchers have reported lengths of filled extents to be overestimated, but the parameters affecting the strength of the illusion are still largely unknown. In the current research, we show that the illusion persists when intermediate stimulations do not provide information about the extent's length. In addition, the results show that the strength of the illusion increases with the number of filler elements. In contrast with earlier research, we control for movement speed differences between filled and unfilled extents. The results suggest that the strength of the illusion is independent of the overall average movement speed. Insight into factors affecting the strength of the illusion may provide a better understanding of the kinematic mechanisms underlying haptic length perception.

  14. An antifungal protein from Ginkgo biloba binds actin and can trigger cell death.

    Science.gov (United States)

    Gao, Ningning; Wadhwani, Parvesh; Mühlhäuser, Philipp; Liu, Qiong; Riemann, Michael; Ulrich, Anne S; Nick, Peter

    2016-07-01

    Ginkbilobin is a short antifungal protein that had been purified and cloned from the seeds of the living fossil Ginkgo biloba. Homologues of this protein can be detected in all seed plants and the heterosporic fern Selaginella and are conserved with respect to domain structures, peptide motifs, and specific cysteine signatures. To get insight into the cellular functions of these conserved motifs, we expressed green fluorescent protein fusions of full-length and truncated ginkbilobin in tobacco BY-2 cells. We show that the signal peptide confers efficient secretion of ginkbilobin. When this signal peptide is either cleaved or masked, ginkbilobin binds and visualizes the actin cytoskeleton. This actin-binding activity of ginkbilobin is mediated by a specific subdomain just downstream of the signal peptide, and this subdomain can also coassemble with actin in vitro. Upon stable overexpression of this domain, we observe a specific delay in premitotic nuclear positioning indicative of a reduced dynamicity of actin. To elucidate the cellular response to the binding of this subdomain to actin, we use chemical engineering based on synthetic peptides comprising different parts of the actin-binding subdomain conjugated with the cell-penetrating peptide BP100 and with rhodamine B as a fluorescent reporter. Binding of this synthetic construct to actin efficiently induces programmed cell death. We discuss these findings in terms of a working model, where ginkbilobin can activate actin-dependent cell death.

  15. Femtosecond pump-probe studies of actinic-wavelength dependence in aqueous chlorine dioxide photochemistry

    Science.gov (United States)

    Bixby, Teresa J.; Bolinger, Joshua C.; Patterson, Joshua D.; Reid, Philip J.

    2009-04-01

    The actinic or photolysis-wavelength dependence of aqueous chlorine dioxide (OClO) photochemistry is investigated using femtosecond pump-probe spectroscopy. Following photoexcitation at 310, 335, and 410 nm the photoinduced evolution in optical density is measured from the UV to the near IR. Analysis of the optical-density evolution illustrates that the quantum yield for atomic chlorine production (ΦCl) increases with actinic energy, with ΦCl=0.16±0.02 for 410 nm excitation and increasing to 0.25±0.01 and 0.54±0.10 for 335 and 310 nm excitations, respectively. Consistent with previous studies, the production of Cl occurs through two channels, with one channel corresponding to prompt (<5 ps) Cl formation and the other corresponding to the thermal decomposition of ClOO formed by OClO photoisomerization. The partitioning between Cl production channels is dependent on actinic energy, with prompt Cl production enhanced with an increase in actinic energy. Limited evidence is found for enhanced ClO production with an increase in actinic energy. Stimulated emission and excited-state absorption features associated with OClO populating the optically prepared A22 surface decrease with an increase in actinic energy suggesting that the excited-state decay dynamics are also actinic energy dependent. The studies presented here provide detailed information on the actinic-wavelength dependence of OClO photochemistry in aqueous solution.

  16. Drosophila Fascin is a novel downstream target of prostaglandin signaling during actin remodeling.

    Science.gov (United States)

    Groen, Christopher M; Spracklen, Andrew J; Fagan, Tiffany N; Tootle, Tina L

    2012-12-01

    Although prostaglandins (PGs)-lipid signals produced downstream of cyclooxygenase (COX) enzymes-regulate actin cytoskeletal dynamics, their mechanisms of action are unknown. We previously established Drosophila oogenesis, in particular nurse cell dumping, as a new model to determine how PGs regulate actin remodeling. PGs, and thus the Drosophila COX-like enzyme Pxt, are required for both the parallel actin filament bundle formation and the cortical actin strengthening required for dumping. Here we provide the first link between Fascin (Drosophila Singed, Sn), an actin-bundling protein, and PGs. Loss of either pxt or fascin results in similar actin defects. Fascin interacts, both pharmacologically and genetically, with PGs, as reduced Fascin levels enhance the effects of COX inhibition and synergize with reduced Pxt levels to cause both parallel bundle and cortical actin defects. Conversely, overexpression of Fascin in the germline suppresses the effects of COX inhibition and genetic loss of Pxt. These data lead to the conclusion that PGs regulate Fascin to control actin remodeling. This novel interaction has implications beyond Drosophila, as both PGs and Fascin-1, in mammalian systems, contribute to cancer cell migration and invasion.

  17. The Actin-Binding Protein α-Adducin Is Required for Maintaining Axon Diameter

    Directory of Open Access Journals (Sweden)

    Sérgio Carvalho Leite

    2016-04-01

    Full Text Available The actin-binding protein adducin was recently identified as a component of the neuronal subcortical cytoskeleton. Here, we analyzed mice lacking adducin to uncover the function of this protein in actin rings. α-adducin knockout mice presented progressive axon enlargement in the spinal cord and optic and sciatic nerves, followed by axon degeneration and loss. Using stimulated emission depletion super-resolution microscopy, we show that a periodic subcortical actin cytoskeleton is assembled in every neuron type inspected including retinal ganglion cells and dorsal root ganglia neurons. In neurons devoid of adducin, the actin ring diameter increased, although the inter-ring periodicity was maintained. In vitro, the actin ring diameter adjusted as axons grew, suggesting the lattice is dynamic. Our data support a model in which adducin activity is not essential for actin ring assembly and periodicity but is necessary to control the diameter of both actin rings and axons and actin filament growth within rings.

  18. THRUMIN1 is a light-regulated actin-bundling protein involved in chloroplast motility.

    Science.gov (United States)

    Whippo, Craig W; Khurana, Parul; Davis, Phillip A; DeBlasio, Stacy L; DeSloover, Daniel; Staiger, Christopher J; Hangarter, Roger P

    2011-01-11

    Chloroplast movement in response to changing light conditions optimizes photosynthetic light absorption. This repositioning is stimulated by blue light perceived via the phototropin photoreceptors and is transduced to the actin cytoskeleton. Some actin-based motility systems use filament reorganizations rather than myosin-based translocations. Recent research favors the hypothesis that chloroplast movement is driven by actin reorganization at the plasma membrane, but no proteins affecting chloroplast movements have been shown to associate with both the plasma membrane and actin filaments in vivo. Here we identified THRUMIN1 as a critical link between phototropin photoreceptor activity at the plasma membrane and actin-dependent chloroplast movements. THRUMIN1 bundles filamentous actin in vitro, and it localizes to the plasma membrane and displays light- and phototropin-dependent localization to microfilaments in vivo. These results suggest that phototropin-induced actin bundling via THRUMIN1 is important for chloroplast movement. A mammalian homolog of THRUMIN1, GRXCR1, has been implicated in auditory responses and hair cell stereocilla development as a regulator of actin architecture. Studies of THRUMIN1 will help elucidate the function of this family of eukaryotic proteins.

  19. Dynamical response of dark matter to galaxy evolution affects direct-detection experiments

    Science.gov (United States)

    Petersen, Michael S.; Katz, Neal; Weinberg, Martin D.

    2016-12-01

    Over a handful of rotation periods, dynamical processes in barred galaxies induce nonaxisymmetric structure in dark matter halos. Using n -body simulations of a Milky Way-like barred galaxy, we identify both a trapped dark matter component, a shadow bar, and a strong response wake in the dark matter distribution that affects the predicted dark matter detection rates for current experiments. The presence of a baryonic disk, together with well-known dynamical processes (e.g. spiral structure and bar instabilities), increases the dark matter density in the disk plane. We find that the magnitude of the combined stellar and shadow bar evolution, when isolated from the effect of the axisymmetric gravitational potential of the disk, accounts for >30 % of this overall increase in disk-plane density. This is significantly larger than that of previously claimed deviations from the standard halo model. The dark matter density and kinematic wakes driven by the Milky Way bar increase the detectability of dark matter overall, especially for the experiments with higher vmin . These astrophysical features increase the detection rate by more than a factor of 2 when compared to the standard halo model and by a factor of 10 for experiments with high minimum recoil energy thresholds. These same features increase (decrease) the annual modulation for low (high) minimum recoil energy experiments. We present physical arguments for why these dynamics are generic for barred galaxies such as the Milky Way rather than contingent on a specific galaxy model.

  20. Asymmetrical loading affects intersegmental dynamics during the swing phase of walking.

    Science.gov (United States)

    Smith, Jeremy D; Royer, Todd D; Martin, Philip E

    2013-08-01

    Much of the work related to lower extremity inertia manipulations has focused on temporal, kinematic and traditional inverse dynamics assessments during locomotion. Intersegmental dynamics is an analytical technique that provides further insights into mechanisms underlying linked-segment motion. The purpose of this study was to determine how intersegmental dynamics during the swing phase of walking are altered during asymmetrical lower extremity loading. Participants walked overground at a speed of 1.57 ms(-1) with 0, 0.5, 1.0, and 2.0 kg attached to one foot. Net, interaction, gravitational, and muscle moments were computed. Moment magnitudes at joints of the loaded leg increased systematically with increasing load, whereas unloaded leg moments were unaffected by loading. With increasing load, relative contributions of interaction moments about the knee and hip and gravitational moment about the ankle increased (i.e., 21%, 8%, and 44% increases, respectively), whereas the relative contributions of muscle moments about all three joints declined (i.e., -4%, -13%, and -8% decreases for the ankle, knee, and hip, respectively for unloaded vs. 2.0 kg). These results suggest that altered inertia properties of the limb not only affected the amount of muscular effort required to swing the leg, but also changed the nature of the interaction between segments.

  1. Molecular dynamics simulation of heat-affected zone of copper metal ablated with femtosecond laser

    Science.gov (United States)

    Hirayama, Yoichi; Obara, Minoru

    2005-03-01

    Femtosecond laser ablation of materials with high thermal conductivity is of paramount importance, because the chemical composition and properties of the area ablated with femtosecond laser are kept unchanged. The material processing by femtosecond laser can well control the heat-affected zone, compared to nanosecond laser ablation. We report on the heat-affected zone of crystalline copper (Cu) by use of femtosecond laser experimentally and theoretically. Laser ablation of Cu is investigated theoretically by two temperature model and molecular dynamics (MD) simulation. The MD simulation takes into account of electron temperature and thermal diffusion length calculated by two temperature model. The dependence of lattice temperature on time and depth is calculated by the MD simulation and two temperature model. The heat-affected zone estimated from the temperature is mainly studied and calculated to be 3 nm at 0.02 J/cm2 which is below the threshold fluence of 0.137 J/cm2. In addition, the thickness of heat-affected zone of copper crystal ablated with femtosecond Ti:sapphire laser is experimentally studied. As a result of X-ray diffraction (XRD) of the ablated surface, the surface crystallinity is partially changed into disordered structure from crystal form. The residual energy left in the metal, which is not used for ablation, will induce liquid phase, leading to the amorphous phase of the metal during resolidification. The thickness of heat-affected zone depends on laser fluence and is experimentally measured to be less than 1 μm at higher laser fluences than the ablation threshold.

  2. Can ocean acidification affect population dynamics of the barnacle Semibalanus balanoides at its southern range edge?

    Science.gov (United States)

    Findlay, Helen S; Burrows, Michael T; Kendall, Michael A; Spicer, John I; Widdicombe, Stephen

    2010-10-01

    The global ocean and atmosphere are warming. There is increasing evidence suggesting that, in addition to other environmental factors, climate change is affecting species distributions and local population dynamics. Additionally, as a consequence of the growing levels of atmospheric carbon dioxide (CO2), the oceans are taking up increasing amounts of this CO2, causing ocean pH to decrease (ocean acidification). The relative impacts of ocean acidification on population dynamics have yet to be investigated, despite many studies indicating that there will be at least a sublethal impact on many marine organisms, particularly key calcifying organisms. Using empirical data, we forced a barnacle (Semibalanus balanoides) population model to investigate the relative influence of sea surface temperature (SST) and ocean acidification on a population nearing the southern limit of its geographic distribution. Hindcast models were compared to observational data from Cellar Beach (southwestern United Kingdom). Results indicate that a declining pH trend (-0.0017 unit/yr), indicative of ocean acidification over the past 50 years, does not cause an observable impact on the population abundance relative to changes caused by fluctuations in temperature. Below the critical temperature (here T(crit) = 13.1 degrees C), pH has a more significant affect on population dynamics at this southern range edge. However, above this value, SST has the overriding influence. At lower SST, a decrease in pH (according to the National Bureau of Standards, pHNBs) from 8.2 to 7.8 can significantly decrease the population abundance. The lethal impacts of ocean acidification observed in experiments on early life stages reduce cumulative survival by approximately 25%, which again will significantly alter the population level at this southern limit. Furthermore, forecast predictions from this model suggest that combined acidification and warming cause this local population to die out 10 years earlier than

  3. Decreased summer drought affects plant productivity and soil carbon dynamics in a Mediterranean woodland

    Directory of Open Access Journals (Sweden)

    M. F. Cotrufo

    2011-09-01

    Full Text Available Precipitation patterns are expected to change in the Mediterranean region within the next decades, with projected decreases in total rainfall and increases in extreme events. We manipulated precipitation patterns in a Mediterranean woodland, dominated by Arbutus unedo L., to study the effects of changing precipitation regimes on above-ground net primary production (ANPP and soil C dynamics, specifically plant-derived C input to soil and soil respiration (SR. Experimental plots were exposed to either a 20 % reduction of throughfall or to water addition targeted at maintaining soil water content above a minimum of 10 % v/v. Treatments were compared to control plots which received ambient precipitation. Enhanced soil moisture during summer months highly stimulated annual stem primary production, litter fall, SR and net annual plant-derived C input to soil which on average increased by 130 %, 26 %, 58 % and 220 %, respectively, as compared to the control. In contrast, the 20 % reduction in throughfall (equivalent to 10 % reduction in precipitation did not significantly change soil moisture at the site, and therefore did not significantly affect ANPP or SR. We conclude that minor changes (around 10 % reduction in precipitation amount are not likely to significantly affect ANPP or soil C dynamics in Mediterranean woodlands. However, if summer rain increases, C cycling will significantly accelerate but soil C stocks are not likely to be changed in the short-term. More studies involving modelling of long-term C dynamics are needed to predict if the estimated increases in soil C input under wet conditions is going to be sustained and if labile C is being substituted to stable C, with a negative effect on long-term soil C stocks.

  4. The actin multigene family of Paramecium tetraurelia

    Directory of Open Access Journals (Sweden)

    Wagner Erika

    2007-03-01

    Full Text Available Abstract Background A Paramecium tetraurelia pilot genome project, the subsequent sequencing of a Megabase chromosome as well as the Paramecium genome project aimed at gaining insight into the genome of Paramecium. These cells display a most elaborate membrane trafficking system, with distinct, predictable pathways in which actin could participate. Previously we had localized actin in Paramecium; however, none of the efforts so far could proof the occurrence of actin in the cleavage furrow of a dividing cell, despite the fact that actin is unequivocally involved in cell division. This gave a first hint that Paramecium may possess actin isoforms with unusual characteristics. The genome project gave us the chance to search the whole Paramecium genome, and, thus, to identify and characterize probably all actin isoforms in Paramecium. Results The ciliated protozoan, P. tetraurelia, contains an actin multigene family with at least 30 members encoding actin, actin-related and actin-like proteins. They group into twelve subfamilies; a large subfamily with 10 genes, seven pairs and one trio with > 82% amino acid identity, as well as three single genes. The different subfamilies are very distinct from each other. In comparison to actins in other organisms, P. tetraurelia actins are highly divergent, with identities topping 80% and falling to 30%. We analyzed their structure on nucleotide level regarding the number and position of introns. On amino acid level, we scanned the sequences for the presence of actin consensus regions, for amino acids of the intermonomer interface in filaments, for residues contributing to ATP binding, and for known binding sites for myosin and actin-specific drugs. Several of those characteristics are lacking in several subfamilies. The divergence of P. tetraurelia actins and actin-related proteins between different P. tetraurelia subfamilies as well as with sequences of other organisms is well represented in a phylogenetic

  5. Mastoid vibration affects dynamic postural control during gait in healthy older adults

    Science.gov (United States)

    Chien, Jung Hung; Mukherjee, Mukul; Kent, Jenny; Stergiou, Nicholas

    2017-01-01

    Vestibular disorders are difficult to diagnose early due to the lack of a systematic assessment. Our previous work has developed a reliable experimental design and the result shows promising results that vestibular sensory input while walking could be affected through mastoid vibration (MV) and changes are in the direction of motion. In the present paper, we wanted to extend this work to older adults and investigate how manipulating sensory input through mastoid vibration (MV) could affect dynamic postural control during walking. Three levels of MV (none, unilateral, and bilateral) applied via vibrating elements placed on the mastoid processes were combined with the Locomotor Sensory Organization Test (LSOT) paradigm to challenge the visual and somatosensory systems. We hypothesized that the MV would affect sway variability during walking in older adults. Our results revealed that MV significantly not only increased the amount of sway variability but also decreased the temporal structure of sway variability only in anterior-posterior direction. Importantly, the bilateral MV stimulation generally produced larger effects than the unilateral. This is an important finding that confirmed our experimental design and the results produced could guide a more reliable screening of vestibular system deterioration. PMID:28128341

  6. Mastoid vibration affects dynamic postural control during gait in healthy older adults

    Science.gov (United States)

    Chien, Jung Hung; Mukherjee, Mukul; Kent, Jenny; Stergiou, Nicholas

    2017-01-01

    Vestibular disorders are difficult to diagnose early due to the lack of a systematic assessment. Our previous work has developed a reliable experimental design and the result shows promising results that vestibular sensory input while walking could be affected through mastoid vibration (MV) and changes are in the direction of motion. In the present paper, we wanted to extend this work to older adults and investigate how manipulating sensory input through mastoid vibration (MV) could affect dynamic postural control during walking. Three levels of MV (none, unilateral, and bilateral) applied via vibrating elements placed on the mastoid processes were combined with the Locomotor Sensory Organization Test (LSOT) paradigm to challenge the visual and somatosensory systems. We hypothesized that the MV would affect sway variability during walking in older adults. Our results revealed that MV significantly not only increased the amount of sway variability but also decreased the temporal structure of sway variability only in anterior-posterior direction. Importantly, the bilateral MV stimulation generally produced larger effects than the unilateral. This is an important finding that confirmed our experimental design and the results produced could guide a more reliable screening of vestibular system deterioration.

  7. Plant villin, lily P-135-ABP, possesses G-actin binding activity and accelerates the polymerization and depolymerization of actin in a Ca2+-sensitive manner.

    Science.gov (United States)

    Yokota, Etsuo; Tominaga, Motoki; Mabuchi, Issei; Tsuji, Yasunori; Staiger, Christopher J; Oiwa, Kazuhiro; Shimmen, Teruo

    2005-10-01

    From germinating pollen of lily, two types of villins, P-115-ABP and P-135-ABP, have been identified biochemically. Ca(2+)-CaM-dependent actin-filament binding and bundling activities have been demonstrated for both villins previously. Here, we examined the effects of lily villins on the polymerization and depolymerization of actin. P-115-ABP and P-135-ABP present in a crude protein extract prepared from germinating pollen bound to a DNase I affinity column in a Ca(2+)-dependent manner. Purified P-135-ABP reduced the lag period that precedes actin filament polymerization from monomers in the presence of either Ca(2+) or Ca(2+)-CaM. These results indicated that P-135-ABP can form a complex with G-actin in the presence of Ca(2+) and this complex acts as a nucleus for polymerization of actin filaments. However, the nucleation activity of P-135-ABP is probably not relevant in vivo because the assembly of G-actin saturated with profilin, a situation that mimics conditions found in pollen, was not accelerated in the presence of P-135-ABP. P-135-ABP also enhanced the depolymerization of actin filaments during dilution-mediated disassembly. Growth from filament barbed ends in the presence of Ca(2+)-CaM was also prevented, consistent with filament capping activity. These results suggested that lily villin is involved not only in the arrangement of actin filaments into bundles in the basal and shank region of the pollen tube, but also in regulating and modulating actin dynamics through its capping and depolymerization (or fragmentation) activities in the apical region of the pollen tube, where there is a relatively high concentration of Ca(2+).

  8. Mesoscopic model of actin-based propulsion.

    Directory of Open Access Journals (Sweden)

    Jie Zhu

    Full Text Available Two theoretical models dominate current understanding of actin-based propulsion: microscopic polymerization ratchet model predicts that growing and writhing actin filaments generate forces and movements, while macroscopic elastic propulsion model suggests that deformation and stress of growing actin gel are responsible for the propulsion. We examine both experimentally and computationally the 2D movement of ellipsoidal beads propelled by actin tails and show that neither of the two models can explain the observed bistability of the orientation of the beads. To explain the data, we develop a 2D hybrid mesoscopic model by reconciling these two models such that individual actin filaments undergoing nucleation, elongation, attachment, detachment and capping are embedded into the boundary of a node-spring viscoelastic network representing the macroscopic actin gel. Stochastic simulations of this 'in silico' actin network show that the combined effects of the macroscopic elastic deformation and microscopic ratchets can explain the observed bistable orientation of the actin-propelled ellipsoidal beads. To test the theory further, we analyze observed distribution of the curvatures of the trajectories and show that the hybrid model's predictions fit the data. Finally, we demonstrate that the model can explain both concave-up and concave-down force-velocity relations for growing actin networks depending on the characteristic time scale and network recoil. To summarize, we propose that both microscopic polymerization ratchets and macroscopic stresses of the deformable actin network are responsible for the force and movement generation.

