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Sample records for actin flap dynamics

  1. Dynamics of active actin networks

    Koehler, Simone

    2014-03-01

    Local mechanical and structural properties of a eukaryotic cell are determined by its cytoskeleton. To adapt to their environment, cells rely on constant self-organized rearrangement processes of their actin cytoskeleton. To shed light on the principles underlying these dynamic self-organization processes we investigate a minimal reconstituted active system consisting of actin filaments, crosslinking molecules and molecular motor filaments. Using quantitative fluorescence microscopy and image analysis, we show, that these minimal model systems exhibit a generic structure formation mechanism. The competition between force generation by molecular motors and the stabilization of the network by crosslinking proteins results in a highly dynamic reorganization process which is characterized by anomalous transport dynamics with a superdiffusive behavior also found in intracellular dynamics. In vitro, these dynamics are governed by chemical and physical parameters that alter the balance of motor and crosslinking proteins, such as pH. These findings can be expected to have broad implications in our understanding of cytoskeletal regulation in vivo.

  2. Dynamics of an actin spring

    Riera, Christophe; Mahadevan, L.; Shin, Jennifer; Matsudaira, Paul

    2003-03-01

    The acrosome of the sperm of the horseshoe crab (Limulus Polyphemus) is an unusual actin based system that shows a spectacular dynamical transition in the presence of Ca++ that is present in abundance in the neighborhood of the egg. During this process, the bundle, which is initially bent and twisted uncoils and becomes straight in a matter of a few seconds. Based on microstructural data, we propose a model for the dynamics of uncoiling that is best represented by a triple-well potential corresponding to the different structural arrangements of the supertwisted filaments. Each of the false, true and coiled states corresponds to a local minimum of the energy, with the true state being the one with the lowest energy. Using an evolution equation derived by balancing torques, we investigate the nucleation and propagation of the phase transition and compare the results with those of experiments. Our model quantifies the hypothesis that the acrosomal bundle behaves like a mechano-chemical spring.

  3. A dynamical system for interacting flapping swimmers

    Oza, Anand; Ramananarivo, Sophie; Ristroph, Leif; Shelley, Michael

    2015-11-01

    We present the results of a theoretical investigation into the dynamics of interacting flapping swimmers. Our study is motivated by the recent experiments of Becker et al., who studied a one-dimensional array of self-propelled flapping wings that swim within each other's wakes in a water tank. They discovered that the system adopts certain ``schooling modes'' characterized by specific spatial phase relationships between swimmers. To rationalize these phenomena, we develop a discrete dynamical system in which the swimmers are modeled as heaving airfoils that shed point vortices during each flapping cycle. We then apply our model to recent experiments in the Applied Math Lab, in which two tandem flapping airfoils are free to choose both their speed and relative positions. We expect that our model may be used to understand how schooling behavior is influenced by hydrodynamics in more general contexts. Thanks to the NSF for its support.

  4. Reactive oxygen species (ROS)-induced actin glutathionylation controls actin dynamics in neutrophils

    Sakai, Jiro; Li, Jingyu; Subramanian, Kulandayan K.; Mondal, Subhanjan; Bajrami, Besnik; Hattori, Hidenori; Jia, Yonghui; Dickinson, Bryan C.; Zhong, Jia; Ye, Keqiang; Chang, Christopher J; Ho, Ye-Shih; Zhou, Jun; Luo, Hongbo R.

    2012-01-01

    Summary The regulation of actin dynamics is pivotal for cellular processes such as cell adhesion, migration, and phagocytosis, and thus is crucial for neutrophils to fulfill their roles in innate immunity. Many factors have been implicated in signal-induced actin polymerization, however the essential nature of the potential negative modulators are still poorly understood. Here we report that NADPH oxidase-dependent physiologically generated reactive oxygen species (ROS) negatively regulate actin polymerization in stimulated neutrophils via driving reversible actin glutathionylation. Disruption of glutaredoxin 1 (Grx1), an enzyme that catalyzes actin deglutathionylation, increased actin glutathionylation, attenuated actin polymerization, and consequently impaired neutrophil polarization, chemotaxis, adhesion, and phagocytosis. Consistently, Grx1-deficient murine neutrophils showed impaired in vivo recruitment to sites of inflammation and reduced bactericidal capability. Together, these results present a physiological role for glutaredoxin and ROS- induced reversible actin glutathionylation in regulation of actin dynamics in neutrophils. PMID:23159440

  5. Actin dynamics and the elasticity of cytoskeletal networks

    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.

  6. Dynamics of Flapping Flag in Axial Flow

    Abderrahmane, Hamid Ait; Fayed, Mohamed; Gunter, Amy-Lee; Paidoussis, Michael P.; Ng, Hoi Dick

    2010-11-01

    We investigate experimentally the phenomenon of the flapping of a flag, placed within a low turbulent axial flow inside a small scale wind tunnel test section. Flags of different sizes and flexural rigidities were used. Image processing technique was used and the time series of a given point on the edge of the flag was analyzed. The stability condition of the flag was obtained and compared to the recent theoretical models and numerical simulations. Afterwards, the nonlinear dynamics of the flapping was investigated using nonlinear time series method. The nonlinear dynamics is depicted in phase space and the correlation dimension of the attractors is determined. On the basis of observations made in this study, some conclusions on the existing models were drawn.

  7. Reactive oxygen species (ROS)-induced actin glutathionylation controls actin dynamics in neutrophils

    Sakai, Jiro; Li, Jingyu; Subramanian, Kulandayan K.; Mondal, Subhanjan; Bajrami, Besnik; Hattori, Hidenori; Jia, Yonghui; Dickinson, Bryan C; Zhong, Jia; Ye, Keqiang; Chang, Christopher J.; Ho, Ye-Shih; Zhou, Jun; Luo, Hongbo R.

    2012-01-01

    The regulation of actin dynamics is pivotal for cellular processes such as cell adhesion, migration, and phagocytosis, and thus is crucial for neutrophils to fulfill their roles in innate immunity. Many factors have been implicated in signal-induced actin polymerization, however the essential nature of the potential negative modulators are still poorly understood. Here we report that NADPH oxidase-dependent physiologically generated reactive oxygen species (ROS) negatively regulate actin poly...

  8. Bacterial Subversion of Host Actin Dynamics at the Plasma Membrane

    Carabeo, Rey

    2011-01-01

    Invasion of non-phagocytic cells by a number of bacterial pathogens involves the subversion of the actin cytoskeletal remodelling machinery to produce actin-rich cell surface projections designed to engulf the bacteria. The signalling that occurs to induce these actin-rich structures has considerable overlap amongst a diverse group of bacteria. The molecular organisation within these structures act in concert to internalise the invading pathogen. This dynamic process could be subdivided into ...

  9. Effects of primary rotor parameters on flapping dynamics

    Chen, R. T. N.

    1980-01-01

    The effects of flapping dynamics of four main rotor design features that influence the agility, stability, and operational safety of helicopters are studied. The parameters include flapping hinge offset, flapping hinge restraint, pitch-flap coupling, and blade lock number. First, the flapping equations of motion are derived that explicitly contain the design parameters. The dynamic equations are then developed for the tip-path plane, and the influence of individual and combined variations in the design parameters determined. The steady state flapping response is examined with respect to control input and aircraft angular rate which leads to a feedforward control law for control decoupling through cross feed, and a feedback control law to decouple the steady state flapping response. The condition for achieving perfect decoupling of the flapping response due to aircraft pitch and roll rates without using feedback control is also found for the hover case. It is indicated that the frequency of the regressing flapping mode of the rotor system can become low enough to require consideration in the assessment of handling characteristics.

  10. Spontaneous actin dynamics in contractile rings

    Kruse, Karsten; Wollrab, Viktoria; Thiagarajan, Raghavan; Wald, Anne; Riveline, Daniel

    Networks of polymerizing actin filaments are known to be capable to self-organize into a variety of structures. For example, spontaneous actin polymerization waves have been observed in living cells in a number of circumstances, notably, in crawling neutrophils and slime molds. During later stages of cell division, they can also spontaneously form a contractile ring that will eventually cleave the cell into two daughter cells. We present a framework for describing networks of polymerizing actin filaments, where assembly is regulated by various proteins. It can also include the effects of molecular motors. We show that the molecular processes driven by these proteins can generate various structures that have been observed in contractile rings of fission yeast and mammalian cells. We discuss a possible functional role of each of these patterns. The work was supported by Agence Nationale de la Recherche, France, (ANR-10-LABX-0030-INRT) and by Deutsche Forschungsgemeinschaft through SFB1027.

  11. Dynamic response of a piezoelectric flapping wing

    Kumar, Alok; Khandwekar, Gaurang; Venkatesh, S.; Mahapatra, D. R.; Dutta, S.

    2015-03-01

    Piezo-composite membranes have advantages over motorized flapping where frequencies are high and certain coupling between bending and twisting is useful to generate lift and forward flight. We draw examples of fruit fly and bumble bee. Wings with Piezo ceramic PZT coating are realized. The passive mechanical response of the wing is characterized experimentally and validated using finite element simulation. Piezoelectric actuation with uniform electrode coating is characterized and optimal frequencies for flapping are identified. The experimental data are used in an empirical model and advanced ratio for a flapping insect like condition for various angular orientations is estimated.

  12. Wnt Signalling Promotes Actin Dynamics during Axon Remodelling through the Actin-Binding Protein Eps8.

    Eleanna Stamatakou

    Full Text Available Upon arrival at their synaptic targets, axons slow down their growth and extensively remodel before the assembly of presynaptic boutons. Wnt proteins are target-derived secreted factors that promote axonal remodelling and synaptic assembly. In the developing spinal cord, Wnts secreted by motor neurons promote axonal remodelling of NT-3 responsive dorsal root ganglia neurons. Axon remodelling induced by Wnts is characterised by growth cone pausing and enlargement, processes that depend on the re-organisation of microtubules. However, the contribution of the actin cytoskeleton has remained unexplored. Here, we demonstrate that Wnt3a regulates the actin cytoskeleton by rapidly inducing F-actin accumulation in growth cones from rodent DRG neurons through the scaffold protein Dishevelled-1 (Dvl1 and the serine-threonine kinase Gsk3β. Importantly, these changes in actin cytoskeleton occurs before enlargement of the growth cones is evident. Time-lapse imaging shows that Wnt3a increases lamellar protrusion and filopodia velocity. In addition, pharmacological inhibition of actin assembly demonstrates that Wnt3a increases actin dynamics. Through a yeast-two hybrid screen, we identified the actin-binding protein Eps8 as a direct interactor of Dvl1, a scaffold protein crucial for the Wnt signalling pathway. Gain of function of Eps8 mimics Wnt-mediated axon remodelling, whereas Eps8 silencing blocks the axon remodelling activity of Wnt3a. Importantly, blockade of the Dvl1-Eps8 interaction completely abolishes Wnt3a-mediated axonal remodelling. These findings demonstrate a novel role for Wnt-Dvl1 signalling through Eps8 in the regulation of axonal remodeling.

  13. Lift Enhancement by Dynamically Changing Wingspan in Forward Flapping Flight

    Wang, Shizhao; He, Guowei; Liu, Tianshu

    2013-01-01

    Stretching and retracting wingspan has been widely observed in the flight of birds and bats, and its effects on the aerodynamic performance particularly lift generation are intriguing. The rectangular flat-plate flapping wing with a sinusoidally stretching and retracting wingspan is proposed as a simple model of biologically-inspired dynamic morphing wings. Direct numerical simulations of the low-Reynolds-number flows around the flapping morphing wing in a parametric space are conducted by using immersed boundary method. It is found that the instantaneous and time-averaged lift coefficients of the wing can be significantly enhanced by dynamically changing wingspan in a flapping cycle. The lift enhancement is caused not only by changing the lifting surface area, but also manipulating the flow structures that are responsible to the generation of the vortex lift. The physical mechanisms behind the lift enhancement are explored by examining the three-dimensional flow structures around the flapping wing.

  14. Flap motion of helicopter rotors with novel, dynamic stall model

    Han Wei

    2016-07-01

    Full Text Available In this paper, a nonlinear flapping equation for large inflow angles and flap angles is established by analyzing the aerodynamics of helicopter blade elements. In order to obtain a generalized flap equation, the Snel stall model was first applied to determine the lift coefficient of the helicopter rotor. A simulation experiment for specific airfoils was then conducted to verify the effectiveness of the Snel stall model as it applies to helicopters. Results show that the model requires no extraneous parameters compared to the traditional stall model and is highly accurate and practically applicable. Based on the model, the relationship between the flapping angle and the angle of attack was analyzed, as well as the advance ratio under the dynamic stall state.

  15. Dynamic buckling of actin within filopodia

    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 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 in...

  16. Flapping dynamics of a flexible flag in a uniform flow

    Hwa Lee, Jae; Jin Sung, Hyung [Department of Mechanical Engineering, KAIST 291 Daehak-ro, Yuseong-gu, Daejeon 305-701 (Korea, Republic of); Huang, Wei-Xi, E-mail: hjsung@kaist.ac.kr, E-mail: hwx@tsinghua.edu.cn [Department of Engineering Mechanics, Tsinghua University, Beijing 100084 (China)

    2014-10-01

    Numerical simulations using the immersed boundary method were performed to investigate the flapping dynamics of a flexible flag in a uniform flow. The relevant parameters related to the problem are the mass ratio (ρ=ρ{sub 1}/ρ{sub f}L), the bending rigidity of the flag (K{sub B}=EI/ρ{sub f}U{sub ∞}{sup 2}L{sup 3}) and the Reynolds number (Re=U{sub ∞}L/ν), where ρ{sub 1} denotes the line density difference between the flag and the surrounding fluid. By varying the parameters over the ranges 0 not <= ρ not <= 10 and 10{sup -4} not < = K{sub B} not <= 10{sup -1} for Re = 200, we identified three dynamical states: the stretched–straight state (I), the regular flapping state (II), and the irregular flapping state (III) with a region in which violent snapping events occurred, characterized by rapid changes in velocity, tension and drag. The description of the flapping dynamics at each dynamic state was provided through a sequence of time-evolving instantaneous fields, and was examined in detail with respect to the frequency and the energy rank based on the dynamic mode decomposition technique. Furthermore, the hysteresis phenomena with varying the mass ratio and the Reynolds number was examined, and the results showed that the hysteresis loop width was varied for approximately 20–65%, depending on the values of the relevant parameters employed. (paper)

  17. Dynamic Actin Controls Polarity Induction de novo in Protoplasts

    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.

  18. Internal dynamics of F-actin and myosin subfragment-1 studied by quasielastic neutron scattering

    Various biological functions related to cell motility are driven by the interaction between the partner proteins, actin and myosin. To obtain insights into how this interaction occurs, the internal dynamics of F-actin and myosin subfragment-1 (S1) were characterized by the quasielastic neutron scattering measurements on the solution samples of F-actin and S1. Contributions of the internal motions of the proteins to the scattering spectra were separated from those of the global macromolecular diffusion. Analysis of the spectra arising from the internal dynamics showed that the correlation times of the atomic motions were about two times shorter for F-actin than for S1, suggesting that F-actin fluctuates more rapidly than S1. It was also shown that the fraction of the immobile atoms is larger for S1 than for F-actin. These results suggest that F-actin actively facilitates the binding of myosin by utilizing the more frequent conformational fluctuations than those of S1. - Highlights: • We studied the internal dynamics of F-actin and myosin S1 by neutron scattering. • The correlation times of the atomic motions were smaller for F-actin than for S1. • The fraction of the immobile atoms was also smaller for F-actin than for S1. • Our results suggest that mobility of atoms in F-actin is higher than that in S1. • We propose that high flexibility of F-actin facilitates the binding of myosin

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

    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.

  20. Effects of morphology on the flapping dynamics of inverted flags

    Fan, Boyu; Cosse, Julia; Sader, John; Gharib, Morteza

    2014-11-01

    The behavior of inverted flags has received recent attention in the study of the interaction of flexible bodies with fluid flows. It has implications in a variety of natural phenomena, such as the fluttering of leaves in the wind. As opposed to a conventional flag, defined by a fixed leading edge and a free trailing edge, an inverted flag has a free leading edge and a fixed trailing edge. The reversed flow orientation of inverted flags has led to a surprising observation. Over a narrow range of wind speeds, they exhibit a large-amplitude flapping motion that is not present in their conventional counterparts. Our study experimentally investigates the effects of flag morphology on the flapping behavior of inverted flags. Different flags ranging from rectangles to triangles are studied in a wind tunnel to assess the underlying parameters that govern their dynamics. We observe a significant shift in the limit-cycle flapping mode that is a function of flag shape parameters. This research is supported by the Lester Lees Aeronautics Summer Undergraduate Research Fellowship and the Gordon and Betty Moore Foundation.

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

    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.

  2. Dynamics of Actin Cables in Polarized Growth of the Filamentous Fungus Aspergillus nidulans

    Bergs, Anna; Ishitsuka, Yuji; Evangelinos, Minoas; Nienhaus, G. U.; Takeshita, Norio

    2016-01-01

    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 have been developed to visualize actin cables in filamentous fungi, the exact organization and dynamics of actin cables has remained elusive. Here, we observed actin cables using tropomyosin (TpmA) and Lifeact fused to fluorescent proteins in living Aspergillus nidulans hyphae 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.

  3. Investigation of flap flexibility of β-secretase using molecular dynamic simulations.

    Kumalo, Hezekiel M; Bhakat, Soumendranath; Soliman, Mahmoud E

    2016-05-01

    Flap motif and its dynamics were extensively reported in aspartate proteases, e.g. HIV proteases and plasmepsins. Herein, we report the first account of flap dynamics amongst different conformations of β-secretase using molecular dynamics simulation. Various parameters were proposed and a selected few were picked which could appropriately describe the flap motion. Three systems were studied, namely Free (BACEFree) and two ligand-bound conformations, which belonged to space groups P6122 (BACEBound1) and C2221 (BACEBound2), respectively and four parameters (distance between the flaps tip residue, Thr72 and Ser325, d1; dihedral angle, ϕ (Thr72-Asp32-Asp228-Ser325); TriCα angles, θ1 (Thr72-Asp32-Ser325), and θ2 (Thr72-Asp228-Ser325)) were proposed to understand the change in dynamics of flap domain and the extent of flap opening and closing. Analysis of, θ2, d1, θ1 and ϕ confirmed that the BACEFree adopted semi-open, open and closed conformations with slight twisting during flap opening. However, BACEBound1 (P6122) showed an adaptation to open conformation due to lack of hydrogen bond interaction between the ligand and flap tip residue. A slight flap twisting, ϕ (lateral twisting) was observed for BACEBound1 during flap opening which correlates with the opening of BACEFree. Contradictory to the BACEBound1, the BACEBound2 locked the flap in a closed conformation throughout the simulation due to formation of a stable hydrogen bond interaction between the flap tip residue and ligand. Analyses of all three systems highlight that d1, θ2 and ϕ can be precisely used to describe the extent of flap opening and closing concurrently with snapshots along the molecular dynamics trajectory across several conformations of β-secretase. PMID:26208540

  4. Coupling of the hydration water dynamics and the internal dynamics of actin detected by quasielastic neutron scattering

    Highlights: ► Quasielastic neutron scattering spectra of F-actin and G-actin were measured. ► Analysis of the samples in D2O and H2O provided the spectra of hydration water. ► The first layer hydration water around F-actin is less mobile than around G-actin. ► This difference in hydration water is in concert with the internal dynamics of actin. ► Water outside the first layer behaves bulk-like but influenced by the first layer. -- Abstract: In order to characterize dynamics of water molecules around F-actin and G-actin, quasielastic neutron scattering experiments were performed on powder samples of F-actin and G-actin, hydrated either with D2O or H2O, at hydration ratios of 0.4 and 1.0. By combined analysis of the quasielastic neutron scattering spectra, the parameter values characterizing the dynamics of the water molecules in the first hydration layer and those of the water molecules outside of the first layer were obtained. The translational diffusion coefficients (DT) of the hydration water in the first layer were found to be 1.2 × 10−5 cm2/s and 1.7 × 10−5 cm2/s for F-actin and G-actin, respectively, while that for bulk water was 2.8 × 10−5 cm2/s. The residence times were 6.6 ps and 5.0 ps for F-actin and G-actin, respectively, while that for bulk water was 0.62 ps. These differences between F-actin and G-actin, indicating that the hydration water around G-actin is more mobile than that around F-actin, are in concert with the results of the internal dynamics of F-actin and G-actin, showing that G-actin fluctuates more rapidly than F-actin. This implies that the dynamics of the hydration water is coupled to the internal dynamics of the actin molecules. The DT values of the water molecules outside of the first hydration layer were found to be similar to that of bulk water though the residence times are strongly affected by the first hydration layer. This supports the recent observation on intracellular water that shows bulk-like behavior

  5. Dynamics of Micro-Air-Vehicle with Flapping Wings

    K. Sibilski

    2004-01-01

    Full Text Available Small (approximately 6 inch long, or hand-held reconnaissance micro air vehicles (MAVs will fly inside buildings, and require hover for observation, and agility at low speeds to move in confined spaces. For this flight envelope insect-like flapping wings seem to be an optimal mode of flying. Investigation of the aerodynamics of flapping wing MAVs is very challenging. The problem involves complex unsteady, viscous flow (mainly laminar, with the moving wing generating vortices and interacting with them. At this early stage of research only a preliminary insight into the nature of the little known aerodynamics of MAVs has been obtained. This paper describes computational models for simulation of the controlled motion of a microelectromechanical flying insect – entomopter. The design of software simulation for entomopter flight (SSEF is presented. In particular, we will estimate the flight control algorithms and performance for a Micromechanical Flying Insect (MFI, a 80–100 mm (wingtip-to-wingtip device capable of sustained autonomous flight. The SSEF is an end-to-end tool composed of several modular blocks which model the wing aerodynamics and dynamics, the body dynamics, and in the future, the environment perception, control algorithms, the actuators dynamics, and the visual and inertial sensors. We present the current state of the art of its implementation, and preliminary results. 

  6. Dynamics and Regulation of Actin Cytoskeleton in Plant Cells

    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.

  7. When fat is not bad: the regulation of actin dynamics by phospholipid signaling molecules

    Roman ePleskot

    2014-01-01

    Full Text Available The actin cytoskeleton plays a key role in the plant morphogenesis and is involved in polar cell growth, movement of subcellular organelles, cell division, and plant defense. Organization of actin cytoskeleton undergoes dynamic remodeling in response to internal developmental cues and diverse environmental signals. This dynamic behavior is regulated by numerous actin-binding proteins that integrate various signaling pathways. Production of the signaling lipids phosphatidylinositol 4,5-bisphosphate and phosphatidic acid affects the activity and subcellular distribution of several actin-binding proteins, and typically correlates with increased actin polymerization. Here we review current knowledge of the inter-regulatory dynamics between signaling phospholipids and the actin cytoskeleton in plant cells.

  8. Actin flow and talin dynamics govern rigidity sensing in actin-integrin linkage through talin extension.

    Hirata, Hiroaki; Chiam, Keng-Hwee; Lim, Chwee Teck; Sokabe, Masahiro

    2014-10-01

    At cell-substrate adhesion sites, the linkage between actin filaments and integrin is regulated by mechanical stiffness of the substrate. Of potential molecular regulators, the linker proteins talin and vinculin are of particular interest because mechanical extension of talin induces vinculin binding with talin, which reinforces the actin-integrin linkage. For understanding the molecular and biophysical mechanism of rigidity sensing at cell-substrate adhesion sites, we constructed a simple physical model to examine a role of talin extension in the stiffness-dependent regulation of actin-integrin linkage. We show that talin molecules linking between retrograding actin filaments and substrate-bound integrin are extended in a manner dependent on substrate stiffness. The model predicts that, in adhesion complexes containing ≈30 talin links, talin is extended enough for vinculin binding when the substrate is stiffer than 1 kPa. The lifetime of talin links needs to be 2-5 s to achieve an appropriate response of talin extension against substrate stiffness. Furthermore, changes in actin velocity drastically shift the range of substrate stiffness that induces talin-vinculin binding. Our results suggest that talin extension is a key step in sensing and responding to substrate stiffness at cell adhesion sites. PMID:25142525

  9. Mammalian Fat1 cadherin regulates actin dynamics and cell–cell contact

    Tanoue, Takuji; Takeichi, Masatoshi

    2004-01-01

    Fat cadherins form a distinct subfamily of the cadherin gene superfamily, and are featured by their unusually large extracellular domain. In this work, we investigated the function of a mammalian Fat cadherin. Fat1 was localized at filopodial tips, lamellipodial edges, and cell–cell boundaries, overlapping with dynamic actin structures. RNA interference–mediated knockdown of Fat1 resulted in disorganization of cell junction–associated F-actin and other actin fibers/cables, disturbance of cell...

  10. Dynamic Chord-wise Tip Curvature on Flexible Flapping Plates

    Martin, Nathan; Gharib, Morteza

    2014-11-01

    The aerodynamic characteristics of long rectangular flapping plates are strongly influenced by the interaction between tip and edge vortices. This has led to the development of many tip actuation mechanisms to independently bend or rotate the tip towards the root of the plate in the span-wise direction. In our current work, the influence of dynamically altering the chord-wise curvature of the tip on the generation of aerodynamic forces is investigated; for this case, the two free corners of the flat plate bend towards each other. The parameters of actuation timing, maximum curvature, Reynolds number, flexibility, and tip speed are independently varied to determine their influence. These results will further the fundamental understanding of unsteady aerodynamics. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship and the Gordon and Betty Moore foundation.

  11. The effect of mouse twinfilin-1 on the structure and dynamics of monomeric actin.

    Takács-Kollár, Veronika; Nyitrai, Miklós; Hild, Gábor

    2016-07-01

    The effect of twinfilin-1 on the structure and dynamics of monomeric actin was investigated with fluorescence spectroscopy and differential scanning calorimetry experiments. Fluorescence anisotropy measurements proved that G-actin and twinfilin-1 could form a complex. Due to the formation of the complexes the dissociation of the nucleotide slowed down from the nucleotide-binding pocket of actin. Fluorescence quenching experiments showed that the accessibility of the actin bound ε-ATP decreased in the presence of twinfilin-1. Temperature dependent fluorescence resonance energy transfer and differential scanning calorimetry experiments revealed that the protein matrix of actin becomes more rigid and more heat resistant in the presence of twinfilin-1. The results suggest that the nucleotide binding cleft shifted into a more closed and stable conformational state of actin in the presence of twinfilin-1. PMID:27079635

  12. TWISTED DWARF1 Mediates the Action of Auxin Transport Inhibitors on Actin Cytoskeleton Dynamics.

    Zhu, Jinsheng; Bailly, Aurelien; Zwiewka, Marta; Sovero, Valpuri; Di Donato, Martin; Ge, Pei; Oehri, Jacqueline; Aryal, Bibek; Hao, Pengchao; Linnert, Miriam; Burgardt, Noelia Inés; Lücke, Christian; Weiwad, Matthias; Michel, Max; Weiergräber, Oliver H; Pollmann, Stephan; Azzarello, Elisa; Mancuso, Stefano; Ferro, Noel; Fukao, Yoichiro; Hoffmann, Céline; Wedlich-Söldner, Roland; Friml, Jiří; Thomas, Clément; Geisler, Markus

    2016-04-01

    Plant growth and architecture is regulated by the polar distribution of the hormone auxin. Polarity and flexibility of this process is provided by constant cycling of auxin transporter vesicles along actin filaments, coordinated by a positive auxin-actin feedback loop. Both polar auxin transport and vesicle cycling are inhibited by synthetic auxin transport inhibitors, such as 1-N-naphthylphthalamic acid (NPA), counteracting the effect of auxin; however, underlying targets and mechanisms are unclear. Using NMR, we map the NPA binding surface on the Arabidopsis thaliana ABCB chaperone TWISTED DWARF1 (TWD1). We identify ACTIN7 as a relevant, although likely indirect, TWD1 interactor, and show TWD1-dependent regulation of actin filament organization and dynamics and that TWD1 is required for NPA-mediated actin cytoskeleton remodeling. The TWD1-ACTIN7 axis controls plasma membrane presence of efflux transporters, and as a consequence act7 and twd1 share developmental and physiological phenotypes indicative of defects in auxin transport. These can be phenocopied by NPA treatment or by chemical actin (de)stabilization. We provide evidence that TWD1 determines downstream locations of auxin efflux transporters by adjusting actin filament debundling and dynamizing processes and mediating NPA action on the latter. This function appears to be evolutionary conserved since TWD1 expression in budding yeast alters actin polarization and cell polarity and provides NPA sensitivity. PMID:27053424

  13. ER sheet persistence is coupled to myosin 1c–regulated dynamic actin filament arrays

    Joensuu, Merja; Belevich, Ilya; Rämö, Olli; Nevzorov, Ilya; Vihinen, Helena; Puhka, Maija; Witkos, Tomasz M.; Lowe, Martin; Vartiainen, Maria K.; Jokitalo, Eija

    2014-01-01

    The endoplasmic reticulum (ER) comprises a dynamic three-dimensional (3D) network with diverse structural and functional domains. Proper ER operation requires an intricate balance within and between dynamics, morphology, and functions, but how these processes are coupled in cells has been unclear. Using live-cell imaging and 3D electron microscopy, we identify a specific subset of actin filaments localizing to polygons defined by ER sheets and tubules and describe a role for these actin arrays in ER sheet persistence and, thereby, in maintenance of the characteristic network architecture by showing that actin depolymerization leads to increased sheet fluctuation and transformations and results in small and less abundant sheet remnants and a defective ER network distribution. Furthermore, we identify myosin 1c localizing to the ER-associated actin filament arrays and reveal a novel role for myosin 1c in regulating these actin structures, as myosin 1c manipulations lead to loss of the actin filaments and to similar ER phenotype as observed after actin depolymerization. We propose that ER-associated actin filaments have a role in ER sheet persistence regulation and thus support the maintenance of sheets as a stationary subdomain of the dynamic ER network. PMID:24523293

  14. ER sheet persistence is coupled to myosin 1c-regulated dynamic actin filament arrays.

    Joensuu, Merja; Belevich, Ilya; Rämö, Olli; Nevzorov, Ilya; Vihinen, Helena; Puhka, Maija; Witkos, Tomasz M; Lowe, Martin; Vartiainen, Maria K; Jokitalo, Eija

    2014-04-01

    The endoplasmic reticulum (ER) comprises a dynamic three-dimensional (3D) network with diverse structural and functional domains. Proper ER operation requires an intricate balance within and between dynamics, morphology, and functions, but how these processes are coupled in cells has been unclear. Using live-cell imaging and 3D electron microscopy, we identify a specific subset of actin filaments localizing to polygons defined by ER sheets and tubules and describe a role for these actin arrays in ER sheet persistence and, thereby, in maintenance of the characteristic network architecture by showing that actin depolymerization leads to increased sheet fluctuation and transformations and results in small and less abundant sheet remnants and a defective ER network distribution. Furthermore, we identify myosin 1c localizing to the ER-associated actin filament arrays and reveal a novel role for myosin 1c in regulating these actin structures, as myosin 1c manipulations lead to loss of the actin filaments and to similar ER phenotype as observed after actin depolymerization. We propose that ER-associated actin filaments have a role in ER sheet persistence regulation and thus support the maintenance of sheets as a stationary subdomain of the dynamic ER network. PMID:24523293

  15. On the wake dynamics of flapping inverted flags

    Gilmanov, Anvar; Sotiropoulos, Fotis; Cosse, Julia; Gharib, Mory

    2014-11-01

    As recently shown experimentally by Kim et al. (JFM, 2013), when a flexible flag with a fixed trailing edge (an inverted flag) is exposed to a uniform inflow it can exhibit complex structural response and rich fluid-structure interaction (FSI) dynamics. We employ a new FSI numerical method to carry out large-eddy simulation (LES) of inverted flags in the range where large-amplitude flapping instabilities have been found experimentally. The numerical method integrates the curvilinear immersed boundary (CURVIB) FSI method of Borazjani et al. (JCP, 2008) with the thin-shell, rotation-free, finite-element (FE) formulation of Stolarski et al. (Int. JNME, 2013) and is able to simulate FSI of flexible thin bodies undergoing oscillations of arbitrarily large amplitude. The dynamic Smagorinsky model is employed for subgrid scale closure and a wall model is employed for reconstructing velocity boundary conditions. Comparisons with the experimental data show that the simulations are able to capture the structural response of the flag with very good accuracy. The computed results are analyzed to elucidate the structure and dynamics of the massively separated, unsteady flow shed off the flag edges. This work is supported by the US Department of Energy and the Minnesota Supercomputing Institute.