  9. The design of MACs (minimal actin cortices).

    Science.gov (United States)

    Vogel, Sven K; Heinemann, Fabian; Chwastek, Grzegorz; Schwille, Petra

    2013-11-01

    The actin cell cortex in eukaryotic cells is a key player in controlling and maintaining the shape of cells, and in driving major shape changes such as in cytokinesis. It is thereby constantly being remodeled. Cell shape changes require forces acting on membranes that are generated by the interplay of membrane coupled actin filaments and assemblies of myosin motors. Little is known about how their interaction regulates actin cell cortex remodeling and cell shape changes. Because of the vital importance of actin, myosin motors and the cell membrane, selective in vivo experiments and manipulations are often difficult to perform or not feasible. Thus, the intelligent design of minimal in vitro systems for actin-myosin-membrane interactions could pave a way for investigating actin cell cortex mechanics in a detailed and quantitative manner. Here, we present and discuss the design of several bottom-up in vitro systems accomplishing the coupling of actin filaments to artificial membranes, where key parameters such as actin densities and membrane properties can be varied in a controlled manner. Insights gained from these in vitro systems may help to uncover fundamental principles of how exactly actin-myosin-membrane interactions govern actin cortex remodeling and membrane properties for cell shape changes.

  10. Structure and stability of self-assembled actin-lysozyme complexes in salty water.

    Science.gov (United States)

    Sanders, Lori K; Guáqueta, Camilo; Angelini, Thomas E; Lee, Jae-Wook; Slimmer, Scott C; Luijten, Erik; Wong, Gerard C L

    2005-09-02

    Interactions between actin, an anionic polyelectrolyte, and lysozyme, a cationic globular protein, have been examined using a combination of synchrotron small-angle x-ray scattering and molecular dynamics simulations. Lysozyme initially bridges pairs of actin filaments, which relax into hexagonally coordinated columnar complexes comprised of actin held together by incommensurate one-dimensional close-packed arrays of lysozyme macroions. These complexes are found to be stable even in the presence of significant concentrations of monovalent salt, which is quantitatively explained from a redistribution of salt between the condensed and the aqueous phases.

  11. Prokaryotic DNA segregation by an actin-like filament

    DEFF Research Database (Denmark)

    Møller-Jensen, Jakob; Bugge Jensen, Rasmus; Löwe, Jan;

    2002-01-01

    The mechanisms responsible for prokaryotic DNA segregation are largely unknown. The partitioning locus (par) encoded by the Escherichia coli plasmid R1 actively segregates its replicon to daughter cells. We show here that the ParM ATPase encoded by par forms dynamic actin-like filaments with prop......The mechanisms responsible for prokaryotic DNA segregation are largely unknown. The partitioning locus (par) encoded by the Escherichia coli plasmid R1 actively segregates its replicon to daughter cells. We show here that the ParM ATPase encoded by par forms dynamic actin-like filaments...... point for ParM polymerization. Hence, we provide evidence for a simple prokaryotic analogue of the eukaryotic mitotic spindle apparatus....

  12. ATP-dependent regulation of actin monomer-filament equilibrium by cyclase-associated protein and ADF/cofilin.

    Science.gov (United States)

    Nomura, Kazumi; Ono, Shoichiro

    2013-07-15

    CAP (cyclase-associated protein) is a conserved regulator of actin filament dynamics. In the nematode Caenorhabditis elegans, CAS-1 is an isoform of CAP that is expressed in striated muscle and regulates sarcomeric actin assembly. In the present study, we report that CAS-2, a second CAP isoform in C. elegans, attenuates the actin-monomer-sequestering effect of ADF (actin depolymerizing factor)/cofilin to increase the steady-state levels of actin filaments in an ATP-dependent manner. CAS-2 binds to actin monomers without a strong preference for either ATP- or ADP-actin. CAS-2 strongly enhances the exchange of actin-bound nucleotides even in the presence of UNC-60A, a C. elegans ADF/cofilin that inhibits nucleotide exchange. UNC-60A induces the depolymerization of actin filaments and sequesters actin monomers, whereas CAS-2 reverses the monomer-sequestering effect of UNC-60A in the presence of ATP, but not in the presence of only ADP or the absence of ATP or ADP. A 1:100 molar ratio of CAS-2 to UNC-60A is sufficient to increase actin filaments. CAS-2 has two independent actin-binding sites in its N- and C-terminal halves, and the C-terminal half is necessary and sufficient for the observed activities of the full-length CAS-2. These results suggest that CAS-2 (CAP) and UNC-60A (ADF/cofilin) are important in the ATP-dependent regulation of the actin monomer-filament equilibrium.

  13. The C-terminal dimerization motif of cyclase-associated protein is essential for actin monomer regulation.

    Science.gov (United States)

    Iwase, Shohei; Ono, Shoichiro

    2016-12-01

    Cyclase-associated protein (CAP) is a conserved actin-regulatory protein that functions together with actin depolymerizing factor (ADF)/cofilin to enhance actin filament dynamics. CAP has multiple functional domains, and the function to regulate actin monomers is carried out by its C-terminal half containing a Wiskott-Aldrich Syndrome protein homology 2 (WH2) domain, a CAP and X-linked retinitis pigmentosa 2 (CARP) domain, and a dimerization motif. WH2 and CARP are implicated in binding to actin monomers and important for enhancing filament turnover. However, the role of the dimerization motif is unknown. Here, we investigated the function of the dimerization motif of CAS-2, a CAP isoform in the nematode Caenorhabditis elegans, in actin monomer regulation. CAS-2 promotes ATP-dependent recycling of ADF/cofilin-bound actin monomers for polymerization by enhancing exchange of actin-bound nucleotides. The C-terminal half of CAS-2 (CAS-2C) has nearly as strong activity as full-length CAS-2. Maltose-binding protein (MBP)-tagged CAS-2C is a dimer. However, MBP-CAS-2C with a truncation of either one or two C-terminal β-strands is monomeric. Truncations of the dimerization motif in MBP-CAS-2C nearly completely abolish its activity to sequester actin monomers from polymerization and enhance nucleotide exchange on actin monomers. As a result, these CAS-2C variants, also in the context of full-length CAS-2, fail to compete with ADF/cofilin to release actin monomers for polymerization. CAS-2C variants lacking the dimerization motif exhibit enhanced binding to actin filaments, which is mediated by WH2. Taken together, these results suggest that the evolutionarily conserved dimerization motif of CAP is essential for its C-terminal region to exert the actin monomer-specific regulatory function.

  14. TIRF microscopy analysis of human Cof1, Cof2, and ADF effects on actin filament severing and turnover.

    Science.gov (United States)

    Chin, Samantha M; Jansen, Silvia; Goode, Bruce L

    2016-04-24

    Dynamic remodeling and turnover of cellular actin networks requires actin filament severing by actin-depolymerizing factor (ADF)/Cofilin proteins. Mammals express three different ADF/Cofilins (Cof1, Cof2, and ADF), and genetic studies suggest that in vivo they perform both overlapping and unique functions. To gain mechanistic insights into their different roles, we directly compared their G-actin and F-actin binding affinities, and quantified the actin filament severing activities of human Cof1, Cof2, and ADF using in vitro total internal reflection fluorescence microscopy. All three ADF/Cofilins had similar affinities for G-actin and F-actin. However, Cof2 and ADF severed filaments much more efficiently than Cof1 at both lower and higher concentrations and using either muscle or platelet actin. Furthermore, Cof2 and ADF were more effective than Cof1 in promoting "enhanced disassembly" when combined with actin disassembly co-factors Coronin-1B and actin-interacting protein 1 (AIP1), and these differences were observed on both preformed and actively growing filaments. To probe the mechanism underlying these differences, we used multi-wavelength total internal reflection fluorescence microscopy to directly observe Cy3-Cof1 and Cy3-Cof2 interacting with actin filaments in real time during severing. Cof1 and Cof2 each bound to filaments with similar kinetics, yet Cof2 induced severing much more rapidly than Cof1, decreasing the time interval between initial binding on a filament and severing at the same location. These differences in ADF/Cofilin activities and mechanisms may be used in cells to tune filament turnover rates, which can vary widely for different actin structures.

  15. Expression of type I collagen and tenascin C is regulated by actin polymerization through MRTF in dedifferentiated chondrocytes.

    Science.gov (United States)

    Parreno, Justin; Raju, Sneha; Niaki, Mortah Nabavi; Andrejevic, Katarina; Jiang, Amy; Delve, Elizabeth; Kandel, Rita

    2014-10-16

    This study examined actin regulation of fibroblast matrix genes in dedifferentiated chondrocytes. We demonstrated that dedifferentiated chondrocytes exhibit increased actin polymerization, nuclear localization of myocardin related transcription factor (MRTF), increased type I collagen (col1) and tenascin C (Tnc) gene expression, and decreased Sox9 gene expression. Induction of actin depolymerization by latrunculin treatment or cell rounding, reduced MRTF nuclear localization, repressed col1 and Tnc expression, and increased Sox9 gene expression in dedifferentiated chondrocytes. Treatment of passaged chondrocytes with MRTF inhibitor repressed col1 and Tnc expression, but did not affect Sox9 expression. Our results show that actin polymerization regulates fibroblast matrix gene expression through MRTF in passaged chondrocytes.

  16. Actin filament attachments for sustained motility in vitro are maintained by filament bundling.

    Directory of Open Access Journals (Sweden)

    Xiaohua Hu

    Full Text Available We reconstructed cellular motility in vitro from individual proteins to investigate how actin filaments are organized at the leading edge. Using total internal reflection fluorescence microscopy of actin filaments, we tested how profilin, Arp2/3, and capping protein (CP function together to propel thin glass nanofibers or beads coated with N-WASP WCA domains. Thin nanofibers produced wide comet tails that showed more structural variation in actin filament organization than did bead substrates. During sustained motility, physiological concentrations of Mg(2+ generated actin filament bundles that processively attached to the nanofiber. Reduction of total Mg(2+ abolished particle motility and actin attachment to the particle surface without affecting actin polymerization, Arp2/3 nucleation, or filament capping. Analysis of similar motility of microspheres showed that loss of filament bundling did not affect actin shell formation or symmetry breaking but eliminated sustained attachments between the comet tail and the particle surface. Addition of Mg(2+, Lys-Lys(2+, or fascin restored both comet tail attachment and sustained particle motility in low Mg(2+ buffers. TIRF microscopic analysis of filaments captured by WCA-coated beads in the absence of Arp2/3, profilin, and CP showed that filament bundling by polycation or fascin addition increased barbed end capture by WCA domains. We propose a model in which CP directs barbed ends toward the leading edge and polycation-induced filament bundling sustains processive barbed end attachment to the leading edge.

  17. Does Climate Change Mitigation Activity Affect Crude Oil Prices? Evidence from Dynamic Panel Model

    Directory of Open Access Journals (Sweden)

    Jude C. Dike

    2014-01-01

    Full Text Available This paper empirically investigates how climate change mitigation affects crude oil prices while using carbon intensity as the indicator for climate change mitigation. The relationship between crude oil prices and carbon intensity is estimated using an Arellano and Bond GMM dynamic panel model. This study undertakes a regional-level analysis because of the geographical similarities among the countries in a region. Regions considered for the study are Africa, Asia and Oceania, Central and South America, the EU, the Middle East, and North America. Results show that there is a positive relationship between crude oil prices and carbon intensity, and a 1% change in carbon intensity is expected to cause about 1.6% change in crude oil prices in the short run and 8.4% change in crude oil prices in the long run while the speed of adjustment is 19%.

  18. Evaluation of actinic cheilitis using fluorescence lifetime spectroscopy

    Science.gov (United States)

    Saito Nogueira, Marcelo; Cosci, Alessandro; Pratavieira, Sebastião.; Takahama, Ademar; Souza Azevedo, Rebeca; Kurachi, Cristina

    2016-03-01

    Actinic cheilitis is a potentially malignant disorder that mostly affects the vermilion border of the lower lip and can lead to squamous cell carcinoma. Because of its heterogeneous clinical aspect, it is difficult to indicate representative biopsy area. Late diagnosis is a limiting factor of therapeutic possibilities available to treat oral cancer. The diagnosis of actinic cheilitis is mainly based on clinical and histopathological analysis and it is a time consuming procedure to get the results. Information about the organization and chemical composition of the tissues can be obtained using fluorescence lifetime spectroscopy techniques without the need for biopsy. The main targeted fluorophores are NADH (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide), which have free and bound states, each one with different average lifetimes. The average lifetimes for free and bound NADH and FAD change according to tissue metabolic alterations and allow a quick and non-invasive clinical investigation of injuries and to help clinicians with the early diagnosis of actinic cheilitis. This study aims to evaluate the fluorescence lifetime parameters at the discrimination of three degrees of epithelial dysplasia, the most important predictor of malignant development, described in up to 100% of actinic cheilitis cases.

  19. Actin gene family in Branchiostoma belched

    Institute of Scientific and Technical Information of China (English)

    2016-01-01

    Actin is a highly conserved cytoskeletal protein that is found in essentially all eukaryotic cells,which plays a paramount role in several basic functions of the organism, such as the maintenance of cellshape, cell division, cell mobility and muscle contraction. However, little is known about actin gene family inChinese amphioxus (Branchiostoma belcheri). Here we systemically analyzed the actin genes family inBranchiostoma belched and found that amphioxus contains 33 actin genes. These genes have undergoneextensive expansion through tandem duplications by phylogenetic analysis. In addition, we also providedevidence indicating that actin genes have divergent functions by specializing their EST data in both Bran-chiostoma belched and Branchiostoma florida. Our results provided an alternative explanation for the evolu-tion of actin genes, and gave new insights into their functional roles.

  20. Functional characterization of skeletal F-actin labeled on the NH2-terminal segment of residues 1-28.

    Science.gov (United States)

    Bertrand, R; Chaussepied, P; Audemard, E; Kassab, R

    1989-05-15

    Rabbit skeletal alpha-actin was covalently labeled in the filamentous state by the fluorescent nucleophile, N-(5-sulfo-1-naphthyl)ethylenediamine (EDANS) in the presence of the carboxyl group activator 1-(3-dimethyl-aminopropyl)-3-ethylcarbodiimide (EDC). The coupling reaction was continued until the incorporation of nearly 1 mol EDANS/mol actin. After limited proteolytic digestion of the labeled protein and chromatographic identification of the EDANS-peptides, about 80% of the attached fluorophore was found on the actin segment of residues 1-28, most probably within the N-terminal acidic region of residues 1-7. A minor labeling site was located on the segment that consists of residues 40-113. No label was incorporated into the COOH-terminal moiety consisting of residues 113-375. The isolated EDANS-G-actin undergoes polymerization in the presence of salts but at a rate significantly greater than unlabeled actin. The EDANS-F-actin could be complexed to skeletal chymotryptic myosin subfragment 1 (S-1) and to tropomyosin. The complex formed between EDANS-F-actin and S-1 could not be further crosslinked by EDC but the two proteins were readily joined by glutaraldehyde as observed for native actin-S-1, suggesting that the EDANS-substituted carboxyl site is also involved in the EDC crosslinking of native actin to S-1. Moreover, the EDANS labeling of F-actin resulted in a 20-fold increase in the Km of the actin-activated Mg2+.ATPase of S-1. Thus, this labeling, while it did not much affect the rigor actin-S-1 interaction, changes the actin binding to the S-1-nucleotide complexes significantly. The selective introduction of a variety of spectral probes, like EDANS, or other classes of fluorophores, on the N-terminal region of actin, through the reported carbodiimide coupling reaction, would provide several different derivatives valuable for assessing the functional role of the negatively charged N-terminus of actin during its interaction with myosin and other actin

  1. Actin cap associated focal adhesions and their distinct role in cellular mechanosensing

    OpenAIRE

    2012-01-01

    The ability for cells to sense and adapt to different physical microenvironments plays a critical role in development, immune responses, and cancer metastasis. Here we identify a small subset of focal adhesions that terminate fibers in the actin cap, a highly ordered filamentous actin structure that is anchored to the top of the nucleus by the LINC complexes; these differ from conventional focal adhesions in morphology, subcellular organization, movements, turnover dynamics, and response to b...

  2. Does consideration of water routing affect simulated water and carbon dynamics in terrestrial ecosystems?

    Directory of Open Access Journals (Sweden)

    G. Tang

    2013-10-01

    Full Text Available The cycling of carbon in terrestrial ecosystems is closely coupled with the cycling of water. An important mechanism connecting ecological and hydrological processes in terrestrial ecosystems is lateral flow of water along landscapes. Few studies, however, have examined explicitly how consideration of water routing affects simulated water and carbon dynamics in terrestrial ecosystems. The objective of this study is to explore how consideration of water routing in a process-based hydroecological model affects simulated water and carbon dynamics. To achieve that end, we rasterized the regional hydroecological simulation systems (RHESSys and employed the rasterized RHESSys (R-RHESSys in a forested watershed. We performed and compared two contrasting simulations, one with and another without water routing. We found that R-RHESSys is able to correctly simulate major hydrological and ecological variables regardless of whether water routing is considered. When water routing was neglected, however, soil water table depth and saturation deficit were simulated to be smaller and spatially more homogeneous. As a result, evaporation, forest productivity and soil heterotrophic respiration also were simulated to be spatially more homogeneous compared to simulation with water routing. When averaged for the entire watershed, however, differences in simulated water and carbon fluxes are not significant between the two simulations. Overall, the study demonstrated that consideration of water routing enabled R-RHESSys to better capture our preconception of the spatial patterns of water table depth and saturation deficit across the watershed. Because the spatial pattern of soil moisture is fundamental to water efflux from land to the atmosphere, forest productivity and soil microbial activity, ecosystem and carbon cycle models, therefore, need to explicitly represent water routing in order to accurately quantify the magnitudes and patterns of water and carbon fluxes

  3. Gβ Regulates Coupling between Actin Oscillators for Cell Polarity and Directional Migration.

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    Oliver Hoeller

    2016-02-01

    Full Text Available For directional movement, eukaryotic cells depend on the proper organization of their actin cytoskeleton. This engine of motility is made up of highly dynamic nonequilibrium actin structures such as flashes, oscillations, and traveling waves. In Dictyostelium, oscillatory actin foci interact with signals such as Ras and phosphatidylinositol 3,4,5-trisphosphate (PIP3 to form protrusions. However, how signaling cues tame actin dynamics to produce a pseudopod and guide cellular motility is a critical open question in eukaryotic chemotaxis. Here, we demonstrate that the strength of coupling between individual actin oscillators controls cell polarization and directional movement. We implement an inducible sequestration system to inactivate the heterotrimeric G protein subunit Gβ and find that this acute perturbation triggers persistent, high-amplitude cortical oscillations of F-actin. Actin oscillators that are normally weakly coupled to one another in wild-type cells become strongly synchronized following acute inactivation of Gβ. This global coupling impairs sensing of internal cues during spontaneous polarization and sensing of external cues during directional motility. A simple mathematical model of coupled actin oscillators reveals the importance of appropriate coupling strength for chemotaxis: moderate coupling can increase sensitivity to noisy inputs. Taken together, our data suggest that Gβ regulates the strength of coupling between actin oscillators for efficient polarity and directional migration. As these observations are only possible following acute inhibition of Gβ and are masked by slow compensation in genetic knockouts, our work also shows that acute loss-of-function approaches can complement and extend the reach of classical genetics in Dictyostelium and likely other systems as well.

  4. A feedback loop between dynamin and actin recruitment during clathrin-mediated endocytosis.

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    Marcus J Taylor

    Full Text Available Clathrin-mediated endocytosis proceeds by a sequential series of reactions catalyzed by discrete sets of protein machinery. The final reaction in clathrin-mediated endocytosis is membrane scission, which is mediated by the large guanosine triophosphate hydrolase (GTPase dynamin and which may involve the actin-dependent recruitment of N-terminal containing BIN/Amphiphysin/RVS domain containing (N-BAR proteins. Optical microscopy has revealed a detailed picture of when and where particular protein types are recruited in the ∼20-30 s preceding scission. Nevertheless, the regulatory mechanisms and functions that underpin protein recruitment are not well understood. Here we used an optical assay to investigate the coordination and interdependencies between the recruitment of dynamin, the actin cytoskeleton, and N-BAR proteins to individual clathrin-mediated endocytic scission events. These measurements revealed that a feedback loop exists between dynamin and actin at sites of membrane scission. The kinetics of dynamin, actin, and N-BAR protein recruitment were modulated by dynamin GTPase activity. Conversely, acute ablation of actin dynamics using latrunculin-B led to a ∼50% decrease in the incidence of scission, an ∼50% decrease in the amplitude of dynamin recruitment, and abolished actin and N-BAR recruitment to scission events. Collectively these data suggest that dynamin, actin, and N-BAR proteins work cooperatively to efficiently catalyze membrane scission. Dynamin controls its own recruitment to scission events by modulating the kinetics of actin and N-BAR recruitment to sites of scission. Conversely actin serves as a dynamic scaffold that concentrates dynamin and N-BAR proteins at sites of scission.

  5. Facial feedback affects valence jugdments of dynamic and static emotional expressions

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    Sylwia eHyniewska

    2015-03-01

    Full Text Available The ability to judge others’ emotions is required for the establishment and maintenance of smooth interactions in a community. Several lines of evidence suggest that the attribution of meaning to a face is influenced by the facial actions produced by an observer during the observation of a face. However, empirical studies testing causal relationships between observers’ facial actions and emotion judgments have reported mixed findings. This study is the first to measure emotion judgments in terms of valence and arousal dimensions while comparing dynamic versus static presentations of facial expressions. We presented pictures and videos of facial expressions of anger and happiness. Participants (N = 36 were asked to differentiate between the gender of faces by activating the corrugator supercilii muscle (brow lowering and zygomaticus major muscle (cheek raising. They were also asked to evaluate the internal states of the stimuli using the affect grid while maintaining the facial action until they finished responding. The cheek-raising condition increased the attributed valence scores compared with the brow-lowering condition. This effect of facial actions was observed for static as well as for dynamic facial expressions. These data suggest that facial feedback mechanisms contribute to the judgment of the valence of emotional facial expressions.

  6. Wolbachia-Host Interactions: Host Mating Patterns Affect Wolbachia Density Dynamics.

    Science.gov (United States)

    Zhao, Dong-Xiao; Zhang, Xiang-Fei; Chen, Da-Song; Zhang, Yan-Kai; Hong, Xiao-Yue

    2013-01-01

    Wolbachia are maternally inherited intracellular bacteria that infect a wide range of arthropods and cause an array of effects on host reproduction, fitness and mating behavior. Although our understanding of the Wolbachia-associated effects on hosts is rapidly expanding, our knowledge of the host factors that mediate Wolbachia dynamics is rudimentary. Here, we explore the interactions between Wolbachia and its host, the two-spotted spider mite Tetranychus urticae Koch. Our results indicate that Wolbachia induces strong cytoplasmic incompatibility (CI), increases host fecundity, but has no effects on the longevity of females and the mating competitiveness of males in T. urticae. Most importantly, host mating pattern was found to affect Wolbachia density dynamics during host aging. Mating of an uninfected mite of either sex with an infected mite attenuates the Wolbachia density in the infected mite. According to the results of Wolbachia localization, this finding may be associated with the tropism of Wolbachia for the reproductive tissue in adult spider mites. Our findings describe a new interaction between Wolbachia and their hosts.

  7. The Dynamical Response of Dark Matter to Galaxy Evolution Affects Direct-Detection Experiments

    CERN Document Server

    Petersen, Michael S; Weinberg, Martin D

    2016-01-01

    Over a handful of rotation periods, dynamical processes in barred galaxies induce non-axisymmetric structure in dark matter halos. Using n-body simulations of a Milky Way-like barred galaxy, we identify both a trapped dark-matter component, a shadow bar, and a strong response wake in the dark-matter distribution that affects the predicted dark-matter detection rates for current experiments. The presence of a baryonic disk together with well-known dynamical processes (e.g. spiral structure and bar instabilities) increase the dark matter density in the disk plane. We find that the magnitude of the combined stellar and shadow bar evolution, when isolated from the effect of the axisymmetric gravitational potential of the disk, accounts for >30% of this overall increase in disk-plane density. This is significantly larger that of previously claimed deviations from the standard halo model. The dark-matter density and kinematic wakes driven by the Milky Way bar increase the detectability of dark matter overall, espec...

  8. Wolbachia-Host Interactions: Host Mating Patterns Affect Wolbachia Density Dynamics.

    Directory of Open Access Journals (Sweden)

    Dong-Xiao Zhao

    Full Text Available Wolbachia are maternally inherited intracellular bacteria that infect a wide range of arthropods and cause an array of effects on host reproduction, fitness and mating behavior. Although our understanding of the Wolbachia-associated effects on hosts is rapidly expanding, our knowledge of the host factors that mediate Wolbachia dynamics is rudimentary. Here, we explore the interactions between Wolbachia and its host, the two-spotted spider mite Tetranychus urticae Koch. Our results indicate that Wolbachia induces strong cytoplasmic incompatibility (CI, increases host fecundity, but has no effects on the longevity of females and the mating competitiveness of males in T. urticae. Most importantly, host mating pattern was found to affect Wolbachia density dynamics during host aging. Mating of an uninfected mite of either sex with an infected mite attenuates the Wolbachia density in the infected mite. According to the results of Wolbachia localization, this finding may be associated with the tropism of Wolbachia for the reproductive tissue in adult spider mites. Our findings describe a new interaction between Wolbachia and their hosts.

  9. Factors affecting population dynamics of maternally transmitted endosymbionts in Bemisia tabaci.

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    Huipeng Pan

    Full Text Available While every individual of Bemisia tabaci (Hemiptera: Aleyrodidae harbors the primary symbiont (P-symbiont Portiera, the infection frequencies of the six secondary symbionts (S-symbionts including Hamiltonella, Arsenophonus, Cardinium, Wolbachia, Rickettsia and Fritschea vary greatly among different populations. To characterize the factors influencing the infection dynamics of the six S-symbionts in B. tabaci, gene-specific PCR were conducted to screen for the presence of the P-symbiont Portiera and the six S-symbionts in 61 (17 B and 44 Q biotypes field populations collected from different plant species and locations in China. All individuals of the 61 populations hosted the P-symbiont Portiera, but none of them harbored Arsenophonus and Fritschea. The presence and infection rates of Hamiltonella, Cardinium, Rickettsia, Wolbachia and their co-infections Rickettsia + Hamiltonella (RH, Rickettsia + Cardinium (RC, Hamiltonella + Cardinium (HC and Rickettsia + Hamiltonella + Cardinium (RHC varied significantly among the 61 field populations; and the observed variations can be explained by biotypes, sexes, host plants and geographical locations of these field populations. Taken together, at least three factors including biotype, host plant and geographical location affect the infection dynamics of S-symbionts in B. tabaci.

  10. Spire, an actin nucleation factor, regulates cell division during Drosophila heart development.

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    Peng Xu

    Full Text Available The Drosophila dorsal vessel is a beneficial model system for studying the regulation of early heart development. Spire (Spir, an actin-nucleation factor, regulates actin dynamics in many developmental processes, such as cell shape determination, intracellular transport, and locomotion. Through protein expression pattern analysis, we demonstrate that the absence of spir function affects cell division in Myocyte enhancer factor 2-, Tinman (Tin-, Even-skipped- and Seven up (Svp-positive heart cells. In addition, genetic interaction analysis shows that spir functionally interacts with Dorsocross, tin, and pannier to properly specify the cardiac fate. Furthermore, through visualization of double heterozygous embryos, we determines that spir cooperates with CycA for heart cell specification and division. Finally, when comparing the spir mutant phenotype with that of a CycA mutant, the results suggest that most Svp-positive progenitors in spir mutant embryos cannot undergo full cell division at cell cycle 15, and that Tin-positive progenitors are arrested at cell cycle 16 as double-nucleated cells. We conclude that Spir plays a crucial role in controlling dorsal vessel formation and has a function in cell division during heart tube morphogenesis.

  11. Filopodia-like actin cables position nuclei in association with perinuclear actin in Drosophila nurse cells.

    Science.gov (United States)

    Huelsmann, Sven; Ylänne, Jari; Brown, Nicholas H

    2013-09-30

    Controlling the position of the nucleus is vital for a number of cellular processes from yeast to humans. In Drosophila nurse cells, nuclear positioning is crucial during dumping, when nurse cells contract and expel their contents into the oocyte. We provide evidence that in nurse cells, continuous filopodia-like actin cables, growing from the plasma membrane and extending to the nucleus, achieve nuclear positioning. These actin cables move nuclei away from ring canals. When nurse cells contract, actin cables associate laterally with the nuclei, in some cases inducing nuclear turning so that actin cables become partially wound around the nuclei. Our data suggest that a perinuclear actin meshwork connects actin cables to nuclei via actin-crosslinking proteins such as the filamin Cheerio. We provide a revised model for how actin structures position nuclei in nurse cells, employing evolutionary conserved machinery.

  12. Mammalian and malaria parasite cyclase-associated proteins catalyze nucleotide exchange on G-actin through a conserved mechanism.

    Science.gov (United States)

    Makkonen, Maarit; Bertling, Enni; Chebotareva, Natalia A; Baum, Jake; Lappalainen, Pekka

    2013-01-11

    Cyclase-associated proteins (CAPs) are among the most highly conserved regulators of actin dynamics, being present in organisms from mammals to apicomplexan parasites. Yeast, plant, and mammalian CAPs are large multidomain proteins, which catalyze nucleotide exchange on actin monomers from ADP to ATP and recycle actin monomers from actin-depolymerizing factor (ADF)/cofilin for new rounds of filament assembly. However, the mechanism by which CAPs promote nucleotide exchange is not known. Furthermore, how apicomplexan CAPs, which lack many domains present in yeast and mammalian CAPs, contribute to actin dynamics is not understood. We show that, like yeast Srv2/CAP, mouse CAP1 interacts with ADF/cofilin and ADP-G-actin through its N-terminal α-helical and C-terminal β-strand domains, respectively. However, in the variation to yeast Srv2/CAP, mouse CAP1 has two adjacent profilin-binding sites, and it interacts with ATP-actin monomers with high affinity through its WH2 domain. Importantly, we revealed that the C-terminal β-sheet domain of mouse CAP1 is essential and sufficient for catalyzing nucleotide exchange on actin monomers, although the adjacent WH2 domain is not required for this function. Supporting these data, we show that the malaria parasite Plasmodium falciparum CAP, which is entirely composed of the β-sheet domain, efficiently promotes nucleotide exchange on actin monomers. Collectively, this study provides evidence that catalyzing nucleotide exchange on actin monomers via the β-sheet domain is the most highly conserved function of CAPs from mammals to apicomplexan parasites. Other functions, including interactions with profilin and ADF/cofilin, evolved in more complex organisms to adjust the specific role of CAPs in actin dynamics.

  13. Packaging of actin into Ebola virus VLPs

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    Harty Ronald N

    2005-12-01

    Full Text Available Abstract The actin cytoskeleton has been implicated in playing an important role assembly and budding of several RNA virus families including retroviruses and paramyxoviruses. In this report, we sought to determine whether actin is incorporated into Ebola VLPs, and thus may play a role in assembly and/or budding of Ebola virus. Our results indicated that actin and Ebola virus VP40 strongly co-localized in transfected cells as determined by confocal microscopy. In addition, actin was packaged into budding VP40 VLPs as determined by a functional budding assay and protease protection assay. Co-expression of a membrane-anchored form of Ebola virus GP enhanced the release of both VP40 and actin in VLPs. Lastly, disruption of the actin cytoskeleton with latrunculin-A suggests that actin may play a functional role in budding of VP40/GP VLPs. These data suggest that VP40 may interact with cellular actin, and that actin may play a role in assembly and/or budding of Ebola VLPs.

  14. N dynamics of Inner Mongolia typical steppe as affected by grazing

    Science.gov (United States)

    Giese, M.; Gao, Y. Z.; Brueck, H.; Butterbach-Bahl, K.

    2012-04-01

    For large areas of Inner Mongolian semi-arid grasslands, as for many regions of the Eurasian steppe belt, substantial land degradation was reported as a consequence of excessive overgrazing during the last decades. Nitrogen is considered as a key element for ecosystem functions and therefore, a comprehensive analysis of the system's N balance and cycle as affected by land-use change is of fundamental importance to maintain, improve or restore ecosystem services such as forage production, carbon sequestration and diversity conservation. In this comprehensive case study of a Chinese typical steppe, we present an in-depth analysis of N dynamics including the balance of N gains and losses, and N cycling. N pools and fluxes were simultaneously quantified on three grassland sites of contrasting grazing intensity. Our N balances indicated the ungrazed site as N sink with annual net N input of up to 3 g N m-2, mainly due to N input by dust deposition, whereas the heavily grazed site must be considered as N source with net losses of up to 1.7 g m-2. Mayor N losses occurred via dust emissions and excrement export from grazing sites, the latter as a consequence of the common practice of keeping sheep in paddocks overnight. Compared to these fluxes, gaseous N losses, export of animal products (live weight and wool) and biological N2 fixation were of minor relevance. Heavy grazing reduced pool sizes of both topsoil organic N, and above- and belowground biomass N. Furthermore, grazing reduced N fluxes with regard to N uptake, decomposition, gross microbial N turnover, and immobilization. Most N-related processes were more intensive in seasons of higher water availability indicating complex interactions between land-use intensity and climate variability. The projected increase of annual atmospheric N wet deposition and changes in rainfall pattern will likely affect the N sink-source pathways and N flux dynamics, indicating high potential impact of future N enrichment and climate

  15. Reduced short term adaptation to robot generated dynamic environment in children affected by Cerebral Palsy

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    Di Rosa Giuseppe

    2011-05-01

    Full Text Available Abstract Background It is known that healthy adults can quickly adapt to a novel dynamic environment, generated by a robotic manipulandum as a structured disturbing force field. We suggest that it may be of clinical interest to evaluate to which extent this kind of motor learning capability is impaired in children affected by cerebal palsy. Methods We adapted the protocol already used with adults, which employs a velocity dependant viscous field, and compared the performance of a group of subjects affected by Cerebral Palsy (CP group, 7 subjects with a Control group of unimpaired age-matched children. The protocol included a familiarization phase (FA, during which no force was applied, a force field adaptation phase (CF, and a wash-out phase (WO in which the field was removed. During the CF phase the field was shut down in a number of randomly selected "catch" trials, which were used in order to evaluate the "learning index" for each single subject and the two groups. Lateral deviation, speed and acceleration peaks and average speed were evaluated for each trajectory; a directional analysis was performed in order to inspect the role of the limb's inertial anisotropy in the different experimental phases. Results During the FA phase the movements of the CP subjects were more curved, displaying greater and variable directional error; over the course of the CF phase both groups showed a decreasing trend in the lateral error and an after-effect at the beginning of the wash-out, but the CP group had a non significant adaptation rate and a lower learning index, suggesting that CP subjects have reduced ability to learn to compensate external force. Moreover, a directional analysis of trajectories confirms that the control group is able to better predict the force field by tuning the kinematic features of the movements along different directions in order to account for the inertial anisotropy of arm. Conclusions Spatial abnormalities in children affected

  16. Reduced short term adaptation to robot generated dynamic environment in children affected by Cerebral Palsy

    Science.gov (United States)

    2011-01-01

    Background It is known that healthy adults can quickly adapt to a novel dynamic environment, generated by a robotic manipulandum as a structured disturbing force field. We suggest that it may be of clinical interest to evaluate to which extent this kind of motor learning capability is impaired in children affected by cerebal palsy. Methods We adapted the protocol already used with adults, which employs a velocity dependant viscous field, and compared the performance of a group of subjects affected by Cerebral Palsy (CP group, 7 subjects) with a Control group of unimpaired age-matched children. The protocol included a familiarization phase (FA), during which no force was applied, a force field adaptation phase (CF), and a wash-out phase (WO) in which the field was removed. During the CF phase the field was shut down in a number of randomly selected "catch" trials, which were used in order to evaluate the "learning index" for each single subject and the two groups. Lateral deviation, speed and acceleration peaks and average speed were evaluated for each trajectory; a directional analysis was performed in order to inspect the role of the limb's inertial anisotropy in the different experimental phases. Results During the FA phase the movements of the CP subjects were more curved, displaying greater and variable directional error; over the course of the CF phase both groups showed a decreasing trend in the lateral error and an after-effect at the beginning of the wash-out, but the CP group had a non significant adaptation rate and a lower learning index, suggesting that CP subjects have reduced ability to learn to compensate external force. Moreover, a directional analysis of trajectories confirms that the control group is able to better predict the force field by tuning the kinematic features of the movements along different directions in order to account for the inertial anisotropy of arm. Conclusions Spatial abnormalities in children affected by cerebral palsy may be

  17. Actin remodeling confers BRAF inhibitor resistance to melanoma cells through YAP/TAZ activation.

    Science.gov (United States)

    Kim, Min Hwan; Kim, Jongshin; Hong, Hyowon; Lee, Si-Hyung; Lee, June-Koo; Jung, Eunji; Kim, Joon

    2016-03-01

    The activation of transcriptional coactivators YAP and its paralog TAZ has been shown to promote resistance to anti-cancer therapies. YAP/TAZ activity is tightly coupled to actin cytoskeleton architecture. However, the influence of actin remodeling on cancer drug resistance remains largely unexplored. Here, we report a pivotal role of actin remodeling in YAP/TAZ-dependent BRAF inhibitor resistance in BRAF V600E mutant melanoma cells. Melanoma cells resistant to the BRAF inhibitor PLX4032 exhibit an increase in actin stress fiber formation, which appears to promote the nuclear accumulation of YAP/TAZ. Knockdown of YAP/TAZ reduces the viability of resistant melanoma cells, whereas overexpression of constitutively active YAP induces resistance. Moreover, inhibition of actin polymerization and actomyosin tension in melanoma cells suppresses both YAP/TAZ activation and PLX4032 resistance. Our siRNA library screening identifies actin dynamics regulator TESK1 as a novel vulnerable point of the YAP/TAZ-dependent resistance pathway. These results suggest that inhibition of actin remodeling is a potential strategy to suppress resistance in BRAF inhibitor therapies.

  18. Cortical instability drives periodic supracellular actin pattern formation in epithelial tubes.

    Science.gov (United States)

    Hannezo, Edouard; Dong, Bo; Recho, Pierre; Joanny, Jean-François; Hayashi, Shigeo

    2015-07-14

    An essential question of morphogenesis is how patterns arise without preexisting positional information, as inspired by Turing. In the past few years, cytoskeletal flows in the cell cortex have been identified as a key mechanism of molecular patterning at the subcellular level. Theoretical and in vitro studies have suggested that biological polymers such as actomyosin gels have the property to self-organize, but the applicability of this concept in an in vivo setting remains unclear. Here, we report that the regular spacing pattern of supracellular actin rings in the Drosophila tracheal tubule is governed by a self-organizing principle. We propose a simple biophysical model where pattern formation arises from the interplay of myosin contractility and actin turnover. We validate the hypotheses of the model using photobleaching experiments and report that the formation of actin rings is contractility dependent. Moreover, genetic and pharmacological perturbations of the physical properties of the actomyosin gel modify the spacing of the pattern, as the model predicted. In addition, our model posited a role of cortical friction in stabilizing the spacing pattern of actin rings. Consistently, genetic depletion of apical extracellular matrix caused strikingly dynamic movements of actin rings, mirroring our model prediction of a transition from steady to chaotic actin patterns at low cortical friction. Our results therefore demonstrate quantitatively that a hydrodynamical instability of the actin cortex can trigger regular pattern formation and drive morphogenesis in an in vivo setting.

  19. The Hippo pathway polarizes the actin cytoskeleton during collective migration of Drosophila border cells.

    Science.gov (United States)

    Lucas, Eliana P; Khanal, Ichha; Gaspar, Pedro; Fletcher, Georgina C; Polesello, Cedric; Tapon, Nicolas; Thompson, Barry J

    2013-06-10

    Collective migration of Drosophila border cells depends on a dynamic actin cytoskeleton that is highly polarized such that it concentrates around the outer rim of the migrating cluster of cells. How the actin cytoskeleton becomes polarized in these cells to enable collective movement remains unknown. Here we show that the Hippo signaling pathway links determinants of cell polarity to polarization of the actin cytoskeleton in border cells. Upstream Hippo pathway components localize to contacts between border cells inside the cluster and signal through the Hippo and Warts kinases to polarize actin and promote border cell migration. Phosphorylation of the transcriptional coactivator Yorkie (Yki)/YAP by Warts does not mediate the function of this pathway in promoting border cell migration, but rather provides negative feedback to limit the speed of migration. Instead, Warts phosphorylates and inhibits the actin regulator Ena to activate F-actin Capping protein activity on inner membranes and thereby restricts F-actin polymerization mainly to the outer rim of the migrating cluster.

  20. p38α regulates actin cytoskeleton and cytokinesis in hepatocytes during development and aging

    Science.gov (United States)

    Jorques, María; Rada, Patricia; Ramirez, Lorena; Valverde, Ángela M.; Nebreda, Ángel R.; Sastre, Juan

    2017-01-01

    Background Hepatocyte poliploidization is an age-dependent process, being cytokinesis failure the main mechanism of polyploid hepatocyte formation. Our aim was to study the role of p38α MAPK in the regulation of actin cytoskeleton and cytokinesis in hepatocytes during development and aging. Methods Wild type and p38α liver-specific knock out mice at different ages (after weaning, adults and old) were used. Results We show that p38α MAPK deficiency induces actin disassembly upon aging and also cytokinesis failure leading to enhanced binucleation. Although the steady state levels of cyclin D1 in wild type and p38α knock out old livers remained unaffected, cyclin B1- a marker for G2/M transition- was significantly overexpressed in p38α knock out mice. Our findings suggest that hepatocytes do enter into S phase but they do not complete cell division upon p38α deficiency leading to cytokinesis failure and binucleation. Moreover, old liver-specific p38α MAPK knock out mice exhibited reduced F-actin polymerization and a dramatic loss of actin cytoskeleton. This was associated with abnormal hyperactivation of RhoA and Cdc42 GTPases. Long-term p38α deficiency drives to inactivation of HSP27, which seems to account for the impairment in actin cytoskeleton as Hsp27-silencing decreased the number and length of actin filaments in isolated hepatocytes. Conclusions p38α MAPK is essential for actin dynamics with age in hepatocytes. PMID:28166285

  1. Live Cell Imaging Reveals Structural Associations between the Actin and Microtubule Cytoskeleton in Arabidopsis [W] [OA

    Science.gov (United States)

    Sampathkumar, Arun; Lindeboom, Jelmer J.; Debolt, Seth; Gutierrez, Ryan; Ehrhardt, David W.; Ketelaar, Tijs; Persson, Staffan

    2011-01-01

    In eukaryotic cells, the actin and microtubule (MT) cytoskeletal networks are dynamic structures that organize intracellular processes and facilitate their rapid reorganization. In plant cells, actin filaments (AFs) and MTs are essential for cell growth and morphogenesis. However, dynamic interactions between these two essential components in live cells have not been explored. Here, we use spinning-disc confocal microscopy to dissect interaction and cooperation between cortical AFs and MTs in Arabidopsis thaliana, utilizing fluorescent reporter constructs for both components. Quantitative analyses revealed altered AF dynamics associated with the positions and orientations of cortical MTs. Reorganization and reassembly of the AF array was dependent on the MTs following drug-induced depolymerization, whereby short AFs initially appeared colocalized with MTs, and displayed motility along MTs. We also observed that light-induced reorganization of MTs occurred in concert with changes in AF behavior. Our results indicate dynamic interaction between the cortical actin and MT cytoskeletons in interphase plant cells. PMID:21693695

  2. Actin polymerization negatively regulates p53 function by impairing its nuclear import in response to DNA damage.

    Directory of Open Access Journals (Sweden)

    Ling Wang

    Full Text Available Actin, one of the most evolutionarily conservative proteins in eukaryotes, is distributed both in the cytoplasm and the nucleus, and its dynamics plays important roles in numerous cellular processes. Previous evidence has shown that actin interacts with p53 and this interaction increases in the process of p53 responding to DNA damage, but the physiological significance of their interaction remains elusive. Here, we show that DNA damage induces both actin polymerization and p53 accumulation. To further understand the implication of actin polymerization in p53 function, cells were treated with actin aggregation agent. We find that the protein level of p53 decrease. The change in p53 is a consequence of the polymeric actin anchoring p53 in the cytoplasm, thus impairing p53 nuclear import. Analysis of phosphorylation and ubiquitination of p53 reveals that actin polymerization promotes the p53 phosphorylation at Ser315 and reduces the stabilization of p53 by recruiting Aurora kinase A. Taken together, our results suggest that the actin polymerization serves as a negative modulator leading to the impairment of nuclear import and destabilization of p53. On the basis of our results, we propose that actin polymerization might be a factor participating in the process of orchestrating p53 function in response to DNA damage.