  16. Calcium influx through CRAC channels controls actin organization and dynamics at the immune synapse

    Hartzell, Catherine A; Jankowska, Katarzyna I; Burkhardt, Janis K; Lewis, Richard S

    2016-01-01

    T cell receptor (TCR) engagement opens Ca2+ release-activated Ca2+ (CRAC) channels and triggers formation of an immune synapse between T cells and antigen-presenting cells. At the synapse, actin reorganizes into a concentric lamellipod and lamella with retrograde actin flow that helps regulate the intensity and duration of TCR signaling. We find that Ca2+ influx is required to drive actin organization and dynamics at the synapse. Calcium acts by promoting actin depolymerization and localizing actin polymerization and the actin nucleation promotion factor WAVE2 to the periphery of the lamellipod while suppressing polymerization elsewhere. Ca2+-dependent retrograde actin flow corrals ER tubule extensions and STIM1/Orai1 complexes to the synapse center, creating a self-organizing process for CRAC channel localization. Our results demonstrate a new role for Ca2+ as a critical regulator of actin organization and dynamics at the synapse, and reveal potential feedback loops through which Ca2+ influx may modulate TCR signaling. DOI: http://dx.doi.org/10.7554/eLife.14850.001 PMID:27440222

  17. Calcium influx through CRAC channels controls actin organization and dynamics at the immune synapse.

    Hartzell, Catherine A; Jankowska, Katarzyna I; Burkhardt, Janis K; Lewis, Richard S

    2016-01-01

    T cell receptor (TCR) engagement opens Ca(2+) release-activated Ca(2+) (CRAC) channels and triggers formation of an immune synapse between T cells and antigen-presenting cells. At the synapse, actin reorganizes into a concentric lamellipod and lamella with retrograde actin flow that helps regulate the intensity and duration of TCR signaling. We find that Ca(2+) influx is required to drive actin organization and dynamics at the synapse. Calcium acts by promoting actin depolymerization and localizing actin polymerization and the actin nucleation promotion factor WAVE2 to the periphery of the lamellipod while suppressing polymerization elsewhere. Ca(2+)-dependent retrograde actin flow corrals ER tubule extensions and STIM1/Orai1 complexes to the synapse center, creating a self-organizing process for CRAC channel localization. Our results demonstrate a new role for Ca(2+) as a critical regulator of actin organization and dynamics at the synapse, and reveal potential feedback loops through which Ca(2+) influx may modulate TCR signaling. PMID:27440222

  18. Flapping Dynamics of an Inverted Flexible Foil in a Uniform Axial Flow

    Gurugubelli Venkata, Pardha Saradhi; Jaiman, Rajeev K.

    2014-11-01

    This work presents a numerical study on self-induced flapping dynamics of an inverted flexible foil in uniform flow. The inverted foil considered in this study is clamped at the trailing edge and the leading edge is allowed to oscillate. A high-order coupled FSI solver based on CFEI formulation has been used to present the flapping response results for a wide range of nondimensional bending rigidity using a fixed Reynolds number of 1000 and a mass-ratio of 0.1. As a function of bending rigidity four flapping regimes have been discovered: fixed point, inverted limit-cycle oscillation, deflected flapping, and flipped flapping. The inverted foil configuration undergoes flapping motion more readily and experiences very large amplitude oscillations than the conventional foil. A wide variety of vortex wakes with a maximum of 14 vortices per oscillation cycle have been observed. The inverted limit-cycle flapping generate novel 4P +6S (14 vortices) and 2P +6S (10 vortices) wakes. On the other hand, the flipped flapping regime is characterized by a von Kármán wake. We also observe that inverted foil can extract 1000 times more energy from the surrounding fluid compared to the conventional foil.

  19. Cortactin promotes exosome secretion by controlling branched actin dynamics.

    Sinha, Seema; Hoshino, Daisuke; Hong, Nan Hyung; Kirkbride, Kellye C; Grega-Larson, Nathan E; Seiki, Motoharu; Tyska, Matthew J; Weaver, Alissa M

    2016-07-18

    Exosomes are extracellular vesicles that influence cellular behavior and enhance cancer aggressiveness by carrying bioactive molecules. The mechanisms that regulate exosome secretion are poorly understood. Here, we show that the actin cytoskeletal regulatory protein cortactin promotes exosome secretion. Knockdown or overexpression of cortactin in cancer cells leads to a respective decrease or increase in exosome secretion, without altering exosome cargo content. Live-cell imaging revealed that cortactin controls both trafficking and plasma membrane docking of multivesicular late endosomes (MVEs). Regulation of exosome secretion by cortactin requires binding to the branched actin nucleating Arp2/3 complex and to actin filaments. Furthermore, cortactin, Rab27a, and coronin 1b coordinately control stability of cortical actin MVE docking sites and exosome secretion. Functionally, the addition of purified exosomes to cortactin-knockdown cells rescued defects of those cells in serum-independent growth and invasion. These data suggest a model in which cortactin promotes exosome secretion by stabilizing cortical actin-rich MVE docking sites. PMID:27402952

  20. Computer Simulations of Mechano-Chemical Networks Choreographing Actin Dynamics in Cell Motility

    Zhuravlev, Pavel I.; Hu, Longhua; Papoian, Garegin A.

    In eukaryotic cells, cell motility is largely driven by self-assembly and growth of filamentous networks comprised of actin. Numerous proteins regulate actin network dynamics either biochemically, or through mechanical interactions. This regulation is rather complex, intricately coordinated both spatially and temporally. Although experiments in vivo and in vitro have provided a trove of structural and biochemical information about actin-based cell motility processes, experimental data is not always easy to interpret unambiguously, sometimes various interpretations being in contradiction with each other. Hence, mathematical modeling approaches are necessary for providing a physical foundation for interpreting and guiding experiments. In particular, computer simulations based on physicochemical interactions provide a systems-level description of protrusion dynamics. In this contribution, we review recent progress in modeling actin-based cell motility using detailed computer simulations. We elaborate on the way actin network dynamics is determined by the interplay between chemical reactions, mechanical feedbacks, and transport bottlenecks. We also discuss the role of inherent randomness of elementary chemical reactions in determining the dynamical behavior of the mechano-chemical network controlling actin polymerization and growth.

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

    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.

  2. A small molecule inhibitor of tropomyosin dissociates actin binding from tropomyosin-directed regulation of actin dynamics

    Teresa T. Bonello; Miro Janco; Jeff Hook; Alex Byun; Mark Appaduray; Irina Dedova; Sarah Hitchcock-DeGregori; Hardeman, Edna C.; Justine R. Stehn; Till Böcking; Gunning, Peter W.

    2016-01-01

    The tropomyosin family of proteins form end-to-end polymers along the actin filament. Tumour cells rely on specific tropomyosin-containing actin filament populations for growth and survival. To dissect out the role of tropomyosin in actin filament regulation we use the small molecule TR100 directed against the C terminus of the tropomyosin isoform Tpm3.1. TR100 nullifies the effect of Tpm3.1 on actin depolymerisation but surprisingly Tpm3.1 retains the capacity to bind F-actin in a cooperativ...

  3. A comparative molecular dynamics study on BACE1 and BACE2 flap flexibility.

    Kumalo, H M; Soliman, Mahmoud E

    2016-10-01

    Beta-amyloid precursor protein cleavage enzyme1 (BACE1) and beta-amyloid precursor protein cleavage enzyme2 (BACE2), members of aspartyl protease family, are close homologs and have high similarity in their protein crystal structures. However, their enzymatic properties are different, which leads to different clinical outcomes. In this study, we performed sequence analysis and all-atom molecular dynamic (MD) simulations for both enzymes in their ligand-free states in order to compare their dynamical flap behaviors. This is to enhance our understanding of the relationship between sequence, structure and the dynamics of this protein family. Sequence analysis shows that in BACE1 and BACE2, most of the ligand-binding sites are conserved, indicative of their enzymatic property as aspartyl protease members. The other conserved residues are more or less unsystematically localized throughout the structure. Herein, we proposed and applied different combined parameters to define the asymmetric flap motion; the distance, d1, between the flap tip and the flexible region; the dihedral angle, φ, to account for the twisting motion and the TriCα angle, θ2 and θ1. All four combined parameters were found to appropriately define the observed "twisting" motion during the flaps different conformational states. Additional analysis of the parameters indicated that the flaps can exist in an ensemble of conformations, i.e. closed, semi-open and open conformations for both systems. However, the behavior of the flap tips during simulations is different between BACE1 and BACE2. The BACE1 active site cavity is more spacious as compared to that of BACE2. The analysis of 10S loop and 113S loop showed a similar trend to that of flaps, with the BACE1 loops being more flexible and less stable than those of BACE2. We believe that the results, methods and perspectives highlighted in this report would assist researchers in the discovery of BACE inhibitors as potential Alzheimer's disease therapies

  4. Cdc28–Cln3 phosphorylation of Sla1 regulates actin patch dynamics in different modes of fungal growth

    Zeng, Guisheng; Wang, Yan-Ming; Wang, Yue

    2012-01-01

    A dynamic balance between targeted transport and endocytosis is critical for polarized cell growth. However, how actin-mediated endocytosis is regulated in different growth modes remains unclear. Here we report differential regulation of cortical actin patch dynamics between the yeast and hyphal growth in Candida albicans. The mechanism involves phosphoregulation of the endocytic protein Sla1 by the cyclin-dependent kinase (CDK) Cdc28–Cln3 and the actin-regulating kinase Prk1. Mutational stud...

  5. Live Cell Imaging of Actin Dynamics in the Filamentous Fungus Aspergillus nidulans.

    Schultzhaus, Zachary; Quintanilla, Laura; Hilton, Angelyn; Shaw, Brian D

    2016-04-01

    Hyphal cells of filamentous fungi grow at their tips in a method analogous to pollen tube and root hair elongation. This process, generally referred to as tip growth, requires precise regulation of the actin cytoskeleton, and characterizing the various actin structures in these cell types is currently an active area of research. Here, the actin marker Lifeact was used to document actin dynamics in the filamentous fungus Aspergillus nidulans. Contractile double rings were observed at septa, and annular clusters of puncta were seen subtending growing hyphal tips, corresponding to the well-characterized subapical endocytic collar. However, Lifeact also revealed two additional structures. One, an apical array, was dynamic on the face opposite the tip, while a subapical web was dynamic on the apical face and was located several microns behind the growth site. Each was observed turning into the other over time, implying that they could represent different localizations of the same structure, although hyphae with a subapical web grew faster than those exhibiting an apical array. The subapical web has not been documented in any filamentous fungus to date, and is separate from the networks of F-actin seen in other tip-growing organisms surrounding septa or stationary along the plasmalemma. PMID:26879694

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

    Matoušková, J.; Janda, M.; Fišer, R.; Šašek, Vladimír; Kocourková, Daniela; Burketová, Lenka; Dušková, J.; Martinec, Jan; Valentová, O.

    2014-01-01

    Roč. 223, JUN 2014 (2014), s. 36-44. ISSN 0168-9452 R&D Projects: GA ČR(CZ) GAP501/11/1654 Institutional support: RVO:61389030 Keywords : Actin dynamics * Salicylic acid * PR genes Subject RIV: CE - Biochemistry Impact factor: 3.607, year: 2014

  7. Arabidopsis Actin-Depolymerizing Factor-4 links pathogen perception, defense activation and transcription to cytoskeletal dynamics.

    Katie Porter

    Full Text Available The primary role of Actin-Depolymerizing Factors (ADFs is to sever filamentous actin, generating pointed ends, which in turn are incorporated into newly formed filaments, thus supporting stochastic actin dynamics. Arabidopsis ADF4 was recently shown to be required for the activation of resistance in Arabidopsis following infection with the phytopathogenic bacterium Pseudomonas syringae pv. tomato DC3000 (Pst expressing the effector protein AvrPphB. Herein, we demonstrate that the expression of RPS5, the cognate resistance protein of AvrPphB, was dramatically reduced in the adf4 mutant, suggesting a link between actin cytoskeletal dynamics and the transcriptional regulation of R-protein activation. By examining the PTI (PAMP Triggered Immunity response in the adf4 mutant when challenged with Pst expressing AvrPphB, we observed a significant reduction in the expression of the PTI-specific target gene FRK1 (Flg22-Induced Receptor Kinase 1. These data are in agreement with recent observations demonstrating a requirement for RPS5 in PTI-signaling in the presence of AvrPphB. Furthermore, MAPK (Mitogen-Activated Protein Kinase-signaling was significantly reduced in the adf4 mutant, while no such reduction was observed in the rps5-1 point mutation under similar conditions. Isoelectric focusing confirmed phosphorylation of ADF4 at serine-6, and additional in planta analyses of ADF4's role in immune signaling demonstrates that nuclear localization is phosphorylation independent, while localization to the actin cytoskeleton is linked to ADF4 phosphorylation. Taken together, these data suggest a novel role for ADF4 in controlling gene-for-gene resistance activation, as well as MAPK-signaling, via the coordinated regulation of actin cytoskeletal dynamics and R-gene transcription.

  8. How does the antagonism between capping and anti-capping proteins affect actin network dynamics?

    Actin-based cell motility is essential to many biological processes. We built a simplified, three-dimensional computational model and subsequently performed stochastic simulations to study the growth dynamics of lamellipodia-like branched networks. In this work, we shed light on the antagonism between capping and anti-capping proteins in regulating actin dynamics in the filamentous network. We discuss detailed mechanisms by which capping and anti-capping proteins affect the protrusion speed of the actin network and the rate of nucleation of filaments. We computed a phase diagram showing the regimes of motility enhancement and inhibition by these proteins. Our work shows that the effects of capping and anti-capping proteins are mainly transmitted by modulation of the filamentous network density and local availability of monomeric actin. We discovered that the combination of the capping/anti-capping regulatory network with nucleation-promoting proteins introduces robustness and redundancy in cell motility machinery, allowing the cell to easily achieve maximal protrusion speeds under a broader set of conditions. Finally, we discuss distributions of filament lengths under various conditions and speculate on their potential implication for the emergence of filopodia from the lamellipodial network.

  9. How does the antagonism between capping and anti-capping proteins affect actin network dynamics?

    Hu, Longhua; Papoian, Garegin A.

    2011-09-01

    Actin-based cell motility is essential to many biological processes. We built a simplified, three-dimensional computational model and subsequently performed stochastic simulations to study the growth dynamics of lamellipodia-like branched networks. In this work, we shed light on the antagonism between capping and anti-capping proteins in regulating actin dynamics in the filamentous network. We discuss detailed mechanisms by which capping and anti-capping proteins affect the protrusion speed of the actin network and the rate of nucleation of filaments. We computed a phase diagram showing the regimes of motility enhancement and inhibition by these proteins. Our work shows that the effects of capping and anti-capping proteins are mainly transmitted by modulation of the filamentous network density and local availability of monomeric actin. We discovered that the combination of the capping/anti-capping regulatory network with nucleation-promoting proteins introduces robustness and redundancy in cell motility machinery, allowing the cell to easily achieve maximal protrusion speeds under a broader set of conditions. Finally, we discuss distributions of filament lengths under various conditions and speculate on their potential implication for the emergence of filopodia from the lamellipodial network.

  10. How does the antagonism between capping and anti-capping proteins affect actin network dynamics?

    Hu Longhua; Papoian, Garegin A, E-mail: gpapoian@umd.edu [Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742 (United States)

    2011-09-21

    Actin-based cell motility is essential to many biological processes. We built a simplified, three-dimensional computational model and subsequently performed stochastic simulations to study the growth dynamics of lamellipodia-like branched networks. In this work, we shed light on the antagonism between capping and anti-capping proteins in regulating actin dynamics in the filamentous network. We discuss detailed mechanisms by which capping and anti-capping proteins affect the protrusion speed of the actin network and the rate of nucleation of filaments. We computed a phase diagram showing the regimes of motility enhancement and inhibition by these proteins. Our work shows that the effects of capping and anti-capping proteins are mainly transmitted by modulation of the filamentous network density and local availability of monomeric actin. We discovered that the combination of the capping/anti-capping regulatory network with nucleation-promoting proteins introduces robustness and redundancy in cell motility machinery, allowing the cell to easily achieve maximal protrusion speeds under a broader set of conditions. Finally, we discuss distributions of filament lengths under various conditions and speculate on their potential implication for the emergence of filopodia from the lamellipodial network.

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

    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.

  12. Quasi-3d aerodynamic code for analyzing dynamic flap response

    Ramos García, Néstor

    is modeled using a panel method whereas the viscous part is modeled by using the integral form of the the laminar and turbulent boundary layer equations and with extensions for 3-D rotational effects. Laminar to turbulent transition can be forced with a boundary layer trip or computed with a modified...... reduced frequencies and oscillation amplitudes, and generally a good agreement is obtained. The capability of the code to simulate a trailing edge flap under steady or unsteady flow conditions has been proven. A parametric study on rotational effects induced by Coriolis and centrifugal forces in the......A computational model for predicting the aerodynamic behavior of wind turbine airfoil profiles subjected to steady and unsteady motions has been developed. The model is based on a viscous-inviscid interaction technique using strong coupling between the viscous and inviscid parts. The inviscid part...

  13. Effects of polymerization and nucleotide identity on the conformational dynamics of the bacterial actin homolog MreB

    Colavin, Alexandre; Hsin, Jen; Huang, Kerwyn Casey

    2014-01-01

    Cytoskeletal filaments drive many dynamic cellular processes, such as the regulation of shape by actin networks in eukaryotes and by the actin homolog MreB in rod-shaped bacteria. Here, we use all-atom molecular dynamics simulations to demonstrate close parallels between the conformational dynamics of actin and MreB, in which polymerization induces flattening of MreB subunits that restructures the ATP binding pocket to promote hydrolysis. We also find that ATP-bound MreB filaments are substan...

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

    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.

  15. Effect of torsional stiffness and inertia on the dynamics of low aspect ratio flapping wings

    Micro air vehicle-motivated aerodynamics in biological flight has been an important subject in the past decade. Inspired by the novel flapping wing mechanisms in insects, birds and bats, we have carried out a numerical study systematically investigating a three-dimensional flapping rigid wing with passively actuated lateral and rotational motion. Distinguishing it from the limited existing studies, this work performs a systematic examination on the effects of wing aspect ratio (AR = 1.0 to infinity), inertia (density ratio σ = 4–32), torsional stiffness (frequency ratio F = 1.5–10 and infinity) and pivot point (from chord-center to leading edge) on the dynamics response of a low AR rectangular wing under an initial zero speed flow field condition. The simulation results show that the symmetry breakdown of the flapping wing results in a forward/backward motion with a rotational pitching. When the wing reaches its stable periodic state, the induced pitching frequency is identical to its forced flapping frequency. However, depending on various kinematic and dynamic system parameters, (i.e. flapping frequency, density ratio and pitching axis), the lateral induced velocity shows a number of different oscillating frequencies. Furthermore, compared with a one degree of freedom (DoF) wing in the lateral direction only, the propulsion performance of such a two DoF wing relies very much on the magnitude of torsional stiffness adding on the pivot point, as well as its pitching axis. In all cases examined here, thrust force and moment generated by a long span wing is larger than that of a short wing, which is remarkably linked to the strong reverse von Kármán vortex street formed in the wake of a wing. (paper)

  16. Effect of torsional stiffness and inertia on the dynamics of low aspect ratio flapping wings.

    Xiao, Qing; Hu, Jianxin; Liu, Hao

    2014-03-01

    Micro air vehicle-motivated aerodynamics in biological flight has been an important subject in the past decade. Inspired by the novel flapping wing mechanisms in insects, birds and bats, we have carried out a numerical study systematically investigating a three-dimensional flapping rigid wing with passively actuated lateral and rotational motion. Distinguishing it from the limited existing studies, this work performs a systematic examination on the effects of wing aspect ratio (AR = 1.0 to infinity), inertia (density ratio σ = 4-32), torsional stiffness (frequency ratio F = 1.5-10 and infinity) and pivot point (from chord-center to leading edge) on the dynamics response of a low AR rectangular wing under an initial zero speed flow field condition. The simulation results show that the symmetry breakdown of the flapping wing results in a forward/backward motion with a rotational pitching. When the wing reaches its stable periodic state, the induced pitching frequency is identical to its forced flapping frequency. However, depending on various kinematic and dynamic system parameters, (i.e. flapping frequency, density ratio and pitching axis), the lateral induced velocity shows a number of different oscillating frequencies. Furthermore, compared with a one degree of freedom (DoF) wing in the lateral direction only, the propulsion performance of such a two DoF wing relies very much on the magnitude of torsional stiffness adding on the pivot point, as well as its pitching axis. In all cases examined here, thrust force and moment generated by a long span wing is larger than that of a short wing, which is remarkably linked to the strong reverse von Kármán vortex street formed in the wake of a wing. PMID:24434625

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

    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.

  18. ATEFlap aerodynamic model, a dynamic stall model including the effects of trailing edge flap deflection

    Bergami, L.; Gaunaa, M.

    2012-02-15

    The report presents the ATEFlap aerodynamic model, which computes the unsteady lift, drag and moment on a 2D airfoil section equipped with Adaptive Trailing Edge Flap. The model captures the unsteady response related to the effects of the vorticity shed into the wake, and the dynamics of flow separation a thin-airfoil potential flow model is merged with a dynamic stall model of the Beddoes-Leishmann type. The inputs required by the model are steady data for lift, drag, and moment coefficients as function of angle of attack and flap deflection. Further steady data used by the Beddoes- Leishmann dynamic stall model are computed in an external preprocessor application, which gives the user the possibility to verify, and eventually correct, the steady data passed to the aerodynamic model. The ATEFlap aerodynamic model is integrated in the aeroelastic simulation tool HAWC2, thus al- lowing to simulate the response of a wind turbine with trailing edge flaps on the rotor. The algorithms used by the preprocessor, and by aerodynamic model are presented, and modifications to previous implementations of the aerodynamic model are briefly discussed. The performance and the validity of the model are verified by comparing the dynamic response computed by the ATEFlap with solutions from CFD simulations. (Author)

  19. Passive control of a dynamically pitching wind turbine airfoil under aeroelastic conditions using a Gurney flap

    Nikoueeyan, Pourya; Magstadt, Andrew; Strike, John; Hind, Michael; Naughton, Jonathan

    2014-11-01

    To reduce the cost of energy, wind turbine design has moved towards larger blades that are heavier and have lower relative structural stiffness compared to shorter blades. To address the lower blade stiffness, different flow control techniques have been considered. The Gurney flap, a small, low-cost and effective control method, is a promising control actuator. Wind tunnel testing has been performed on a DU97-W-300 10% flatback airfoil undergoing dynamic pitching relevant to flow conditions encountered by wind turbine blades. To mimic blade compliance, the airfoil is actively driven through a torsionally elastic element. Time-resolved surface pressure measurements have been acquired from which lift Cl and moment Cm coefficients were calculated. Changes in Cl and Cm in moderate and deep dynamic stall regimes for different Gurney flap heights were studied for different pitch drive conditions (amplitude and frequency). The results show the significant impact of compliance on the angle of attack (α) range experienced by the airfoil. Shifts in α range result in different hysteresis behavior in both Cl and Cm and demonstrate the effectiveness of the Gurney flap in modifying the aerodynamics of wind turbine blades experiencing dynamic pitching. This work supported by DOE and a gift from BP.

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

    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

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

    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. PMID:23644458

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

    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

  3. Comparative dynamics of retrograde actin flow and focal adhesions: formation of nascent adhesions triggers transition from fast to slow flow.

    Antonina Y Alexandrova

    Full Text Available Dynamic actin network at the leading edge of the cell is linked to the extracellular matrix through focal adhesions (FAs, and at the same time it undergoes retrograde flow with different dynamics in two distinct zones: the lamellipodium (peripheral zone of fast flow, and the lamellum (zone of slow flow located between the lamellipodium and the cell body. Cell migration involves expansion of both the lamellipodium and the lamellum, as well as formation of new FAs, but it is largely unknown how the position of the boundary between the two flow zones is defined, and how FAs and actin flow mutually influence each other. We investigated dynamic relationship between focal adhesions and the boundary between the two flow zones in spreading cells. Nascent FAs first appeared in the lamellipodium. Within seconds after the formation of new FAs, the rate of actin flow decreased locally, and the lamellipodium/lamellum boundary advanced towards the new FAs. Blocking fast actin flow with cytochalasin D resulted in rapid dissolution of nascent FAs. In the absence of FAs (spreading on poly-L-lysine-coated surfaces retrograde flow was uniform and the velocity transition was not observed. We conclude that formation of FAs depends on actin dynamics, and in its turn, affects the dynamics of actin flow by triggering transition from fast to slow flow. Extension of the cell edge thus proceeds through a cycle of lamellipodium protrusion, formation of new FAs, advance of the lamellum, and protrusion of the lamellipodium from the new base.

  4. Comparative dynamics of retrograde actin flow and focal adhesions: formation of nascent adhesions triggers transition from fast to slow flow.

    Alexandrova, Antonina Y; Arnold, Katya; Schaub, Sébastien; Vasiliev, Jury M; Meister, Jean-Jacques; Bershadsky, Alexander D; Verkhovsky, Alexander B

    2008-01-01

    Dynamic actin network at the leading edge of the cell is linked to the extracellular matrix through focal adhesions (FAs), and at the same time it undergoes retrograde flow with different dynamics in two distinct zones: the lamellipodium (peripheral zone of fast flow), and the lamellum (zone of slow flow located between the lamellipodium and the cell body). Cell migration involves expansion of both the lamellipodium and the lamellum, as well as formation of new FAs, but it is largely unknown how the position of the boundary between the two flow zones is defined, and how FAs and actin flow mutually influence each other. We investigated dynamic relationship between focal adhesions and the boundary between the two flow zones in spreading cells. Nascent FAs first appeared in the lamellipodium. Within seconds after the formation of new FAs, the rate of actin flow decreased locally, and the lamellipodium/lamellum boundary advanced towards the new FAs. Blocking fast actin flow with cytochalasin D resulted in rapid dissolution of nascent FAs. In the absence of FAs (spreading on poly-L-lysine-coated surfaces) retrograde flow was uniform and the velocity transition was not observed. We conclude that formation of FAs depends on actin dynamics, and in its turn, affects the dynamics of actin flow by triggering transition from fast to slow flow. Extension of the cell edge thus proceeds through a cycle of lamellipodium protrusion, formation of new FAs, advance of the lamellum, and protrusion of the lamellipodium from the new base. PMID:18800171

  5. Dynamics of a pneumatic artificial muscle actuation system driving a trailing edge flap

    Woods, Benjamin K. S.; Kothera, Curt S.; Wang, Gang; Wereley, Norman M.

    2014-09-01

    This study presents a time domain dynamic model of an antagonistic pneumatic artificial muscle (PAM) driven trailing edge flap (TEF) system for next generation active helicopter rotors. Active rotor concepts are currently being widely researched in the rotorcraft community as a means to provide a significant leap forward in performance through primary aircraft control, vibration mitigation and noise reduction. Recent work has shown PAMs to be a promising candidate for active rotor actuation due to their combination of high force, large stroke, light weight, and suitable bandwidth. When arranged into biologically inspired agonist/antagonist muscle pairs they can produce bidirectional torques for effectively driving a TEF. However, there are no analytical dynamic models in the literature that can accurately capture the behavior of such systems across the broad range of frequencies required for this demanding application. This work combines mechanical, pneumatic, and aerodynamic component models into a global flap system model developed for the Bell 407 rotor system. This model can accurately predict pressure, force, and flap angle response to pneumatic control valve inputs over a range of operating frequencies from 7 to 35 Hz (1/rev to 5/rev for the Bell 407) and operating pressures from 30 to 90 psi.