  3. Phototropin-dependent biased relocalization of cp-actin filaments can be induced even when chloroplast movement is inhibited.

    Science.gov (United States)

    Yamada, Noboru; Suetsugu, Noriyuki; Wada, Masamitsu; Kadota, Akeo

    2011-11-01

    In a recent publication using an actin-visualized line of Arabidopsis (Ichikawa et al. 2011, ref. 11), we reported a detailed analysis with higher time resolution on the dynamics of chloroplast actin filaments (cp-actin filaments) during chloroplast avoidance movement and demonstrated a good correlation between the biased configuration of cp-actin filaments and chloroplast movement. However, we could not conclusively determine whether the reorganization of cp-actin filaments into a biased configuration preceded actual chloroplast movement (and, thus, whether it could be a cause of the movement). In this report, we present clear evidence that the reorganization of cp-actin filaments into a biased distribution is induced even in the absence of the actual movement of chloroplasts. When the cells were treated with 2,3-butanedione monoxime (BDM), a potent inhibitor of myosin ATPase, chloroplast motility was completely suppressed. Nevertheless, the disappearance and biased relocalization of cp-actin filaments toward the side of the prospective movement direction were induced by irradiation with a strong blue light microbeam. The results definitively indicate that the reorganization of cp-actin filaments is not an effect of chloroplast movement; however, it is feasible that the biased localization of cp-actin filaments is an event leading to chloroplast movement.

  4. Patterning and lifetime of plasma membrane-localized cellulose synthase is dependent on actin organization in Arabidopsis interphase cells.

    Science.gov (United States)

    Sampathkumar, Arun; Gutierrez, Ryan; McFarlane, Heather E; Bringmann, Martin; Lindeboom, Jelmer; Emons, Anne-Mie; Samuels, Lacey; Ketelaar, Tijs; Ehrhardt, David W; Persson, Staffan

    2013-06-01

    The actin and microtubule cytoskeletons regulate cell shape across phyla, from bacteria to metazoans. In organisms with cell walls, the wall acts as a primary constraint of shape, and generation of specific cell shape depends on cytoskeletal organization for wall deposition and/or cell expansion. In higher plants, cortical microtubules help to organize cell wall construction by positioning the delivery of cellulose synthase (CesA) complexes and guiding their trajectories to orient newly synthesized cellulose microfibrils. The actin cytoskeleton is required for normal distribution of CesAs to the plasma membrane, but more specific roles for actin in cell wall assembly and organization remain largely elusive. We show that the actin cytoskeleton functions to regulate the CesA delivery rate to, and lifetime of CesAs at, the plasma membrane, which affects cellulose production. Furthermore, quantitative image analyses revealed that actin organization affects CesA tracking behavior at the plasma membrane and that small CesA compartments were associated with the actin cytoskeleton. By contrast, localized insertion of CesAs adjacent to cortical microtubules was not affected by the actin organization. Hence, both actin and microtubule cytoskeletons play important roles in regulating CesA trafficking, cellulose deposition, and organization of cell wall biogenesis.

  5. The formin DAD domain plays dual roles in autoinhibition and actin nucleation.

    Science.gov (United States)

    Gould, Christopher J; Maiti, Sankar; Michelot, Alphée; Graziano, Brian R; Blanchoin, Laurent; Goode, Bruce L

    2011-03-08

    Formins are a large family of actin assembly-promoting proteins with many important biological roles. However, it has remained unclear how formins nucleate actin polymerization. All other nucleators are known to recruit actin monomers as a central part of their mechanisms. However, the actin-nucleating FH2 domain of formins lacks appreciable affinity for monomeric actin. Here, we found that yeast and mammalian formins bind actin monomers but that this activity requires their C-terminal DAD domains. Furthermore, we observed that the DAD works in concert with the FH2 to enhance nucleation without affecting the rate of filament elongation. We dissected this mechanism in mDia1, mapped nucleation activity to conserved residues in the DAD, and demonstrated that DAD roles in nucleation and autoinhibition are separable. Furthermore, DAD enhancement of nucleation was independent of contributions from the FH1 domain to nucleation. Together, our data show that (1) the DAD has dual functions in autoinhibition and nucleation; (2) the FH1, FH2, and DAD form a tripartite nucleation machine; and (3) formins nucleate by recruiting actin monomers and therefore are more similar to other nucleators than previously thought.

  6. Population dynamics of dechlorinators and factors affecting the level and products of PCB dechlorination in sediments

    Energy Technology Data Exchange (ETDEWEB)

    Kim, J.S.; Sokol, R.C.; Liu, X.; Bethoney, C.M.; Rhee, G.Y. [State Univ. of New York and New York State Department of Health, Albany, NY (United States)

    1996-12-31

    Microbial dechlorination of polychlorinated biphenyls (PCBs) often stops although a significant number of removable chlorines remain. To determine the reason for the cessation, we investigated the limitation of organic carbon, PCB bioavailability, and inhibition by metabolic products. Enrichment with carbon sources did not induce additional chlorination, indicating the plateau was not due to depletion of organic carbon. The bioavailability was not limiting, since a subcritical micelle concentration of the surfactant, which enhanced desorption without inhibiting dechlorinating microorganisms, failed to lower the plateau. Neither was it due to accumulation of metabolites, since no additional dechlorination was detected when plateau sediments were incubated with fresh medium. Similarly, dechlorination was not inhibited in freshly spiked sediment slurries. Dechlorination ended up at the same level with nearly identical congener profiles, regardless of treatment. These results indicate that cessation of dechlorination was due to the accumulation of daughter congeners, which cannot be used as electron acceptors by microbes. To determine whether the decreasing availability affected the microorganisms, we determined the population dynamics of dechlorinators using the most probable number technique. The growth dynamics of the dechlorinators mirrored the time course of dechlorination. It started when the population increased by two orders of magnitude. Once dechlorination stopped the dechlorinating population also began to decrease. When dechlorinators were inoculated into PCB-free sediments, the population decreased over time. The decrease of the population as dechlorination ceased confirms that the diminishing availability of congeners was the reason for the incomplete dechlorination. Recent findings have shown that a second phase of dechlorination of certain congeners can occur after a long lag. 45 refs., 8 figs.

  7. Actin-based propulsion of spatially extended objects

    Energy Technology Data Exchange (ETDEWEB)

    Enculescu, Mihaela [Institute for Theoretical Physics, Technische Universitaet Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany); Falcke, Martin, E-mail: mihaela.enculescu@tu-berlin.de [Max-Delbrueck-Center for Molecular Medicine, Mathematical Cell Physiology, Robert-Roessle-Street 10, 13125 Berlin (Germany)

    2011-05-15

    We propose a mathematical model of the actin-based propulsion of spatially extended obstacles. It starts from the properties of individual actin filaments and includes transient attachment to the obstacle, polymerization as well as cross-linking. Two particular geometries are discussed, which apply to the motion of protein-coated beads in a cell-like medium and the leading edge of a cell protrusion, respectively. The model gives rise to both steady and saltatory movement of beads and can explain the experimentally observed transitions of the dynamic regime with changing bead radius and protein surface density. Several spatiotemporal patterns are obtained with a soft obstacle under tension, including the experimentally observed spontaneous emergence of lateral traveling waves in crawling cells. Thus, we suggest a unifying mechanism for systems that are currently described by differential concepts.

  8. An atomic model of the tropomyosin cable on F-actin.

    Science.gov (United States)

    Orzechowski, Marek; Li, Xiaochuan Edward; Fischer, Stefan; Lehman, William

    2014-08-05

    Tropomyosin regulates a wide variety of actin filament functions and is best known for the role that it plays together with troponin in controlling muscle activity. For effective performance on actin filaments, adjacent 42-nm-long tropomyosin molecules are joined together by a 9- to 10-residue head-to-tail overlapping domain to form a continuous cable that wraps around the F-actin helix. Yet, despite the apparent simplicity of tropomyosin's coiled-coil structure and its well-known periodic association with successive actin subunits along F-actin, the structure of the tropomyosin cable on actin is uncertain. This is because the conformation of the overlap region that joins neighboring molecules is poorly understood, thus leaving a significant gap in our understanding of thin-filament structure and regulation. However, recent molecular-dynamics simulations of overlap segments defined their overall shape and provided unique and sufficient cues to model the whole actin-tropomyosin filament assembly in atomic detail. In this study, we show that these MD structures merge seamlessly onto the ends of tropomyosin coiled-coils. Adjacent tropomyosin molecules can then be joined together to provide a comprehensive model of the tropomyosin cable running continuously on F-actin. The resulting complete model presented here describes for the first time (to our knowledge) an atomic-level structure of αα-striated muscle tropomyosin bound to an actin filament that includes the critical overlap domain. Thus, the model provides a structural correlate to evaluate thin-filament mechanics, self-assembly mechanisms, and the effect of disease-causing mutations.

  9. F- and G-actin homeostasis regulates mechanosensitive actin nucleation by formins.

    Science.gov (United States)

    Higashida, Chiharu; Kiuchi, Tai; Akiba, Yushi; Mizuno, Hiroaki; Maruoka, Masahiro; Narumiya, Shuh; Mizuno, Kensaku; Watanabe, Naoki

    2013-04-01

    Physical force evokes rearrangement of the actin cytoskeleton. Signalling pathways such as tyrosine kinases, stretch-activated Ca(2+) channels and Rho GTPases are involved in force sensing. However, how signals are transduced to actin assembly remains obscure. Here we show mechanosensitive actin polymerization by formins (formin homology proteins). Cells overexpressing mDia1 increased the amount of F-actin on release of cell tension. Fluorescence single-molecule speckle microscopy revealed rapid induction of processive actin assembly by mDia1 on cell cortex deformation. mDia1 lacking the Rho-binding domain and other formins exhibited mechanosensitive actin nucleation, suggesting Rho-independent activation. Mechanosensitive actin nucleation by mDia1 required neither Ca(2+) nor kinase signalling. Overexpressing LIM kinase abrogated the induction of processive mDia1. Furthermore, s-FDAPplus (sequential fluorescence decay after photoactivation) analysis revealed a rapid actin monomer increase on cell cortex deformation. Our direct visualization of the molecular behaviour reveals a mechanosensitive actin filament regeneration mechanism in which G-actin released by actin remodelling plays a pivotal role.

  10. Arabidopsis CAP1 - a key regulator of actin organisation and development.

    Science.gov (United States)

    Deeks, Michael J; Rodrigues, Cecília; Dimmock, Simon; Ketelaar, Tijs; Maciver, Sutherland K; Malhó, Rui; Hussey, Patrick J

    2007-08-01

    Maintenance of F-actin turnover is essential for plant cell morphogenesis. Actin-binding protein mutants reveal that plants place emphasis on particular aspects of actin biochemistry distinct from animals and fungi. Here we show that mutants in CAP1, an A. thaliana member of the cyclase-associated protein family, display a phenotype that establishes CAP1 as a fundamental facilitator of actin dynamics over a wide range of plant tissues. Plants homozygous for cap1 alleles show a reduction in stature and morphogenetic disruption of multiple cell types. Pollen grains exhibit reduced germination efficiency, and cap1 pollen tubes and root hairs grow at a decreased rate and to a reduced length. Live cell imaging of growing root hairs reveals actin filament disruption and cytoplasmic disorganisation in the tip growth zone. Mutant cap1 alleles also show synthetic phenotypes when combined with mutants of the Arp2/3 complex pathway, which further suggests a contribution of CAP1 to in planta actin dynamics. In yeast, CAP interacts with adenylate cyclase in a Ras signalling cascade; but plants do not have Ras. Surprisingly, cap1 plants show disruption in plant signalling pathways required for co-ordinated organ expansion suggesting that plant CAP has evolved to attain plant-specific signalling functions.

  11. Drosophila Imp iCLIP identifies an RNA assemblage coordinating F-actin formation

    DEFF Research Database (Denmark)

    Hansen, Heidi Theil; Rasmussen, Simon Horskjær; Adolph, Sidsel Kramshøj;

    2015-01-01

    CLIP) technologies in Drosophila cells to identify transcripts associated with cytoplasmic ribonucleoproteins (RNPs) containing the RNA-binding protein Imp. RESULTS: We find extensive binding of Imp to 3'UTRs of transcripts that are involved in F-actin formation. A common denominator of the RNA-protein interface....... This demonstrates a physiological significance of the defined RNA regulon. CONCLUSIONS: Our data imply that Drosophila Imp RNPs may function as cytoplasmic mRNA assemblages that encode proteins which participate in actin cytoskeletal remodeling. Thus, they may facilitate co-ordinated protein expression in sub...... is the presence of multiple motifs with a central UA-rich element flanked by CA-rich elements. Experiments in single cells and intact flies reveal compromised actin cytoskeletal dynamics associated with low Imp levels. The former shows reduced F-actin formation and the latter exhibits abnormal neuronal patterning...

  12. A method for rapidly screening functionality of actin mutants and tagged actins

    Directory of Open Access Journals (Sweden)

    Rommelaere Heidi

    2004-01-01

    Full Text Available Recombinant production and biochemical analysis of actin mutants has been hampered by the fact that actin has an absolute requirement for the eukaryotic chaperone CCT to reach its native state. We therefore have developed a method to rapidly screen the folding capacity and functionality of actin variants, by combining in vitro expression of labelled actin with analysis on native gels, band shift assays or copolymerization tests. Additionally, we monitor, using immuno-fluorescence, incorporation of actin variants in cytoskeletal structures in transfected cells. We illustrate the method by two examples. In one we show that tagged versions of actin do not always behave native-like and in the other we study some of the molecular defects of three &bgr;-actin mutants that have been associated with diseases.

  13. Load fluctuations drive actin network growth

    CERN Document Server

    Shaevitz, Joshua W

    2007-01-01

    The growth of actin filament networks is a fundamental biological process that drives a variety of cellular and intracellular motions. During motility, eukaryotic cells and intracellular pathogens are propelled by actin networks organized by nucleation-promoting factors, which trigger the formation of nascent filaments off the side of existing filaments in the network. A Brownian ratchet (BR) mechanism has been proposed to couple actin polymerization to cellular movements, whereby thermal motions are rectified by the addition of actin monomers at the end of growing filaments. Here, by following actin--propelled microspheres using three--dimensional laser tracking, we find that beads adhered to the growing network move via an object--fluctuating BR. Velocity varies with the amplitude of thermal fluctuation and inversely with viscosity as predicted for a BR. In addition, motion is saltatory with a broad distribution of step sizes that is correlated in time. These data point to a model in which thermal fluctuati...

  14. Spatiotemporal dynamics of black-tailed prairie dog colonies affected by plague

    Science.gov (United States)

    Augustine, D.J.; Matchett, M.R.; Toombs, T.P.; Cully, J.F.; Johnson, T.L.; Sidle, John G.

    2008-01-01

    Black-tailed prairie dogs (Cynomys ludovicianus) are a key component of the disturbance regime in semi-arid grasslands of central North America. Many studies have compared community and ecosystem characteristics on prairie dog colonies to grasslands without prairie dogs, but little is known about landscape-scale patterns of disturbance that prairie dog colony complexes may impose on grasslands over long time periods. We examined spatiotemporal dynamics in two prairie dog colony complexes in southeastern Colorado (Comanche) and northcentral Montana (Phillips County) that have been strongly influenced by plague, and compared them to a complex unaffected by plague in northwestern Nebraska (Oglala). Both plague-affected complexes exhibited substantial spatiotemporal variability in the area occupied during a decade, in contrast to the stability of colonies in the Oglala complex. However, the plague-affected complexes differed in spatial patterns of colony movement. Colonies in the Comanche complex in shortgrass steppe shifted locations over a decade. Only 10% of the area occupied in 1995 was still occupied by prairie dogs in 2006. In 2005 and 2006 respectively, 74 and 83% of the total area of the Comanche complex occurred in locations that were not occupied in 1995, and only 1% of the complex was occupied continuously over a decade. In contrast, prairie dogs in the Phillips County complex in mixed-grass prairie and sagebrush steppe primarily recolonized previously occupied areas after plague-induced colony declines. In Phillips County, 62% of the area occupied in 1993 was also occupied by prairie dogs in 2004, and 12% of the complex was occupied continuously over a decade. Our results indicate that plague accelerates spatiotemporal movement of prairie dog colonies, and have significant implications for landscape-scale effects of prairie dog disturbance on grassland composition and productivity. These findings highlight the need to combine landscape-scale measures of

  15. Effects of a disease affecting a predator on the dynamics of a predator-prey system.

    Science.gov (United States)

    Auger, Pierre; McHich, Rachid; Chowdhury, Tanmay; Sallet, Gauthier; Tchuente, Maurice; Chattopadhyay, Joydev

    2009-06-07

    We study the effects of a disease affecting a predator on the dynamics of a predator-prey system. We couple an SIRS model applied to the predator population, to a Lotka-Volterra model. The SIRS model describes the spread of the disease in a predator population subdivided into susceptible, infected and removed individuals. The Lotka-Volterra model describes the predator-prey interactions. We consider two time scales, a fast one for the disease and a comparatively slow one for predator-prey interactions and for predator mortality. We use the classical "aggregation method" in order to obtain a reduced equivalent model. We show that there are two possible asymptotic behaviors: either the predator population dies out and the prey tends to its carrying capacity, or the predator and prey coexist. In this latter case, the predator population tends either to a "disease-free" or to a "disease-endemic" state. Moreover, the total predator density in the disease-endemic state is greater than the predator density in the "disease-free" equilibrium (DFE).

  16. A dynamic evolution model of human opinion as affected by advertising

    Science.gov (United States)

    Luo, Gui-Xun; Liu, Yun; Zeng, Qing-An; Diao, Su-Meng; Xiong, Fei

    2014-11-01

    We propose a new model to investigate the dynamics of human opinion as affected by advertising, based on the main idea of the CODA model and taking into account two practical factors: one is that the marginal influence of an additional friend will decrease with an increasing number of friends; the other is the decline of memory over time. Simulations show several significant conclusions for both advertising agencies and the general public. A small difference of advertising’s influence on individuals or advertising coverage will result in significantly different advertising effectiveness within a certain interval of value. Compared to the value of advertising’s influence on individuals, the advertising coverage plays a more important role due to the exponential decay of memory. Meanwhile, some of the obtained results are in accordance with people’s daily cognition about advertising. The real key factor in determining the success of advertising is the intensity of exchanging opinions, and people’s external actions always follow their internal opinions. Negative opinions also play an important role.

  17. Carbon and nitrogen dynamics in early stages of forest litter decomposition as affected by nitrogen addition

    Institute of Scientific and Technical Information of China (English)

    DENG Xiao-wen; LIU Ying; HAN Shi-jie

    2009-01-01

    The effects of nitrogen (N) availability and tree species on the dynamics of carbon and nitrogen at early stage of decomposition of forest litter were studied in a 13-week laboratory incubation experiment. Fresh litter samples including needle litter (Pinus koraiensis) and two types of broadleaf litters (Quercus mongolica and Tilia amurensis) were collected from a broadleaf-korean pine mixed forest in the northern slope of Changbai Mountain (China). Different doses of N (equal to 0, 30 and 50 kg·ha-1yr-1, respectively, as NH4NO3) were added to litter during the experiment period. The litter decomposition rate expressed as mass loss and respiration rate increased significantly with increasing N availability. The mass loss and cumulative CO2-C emission were higher in leaf litter compared to that in needle litter. The dissolved organic Carbon (DOC) concentrations in litter leachate varied widely between the species, but were not greatly affected by N treatments. Regardless of the N addition rate, both N treatments and species had no significant effect on dissolved organic N (DON) concentrations in litter leachate. About 52·78% of added N was retained in the litter. The percentage of N retention was positively correlated (R2=0.91, p<0.05) with the litter mass loss. This suggested that a forest floor with easily decomposed litter might have higher potential N sink strength than that with more slowly decomposed litter.

  18. How Major Depressive Disorder affects the ability to decode multimodal dynamic emotional stimuli

    Directory of Open Access Journals (Sweden)

    FILOMENA SCIBELLI

    2016-09-01

    Full Text Available Most studies investigating the processing of emotions in depressed patients reported impairments in the decoding of negative emotions. However, these studies adopted static stimuli (mostly stereotypical facial expressions corresponding to basic emotions which do not reflect the way people experience emotions in everyday life. For this reason, this work proposes to investigate the decoding of emotional expressions in patients affected by Recurrent Major Depressive Disorder (RMDDs using dynamic audio/video stimuli. RMDDs’ performance is compared with the performance of patients with Adjustment Disorder with Depressed Mood (ADs and healthy (HCs subjects. The experiments involve 27 RMDDs (16 with acute depression - RMDD-A, and 11 in a compensation phase - RMDD-C, 16 ADs and 16 HCs. The ability to decode emotional expressions is assessed through an emotion recognition task based on short audio (without video, video (without audio and audio/video clips. The results show that AD patients are significantly less accurate than HCs in decoding fear, anger, happiness, surprise and sadness. RMDD-As with acute depression are significantly less accurate than HCs in decoding happiness, sadness and surprise. Finally, no significant differences were found between HCs and RMDD-Cs in a compensation phase. The different communication channels and the types of emotion play a significant role in limiting the decoding accuracy.

  19. Crystal structure of an archaeal actin homolog.

    Science.gov (United States)

    Roeben, Annette; Kofler, Christine; Nagy, István; Nickell, Stephan; Hartl, F Ulrich; Bracher, Andreas

    2006-04-21

    Prokaryotic homologs of the eukaryotic structural protein actin, such as MreB and ParM, have been implicated in determination of bacterial cell shape, and in the segregation of genomic and plasmid DNA. In contrast to these bacterial actin homologs, little is known about the archaeal counterparts. As a first step, we expressed a predicted actin homolog of the thermophilic archaeon Thermoplasma acidophilum, Ta0583, and determined its crystal structure at 2.1A resolution. Ta0583 is expressed as a soluble protein in T.acidophilum and is an active ATPase at physiological temperature. In vitro, Ta0583 forms sheets with spacings resembling the crystal lattice, indicating an inherent propensity to form filamentous structures. The fold of Ta0583 contains the core structure of actin and clearly belongs to the actin/Hsp70 superfamily of ATPases. Ta0583 is approximately equidistant from actin and MreB on the structural level, and combines features from both eubacterial actin homologs, MreB and ParM. The structure of Ta0583 co-crystallized with ADP indicates that the nucleotide binds at the interface between the subdomains of Ta0583 in a manner similar to that of actin. However, the conformation of the nucleotide observed in complex with Ta0583 clearly differs from that in complex with actin, but closely resembles the conformation of ParM-bound nucleotide. On the basis of sequence and structural homology, we suggest that Ta0583 derives from a ParM-like actin homolog that was once encoded by a plasmid and was transferred into a common ancestor of Thermoplasma and Ferroplasma. Intriguingly, both genera are characterized by the lack of a cell wall, and therefore Ta0583 could have a function in cellular organization.