  6. Dynamics of a pneumatic artificial muscle actuation system driving a trailing edge flap

    This study presents a time domain dynamic model of an antagonistic pneumatic artificial muscle (PAM) driven trailing edge flap (TEF) system for next generation active helicopter rotors. Active rotor concepts are currently being widely researched in the rotorcraft community as a means to provide a significant leap forward in performance through primary aircraft control, vibration mitigation and noise reduction. Recent work has shown PAMs to be a promising candidate for active rotor actuation due to their combination of high force, large stroke, light weight, and suitable bandwidth. When arranged into biologically inspired agonist/antagonist muscle pairs they can produce bidirectional torques for effectively driving a TEF. However, there are no analytical dynamic models in the literature that can accurately capture the behavior of such systems across the broad range of frequencies required for this demanding application. This work combines mechanical, pneumatic, and aerodynamic component models into a global flap system model developed for the Bell 407 rotor system. This model can accurately predict pressure, force, and flap angle response to pneumatic control valve inputs over a range of operating frequencies from 7 to 35 Hz (1/rev to 5/rev for the Bell 407) and operating pressures from 30 to 90 psi. (paper)

  7. Ornithine decarboxylase and extracellular polyamines regulate microvascular sprouting and actin cytoskeleton dynamics in endothelial cells

    The polyamines are essential for cancer cell proliferation during tumorigenesis. Targeted inhibition of ornithine decarboxylase (ODC), i.e. a key enzyme of polyamine biosynthesis, by α-difluoromethylornithine (DFMO) has shown anti-neoplastic activity in various experimental models. This activity has mainly been attributed to the anti-proliferative effect of DFMO in cancer cells. Here, we provide evidence that unperturbed ODC activity is a requirement for proper microvessel sprouting ex vivo as well as the migration of primary human endothelial cells. DFMO-mediated ODC inhibition was reversed by extracellular polyamine supplementation, showing that anti-angiogenic effects of DFMO were specifically related to polyamine levels. ODC inhibition was associated with an abnormal morphology of the actin cytoskeleton during cell spreading and migration. Moreover, our data suggest that de-regulated actin cytoskeleton dynamics in DFMO treated endothelial cells may be related to constitutive activation of the small GTPase CDC42, i.e. a well-known regulator of cell motility and actin cytoskeleton remodeling. These insights into the potential role of polyamines in angiogenesis should stimulate further studies testing the combined anti-tumor effect of polyamine inhibition and established anti-angiogenic therapies in vivo.

  8. Shank–cortactin interactions control actin dynamics to maintain flexibility of neuronal spines and synapses

    MacGillavry, Harold D.; Kerr, Justin M.; Kassner, Josh; Frost, Nicholas A.; Blanpied, Thomas A.

    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 Shank proteins in neurons has been complicated because the different Shank isoforms share a very high degree of sequence and domain homology. Therefore, to control Shank content while minimizing potential compensatory effects, a miRNA-based knockdown strategy was developed to reduce the expression of all synaptically targeted Shank isoforms simultaneously in rat hippocampal neurons. Using this approach, a strong (>75%) reduction in total Shank protein levels was achieved at individual dendritic spines, prompting an approximately 40% decrease in mushroom spine density. Furthermore, Shank knockdown reduced spine actin levels and increased sensitivity to the actin depolymerizing agent Latrunculin A. A SHANK2 mutant lacking the proline-rich cortactin-binding motif (SHANK2-ΔPRO) was unable to rescue these defects. Furthermore, Shank knockdown reduced cortactin levels in spines and increased the mobility of spine cortactin as measured by single-molecule tracking photoactivated localization microscopy, suggesting that Shank proteins recruit and stabilize cortactin at the synapse. Furthermore, it was found that Shank knockdown significantly reduced spontaneous remodelling of synapse morphology that could not be rescued by the SHANK2-ΔPRO mutant. It was concluded that Shank proteins are key intermediates between the synapse and the spine interior that, via cortactin, permit the actin cytoskeleton to dynamically regulate synapse morphology and function. PMID:26547831

  9. Enabled Negatively Regulates Diaphanous-Driven Actin Dynamics In Vitro and In Vivo

    Bilancia, C.G.; Winkelman, J.D.; Tsygankov, D.; Nowotarski, S.H.; Sees, J.A.; Comber, K.; Evans, I.; Lakhani, V.; Wood, W.; Elston, T.C.; Kovar, D.R.; Peifer, M

    2014-01-01

    Summary Actin regulators facilitate cell migration by controlling cell protrusion architecture and dynamics. As the behavior of individual actin regulators becomes clear, we must address why cells require multiple regulators with similar functions and how they cooperate to create diverse protrusions. We characterized Diaphanous (Dia) and Enabled (Ena) as a model, using complementary approaches: cell culture, biophysical analysis, and Drosophila morphogenesis. We found that Dia and Ena have di...

  10. Protocadherin FAT1 binds Ena/VASP proteins and is necessary for actin dynamics and cell polarization

    Moeller, Marcus J.; Soofi, Abdulsalam; Braun, Gerald S; Li, Xiaodong; Watzl, Carsten; Kriz, Wilhelm; Holzman, Lawrence B.

    2004-01-01

    Cell migration requires integration of cellular processes resulting in cell polarization and actin dynamics. Previous work using tools of Drosophila genetics suggested that protocadherin fat serves in a pathway necessary for determining cell polarity in the plane of a tissue. Here we identify mammalian FAT1 as a proximal element of a signaling pathway that determines both cellular polarity in the plane of the monolayer and directed actin-dependent cell motility. FAT1 is localized to the leadi...

  11. Structural dynamics and aerodynamics measurements of biologically inspired flexible flapping wings

    Flapping wing flight as seen in hummingbirds and insects poses an interesting unsteady aerodynamic problem: coupling of wing kinematics, structural dynamics and aerodynamics. There have been numerous studies on the kinematics and aerodynamics in both experimental and computational cases with both natural and artificial wings. These studies tend to ignore wing flexibility; however, observation in nature affirms that passive wing deformation is predominant and may be crucial to the aerodynamic performance. This paper presents a multidisciplinary experimental endeavor in correlating a flapping micro air vehicle wing's aeroelasticity and thrust production, by quantifying and comparing overall thrust, structural deformation and airflow of six pairs of hummingbird-shaped membrane wings of different properties. The results show that for a specific spatial distribution of flexibility, there is an effective frequency range in thrust production. The wing deformation at the thrust-productive frequencies indicates the importance of flexibility: both bending and twisting motion can interact with aerodynamic loads to enhance wing performance under certain conditions, such as the deformation phase and amplitude. By measuring structural deformations under the same aerodynamic conditions, beneficial effects of passive wing deformation can be observed from the visualized airflow and averaged thrust. The measurements and their presentation enable observation and understanding of the required structural properties for a thrust effective flapping wing. The intended passive responses of the different wings follow a particular pattern in correlation to their aerodynamic performance. Consequently, both the experimental technique and data analysis method can lead to further studies to determine the design principles for micro air vehicle flapping wings.

  12. Structural dynamics and aerodynamics measurements of biologically inspired flexible flapping wings

    Wu, P; Stanford, B K; Ifju, P G [Department of Mechanical and Aerospace Engineering, MAE-A 231, University of Florida, Gainesville, FL 32611 (United States); Saellstroem, E; Ukeiley, L, E-mail: diccidwp@ufl.edu [Department of Mechanical and Aerospace Engineering, University of Florida, Shalimar, FL 32579 (United States)

    2011-03-15

    Flapping wing flight as seen in hummingbirds and insects poses an interesting unsteady aerodynamic problem: coupling of wing kinematics, structural dynamics and aerodynamics. There have been numerous studies on the kinematics and aerodynamics in both experimental and computational cases with both natural and artificial wings. These studies tend to ignore wing flexibility; however, observation in nature affirms that passive wing deformation is predominant and may be crucial to the aerodynamic performance. This paper presents a multidisciplinary experimental endeavor in correlating a flapping micro air vehicle wing's aeroelasticity and thrust production, by quantifying and comparing overall thrust, structural deformation and airflow of six pairs of hummingbird-shaped membrane wings of different properties. The results show that for a specific spatial distribution of flexibility, there is an effective frequency range in thrust production. The wing deformation at the thrust-productive frequencies indicates the importance of flexibility: both bending and twisting motion can interact with aerodynamic loads to enhance wing performance under certain conditions, such as the deformation phase and amplitude. By measuring structural deformations under the same aerodynamic conditions, beneficial effects of passive wing deformation can be observed from the visualized airflow and averaged thrust. The measurements and their presentation enable observation and understanding of the required structural properties for a thrust effective flapping wing. The intended passive responses of the different wings follow a particular pattern in correlation to their aerodynamic performance. Consequently, both the experimental technique and data analysis method can lead to further studies to determine the design principles for micro air vehicle flapping wings.

  13. Binding of single walled carbon nanotube to WT and mutant HIV-1 proteases: analysis of flap dynamics and binding mechanism.

    Meher, Biswa Ranjan; Wang, Yixuan

    2012-09-01

    Most of the currently treated HIV-1 protease (HIV-PR) inhibitors have been prone to suffer from the mutations associated drug resistance. Therefore, it is necessary to search for potent alternatives against the drug resistance. In the current study we have tested the single-walled carbon nanotube (SWCNT) as an inhibitor in wild type (WT) as well as in three primary mutants (I50V(PR), V82A(PR) and I84V(PR)) of the HIV-1-PR through docking the SWCNT in the active site region, and then performed all-atom MD simulations for the complexes. The conformational dynamics of HIV-PR with a 20 ns trajectory reveals that the SWCNT can effectively bind to the HIV-1-PR active site and regulate the flap dynamics such as maintaining the flap-flap closed. To gain an insight into the binding affinity, we also performed the MM-PBSA based binding free energy calculations for the four HIV-PR/SWCNT complexes. It was observed that, although the binding between the SWCNT and the HIV-PR decreases due to the mutations, the SWCNTs bind to the HIV-PRs 3-5 folds stronger than the most potent HIV-1-PR inhibitor, TMC114. Remarkably, the significant interactions with binding energy higher than 1kcal/mol focus on the flap and active regions, which favors closing flap-flap and deactivating the active residues of the HIV-PR. The flap dynamics and binding strength information for HIV-PR and SWCNTs can help design SWCNT-based HIV-1-PR inhibitors. PMID:23142620

  14. Transition from a Linear to a Harmonic Potential in Collective Dynamics of a Multifilament Actin Bundle

    Schnauß, Jörg; Golde, Tom; Schuldt, Carsten; Schmidt, B. U. Sebastian; Glaser, Martin; Strehle, Dan; Händler, Tina; Heussinger, Claus; Käs, Josef A.

    2016-03-01

    Attractive depletion forces between rodlike particles in highly crowded environments have been shown through recent modeling and experimental approaches to induce different structural and dynamic signatures depending on relative orientation between rods. For example, it has been demonstrated that the axial attraction between two parallel rods yields a linear energy potential corresponding to a constant contractile force of 0.1 pN. Here, we extend pairwise, depletion-induced interactions to a multifilament level with actin bundles, and find contractile forces up to 3 pN. Forces generated due to bundle relaxation were not constant, but displayed a harmonic potential and decayed exponentially with a mean decay time of 3.4 s. Through an analytical model, we explain these different fundamental dynamics as an emergent, collective phenomenon stemming from the additive, pairwise interactions of filaments within a bundle.

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

    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. (paper)

  16. The actin binding domain of βI-spectrin regulates the morphological and functional dynamics of dendritic spines.

    Michael W Nestor

    Full Text Available Actin microfilaments regulate the size, shape and mobility of dendritic spines and are in turn regulated by actin binding proteins and small GTPases. The βI isoform of spectrin, a protein that links the actin cytoskeleton to membrane proteins, is present in spines. To understand its function, we expressed its actin-binding domain (ABD in CA1 pyramidal neurons in hippocampal slice cultures. The ABD of βI-spectrin bundled actin in principal dendrites and was concentrated in dendritic spines, where it significantly increased the size of the spine head. These effects were not observed after expression of homologous ABDs of utrophin, dystrophin, and α-actinin. Treatment of slice cultures with latrunculin-B significantly decreased spine head size and decreased actin-GFP fluorescence in cells expressing the ABD of α-actinin, but not the ABD of βI-spectrin, suggesting that its presence inhibits actin depolymerization. We also observed an increase in the area of GFP-tagged PSD-95 in the spine head and an increase in the amplitude of mEPSCs at spines expressing the ABD of βI-spectrin. The effects of the βI-spectrin ABD on spine size and mEPSC amplitude were mimicked by expressing wild-type Rac3, a small GTPase that co-immunoprecipitates specifically with βI-spectrin in extracts of cultured cortical neurons. Spine size was normal in cells co-expressing a dominant negative Rac3 construct with the βI-spectrin ABD. We suggest that βI-spectrin is a synaptic protein that can modulate both the morphological and functional dynamics of dendritic spines, perhaps via interaction with actin and Rac3.

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

    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.

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

    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...... tip and the retrograde flow at the base of the filopodium. Adhesion of a bead to the filopodial tip locally reduces actin polymerization and leads to retraction via retrograde flow, reminiscent of a process used by pathogens to invade cells. Using optical tweezers, we show that filopodial retraction...... occurs at a constant speed against counteracting forces up to 50 pN. Our measurements point toward retrograde flow in the cortex together with frictional coupling between the filopodial and cortical actin networks as the main retraction-force generator for filopodia. The force exerted by filopodial...

  19. Vortex dynamics and flapping patterns of the inverted flag with a bluff body

    Kim, Hyeonseong; Kim, Junyoung; Kim, Daegyoum

    2015-11-01

    Flow-induced vibration of flexible structures for energy harvesting has drawn attention recently. The inverted flag whose trailing edge is clamped and leading edge is free to move was known to self-excite in a uniform flow of both water and air. In this study, we investigated the effect of an upstream bluff body, a flat plate, on the dynamics of the downstream inverted flag. Periodic vortical structures created by an upstream bluff body make the dynamics of the inverted flag quite different from those of the inverted flag without the bluff body. We examined the motion of the inverted flag by varying the relative displacement of the inverted flag from the bluff body and their relative size. Our results show that the inverted flag can flap with higher frequency and larger amplitude with the upstream bluff body. We also compared the dynamics of the inverted flag with those of the general flag with the upstream bluff body. In order to better understand the dynamics of the flag, the analysis of the flow patterns using particle image velocimetry was also conducted.

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

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

    2014-06-15

    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 42nm 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 20-40 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 137Å, a superhelical pitch of 770Å, and no

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

    Nadia D'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.

  2. Clathrin is Important for Normal Actin Dynamics and Progression of Sla2p-Containing Patches During Endocytosis in Yeast

    Newpher, Thomas M.; Lemmon, Sandra K.

    2006-01-01

    Clathrin is a major vesicle coat protein involved in receptor-mediated endocytosis. In yeast and higher eukaryotes, clathrin is recruited to the plasma membrane during the early stage of endocytosis along with clathrin-associated adaptors. As coated pits undergo maturation, a burst of actin polymerization accompanies and helps drive vesicle internalization. Here, we investigate the dynamics of clathrin relative to the early endocytic patch protein Sla2p. We find that clathrin is recruited to ...

  3. Actinic Cheilitis

    ... actinic cheilitis. Overview Actinic cheilitis, sometimes known as "farmer's lip" or "sailor's lip," is a precancerous condition ... Last Updated: 22 Dec 2008 Information for other ages: Table of Contents: Overview Who's At Risk Signs ...

  4. A flight-dynamic helicopter mathematical model with a single flap-lag-torsion main rotor

    Takahashi, Marc D.

    1990-01-01

    A mathematical model of a helicopter system with a single main rotor that includes rigid, hinge-restrained rotor blades with flap, lag, and torsion degrees of freedom is described. The model allows several hinge sequences and two offsets in the hinges. Quasi-steady Greenberg theory is used to calculate the blade-section aerodynamic forces, and inflow effects are accounted for by using three-state nonlinear dynamic inflow model. The motion of the rigid fuselage is defined by six degrees of freedom, and an optional rotor rpm degree of freedom is available. Empennage surfaces and the tail rotor are modeled, and the effect of main-rotor downwash on these elements is included. Model trim linearization, and time-integration operations are described and can be applied to a subset of the model in the rotating or nonrotating coordinate frame. A preliminary validation of the model is made by comparing its results with those of other analytical and experimental studies. This publication presents the results of research compiled in November 1989.

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

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

    1999-01-01

    control cells and cells treated with VPA, indicating that VPA affected the cytoskeletal determinants of cell morphology. Furthermore, VPA treatment induced an increase of F-actin, and of FAK, paxillin, vinculin, and phosphotyrosine in focal adhesion complexes. These changes were accompanied by increased...... adhesion of VPA-treated cells to the extracellular matrix. Treatment with an RGD-containing peptide reducing integrin binding to components of the extracellular matrix partially reverted the motility inhibition induced by VPA, indicating that altered adhesion contributed to, but was not the sole reason for......, VPA caused a redistribution of the actin severing protein gelsolin, and left the cells unable to respond to treatment with a gelsolin-peptide known to reduce the amount of gelsolin bound to phosphatidylinositol bisphosphate (PIP2), leaving a larger amount of the protein in a potential actin binding...

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

    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.

  7. AtFH1 formin mutation affects actin filament and microtubule dynamics in Arabidopsis thaliana

    Rosero, A.; Žárský, Viktor; Cvrčková, F.

    2013-01-01

    Roč. 64, č. 2 (2013), s. 585-597. ISSN 0022-0957 R&D Projects: GA ČR GAP305/10/0433 Institutional research plan: CEZ:AV0Z50380511 Keywords : Actin * Arabidopsis * At5g25500 Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 5.794, year: 2013

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

    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.

  9. Actinic keratosis

    Solar keratosis; Sun-induced skin changes - keratosis; Keratosis - actinic (solar) ... laser treatment called photodynamic therapy Chemical peels Skin creams such as 5-fluorouracil (5-FU) and imiquimod

  10. Toxofilin upregulates the host cortical actin cytoskeleton dynamics, facilitating Toxoplasma invasion

    Delorme-Walker, Violaine; Abrivard, Marie; Lagal, Vanessa; Anderson, Karen; Perazzi, Audrey; Gonzalez, Virginie; Page, Christopher; Chauvet, Juliette; Ochoa, Wendy; Volkmann, Niels; Hanein, Dorit; Tardieux, Isabelle

    2012-01-01

    Toxoplasma gondii, a human pathogen and a model apicomplexan parasite, actively and rapidly invades host cells. To initiate invasion, the parasite induces the formation of a parasite–cell junction, and progressively propels itself through the junction, inside a newly formed vacuole that encloses the entering parasite. Little is known about how a parasite that is a few microns in diameter overcomes the host cell cortical actin barrier to achieve the remarkably rapid process of internalization ...

  11. Dynamic actin polymerization on endosomes regulates integrin trafficking, cell adhesion and cell migration

    Duleh, Steve Niessen

    2012-01-01

    Activators of the Arp2/3 complex, termed nucleation-promoting factors (NPFs), are required for the proper spatial and temporal control of actin assembly in cells. Mammalian cells express several NPFs, each of which serve distinct functions in specific cellular processes, including N-WASP in phagocytosis and endocytosis, WAVE and JMY in cell migration, and WHAMM in ER-to-Golgi transport. Although another NPF termed WASH was recently identified, the cellular function and activity of this prot...

  12. RNase L Interacts with Filamin A To Regulate Actin Dynamics and Barrier Function for Viral Entry

    Siddiqui, Mohammad Adnan; Dayal, Shubham; Naji, Merna; Ezelle, Heather J.; Zeng, Chun; Zhou, Aimin; Hassel, Bret A.

    2014-01-01

    ABSTRACT The actin cytoskeleton and its network of associated proteins constitute a physical barrier that viruses must circumvent to gain entry into cells for productive infection. The mechanisms by which the physical signals of infection are sensed by the host to activate an innate immune response are not well understood. The antiviral endoribonuclease RNase L is ubiquitously expressed in a latent form and activated upon binding 2-5A, a unique oligoadenylate produced during viral infections. We provide evidence that RNase L in its inactive form interacts with the actin-binding protein Filamin A to modulate the actin cytoskeleton and inhibit virus entry. Cells lacking either RNase L or Filamin A displayed increased virus entry which was exacerbated in cells lacking both proteins. RNase L deletion mutants that reduced Filamin A interaction displayed a compromised ability to restrict virus entry, supporting the idea of an important role for the RNase L-Filamin A complex in barrier function. Remarkably, both the wild type and a catalytically inactive RNase L mutant were competent to reduce virus entry when transfected into RNase L-deficient cells, indicating that this novel function of RNase L is independent of its enzymatic activity. Virus infection and RNase L activation disrupt its association with Filamin A and release RNase L to mediate its canonical nuclease-dependent antiviral activities. The dual functions of RNase L as a constitutive component of the actin cytoskeleton and as an induced mediator of antiviral signaling and effector functions provide insights into its mechanisms of antiviral activity and opportunities for the development of novel antiviral agents. PMID:25352621

  13. Actin flow and talin dynamics govern rigidity sensing in actin–integrin linkage through talin extension

    Hirata, Hiroaki; Chiam, Keng-Hwee; Lim, Chwee Teck; Sokabe, Masahiro

    2014-01-01

    At cell–substrate adhesion sites, the linkage between actin filaments and integrin is regulated by mechanical stiffness of the substrate. Of potential molecular regulators, the linker proteins talin and vinculin are of particular interest because mechanical extension of talin induces vinculin binding with talin, which reinforces the actin–integrin linkage. For understanding the molecular and biophysical mechanism of rigidity sensing at cell–substrate adhesion sites, we constructed a simple ph...

  14. Antiobesity Action of ACAM by Modulating the Dynamics of Cell Adhesion and Actin Polymerization in Adipocytes.

    Murakami, Kazutoshi; Eguchi, Jun; Hida, Kazuyuki; Nakatsuka, Atsuko; Katayama, Akihiro; Sakurai, Miwa; Choshi, Haruki; Furutani, Masumi; Ogawa, Daisuke; Takei, Kohji; Otsuka, Fumio; Wada, Jun

    2016-05-01

    Coxsackie virus and adenovirus receptor-like membrane protein (CLMP) was identified as the tight junction-associated transmembrane protein of epithelial cells with homophilic binding activities. CLMP is also recognized as adipocyte adhesion molecule (ACAM), and it is upregulated in mature adipocytes in rodents and humans with obesity. Here, we present that aP2 promoter-driven ACAM transgenic mice are protected from obesity and diabetes with the prominent reduction of adipose tissue mass and smaller size of adipocytes. ACAM is abundantly expressed on plasma membrane of mature adipocytes and associated with formation of phalloidin-positive polymerized form of cortical actin (F-actin). By electron microscopy, the structure of zonula adherens with an intercellular space of ∼10-20 nm was observed with strict parallelism of the adjoining cell membranes over distances of 1-20 μm, where ACAM and γ-actin are abundantly expressed. The formation of zonula adherens may increase the mechanical strength, inhibit the adipocyte hypertrophy, and improve the insulin sensitivity. PMID:26956488

  15. Actin flow and talin dynamics govern rigidity sensing in actin–integrin linkage through talin extension

    Hirata, Hiroaki; Chiam, Keng-Hwee; Lim, Chwee Teck; Sokabe, Masahiro

    2014-01-01

    At cell–substrate adhesion sites, the linkage between actin filaments and integrin is regulated by mechanical stiffness of the substrate. Of potential molecular regulators, the linker proteins talin and vinculin are of particular interest because mechanical extension of talin induces vinculin binding with talin, which reinforces the actin–integrin linkage. For understanding the molecular and biophysical mechanism of rigidity sensing at cell–substrate adhesion sites, we constructed a simple physical model to examine a role of talin extension in the stiffness-dependent regulation of actin–integrin linkage. We show that talin molecules linking between retrograding actin filaments and substrate-bound integrin are extended in a manner dependent on substrate stiffness. The model predicts that, in adhesion complexes containing ≈30 talin links, talin is extended enough for vinculin binding when the substrate is stiffer than 1 kPa. The lifetime of talin links needs to be 2–5 s to achieve an appropriate response of talin extension against substrate stiffness. Furthermore, changes in actin velocity drastically shift the range of substrate stiffness that induces talin–vinculin binding. Our results suggest that talin extension is a key step in sensing and responding to substrate stiffness at cell adhesion sites. PMID:25142525

  16. Control of actin-based motility through localized actin binding

    A wide variety of cell biological and biomimetic systems use actin polymerization to drive motility. It has been suggested that an object such as a bacterium can propel itself by self-assembling a high concentration of actin behind it, if it is repelled by actin. However, it is also known that it is essential for the moving object to bind actin. Therefore, a key question is how the actin tail can propel an object when it both binds and repels the object. We present a physically consistent Brownian dynamics model for actin-based motility that includes the minimal components of the dendritic nucleation model and allows for both attractive and repulsive interactions between actin and a moveable disc. We find that the concentration gradient of filamentous actin generated by polymerization is sufficient to propel the object, even with moderately strong binding interactions. Additionally, actin binding can act as a biophysical cap, and may directly control motility through modulation of network growth. Overall, this mechanism is robust in that it can drive motility against a load up to a stall pressure that depends on the Young’s modulus of the actin network and can explain several aspects of actin-based motility. (paper)

  17. New compliant strain gauges for self-sensing dynamic deformation of flapping wings on miniature air vehicles

    Wissman, James; Perez-Rosado, Ariel; Edgerton, Alex; Levi, Benjamin M.; Karakas, Zeynep N.; Kujawski, Mark; Philipps, Alyssa; Papavizas, Nicholas; Fallon, Danielle; Bruck, Hugh A.; Smela, Elisabeth

    2013-08-01

    Over the past several years there has been an increasing interest in the development of miniature air vehicles (MAVs) with flapping wings. To allow these MAVs to adjust to changes in wind direction and to maximize their efficiency, it is desirable to monitor the deformation of the wing during flight. This paper presents a step in this direction, demonstrating the measurement of strain on the surface of the wing using minimally invasive compliant piezoresistive sensors. The strain gauges consisted of latex mixed with electrically conducting exfoliated graphite, and they were applied by spray coating. To calibrate the gauges, both static and dynamic testing up to 10 Hz were performed using cantilever structures. In tension the static sensitivity was a linear 0.4 Ω μɛ-1 and the gauge factor was 28; in compression, the gauge factor was -5. Although sensitivities in tension and compression differed by a factor of almost six, this was not reflected in the dynamic data, which followed the strain reversibly with little distortion. There was no attenuation with frequency, indicating a sufficiently small time constant for this application. The gauges were thin, compliant, and light enough to measure, without interference, deformations due to shape changes of the flexible wing associated with generating lift and thrust. During flapping the resistance closely tracked the generated thrust, measured on a test stand, with both signals tracing figure-8 loops as a function of wing position throughout each cycle.

  18. New compliant strain gauges for self-sensing dynamic deformation of flapping wings on miniature air vehicles

    Over the past several years there has been an increasing interest in the development of miniature air vehicles (MAVs) with flapping wings. To allow these MAVs to adjust to changes in wind direction and to maximize their efficiency, it is desirable to monitor the deformation of the wing during flight. This paper presents a step in this direction, demonstrating the measurement of strain on the surface of the wing using minimally invasive compliant piezoresistive sensors. The strain gauges consisted of latex mixed with electrically conducting exfoliated graphite, and they were applied by spray coating. To calibrate the gauges, both static and dynamic testing up to 10 Hz were performed using cantilever structures. In tension the static sensitivity was a linear 0.4 Ω με−1 and the gauge factor was 28; in compression, the gauge factor was −5. Although sensitivities in tension and compression differed by a factor of almost six, this was not reflected in the dynamic data, which followed the strain reversibly with little distortion. There was no attenuation with frequency, indicating a sufficiently small time constant for this application. The gauges were thin, compliant, and light enough to measure, without interference, deformations due to shape changes of the flexible wing associated with generating lift and thrust. During flapping the resistance closely tracked the generated thrust, measured on a test stand, with both signals tracing figure-8 loops as a function of wing position throughout each cycle. (paper)

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

    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...

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

    Rasmussen Izabela; Pedersen Line H; Byg Luise; Suzuki Kazuhiro; Sumimoto Hideki; Vilhardt Frederik

    2010-01-01

    Abstract Background 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 dynamics, and without consideration for the subcellular distribution of the perturbed actin cytoskeleton. Results Here, we in addition to toxins use conditional expression of the ma...

  1. Strategies for the stabilization of longitudinal forward flapping flight revealed using a dynamically-scaled robotic fly.

    Elzinga, Michael J; van Breugel, Floris; Dickinson, Michael H

    2014-06-01

    The ability to regulate forward speed is an essential requirement for flying animals. Here, we use a dynamically-scaled robot to study how flapping insects adjust their wing kinematics to regulate and stabilize forward flight. The results suggest that the steady-state lift and thrust requirements at different speeds may be accomplished with quite subtle changes in hovering kinematics, and that these adjustments act primarily by altering the pitch moment. This finding is consistent with prior hypotheses regarding the relationship between body pitch and flight speed in fruit flies. Adjusting the mean stroke position of the wings is a likely mechanism for trimming the pitch moment at all speeds, whereas changes in the mean angle of attack may be required at higher speeds. To ensure stability, the flapping system requires additional pitch damping that increases in magnitude with flight speed. A compensatory reflex driven by fast feedback of pitch rate from the halteres could provide such damping, and would automatically exhibit gain scheduling with flight speed if pitch torque was regulated via changes in stroke deviation. Such a control scheme would provide an elegant solution for stabilization across a wide range of forward flight speeds. PMID:24855029

  2. Strategies for the stabilization of longitudinal forward flapping flight revealed using a dynamically-scaled robotic fly

    The ability to regulate forward speed is an essential requirement for flying animals. Here, we use a dynamically-scaled robot to study how flapping insects adjust their wing kinematics to regulate and stabilize forward flight. The results suggest that the steady-state lift and thrust requirements at different speeds may be accomplished with quite subtle changes in hovering kinematics, and that these adjustments act primarily by altering the pitch moment. This finding is consistent with prior hypotheses regarding the relationship between body pitch and flight speed in fruit flies. Adjusting the mean stroke position of the wings is a likely mechanism for trimming the pitch moment at all speeds, whereas changes in the mean angle of attack may be required at higher speeds. To ensure stability, the flapping system requires additional pitch damping that increases in magnitude with flight speed. A compensatory reflex driven by fast feedback of pitch rate from the halteres could provide such damping, and would automatically exhibit gain scheduling with flight speed if pitch torque was regulated via changes in stroke deviation. Such a control scheme would provide an elegant solution for stabilization across a wide range of forward flight speeds. (paper)

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

    Rasmussen Izabela

    2010-09-01

    Full Text Available Abstract Background 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 dynamics, and without consideration for the subcellular distribution of the perturbed actin cytoskeleton. Results Here, we in addition to toxins use conditional expression of the major actin regulatory protein LIM kinase-1 (LIMK1, and shRNA knock-down of cofilin to modulate the cellular F/G-actin ratio in the Ra2 microglia cell line, and we use Fluorescence Recovery after Photobleaching (FRAP in β-actin-YFP-transduced cells to obtain a dynamic measure of actin recovery rates (actin turn-over rates in different F/G-actin states of the actin cytoskeleton. Our data demonstrate that stimulated NADPH oxidase function was severely impaired only at extreme actin recovery rates and F/G-actin ratios, and surprisingly, that any moderate changes of these parameters of the actin cytoskeleton invariably resulted in an increased NADPH oxidase activity. Conclusion moderate actin polymerization and depolymerization both increase the FMLP and PMA-stimulated NADPH oxidase activity of microglia, which is directly correlated with neither actin recovery rate nor F/G- actin ratio. Our results indicate that NADPH oxidase functions in an enhanced state of activity in stimulated phagocytes despite widely different states of the actin cytoskeleton.

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

    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.

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

    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.

  6. Fluid dynamics of flapping aquatic flight in the bird wrasse: three-dimensional unsteady computations with fin deformation.

    Ramamurti, Ravi; Sandberg, William C; Löhner, Rainald; Walker, Jeffrey A; Westneat, Mark W

    2002-10-01

    Many fishes that swim with the paired pectoral fins use fin-stroke parameters that produce thrust force from lift in a mechanism of underwater flight. These locomotor mechanisms are of interest to behavioral biologists, biomechanics researchers and engineers. In the present study, we performed the first three-dimensional unsteady computations of fish swimming with oscillating and deforming fins. The objective of these computations was to investigate the fluid dynamics of force production associated with the flapping aquatic flight of the bird wrasse Gomphosus varius. For this computational work, we used the geometry of the wrasse and its pectoral fin, and previously measured fin kinematics, as the starting points for computational investigation of three-dimensional (3-D) unsteady fluid dynamics. We performed a 3-D steady computation and a complete set of 3-D quasisteady computations for a range of pectoral fin positions and surface velocities. An unstructured, grid-based, unsteady Navier-Stokes solver with automatic adaptive remeshing was then used to compute the unsteady flow about the wrasse through several complete cycles of pectoral fin oscillation. The shape deformation of the pectoral fin throughout the oscillation was taken from the experimental kinematics. The pressure distribution on the body of the bird wrasse and its pectoral fins was computed and integrated to give body and fin forces which were decomposed into lift and thrust. The velocity field variation on the surface of the wrasse body, on the pectoral fins and in the near-wake was computed throughout the swimming cycle. We compared our computational results for the steady, quasi-steady and unsteady cases with the experimental data on axial and vertical acceleration obtained from the pectoral fin kinematics experiments. These comparisons show that steady state computations are incapable of describing the fluid dynamics of flapping fins. Quasi-steady state computations, with correct incorporation of

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

    Lehman, William; Li, Xiaochuan; 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, th...

  8. Dynamin-2 regulates fusion pore expansion and quantal release through a mechanism that involves actin dynamics in neuroendocrine chromaffin cells.

    Arlek M González-Jamett

    Full Text Available Over the past years, dynamin has been implicated in tuning the amount and nature of transmitter released during exocytosis. However, the mechanism involved remains poorly understood. Here, using bovine adrenal chromaffin cells, we investigated whether this mechanism rely on dynamin's ability to remodel actin cytoskeleton. According to this idea, inhibition of dynamin GTPase activity suppressed the calcium-dependent de novo cortical actin and altered the cortical actin network. Similarly, expression of a small interfering RNA directed against dynamin-2, an isoform highly expressed in chromaffin cells, changed the cortical actin network pattern. Disruption of dynamin-2 function, as well as the pharmacological inhibition of actin polymerization with cytochalasine-D, slowed down fusion pore expansion and increased the quantal size of individual exocytotic events. The effects of cytochalasine-D and dynamin-2 disruption were not additive indicating that dynamin-2 and F-actin regulate the late steps of exocytosis by a common mechanism. Together our data support a model in which dynamin-2 directs actin polymerization at the exocytosis site where both, in concert, adjust the hormone quantal release to efficiently respond to physiological demands.

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

    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.

  10. Shallow and deep dynamic stall for flapping low Reynolds number airfoils

    Ol, Michael V. [Wright-Patterson AFB, Air Force Research Lab., Dayton, OH (United States); Bernal, Luis; Kang, Chang-Kwon; Shyy, Wei [University of Michigan, Department of Aerospace Engineering, Ann Arbor, MI (United States)

    2009-05-15

    We consider a combined experimental (based on flow visualization, direct force measurement and phase-averaged 2D particle image velocimetry in a water tunnel), computational (2D Reynolds-averaged Navier-Stokes) and theoretical (Theodorsen's formula) approach to study the fluid physics of rigid-airfoil pitch-plunge in nominally two-dimensional conditions. Shallow-stall (combined pitch-plunge) and deep-stall (pure-plunge) are compared at a reduced frequency commensurate with flapping-flight in cruise in nature. Objectives include assessment of how well attached-flow theory can predict lift coefficient even in the presence of significant separation, and how well 2D velocimetry and 2D computation can mutually validate one another. The shallow-stall case shows promising agreement between computation and experiment, while in the deep-stall case, the computation's prediction of flow separation lags that of the experiment, but eventually evinces qualitatively similar leading edge vortex size. Dye injection was found to give good qualitative match with particle image velocimetry in describing leading edge vortex formation and return to flow reattachment, and also gave evidence of strong spanwise growth of flow separation after leading-edge vortex formation. Reynolds number effects, in the range of 10,000-60,000, were found to influence the size of laminar separation in those phases of motion where instantaneous angle of attack was well below stall, but have limited effect on post-stall flowfield behavior. Discrepancy in lift coefficient time history between experiment, theory and computation was mutually comparable, with no clear failure of Theodorsen's formula. This is surprising and encouraging, especially for the deep-stall case, because the theory's assumptions are clearly violated, while its prediction of lift coefficient remains useful for capturing general trends. (orig.)

  11. Canonical and Noncanonical G-Protein Signaling Helps Coordinate Actin Dynamics To Promote Macrophage Phagocytosis of Zymosan

    Huang, Ning-Na; Becker, Steven; Boularan, Cedric; Kamenyeva, Olena; Vural, Ali; Hwang, Il-Young; Shi, Chong-Shan; Kehrl, John H

    2014-01-01

    Both chemotaxis and phagocytosis depend upon actin-driven cell protrusions and cell membrane remodeling. While chemoattractant receptors rely upon canonical G-protein signaling to activate downstream effectors, whether such signaling pathways affect phagocytosis is contentious. Here, we report that Gαi nucleotide exchange and signaling helps macrophages coordinate the recognition, capture, and engulfment of zymosan bioparticles. We show that zymosan exposure recruits F-actin, Gαi proteins, an...

  12. Actin-dependent mechanisms in AMPA receptor trafficking

    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.

  13. Actin turnover is required to prevent axon retraction driven by endogenous actomyosin contractility

    Gallo, Gianluca; Yee, Hal F.; Letourneau, Paul C.

    2002-01-01

    Growth cone motility and guidance depend on the dynamic reorganization of filamentous actin (F-actin). In the growth cone, F-actin undergoes turnover, which is the exchange of actin subunits from existing filaments. However, the function of F-actin turnover is not clear. We used jasplakinolide (jasp), a cell-permeable macrocyclic peptide that inhibits F-actin turnover, to study the role of F-actin turnover in axon extension. Treatment with jasp caused axon retraction, demonstrating that axon ...

  14. Rho, nuclear actin, and actin-binding proteins in the regulation of transcription and gene expression.

    Rajakylä, Eeva Kaisa; Vartiainen, Maria K

    2014-01-01

    Actin cytoskeleton is one of the main targets of Rho GTPases, which act as molecular switches on many signaling pathways. During the past decade, actin has emerged as an important regulator of gene expression. Nuclear actin plays a key role in transcription, chromatin remodeling, and pre-mRNA processing. In addition, the "status" of the actin cytoskeleton is used as a signaling intermediate by at least the MKL1-SRF and Hippo-pathways, which culminate in the transcriptional regulation of cytoskeletal and growth-promoting genes, respectively. Rho GTPases may therefore regulate gene expression by controlling either cytoplasmic or nuclear actin dynamics. Although the regulation of nuclear actin polymerization is still poorly understood, many actin-binding proteins, which are downstream effectors of Rho, are found in the nuclear compartment. In this review, we discuss the possible mechanisms and key proteins that may mediate the transcriptional regulation by Rho GTPases through actin. PMID:24603113

  15. Dynamic phosphoregulation of the cortical actin cytoskeleton and endocytic machinery revealed by real-time chemical genetic analysis

    Sekiya-Kawasaki, Mariko; Groen, Aaron Chris; Cope, M. Jamie T.V.; Kaksonen, Marko; Watson, Hadiya A.; Zhang, Chao; Shokat, Kevan M.; Wendland, Beverly; McDonald, Kent L.; McCaffery, J. Michael; Drubin, David G.

    2003-01-01

    We used chemical genetics to control the activity of budding yeast Prk1p, which is a protein kinase that is related to mammalian GAK and AAK1, and which targets several actin regulatory proteins implicated in endocytosis. In vivo Prk1p inhibition blocked pheromone receptor endocytosis, and caused cortical actin patches to rapidly aggregate into large clumps that contained Abp1p, Sla2p, Pan1p, Sla1p, and Ent1p. Clump formation depended on Arp2p, suggesting that this phenotype might result from...

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

    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.

  17. Dynamic boundaries in flowing fluids, from erosion sculptures to flapping wing flight

    Ristroph, Leif

    2014-01-01

    Textbook fluid mechanics addresses steady flows past fixed, rigid objects. However, Nature rarely obeys such restrictions and instead offers many fascinating situations involving the mutual influence of dynamic structures and unsteady flows. Such problems are complex because changes in shape affect flow, which in turn alters shape, and so on. Drawing inspiration from biological and geophysical flows, our Applied Math Lab attacks such fluid–structure interaction problems through tabletop exper...

  18. Dynamic Regulation of Activated Leukocyte Cell Adhesion Molecule–mediated Homotypic Cell Adhesion through the Actin CytoskeletonV⃞

    Nelissen, Judith M. D. T.; Peters, Inge M.; de Grooth, Bart G.; Van Kooyk, Yvette; Figdor, Carl G.

    2000-01-01

    Restricted expression of activated leukocyte cell adhesion molecule (ALCAM) by hematopoietic cells suggests an important role in the immune system and hematopoiesis. To get insight into the mechanisms that control ALCAM-mediated adhesion we have investigated homotypic ALCAM–ALCAM interactions. Here, we demonstrate that the cytoskeleton regulates ALCAM-mediated cell adhesion because inhibition of actin polymerization by cytochalasin D (CytD) strongly induces homotypic ALCAM–ALCAM interactions....

  19. Plekhh2, a novel podocyte protein downregulated in human focal segmental glomerulosclerosis, is involved in matrix adhesion and actin dynamics.

    Perisic, Ljubica; Lal, Mark; Hulkko, Jenny; Hultenby, Kjell; Önfelt, Björn; Sun, Ying; Dunér, Fredrik; Patrakka, Jaakko; Betsholtz, Christer; Uhlen, Mathias; Brismar, Hjalmar; Tryggvason, Karl; Wernerson, Annika; Pikkarainen, Timo

    2012-11-01

    Pleckstrin homology domain-containing, family H (with MyTH4 domain), member 2 (Plekhh2) is a 1491-residue intracellular protein highly enriched in renal glomerular podocytes for which no function has been ascribed. Analysis of renal biopsies from patients with focal segmental glomerulosclerosis revealed a significant reduction in total podocyte Plekhh2 expression compared to controls. Sequence analysis indicated a putative α-helical coiled-coil segment as the only recognizable domain within the N-terminal half of the polypeptide, while the C-terminal half contains two PH, a MyTH4, and a FERM domain. We identified a phosphatidylinositol-3-phosphate consensus-binding site in the PH1 domain required for Plekhh2 localization to peripheral regions of cell lamellipodia. The N-terminal half of Plekkh2 is not necessary for lamellipodial targeting but mediates self-association. Yeast two-hybrid screening showed that Plekhh2 directly interacts through its FERM domain with the focal adhesion protein Hic-5 and actin. Plekhh2 and Hic-5 coprecipitated and colocalized at the soles of podocyte foot processes in situ and Hic-5 partially relocated from focal adhesions to lamellipodia in Plekhh2-expressing podocytes. In addition, Plekhh2 stabilizes the cortical actin cytoskeleton by attenuating actin depolymerization. Our findings suggest a structural and functional role for Plekhh2 in the podocyte foot processes. PMID:22832517

  20. Exploring the drug resistance of V32I and M46L mutant HIV-1 protease to inhibitor TMC114: flap dynamics and binding mechanism.

    Meher, Biswa Ranjan; Wang, Yixuan

    2015-03-01

    Inhibitors of HIV-1 protease (HIV-1-pr) generally only bind to the active site of the protease. However, for some mutants such as V32I and M46L the TMC114 can bind not only to the active cavity but also to the groove of the flexible flaps. Although the second binding site suggests the higher efficiency of the drug against HIV-1-pr, the drug resistance in HIV-1-pr due to mutations cannot be ignored, which prompts us to investigate the molecular mechanisms of drug resistance and behavior of double bound TMC114 (2T) to HIV-1-pr. The conformational dynamics of HIV-1-pr and the binding of TMC114 to the WT, V32I and M46L mutants were investigated with all-atom molecular dynamic (MD) simulation. The 20 ns MD simulation shows many fascinating effects of the inhibitor binding to the WT and mutant proteases. MM-PBSA calculations explain the binding free energies unfavorable for the M46L and V32I mutants as compared to the WT. For the single binding (1T) the less binding affinity can be attributed to the entropic loss for both V32I-1T and M46L-1T. Although the second binding of TMC114 with flap does increase binding energy for the mutants (V32I-2T and M46L-2T), the considerable entropy loss results in the lower binding Gibbs free energies. Thus, binding of TMC114 in the flap region does not help much in the total gain in binding affinity of the system, which was verified from this study and thereby validating experiments. PMID:25562662

  1. Mechanics of Flapping Flight: Analytical Formulations of Unsteady Aerodynamics, Kinematic Optimization, Flight Dynamics, and Control

    Taneja, Jayant Kumar

    Electricity is an indispensable commodity to modern society, yet it is delivered via a grid architecture that remains largely unchanged over the past century. A host of factors are conspiring to topple this dated yet venerated design: developments in renewable electricity generation technology, policies to reduce greenhouse gas emissions, and advances in information technology for managing energy systems. Modern electric grids are emerging as complex distributed systems in which a portfolio of power generation resources, often incorporating fluctuating renewable resources such as wind and solar, must be managed dynamically to meet uncontrolled, time-varying demand. Uncertainty in both supply and demand makes control of modern electric grids fundamentally more challenging, and growing portfolios of renewables exacerbate the challenge. We study three electricity grids: the state of California, the province of Ontario, and the country of Germany. To understand the effects of increasing renewables, we develop a methodology to scale renewables penetration. Analyzing these grids yields key insights about rigid limits to renewables penetration and their implications in meeting long-term emissions targets. We argue that to achieve deep penetration of renewables, the operational model of the grid must be inverted, changing the paradigm from load-following supplies to supply-following loads. To alleviate the challenge of supply-demand matching on deeply renewable grids, we first examine well-known techniques, including altering management of existing supply resources, employing utility-scale energy storage, targeting energy efficiency improvements, and exercising basic demand-side management. Then, we create several instantiations of supply-following loads -- including refrigerators, heating and cooling systems, and laptop computers -- by employing a combination of sensor networks, advanced control techniques, and enhanced energy storage. We examine the capacity of each load

  2. Architecture and Connectivity Govern Actin Network Contractility.

    Ennomani, Hajer; Letort, Gaëlle; Guérin, Christophe; Martiel, Jean-Louis; Cao, Wenxiang; Nédélec, François; De La Cruz, Enrique M; Théry, Manuel; Blanchoin, Laurent

    2016-03-01

    Actomyosin contractility plays a central role in a wide range of cellular processes, including the establishment of cell polarity, cell migration, tissue integrity, and morphogenesis during development. The contractile response is variable and depends on actomyosin network architecture and biochemical composition. To determine how this coupling regulates actomyosin-driven contraction, we used a micropatterning method that enables the spatial control of actin assembly. We generated a variety of actin templates and measured how defined actin structures respond to myosin-induced forces. We found that the same actin filament crosslinkers either enhance or inhibit the contractility of a network, depending on the organization of actin within the network. Numerical simulations unified the roles of actin filament branching and crosslinking during actomyosin contraction. Specifically, we introduce the concept of "network connectivity" and show that the contractions of distinct actin architectures are described by the same master curve when considering their degree of connectivity. This makes it possible to predict the dynamic response of defined actin structures to transient changes in connectivity. We propose that, depending on the connectivity and the architecture, network contraction is dominated by either sarcomeric-like or buckling mechanisms. More generally, this study reveals how actin network contractility depends on its architecture under a defined set of biochemical conditions. PMID:26898468

  3. 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.

    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. PMID:27101990

  4. Canonical and noncanonical g-protein signaling helps coordinate actin dynamics to promote macrophage phagocytosis of zymosan.

    Huang, Ning-Na; Becker, Steven; Boularan, Cedric; Kamenyeva, Olena; Vural, Ali; Hwang, Il-Young; Shi, Chong-Shan; Kehrl, John H

    2014-11-15

    Both chemotaxis and phagocytosis depend upon actin-driven cell protrusions and cell membrane remodeling. While chemoattractant receptors rely upon canonical G-protein signaling to activate downstream effectors, whether such signaling pathways affect phagocytosis is contentious. Here, we report that Gαi nucleotide exchange and signaling helps macrophages coordinate the recognition, capture, and engulfment of zymosan bioparticles. We show that zymosan exposure recruits F-actin, Gαi proteins, and Elmo1 to phagocytic cups and early phagosomes. Zymosan triggered an increase in intracellular Ca(2+) that was partially sensitive to Gαi nucleotide exchange inhibition and expression of GTP-bound Gαi recruited Elmo1 to the plasma membrane. Reducing GDP-Gαi nucleotide exchange, decreasing Gαi expression, pharmacologically interrupting Gβγ signaling, or reducing Elmo1 expression all impaired phagocytosis, while favoring the duration that Gαi remained GTP bound promoted it. Our studies demonstrate that targeting heterotrimeric G-protein signaling offers opportunities to enhance or retard macrophage engulfment of phagocytic targets such as zymosan. PMID:25225330

  5. Pedicled perforator flaps

    Demirtas, Yener; Ozturk, Nuray; Kelahmetoglu, Osman; Demir, Ahmet

    2009-01-01

    Described in this study is a surgical concept that supports the "consider and use a pedicled perforator flap whenever possible and indicated" approach to reconstruct a particular skin defect. The operation is entirely free-style; the only principle is to obtain a pedicled perforator flap to...... reconstruct the defect. The perforators are marked with a hand-held Doppler probe and multiple flaps are designed. The appropriate flap is elevated after identifying the perforator(s). Dissection of the perforator(s) or complete incision of the flap margins are not mandatory if the flap is mobilized...... adequately to cover the defect. Defects measuring 3 x 3 cm up to 20 x 20 cm at diverse locations were successfully reconstructed in 20 of 21 patients with 26 flaps. Pedicled perforator flaps offer us reliable and satisfactory results of reconstruction at different anatomic territories of the body. It sounds...

  6. Addition of Phenylboronic Acid to Malus domestica Pollen Tubes Alters Calcium Dynamics, Disrupts Actin Filaments and Affects Cell Wall Architecture

    Fang, Kefeng; Gao, Sai; Zhang, Weiwei; Xing, Yu; Cao, Qingqin; Qin, Ling

    2016-01-01

    A key role of boron in plants is to cross-link the cell wall pectic polysaccharide rhamnogalacturonan-II (RG-II) through borate diester linkages. Phenylboronic acid (PBA) can form the same reversible ester bonds but cannot cross-link two molecules, so can be used as an antagonist to study the function of boron. This study aimed to evaluate the effect of PBA on apple (Malus domestica) pollen tube growth and the underlying regulatory mechanism. We observed that PBA caused an inhibition of pollen germination, tube growth and led to pollen tube morphological abnormalities. Fluorescent labeling, coupled with a scanning ion-selective electrode technique, revealed that PBA induced an increase in extracellular Ca2+ influx, thereby elevating the cytosolic Ca2+ concentration [Ca2+]c and disrupting the [Ca2+]c gradient, which is critical for pollen tube growth. Moreover the organization of actin filaments was severely perturbed by the PBA treatment. Immunolocalization studies and fluorescent labeling, together with Fourier-transform infrared analysis (FTIR) suggested that PBA caused an increase in the abundance of callose, de-esterified pectins and arabinogalactan proteins (AGPs) at the tip. However, it had no effect on the deposition of the wall polymers cellulose. These effects are similar to those of boron deficiency in roots and other organs, indicating that PBA can induce boron deficiency symptoms. The results provide new insights into the roles of boron in pollen tube development, which likely include regulating [Ca2+]c and the formation of the actin cytoskeleton, in addition to the synthesis and assembly of cell wall components. PMID:26886907

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

    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

  8. [Cytoskeletal actin and its associated proteins. Some examples in Protista].

    Guillén, N; Carlier, M F; Brugerolle, G; Tardieux, I; Ausseil, J

    1998-06-01

    Many processes, cell motility being an example, require cells to remodel the actin cytoskeleton in response to both intracellular and extracellular signals. Reorganization of the actin cytoskeleton involves the rapid disassembly and reassembly of actin filaments, a phenomenon regulated by the action of particular actin-binding proteins. In recent years, an interest in studying actin regulation in unicellular organisms has arisen. Parasitic protozoan are among these organisms and studies of the cytoskeleton functions of these protozoan are relevant related to either cell biology or pathogenicity. To discuss recent data in this field, a symposium concerning "Actin and actin-binding proteins in protists" was held on May 8-11 in Paris, France, during the XXXV meeting of the French Society of Protistology. As a brief summary of the symposium we report here findings concerning the in vitro actin dynamic assembly, as well as the characterization of several actin-binding proteins from the parasitic protozoan Entamoeba histolytica, Trichomonas vaginalis and Plasmodium knowlesi. In addition, localization of actin in non-pathogen protists such as Prorocentrum micans and Crypthecodinium cohnii is also presented. The data show that some actin-binding proteins facilitate organization of filaments into higher order structures as pseudopods, while others have regulatory functions, indicating very particular roles for actin-binding proteins. One of the proteins discussed during the symposium, the actin depolymerizing factor ADF, was shown to enhance the treadmilling rate of actin filaments. In vitro, ADF binds to the ADP-bound forms of G-actin and F-actin, thereby participating in and changing the rate of actin assembly. Biochemical approaches allowed the identification of a protein complex formed by HSP/C70-cap32-34 which might also be involved in depolymerization of F-actin in P. knowlesi. Molecular and cellular approaches were used to identify proteins such as ABP-120 and myosin

  9. Polarity protein Crumbs homolog-3 (CRB3) regulates ectoplasmic specialization dynamics through its action on F-actin organization in Sertoli cells

    Gao, Ying; Lui, Wing-yee; Lee, Will M.; Cheng, C. Yan

    2016-01-01

    Crumbs homolog 3 (or Crumbs3, CRB3) is a polarity protein expressed by Sertoli and germ cells at the basal compartment in the seminiferous epithelium. CRB3 also expressed at the blood-testis barrier (BTB), co-localized with F-actin, TJ proteins occludin/ZO-1 and basal ES (ectoplasmic specialization) proteins N-cadherin/β-catenin at stages IV-VII only. The binding partners of CRB3 in the testis were the branched actin polymerization protein Arp3, and the barbed end-capping and bundling protein Eps8, illustrating its possible role in actin organization. CRB3 knockdown (KD) by RNAi in Sertoli cells with an established tight junction (TJ)-permeability barrier perturbed the TJ-barrier via changes in the distribution of TJ- and basal ES-proteins at the cell-cell interface. These changes were the result of CRB3 KD-induced re-organization of actin microfilaments, in which actin microfilaments were truncated, and extensively branched, thereby destabilizing F-actin-based adhesion protein complexes at the BTB. Using Polyplus in vivo-jetPEI as a transfection medium with high efficiency for CRB3 KD in the testis, the CRB3 KD testes displayed defects in spermatid and phagosome transport, and also spermatid polarity due to a disruption of F-actin organization. In summary, CRB3 is an actin microfilament regulator, playing a pivotal role in organizing actin filament bundles at the ES. PMID:27358069

  10. Design of Insect-Scale Flapping Wing Vehicles

    Ahmed Nabawy, Mostafa Ramadan

    2015-01-01

    This thesis contributes to the state of the art in integrated design of insect-scale piezoelectric actuated flapping wing vehicles through the development of novel theoretical models for flapping wing aerodynamics and piezoelectric actuator dynamics, and integration of these models into a closed form design process.A comprehensive literature review of available engineered designs of miniature rotary and flapping wing vehicles is provided. A novel taxonomy based on wing and actuator kinematics...

  11. Stimulation of Actin Polymerization by Filament Severing

    Carlsson, A E

    2005-01-01

    The extent and dynamics of actin polymerization in solution are calculated as functions of the filament severing rate, using a simple model of in vitro polymerization. The model is solved by both analytic theory and stochastic-growth simulation. The results show that severing essentially always enhances actin polymerization by freeing up barbed ends, if barbed-end cappers are present. Severing has much weaker effects if only pointed-end cappers are present. In the early stages of polymerizati...

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

    Du, Juan; Wang, Xue; Dong, Chun-Hai; Yang, Jian Ming; Yao, Xiao Jun

    2016-01-01

    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. PMID:27414648

  13. The platysma myocutaneous flap.

    Baur, Dale A; Williams, Jonathan; Alakaily, Xena

    2014-08-01

    Reconstructing defects of the oral mucosa or skin of the lower one-third of the face can be accomplished by a variety of techniques. This article presents two versions of the platysma myocutaneous flap, which is a reliable, axial pattern, pedicled flap capable of providing excellent one-stage reconstruction of such defects. As discussed herein, the superiorly based and posteriorly based versions of the flap have wide application in the oral and facial region. Also provided is a review of other uses of this flap in head and neck surgery. PMID:24958382

  14. Propeller TAP flap

    Thomsen, Jørn Bo; Bille, Camilla; Wamberg, Peter;

    2013-01-01

    The aim of this study was to examine if a propeller thoracodorsal artery perforator (TAP) flap can be used for breast reconstruction. Fifteen women were reconstructed using a propeller TAP flap, an implant, and an ADM. Preoperative colour Doppler ultrasonography was used for patient selection to...... major complications needing additional surgery. One flap was lost due to a vascular problem. Breast reconstruction can be performed by a propeller TAP flap without cutting the descending branch of the thoracodorsal vessels. However, the authors would recommend that a small cuff of muscle is left around...

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

    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.

  16. TccP2-mediated subversion of actin dynamics by EPEC 2 – a distinct evolutionary lineage of enteropathogenic Escherichia coli

    Whale, Andrew D.; Hernandes, Rodrigo T.; Ooka, Tadasuke; Beutin, Lothar; Schüller, Stephanie; Garmendia, Junkal; Crowther, Lynette; Vieira, Mônica A. M.; Ogura, Yoshitoshi; Krause, Gladys; Phillips, Alan D.; Tania A. T. Gomes; Hayashi, Tetsuya; Frankel, Gad

    2007-01-01

    Enteropathogenic Escherichia coli (EPEC) is a major cause of infantile diarrhoea in developing countries. While colonizing the gut mucosa, EPEC triggers extensive actin-polymerization activity at the site of intimate bacterial attachment, which is mediated by avid interaction between the outer-membrane adhesin intimin and the type III secretion system (T3SS) effector Tir. The prevailing dogma is that actin polymerization by EPEC is achieved following tyrosine phosphorylation of Tir, recruitme...

  17. The rhombic bilobed flap, a simple, geometrically designed flap

    Yoshiaki Sakamoto

    2014-01-01

    Full Text Available We describe a combination of the common rhomboid flap and bilobed flap and provide an example of its use. The rhombic bilobed flap is simple to use and is associated with fewer complications, such as pin-cushioning and standing cone deformities, while minimizing the risk of skin necrosis and tension on the flap.

  18. Probing GFP-actin diffusion in living cells using fluorescence correlation spectroscopy

    The cytoskeleton of eukaryotic cells is continuously remodeled by polymerization and depolymerization of actin. Consequently, the relative content of polymerized filamentous actin (F-actin) and monomeric globular actin (G-actin) is subject to temporal and spatial fluctuations. Since fluorescence correlation spectroscopy (FCS) can measure the diffusion of fluorescently labeled actin it seems likely that FCS allows us to determine the dynamics and hence indirectly the structural properties of the cytoskeleton components with high spatial resolution. To this end we investigate the FCS signal of GFP-actin in living Dictyostelium discoideum cells and explore the inherent spatial and temporal signatures of the actin cytoskeleton. Using the free green fluorescent protein (GFP) as a reference, we find that actin diffusion inside cells is dominated by G-actin and slower than diffusion in diluted cell extract. The FCS signal in the dense cortical F-actin network near the cell membrane is probed using the cytoskeleton protein LIM and is found to be slower than cytosolic G-actin diffusion. Furthermore, we show that polymerization of the cytoskeleton induced by Jasplakinolide leads to a substantial decrease of G-actin diffusion. Pronounced fluctuations in the distribution of the FCS correlation curves can be induced by latrunculin, which is known to induce actin waves. Our work suggests that the FCS signal of GFP-actin in combination with scanning or spatial correlation techniques yield valuable information about the local dynamics and concomitant cytoskeletal properties

  19. A novel method to study the electrodynamic behavior of actin filaments. Evidence for cable-like properties of actin.

    Lin, E C; Cantiello, H. F.