  20. Pyk2 controls filamentous actin formation in human glomerular mesangial cells via modulation of profilin expression

    Directory of Open Access Journals (Sweden)

    Victoriya A Rufanova

    2009-06-01

    Full Text Available Victoriya A Rufanova1, Anna Alexanian1, Tetsuro Wakatsuki2,3, Andrey Sorokin11Department of Medicine, Division of Nephrology, Kidney Disease Center Milwaukee, WI, USA; 2Department of Physiology, 3Bioengineering and Biotechnology Center, Medical College of Wisconsin, Milwaukee, WI, USAAbstract: In glomerular mesangial cell (GMC, important regulators of glomerular filtration, adenovirus-mediated overexpression of calcium regulated nonkinase (CRNK, a dominant interfering calcium-regulated nonreceptor proline-rich tyrosine kinase 2 (Pyk2 construct, inhibited Pyk2 activity and caused enhanced RhoA activity, enriched cortical actin formation at time of cell replating, and reduction of spreading. We aimed to further explore Pyk2 regulation of the actin dynamic during cell spreading as a vital characteristic of GMC function. GMC were infected with adenovirus encoding CRNK or green fluorescent protein (GFP as a control and 48 hours after infection cells were harvested and either re-plated or left in suspension for one hour. De novo adhesion to substrate was significantly decreased after Pyk2 activity inhibition and was further diminished after treatment with Rho-associated kinase inhibitor. Inhibition of Pyk2 was associated with increased filamentous actin formation and a corresponding decrease in globular to filamentous actin ratio during cell spreading. Phosphorylation and expression of cofilin, a RhoA-regulated filamentous actin destabilizing factor, were similar in CRNK-expressing and control GMC. Expression of profilin, an activator of actin polymerization, was enhanced, whereas phosphorylation of Pyk2 and p130Cas was decreased. Our data suggest that Pyk2 signaling controls the filamentous actin formation during cell spreading via upregulation of profilin expression.Keywords: Pyk2, profilin, cell spreading, adhesion, glomerular mesangial cells, p130Cas, actin dynamic, ROCK inhibition

  1. GROWTH AND MORPHOLOGY OF POLYMER-ACTIN COMPLEXES

    Institute of Scientific and Technical Information of China (English)

    Hyuck Joon Kwon; Kazuhiro Shikinaka; Akira Kakugo; Hidemitsu Furukawa; Yoshihito Osada; Jian Ping Gong

    2007-01-01

    F-actins are semi-flexible polyelectrolytes and can be assembled into large polymer-actin complex with polymorphism through electrostatic interaction with polycations. This study investigates the structural phase behavior and the growth of polymer-actin complexes in terms of its longitudinal and lateral sizes. Our results show that formation of polymer-actin complexes is cooperative, and morphology and growth of polymer-actin complexes depend on polycation species and concentrations of polycation and salt in a constant actin concentration. We found that the longitudinal growth and lateral growth of polymer-actin complexes are dominated by different factors. This induces the structural polymorphism of polymer-actin complexes. Major factors to influence the polymorphism of polymer-actin complexes in polyelectrolyte system have been discussed. Our results indicate that the semi-flexible polyelectrolyte nature of F-actins is important for controlling the morphology and growth of actin architectures in cell.

  2. Nano-ZnO leads to tubulin macrotube assembly and actin bundling, triggering cytoskeletal catastrophe and cell necrosis

    Science.gov (United States)

    García-Hevia, Lorena; Valiente, Rafael; Martín-Rodríguez, Rosa; Renero-Lecuna, Carlos; González, Jesús; Rodríguez-Fernández, Lidia; Aguado, Fernando; Villegas, Juan C.; Fanarraga, Mónica L.

    2016-05-01

    Zinc is a crucial element in biology that plays chief catalytic, structural and protein regulatory roles. Excess cytoplasmic zinc is toxic to cells so there are cell-entry and intracellular buffering mechanisms that control intracellular zinc availability. Tubulin and actin are two zinc-scavenging proteins that are essential components of the cellular cytoskeleton implicated in cell division, migration and cellular architecture maintenance. Here we demonstrate how exposure to different ZnO nanostructures, namely ZnO commercial nanoparticles and custom-made ZnO nanowires, produce acute cytotoxic effects in human keratinocytes (HaCat) and epithelial cells (HeLa) triggering a dose-dependent cell retraction and collapse. We show how engulfed ZnO nanoparticles dissolve intracellularly, triggering actin filament bundling and structural changes in microtubules, transforming these highly dynamic 25 nm diameter polymers into rigid macrotubes of tubulin, severely affecting cell proliferation and survival. Our results demonstrate that nano-ZnO causes acute cytoskeletal collapse that triggers necrosis, followed by a late reactive oxygen species (ROS)-dependent apoptotic process.Zinc is a crucial element in biology that plays chief catalytic, structural and protein regulatory roles. Excess cytoplasmic zinc is toxic to cells so there are cell-entry and intracellular buffering mechanisms that control intracellular zinc availability. Tubulin and actin are two zinc-scavenging proteins that are essential components of the cellular cytoskeleton implicated in cell division, migration and cellular architecture maintenance. Here we demonstrate how exposure to different ZnO nanostructures, namely ZnO commercial nanoparticles and custom-made ZnO nanowires, produce acute cytotoxic effects in human keratinocytes (HaCat) and epithelial cells (HeLa) triggering a dose-dependent cell retraction and collapse. We show how engulfed ZnO nanoparticles dissolve intracellularly, triggering actin

  3. Erbium laser resurfacing for actinic cheilitis.

    Science.gov (United States)

    Cohen, Joel L

    2013-11-01

    Actinic cheilitis is a precancerous condition characterized by grayish-whitish area(s) of discoloration on the mucosal lip, often blunting the demarcation between mucosa and cutaneous lip. Actinic cheilitis is considered to be an early part of the spectrum of squamous cell carcinoma. Squamous cell carcinoma specifically of the lip has a high rate of recurrence and metastasis through the oral cavity leading to a poor overall survival. Risk factors for the development of actinic cheilitis include chronic solar irradiation, increasing age, male gender, light skin complexion, immunosuppression, and possibly tobacco and alcohol consumption. Treatment options include topical pharmacotherapy (eg, fluorouracil, imiquimod) or procedural interventions (eg, cryotherapy, electrosurgery, surgical vermillionectomy, laser resurfacing), each with their known advantages and disadvantages. There is little consensus as to which treatment options offer the most clinical utility given the paucity of comparative clinical data. In my practice, laser resurfacing has become an important tool for the treatment of actinic cheilitis owing to its ease of use and overall safety, tolerability, and cosmetic acceptability. Herein the use of erbium laser resurfacing is described for three actinic cheilitis presentations for which I find it particularly useful: clinically prominent actinic cheilitis, biopsy-proven actinic cheilitis, and treatment of the entire lip following complete tumor excision of squamous cell carcinoma. All patients were treated with a 2940-nm erbium laser (Sciton Profile Contour Tunable Resurfacing Laser [TRL], Sciton, Inc., Palo Alto, CA).

  4. Differential remodeling of actin cytoskeleton architecture by profilin isoforms leads to distinct effects on cell migration and invasion.

    Science.gov (United States)

    Mouneimne, Ghassan; Hansen, Scott D; Selfors, Laura M; Petrak, Lara; Hickey, Michele M; Gallegos, Lisa L; Simpson, Kaylene J; Lim, James; Gertler, Frank B; Hartwig, John H; Mullins, R Dyche; Brugge, Joan S

    2012-11-13

    Dynamic actin cytoskeletal reorganization is integral to cell motility. Profilins are well-characterized regulators of actin polymerization; however, functional differences among coexpressed profilin isoforms are not well defined. Here, we demonstrate that profilin-1 and profilin-2 differentially regulate membrane protrusion, motility, and invasion; these processes are promoted by profilin-1 and suppressed by profilin-2. Compared to profilin-1, profilin-2 preferentially drives actin polymerization by the Ena/VASP protein, EVL. Profilin-2 and EVL suppress protrusive activity and cell motility by an actomyosin contractility-dependent mechanism. Importantly, EVL or profilin-2 downregulation enhances invasion in vitro and in vivo. In human breast cancer, lower EVL expression correlates with high invasiveness and poor patient outcome. We propose that profilin-2/EVL-mediated actin polymerization enhances actin bundling and suppresses breast cancer cell invasion.

  5. Emotion expression of an affective state space; a humanoid robot displaying a dynamic emotional state during a soccer game

    NARCIS (Netherlands)

    van der Mey, A.; Smit, F; Droog, K.J.; Visser, A.

    2010-01-01

    Following a soccer game is an example where clear emotions are displayed. This example is worked out for a humanoid robot which can express emotions with body language. The emotions expressed by the robot are not just stimuli-response, but are based on an affective state which shows dynamic behavior

  6. Nitrogen storage dynamics are affected by masting events in Fagus crenata.

    Science.gov (United States)

    Han, Qingmin; Kabeya, Daisuke; Iio, Atsuhiro; Inagaki, Yoshiyuki; Kakubari, Yoshitaka

    2014-03-01

    It is generally assumed that the production of a large crop of seeds depletes stores of resources and that these take more than 1 year to replenish; this is accepted, theoretically, as the proximate mechanism of mast seeding (resource budget model). However, direct evidence of resource depletion in masting trees is very rare. Here, we trace seasonal and inter-annual variations in nitrogen (N) concentration and estimate the N storage pool of individuals after full masting of Fagus crenata in two stands. In 2005, a full masting year, the amount of N in fruit litter represented half of the N present in mature leaves in an old stand (age 190-260 years), and was about equivalent to the amount of N in mature leaves in a younger stand (age 83-84 years). Due to this additional burden, both tissue N concentration and individual N storage decreased in 2006; this was followed by significant replenishment in 2007, although a substantial N store remained even after full masting. These results indicate that internal storage may be important and that N may be the limiting factor for fruiting. In the 4 years following full masting, the old stand experienced two moderate masting events separated by 2 years, whilst trees in the younger stand did not fruit. This different fruiting behavior may be related to different "costs of reproduction" in the full masting year 2005, thus providing more evidence that N may limit fruiting. Compared to the non-fruiting stand, individuals in the fruiting stand exhibited an additional increase in N concentrations in roots early in the 2007 growing season, suggesting additional N uptake from the soil to supply resource demand. The enhanced uptake may alleviate the N storage depletion observed in the full masting year. This study suggests that masting affects N cycle dynamics in mature Fagus crenata and N may be one factor limiting fruiting.

  7. Early disruption of the actin cytoskeleton in cultured cerebellar granule neurons exposed to 3-morpholinosydnonimine-oxidative stress is linked to alterations of the cytosolic calcium concentration.

    Science.gov (United States)

    Tiago, Teresa; Marques-da-Silva, Dorinda; Samhan-Arias, Alejandro K; Aureliano, Manuel; Gutierrez-Merino, Carlos

    2011-03-01

    Cytoskeleton damage is a frequent feature in neuronal cell death and one of the early events in oxidant-induced cell injury. This work addresses whether actin cytoskeleton reorganization is an early event of SIN-1-induced extracellular nitrosative/oxidative stress in cultured cerebellar granule neurons (CGN). The actin polymerization state, i.e. the relative levels of G-/F-actin, was quantitatively assessed by the ratio of the fluorescence intensities of microscopy images obtained from CGN double-labelled with Alexa594-DNase-I (for actin monomers) and Bodipy-FL-phallacidin (for actin filaments). Exposure of CGN to a flux of peroxynitrite as low as 0.5-1μM/min during 30min (achieved with 0.1mM SIN-1) was found to promote alterations of the actin cytoskeleton dynamics as it increases the G-actin/F-actin ratio. Because L-type voltage-operated Ca(2+) channels (L-VOCC) are primary targets in CGN exposed to SIN-1, the possible role of Ca(2+) dynamics on the perturbation of the actin cytoskeleton was also assessed from the cytosolic Ca(2+) concentration response to the L-VOCC's agonist FPL-64176 and to the L-VOCC's blocker nifedipine. The results showed that SIN-1 induced changes in the actin polymerization state correlated with its ability to decrease Ca(2+) influx through L-VOCC. Combined analysis of cytosolic Ca(2+) concentration and G-actin/F-actin ratio alterations by SIN-1, cytochalasin D, latrunculin B and jasplakinolide support that disruption of the actin cytoskeleton is linked to cytosolic calcium concentration changes.

  8. Actinic Granuloma with Focal Segmental Glomerulosclerosis

    Directory of Open Access Journals (Sweden)

    Ruedee Phasukthaworn

    2016-02-01

    Full Text Available Actinic granuloma is an uncommon granulomatous disease, characterized by annular erythematous plaque with central clearing predominately located on sun-damaged skin. The pathogenesis is not well understood, ultraviolet radiation is recognized as precipitating factor. We report a case of a 52-year-old woman who presented with asymptomatic annular erythematous plaques on the forehead and both cheeks persisting for 2 years. The clinical presentation and histopathologic findings support the diagnosis of actinic granuloma. During that period of time, she also developed focal segmental glomerulosclerosis. The association between actinic granuloma and focal segmental glomerulosclerosis needs to be clarified by further studies.

  9. Force-producing ADP state of myosin bound to actin.

    Science.gov (United States)

    Wulf, Sarah F; Ropars, Virginie; Fujita-Becker, Setsuko; Oster, Marco; Hofhaus, Goetz; Trabuco, Leonardo G; Pylypenko, Olena; Sweeney, H Lee; Houdusse, Anne M; Schröder, Rasmus R

    2016-03-29

    Molecular motors produce force when they interact with their cellular tracks. For myosin motors, the primary force-generating state has MgADP tightly bound, whereas myosin is strongly bound to actin. We have generated an 8-Å cryoEM reconstruction of this state for myosin V and used molecular dynamics flexed fitting for model building. We compare this state to the subsequent state on actin (Rigor). The ADP-bound structure reveals that the actin-binding cleft is closed, even though MgADP is tightly bound. This state is accomplished by a previously unseen conformation of the β-sheet underlying the nucleotide pocket. The transition from the force-generating ADP state to Rigor requires a 9.5° rotation of the myosin lever arm, coupled to a β-sheet rearrangement. Thus, the structure reveals the detailed rearrangements underlying myosin force generation as well as the basis of strain-dependent ADP release that is essential for processive myosins, such as myosin V.

  10. Importance of a Lys113-Glu195 intermonomer ionic bond in F-actin stabilization and regulation by yeast formins Bni1p and Bnr1p.

    Science.gov (United States)

    Wen, Kuo-Kuang; McKane, Melissa; Rubenstein, Peter A

    2013-06-28

    Proper actin cytoskeletal function requires actin's ability to generate a stable filament and requires that this reaction be regulated by actin-binding proteins via allosteric effects on the actin. A proposed ionic interaction in the actin filament interior between Lys(113) of one monomer and Glu(195) of a monomer in the apposing strand potentially fosters cross-strand stabilization and allosteric communication between the filament interior and exterior. We interrupted the potential interaction by creating either K113E or E195K actin. By combining the two, we also reversed the interaction with a K113E/E195K (E/K) mutant. In all cases, we isolated viable cells expressing only the mutant actin. Either single mutant cell displays significantly decreased growth in YPD medium. This deficit is rescued in the double mutant. All three mutants display abnormal phalloidin cytoskeletal staining. K113E actin exhibits a critical concentration of polymerization 4 times higher than WT actin, nucleates more poorly, and forms shorter filaments. Restoration of the ionic bond, E/K, eliminates most of these problems. E195K actin behaves much more like WT actin, indicating accommodation of the neighboring lysines. Both Bni1 and Bnr1 formin FH1-FH2 fragment accelerate polymerization of WT, E/K, and to a lesser extent E195K actin. Bni1p FH1-FH2 dramatically inhibits K113E actin polymerization, consistent with barbed end capping. However, Bnr1p FH1-FH2 restores K113E actin polymerization, forming single filaments. In summary, the proposed ionic interaction plays an important role in filament stabilization and in the propagation of allosteric changes affecting formin regulation in an isoform-specific fashion.

  11. Dynamic Association between Negative Affect and Alcohol Lapses following Alcohol Treatment

    Science.gov (United States)

    Witkiewitz, Katie; Villarroel, Nadia Aracelliz

    2009-01-01

    Clinical research has found a strong association between negative affect and returning to alcohol use after a period of abstinence. Yet little is known about the probability of a lapse given a particular level of negative affect or whether there is a reciprocal relationship between negative affect and alcohol use across time. The goal of the…

  12. Actin filaments are involved in the maintenance of Golgi cisternae morphology and intra-Golgi pH.

    Science.gov (United States)

    Lázaro-Diéguez, Francisco; Jiménez, Nuria; Barth, Holger; Koster, Abraham J; Renau-Piqueras, Jaime; Llopis, Juan L; Burger, Koert N J; Egea, Gustavo

    2006-12-01

    Here we examine the contribution of actin dynamics to the architecture and pH of the Golgi complex. To this end, we have used toxins that depolymerize (cytochalasin D, latrunculin B, mycalolide B, and Clostridium botulinum C2 toxin) or stabilize (jasplakinolide) filamentous actin. When various clonal cell lines were examined by epifluorescence microscopy, all of these actin toxins induced compaction of the Golgi complex. However, ultrastructural analysis by transmission electron microscopy and electron tomography/three-dimensional modelling of the Golgi complex showed that F-actin depolymerization first induces perforation/fragmentation and severe swelling of Golgi cisternae, which leads to a completely disorganized structure. In contrast, F-actin stabilization results only in cisternae perforation/fragmentation. Concomitantly to actin depolymerization-induced cisternae swelling and disorganization, the intra-Golgi pH significantly increased. Similar ultrastructural and Golgi pH alkalinization were observed in cells treated with the vacuolar H+ -ATPases inhibitors bafilomycin A1 and concanamycin A. Overall, these results suggest that actin filaments are implicated in the preservation of the flattened shape of Golgi cisternae. This maintenance seems to be mediated by the regulation of the state of F-actin assembly on the Golgi pH homeostasis.

  13. Scanning coherent scattering methods for actinic EUV mask inspection

    Science.gov (United States)

    Ekinci, Y.; Helfenstein, P.; Rajeev, R.; Mochi, I.; Mohacsi, I.; Gobrecht, J.; Yoshitake, S.

    2016-10-01

    Actinic mask inspection for EUV lithography with targeted specifications of resolution, sensitivity, and throughput remains a big hurdle for the successful insertion of EUVL into high volume manufacturing and effective solutions are needed to address this. We present a method for actinic mask inspection based on scanning coherent scattering microscopy. In this method, the mask is scanned with an EUV beam of relatively small spot size and the scattered light is recorded with a pixel detector. Customized algorithms reconstruct the aerial image by iteratively solving the phaseproblem using over-determined diffraction data gathered by scanning across the specimen with a finite illumination. This approach provides both phase and amplitude of actinic aerial images of the mask with high resolution without the need to use high NA (numerical aperture) lenses. Futher, we describe a reflective mode EUV mask scanning lensless imaging tool (RESCAN), which was installed at the XIL-II beamline and later at the SIM beamline of the Swiss Light Source and show reconstructed aerial images down to 10 nm (on-wafer) resolution. As a complementary method, the a-priori knowledge of the sample is employed to identify potential defect sites by analyzing the diffraction patterns. In this method, the recorded diffraction patterns are compared with the die or database data (i.e. previously measured or calculated diffraction data from the defect-free mask layout respectively) and their difference is interpreted as the defect signal. Dynamic software filtering helps to suppress the strong diffraction from defect-free structures and allows registration of faint defects with high sensitivity. Here, we discuss the basic principles of these Fourier domain techniques and its potential for actinic mask inspection with high signal-to-noise ratio and high throughput.

  14. Molecular architecture of synaptic actin cytoskeleton in hippocampal neurons reveals a mechanism of dendritic spine morphogenesis.

    Science.gov (United States)

    Korobova, Farida; Svitkina, Tatyana

    2010-01-01

    Excitatory synapses in the brain play key roles in learning and memory. The formation and functions of postsynaptic mushroom-shaped structures, dendritic spines, and possibly of presynaptic terminals, rely on actin cytoskeleton remodeling. However, the cytoskeletal architecture of synapses remains unknown hindering the understanding of synapse morphogenesis. Using platinum replica electron microscopy, we characterized the cytoskeletal organization and molecular composition of dendritic spines, their precursors, dendritic filopodia, and presynaptic boutons. A branched actin filament network containing Arp2/3 complex and capping protein was a dominant feature of spine heads and presynaptic boutons. Surprisingly, the spine necks and bases, as well as dendritic filopodia, also contained a network, rather than a bundle, of branched and linear actin filaments that was immunopositive for Arp2/3 complex, capping protein, and myosin II, but not fascin. Thus, a tight actin filament bundle is not necessary for structural support of elongated filopodia-like protrusions. Dynamically, dendritic filopodia emerged from densities in the dendritic shaft, which by electron microscopy contained branched actin network associated with dendritic microtubules. We propose that dendritic spine morphogenesis begins from an actin patch elongating into a dendritic filopodium, which tip subsequently expands via Arp2/3 complex-dependent nucleation and which length is modulated by myosin II-dependent contractility.

  15. High-speed depolymerization at actin filament ends jointly catalysed by Twinfilin and Srv2/CAP.

    Science.gov (United States)

    Johnston, Adam B; Collins, Agnieszka; Goode, Bruce L

    2015-11-01

    Purified actin filaments depolymerize slowly, and cytosolic conditions strongly favour actin assembly over disassembly, which has left our understanding of how actin filaments are rapidly turned over in vivo incomplete. One mechanism for driving filament disassembly is severing by factors such as Cofilin. However, even after severing, pointed-end depolymerization remains slow and unable to fully account for observed rates of actin filament turnover in vivo. Here we describe a mechanism by which Twinfilin and Cyclase-associated protein work in concert to accelerate depolymerization of actin filaments by 3-fold and 17-fold at their barbed and pointed ends, respectively. This mechanism occurs even under assembly conditions, allowing reconstitution and direct visualization of individual filaments undergoing tunable, accelerated treadmilling. Further, we use specific mutations to demonstrate that this activity is critical for Twinfilin function in vivo. These findings fill a major gap in our knowledge of cellular disassembly mechanisms, and suggest that depolymerization and severing may be deployed separately or together to control the dynamics and architecture of distinct actin networks.

  16. High Speed Depolymerization at Actin Filament Ends Jointly Catalyzed by Twinfilin and Srv2/CAP

    Science.gov (United States)

    Johnston, Adam B.; Collins, Agnieszka; Goode, Bruce L.

    2015-01-01

    Purified actin filaments depolymerize slowly, and cytosolic conditions strongly favor actin assembly over disassembly, which has left our understanding of how actin filaments are rapidly turned over in vivo incomplete 1,2. One mechanism for driving filament disassembly is severing by factors such as Cofilin. However, even after severing, pointed end depolymerization remains slow and unable to fully account for observed rates of actin filament turnover in vivo. Here we describe a mechanism by which Twinfilin and Cyclase-associated protein work in concert to accelerate depolymerization of actin filaments by 3-fold and 17-fold at their barbed and pointed ends, respectively. This mechanism occurs even under assembly conditions, allowing reconstitution and direct visualization of individual filaments undergoing tunable, accelerated treadmilling. Further, we use specific mutations to demonstrate that this activity is critical for Twinfilin function in vivo. These findings fill a major gap in our knowledge of mechanisms, and suggest that depolymerization and severing may be deployed separately or together to control the dynamics and architecture of distinct actin networks. PMID:26458246

  17. Molecular requirements for actin-based lamella formation in Drosophila S2 cells.

    Science.gov (United States)

    Rogers, Stephen L; Wiedemann, Ursula; Stuurman, Nico; Vale, Ronald D

    2003-09-15

    Cell migration occurs through the protrusion of the actin-enriched lamella. Here, we investigated the effects of RNAi depletion of approximately 90 proteins implicated in actin function on lamella formation in Drosophila S2 cells. Similar to in vitro reconstitution studies of actin-based Listeria movement, we find that lamellae formation requires a relatively small set of proteins that participate in actin nucleation (Arp2/3 and SCAR), barbed end capping (capping protein), filament depolymerization (cofilin and Aip1), and actin monomer binding (profilin and cyclase-associated protein). Lamellae are initiated by parallel and partially redundant signaling pathways involving Rac GTPases and the adaptor protein Nck, which stimulate SCAR, an Arp2/3 activator. We also show that RNAi of three proteins (kette, Abi, and Sra-1) known to copurify with and inhibit SCAR in vitro leads to SCAR degradation, revealing a novel function of this protein complex in SCAR stability. Our results have identified an essential set of proteins involved in actin dynamics during lamella formation in Drosophila S2 cells.

  18. T lymphocyte migration: an action movie starring the actin and associated actors

    Directory of Open Access Journals (Sweden)

    Loïc eDupré

    2015-11-01

    Full Text Available The actin cytoskeleton is composed of a dynamic filament meshwork that builds the architecture of the cell to sustain its fundamental properties. This physical structure is characterized by a continuous remodeling, which allows cells to accomplish complex motility steps such as directed migration, crossing of biological barriers and interaction with other cells. T lymphocytes excel in these motility steps to ensure their immune surveillance duties. In particular, actin cytoskeleton remodeling is key to facilitate the journey of T lymphocytes through distinct tissue environments and to tune their stop and go behavior during the scanning of antigen-presenting cells. The molecular mechanisms controlling actin cytoskeleton remodeling during T lymphocyte motility have been only partially unraveled, since the function of many actin regulators has not yet been assessed in these cells. Our review aims to integrate the current knowledge into a comprehensive picture of how the actin cytoskeleton drives T lymphocyte migration. We will present the molecular actors that control actin cytoskeleton remodeling, as well as their role in the different T lymphocyte motile steps. We will also highlight which challenges remain to be addressed experimentally and which approaches appear promising to tackle them.

  19. Communication: Microsecond dynamics of the protein and water affect electron transfer in a bacterial bc{sub 1} complex

    Energy Technology Data Exchange (ETDEWEB)

    Martin, Daniel R.; Matyushov, Dmitry V., E-mail: dmitrym@asu.edu [Department of Physics and Department of Chemistry and Biochemistry, Arizona State University, P.O. Box 871504, Tempe, Arizona 85287 (United States)

    2015-04-28

    Cross-membrane electron transport between cofactors localized in proteins of mitochondrial respiration and bacterial photosynthesis is the source of all biological energy. The statistics and dynamics of nuclear fluctuations in these protein/membrane/water heterogeneous systems are critical for their energetic efficiency. The results of 13 μs of atomistic molecular dynamics simulations of the membrane-bound bc{sub 1} bacterial complex are analyzed here. The reaction is affected by a broad spectrum of nuclear modes, with the slowest dynamics in the range of time-scales ∼0.1-1.6 μs contributing half of the reaction reorganization energy. Two reorganization energies are required to describe protein electron transfer due to dynamical arrest of protein conformations on the observation window. This mechanistic distinction allows significant lowering of activation barriers for reactions in proteins.

  20. Biophysical model of the role of actin remodeling on dendritic spine morphology

    Science.gov (United States)

    Miermans, C. A.; Kusters, R. P. T.; Hoogenraad, C. C.; Storm, C.

    2017-01-01

    Dendritic spines are small membranous structures that protrude from the neuronal dendrite. Each spine contains a synaptic contact site that may connect its parent dendrite to the axons of neighboring neurons. Dendritic spines are markedly distinct in shape and size, and certain types of stimulation prompt spines to evolve, in fairly predictable fashion, from thin nascent morphologies to the mushroom-like shapes associated with mature spines. It is well established that the remodeling of spines is strongly dependent upon the actin cytoskeleton inside the spine. A general framework that details the precise role of actin in directing the transitions between the various spine shapes is lacking. We address this issue, and present a quantitative, model-based scenario for spine plasticity validated using realistic and physiologically relevant parameters. Our model points to a crucial role for the actin cytoskeleton. In the early stages of spine formation, the interplay between the elastic properties of the spine membrane and the protrusive forces generated in the actin cytoskeleton propels the incipient spine. In the maturation stage, actin remodeling in the form of the combined dynamics of branched and bundled actin is required to form mature, mushroom-like spines. Importantly, our model shows that constricting the spine-neck aids in the stabilization of mature spines, thus pointing to a role in stabilization and maintenance for additional factors such as ring-like F-actin structures. Taken together, our model provides unique insights into the fundamental role of actin remodeling and polymerization forces during spine formation and maturation. PMID:28158194

  1. Mechanics model for actin-based motility.

    Science.gov (United States)

    Lin, Yuan

    2009-02-01

    We present here a mechanics model for the force generation by actin polymerization. The possible adhesions between the actin filaments and the load surface, as well as the nucleation and capping of filament tips, are included in this model on top of the well-known elastic Brownian ratchet formulation. A closed form solution is provided from which the force-velocity relationship, summarizing the mechanics of polymerization, can be drawn. Model predictions on the velocity of moving beads driven by actin polymerization are consistent with experiment observations. This model also seems capable of explaining the enhanced actin-based motility of Listeria monocytogenes and beads by the presence of Vasodilator-stimulated phosphoprotein, as observed in recent experiments.

  2. Cross-linking study on skeletal muscle actin: properties of suberimidate-treated actin.

    Science.gov (United States)

    Ohara, O; Takahashi, S; Ooi, T; Fujiyoshi, Y

    1982-06-01

    Cross-linking experiments were performed on muscle skeletal actin, using imidoesters of various chain lengths. Chemical analyses on all products except one (derived from succinimidate) show evidence of the presence of intramolecular cross-links in the molecule. The detailed properties of suberimidate-treated actin (SA) are as follows: SA contains nearly 1 mol of intramolecular cross-link per mol of actin and less than 15% of intermolecularly cross-linked products. Even at a low salt concentration, SA is polymeric, exchanges slowly its bound nucleotide with free nucleotides in solution, and shows an F-actin-type CD spectrum. Electron micrographs of SA reveal that SA exists actually as fibrous polymers in solutions of low ionic strength, although the fibers seem to be less rigid than those at high salt concentration. The F-form of SA at a high salt concentration is indistinguishable from intact F-actin. SA can bind heavy meromyosin and activate the ATPase of heavy meromyosin as observed for intact F-actin. Tropomyosin binds SA only at a high salt concentration. These results show that SA possesses the properties of F-actin even in media of low salt concentration, which are favorable for depolymerization of F-actin. Thus, we may infer that the conformation of SA is frozen in the F-state of actin by the introduction of intramolecular cross-links in the protein.

  3. Molecular characterization of Toxoplasma gondii formin 3, an actin nucleator dispensable for tachyzoite growth and motility.

    Science.gov (United States)

    Daher, Wassim; Klages, Natacha; Carlier, Marie-France; Soldati-Favre, Dominique

    2012-03-01

    Toxoplasma gondii belongs to the phylum Apicomplexa, a group of obligate intracellular parasites that rely on gliding motility to enter host cells. Drugs interfering with the actin cytoskeleton block parasite motility, host cell invasion, and egress from infected cells. Myosin A, profilin, formin 1, formin 2, and actin-depolymerizing factor have all been implicated in parasite motility, yet little is known regarding the importance of actin polymerization and other myosins for the remaining steps of the parasite lytic cycle. Here we establish that T. gondii formin 3 (TgFRM3), a newly described formin homology 2 domain (FH2)-containing protein, binds to Toxoplasma actin and nucleates rabbit actin assembly in vitro. TgFRM3 expressed as a transgene exhibits a patchy localization at several distinct structures within the parasite. Disruption of the TgFRM3 gene by double homologous recombination in a ku80-ko strain reveals no vital function for tachyzoite propagation in vitro, which is consistent with its weak level of expression in this life stage. Conditional stabilization of truncated forms of TgFRM3 suggests that different regions of the molecule contribute to distinct localizations. Moreover, expression of TgFRM3 lacking the C-terminal domain severely affects parasite growth and replication. This work provides a first insight into how this specialized formin, restricted to the group of coccidia, completes its actin-nucleating activity.

  4. Actin: its cumbersome pilgrimage through cellular compartments.

    Science.gov (United States)

    Schleicher, Michael; Jockusch, Brigitte M

    2008-06-01

    In this article, we follow the history of one of the most abundant, most intensely studied proteins of the eukaryotic cells: actin. We report on hallmarks of its discovery, its structural and functional characterization and localization over time, and point to present days' knowledge on its position as a member of a large family. We focus on the rather puzzling number of diverse functions as proposed for actin as a dual compartment protein. Finally, we venture on some speculations as to its origin.

  5. [When and why treat actinic keratoses?].

    Science.gov (United States)

    Wulf, Hans Christian

    2014-02-03

    Actinic keratoses (AK) are small, inflamed, hyperkeratotic, sunprovoked lesions which may progress to squamous cell carcinoma (SCC). There are two main reasons for treating AK: one is as prophylaxis against SCC, the other is because of cosmetic discomfort, with clothes getting caught in the hyperkeratotic AK. Visible AK and neighbouring invisible AK should be treated. As AK are provoked by UV radiation, protection against UV is essential. This paper comments on a Cochrane review: "Interventions for actinic keratosis" and treatments avaliable in Denmark.

  6. Sarcomeric pattern formation by actin cluster coalescence.

    Directory of Open Access Journals (Sweden)

    Benjamin M Friedrich

    Full Text Available Contractile function of striated muscle cells depends crucially on the almost crystalline order of actin and myosin filaments in myofibrils, but the physical mechanisms that lead to myofibril assembly remains ill-defined. Passive diffusive sorting of actin filaments into sarcomeric order is kinetically impossible, suggesting a pivotal role of active processes in sarcomeric pattern formation. Using a one-dimensional computational model of an initially unstriated actin bundle, we show that actin filament treadmilling in the presence of processive plus-end crosslinking provides a simple and robust mechanism for the polarity sorting of actin filaments as well as for the correct localization of myosin filaments. We propose that the coalescence of crosslinked actin clusters could be key for sarcomeric pattern formation. In our simulations, sarcomere spacing is set by filament length prompting tight length control already at early stages of pattern formation. The proposed mechanism could be generic and apply both to premyofibrils and nascent myofibrils in developing muscle cells as well as possibly to striated stress-fibers in non-muscle cells.

  7. Sarcomeric Pattern Formation by Actin Cluster Coalescence

    Science.gov (United States)

    Friedrich, Benjamin M.; Fischer-Friedrich, Elisabeth; Gov, Nir S.; Safran, Samuel A.

    2012-01-01

    Contractile function of striated muscle cells depends crucially on the almost crystalline order of actin and myosin filaments in myofibrils, but the physical mechanisms that lead to myofibril assembly remains ill-defined. Passive diffusive sorting of actin filaments into sarcomeric order is kinetically impossible, suggesting a pivotal role of active processes in sarcomeric pattern formation. Using a one-dimensional computational model of an initially unstriated actin bundle, we show that actin filament treadmilling in the presence of processive plus-end crosslinking provides a simple and robust mechanism for the polarity sorting of actin filaments as well as for the correct localization of myosin filaments. We propose that the coalescence of crosslinked actin clusters could be key for sarcomeric pattern formation. In our simulations, sarcomere spacing is set by filament length prompting tight length control already at early stages of pattern formation. The proposed mechanism could be generic and apply both to premyofibrils and nascent myofibrils in developing muscle cells as well as possibly to striated stress-fibers in non-muscle cells. PMID:22685394

  8. Colocalization of synapsin and actin during synaptic vesicle recycling

    DEFF Research Database (Denmark)

    Bloom, Ona; Evergren, Emma; Tomilin, Nikolay;

    2003-01-01

    activity, however, synapsin was detected in the pool of vesicles proximal to the active zone. In addition, actin and synapsin were found colocalized in a dynamic filamentous cytomatrix at the sites of synaptic vesicle recycling, endocytic zones. Synapsin immunolabeling was not associated with clathrin......-coated intermediates but was found on vesicles that appeared to be recycling back to the cluster. Disruption of synapsin function by microinjection of antisynapsin antibodies resulted in a prominent reduction of the cytomatrix at endocytic zones of active synapses. Our data suggest that in addition to its known...

  9. Internal Motility in Stiffening Actin-Myosin Networks

    CERN Document Server

    Uhde, J; Sackmann, E; Parmeggiani, A; Frey, E; Uhde, Joerg; Keller, Manfred; Sackmann, Erich; Parmeggiani, Andrea; Frey, Erwin

    2003-01-01

    We present a study on filamentous actin solutions containing heavy meromyosin subfragments of myosin II motor molecules. We focus on the viscoelastic phase behavior and internal dynamics of such networks during ATP depletion. Upon simultaneously using micro-rheology and fluorescence microscopy as complementary experimental tools, we find a sol-gel transition accompanied by a sudden onset of directed filament motion. We interpret the sol-gel transition in terms of myosin II enzymology, and suggest a "zipping" mechanism to explain the filament motion in the vicinity of the sol-gel transition.

  10. Structure of a Longitudinal Actin Dimer Assembled by Tandem W Domains: Implications for Actin Filament Nucleation

    Energy Technology Data Exchange (ETDEWEB)

    Rebowski, Grzegorz; Namgoong, Suk; Boczkowska, Malgorzata; Leavis, Paul C.; Navaza, Jorge; Dominguez, Roberto (IBS); (BBRI); (UPENN-MED)

    2013-11-20

    Actin filament nucleators initiate polymerization in cells in a regulated manner. A common architecture among these molecules consists of tandem WASP homology 2 domains (W domains) that recruit three to four actin subunits to form a polymerization nucleus. We describe a low-resolution crystal structure of an actin dimer assembled by tandem W domains, where the first W domain is cross-linked to Cys374 of the actin subunit bound to it, whereas the last W domain is followed by the C-terminal pointed end-capping helix of thymosin {beta}4. While the arrangement of actin subunits in the dimer resembles that of a long-pitch helix of the actin filament, important differences are observed. These differences result from steric hindrance of the W domain with intersubunit contacts in the actin filament. We also determined the structure of the first W domain of Vibrio parahaemolyticus VopL cross-linked to actin Cys374 and show it to be nearly identical with non-cross-linked W-Actin structures. This result validates the use of cross-linking as a tool for the study of actin nucleation complexes, whose natural tendency to polymerize interferes with most structural methods. Combined with a biochemical analysis of nucleation, the structures may explain why nucleators based on tandem W domains with short inter-W linkers have relatively weak activity, cannot stay bound to filaments after nucleation, and are unlikely to influence filament elongation. The findings may also explain why nucleation-promoting factors of the Arp2/3 complex, which are related to tandem-W-domain nucleators, are ejected from branch junctions after nucleation. We finally show that the simple addition of the C-terminal pointed end-capping helix of thymosin {beta}4 to tandem W domains can change their activity from actin filament nucleation to monomer sequestration.

  11. Structure of a longitudinal actin dimer assembled by tandem w domains: implications for actin filament nucleation.

    Science.gov (United States)

    Rebowski, Grzegorz; Namgoong, Suk; Boczkowska, Malgorzata; Leavis, Paul C; Navaza, Jorge; Dominguez, Roberto

    2010-10-15

    Actin filament nucleators initiate polymerization in cells in a regulated manner. A common architecture among these molecules consists of tandem WASP homology 2 domains (W domains) that recruit three to four actin subunits to form a polymerization nucleus. We describe a low-resolution crystal structure of an actin dimer assembled by tandem W domains, where the first W domain is cross-linked to Cys374 of the actin subunit bound to it, whereas the last W domain is followed by the C-terminal pointed end-capping helix of thymosin β4. While the arrangement of actin subunits in the dimer resembles that of a long-pitch helix of the actin filament, important differences are observed. These differences result from steric hindrance of the W domain with intersubunit contacts in the actin filament. We also determined the structure of the first W domain of Vibrio parahaemolyticus VopL cross-linked to actin Cys374 and show it to be nearly identical with non-cross-linked W-Actin structures. This result validates the use of cross-linking as a tool for the study of actin nucleation complexes, whose natural tendency to polymerize interferes with most structural methods. Combined with a biochemical analysis of nucleation, the structures may explain why nucleators based on tandem W domains with short inter-W linkers have relatively weak activity, cannot stay bound to filaments after nucleation, and are unlikely to influence filament elongation. The findings may also explain why nucleation-promoting factors of the Arp2/3 complex, which are related to tandem-W-domain nucleators, are ejected from branch junctions after nucleation. We finally show that the simple addition of the C-terminal pointed end-capping helix of thymosin β4 to tandem W domains can change their activity from actin filament nucleation to monomer sequestration.

  12. Drosophila cyfip regulates synaptic development and endocytosis by suppressing filamentous actin assembly.

    Science.gov (United States)

    Zhao, Lu; Wang, Dan; Wang, Qifu; Rodal, Avital A; Zhang, Yong Q

    2013-04-01

    The formation of synapses and the proper construction of neural circuits depend on signaling pathways that regulate cytoskeletal structure and dynamics. After the mutual recognition of a growing axon and its target, multiple signaling pathways are activated that regulate cytoskeletal dynamics to determine the morphology and strength of the connection. By analyzing Drosophila mutations in the cytoplasmic FMRP interacting protein Cyfip, we demonstrate that this component of the WAVE complex inhibits the assembly of filamentous actin (F-actin) and thereby regulates key aspects of synaptogenesis. Cyfip regulates the distribution of F-actin filaments in presynaptic neuromuscular junction (NMJ) terminals. At cyfip mutant NMJs, F-actin assembly was accelerated, resulting in shorter NMJs, more numerous satellite boutons, and reduced quantal content. Increased synaptic vesicle size and failure to maintain excitatory junctional potential amplitudes under high-frequency stimulation in cyfip mutants indicated an endocytic defect. cyfip mutants exhibited upregulated bone morphogenetic protein (BMP) signaling, a major growth-promoting pathway known to be attenuated by endocytosis at the Drosophila NMJ. We propose that Cyfip regulates synapse development and endocytosis by inhibiting actin assembly.

  13. Noisy Oscillations in the Actin Cytoskeleton of Chemotactic Amoeba

    Science.gov (United States)

    Negrete, Jose; Pumir, Alain; Hsu, Hsin-Fang; Westendorf, Christian; Tarantola, Marco; Beta, Carsten; Bodenschatz, Eberhard

    2016-09-01

    Biological systems with their complex biochemical networks are known to be intrinsically noisy. Here we investigate the dynamics of actin polymerization of amoeboid cells, which are close to the onset of oscillations. We show that the large phenotypic variability in the polymerization dynamics can be accurately captured by a generic nonlinear oscillator model in the presence of noise. We determine the relative role of the noise with a single dimensionless, experimentally accessible parameter, thus providing a quantitative description of the variability in a population of cells. Our approach, which rests on a generic description of a system close to a Hopf bifurcation and includes the effect of noise, can characterize the dynamics of a large class of noisy systems close to an oscillatory instability.

  14. Unveiling interactions among mitochondria, caspase-like proteases, and the actin cytoskeleton during plant programmed cell death (PCD.

    Directory of Open Access Journals (Sweden)

    Christina E N Lord

    Full Text Available Aponogeton madagascariensis produces perforations over its leaf surface via programmed cell death (PCD. PCD begins between longitudinal and transverse veins at the center of spaces regarded as areoles, and continues outward, stopping several cells from these veins. The gradient of PCD that exists within a single areole of leaves in an early stage of development was used as a model to investigate cellular dynamics during PCD. Mitochondria have interactions with a family of proteases known as caspases, and the actin cytoskeleton during metazoan PCD; less is known regarding these interactions during plant PCD. This study employed the actin stain Alexa Fluor 488 phalloidin, the actin depolymerizer Latrunculin B (Lat B, a synthetic caspase peptide substrate and corresponding specific inhibitors, as well as the mitochondrial pore inhibitor cyclosporine A (CsA to analyze the role of these cellular constituents during PCD. Results depicted that YVADase (caspase-1 activity is higher during the very early stages of perforation formation, followed by the bundling and subsequent breakdown of actin. Actin depolymerization using Lat B caused no change in YVADase activity. In vivo inhibition of YVADase activity prevented PCD and actin breakdown, therefore substantiating actin as a likely substrate for caspase-like proteases (CLPs. The mitochondrial pore inhibitor CsA significantly decreased YVADase activity, and prevented both PCD and actin breakdown; therefore suggesting the mitochondria as a possible trigger for CLPs during PCD in the lace plant. To our knowledge, this is the first in vivo study using either caspase-1 inhibitor (Ac-YVAD-CMK or CsA, following which the actin cytoskeleton was examined. Overall, our findings suggest the mitochondria as a possible upstream activator of YVADase activity and implicate these proteases as potential initiators of actin breakdown during perforation formation via PCD in the lace plant.