    1993-01-01

    Actin, one of the most abundant intracellular proteins, forms long linear polyelectrolytic polymers in solution. A novel technique to handle single actin filaments in solution was developed that allows the study of ionic currents elicited along the surface of electrically stimulated actin filaments. Electrical currents were observed about the polymer's surface under both high (100 mM KCl) and low (1 mM KCl) ionic strength conditions. The data are consistent with a dynamic behavior of the coun...

  20. Aerodynamic flight performance in flap-gliding birds and bats.

    Muijres, Florian T; Henningsson, Per; Stuiver, Melanie; Hedenström, Anders

    2012-08-01

    Many birds use a flight mode called undulating or flap-gliding flight, where they alternate between flapping and gliding phases, while only a few bats make use of such a flight mode. Among birds, flap-gliding is commonly used by medium to large species, where it is regarded to have a lower energetic cost than continuously flapping flight. Here, we introduce a novel model for estimating the energetic flight economy of flap-gliding animals, by determining the lift-to-drag ratio for flap-gliding based on empirical lift-to-drag ratio estimates for continuous flapping flight and for continuous gliding flight, respectively. We apply the model to flight performance data of the common swift (Apus apus) and of the lesser long-nosed bat (Leptonycteris yerbabuenae). The common swift is a typical flap-glider while-to the best of our knowledge-the lesser long-nosed bat does not use flap-gliding. The results show that, according to the model, the flap-gliding common swift saves up to 15% energy compared to a continuous flapping swift, and that this is primarily due to the exceptionally high lift-to-drag ratio in gliding flight relative to that in flapping flight for common swifts. The lesser long-nosed bat, on the other hand, seems not to be able to reduce energetic costs by flap-gliding. The difference in relative costs of flap-gliding flight between the common swift and the lesser long-nosed bat can be explained by differences in morphology, flight style and wake dynamics. The model presented here proves to be a valuable tool for estimating energetic flight economy in flap-gliding animals. The results show that flap-gliding flight that is naturally used by common swifts is indeed the most economic one of the two flight modes, while this is not the case for the non-flap-gliding lesser long-nosed bat. PMID:22726811

  1. Sequence and comparative genomic analysis of actin-related proteins.

    Muller, Jean; Oma, Yukako; Vallar, Laurent; Friederich, Evelyne; Poch, Olivier; Winsor, Barbara

    2005-12-01

    Actin-related proteins (ARPs) are key players in cytoskeleton activities and nuclear functions. Two complexes, ARP2/3 and ARP1/11, also known as dynactin, are implicated in actin dynamics and in microtubule-based trafficking, respectively. ARP4 to ARP9 are components of many chromatin-modulating complexes. Conventional actins and ARPs codefine a large family of homologous proteins, the actin superfamily, with a tertiary structure known as the actin fold. Because ARPs and actin share high sequence conservation, clear family definition requires distinct features to easily and systematically identify each subfamily. In this study we performed an in depth sequence and comparative genomic analysis of ARP subfamilies. A high-quality multiple alignment of approximately 700 complete protein sequences homologous to actin, including 148 ARP sequences, allowed us to extend the ARP classification to new organisms. Sequence alignments revealed conserved residues, motifs, and inserted sequence signatures to define each ARP subfamily. These discriminative characteristics allowed us to develop ARPAnno (http://bips.u-strasbg.fr/ARPAnno), a new web server dedicated to the annotation of ARP sequences. Analyses of sequence conservation among actins and ARPs highlight part of the actin fold and suggest interactions between ARPs and actin-binding proteins. Finally, analysis of ARP distribution across eukaryotic phyla emphasizes the central importance of nuclear ARPs, particularly the multifunctional ARP4. PMID:16195354

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

    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. PMID:25155506

  3. Folding in and out: passive morphing in flapping wings.

    Stowers, Amanda K; Lentink, David

    2015-04-01

    We present a new mechanism for passive wing morphing of flapping wings inspired by bat and bird wing morphology. The mechanism consists of an unactuated hand wing connected to the arm wing with a wrist joint. Flapping motion generates centrifugal accelerations in the hand wing, forcing it to unfold passively. Using a robotic model in hover, we made kinematic measurements of unfolding kinematics as functions of the non-dimensional wingspan fold ratio (2-2.5) and flapping frequency (5-17 Hz) using stereo high-speed cameras. We find that the wings unfold passively within one to two flaps and remain unfolded with only small amplitude oscillations. To better understand the passive dynamics, we constructed a computer model of the unfolding process based on rigid body dynamics, contact models, and aerodynamic correlations. This model predicts the measured passive unfolding within about one flap and shows that unfolding is driven by centrifugal acceleration induced by flapping. The simulations also predict that relative unfolding time only weakly depends on flapping frequency and can be reduced to less than half a wingbeat by increasing flapping amplitude. Subsequent dimensional analysis shows that the time required to unfold passively is of the same order of magnitude as the flapping period. This suggests that centrifugal acceleration can drive passive unfolding within approximately one wingbeat in small and large wings. Finally, we show experimentally that passive unfolding wings can withstand impact with a branch, by first folding and then unfolding passively. This mechanism enables flapping robots to squeeze through clutter without sophisticated control. Passive unfolding also provides a new avenue in morphing wing design that makes future flapping morphing wings possibly more energy efficient and light-weight. Simultaneously these results point to possible inertia driven, and therefore metabolically efficient, control strategies in bats and birds to morph or recover

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

    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...

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

    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. PMID:25948734

  6. Flapping of Insectile Wings

    Huang, Yangyang; Kanso, Eva

    2015-11-01

    Insects use flight muscles attached at the base of the wings to produce impressive wing flapping frequencies. Yet the effects of muscle stiffness on the performance of insect wings remain unclear. Here, we construct an insectile wing model, consisting of two rigid wings connected at their base by an elastic torsional spring and submerged in an oscillatory flow. The wing system is free to rotate and flap. We first explore the extent to which the flyer can withstand roll perturbations, then study its flapping behavior and performance as a function of spring stiffness. We find an optimal range of spring stiffness that results in large flapping amplitudes, high force generation and good storage of elastic energy. We conclude by conjecturing that insects may select and adjust the muscle spring stiffness to achieve desired movement. These findings may have significant implications on the design principles of wings in micro air-vehicles.

  7. Control of Flap Vortices

    Greenblatt, David

    2005-01-01

    A wind tunnel investigation was carried out on a semi-span wing model to assess the feasibility of controlling vortices emanating from outboard flaps and tip-flaps by actively varying the degree of boundary layer separation. Separation was varied by means of perturbations produced from segmented zero-efflux oscillatory blowing slots, while estimates of span loadings and vortex sheet strengths were obtained by integrating wing surface pressures. These estimates were used as input to inviscid rollup relations as a means of predicting changes to the vortex characteristics resulting from the perturbations. Surveys of flow in the wake of the outboard and tip-flaps were made using a seven-hole probe, from which the vortex characteristics were directly deduced. Varying the degree of separation had a marked effect on vortex location, strength, tangential velocity, axial velocity and size for both outboard and tip-flaps. Qualitative changes in vortex characteristics were well predicted by the inviscid rollup relations, while the failure to account for viscosity was presumed to be the main reason for observed discrepancies. Introducing perturbations near the outboard flap-edges or on the tip-flap exerted significant control over vortices while producing negligible lift excursions.

  8. Quantifying Blood Flow in the DIEP Flap: An Ultrasonographic Study

    Pennington, David G.

    2014-01-01

    Background: The maximum weight of tissue that a single perforator can perfuse remains an important question in reconstructive microsurgery. An empirically based equation, known as the flap viability index (FVI), has been established to determine what weight of tissue will survive on one or more perforators. The equation is FVI = Sum d(n)^4/W, where d is the internal diameter of each perforator and W is the final weight of the flap. It has been shown that if FVI exceeds 10, total flap survival is likely, but if under 10, partial flap necrosis is probable. The aim of this study was to measure absolute flow rates in deep inferior epigastric perforator (DIEP) flap pedicles and assess correlation with the determinants of the FVI, perforator diameter and flap weight. Methods: Color Doppler ultrasound was used to quantify arterial flow in 10 consecutive DIEP flap pedicles 24 hours after anastomosis. Results: In single-perforator DIEP flaps, flow rate was highly correlated with perforator diameter (r = 0.82, P = 0.01). Mean arterial flow rate was significantly reduced in DIEP flaps with 2 or more perforators (6 vs 38 cm3/min; P perforator size is a critical factor in optimizing blood flow in perforator-based free tissue transfer. Further research is required to understand the flow dynamics of perforator flaps based on multiple perforators. However, surgeons should be cognizant that a single large perforator may have substantially higher flow rates than multiple small perforators. Routine FVI calculation is recommended to ensure complete flap survival. PMID:25426345

  9. Perforator Flaps for Perineal Reconstructions

    Niranjan, Niri S.

    2006-01-01

    Whenever there is soft tissue loss from the perineum there are many options for reconstruction. These include allowing the wound to heal by secondary intention and the use of local random or axial pattern flaps, regional flaps, or free flaps. The axial skin flap can be defined as a flap based on known constant vessels of the subcutaneous tissue and its vena comitantes. The perforator flap on the other hand is a randomly selected perforator consisting of an artery with vena comitantes, which p...

  10. Orientational Order of the Lamellipodial Actin Network as Demonstrated in Living Motile CellsV⃞

    Alexander B. Verkhovsky; Chaga, Oleg Y.; Schaub, Sébastien; Svitkina, Tatyana M.; Meister, Jean-Jacques; Borisy, Gary G.

    2003-01-01

    Lamellipodia of crawling cells represent both the motor for cell advance and the primary building site for the actin cytoskeleton. The organization of actin in the lamellipodium reflects actin dynamics and is of critical importance for the mechanism of cell motility. In previous structural studies, the lamellipodial actin network was analyzed primarily by electron microscopy (EM). An understanding of lamellipodial organization would benefit significantly if the EM data were complemented and p...

  11. Cell Elasticity Is Regulated by the Tropomyosin Isoform Composition of the Actin Cytoskeleton

    Jalilian, Iman; Heu, Celine; Cheng, Hong; Freittag, Hannah; Desouza, Melissa; Justine R. Stehn; 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...

  12. Cooperation between actin-binding proteins of invasive Salmonella: SipA potentiates SipC nucleation and bundling of actin

    Emma J McGhie; Hayward, Richard D.; Koronakis, Vassilis

    2001-01-01

    Pathogen-induced remodelling of the host cell actin cytoskeleton drives internalization of invasive Salmon ella by non-phagocytic intestinal epithelial cells. Two Salmonella actin-binding proteins are involved in internalization: SipC is essential for the process, while SipA enhances its efficiency. Using purified SipC and SipA proteins in in vitro assays of actin dynamics and F-actin bundling, we demonstrate that SipA stimulates substantially SipC-mediated nucleation of actin polymerization....

  13. The Evolution of Perforator Flaps

    Khan, Farah N.; Spiegel, Aldona J.

    2006-01-01

    Perforator flaps have recently become ubiquitous in the field of plastic surgery. To understand and appreciate their unique nature, it is necessary to compare and contrast them with the development of other types of flaps. A complete yet abridged version of the history of flap surgery is presented in this article. Beginning with Sushruta's Indian cheek flap method for nasal reconstruction, a trip through time and space is taken to highlight the milestones leading to the evolution of the perfo...

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

    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...... findings highlight a previously unrecognized involvement of the ubiquitin cycle in bacterial entry. UCH-L1 is highly expressed in malignant cells that may therefore be particularly susceptible to invasion by bacteria-based drug delivery systems.......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...

  15. Membrane waves driven by forces from actin filaments

    Membrane waves propagating along the cell circumference in a top down view have been observed with several eukaryotic cells (Döbereiner et al 2006 Phys. Rev. Lett. 97 10; Machacek and Danuser 2006 Biophys. J. 90 1439–52). We present a mathematical model reproducing these traveling membrane undulations during lamellipodial motility of cells on flat substrates. The model describes the interplay of pushing forces exerted by actin polymerization on the membrane, pulling forces of attached actin filaments on the cell edge, contractile forces powered by molecular motors across the actin gel and resisting membrane tension. The actin filament network in the bulk of lamellipodia obeys gel flow equations. We investigated in particular the dependence of wave properties on gel parameters and found that inhibition of myosin motors abolishes waves in some cells but not in others in agreement with experimental observations. The model provides a unifying mechanism explaining the dynamics of actin-based motility in a variety of systems. (paper)

  16. The Actin-Binding Protein α-Adducin Is Required for Maintaining Axon Diameter.

    Leite, Sérgio Carvalho; Sampaio, Paula; Sousa, Vera Filipe; Nogueira-Rodrigues, Joana; Pinto-Costa, Rita; Peters, Luanne Laurel; Brites, Pedro; Sousa, Mónica Mendes

    2016-04-19

    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. PMID:27068466

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

    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.

  18. Computational analysis of viscoelastic properties of crosslinked actin networks.

    Taeyoon Kim

    2009-07-01

    Full Text Available Mechanical force plays an important role in the physiology of eukaryotic cells whose dominant structural constituent is the actin cytoskeleton composed mainly of actin and actin crosslinking proteins (ACPs. Thus, knowledge of rheological properties of actin networks is crucial for understanding the mechanics and processes of cells. We used Brownian dynamics simulations to study the viscoelasticity of crosslinked actin networks. Two methods were employed, bulk rheology and segment-tracking rheology, where the former measures the stress in response to an applied shear strain, and the latter analyzes thermal fluctuations of individual actin segments of the network. It was demonstrated that the storage shear modulus (G' increases more by the addition of ACPs that form orthogonal crosslinks than by those that form parallel bundles. In networks with orthogonal crosslinks, as crosslink density increases, the power law exponent of G' as a function of the oscillation frequency decreases from 0.75, which reflects the transverse thermal motion of actin filaments, to near zero at low frequency. Under increasing prestrain, the network becomes more elastic, and three regimes of behavior are observed, each dominated by different mechanisms: bending of actin filaments, bending of ACPs, and at the highest prestrain tested (55%, stretching of actin filaments and ACPs. In the last case, only a small portion of actin filaments connected via highly stressed ACPs support the strain. We thus introduce the concept of a 'supportive framework,' as a subset of the full network, which is responsible for high elasticity. Notably, entropic effects due to thermal fluctuations appear to be important only at relatively low prestrains and when the average crosslinking distance is comparable to or greater than the persistence length of the filament. Taken together, our results suggest that viscoelasticity of the actin network is attributable to different mechanisms depending on

  19. Flap-edge aeroacoustic measurements and predictions

    Brooks, Thomas F.; Humphreys, William M.

    2003-03-01

    An aeroacoustic model test has been conducted to investigate the mechanisms of sound generation on high-lift wing configurations. This paper presents an analysis of flap side-edge noise, which is often the most dominant source. A model of a main element wing section with a half-span flap was tested at low speeds of up to a Mach number of 0.17, corresponding to a wing chord Reynolds number of approximately 1.7 million. Results are presented for flat (or blunt), flanged, and round flap-edge geometries, with and without boundary-layer tripping, deployed at both moderate and high flap angles. The acoustic database is obtained from a small aperture directional array (SADA) of microphones, which was constructed to electronically steer to different regions of the model and to obtain farfield noise spectra and directivity from these regions. The basic flap-edge aerodynamics is established by static surface pressure data, as well as by computational fluid dynamics (CFD) calculations and simplified edge flow analyses. Distributions of unsteady pressure sensors over the flap allow the noise source regions to be defined and quantified via cross-spectral diagnostics using the SADA output. It is found that shear layer instability and related pressure scatter is the primary noise mechanism. For the flat edge flap, two noise prediction methods based on unsteady-surface-pressure measurements are evaluated and compared to measured noise. One is a new causality spectral approach developed here. The other is a new application of an edge-noise scatter prediction method. The good comparisons for both approaches suggest that the prediction models capture much of the physics. Areas of disagreement appear to reveal when the assumed edge noise mechanism does not fully define the noise production. For the different edge conditions, extensive spectra and directivity are presented. The complexity of the directivity results demonstrate the strong role of edge source geometry and frequency in

  20. Flap Edge Aeroacoustic Measurements and Predictions

    Brooks, Thomas F.; Humphreys, William M., Jr.

    2000-01-01

    An aeroacoustic model test has been conducted to investigate the mechanisms of sound generation on high-lift wing configurations. This paper presents an analysis of flap side-edge noise, which is often the most dominant source. A model of a main element wing section with a half-span flap was tested at low speeds of up to a Mach number of 0.17, corresponding to a wing chord Reynolds number of approximately 1.7 million. Results are presented for flat (or blunt), flanged, and round flap-edge geometries, with and without boundary-layer tripping, deployed at both moderate and high flap angles. The acoustic database is obtained from a Small Aperture Directional Array (SADA) of microphones, which was constructed to electronically steer to different regions of the model and to obtain farfield noise spectra and directivity from these regions. The basic flap-edge aerodynamics is established by static surface pressure data, as well as by Computational Fluid Dynamics (CFD) calculations and simplified edge flow analyses. Distributions of unsteady pressure sensors over the flap allow the noise source regions to be defined and quantified via cross-spectral diagnostics using the SADA output. It is found that shear layer instability and related pressure scatter is the primary noise mechanism. For the flat edge flap, two noise prediction methods based on unsteady surface pressure measurements are evaluated and compared to measured noise. One is a new causality spectral approach developed here. The other is a new application of an edge-noise scatter prediction method. The good comparisons for both approaches suggest that much of the physics is captured by the prediction models. Areas of disagreement appear to reveal when the assumed edge noise mechanism does not fully define the noise production. For the different edge conditions, extensive spectra and directivity are presented. Significantly, for each edge configuration, the spectra for different flow speeds, flap angles, and

  1. Hydrodynamic schooling of flapping swimmers

    Becker, Alexander D.; Masoud, Hassan; Newbolt, Joel W.; Shelley, Michael; Ristroph, Leif

    2015-10-01

    Fish schools and bird flocks are fascinating examples of collective behaviours in which many individuals generate and interact with complex flows. Motivated by animal groups on the move, here we explore how the locomotion of many bodies emerges from their flow-mediated interactions. Through experiments and simulations of arrays of flapping wings that propel within a collective wake, we discover distinct modes characterized by the group swimming speed and the spatial phase shift between trajectories of neighbouring wings. For identical flapping motions, slow and fast modes coexist and correspond to constructive and destructive wing-wake interactions. Simulations show that swimming in a group can enhance speed and save power, and we capture the key phenomena in a mathematical model based on memory or the storage and recollection of information in the flow field. These results also show that fluid dynamic interactions alone are sufficient to generate coherent collective locomotion, and thus might suggest new ways to characterize the role of flows in animal groups.

  2. Flapping wing aerodynamics: from insects to vertebrates.

    Chin, Diana D; Lentink, David

    2016-04-01

    More than a million insects and approximately 11,000 vertebrates utilize flapping wings to fly. However, flapping flight has only been studied in a few of these species, so many challenges remain in understanding this form of locomotion. Five key aerodynamic mechanisms have been identified for insect flight. Among these is the leading edge vortex, which is a convergent solution to avoid stall for insects, bats and birds. The roles of the other mechanisms - added mass, clap and fling, rotational circulation and wing-wake interactions - have not yet been thoroughly studied in the context of vertebrate flight. Further challenges to understanding bat and bird flight are posed by the complex, dynamic wing morphologies of these species and the more turbulent airflow generated by their wings compared with that observed during insect flight. Nevertheless, three dimensionless numbers that combine key flow, morphological and kinematic parameters - the Reynolds number, Rossby number and advance ratio - govern flapping wing aerodynamics for both insects and vertebrates. These numbers can thus be used to organize an integrative framework for studying and comparing animal flapping flight. Here, we provide a roadmap for developing such a framework, highlighting the aerodynamic mechanisms that remain to be quantified and compared across species. Ultimately, incorporating complex flight maneuvers, environmental effects and developmental stages into this framework will also be essential to advancing our understanding of the biomechanics, movement ecology and evolution of animal flight. PMID:27030773

  3. Pathogenic microbes manipulate cofilin activity to subvert actin cytoskeleton.

    Zheng, Kai; Kitazato, Kaio; Wang, Yifei; He, Zhendan

    2016-09-01

    Actin-depolymerizing factor (ADF)/cofilin proteins are key players in controlling the temporal and spatial extent of actin dynamics, which is crucial for mediating host-pathogen interactions. Pathogenic microbes have evolved molecular mechanisms to manipulate cofilin activity to subvert the actin cytoskeletal system in host cells, promoting their internalization into the target cells, modifying the replication niche and facilitating their intracellular and intercellular dissemination. The study of how these pathogens exploit cofilin pathways is crucial for understanding infectious disease and providing potential targets for drug therapies. PMID:25853495

  4. Papilla Preservation Flap as Aesthetic Consideration in Periodontal Flap Surgery

    Sandra Olivia; Natalina Natalina; Felix Hartono

    2013-01-01

    Flap surgery is treatment for periodontal disease with alveolar bone destruction. Surgical periodontal flap with conventional incision will result in gingival recession and loss of interdental papillae after treatment. Dilemma arises in areas required high aesthetic value or regions with a fixed denture. It is challenging to perform periodontal flap with good aesthetic results and minimal gingival recession. This case report aimed to inform and to explain the work procedures, clinical and rad...

  5. Mechanical force-induced polymerization and depolymerization of F-actin at water/solid interfaces

    Zhang, Xueqiang; Hu, Xiuyuan; Lei, Haozhi; Hu, Jun; Zhang, Yi

    2016-03-01

    Actin molecules are among the three main cytoskeleton proteins of cells and undergo rapid cycling to regulate critical processes such as endocytosis, cytokinesis, cell polarity, and cell morphogenesis. Although extensive studies have been carried out on the dynamics as well as biological functions of actin polymerization and depolymerization both in vivo and in vitro, the molecular mechanisms by which cells sense and respond to mechanical signals are not fully understood. In particular, little attention has been paid to the effect of a physical force that is exerted directly on the actin cytoskeleton. In this paper, we have explored how the mechanical force affects the actin polymerization and depolymerization behaviors at water/solid interfaces using an atomic force microscope (AFM) operated in liquid. By raster scanning an AFM probe on a substrate surface with a certain load, it was found that actin monomers could polymerize into filaments without the help of actin related proteins (ARPs). Further study indicated that actin monomers were inclined to form filaments only under a small scanning load. The polymerized actin filaments would be depolymerized when the mechanical force was stronger. A possible mechanism has been suggested to explain the mechanical force induced actin polymerization.Actin molecules are among the three main cytoskeleton proteins of cells and undergo rapid cycling to regulate critical processes such as endocytosis, cytokinesis, cell polarity, and cell morphogenesis. Although extensive studies have been carried out on the dynamics as well as biological functions of actin polymerization and depolymerization both in vivo and in vitro, the molecular mechanisms by which cells sense and respond to mechanical signals are not fully understood. In particular, little attention has been paid to the effect of a physical force that is exerted directly on the actin cytoskeleton. In this paper, we have explored how the mechanical force affects the actin

  6. Numerical simulation of self-propulsion of flapping flexible plates

    Lu, Xi-Yun; Hua, Ru-Nan; Fluid Mechanics Team

    2012-11-01

    Self-propulsion of flapping flexible plates has been studied numerically by means of an immersed boundary-lattice Boltzmann method for the fluid dynamics around the plate and a finite element method for the deformable flapping motion of the plate. Both the two- and three-dimensional flexible plates are investigated to reveal the propulsion properties and their differences. As a result of the fluid-plate interaction, three typical movement regimes have been identified and can be briefly described as forward, backward, and irregular movements which mainly depend on the flapping amplitude and bending rigidity. It is found that there exists an optimal range of the bending rigidity for large propulsive speed or high efficiency in the forward movement regime, consistent with the observation and measurement of swimming and flying animals. The results obtained in this study provide physical insights into understanding of the propulsive mechanisms of the flapping fin or wing of animals.

  7. Flap Conformations in HIV-1 Protease are Altered by Mutations

    Fanucci, Gail; Blackburn, Mandy; Veloro, Angelo; Galiano, Luis; Fangu, Ding; Simmerling, Carlos

    2009-03-01

    HIV-1 protease (PR) is an enzyme that is a major drug target in the treatment of AIDS. Although the structure and function of HIV-1 PR have been studied for over 20 years, questions remain regarding the conformations and dynamics of the β-hairpin turns (flaps) that cover the active site cavity. Distance measurements with pulsed EPR spectroscopy of spin labeled constructs of HIV-1 PR have been used to characterize the flap conformations in the apo and inhibitor bound states. From the most probably distances and the breadth of the distance distribution profiles from analysis of the EPR data, insights regarding the flap conformations and flexibility are gained. The EPR results clearly show how drug pressure selected mutations alter the average conformation of the flaps and the degree of opening of the flaps. Molecular dynamics simulations successfully regenerate the experimentally determined distance distribution profiles, and more importantly, provide structural models for full interpretation of the EPR results. By combining experiment and theory to understand the role that altered flap flexibility/conformations play in the mechanism of drug resistance, key insights are gained toward the rational development of new inhibitors of this important enzyme.

  8. A Miniature Controllable Flapping Wing Robot

    Arabagi, Veaceslav Gheorghe

    The agility and miniature size of nature's flapping wing fliers has long baffled researchers, inspiring biological studies, aerodynamic simulations, and attempts to engineer their robotic replicas. Flapping wing flight is characterized by complex reciprocating wing kinematics, transient aerodynamic effects, and very small body lengths. These characteristics render robotic flapping wing aerial vehicles ideal for surveillance and defense applications, search and rescue missions, and environment monitoring, where their ability to hover and high maneuverability is immensely beneficial. One of the many difficulties in creating flapping wing based miniature robotic aerial vehicles lies in generating a proper wing trajectory that would result in sufficient lift forces for hovering and maneuvering. Since design of a flapping wing system is a balance between overall weight and the number of actuated inputs, we take the approach of having minimal controlled inputs, allowing passive behavior wherever possible. Hence, we propose a completely passive wing pitch reversal design that relies on wing inertial dynamics, an elastic energy storage mechanism, and low Reynolds number aerodynamic effects. Theoretical models, compiling previous research on piezoelectric actuators, four-bar transmissions, and aerodynamics effects, are developed and used as basis for a complete numerical simulation. Limitations of the model are discussed in comparison to experimental results obtained from a working prototype of the proposed passive pitch reversal flapping wing mechanism. Given that the mechanism is under-actuated, methods to control lift force generation by actively varying system parameters are proposed, discussed, and tested experimentally. A dual wing aerial platform is developed based on the passive pitch reversal wing concept. Design considerations are presented, favoring controllability and structural rigidity of the final platform. Finite element analysis and experimental

  9. Smart dynamic rotor control using active flaps on a small-scale wind turbine: aeroelastic modeling and comparison with wind tunnel measurements

    Barlas, Thanasis K.; van Wingerden, W.; Hulskamp, A.W.;

    2013-01-01

    using the aeroelastic tool, load predictions are compared with the wind tunnel measurements, and similar control concepts are compared and evaluated in the numerical environment. Conclusions regarding evaluation of the performance of smart rotor concepts for wind turbines are drawn from this threefold......In this paper, the proof of concept of a smart rotor is illustrated by aeroelastic simulations on a small-scale rotor and comparison with wind tunnel experiments. The application of advanced feedback controllers using actively deformed flaps in the wind tunnel measurements is shown to alleviate...

  10. Exploring the drug resistance of V32I and M46L mutant HIV-1 protease to inhibitor TMC114: flap dynamics and binding mechanism

    Meher, Biswa Ranjan; Wang, Yixuan

    2014-01-01

    Inhibitors of HIV-1 protease (HIV-1-pr) generally only bind to the active site of the protease. However, for some mutants such as V32I and M46L the TMC114 can bind not only to the active cavity also to the groove of the flexible flaps. Although the second binding site suggests the higher efficiency of the drug against HIV-1-pr, the drug resistance in HIV-1-pr due to mutations cannot be ignored, which prompts us to investigate the molecular mechanisms of drug resistance and behavior of double ...

  11. Flag flapping in a channel

    Alben, Silas; Shoele, Kourosh; Mittal, Rajat; Jha, Sourabh; Glezer, Ari

    2015-11-01

    We study the flapping of a flag in an inviscid channel flow. We focus especially on how quantities vary with channel spacing. As the channel walls move inwards towards the flag, heavier flags become more unstable, while light flags' stability is less affected. We use a vortex sheet model to compute large-amplitude flapping, and find that the flag undergoes a series of jumps to higher flapping modes as the channel walls are moved towards the flag. Meanwhile, the drag on the flag and the energy lost to the wake first rise as the walls become closer, then drop sharply as the flag moves to a higher flapping mode.

  12. Keystone flaps in coloured skin: Flap technology for the masses?

    Satish P Bhat

    2013-01-01

    Full Text Available Introduction: Viscoelastic properties of skin in coloured ethnic groups are less favourable compared to Caucasians for executing Keystone flaps. Keystone flaps have so far been evaluated and reported only in Caucasians. The potential of Keystone flaps in a coloured ethnic group is yet unknown. Aim: This article reviews the experience to reconstruct skin defects presenting in a coloured ethnic group, by using Keystone flaps, with a review of existing literature. Design: Uncontrolled case series. Materials and Methods: This retrospective review involves 55 consecutive Keystone flaps used from 2009 to 2012, for skin defects in various locations. Patient demographic data, medical history, co-morbidity, surgical indication, defect features, complications, and clinical outcomes are evaluated and presented. Results: In this population group with Fitzpatrick type 4 and 5 skin, the average patient age was 35.73. Though 60% of flaps (33/55 in the series involved specific risk factors, only two flaps failed. Though seven flaps had complications, sound healing was achieved by suitable intervention giving a success rate of 96.36%. Skin grafts were needed in only four cases. Conclusions: Keystone flaps achieve primary wound healing for a wide spectrum of defects with an acceptable success rate in a coloured skin population with unfavorable biophysical properties. By avoiding conventional local flaps and at times even microsurgical flaps, good aesthetic outcome is achieved without additional skin grafts or extensive operative time. All advantages seen in previous studies were verified. These benefits can be most appreciated in coloured populations, with limited resources and higher proportion of younger patients and unfavorable defects.