  15. The actin-binding proteins eps8 and gelsolin have complementary roles in regulating the growth and stability of mechanosensory hair bundles of mammalian cochlear outer hair cells.

    Directory of Open Access Journals (Sweden)

    Jennifer Olt

    Full Text Available Sound transduction depends upon mechanosensitive channels localized on the hair-like bundles that project from the apical surface of cochlear hair cells. Hair bundles show a stair-case structure composed of rows of stereocilia, and each stereocilium contains a core of tightly-packed and uniformly-polarized actin filaments. The growth and maintenance of the stereociliary actin core are dynamically regulated. Recently, it was shown that the actin-binding protein gelsolin is expressed in the stereocilia of outer hair cells (OHCs and in its absence they become long and straggly. Gelsolin is part of a whirlin scaffolding protein complex at the stereocilia tip, which has been shown to interact with other actin regulatory molecules such as Eps8. Here we investigated the physiological effects associated with the absence of gelsolin and its possible overlapping role with Eps8. We found that, in contrast to Eps8, gelsolin does not affect mechanoelectrical transduction during immature stages of development. Moreover, OHCs from gelsolin knockout mice were able to mature into fully functional sensory receptors as judged by the normal resting membrane potential and basolateral membrane currents. Mechanoelectrical transducer current in gelsolin-Eps8 double knockout mice showed a profile similar to that observed in the single mutants for Eps8. We propose that gelsolin has a non-overlapping role with Eps8. While Eps8 is mainly involved in the initial growth of stereocilia in both inner hair cells (IHCs and OHCs, gelsolin is required for the maintenance of mature hair bundles of low-frequency OHCs after the onset of hearing.

  16. Depolymerization of cortical actin inhibits UT-A1 urea transporter endocytosis but promotes forskolin-stimulated membrane trafficking.

    Science.gov (United States)

    Xu, Gang; Su, Hua; Carter, Conner B; Fröhlich, Otto; Chen, Guangping

    2012-04-01

    The cytoskeleton participates in many aspects of transporter protein regulation. In this study, by using yeast two-hybrid screening, we identified the cytoskeletal protein actin as a binding partner with the UT-A1 urea transporter. This suggests that actin plays a role in regulating UT-A1 activity. Actin specifically binds to the carboxyl terminus of UT-A1. A serial mutation study shows that actin binding to UT-A1's carboxyl terminus was abolished when serine 918 was mutated to alanine. In polarized UT-A1-MDCK cells, cortical filamentous (F) actin colocalizes with UT-A1 at the apical membrane and the subapical cytoplasm. In the cell surface, both actin and UT-A1 are distributed in the lipid raft microdomains. Disruption of the F-actin cytoskeleton by latrunculin B resulted in UT-A1 accumulation in the cell membrane as measured by biotinylation. This effect was mainly due to inhibition of UT-A1 endocytosis in both clathrin and caveolin-mediated endocytic pathways. In contrast, actin depolymerization facilitated forskolin-stimulated UT-A1 trafficking to the cell surface. Functionally, depolymerization of actin by latrunculin B significantly increased UT-A1 urea transport activity in an oocyte expression system. Our study shows that cortical F-actin not only serves as a structural protein, but directly interacts with UT-A1 and plays an important role in controlling UT-A1 cell surface expression by affecting both endocytosis and trafficking, therefore regulating UT-A1 bioactivity.

  17. Lamellipodin promotes actin assembly by clustering Ena/VASP proteins and tethering them to actin filaments.

    Science.gov (United States)

    Hansen, Scott D; Mullins, R Dyche

    2015-01-01

    Enabled/Vasodilator (Ena/VASP) proteins promote actin filament assembly at multiple locations, including: leading edge membranes, focal adhesions, and the surface of intracellular pathogens. One important Ena/VASP regulator is the mig-10/Lamellipodin/RIAM family of adaptors that promote lamellipod formation in fibroblasts and drive neurite outgrowth and axon guidance in neurons. To better understand how MRL proteins promote actin network formation we studied the interactions between Lamellipodin (Lpd), actin, and VASP, both in vivo and in vitro. We find that Lpd binds directly to actin filaments and that this interaction regulates its subcellular localization and enhances its effect on VASP polymerase activity. We propose that Lpd delivers Ena/VASP proteins to growing barbed ends and increases their polymerase activity by tethering them to filaments. This interaction represents one more pathway by which growing actin filaments produce positive feedback to control localization and activity of proteins that regulate their assembly.

  18. Septins promote F-actin ring formation by crosslinking actin filaments into curved bundles.

    Science.gov (United States)

    Mavrakis, Manos; Azou-Gros, Yannick; Tsai, Feng-Ching; Alvarado, José; Bertin, Aurélie; Iv, Francois; Kress, Alla; Brasselet, Sophie; Koenderink, Gijsje H; Lecuit, Thomas

    2014-04-01

    Animal cell cytokinesis requires a contractile ring of crosslinked actin filaments and myosin motors. How contractile rings form and are stabilized in dividing cells remains unclear. We address this problem by focusing on septins, highly conserved proteins in eukaryotes whose precise contribution to cytokinesis remains elusive. We use the cleavage of the Drosophila melanogaster embryo as a model system, where contractile actin rings drive constriction of invaginating membranes to produce an epithelium in a manner akin to cell division. In vivo functional studies show that septins are required for generating curved and tightly packed actin filament networks. In vitro reconstitution assays show that septins alone bundle actin filaments into rings, accounting for the defects in actin ring formation in septin mutants. The bundling and bending activities are conserved for human septins, and highlight unique functions of septins in the organization of contractile actomyosin rings.

  19. Actin-Sorting Nexin 27 (SNX27)-Retromer Complex Mediates Rapid Parathyroid Hormone Receptor Recycling.

    Science.gov (United States)

    McGarvey, Jennifer C; Xiao, Kunhong; Bowman, Shanna L; Mamonova, Tatyana; Zhang, Qiangmin; Bisello, Alessandro; Sneddon, W Bruce; Ardura, Juan A; Jean-Alphonse, Frederic; Vilardaga, Jean-Pierre; Puthenveedu, Manojkumar A; Friedman, Peter A

    2016-05-20

    The G protein-coupled parathyroid hormone receptor (PTHR) regulates mineral-ion homeostasis and bone remodeling. Upon parathyroid hormone (PTH) stimulation, the PTHR internalizes into early endosomes and subsequently traffics to the retromer complex, a sorting platform on early endosomes that promotes recycling of surface receptors. The C terminus of the PTHR contains a type I PDZ ligand that binds PDZ domain-containing proteins. Mass spectrometry identified sorting nexin 27 (SNX27) in isolated endosomes as a PTHR binding partner. PTH treatment enriched endosomal PTHR. SNX27 contains a PDZ domain and serves as a cargo selector for the retromer complex. VPS26, VPS29, and VPS35 retromer subunits were isolated with PTHR in endosomes from cells stimulated with PTH. Molecular dynamics and protein binding studies establish that PTHR and SNX27 interactions depend on the PDZ recognition motif in PTHR and the PDZ domain of SNX27. Depletion of either SNX27 or VPS35 or actin depolymerization decreased the rate of PTHR recycling following agonist stimulation. Mutating the PDZ ligand of PTHR abolished the interaction with SNX27 but did not affect the overall rate of recycling, suggesting that PTHR may directly engage the retromer complex. Coimmunoprecipitation and overlay experiments show that both intact and mutated PTHR bind retromer through the VPS26 protomer and sequentially assemble a ternary complex with PTHR and SNX27. SNX27-independent recycling may involve N-ethylmaleimide-sensitive factor, which binds both PDZ intact and mutant PTHRs. We conclude that PTHR recycles rapidly through at least two pathways, one involving the ASRT complex of actin, SNX27, and retromer and another possibly involving N-ethylmaleimide-sensitive factor.

  20. Dynamic and Geological-Ecological Spatial Planning Approach in Hot Mud Volcano Affected Area in Porong-Sidoarjo

    Directory of Open Access Journals (Sweden)

    Haryo Sulistyarso

    2010-08-01

    Full Text Available By May 29t h 2006 with an average hot mud volcano volume of 100,000 m3 /per day, disasters on well kick (i.e. Lapindo Brantas Ltd. in Banjar Panji 1 drilling well have deviated the Spatial Planning of Sidoarjo’s Regency for 2003- 2013. Regional Development Concept that is aimed at developing triangle growth pole model on SIBORIAN (SIdoarjo-JaBOn-KRIaAN could not be implemented. This planning cannot be applied due to environmental imbalance to sub district of Porong that was damaged by hot mud volcano. In order to anticipate deviations of the Regional and Spatial Planning of Sidoarjo Regency for 2003-2013, a review on regional planning and dynamic implementation as well as Spatial Planning Concept based on geologicalecological condition are required, especially the regions affected by well kick disaster. The spatial analysis is based on the geological and ecological condition by using an overlay technique using several maps of hot mud volcano affected areas. In this case, dynamic implementation is formulated to the responsiblity plan that can happen at any time because of uncertain ending of the hot mud volcano eruption disaster in Porong. The hot mud volcano affected areas in the Sidoarjo’s Spatial Planning 2009-2029 have been decided as a geologic protected zone. The result of this research is scenarios of spatial planning for the affected area (short term, medium term and long term spatial planning scenarios.

  1. Delayed system response times affect immediate physiology and the dynamics of subsequent button press behavior.

    Science.gov (United States)

    Kohrs, Christin; Hrabal, David; Angenstein, Nicole; Brechmann, André

    2014-11-01

    System response time research is an important issue in human-computer interactions. Experience with technical devices and general rules of human-human interactions determine the user's expectation, and any delay in system response time may lead to immediate physiological, emotional, and behavioral consequences. We investigated such effects on a trial-by-trial basis during a human-computer interaction by measuring changes in skin conductance (SC), heart rate (HR), and the dynamics of button press responses. We found an increase in SC and a deceleration of HR for all three delayed system response times (0.5, 1, 2 s). Moreover, the data on button press dynamics was highly informative since subjects repeated a button press with more force in response to delayed system response times. Furthermore, the button press dynamics could distinguish between correct and incorrect decisions and may thus even be used to infer the uncertainty of a user's decision.

  2. p95-APP1 links membrane transport to Rac-mediated reorganization of actin

    DEFF Research Database (Denmark)

    Di Cesare, A; Paris, S; Albertinazzi, C;

    2000-01-01

    Motility requires protrusive activity at the cellular edge, where Rho family members regulate actin dynamics. Here we show that p95-APP1 (ArfGAP-putative, Pix-interacting, paxillin-interacting protein 1), a member of the GIT1/PKL family, is part of a complex that interacts with Rac. Wild-type and...

  3. Incorporation of mammalian actin into microfilaments in plant cell nucleus

    Directory of Open Access Journals (Sweden)

    Paves Heiti

    2004-04-01

    Full Text Available Abstract Background Actin is an ancient molecule that shows more than 90% amino acid homology between mammalian and plant actins. The regions of the actin molecule that are involved in F-actin assembly are largely conserved, and it is likely that mammalian actin is able to incorporate into microfilaments in plant cells but there is no experimental evidence until now. Results Visualization of microfilaments in onion bulb scale epidermis cells by different techniques revealed that rhodamine-phalloidin stained F-actin besides cytoplasm also in the nuclei whereas GFP-mouse talin hybrid protein did not enter the nuclei. Microinjection of fluorescently labeled actin was applied to study the presence of nuclear microfilaments in plant cells. Ratio imaging of injected fluorescent rabbit skeletal muscle actin and phalloidin staining of the microinjected cells showed that mammalian actin was able to incorporate into plant F-actin. The incorporation occurred preferentially in the nucleus and in the perinuclear region of plant cells whereas part of plant microfilaments, mostly in the periphery of cytoplasm, did not incorporate mammalian actin. Conclusions Microinjected mammalian actin is able to enter plant cell's nucleus, whereas incorporation of mammalian actin into plant F-actin occurs preferentially in the nucleus and perinuclear area.

  4. Self-organized podosomes are dynamic mechanosensors

    OpenAIRE

    2008-01-01

    Podosomes are self-organized dynamic actin-containing structures that adhere to the extracellular matrix via integrins [1–5]. Yet it is not clear what regulates podosome dynamics and whether podosomes can function as direct mechanosensors like focal adhesions [6–9]. We show here that myosin IIs form circular structures outside and at the podosome actin ring to regulate podosome dynamics. Inhibiting myosin II-dependent tension dissipated podosome actin rings before dissipating the myosin ring ...

  5. 动力性肺动脉高压犬肺动脉PCNA及α-平滑肌肌动蛋白的表达%Expression of PCNA and α-smooth muscle actin in pulmonary arteries of dogs with dynamic pulmonary hypertension

    Institute of Scientific and Technical Information of China (English)

    崔勤; 杨景学; 赵建斌; 朱海龙

    2001-01-01

    目的探讨平滑肌细胞增殖在动力性肺动脉高压形成中的作用. 方法利用降主动脉—左下肺动脉分流建立的幼犬动力性肺动脉高压模型,取90 d肺组织病理切片,应用鼠抗人增殖细胞核抗原(PCNA)抗体、α-平滑肌细胞肌动蛋白抗体(α-actin)、及Dako二抗免疫组化检测,图像分析仪对所得结果进行分析,然后计数高倍镜下平滑肌细胞总数及PCNA细胞阳性数,计算细胞增殖指数. 结果分流犬左下肺动脉中膜α-actin免疫组化染色呈强阳性表达,右下肺动脉弱阳性,而对照组均呈阴性;分流犬左下肺动脉PCNA阳性信号表达明显多于右肺动脉,而右肺动脉及左上肺动脉仅有少量表达;增殖指数左下肺动脉内膜为33%,中膜11%,外膜7%,右下肺动脉仅为少量. 结论平滑肌细胞增殖参与实验犬动力性肺动脉高压形成过程并与肺动脉压力增高程度和肺血管重构改变一致.%AIM To explore the action of pulmonary artery smooth muscle cell proliferation in formation of dynamic pulmonary hypertension. METHODS Using the pulmonary hypertension(PH) model of shunt from descending aorta-to-left lower pulmonary artery, the sample of the lung tissue in shunt dogs was obtained on the 90th day postoperation. The examination of PCNA and a-actin was done by immunohistochemistry method using PCAN and a-actin antibodies. The slices of pulmonary tissue were observed under high power microscope, and the data were analyzed by image pattern analysor. The positive cells of PCNA and a-actin were recorded and the percentage was calculated. RESULTS Expression of a-actin in left lower pulmonary artery was strong positive and right pulmonary artery milder than that in left pulmonary, and control group was negative. The positive expression of PCNA in left lower pulmonary arteries was more than that of right lung and upper left lobe. The index of cell proliferation was 33% in intima, 11

  6. Bacillus subtilis actin-like protein MreB influences the positioning of the replication machinery and requires membrane proteins MreC/D and other actin-like proteins for proper localization

    Directory of Open Access Journals (Sweden)

    Defeu Soufo Hervé Joël

    2005-03-01

    Full Text Available Abstract Background Bacterial actin-like proteins have been shown to perform essential functions in several aspects of cellular physiology. They affect cell growth, cell shape, chromosome segregation and polar localization of proteins, and localize as helical filaments underneath the cell membrane. Bacillus subtilis MreB and Mbl have been shown to perform dynamic motor like movements within cells, extending along helical tracks in a time scale of few seconds. Results In this work, we show that Bacillus subtilis MreB has a dual role, both in the formation of rod cell shape, and in chromosome segregation, however, its function in cell shape is distinct from that of MreC. Additionally, MreB is important for the localization of the replication machinery to the cell centre, which becomes aberrant soon after depletion of MreB. 3D image reconstructions suggest that frequently, MreB filaments consist of several discontinuous helical filaments with varying length. The localization of MreB was abnormal in cells with decondensed chromosomes, as well as during depletion of Mbl, MreBH and of the MreC/MreD proteins, which we show localize to the cell membrane. Thus, proper positioning of MreB filaments depends on and is affected by a variety of factors in the cell. Conclusion Our data provide genetic and cytological links between MreB and the membrane, as well as with other actin like proteins, and further supports the connection of MreB with the chromosome. The functional dependence on MreB of the localization of the replication machinery suggests that the replisome is not anchored at the cell centre, but is positioned in a dynamic manner.

  7. Dynamic and Static Exercises Differentially Affect Plasma Cytokine Content in Elite Endurance- and Strength-Trained Athletes and Untrained Volunteers

    Science.gov (United States)

    Kapilevich, Leonid V.; Zakharova, Anna N.; Kabachkova, Anastasia V.; Kironenko, Tatyana A.; Orlov, Sergei N.

    2017-01-01

    Extensive exercise increases the plasma content of IL-6, IL-8, IL-15, leukemia inhibitory factor (LIF), and several other cytokines via their augmented transcription in skeletal muscle cells. However, the relative impact of aerobic and resistant training interventions on cytokine production remains poorly defined. In this study, we compared effects of dynamic and static load on cytokine plasma content in elite strength- and endurance-trained athletes vs. healthy untrained volunteers. The plasma cytokine content was measured before, immediately after, and 30 min post-exercise using enzyme-linked immunosorbent assay. Pedaling on a bicycle ergometer increased IL-6 and IL-8 content in the plasma of trained athletes by about 4- and 2-fold, respectively. In contrast to dynamic load, weightlifting had negligible impact on these parameters in strength exercise-trained athletes. Unlike IL-6 and IL-8, dynamic exercise had no impact on IL-15 and LIF, whereas static load increases the content of these cytokines by ~50%. Two-fold increment of IL-8 content seen in athletes subjected to dynamic exercise was absent in untrained individuals, whereas the ~50% increase in IL-15 triggered by static load in the plasma of weightlifting athletes was not registered in the control group. Thus, our results show the distinct impact of static and dynamic exercises on cytokine content in the plasma of trained athletes. They also demonstrate that both types of exercises differentially affect cytokine content in plasma of athletes and untrained persons.

  8. Forces affecting employment dynamics in Drenthe; Case study in a leading rural region in the Netherlands

    NARCIS (Netherlands)

    Terluin, I.J.; Post, J.H.; Wisselink, A.J.; Overbeek, M.M.M.

    1999-01-01

    In this report the focus is on employment dynamics in Drenthe since the beginning of the 1980s. This study is part of an EU wide research project on employment development in leading and lagging rural regions of the EU. Total employment in Drenthe increased by 24,500 jobs or with over 20% in the per

  9. Lipopolysaccharide infusion enhances dynamic cerebral autoregulation without affecting cerebral oxygen vasoreactivity in healthy volunteers

    DEFF Research Database (Denmark)

    Berg, Ronan Mg; Plovsing, Ronni R; Evans, Kevin A;

    2013-01-01

    Sepsis may be associated with disturbances in cerebral oxygen transport and cerebral haemodynamic function, thus rendering the brain particularly susceptible to hypoxia. The purpose of this study was to assess the impact of isocapnic hypoxia and hyperoxia on dynamic cerebral autoregulation...... in a human-experimental model of the systemic inflammatory response during the early stages of sepsis....

  10. Forces affecting employment dynamics in Groningen; Case study in a lagging rural region in the Netherlands

    NARCIS (Netherlands)

    Terluin, I.J.; Post, J.H.; Wisselink, A.J.; Overbeek, M.M.M.

    1999-01-01

    In this report the focus is on employment dynamics in Groningen since the beginning of the 1980s. This study is part of an EU wide research project on employment development in leading and lagging rural regions of the EU. Total employment in Groningen increased by 36,000 jobs or with one quarter in

  11. The Role of Self-Efficacy, Goal, and Affect in Dynamic Motivational Self-Regulation

    Science.gov (United States)

    Seo, Myeong-gu; Ilies, Remus

    2009-01-01

    In this paper, we examined the within-person relationship between self-efficacy and performance in an Internet-based stock investment simulation in which participants engaged in a series of stock trading activities trying to achieve performance goals in response to dynamic task environments (performance feedback and stock market movements).…

  12. Mechanisms of mindfulness: The dynamics of affective adaptation during open monitoring.

    Science.gov (United States)

    Uusberg, Helen; Uusberg, Andero; Talpsep, Teri; Paaver, Marika

    2016-07-01

    Mindfulness - the nonjudgmental awareness of the present experience - is thought to facilitate affective adaptation through increased exposure to emotions and faster extinction of habitual responses. To test this framework, the amplification of the Late Positive Potential (LPP) by negative relative to neutral images was analyzed across stimulus repetitions while 37 novices performed an open monitoring mindfulness exercise. Compared to two active control conditions where attention was either diverted to a distracting task or the stimuli were attended without mindfulness instructions, open monitoring enhanced the initial LPP response to negative stimuli, indicating increased emotional exposure. Across successive repetitions, mindfulness reduced and ultimately removed the affective LPP amplification, suggesting extinction of habitual emotional reactions. This effect arose from reduced negative as well enlarged neutral LPPs. Unlike stimuli from control conditions, the images previously viewed with mindfulness instructions did not elicit affective LPP amplification during subsequent re-exposure, suggesting reconsolidation of stimulus meaning.

  13. F-actin-like filaments formed by plasmid segregation protein ParM

    DEFF Research Database (Denmark)

    van den Ent, Fusinita; Møller-Jensen, Jakob; Amos, Linda A.;

    2002-01-01

    It was the general belief that DNA partitioning in prokaryotes is independent of a cytoskeletal structure, which in eukaryotic cells is indispensable for DNA segregation. Recently, however, immunofluorescence microscopy revealed highly dynamic, filamentous structures along the longitudinal axis...... of Escherichia coli formed by ParM, a plasmid-encoded protein required for accurate segregation of low-copy-number plasmid R1. We show here that ParM polymerizes into double helical protofilaments with a longitudinal repeat similar to filamentous actin (F-actin) and MreB filaments that maintain the cell shape...

  14. Control of electrostatic interactions between F-actin and genetically modified lysozyme in aqueous media

    Energy Technology Data Exchange (ETDEWEB)

    Sanders, Lori K.; Xian, Wujing; Guaqueta, Camilo; Strohman, Michael J.; Vrasich, Chuck R.; Luijten, Erik; Wong, Gerard C.L. (UIUC)

    2008-07-11

    The aim for deterministic control of the interactions between macroions in aqueous media has motivated widespread experimental and theoretical work. Although it has been well established that like-charged macromolecules can aggregate under the influence of oppositely charged condensing agents, the specific conditions for the stability of such aggregates can only be determined empirically. We examine these conditions, which involve an interplay of electrostatic and osmotic effects, by using a well defined model system composed of F-actin, an anionic rod-like polyelectrolyte, and lysozyme, a cationic globular protein with a charge that can be genetically modified. The structure and stability of actin-lysozyme complexes for different lysozyme charge mutants and salt concentrations are examined by using synchrotron x-ray scattering and molecular dynamics simulations. We provide evidence that supports a structural transition from columnar arrangements of F-actin held together by arrays of lysozyme at the threefold interstitial sites of the actin sublattice to marginally stable complexes in which lysozyme resides at twofold bridging sites between actin. The reduced stability arises from strongly reduced partitioning of salt between the complex and the surrounding solution. Changes in the stability of actin-lysozyme complexes are of biomedical interest because their formation has been reported to contribute to the persistence of airway infections in cystic fibrosis by sequestering antimicrobials such as lysozyme. We present x-ray microscopy results that argue for the existence of actin-lysozyme complexes in cystic fibrosis sputum and demonstrate that, for a wide range of salt conditions, charge-reduced lysozyme is not sequestered in ordered complexes while retaining its bacterial killing activity.

  15. Control of Electrostatic Interactions Between F-Actin And Genetically Modified Lysozyme in Aqueous Media

    Energy Technology Data Exchange (ETDEWEB)

    Sanders, L.K.; Xian, W.; Guaqueta, C.; Strohman, M.; Vrasich, C.R.; Luijten, E.; Wong, G.C.L.

    2009-06-04

    The aim for deterministic control of the interactions between macroions in aqueous media has motivated widespread experimental and theoretical work. Although it has been well established that like-charged macromolecules can aggregate under the influence of oppositely charged condensing agents, the specific conditions for the stability of such aggregates can only be determined empirically. We examine these conditions, which involve an interplay of electrostatic and osmotic effects, by using a well defined model system composed of F-actin, an anionic rod-like polyelectrolyte, and lysozyme, a cationic globular protein with a charge that can be genetically modified. The structure and stability of actin-lysozyme complexes for different lysozyme charge mutants and salt concentrations are examined by using synchrotron x-ray scattering and molecular dynamics simulations. We provide evidence that supports a structural transition from columnar arrangements of F-actin held together by arrays of lysozyme at the threefold interstitial sites of the actin sublattice to marginally stable complexes in which lysozyme resides at twofold bridging sites between actin. The reduced stability arises from strongly reduced partitioning of salt between the complex and the surrounding solution. Changes in the stability of actin-lysozyme complexes are of biomedical interest because their formation has been reported to contribute to the persistence of airway infections in cystic fibrosis by sequestering antimicrobials such as lysozyme. We present x-ray microscopy results that argue for the existence of actin-lysozyme complexes in cystic fibrosis sputum and demonstrate that, for a wide range of salt conditions, charge-reduced lysozyme is not sequestered in ordered complexes while retaining its bacterial killing activity.

  16. The circular F-actin bundles provide a track for turnaround and bidirectional movement of mitochondria in Arabidopsis root hair.

    Directory of Open Access Journals (Sweden)

    Yu Zhang

    Full Text Available The movement of organelles in root hairs primarily occurs along the actin cytoskeleton. Circulation and "reverse fountain" cytoplasmic streaming constitute the typical forms by which most organelles (such as mitochondria and the Golgi apparatus in plant root hair cells engage in bidirectional movement. However, there remains a lack of in-depth research regarding the relationship between the distribution of the actin cytoskeleton and turnaround organelle movement in plant root hair cells.In this paper, Arabidopsis seedlings that had been stably transformed with a GFP-ABD2-GFP (green fluorescent protein-actin-binding domain 2-green fluorescent protein construct were utilized to study the distribution of bundles of filamentous (F-actin and the directed motion of mitochondria along these bundles in root hairs. Observations with a confocal laser scanning microscope revealed that there were widespread circular F-actin bundles in the epidermal cells and root hairs of Arabidopsis roots. In root hairs, these circular bundles primarily start at the sub-apical region, which is the location where the turnaround movement of organelles occurs. MitoTracker probes were used to label mitochondria, and the dynamic observation of root hair cells with a confocal laser scanning microscope indicated that turnaround mitochondrial movement occurred along circular F-actin bundles.Relevant experimental results demonstrated that the circular F-actin bundles provide a track for the turnaround and bidirectional movement of mitochondria.

  17. Mammalian adenylyl cyclase-associated protein 1 (CAP1) regulates cofilin function, the actin cytoskeleton, and cell adhesion.

    Science.gov (United States)

    Zhang, Haitao; Ghai, Pooja; Wu, Huhehasi; Wang, Changhui; Field, Jeffrey; Zhou, Guo-Lei

    2013-07-19

    CAP (adenylyl cyclase-associated protein) was first identified in yeast as a protein that regulates both the actin cytoskeleton and the Ras/cAMP pathway. Although the role in Ras signaling does not extend beyond yeast, evidence supports that CAP regulates the actin cytoskeleton in all eukaryotes including mammals. In vitro actin polymerization assays show that both mammalian and yeast CAP homologues facilitate cofilin-driven actin filament turnover. We generated HeLa cells with stable CAP1 knockdown using RNA interference. Depletion of CAP1 led to larger cell size and remarkably developed lamellipodia as well as accumulation of filamentous actin (F-actin). Moreover, we found that CAP1 depletion also led to changes in cofilin phosphorylation and localization as well as activation of focal adhesion kinase (FAK) and enhanced cell spreading. CAP1 forms complexes with the adhesion molecules FAK and Talin, which likely underlie the cell adhesion phenotypes through inside-out activation of integrin signaling. CAP1-depleted HeLa cells also had substantially elevated cell motility as well as invasion through Matrigel. In summary, in addition to generating in vitro and in vivo evidence further establishing the role of mammalian CAP1 in actin dynamics, we identified a novel cellular function for CAP1 in regulating cell adhesion.

  18. Dual chemotaxis signalling regulates Dictyostelium development: intercellular cyclic AMP pulses and intracellular F-actin disassembly waves induce each other.

    Science.gov (United States)

    Vicker, Michael G; Grutsch, James F

    2008-10-01

    Aggregating Dictyostelium discoideum amoebae periodically emit and relay cAMP, which regulates their chemotaxis and morphogenesis into a multicellular, differentiated organism. Cyclic AMP also stimulates F-actin assembly and chemotactic pseudopodium extension. We used actin-GFP expression to visualise for the first time intracellular F-actin assembly as a spatio-temporal indicator of cell reactions to cAMP, and thus the kinematics of cell communication, in aggregating streams. Every natural cAMP signal pulse induces an autowave of F-actin disassembly, which propagates from each cell's leading end to its trailing end at a linear rate, much slower than the calculated and measured velocities of cAMP diffusion in aggregating Dictyostelium. A sequence of transient reactions follows behind the wave, including anterior F-actin assembly, chemotactic pseudopodium extension and cell advance at the cell front and, at the back, F-actin assembly, extension of a small retrograde pseudopodium (forcing a brief cell retreat) and chemotactic stimulation of the following cell, yielding a 20s cAMP relay delay. These dynamics indicate that stream cell behaviour is mediated by a dual signalling system: a short-range cAMP pulse directed from one cell tail to an immediately following cell front and a slower, long-range wave of intracellular F-actin disassembly, each inducing the other.

  19. Treatment Options for Actinic Keratosis

    Science.gov (United States)

    ... Skin Cancer Skin Cancer Screening Research Skin Cancer Treatment (PDQ®)–Patient Version General Information About Skin Cancer ... Certain factors affect prognosis (chance of recovery) and treatment options. The prognosis (chance of recovery ) depends mostly ...

  20. The Developmental Dynamics of Children's Academic Performance and Mothers' Homework-Related Affect and Practices

    Science.gov (United States)

    Silinskas, Gintautas; Kiuru, Noona; Aunola, Kaisa; Lerkkanen, Marja-Kristiina; Nurmi, Jari-Erik

    2015-01-01

    This study investigated the longitudinal associations between children's academic performance and their mothers' affect, practices, and perceptions of their children in homework situations. The children's (n = 2,261) performance in reading and math was tested in Grade 1 and Grade 4, and the mothers (n = 1,476) filled out questionnaires on their…

  1. Temporal Dynamics of Physical Activity and Affect in Depressed and Nondepressed Individuals

    NARCIS (Netherlands)

    Stavrakakis, Nikolaos; Booij, Sanne H.; Roest, Annelieke M.; de Jonge, Peter; Oldehinkel, Albertine J.; Bos, Elisabeth H.

    2015-01-01

    Objective: The association between physical activity and affect found in longitudinal observational studies is generally small to moderate. It is unknown how this association generalizes to individuals. The aim of the present study was to investigate interindividual differences in the bidirectional

  2. Exploring Dynamical Assessments of Affect, Behavior, and Cognition and Math State Test Achievement

    Science.gov (United States)

    San Pedro, Maria Ofelia Z.; Snow, Erica L.; Baker, Ryan S.; McNamara, Danielle S.; Heffernan, Neil T.

    2015-01-01

    There is increasing evidence that fine-grained aspects of student performance and interaction within educational software are predictive of long-term learning. Machine learning models have been used to provide assessments of affect, behavior, and cognition based on analyses of system log data, estimating the probability of a student's particular…

  3. Patterning and Lifetime of Plasma Membrane-Localized Cellulose Synthase Is Dependent on Actin Organization in Arabidopsis Interphase Cells1[W

    Science.gov (United States)

    Sampathkumar, Arun; Gutierrez, Ryan; McFarlane, Heather E.; Bringmann, Martin; Lindeboom, Jelmer; Emons, Anne-Mie; Samuels, Lacey; Ketelaar, Tijs; Ehrhardt, David W.; Persson, Staffan

    2013-01-01

    The actin and microtubule cytoskeletons regulate cell shape across phyla, from bacteria to metazoans. In organisms with cell walls, the wall acts as a primary constraint of shape, and generation of specific cell shape depends on cytoskeletal organization for wall deposition and/or cell expansion. In higher plants, cortical microtubules help to organize cell wall construction by positioning the delivery of cellulose synthase (CesA) complexes and guiding their trajectories to orient newly synthesized cellulose microfibrils. The actin cytoskeleton is required for normal distribution of CesAs to the plasma membrane, but more specific roles for actin in cell wall assembly and organization remain largely elusive. We show that the actin cytoskeleton functions to regulate the CesA delivery rate to, and lifetime of CesAs at, the plasma membrane, which affects cellulose production. Furthermore, quantitative image analyses revealed that actin organization affects CesA tracking behavior at the plasma membrane and that small CesA compartments were associated with the actin cytoskeleton. By contrast, localized insertion of CesAs adjacent to cortical microtubules was not affected by the actin organization. Hence, both actin and microtubule cytoskeletons play important roles in regulating CesA trafficking, cellulose deposition, and organization of cell wall biogenesis. PMID:23606596

  4. A shift from exploitation to interference competition with increasing density affects population and community dynamics

    OpenAIRE

    Holdridge, Erica M.; Cuellar‐Gempeler, Catalina; terHorst, Casey P.

    2016-01-01

    Abstract Intraspecific competition influences population and community dynamics and occurs via two mechanisms. Exploitative competition is an indirect effect that occurs through use of a shared resource and depends on resource availability. Interference competition occurs by obstructing access to a resource and may not depend on resource availability. Our study tested whether the strength of interference competition changes with protozoa population density. We grew experimental microcosms of ...

  5. Wolbachia-Host Interactions: Host Mating Patterns Affect Wolbachia Density Dynamics

    OpenAIRE

    Dong-Xiao Zhao; Xiang-Fei Zhang; Da-Song Chen; Yan-Kai Zhang; Xiao-Yue Hong

    2013-01-01

    Wolbachia are maternally inherited intracellular bacteria that infect a wide range of arthropods and cause an array of effects on host reproduction, fitness and mating behavior. Although our understanding of the Wolbachia-associated effects on hosts is rapidly expanding, our knowledge of the host factors that mediate Wolbachia dynamics is rudimentary. Here, we explore the interactions between Wolbachia and its host, the two-spotted spider mite Tetranychus urticae Koch. Our results indicate th...

  6. A stage-structured, spatially explicit migration model for Myotis bats: mortality location affects system dynamics

    Science.gov (United States)

    Erickson, Richard A.; Thogmartin, Wayne E.; Russell, Robin E.; Diffendorfer, James E.; Jennifer A. Szymanski,; ,

    2014-01-01

    Bats are ecologically and economically important species because they consume insects, transport nutrients, and pollinate flowers.  Many species of bats, including those in the Myotis genus, are facing population decline and increased extinction risk.  Despite these conservation concerns, few models exist for providing insight into the population dynamics of bats in a spatially explicit context.  We developed a model for bats by considering the stage-structured colonial life history of Myotis bats with their annual migration behavior.  This model provided insight into network dynamics.  We specifically focused on two Myotis species living in the eastern United States: the Indiana bat (M. sodalis), which is a Federally listed endangered species, and the little brown bat (M. lucifugus), which is under consideration for listing as an endangered species.  We found that multiple equilibria exist for the local, migratory subpopulations even though the total population was constant.  These equilibria suggest the location and magnitude of stressors such as White-nose Syndrome, meteorological phenomena, or impacts of wind turbines on survival influence system dynamics and risk of population extirpation in difficult to predict ways.

  7. Nucleotide binding affects intrinsic dynamics and structural communication in Ras GTPases.

    Science.gov (United States)

    Fanelli, Francesca; Raimondi, Francesco

    2013-01-01

    The Ras superfamily comprises many guanine nucleotide-binding proteins (G proteins) that are essential to intracellular signal transduction. These proteins act biologically as molecular switches, which, cycling between OFF and ON states, play fundamental role in cell biology. This review article summarizes the inferences from the widest computational analyses done so far on Ras GTPases aimed at providing a comprehensive structural/dynamic view of the trans-family and family-specific functioning mechanisms. These variegated comparative analyses could infer the evolutionary and intrinsic flexibilities as well as the structural communication features in the most representative G protein families in different functional states. In spite of the low sequence similarities, the members of the Ras superfamily share the topology of the Ras-like domain, including the nucleotide binding site. GDP and GTP make very similar interactions in all GTPases and differences in their binding modes are localized around the γ-phosphate of GTP. Remarkably, such subtle local differences result in significant differences in the functional dynamics and structural communication features of the protein. In Ras GTPases, the nucleotide plays a central and active role in dictating functional dynamics, establishing the major structure network, and mediating the communication paths instrumental in function retention and specialization. Collectively, the results of these studies support the speculation that an "extended conformational selection model" that embraces a repertoire of selection and adjustment processes is likely more suitable to describe the nucleotide behavior in these important molecular switches.

  8. Nonequilibrium water dynamics in the rhizosphere: How mucilage affects water flow in soils

    Science.gov (United States)

    Kroener, Eva; Zarebanadkouki, Mohsen; Kaestner, Anders; Carminati, Andrea

    2014-08-01

    The flow of water from soil to plant roots is controlled by the properties of the narrow region of soil close to the roots, the rhizosphere. In particular, the hydraulic properties of the rhizosphere are altered by mucilage, a polymeric gel exuded by the roots. In this paper we present experimental results and a conceptual model of water flow in unsaturated soils mixed with mucilage. A central hypothesis of the model is that the different drying/wetting rate of mucilage compared to the bulk soil results in nonequilibrium relations between water content and water potential in the rhizosphere. We coupled this nonequilibrium relation with the Richards equation and obtained a constitutive equation for water flow in soil and mucilage. To test the model assumptions, we measured the water retention curve and the saturated hydraulic conductivity of sandy soil mixed with mucilage from chia seeds. Additionally, we used neutron radiography to image water content in a layer of soil mixed with mucilage during drying and wetting cycles. The radiographs demonstrated the occurrence of nonequilibrium water dynamics in the soil-mucilage mixture. The experiments were simulated by numerically solving the nonequilibrium model. Our study provides conceptual and experimental evidences that mucilage has a strong impact on soil water dynamics. During drying, mucilage maintains a greater soil water content for an extended time, while during irrigation it delays the soil rewetting. We postulate that mucilage exudation by roots attenuates plant water stress by modulating water content dynamics in the rhizosphere.

  9. Direct visualization of flow-induced conformational transitions of single actin filaments in entangled solutions

    CERN Document Server

    Kirchenbuechler, Inka; Kurniawan, Nicholas A; Koenderink, Gijsje H; Lettinga, M Paul

    2015-01-01

    While semi-flexible polymers and fibers are an important class of material due to their rich mechanical properties, it remains unclear how these properties relate to the microscopic conformation of the polymers. Actin filaments constitute an ideal model polymer system due to their micron-sized length and relatively high stiffness that allow imaging at the single filament level. Here we study the effect of entanglements on the conformational dynamics of actin filaments in shear flow. We directly measure the full three-dimensional conformation of single actin filaments, using confocal microscopy in combination with a counter-rotating cone-plate shear cell. We show that initially entangled filaments form disentangled orientationally ordered hairpins, confined in the flow-vorticity plane. In addition, shear flow causes stretching and shear alignment of the hairpin tails, while the filament length distribution remains unchanged. These observations explain the strain-softening and shear-thinning behavior of entangl...

  10. Apical domain polarization localizes actin-myosin activity to drive ratchet-like apical constriction.

    Science.gov (United States)

    Mason, Frank M; Tworoger, Michael; Martin, Adam C

    2013-08-01

    Apical constriction promotes epithelia folding, which changes tissue architecture. During Drosophila gastrulation, mesoderm cells exhibit repeated contractile pulses that are stabilized such that cells apically constrict like a ratchet. The transcription factor Twist is required to stabilize cell shape. However, it is unknown how Twist spatially coordinates downstream signals to prevent cell relaxation. We find that during constriction, Rho-associated kinase (Rok) is polarized to the middle of the apical domain (medioapical cortex), separate from adherens junctions. Rok recruits or stabilizes medioapical myosin II (Myo-II), which contracts dynamic medioapical actin cables. The formin Diaphanous mediates apical actin assembly to suppress medioapical E-cadherin localization and form stable connections between the medioapical contractile network and adherens junctions. Twist is not required for apical Rok recruitment, but instead polarizes Rok medioapically. Therefore, Twist establishes radial cell polarity of Rok/Myo-II and E-cadherin and promotes medioapical actin assembly in mesoderm cells to stabilize cell shape fluctuations.

  11. Cytosolic SYT/SS18 isoforms are actin-associated proteins that function in matrix-specific adhesion.

    Directory of Open Access Journals (Sweden)

    Jaehong Kim

    Full Text Available SYT (SYnovial sarcoma Translocated gene or SS18 is widely produced as two isoforms, SYT/L and SYT/S, that are thought to function in the nucleus as transcriptional coactivators. Using isoform-specific antibodies, we detected a sizable pool of SYT isoforms in the cytosol where the proteins were organized into filamentous arrays. Actin and actin-associated proteins co-immunoprecipitated with SYT isoforms, which also co-sedimented and co-localized with the actin cytoskeleton in cultured cells and tissues. The association of SYT with actin bundles was extensive yet stopped short of the distal ends at focal adhesions. Disruption of the actin cytoskeleton also led to a breakdown of the filamentous organization of SYT isoforms in the cytosol. RNAi ablation of SYT/L alone or both isoforms markedly impaired formation of stress fibers and focal adhesions but did not affect formation of cortical actin bundles. Furthermore, ablation of SYT led to markedly impaired adhesion and spreading on fibronectin and laminin-111 but not on collagen types I or IV. These findings indicate that cytoplasmic SYT isoforms interact with actin filaments and function in the ability cells to bind and react to specific extracellular matrices.

  12. Redox regulation of actin by thioredoxin-1 is mediated by the interaction of the proteins via cysteine 62.

    Science.gov (United States)

    Wang, Xiaogang; Ling, Shukuan; Zhao, Dingsheng; Sun, Qiao; Li, Qi; Wu, Feng; Nie, Jielin; Qu, Lina; Wang, Bo; Shen, Xun; Bai, Yanqiang; Li, Yingxian; Li, Yinghui

    2010-09-01

    Actin is a highly conserved protein in eukaryotic cells, and has been identified as one of the main redox targets by redox proteomics under oxidative stress. However, little is known about the mechanisms of regulation of the redox state of actin. In this study, we investigated how thioredoxin-1 (Trx1) affected the redox state of actin and its polymerization under oxidative stress in SH-SY5Y cells. Trx1 decreased the levels of reactive oxygen species (ROS) in the cells, and cysteine residues at positions 32, 35, and 69 of the Trx1 protein were active sites for redox regulation. Actin could be kept in a reduced state by Trx1 under H(2)O(2) stimulation. A physical interaction was found to exist between actin and Trx1. Cysteine 62 in Trx1 was the key site that interacted with actin, and it was required to maintain cellular viability and anti-apoptotic function. Taken together, these results suggested that Trx1 could protect cells from apoptosis under oxidative stress not only by increasing the total antioxidant capability and decreasing the ROS levels, but also by stabilizing the actin cytoskeletal system, which cooperatively contributed to the enhancement of cell viability and worked against apoptosis.

  13. Wave Patterns in Cell Membrane and Actin Cortex Uncoupled from Chemotactic Signals.

    Science.gov (United States)

    Gerisch, Günther; Ecke, Mary

    2016-01-01

    When cells of Dictyostelium discoideum orientate in a gradient of chemoattractant, they are polarized into a protruding front pointing toward the source of attractant, and into a retracting tail. Under the control of chemotactic signal inputs, Ras is activated and PIP3 is synthesized at the front, while the PIP3-degrading phosphatase PTEN decorates the tail region. As a result of signal transduction, actin filaments assemble at the front into dendritic structures associated with the Arp2/3 complex, in contrast to the tail region where a loose actin meshwork is associated with myosin-II and cortexillin, an antiparallel actin-bundling protein. In axenically growing strains of D. discoideum, wave patterns built by the same components evolve in the absence of any external signal