  13. Locomotion of a flapping flexible plate

    Hua, Ru-Nan; Zhu, Luoding; Lu, Xi-Yun

    2013-12-01

    The locomotion of a flapping flexible plate in a viscous incompressible stationary fluid is numerically studied by an immersed boundary-lattice Boltzmann method for the fluid and a finite element method for the plate. When the leading-edge of the flexible plate is forced to heave sinusoidally, the entire plate starts to move freely as a result of the fluid-structure interaction. Mechanisms underlying the dynamics of the plate are elucidated. Three distinct states of the plate motion are identified and can be described as forward, backward, and irregular. Which state to occur depends mainly on the heaving amplitude and the bending rigidity of the plate. In the forward motion regime, analysis of the dynamic behaviors of the flapping flexible plate indicates that a suitable degree of flexibility can improve the propulsive performance. Moreover, there exist two kinds of vortex streets in the downstream of the plate which are normal and deflected wake. Further the forward motion is compared with the flapping-based locomotion of swimming and flying animals. The results obtained in the present study are found to be consistent with the relevant observations and measurements and can provide some physical insights into the understanding of the propulsive mechanisms of swimming and flying animals.

  14. Managing Flap Vortices via Separation Control

    Greenblatt, David

    2006-01-01

    A pilot study was conducted on a flapped semi-span model to investigate the concept and viability of near-wake vortex management by means of boundary layer separation control. Passive control was achieved using a simple fairing and active control was achieved via zero mass-flux blowing slots. Vortex sheet strength, estimated by integrating surface pressures, was used to predict vortex characteristics based on inviscid rollup relations and vortices trailing the flaps were mapped using a seven-hole probe. Separation control was found to have a marked effect on vortex location, strength, tangential velocity, axial velocity and size over a wide range of angles of attack and control conditions. In general, the vortex trends were well predicted by the inviscid rollup relations. Manipulation of the separated flow near the flap edges exerted significant control over either outboard or inboard edge vortices while producing small lift and moment excursions. Unsteady surface pressures indicated that dynamic separation and attachment control can be exploited to perturb vortices at wavelengths shorter than a typical wingspan. In summary, separation control has the potential for application to time-independent or time-dependent wake alleviation schemes, where the latter can be deployed to minimize adverse effects on ride-quality and dynamic structural loading.

  15. The role of the cofilin-actin rod stress response in neurodegenerative diseases uncovers potential new drug targets

    Munsie, Lise N.; Truant, Ray

    2012-01-01

    The cofilin-actin rod stress response is an actin cytoskeletal dynamic arrest that occurs in cells under a variety of stress conditions. Upon stress, the rapidly activated cofilin saturates actin filaments causing them to bundle into rod structures in either the nucleus or cytoplasm, halting actin polymerization and thus freeing ATP. Importantly, these rods dissociate quickly following relief of the transient stress. The rods form inappropriately in neurons involved in the progression of Alzh...

  16. Antenna mechanism of length control of actin cables

    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...

  17. The Actin Cytoskeleton as a Therapeutic Target for the Prevention of Relapse to Methamphetamine Use.

    Young, Erica J; Briggs, Sherri B; Miller, Courtney A

    2015-01-01

    A high rate of relapse is a defining characteristic of substance use disorder for which few treatments are available. Exposure to environmental cues associated with previous drug use can elicit relapse by causing the involuntary retrieval of deeply engrained associative memories that trigger a strong motivation to seek out drugs. Our lab is focused on identifying and disrupting mechanisms that support these powerful consolidated memories, with the goal of developing therapeutics. A particularly promising mechanism is regulation of synaptic dynamics by actin polymerization within dendritic spines. Emerging evidence indicates that memory is supported by structural and functional plasticity dendritic spines, for which actin polymerization is critical, and that prior drug use increases both spine and actin dynamics. Indeed we have found that inhibiting amygdala (AMY) actin polymerization immediately or twenty-four hours prior to testing disrupted methamphetamine (METH)-associated memories, but not food reward or fear memories. Furthermore, METH training increased AMY spine density which was reversed by actin depolymerization treatment. Actin dynamics were also shifted to a more dynamic state by METH training. While promising, actin polymerization inhibitors are not a viable therapeutic, as a multitude of peripheral process (e.g. cardiac function) rely on dynamic actin. For this reason, we have shifted our focus upstream of actin polymerization to nonmuscle myosin II. We and others have demonstrated that myosin IIb imparts a mechanical force that triggers spine actin polymerization in response to synaptic stimulation. Similar to an actin depolymerizing compound, pre-test inhibition of myosin II ATPase activity in the AMY produced a rapid and lasting disruption of drug-seeking behavior. While many questions remain, these findings indicate that myosin II represents a potential therapeutic avenue to target the actin cytoskeleton and disrupt the powerful, extinction

  18. Regulation of T cell receptor signaling by the actin cytoskeleton and poroelastic cytoplasm

    Beemiller, Peter; Krummel, Matthew F.

    2013-01-01

    Summary The actin cytoskeleton plays essential roles in modulating T-cell activation. Most models of T-cell receptor (TCR) triggering, signalosome assembl, y and immune synapse formation invoke actin-dependent mechanisms. As T cells are constitutively motile cells, TCR triggering and signaling occur against a cytoskeletal backdrop that is constantly remodeling. While the interplay between actin dynamics and TCR signaling have been the focus of research for many years, much of the work in T cells has considered actin largely for its ‘scaffolding’ function. We examine the roles of the actin cytoskeleton in TCR signaling and immune synapse formation with an emphasis on how poroelasticity, an ensemble feature of actin dynamics with the cytosol, relates to how T cells respond to stimulation. PMID:24117819

  19. Regulation of T-cell receptor signaling by the actin cytoskeleton and poroelastic cytoplasm.

    Beemiller, Peter; Krummel, Matthew F

    2013-11-01

    The actin cytoskeleton plays essential roles in modulating T-cell activation. Most models of T-cell receptor (TCR) triggering signalosome assembly and immune synapse formation invoke actin-dependent mechanisms. As T cells are constitutively motile cells, TCR triggering and signaling occur against a cytoskeletal backdrop that is constantly remodeling. While the interplay between actin dynamics and TCR signaling have been the focus of research for many years, much of the work in T cells has considered actin largely for its 'scaffolding' function. We examine the roles of the actin cytoskeleton in TCR signaling and immune synapse formation with an emphasis on how poroelasticity, an ensemble feature of actin dynamics with the cytosol, relates to how T cells respond to stimulation. PMID:24117819

  20. Direct Microtubule-Binding by Myosin-10 Orients Centrosomes toward Retraction Fibers and Subcortical Actin Clouds.

    Kwon, Mijung; Bagonis, Maria; Danuser, Gaudenz; Pellman, David

    2015-08-10

    Positioning of centrosomes is vital for cell division and development. In metazoan cells, spindle positioning is controlled by a dynamic pool of subcortical actin that organizes in response to the position of retraction fibers. These actin "clouds" are proposed to generate pulling forces on centrosomes and mediate spindle orientation. However, the motors that pull astral microtubules toward these actin structures are not known. Here, we report that the unconventional myosin, Myo10, couples actin-dependent forces from retraction fibers and subcortical actin clouds to centrosomes. Myo10-mediated centrosome positioning requires its direct microtubule binding. Computational image analysis of large microtubule populations reveals a direct effect of Myo10 on microtubule dynamics and microtubule-cortex interactions. Myo10's role in centrosome positioning is distinct from, but overlaps with, that of dynein. Thus, Myo10 plays a key role in integrating the actin and microtubule cytoskeletons to position centrosomes and mitotic spindles. PMID:26235048

  1. Regulation of T cell receptor signaling by the actin cytoskeleton and poroelastic cytoplasm

    Beemiller, Peter; Krummel, Matthew F.

    2013-01-01

    The actin cytoskeleton plays essential roles in modulating T-cell activation. Most models of T-cell receptor (TCR) triggering, signalosome assembl, y and immune synapse formation invoke actin-dependent mechanisms. As T cells are constitutively motile cells, TCR triggering and signaling occur against a cytoskeletal backdrop that is constantly remodeling. While the interplay between actin dynamics and TCR signaling have been the focus of research for many years, much of the work in T cells has ...

  2. Forces generated during actin-based propulsion: A direct measurement by micromanipulation

    Marcy, Yann; Prost, Jacques; Carlier, Marie-France; Sykes, Cécile

    2004-01-01

    Dynamic actin networks generate forces for numerous types of movements such as lamellipodia protrusion or the motion of endocytic vesicles. The actin-based propulsive movement of Listeria monocytogenes or of functionalized microspheres have been extensively used as model systems to identify the biochemical components that are necessary for actin-based motility. However, quantitative force measurements are required to elucidate the mechanism of force generation, which is still under debate. To...

  3. Arp2/3-mediated F-actin formation controls regulated exocytosis in vivo

    Tran, Duy T.; Masedunskas, Andrius; Weigert, Roberto; Ten Hagen, Kelly G.

    2015-01-01

    The actin cytoskeleton plays crucial roles in many cellular processes, including regulated secretion. However, the mechanisms controlling F-actin dynamics in this process are largely unknown. Through 3D time-lapse imaging in a secreting organ, we show that F-actin is actively disassembled along the apical plasma membrane at the site of secretory vesicle fusion and re-assembled directionally on vesicle membranes. Moreover, we show that fusion pore formation and PIP2 redistribution precedes act...

  4. The role of actin networks in cellular mechanosensing

    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

  5. Characterization of ring-like F-actin structure as a mechanical partner for spindle positioning in mitosis.

    Huan Lu

    Full Text Available Proper spindle positioning and orientation are essential for accurate mitosis which requires dynamic interactions between microtubule and actin filament (F-actin. Although mounting evidence demonstrates the role of F-actin in cortical cytoskeleton dynamics, it remains elusive as to the structure and function of F-actin-based networks in spindle geometry. Here we showed a ring-like F-actin structure surrounding the mitotic spindle which forms since metaphase and maintains in MG132-arrested metaphase HeLa cells. This cytoplasmic F-actin structure is relatively isotropic and less dynamic. Our computational modeling of spindle position process suggests a possible mechanism by which the ring-like F-actin structure can regulate astral microtubule dynamics and thus mitotic spindle orientation. We further demonstrated that inhibiting Plk1, Mps1 or Myosin, and disruption of microtubules or F-actin polymerization perturbs the formation of the ring-like F-actin structure and alters spindle position and symmetric division. These findings reveal a previously unrecognized but important link between mitotic spindle and ring-like F-actin network in accurate mitosis and enables the development of a method to theoretically illustrate the relationship between mitotic spindle and cytoplasmic F-actin.

  6. Feedback Interactions of Polymerized Actin with the Cell Membrane: Waves, Pulses, and Oscillations

    Carlsson, Anders

    Polymerized filaments of the protein actin have crucial functions in cell migration, and in bending the cell membrane to drive endocytosis or the formation of protrusions. The nucleation and polymerization of actin filaments are controlled by upstream agents in the cell membrane, including nucleation-promoting factors (NPFs) that activate the Arp2/3 complex to form new branches on pre-existing filaments. But polymerized actin (F-actin) also feeds back on the assembly of NPFs. We explore the effects of the resulting feedback loop of F-actin and NPFs on two phenomena: actin pulses that drive endocytosis in yeast, and actin waves traveling along the membrane of several cell types. In our model of endocytosis in yeast, the actin network is grown explicitly in three dimensions, exerts a negative feedback interaction on localized patch of NPFs in the membrane, and bends the membrane by exerting a distribution of forces. This model explains observed actin and NPF pulse dynamics, and the effects of several interventions including i) NPF mutations, ii) inhibition of actin polymerization, and iii) deletion of a protein that allows F-actin to bend the cell membrane. The model predicts that mutation of the active region of an NPF will enhance the accumulation of that NPF, and we confirm this prediction by quantitative fluorescence microscopy. For actin waves, we treat a similar model, with NPFs distributed over a larger region of the cell membrane. This model naturally generates actin waves, and predicts a transition from wave behavior to spatially localized oscillations when NPFs are confined to a small region. We also predict a transition from waves to static polarization as the negative-feedback coupling between F-actin and the NPFs is reduced. Supported by NIGMS Grant R01 GM107667.

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

    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.

  8. Active Control of Long Bridges Using Flaps

    Hansen, H. I.; Thoft-Christensen, Palle

    The main problem in designing ultra-long span suspension bridges is flutter. A solution to this problem might be to introduce an active flap control system to increase the flutter wind velocity. The investigated flap control system consists of flaps integrated in the bridge girder so each flap is...... different flap configurations for a bridge section model by using aerodynamic derivatives for a flat plate. The example shows that different flap configurations can either increase or decrease the flutter wind velocity. for optimal flap configurations flutter will not occur....

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

    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.

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

    Domínguez-Iturza, Nuria; Calvo, María; Benoist, Marion; Esteban, José Antonio; Morales, Miguel

    2016-01-01

    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. PMID:26881098

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

    Lamprecht, Raphael

    2016-01-01

    The central, lateral and basolateral amygdala (BLA) nuclei are essential for the formation of long-term memories including emotional and drug-related memories. Studying cellular and molecular mechanisms of memory in amygdala may lead to better understanding of how memory is formed and of 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 (LTM) 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. PMID:27065800

  12. Progresses in studies of nuclear actin

    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.

  13. Flap Edge Noise Reduction Fins

    Khorrami, Mehdi R. (Inventor); Choudhan, Meelan M. (Inventor)

    2015-01-01

    A flap of the type that is movably connected to an aircraft wing to provide control of an aircraft in flight includes opposite ends, wherein at least a first opposite end includes a plurality of substantially rigid, laterally extending protrusions that are spaced apart to form a plurality of fluidly interconnected passageways. The passageways have openings adjacent to upper and lower sides of the flap, and the passageways include a plurality of bends such that high pressure fluid flows from a high pressure region to a low pressure region to provide a boundary condition that inhibits noise resulting from airflow around the end of the flap.

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

    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. PMID:26021350

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

    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.

  16. Characterization of engineered actin binding proteins that control filament assembly and structure.

    Crista M Brawley

    Full Text Available BACKGROUND: Eukaryotic cells strictly regulate the structure and assembly of their actin filament networks in response to various stimuli. The actin binding proteins that control filament assembly are therefore attractive targets for those who wish to reorganize actin filaments and reengineer the cytoskeleton. Unfortunately, the naturally occurring actin binding proteins include only a limited set of pointed-end cappers, or proteins that will block polymerization from the slow-growing end of actin filaments. Of the few that are known, most are part of large multimeric complexes that are challenging to manipulate. METHODOLOGY/PRINCIPAL FINDINGS: We describe here the use of phage display mutagenesis to generate of a new class of binding protein that can be targeted to the pointed-end of actin. These proteins, called synthetic antigen binders (sABs, are based on an antibody-like scaffold where sequence diversity is introduced into the binding loops using a novel "reduced genetic code" phage display library. We describe effective strategies to select and screen for sABs that ensure the generated sABs bind to the pointed-end surface of actin exclusively. CONCLUSIONS/SIGNIFICANCE: From our set of pointed-end binders, we identify three sABs with particularly useful properties to systematically probe actin dynamics: one protein that caps the pointed end, a second that crosslinks actin filaments, and a third that severs actin filaments and promotes disassembly.

  17. A Potential Yeast Actin Allosteric Conduit Dependent on Hydrophobic Core Residues Val-76 and Trp-79*

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

    2010-01-01

    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...

  18. The Actin Binding Protein Adseverin Regulates Osteoclastogenesis

    Hassanpour, Siavash; Jiang, Hongwei; Wang, Yongqiang; Kuiper, Johannes W. P.; Glogauer, Michael

    2014-01-01

    Adseverin (Ads), a member of the Gelsolin superfamily of actin binding proteins, regulates the actin cytoskeleton architecture by severing and capping existing filamentous actin (F-actin) strands and nucleating the assembly of new F-actin filaments. Ads has been implicated in cellular secretion, exocytosis and has also been shown to regulate chondrogenesis and megakaryoblastic leukemia cell differentiation. Here we report for the first time that Ads is involved in regulating osteoclastogenesi...

  19. Inhibiting actin depolymerization enhances osteoblast differentiation and bone formation in human stromal stem cells

    Chen, Li; Shi, Kaikai; Frary, Charles Edward;

    2015-01-01

    Remodeling of the actin cytoskeleton through actin dynamics is involved in a number of biological processes, but its role in human stromal (skeletal) stem cells (hMSCs) differentiation is poorly understood. In the present study, we demonstrated that stabilizing actin filaments by inhibiting gene...... expression of the two main actin depolymerizing factors (ADFs): Cofilin 1 (CFL1) and Destrin (DSTN) in hMSCs, enhanced cell viability and differentiation into osteoblastic cells (OB) in vitro, as well as heterotopic bone formation in vivo. Similarly, treating hMSC with Phalloidin, which is known to stabilize...... polymerized actin filaments, increased hMSCs viability and OB differentiation. Conversely, Cytocholasin D, an inhibitor of actin polymerization, reduced cell viability and inhibited OB differentiation of hMSC. At a molecular level, preventing Cofilin phosphorylation through inhibition of LIM domain kinase 1...

  20. Distribution of G-actin is Related to Root Hair Growth of Wheat

    He, Xue; Liu, Yi-Min; Wang, Wei; LI Yan

    2006-01-01

    • Background and Aims Actin distribution in root hair tips is a controversial topic. Although the relationship between Ca2+ gradient and actin dynamics in plant tip-growth has been a focus of study, there is still little direct evidence on the exact relationship in root hair tip-growth.

  1. The freestyle pedicle perforator flap

    Gunnarsson, Gudjon Leifur; Jackson, Ian T; Westvik, Tormod S; Thomsen, Jorn Bo

    2015-01-01

    not widely performed by the general plastic surgeons. The aim of this paper is to present the simplicity of pedicled perforator flap reconstruction of moderate-sized defects of the extremities and torso. METHODS: We retrospectively reviewed the charts of 34 patients reconstructed using 34 freestyle...... aspects in the context of current literature. RESULTS: The reconstructive goals were achieved in all cases without any total flap loss or major complications. Minor complications occurred in 7/34 (21 %) cases consisting of venous congestion leading to distal tip necrosis or epidermolysis; partial flap...... loss was significant in 4 cases, however never more than 10 % of the total flap size. Reconstruction was performed on the lower limb in 13 cases, upper limb in 12, and 9 cases were on the truncus. The angle of rotation was 90° in 21 cases and 180° in 13 cases. The most common indication was...

  2. Modeling of Airfoil Trailing Edge Flap with Immersed Boundary Method

    Zhu, Wei Jun; Shen, Wen Zhong; Sørensen, Jens Nørkær

    2011-01-01

    The present work considers incompressible flow over a 2D airfoil with a deformable trailing edge. The aerodynamic characteristics of an airfoil with a trailing edge flap is numerically investigated using computational fluid dynamics. A novel hybrid immersed boundary (IB) technique is applied to...... simulate the moving part of the trailing edge. Over the main fixed part of the airfoil the Navier-Stokes (NS) equations are solved using a standard body-fitted finite volume technique whereas the moving trailing edge flap is simulated with the immersed boundary method on a curvilinear mesh. The obtained...

  3. Differential effects of LifeAct-GFP and actin-GFP on cell mechanics assessed using micropipette aspiration

    Sliogeryte, Kristina; Stephen D Thorpe; Wang, Zhao; Thompson, Clare L.; Gavara, Nuria; Knight, Martin M.

    2016-01-01

    The actin cytoskeleton forms a dynamic structure involved in many fundamental cellular processes including the control of cell morphology, migration and biomechanics. Recently LifeAct-GFP (green fluorescent protein) has been proposed for visualising actin structure and dynamics in live cells as an alternative to actin-GFP which has been shown to affect cell mechanics. Here we compare the two approaches in terms of their effect on cellular mechanical behaviour. Human mesenchymal stem cells (hM...

  4. Modified osteomyocutaneous iliac crest flaps transplantation.

    Liu, Jun; Song, Dajiang; Li, Jinsong; Xu, Jian; Lv, Hongbin

    2015-04-01

    The paper aims to improve the operative technique of osteomyocutaneous iliac crest flap harvesting, further minimise morbidity of donor site, and improve the effect of recipient site reconstruction. From March 2005 to March 2011, 55 cases of osteomyocutaneous iliac crest flap harvested by different methods were performed to reconstruct the defects of the extremities. Twenty-nine cases were reconstructed with a traditional deep circumflex iliac artery osteomusculocutaneous flap. Twenty-six cases were repaired with modified osteomyocutaneous iliac crest flaps. In 29 cases with a traditional DCIA osteomusculocutaneous flap, two cases showed the injured lateral femoral cutaneous nerve. Flapnecrosis was significant in two cases. Arterial compromise occurred in one case 5 days after operation completion and led to flap failure. Three flaps developed postoperative venous congestion, but only one flap received re-exploration. In the other two cases, some stitches were removed for decompression. All three flaps survived. In two cases, marginal flap necrosis occurred, but no secondary skin grafting was required. In 26 cases with modified flap transplantation, one case showed the injured lateral femoral cutaneous nerve. All flaps survived totally. Osseous integration was achieved in all 55 cases in 3 ∼ 9 months after operation. The modified osteomyocutaneous iliac crest flap technique enhances flap safety, provides the additional advantages of reducing donor-site morbidity, and improves the recipient-site contour. PMID:25001367

  5. Regulation of water flow by actin-binding protein-induced actin gelatin.

    Ito, T.; Suzuki, A.; Stossel, T. P.

    1992-01-01

    Actin filaments inhibit osmotically driven water flow (Ito, T., K.S. Zaner, and T.P. Stossel. 1987. Biophys. J. 51: 745-753). Here we show that the actin gelation protein, actin-binding protein (ABP), impedes both osmotic shrinkage and swelling of an actin filament solution and reduces markedly the concentration of actin filaments required for this inhibition. These effects depend on actin filament immobilization, because the ABP concentration that causes initial impairment of water flow by a...

  6. Four-winged flapping flyer in forward flight

    Godoy-Diana, Ramiro; Centeno, Mariana; Weinreb, Alexis; Thiria, Benjamin

    2015-01-01

    We study experimentally a four-winged flapping flyer with chord-wise flexible wings in a self-propelled setup. For a given physical configuration of the flyer (i.e. fixed distance between the forewing and hindwing pairs and fixed wing flexibility), we explore the kinematic parameter space constituted by the flapping frequency and the forewing-hindwing phase lag. Cruising speed and consumed electric power measurements are performed for each point in the $(f,\\varphi)$ parameter space and allow us to discuss the problem of performance and efficiency in four-winged flapping flight. We show that different phase-lags are needed for the system to be optimised for fastest flight or lowest energy consumption. A conjecture of the underlying mechanism is proposed in terms of the coupled dynamics of the forewing-hindwing phase lag and the deformation kinematics of the flexible wings.

  7. Interaction of Two Flapping Flags in Axial Flow

    Gunter, Amy-Lee; Fayed, Mohamed; Abderrahmane, Hamid Ait; Paidoussis, Michael P.; Ng, Hoi Dick

    2010-11-01

    The flapping of two parallel flags in axial low turbulence flow is investigated experimentally inside a small scale wind tunnel test section. The variables of the problem are the size and flexural rigidity of the flags, and the distance that separates the two flags. The flow velocity represents the control parameter that governs the coupling and flapping mode of the flags. Two flapping modes, in-phase and out-of-phase modes, were observed in the experiment. Image processing technique was used and the time series of a given point on the flag edge was analyzed. The stability condition of the flags was obtained and compared to the recent theoretical models. The dynamics of the coupling between the two flags is also studied.

  8. Chord-wise Tip Actuation on Flexible Flapping Plates

    Martin, Nathan; Gharib, Morteza

    2015-11-01

    The aerodynamic characteristics of low aspect ratio flapping plates are strongly influenced by the interaction between tip and edge vortices. This has led to the development of tip actuation mechanisms which bend the tip towards the root of the plate in the span-wise direction during oscillation to investigate its impact. In our current work, a tip actuation mechanism to bend a flat plate's two free corners towards one another in the chord-wise direction is developed using a shape memory alloy. The aerodynamic forces and resulting flow field are investigated from dynamically altering the tip chord-wise curvature while flapping. The frequency of oscillation, stroke angle, flexibility, and tip actuation timing are independently varied to determine their individual effects. These results will further the fundamental understanding of flapping wing aerodynamics. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE 1144469.

  9. A Robust Actin Filaments Image Analysis Framework.

    Alioscha-Perez, Mitchel; Benadiba, Carine; Goossens, Katty; Kasas, Sandor; Dietler, Giovanni; Willaert, Ronnie; Sahli, Hichem

    2016-08-01

    The cytoskeleton is a highly dynamical protein network that plays a central role in numerous cellular physiological processes, and is traditionally divided into three components according to its chemical composition, i.e. actin, tubulin and intermediate filament cytoskeletons. Understanding the cytoskeleton dynamics is of prime importance to unveil mechanisms involved in cell adaptation to any stress type. Fluorescence imaging of cytoskeleton structures allows analyzing the impact of mechanical stimulation in the cytoskeleton, but it also imposes additional challenges in the image processing stage, such as the presence of imaging-related artifacts and heavy blurring introduced by (high-throughput) automated scans. However, although there exists a considerable number of image-based analytical tools to address the image processing and analysis, most of them are unfit to cope with the aforementioned challenges. Filamentous structures in images can be considered as a piecewise composition of quasi-straight segments (at least in some finer or coarser scale). Based on this observation, we propose a three-steps actin filaments extraction methodology: (i) first the input image is decomposed into a 'cartoon' part corresponding to the filament structures in the image, and a noise/texture part, (ii) on the 'cartoon' image, we apply a multi-scale line detector coupled with a (iii) quasi-straight filaments merging algorithm for fiber extraction. The proposed robust actin filaments image analysis framework allows extracting individual filaments in the presence of noise, artifacts and heavy blurring. Moreover, it provides numerous parameters such as filaments orientation, position and length, useful for further analysis. Cell image decomposition is relatively under-exploited in biological images processing, and our study shows the benefits it provides when addressing such tasks. Experimental validation was conducted using publicly available datasets, and in osteoblasts grown in

  10. A Robust Actin Filaments Image Analysis Framework

    Alioscha-Perez, Mitchel; Benadiba, Carine; Goossens, Katty; Kasas, Sandor; Dietler, Giovanni; Willaert, Ronnie; Sahli, Hichem

    2016-01-01

    The cytoskeleton is a highly dynamical protein network that plays a central role in numerous cellular physiological processes, and is traditionally divided into three components according to its chemical composition, i.e. actin, tubulin and intermediate filament cytoskeletons. Understanding the cytoskeleton dynamics is of prime importance to unveil mechanisms involved in cell adaptation to any stress type. Fluorescence imaging of cytoskeleton structures allows analyzing the impact of mechanical stimulation in the cytoskeleton, but it also imposes additional challenges in the image processing stage, such as the presence of imaging-related artifacts and heavy blurring introduced by (high-throughput) automated scans. However, although there exists a considerable number of image-based analytical tools to address the image processing and analysis, most of them are unfit to cope with the aforementioned challenges. Filamentous structures in images can be considered as a piecewise composition of quasi-straight segments (at least in some finer or coarser scale). Based on this observation, we propose a three-steps actin filaments extraction methodology: (i) first the input image is decomposed into a ‘cartoon’ part corresponding to the filament structures in the image, and a noise/texture part, (ii) on the ‘cartoon’ image, we apply a multi-scale line detector coupled with a (iii) quasi-straight filaments merging algorithm for fiber extraction. The proposed robust actin filaments image analysis framework allows extracting individual filaments in the presence of noise, artifacts and heavy blurring. Moreover, it provides numerous parameters such as filaments orientation, position and length, useful for further analysis. Cell image decomposition is relatively under-exploited in biological images processing, and our study shows the benefits it provides when addressing such tasks. Experimental validation was conducted using publicly available datasets, and in osteoblasts

  11. Robotics in microsurgery: use of a surgical robot to perform a free flap in a pig.

    Katz, Ryan D; Rosson, Gedge D; Taylor, Jesse A; Singh, Navin K

    2005-01-01

    We present the concept that a surgical robot may be used to successfully perform a free flap. To study different microsurgical techniques, a porcine free flap model was developed in our laboratory. Dissection of the free flap model and isolation of the vessels were completed under traditional loupe magnification. The da Vinci robot was then used to perform vessel adventitiectomy and microanastomoses. The model was observed for 4 h postoperatively, noting flap color, temperature, capillary refill, and Doppler signal. At the end of this period, the flap was noted to be viable; anastomoses were evaluated and found to be grossly and microscopically patent. Advantages conferred by the da Vinci robot include elimination of tremor, scalable movements, fully articulating instruments with six degrees of spatial freedom, and a dynamic three-dimensional visualization system. Drawbacks include the cost and the absence of true microsurgical instruments. PMID:16178007

  12. Boolean gates on actin filaments

    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.

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

    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.

  14. Epidermolysis Bullosa Simplex-Type Mutations Alter the Dynamics of the Keratin Cytoskeleton and Reveal a Contribution of Actin to the Transport of Keratin SubunitsD⃞V⃞

    Werner, Nicola Susann; Windoffer, Reinhard; Strnad, Pavel; Grund, Christine; Leube, Rudolf Eberhard; Magin, Thomas Michael

    2004-01-01

    Dominant keratin mutations cause epidermolysis bullosa simplex by transforming keratin (K) filaments into aggregates. As a first step toward understanding the properties of mutant keratins in vivo, we stably transfected epithelial cells with an enhanced yellow fluorescent protein-tagged K14R125C mutant. K14R125C became localized as aggregates in the cell periphery and incorporated into perinuclear keratin filaments. Unexpectedly, keratin aggregates were in dynamic equilibrium with soluble sub...

  15. Experience in Reconstruction for Small Digital Defects With Free Flaps.

    Hung, Min-Hsiang; Huang, Kuo-Feng; Chiu, Haw-Yen; Chao, Wai-Nang

    2016-03-01

    Traumatic injuries to the digits resulting in soft tissue or bone loss require reconstruction. Traditionally, local flaps, such as homodigital flaps, heterodigital flaps, pedicled flaps, or distant flaps, are used for digital resurfacing. However, free tissue transfers can be used in selected patients. In this study, we present the use of different free flaps including groin skin flaps, groin osteocutaneous flaps, groin chimeric flaps, second dorsal metacarpal artery flaps, and partial toe flaps for digital reconstruction. A total of 19 digits were treated with 16 free flaps in our hospital. Of the flaps used, 5 were free groin skin flaps, 4 were free partial toe flaps, 3 were free groin chimeric flaps, 2 were free groin osteocutaneous flaps, and 2 were free second dorsal metacarpal artery flaps. The average flap size was 4.7 × 2.0 cm (range, 1.5 × 1 to 5 × 4 cm), and the average operative time was 6.0 hours (range, 4-9 hours). All flaps survived without partial or total necrosis. In conclusion, the free flap is a reliable and safe alternative for digital reconstruction. Moreover, the free groin flap provides not only a chimeric pattern for multiple fingers coverage but also an osteocutaneous pattern for thumb lengthening. The free second dorsal metacarpal artery flap provides a tenocutaneous pattern for tendon reconstruction and soft tissue coverage simultaneously, and the free partial toe flap is an excellent alternative for pulp reconstruction in terms of aesthetic appearance and functional outcome. PMID:26808771

  16. Flapping propulsion with tip pitch control

    Huera-Huarte, Francisco; Gharib, Morteza

    2014-11-01

    The effect of flexibility in the propulsion performance and efficiency of oscillating pitching foils has received a large amount of attention in the past years. Scientists have used simplified robotic models that mimic the kinematics of flying and swimming animals, in order to get inspiration to build more efficient engineering systems. Compliance is one of the aspects that has received more attention, as it seems to be a common feature in nature's flyers and swimmers. Active or passive control elements are also common in nature. We will show how thrust generation in a pitching fin, can be greatly affected by controlling the tip pitch motion dynamically and independently of the fin itself. This is in fact a controlled local change of curvature of the end of the fin. A robotic system has been designed in a way that not only flapping amplitudes and frequencies can be controlled, but also the amplitudes and frequencies of the tip and the phase difference between the tip and the fin. We measured thrust forces and the vortex dynamics in the near wake of the system, by using planar DPIV (Digital Particle Image Velocimetry) in a wide variety of flapping situations with tip control. Funding from Spanish Ministry of Science through Grant DPI2012-37904 is gratefully acknowledged.

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

    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.

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

    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

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

    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.

  20. Experimental Study of Wake / Flap Interaction Noise and the Reduction of Flap Side Edge Noise

    Hutcheson, Florence V.; Stead, Daniel J.; Plassman, Gerald E.

    2016-01-01

    The effects of the interaction of a wake with a half-span flap on radiated noise are examined. The incident wake is generated by bars of various widths and lengths or by a simplified landing gear model. Single microphone and phased array measurements are used to isolate the effects of the wake interaction on the noise radiating from the flap side edge and flap cove regions. The effects on noise of the wake generator's geometry and relative placement with respect to the flap are assessed. Placement of the wake generators upstream of the flap side edge is shown to lead to the reduction of flap side edge noise by introducing a velocity deficit and likely altering the instabilities in the flap side edge vortex system. Significant reduction in flap side edge noise is achieved with a bar positioned directly upstream of the flap side edge. The noise reduction benefit is seen to improve with increased bar width, length and proximity to the flap edge. Positioning of the landing gear model upstream of the flap side edge also leads to decreased flap side edge noise. In addition, flap cove noise levels are significantly lower than when the landing gear is positioned upstream of the flap mid-span. The impact of the local flow velocity on the noise radiating directly from the landing gear is discussed. The effects of the landing gear side-braces on flap side edge, flap cove and landing gear noise are shown.

  1. Calcium-actin waves and oscillations of cellular membranes.

    Veksler, Alex; Gov, Nir S

    2009-09-16

    We propose a mechanism for the formation of membrane oscillations and traveling waves, which arise due to the coupling between the actin cytoskeleton and the calcium flux through the membrane. In our model, the fluid cell membrane has a mobile but constant population of proteins with a convex spontaneous curvature, which act as nucleators of actin polymerization and adhesion. Such a continuum model couples the forces of cell-substrate adhesion, actin polymerization, membrane curvature, and the flux of calcium through the membrane. Linear stability analysis shows that sufficiently strong coupling among the calcium, membrane, and protein dynamics may induce robust traveling waves on the membrane. This result was checked for a reduced feedback scheme and is compared to the results without the effects of calcium, where permanent phase separation without waves or oscillations is obtained. The model results are compared to the published observations of calcium waves in cell membranes, and a number of testable predictions are proposed. PMID:19751660

  2. Spiral actin-polymerization waves can generate amoeboidal cell crawling

    Amoeboidal cell crawling on solid substrates is characterized by protrusions that seemingly appear randomly along the cell periphery and drive the cell forward. For many cell types, it is known that the protrusions result from polymerization of the actin cytoskeleton. However, little is known about how the formation of protrusions is triggered and whether the appearance of subsequent protrusions is coordinated. Recently, the spontaneous formation of actin-polymerization waves was observed. These waves have been proposed to orchestrate the cytoskeletal dynamics during cell crawling. Here, we study the impact of cytoskeletal polymerization waves on cell migration using a phase-field approach. In addition to directionally moving cells, we find states reminiscent of amoeboidal cell crawling. In this framework, new protrusions are seen to emerge from a nucleation process, generating spiral actin waves in the cell interior. Nucleation of new spirals does not require noise, but occurs in a state that is apparently displaying spatio-temporal chaos. (paper)

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

    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. PMID:22514279

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

    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.

  5. Antenna Mechanism of Length Control of Actin Cables.

    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.

  6. Free thin paraumbilical perforator-based flaps.

    Koshima, I; Moriguchi, T; Soeda, S; Tanaka, H; Umeda, N

    1992-07-01

    A free paraumbilical perforator-based flap fed by a muscle perforator from the inferior deep epigastric artery and with no muscle was used in 13 patients. Among them, a free thin paraumbilical perforator-based flap with a thin layer of fat, to protect the subdermal plexus of the vessels, was used in seven patients. The dominant pedicle perforator of this thin flap is usually located around the umbilicus and a large flap can be obtained. Its critical length-to-breath ratio is considered to be 4:3. The advantages of this flap are a long and large vascular pedicle, rare postoperative abdominal herniation, little bulkiness of the flap, and a relatively large skin territory. The disadvantages are technical difficulties in dissection of the perforator and anatomical variation in the location of the perforator. We believe this flap largely overcomes the problems of the conventional rectus abdominis musculocutaneous flap. PMID:1386718

  7. Identification of Actin-Binding Proteins from Maize Pollen

    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.

  8. Steady-state nuclear actin levels are determined by export competent actin pool.

    Skarp, Kari-Pekka; Huet, Guillaume; Vartiainen, Maria K

    2013-10-01

    A number of studies in the last decade have irrevocably promoted actin into a fully fledged member of the nuclear compartment, where it, among other crucial tasks, facilitates transcription and chromatin remodeling. Changes in nuclear actin levels have been linked to different cellular processes: decreased nuclear actin to quiescence and increased nuclear actin to differentiation. Importin 9 and exportin 6 transport factors are responsible for the continuous nucleocytoplasmic shuttling of actin, but the mechanisms, which result in modulated actin levels, have not been characterized. We find that in cells growing under normal growth conditions, the levels of nuclear actin vary considerably from cell to cell. To understand the basis for this, we have extensively quantified several cellular parameters while at the same time recording the import and export rates of green fluorescent protein (GFP)-tagged actin. Surprisingly, our dataset shows that the ratio of nuclear to cytoplasmic fluorescence intensity, but not nuclear shape, size, cytoplasm size, or their ratio, correlates negatively with both import and export rate of actin. This suggests that high-nuclear actin content is maintained by both diminished import and export. The high nuclear actin containing cells still show high mobility of actin, but it is not export competent, suggesting increased binding of actin to nuclear complexes. Creation of such export incompetent actin pool would ensure enough actin is retained in the nucleus and make it available for the various nuclear functions described for actin. PMID:23749625

  9. Efficient flapping flight of pterosaurs

    Strang, Karl Axel

    In the late eighteenth century, humans discovered the first pterosaur fossil remains and have been fascinated by their existence ever since. Pterosaurs exploited their membrane wings in a sophisticated manner for flight control and propulsion, and were likely the most efficient and effective flyers ever to inhabit our planet. The flapping gait is a complex combination of motions that sustains and propels an animal in the air. Because pterosaurs were so large with wingspans up to eleven meters, if they could have sustained flapping flight, they would have had to achieve high propulsive efficiencies. Identifying the wing motions that contribute the most to propulsive efficiency is key to understanding pterosaur flight, and therefore to shedding light on flapping flight in general and the design of efficient ornithopters. This study is based on published results for a very well-preserved specimen of Coloborhynchus robustus, for which the joints are well-known and thoroughly described in the literature. Simplifying assumptions are made to estimate the characteristics that can not be inferred directly from the fossil remains. For a given animal, maximizing efficiency is equivalent to minimizing power at a given thrust and speed. We therefore aim at finding the flapping gait, that is the joint motions, that minimize the required flapping power. The power is computed from the aerodynamic forces created during a given wing motion. We develop an unsteady three-dimensional code based on the vortex-lattice method, which correlates well with published results for unsteady motions of rectangular wings. In the aerodynamic model, the rigid pterosaur wing is defined by the position of the bones. In the aeroelastic model, we add the flexibility of the bones and of the wing membrane. The nonlinear structural behavior of the membrane is reduced to a linear modal decomposition, assuming small deflections about the reference wing geometry. The reference wing geometry is computed for

  10. Effects of leading-edge flap oscillation on unsteady delta wing flow and rock control

    Kandil, Osama A.; Salman, Ahmed A.

    1991-01-01

    The isolated and interdisciplinary problems of unsteady fluid dynamics and rigid-body dynamics and control of delta wings with and without leading-edge flap oscillation are considered. For the fluid dynamics problem, the unsteady, compressible, thin-layer Navier-Stokes (NS) equations, which are written relative to a moving frame of reference, are solved along with the unsteady, linearized, Navier-displacement (ND) equations. The NS equations are solved for the flowfield using an implicit finite-volume scheme. The ND equations are solved for the grid deformation, if the leading-edge flaps oscillate, using an ADI scheme. For the dynamics and control problem, the Euler equation of rigid-body rolling motion for a wing and its flaps are solved interactively with the fluid dynamics equations for the wing-rock motion and subsequently for its control. A four-stage Runge-Kutta scheme is used to explicitly integrate the dynamics equation.

  11. A new twist on gyroscopic sensing: body rotations lead to torsion in flapping, flexing insect wings.

    Eberle, A L; Dickerson, B H; Reinhall, P G; Daniel, T L

    2015-03-01

    Insects perform fast rotational manoeuvres during flight. While two insect orders use flapping halteres (specialized organs evolved from wings) to detect body dynamics, it is unknown how other insects detect rotational motions. Like halteres, insect wings experience gyroscopic forces when they are flapped and rotated and recent evidence suggests that wings might indeed mediate reflexes to body rotations. But, can gyroscopic forces be detected using only changes in the structural dynamics of a flapping, flexing insect wing? We built computational and robotic models to rotate a flapping wing about an axis orthogonal to flapping. We recorded high-speed video of the model wing, which had a flexural stiffness similar to the wing of the Manduca sexta hawkmoth, while flapping it at the wingbeat frequency of Manduca (25 Hz). We compared the three-dimensional structural dynamics of the wing with and without a 3 Hz, 10° rotation about the yaw axis. Our computational model revealed that body rotation induces a new dynamic mode: torsion. We verified our result by measuring wing tip displacement, shear strain and normal strain of the robotic wing. The strains we observed could stimulate an insect's mechanoreceptors and trigger reflexive responses to body rotations. PMID:25631565

  12. The IpaC carboxyterminal effector domain mediates Src-dependent actin polymerization during Shigella invasion of epithelial cells

    Mounier, Joëlle; Popoff, Michel R.; Enninga, Jost; Frame, Margaret C; Sansonetti, Philippe J.; Van Nhieu, Guy Tran

    2009-01-01

    Shigella, the causative agent of bacillary dysentery, invades epithelial cells by locally reorganizing the actin cytoskeleton. Shigella invasion requires actin polymerization dependent on the Src tyrosine kinase and a functional bacterial type III secretion (T3S) apparatus. Using dynamic as well as immunofluorescence microscopy, we show that the T3S translocon component IpaC allows the recruitment of the Src kinase required for actin polymerization at bacterial entry sites during the initial ...

  13. The IpaC Carboxyterminal Effector Domain Mediates Src-Dependent Actin Polymerization during Shigella Invasion of Epithelial Cells

    Mounier, Joëlle; Popoff, Michel R.; Enninga, Jost; Frame, Margaret C; Sansonetti, Philippe J.; Van Nhieu, Guy Tran

    2009-01-01

    Shigella, the causative agent of bacillary dysentery, invades epithelial cells by locally reorganizing the actin cytoskeleton. Shigella invasion requires actin polymerization dependent on the Src tyrosine kinase and a functional bacterial type III secretion (T3S) apparatus. Using dynamic as well as immunofluorescence microscopy, we show that the T3S translocon component IpaC allows the recruitment of the Src kinase required for actin polymerization at bacterial entry sites during the initial ...

  14. Uncertainty Analysis for a Jet Flap Airfoil

    Green, Lawrence L.; Cruz, Josue

    2006-01-01

    An analysis of variance (ANOVA) study was performed to quantify the potential uncertainties of lift and pitching moment coefficient calculations from a computational fluid dynamics code, relative to an experiment, for a jet flap airfoil configuration. Uncertainties due to a number of factors including grid density, angle of attack and jet flap blowing coefficient were examined. The ANOVA software produced a numerical model of the input coefficient data, as functions of the selected factors, to a user-specified order (linear, 2-factor interference, quadratic, or cubic). Residuals between the model and actual data were also produced at each of the input conditions, and uncertainty confidence intervals (in the form of Least Significant Differences or LSD) for experimental, computational, and combined experimental / computational data sets were computed. The LSD bars indicate the smallest resolvable differences in the functional values (lift or pitching moment coefficient) attributable solely to changes in independent variable, given just the input data points from selected data sets. The software also provided a collection of diagnostics which evaluate the suitability of the input data set for use within the ANOVA process, and which examine the behavior of the resultant data, possibly suggesting transformations which should be applied to the data to reduce the LSD. The results illustrate some of the key features of, and results from, the uncertainty analysis studies, including the use of both numerical (continuous) and categorical (discrete) factors, the effects of the number and range of the input data points, and the effects of the number of factors considered simultaneously.

  15. Actomyosin contraction, aggregation and traveling waves in a treadmilling actin array

    Oelz, Dietmar; Mogilner, Alex

    2016-04-01

    We use perturbation theory to derive a continuum model for the dynamic actomyosin bundle/ring in the regime of very strong crosslinking. Actin treadmilling is essential for contraction. Linear stability analysis and numerical solutions of the model equations reveal that when the actin treadmilling is very slow, actin and myosin aggregate into equidistantly spaced peaks. When treadmilling is significant, actin filament of one polarity are distributed evenly, while filaments of the opposite polarity develop a shock wave moving with the treadmilling velocity. Myosin aggregates into a sharp peak surfing the crest of the actin wave. Any actomyosin aggregation diminishes contractile stress. The easiest way to maintain higher contraction is to upregulate the actomyosin turnover which destabilizes nontrivial patterns and stabilizes the homogeneous actomyosin distributions. We discuss the model's implications for the experiment.

  16. Stability of actin-lysozyme complexes formed in cystic fibrosis disease.

    Mohammadinejad, Sarah; Ghamkhari, Behnoush; Abdolmaleki, Sarah

    2016-08-21

    Finding the conditions for destabilizing actin-lysozyme complexes is of biomedical importance in preventing infections in cystic fibrosis. In this manuscript, the effects of different charge-mutants of lysozyme and salt concentration on the stability of actin-lysozyme complexes are studied using Langevin dynamics simulation. A coarse-grained model of F-actin is used in which both its twist and bending rigidities are considered. We observe that the attraction between F-actins is stronger in the presence of wild-type lysozymes relative to the mutated lysozymes of lower charges. By calculating the potential of mean force between F-actins, we conclude that the stability of actin-lysozyme complexes is decreased by reducing the charge of lysozyme mutants. The distributions of different lysozyme charge-mutants show that wild-type (+9e) lysozymes are mostly accumulated in the center of triangles formed by three adjacent F-actins, while lysozyme mutants of charges +7e and +5e occupy the bridging regions between F-actins. Low-charge mutants of lysozyme (+3e) distribute uniformly around F-actins. A rough estimate of the electrostatic energy for these different distributions proves that the distribution in which lysozymes reside in the center of triangles leads to more stable complexes. Also our results in the presence of a salt suggest that at physiological salt concentration of airway, F-actin complexes are not formed by charge-reduced mutants of lysozyme. The findings are interesting because if we can design charge-reduced lysozyme mutants with considerable antibacterial activity, they are not sequestered inside F-actin aggregates and can play their role as antibacterial agents against airway infection. PMID:27436705

  17. Alpha-herpesvirus infection induces the formation of nuclear actin filaments.

    Feierbach, Becket; Piccinotti, Silvia; Bisher, Margaret; Denk, Winfried; Enquist, Lynn W

    2006-08-01

    Herpesviruses are large double-stranded DNA viruses that replicate in the nuclei of infected cells. Spatial control of viral replication and assembly in the host nucleus is achieved by the establishment of nuclear compartments that serve to concentrate viral and host factors. How these compartments are established and maintained remains poorly understood. Pseudorabies virus (PRV) is an alpha-herpesvirus often used to study herpesvirus invasion and spread in the nervous system. Here, we report that PRV and herpes simplex virus type 1 infection of neurons results in formation of actin filaments in the nucleus. Filamentous actin is not found in the nucleus of uninfected cells. Nuclear actin filaments appear physically associated with the viral capsids, as shown by serial block-face scanning electron micropscopy and confocal microscopy. Using a green fluorescent protein-tagged viral capsid protein (VP26), we show that nuclear actin filaments form prior to capsid assembly and are required for the efficient formation of viral capsid assembly sites. We find that actin polymerization dynamics (e.g., treadmilling) are not necessary for the formation of these sites. Green fluorescent protein-VP26 foci co-localize with the actin motor myosin V, suggesting that viral capsids travel along nuclear actin filaments using myosin-based directed transport. Viral transcription, but not viral DNA replication, is required for actin filament formation. The finding that infection, by either PRV or herpes simplex virus type 1, results in formation of nuclear actin filaments in neurons, and that PRV infection of an epithelial cell line results in a similar phenotype is evidence that F-actin plays a conserved role in herpesvirus assembly. Our results suggest a mechanism by which assembly domains are organized within infected cells and provide insight into how the viral infectious cycle and host actin cytoskeleton are integrated to promote the infection process. PMID:16933992

  18. Membrane Supply and Demand Regulates F-Actin in a Cell Surface Reservoir.

    Figard, Lauren; Wang, Mengyu; Zheng, Liuliu; Golding, Ido; Sokac, Anna Marie

    2016-05-01

    Cells store membrane in surface reservoirs of pits and protrusions. These membrane reservoirs facilitate cell shape change and buffer mechanical stress, but we do not know how reservoir dynamics are regulated. During cellularization, the first cytokinesis in Drosophila embryos, a reservoir of microvilli unfolds to fuel cleavage furrow ingression. We find that regulated exocytosis adds membrane to the reservoir before and during unfolding. Dynamic F-actin deforms exocytosed membrane into microvilli. Single microvilli extend and retract in ∼20 s, while the overall reservoir is depleted in sync with furrow ingression over 60-70 min. Using pharmacological and genetic perturbations, we show that exocytosis promotes microvillar F-actin assembly, while furrow ingression controls microvillar F-actin disassembly. Thus, reservoir F-actin and, consequently, reservoir dynamics are regulated by membrane supply from exocytosis and membrane demand from furrow ingression. PMID:27165556

  19. The need for higher-order averaging in the stability analysis of hovering, flapping-wing flight

    Because of the relatively high flapping frequency associated with hovering insects and flapping wing micro-air vehicles (FWMAVs), dynamic stability analysis typically involves direct averaging of the time-periodic dynamics over a flapping cycle. However, direct application of the averaging theorem may lead to false conclusions about the dynamics and stability of hovering insects and FWMAVs. Higher-order averaging techniques may be needed to understand the dynamics of flapping wing flight and to analyze its stability. We use second-order averaging to analyze the hovering dynamics of five insects in response to high-amplitude, high-frequency, periodic wing motion. We discuss the applicability of direct averaging versus second-order averaging for these insects. (paper)

  20. The need for higher-order averaging in the stability analysis of hovering, flapping-wing flight.

    Taha, Haithem E; Tahmasian, Sevak; Woolsey, Craig A; Nayfeh, Ali H; Hajj, Muhammad R

    2015-01-01

    Because of the relatively high flapping frequency associated with hovering insects and flapping wing micro-air vehicles (FWMAVs), dynamic stability analysis typically involves direct averaging of the time-periodic dynamics over a flapping cycle. However, direct application of the averaging theorem may lead to false conclusions about the dynamics and stability of hovering insects and FWMAVs. Higher-order averaging techniques may be needed to understand the dynamics of flapping wing flight and to analyze its stability. We use second-order averaging to analyze the hovering dynamics of five insects in response to high-amplitude, high-frequency, periodic wing motion. We discuss the applicability of direct averaging versus second-order averaging for these insects. PMID:25561166

  1. The Actin-Binding Protein α-Adducin Is Required for Maintaining Axon Diameter

    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.

  2. Actinic Keratoses: A Comprehensive Update

    Ibrahim, Sherrif F.; Brown, Marc D.

    2009-01-01

    Actinic keratoses are common intra-epidermal neoplasms that lie on a continuum with squamous cell carcinoma. Tightly linked to ultraviolet irradiation, they occur in areas of chronic sun exposure, and early treatment of these lesions may prevent their progression to invasive disease. A large variety of effective treatment modalities exist, and the optimal therapeutic choice is dependent on a variety of patient- and physician-associated variables. Many established and more recent approaches ar...

  3. The possibility for use of venous flaps in plastic surgery

    The use of venous flaps is controversial. The mechanism of perfusion of venous flaps is still not fully understood. The research was conducted on 56 white rats. In our experimental work we studied two different models of venous flaps: pedicled venous flap (PVF) and pedicled arterialized venous flap (PAVF). Our results showed that postoperative congestion was present in all flaps. However 66.7% of all pedicled venous flaps and 100% of all pedicled arterialized venous flaps eventually survived. Histological examination revealed that postoperatively the blood flow in the skin of the pedicled arterialized venous flap became «re-reversed» again; there were no differences between mechanism of survival of venous flaps and other flaps. On the 7-14th day in the skin of all flaps were processes of neoangiogenesis and proliferation. Hence the best scenario for the clinical use of venous flaps unfolds when both revascularization and skin coverage are required

  4. The possibility for use of venous flaps in plastic surgery

    Baytinger, V. F.; Kurochkina, O. S.; Selianinov, K. V.; Baytinger, A. V.; Dzyuman, A. N.

    2015-11-01

    The use of venous flaps is controversial. The mechanism of perfusion of venous flaps is still not fully understood. The research was conducted on 56 white rats. In our experimental work we studied two different models of venous flaps: pedicled venous flap (PVF) and pedicled arterialized venous flap (PAVF). Our results showed that postoperative congestion was present in all flaps. However 66.7% of all pedicled venous flaps and 100% of all pedicled arterialized venous flaps eventually survived. Histological examination revealed that postoperatively the blood flow in the skin of the pedicled arterialized venous flap became «re-reversed» again; there were no differences between mechanism of survival of venous flaps and other flaps. On the 7-14th day in the skin of all flaps were processes of neoangiogenesis and proliferation. Hence the best scenario for the clinical use of venous flaps unfolds when both revascularization and skin coverage are required.

  5. The possibility for use of venous flaps in plastic surgery

    Baytinger, V. F., E-mail: baitinger@mail.tomsknet.ru; Kurochkina, O. S., E-mail: kurochkinaos@yandex.ru; Selianinov, K. V.; Baytinger, A. V. [Research Institute of Microsurgery, Tomsk (Russian Federation); Dzyuman, A. N. [Siberian State Medical University, Tomsk (Russian Federation)

    2015-11-17

    The use of venous flaps is controversial. The mechanism of perfusion of venous flaps is still not fully understood. The research was conducted on 56 white rats. In our experimental work we studied two different models of venous flaps: pedicled venous flap (PVF) and pedicled arterialized venous flap (PAVF). Our results showed that postoperative congestion was present in all flaps. However 66.7% of all pedicled venous flaps and 100% of all pedicled arterialized venous flaps eventually survived. Histological examination revealed that postoperatively the blood flow in the skin of the pedicled arterialized venous flap became «re-reversed» again; there were no differences between mechanism of survival of venous flaps and other flaps. On the 7-14th day in the skin of all flaps were processes of neoangiogenesis and proliferation. Hence the best scenario for the clinical use of venous flaps unfolds when both revascularization and skin coverage are required.

  6. Modelling phagosomal lipid networks that regulate actin assembly

    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

  7. From pollen actin to crop male sterility

    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.

  8. Mesoscopic model of actin-based propulsion.

    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. Effects of torsion frequencies on rotor performance and structural loads with trailing edge flap

    The effects of variation of blade torsion frequency on rotor performance and structural loads are investigated for a 1/rev active flap rotor and baseline rotor (no active control). The UH-60A four-bladed articulated main rotor is studied at a high-speed forward flight condition. The torsion frequencies are varied by modifying the spanwise torsional stiffness of the blade and/or the pitch link stiffness. First, a parametric/optimization study on the flap deployment schedule is carried out using lifting-line comprehensive analysis for the soft, baseline, and stiff rotor configurations, and then a higher fidelity coupled computational fluid dynamics–computational structural dynamics analysis is carried out for the optimal flap deployment. It is shown that with the soft rotor there is degradation in performance—of about 6% with respect to the baseline rotor in the case where the flaps are not activated, and of about 1% if flap deflections are applied. On the other hand, for the stiff rotor there is a slight improvement in performance of about 2.3% when the flaps are not activated, and no appreciable change in the case where active flap deflections are applied. It appears that the peak performance achievable with using active flaps on a baseline stiffness rotor cannot be further improved significantly by varying the torsional frequencies. Variation of torsion frequency does not appear to have a significant influence on blade torsion moments and pitch link loads, although the 1/rev flap activation examined has an important role. (paper)

  10. Aerodynamic response of an airfoil section undergoing pitch motion and trailing edge flap deflection: a comparison of simulation methods

    Bergami, Leonardo; Riziotis, Vasilis A.; Gaunaa, Mac

    2015-01-01

    generated by the airfoil undergoing harmonic pitching motions and harmonic flap deflections. The unsteady aerodynamic coefficients exhibit significant variations over the corresponding steady-state values. The dynamic characteristics of the unsteady response are predicted with an excellent agreement among...

  11. Differential Effects of Caldesmon on the Intermediate Conformational States of Polymerizing Actin*

    Huang, Renjian; Grabarek, Zenon; Wang, Chih-Lueh Albert

    2009-01-01

    The actin-binding protein caldesmon (CaD) reversibly inhibits smooth muscle contraction. In non-muscle cells, a shorter CaD isoform co-exists with microfilaments in the stress fibers at the quiescent state, but the phosphorylated CaD is found at the leading edge of migrating cells where dynamic actin filament remodeling occurs. We have studied the effect of a C-terminal fragment of CaD (H32K) on the kinetics of the in vitro actin polymerization by monitoring the fluorescence of pyrene-labeled...

  12. Comparison of heaving buoy and oscillating flap wave energy converters

    Abu Bakar, Mohd Aftar; Green, David A.; Metcalfe, Andrew V.; Najafian, G.

    2013-04-01

    Waves offer an attractive source of renewable energy, with relatively low environmental impact, for communities reasonably close to the sea. Two types of simple wave energy converters (WEC), the heaving buoy WEC and the oscillating flap WEC, are studied. Both WECs are considered as simple energy converters because they can be modelled, to a first approximation, as single degree of freedom linear dynamic systems. In this study, we estimate the response of both WECs to typical wave inputs; wave height for the buoy and corresponding wave surge for the flap, using spectral methods. A nonlinear model of the oscillating flap WEC that includes the drag force, modelled by the Morison equation is also considered. The response to a surge input is estimated by discrete time simulation (DTS), using central difference approximations to derivatives. This is compared with the response of the linear model obtained by DTS and also validated using the spectral method. Bendat's nonlinear system identification (BNLSI) technique was used to analyze the nonlinear dynamic system since the spectral analysis was only suitable for linear dynamic system. The effects of including the nonlinear term are quantified.

  13. Mechanosensitive kinetic preference of actin-binding protein to actin filament

    Inoue, Yasuhiro; Adachi, Taiji

    2016-04-01

    The kinetic preference of actin-binding proteins to actin filaments is altered by external forces on the filament. Such an altered kinetic preference is largely responsible for remodeling the actin cytoskeletal structure in response to intracellular forces. During remodeling, actin-binding proteins and actin filaments interact under isothermal conditions, because the cells are homeostatic. In such a temperature homeostatic state, we can rigorously and thermodynamically link the chemical potential of actin-binding proteins to stresses on the actin filaments. From this relationship, we can construct a physical model that explains the force-dependent kinetic preference of actin-binding proteins to actin filaments. To confirm the model, we have analyzed the mechanosensitive alternation of the kinetic preference of Arp2/3 and cofilin to actin filaments. We show that this model captures the qualitative responses of these actin-binding proteins to the forces, as observed experimentally. Moreover, our theoretical results demonstrate that, depending on the structural parameters of the binding region, actin-binding proteins can show different kinetic responses even to the same mechanical signal tension, in which the double-helix nature of the actin filament also plays a critical role in a stretch-twist coupling of the filament.

  14. Adjoint-based optimization of flapping plates hinged with a trailing-edge flap

    Min Xu

    2015-01-01

    Full Text Available It is important to understand the impact of wing-morphing on aerodynamic performance in the study of flapping-wing flight of birds and insects. We use a flapping plate hinged with a trailing-edge flap as a simplified model for flexible/morphing wings in hovering. The trailing-edge flapping motion is optimized by an adjoint-based approach. The optimized configuration suggests that the trailing-edge flap can substantially enhance the overall lift. Further analysis indicates that the lift enhancement by the trailing-edge flapping is from the change of circulation in two ways: the local circulation change by the rotational motion of the flap, and the modification of vortex shedding process by the relative location between the trailing-edge flap and leading-edge main plate.

  15. Actin gene family in Branchiostoma belched

    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.

  16. Prokaryotic DNA segregation by an actin-like filament

    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...... point for ParM polymerization. Hence, we provide evidence for a simple prokaryotic analogue of the eukaryotic mitotic spindle apparatus....

  17. Internal Motility in Stiffening Actin-Myosin Networks

    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 sug...

  18. Development of an improved aeroelastic model for the investigation of vibration reduction in helicopter rotors using trailing edge flaps

    Myrtle, Timothy Fitzgerald

    1998-12-01

    This dissertation describes the development of an aeroelastic model of a helicopter rotor incorporating partial span trailing edge flaps on the blade and its application to the investigation of vibration reduction using active control. A new two-dimensional unsteady aerodynamic model for an airfoil/flap combination is described that includes compressibility and unsteady freestream effects. This new aerodynamic model is based on a rational function approximation (RFA) approach. In this approach, oscillatory response data obtained for a selected set of generalized airfoil and flap motions is used to generate an approximate aerodynamic transfer function which can be transformed to the time domain to form a state space aerodynamic model. In this dissertation, a method is described for adapting the conventional RFA approach to include unsteady freestream effects. Excellent agreement is demonstrated between the response of the new aerodynamic model and an exact incompressible solution to the unsteady freestream case. This model provides a complete description of the unsteady flap hinge moments due to airfoil and flap motion, allowing a complete and accurate characterization of control actuation requirements. The structural model utilizes an elastic blade model which includes fully coupled flap-lag-torsional dynamics and includes the effects of moderate deflections. The aeroelastic model is formulated in the time domain, with the coupled trim/response solution obtained using direct numerical integration in combination with autopilot type controller. A conventional higher harmonic control approach is used to investigate vibration reduction. Vibration control studies are performed which compare results using the new aerodynamic model and incompressible quasisteady Theodorsen aerodynamics. Significant differences were observed in the required deflections and control moments, indicating that compressibility and unsteady effects are necessary to properly characterize the

  19. Davis flap: the glory still present

    El-Sabbagh, Ahmed Hassan

    2016-01-01

    Background: Upper third defects of the ear are too large to be closed primarily without distorting the auricle. Full thickness defects can be reconstructed with local flaps. In this article, Davis flap was used to fill the upper third defects of the ear with some modifications. Patients and methods: Eight patients underwent reconstruction of full thickness auricular defects with Davis flaps from July 2012 to December 2014. The posterior surface of the flap and the raw area of conchal area were covered by full thickness graft taken from posterior surface of ear. Results: All flaps survived. No congestion was noted. The donor sites and skin grafts healed uneventfully. Conclusion: Davis flap is a simple and reproducible tool for reconstruction of upper third of ear. PMID:27274439

  20. Probing the role of the actin cytoskeleton during regulated exocytosis by intravital microscopy

    Milberg, Oleg; Tora, Muhibullah; Shitara, Akiko; Masedunskas, Andrius; Weigert, Roberto

    2014-01-01

    The actin cytoskeleton plays a fundamental role in controlling several steps during regulated exocytosis. Here we describe a combination of procedures that are aimed at studying the dynamics and the mechanism of the actin cytoskeleton in the salivary glands of live rodents, a model for exocrine secretion. Our approach relies on intravital microscopy, an imaging technique that enables imaging biological events in live animals at a subcellular resolution, and it is complemented by the use of ph...

  1. Invadosomes - shaping actin networks to follow mechanical cues.

    Kedziora, Katarzyna M; Isogai, Tadamoto; Jalink, Kees; Innocenti, Metello

    2016-01-01

    Invadosomes are actin-based protrusions formed by cells in response to obstacles in their microenvironment, especially basement membranes and dense interstitial matrices. A versatile set of proteins controls assembly and dynamics of the actin networks at invadosomes and adhesive molecules link them with the extracellular matrix. Furthermore, polarized delivery of proteases makes invadosomes degradative. Therefore, invadosomes have been classically viewed as specialized protrusions involved in cell migration and remodeling of the microenvironment. Recent discoveries have considerably broadened this picture by showing that invadosomes respond to traction forces and can self-organize into dynamic arrays capable of following the topography of the substrate. Although these findings suggest that invadosomes may function as mechanosensors, this possibility has not been critically evaluated. In this review, we first summarize the organization and dynamics of actin in invadosomes and their superstructures with emphasis on force-production mechanisms. Next, we outline our current understanding of how mechanical cues impinge on invadosomes and modify their behavior. From this perspective, we provide an outlook of the outstanding open questions and the main challenges in the field. PMID:27100494

  2. Experimental skin flaps and nitric oxide

    Gribbe, Örjan

    2006-01-01

    Abstract. Surgical flaps are used in plastic surgery to reconstruct tissue defects due to trauma or cancer removal. Occasionally flaps are subjected to ischemia and reperfusion injury leading to flap failure. Nitric oxide (NO), a small gaseous molecule, has vast physiological importance as it participates in the regulation of blood pressure, blood flow, neurotransmission and immune response. NO is synthesized by the enzyme NO synthase (NOS), which exists in both constitutiv...

  3. Packaging of actin into Ebola virus VLPs

    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.

  4. Wing flapping with minimum energy

    Jones, R. T.

    1980-01-01

    A technique employed by Prandtl and Munk is adapted for the case of a wing in flapping motion to determine its lift distribution. The problem may be reduced to one of minimizing induced drag for a specified and periodically varying bending moment at the wing root. It is concluded that two wings in close tandem arrangement, moving in opposite phase, would eliminate the induced aerodynamic losses calculated

  5. Optimal propulsive flapping in Stokes flows

    Swimming fish and flying insects use the flapping of fins and wings to generate thrust. In contrast, microscopic organisms typically deform their appendages in a wavelike fashion. Since a flapping motion with two degrees of freedom is able, in theory, to produce net forces from a time-periodic actuation at all Reynolds numbers, we compute in this paper the optimal flapping kinematics of a rigid spheroid in a Stokes flow. The hydrodynamics for the force generation and energetics of the flapping motion is solved exactly. We then compute analytically the gradient of a flapping efficiency in the space of all flapping gaits and employ it to derive numerically the optimal flapping kinematics as a function of the shape of the flapper and the amplitude of the motion. The kinematics of optimal flapping are observed to depend weakly on the flapper shape and are very similar to the figure-eight motion observed in the motion of insect wings. Our results suggest that flapping could be a exploited experimentally as a propulsion mechanism valid across the whole range of Reynolds numbers. (paper)

  6. Optimal propulsive flapping in Stokes flows

    Was, Loic

    2014-01-01

    Swimming fish and flying insects use the flapping of fins and wings to generate thrust. In contrast, microscopic organisms typically deform their appendages in a wavelike fashion. Since a flapping motion with two degrees of freedom is able, in theory, to produce net forces from a time-periodic actuation at all Reynolds number, we compute in this paper the optimal flapping kinematics of a rigid spheroid in a Stokes flow. The hydrodynamics for the force generation and energetics of the flapping motion is solved exactly. We then compute analytically the gradient of a flapping efficiency in the space of all flapping gaits and employ it to derive numerically the optimal flapping kinematics as a function of the shape of the flapper and the amplitude of the motion. The kinematics of optimal flapping are observed to depend weakly on the flapper shape and are very similar to the figure-eight motion observed in the motion of insect wings. Our results suggest that flapping could be a exploited experimentally as a propul...

  7. Inferior Gluteal Perforator Flaps for Breast Reconstruction

    Allen, Robert J.; LoTempio, Maria M.; Granzow, Jay W.

    2006-01-01

    Perforator flaps represent the latest in the evolution of soft tissue flaps. They allow the transfer of the patient's own skin and fat in a reliable manner with minimal donor-site morbidity. The powerful perforator flap concept allows transfer of tissue from numerous, well-described donor sites to almost any distant site with suitable recipient vessels. The inferior gluteal artery perforator (I-GAP) flap is one option that allows a large volume of tissue to be used for breast reconstruction w...

  8. Basic Perforator Flap Hemodynamic Mathematical Model

    Tao, Youlun; Ding, Maochao; Wang, Aiguo; Zhuang, Yuehong; Chang, Shi-Min; Mei, Jin; Hallock, Geoffrey G.

    2016-01-01

    Background: A mathematical model to help explain the hemodynamic characteristics of perforator flaps based on blood flow resistance systems within the flap will serve as a theoretical guide for the future study and clinical applications of these flaps. Methods: There are 3 major blood flow resistance network systems of a perforator flap. These were defined as the blood flow resistance of an anastomosis between artery and artery of adjacent perforasomes, between artery and vein within a perforasome, and then between vein and vein corresponding to the outflow of that perforasome. From this, a calculation could be made of the number of such blood flow resistance network systems that must be crossed for all perforasomes within a perforator flap to predict whether that arrangement would be viable. Results: The summation of blood flow resistance networks from each perforasome in a given perforator flap could predict which portions would likely survive. This mathematical model shows how this is directly dependent on the location of the vascular pedicle to the flap and whether supercharging or superdrainage maneuvers have been added. These configurations will give an estimate of the hemodynamic characteristics for the given flap design. Conclusions: This basic mathematical model can (1) conveniently determine the degree of difficulty for each perforasome within a perforator flap to survive; (2) semiquantitatively allow the calculation of basic hemodynamic parameters; and (3) allow the assessment of the pros and cons expected for each pattern of perforasomes encountered clinically based on predictable hemodynamic observations.

  9. Optimal propulsive flapping in Stokes flows.

    Was, Loïc; Lauga, Eric

    2014-03-01

    Swimming fish and flying insects use the flapping of fins and wings to generate thrust. In contrast, microscopic organisms typically deform their appendages in a wavelike fashion. Since a flapping motion with two degrees of freedom is able, in theory, to produce net forces from a time-periodic actuation at all Reynolds numbers, we compute in this paper the optimal flapping kinematics of a rigid spheroid in a Stokes flow. The hydrodynamics for the force generation and energetics of the flapping motion is solved exactly. We then compute analytically the gradient of a flapping efficiency in the space of all flapping gaits and employ it to derive numerically the optimal flapping kinematics as a function of the shape of the flapper and the amplitude of the motion. The kinematics of optimal flapping are observed to depend weakly on the flapper shape and are very similar to the figure-eight motion observed in the motion of insect wings. Our results suggest that flapping could be a exploited experimentally as a propulsion mechanism valid across the whole range of Reynolds numbers. PMID:24343130

  10. Development and whirl tower test of the SMART active flap rotor

    Straub, Friedrich K.; Kennedy, Dennis K.; Stemple, Alan D.; Anand, V. R.; Birchette, Terry S.

    2004-07-01

    A full scale Smart Material Actuated Rotor Technology (SMART) system with piezoelectric actuated blade flaps was developed and whirl tower tested. The development effort included design, fabrication, and component testing of rotor blades, trailing edge flaps, piezoelectric actuators, switching power amplifiers, and the data/power system. Simulations and model scale wind tunnel tests have shown that this system can provide 80% vibration reduction, 10dB noise reduction for a helicopter passing overhead, and substantial aerodynamic performance gains. Whirl tower testing of the 34-foot diameter rotor demonstrated the functionality, robustness, and required authority of the active flap system. The program involved extensive development work and risk reduction tests which resulted in a robust, high performance actuator and a tightly integrated actuator, flap, and blade system. The actuator demonstrated excellent performance during bench testing and has accumulated over 60 million cycles under a spectrum of loading conditions. The flight worthy active flap rotor blades were based on a modified design of the FAA certified MD900 Explorer production rotor blade. Whirl tower testing was conducted with full rotor instrumentation and a 5-component balance. The rotor was tested for 13 hours under a range of conditions, including 7 hours of flap operation. Flap inputs included open loop static and dynamic commands. The flaps showed excellent authority with oscillatory thrust greater than 10% of the steady baseline thrust. Various flap actuation frequency sweeps were run to investigate the dynamics of the rotor and the flap system. Limited closed loop tests used hub accelerations and hub loads for feedback. Proving the integration, robust operation, and authority of the flap system were the key objectives met by the whirl tower test. This success depended on tailoring the piezoelectric materials and actuator to the application and meeting actuator/blade integration requirements

  11. Hierarchical Cross-linked F-actin Networks: Understanding Structure and Assembly

    Hirst, Linda; Nguyen, Lam

    2009-11-01

    The protein, F-actin provides us with an interesting system in which to investigate the assembly properties of semi-flexible filaments in the presence of cross-linkers. Recently it was observed that F-actin, in the presence of the cross-linker alpha-actinin at high molar ratios will generate a novel hierarchical network of filament bundles. We investigate this system using coarse-grained molecular dynamics (MD) simulation, confocal microscopy and x-ray scattering. We have studied the F-actin/alpha-actinin system in detail with different actin conc. (C) and alpha-actinin/actin molar ratios (gamma). Confocal microscopy and analysis shows that the assembled systems fall into one of 3 phases depending on C and gamma: (1) loosely connected network of F-actin and bundles, (2) loosely connected network of dense domains and (3) uniform network of bundles. This can be explained and replicated using MD simulation. We have also examined different types of cross-linkers to represent the proteins, fascin and filamin. Results show that phase formation is related to the flexibility in binding between F-actin and cross-linkers. This degree of freedom, possible with longer cross-linkers allows the formation of branch points and thus bundle networks.

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

    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.

  13. The Actin Filament-Binding Protein Coronin Regulates Motility in Plasmodium Sporozoites

    Bane, Kartik S.; Singer, Mirko; Reinig, Miriam; Klug, Dennis; Heiss, Kirsten; Baum, Jake; Mueller, Ann-Kristin; Frischknecht, Friedrich

    2016-01-01

    Parasites causing malaria need to migrate in order to penetrate tissue barriers and enter host cells. Here we show that the actin filament-binding protein coronin regulates gliding motility in Plasmodium berghei sporozoites, the highly motile forms of a rodent malaria-causing parasite transmitted by mosquitoes. Parasites lacking coronin show motility defects that impair colonization of the mosquito salivary glands but not migration in the skin, yet result in decreased transmission efficiency. In non-motile sporozoites low calcium concentrations mediate actin-independent coronin localization to the periphery. Engagement of extracellular ligands triggers an intracellular calcium release followed by the actin-dependent relocalization of coronin to the rear and initiation of motility. Mutational analysis and imaging suggest that coronin organizes actin filaments for productive motility. Using coronin-mCherry as a marker for the presence of actin filaments we found that protein kinase A contributes to actin filament disassembly. We finally speculate that calcium and cAMP-mediated signaling regulate a switch from rapid parasite motility to host cell invasion by differentially influencing actin dynamics. PMID:27409081

  14. Force of an actin spring

    Shin, Jennifer; Mahadevan, L.; Matsudaira, Paul

    2003-03-01

    The acrosomal process of the horseshoe crab sperm is a novel mechanochemical molecular spring that converts its elastic stain energy to mechanical work upon the chemical activation by Ca2+. Twisted and bent, the initial state of the acrosomal bundle features a high degree of complexity in its structure and the energy is believed to be stored in the highly strained actin filaments as an elastic potential energy. When activated, the bundle relaxes from the coil of the highly twisted and bent filaments to its straight conformation at a mean velocity of 15um/s. The mean extension velocity increases dramatically from 3um/s to 27um/s when temperature of the medium is changed from 9.6C to 32C (respective viscosities of 1.25-0.75cp), yet it exhibits a very weak dependence on changes in the medium viscosity (1cp-33cp). These experiments suggest that the uncoiling of the actin spring should be limited not by the viscosity of the medium but by the unlatching events of involved proteins at a molecular level. Unlike the viscosity-limited processes, where force is directly related to the rate of the reaction, a direct measurement is required to obtain the spring force of the acrosomal process. The extending acrosomal bundle is forced to push against a barrier and its elastic buckling response is analyzed to measure the force generated during the uncoiling.

  15. Nonlinear flap-lag axial equations of a rotating beam

    Kaza, K. R. V.; Kvaternik, R. G.

    1977-01-01

    It is possible to identify essentially four approaches by which analysts have established either the linear or nonlinear governing equations of motion for a particular problem related to the dynamics of rotating elastic bodies. The approaches include the effective applied load artifice in combination with a variational principle and the use of Newton's second law, written as D'Alembert's principle, applied to the deformed configuration. A third approach is a variational method in which nonlinear strain-displacement relations and a first-degree displacement field are used. The method introduced by Vigneron (1975) for deriving the linear flap-lag equations of a rotating beam constitutes the fourth approach. The reported investigation shows that all four approaches make use of the geometric nonlinear theory of elasticity. An alternative method for deriving the nonlinear coupled flap-lag-axial equations of motion is also discussed.

  16. A radioimmunoassay for determination of anti-actin antibodies

    The reaction of spontaneously occurring human anti-actin antibodies and experimentally produced rabbit anti-actin antibodies was investigated in a solid-phase radioimmunoassay (RIA). Three structurally different in vitro forms of actin, monomeric G-actin, filamentous F-actin and aggregated denatured actin were used as antigens. Human anti-actin antibodies reacted with F- and G-actin but not with aggregated actin, while rabbit anti-actin antibodies gave a strong reaction with all 3 forms of actin indicating differences in antibody specificities. The results of the anti-actin RIA were compared with those obtained by indirect immunofluorescence (IFL) on cryostat sections of rat stomach. The anti-actin RIA discriminated between patients' sera and control sera in most cases, although the indirect IFL test gave more conclusive results. The seemingly low sensitivity of the anti-actin RIA compared with that of indirect IFL test for detection of human anti-actin antibodies is probably due to favourable antigen distribution in tissue, not available in the solid phase. The anti-actin RIA was able to detect anti-actin antibodies in 8 out of 8 immunized rabbits although only two produced antibodies detectable by indirect IFL. The differences in reactivity between the two methods may depend on the presence of aggregated denatured actin in the antigen preparation used for immunization and exposure of the corresponding antigenic determinants of actin on the solid phase. (Auth.)

  17. Papaverine Prevents Vasospasm by Regulation of Myosin Light Chain Phosphorylation and Actin Polymerization in Human Saphenous Vein

    Hocking, Kyle M.; Putumbaka, Gowthami; Wise, Eric S.; Cheung-Flynn, Joyce; Brophy, Colleen M.; Komalavilas, Padmini

    2016-01-01

    Objective Papaverine is used to prevent vasospasm in human saphenous veins (HSV) during vein graft preparation prior to implantation as a bypass conduit. Papaverine is a nonspecific inhibitor of phosphodiesterases, leading to increases in both intracellular cGMP and cAMP. We hypothesized that papaverine reduces force by decreasing intracellular calcium concentrations ([Ca2+]i) and myosin light chain phosphorylation, and increasing actin depolymerization via regulation of actin regulatory protein phosphorylation. Approach and Results HSV was equilibrated in a muscle bath, pre-treated with 1 mM papaverine followed by 5 μM norepinephrine, and force along with [Ca2+]i levels were concurrently measured. Filamentous actin (F-actin) level was measured by an in vitro actin assay. Tissue was snap frozen to measure myosin light chain and actin regulatory protein phosphorylation. Pre-treatment with papaverine completely inhibited norepinephrine-induced force generation, blocked increases in [Ca2+]i and led to a decrease in the phosphorylation of myosin light chain. Papaverine pre-treatment also led to increased phosphorylation of the heat shock-related protein 20 (HSPB6) and the vasodilator stimulated phosphoprotein (VASP), as well as decreased filamentous actin (F-actin) levels suggesting depolymerization of actin. Conclusions These results suggest that papaverine-induced force inhibition of HSV involves [Ca2+]i-mediated inhibition of myosin light chain phosphorylation and actin regulatory protein phosphorylation-mediated actin depolymerization. Thus, papaverine induces sustained inhibition of contraction of HSV by the modulation of both myosin cross-bridge formation and actin cytoskeletal dynamics and is a pharmacological alternative to high pressure distention to prevent vasospasm. PMID:27136356

  18. Differential effects of LifeAct-GFP and actin-GFP on cell mechanics assessed using micropipette aspiration.

    Sliogeryte, Kristina; Thorpe, Stephen D; Wang, Zhao; Thompson, Clare L; Gavara, Nuria; Knight, Martin M

    2016-01-25

    The actin cytoskeleton forms a dynamic structure involved in many fundamental cellular processes including the control of cell morphology, migration and biomechanics. Recently LifeAct-GFP (green fluorescent protein) has been proposed for visualising actin structure and dynamics in live cells as an alternative to actin-GFP which has been shown to affect cell mechanics. Here we compare the two approaches in terms of their effect on cellular mechanical behaviour. Human mesenchymal stem cells (hMSCs) were analysed using micropipette aspiration and the effective cellular equilibrium and instantaneous moduli calculated using the standard linear solid model. We show that LifeAct-GFP provides clearer visualisation of F-actin organisation and dynamics. Furthermore, LifeAct-GFP does not alter effective cellular mechanical properties whereas actin-GFP expression causes an increase in the cell modulus. Interestingly, LifeAct-GFP expression did produce a small (~10%) increase in the percentage of cells exhibiting aspiration-induced membrane bleb formation, whilst actin-GFP expression reduced blebbing. Further studies examined the influence of LifeAct-GFP in other cell types, namely chondrogenically differentiated hMSCs and murine chondrocytes. LifeAct-GFP also had no effect on the moduli of these non-blebbing cells for which mechanical properties are largely dependent on the actin cortex. In conclusion we show that LifeAct-GFP enables clearer visualisation of actin organisation and dynamics without disruption of the biomechanical properties of either the whole cell or the actin cortex. Thus the study provides new evidence supporting the use of LifeAct-GFP rather than actin-GFP for live cell microscopy and the study of cellular mechanobiology. PMID:26792287

  19. [The super extended sub-mental flap or combo sub-mental flap].

    Martin, D

    2014-08-01

    The author presents a technical variation of the sub-mental flap including in a conventional pedicled flap both sub-mental axes and their anastomoses on the midline. The assessment of the first flaps raised according to this method confirms the improvement of the distal blood supply. It allows the possibility to harvest "super extended" flaps reaching the contralateral auricular lobula. This variation can be considered as an axial flap which only the tip, located beyond the mandibular angle, is at random. The evolution of the sub-mental flap from its original description to this variation called "combo sub-mental flap" is then presented. Its reliability and the technical simplification it provides will have to be assessed in the future. PMID:24840945

  20. Secondary onlay free flap reconstruction of glossectomy defects following initial successful flap restoration.

    Rihani, Jordan; Lee, Thomas; Ducic, Yadranko

    2013-08-01

    Patients who undergo tongue reconstruction over time may develop gradual worsening of dysarthria and dysphagia secondary to flap atrophy. At our institution, these patients undergo a secondary flap onlay procedure for augmentation of the neotongue. We review a total of 11 patients with total glossectomy defect who underwent secondary tongue augmentation with secondary onlay free flap consisting of radial forearm free flap (n = 6) and rectus free flap (n = 5). There was improvement in swallowing in 7 of 11 patients. Five (45.4%) patients achieved gastric tube independence. Seven (63.6%) patients achieved a varying degree of oral intake. All patients achieved tracheostomy independence. Dysarthria was improved in all patients. There were no flap failures. Therefore, a secondary onlay flap technique is feasible and may improve dysphagia and dysarthria to achieve gastric tube and tracheostomy independence in total glossectomy patients with delayed tongue atrophy. PMID:23625797

  1. Actin-based propulsion of spatially extended objects

    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.

  2. Actin as deathly switch? How auxin can suppress cell-death related defence.

    Xiaoli Chang

    Full Text Available Plant innate immunity is composed of two layers--a basal immunity, and a specific effector-triggered immunity, which is often accompanied by hypersensitive cell death. Initiation of cell death depends on a complex network of signalling pathways. The phytohormone auxin as central regulator of plant growth and development represents an important component for the modulation of plant defence. In our previous work, we showed that cell death is heralded by detachment of actin from the membrane. Both, actin response and cell death, are triggered by the bacterial elicitor harpin in grapevine cells. In this study we investigated, whether harpin-triggered actin bundling is necessary for harpin-triggered cell death. Since actin organisation is dependent upon auxin, we used different auxins to suppress actin bundling. Extracellular alkalinisation and transcription of defence genes as the basal immunity were examined as well as cell death. Furthermore, organisation of actin was observed in response to pharmacological manipulation of reactive oxygen species and phospholipase D. We find that induction of defence genes is independent of auxin. However, auxin can suppress harpin-induced cell death and also counteract actin bundling. We integrate our findings into a model, where harpin interferes with an auxin dependent pathway that sustains dynamic cortical actin through the activity of phospholipase D. The antagonism between growth and defence is explained by mutual competition for signal molecules such as superoxide and phosphatidic acid. Perturbations of the auxin-actin pathway might be used to detect disturbed integrity of the plasma membrane and channel defence signalling towards programmed cell death.

  3. Thumb Reconstruction Using Foucher’s Flap

    Kola, Nardi

    2016-01-01

    BACKGROUND: Extensive pulp defects of the thumb, with the exposure of tendon or bone, are challenging reconstructive problems. Surgical treatment includes the use of local, regional, and free flaps. AIM: This paper is focused in Foucher’s neuro vascular flap. First DMCA or Foucher’s pedicle flap is a successful thumb reconstruction method, especially in patients not disturbed by its cosmetic appearance. MATERIAL AND METHODS: The first dorsal metacarpal artery (FDMCA) arises from the radial artery in the first intermetacarpal space, just distal to the tendon of the extensor pollicis longus. Pulp area of the thumb is the area where Foucher’s flap is more utilizable. This technique has other applications such as first web reconstruction, thumb lengthening, and following resection of tumors on the dorsum of the hand. RESULTS: We have in study 7 cases with work related trauma in two years period of time, between 2012 and 2014. We had only one partial flap survival and all the other flaps survived entirely. We have also taken in consideration subjective satisfaction with a range score from 4 to 10, cold intolerance, flap area and donor site sensibility with a range score from low to medium to normal. CONCLUSION: Careful pedicle discovery, secured elevation, pedicle strangulation prevention are very important for flap survival.

  4. Analysis of tail effects in flapping flight

    Tay, W.B.; Bijl, H.; Van Oudheusden, B.W.

    2011-01-01

    Numerical simulations have been performed to examine the interference effects between an upstream flapping airfoil and a downstream stationary airfoil in a tandem configuration at a Reynolds number of 1000, which is around the regime of small flapping micro aerial vehicles. The object

  5. Dynamin 2 is required for actin assembly in phagocytosis in Sertoli cells

    Dynamin 2 has been reported to be implicated in phagocytosis. However, the mode of action of dynamin is poorly understood. In this study, we examined whether dynamin 2 participates in actin assembly during phagocytosis in Sertoli cells. In the presence of dynasore, a dynamin inhibitor, phagocytosis was reduced by 60-70% in Sertoli cells and macrophages. Scanning electron microscopy revealed that Sertoli cells treated with dynasore were unable to form phagocytic cups. In addition, dysfunction of dynamin 2 reduced both actin polymerization and recruitment of actin and dynamin 2 to phosphatidylinositol (4,5) bisphosphate [PI(4,5)P2]-containing liposomes. The formation of dynamin 2-positive ruffles of Sertoli cells was decreased by 60-70% by sequestering PI(4,5)P2 either by expression of PH domain of PLCδ or treatment with neomycin. These results strongly suggest that dynamin 2 is involved in actin dynamics and the formation of dynamin 2-positive ruffles during phagocytosis.

  6. Redundant mechanisms recruit actin into the contractile ring in silkworm spermatocytes.

    Wei Chen

    2008-09-01

    Full Text Available Cytokinesis is powered by the contraction of actomyosin filaments within the newly assembled contractile ring. Microtubules are a spindle component that is essential for the induction of cytokinesis. This induction could use central spindle and/or astral microtubules to stimulate cortical contraction around the spindle equator (equatorial stimulation. Alternatively, or in addition, induction could rely on astral microtubules to relax the polar cortex (polar relaxation. To investigate the relationship between microtubules, cortical stiffness, and contractile ring assembly, we used different configurations of microtubules to manipulate the distribution of actin in living silkworm spermatocytes. Mechanically repositioned, noninterdigitating microtubules can induce redistribution of actin at any region of the cortex by locally excluding cortical actin filaments. This cortical flow of actin promotes regional relaxation while increasing tension elsewhere (normally at the equatorial cortex. In contrast, repositioned interdigitating microtubule bundles use a novel mechanism to induce local stimulation of contractility anywhere within the cortex; at the antiparallel plus ends of central spindle microtubules, actin aggregates are rapidly assembled de novo and transported laterally to the equatorial cortex. Relaxation depends on microtubule dynamics but not on RhoA activity, whereas stimulation depends on RhoA activity but is largely independent of microtubule dynamics. We conclude that polar relaxation and equatorial stimulation mechanisms redundantly supply actin for contractile ring assembly, thus increasing the fidelity of cleavage.

  7. Two-Photon Correlation Spectroscopy in Single Dendritic Spines Reveals Fast Actin Filament Reorganization during Activity-Dependent Growth.

    Jian-Hua Chen

    Full Text Available Two-photon fluorescence correlation spectroscopy (2P-FCS within single dendritic spines of living hippocampal pyramidal neurons was used to resolve various subpopulations of mobile F-actin during activity-dependent structural changes such as potentiation induced spine head growth. Two major classes of mobile F-actin were discovered: very dynamic and about a hundred times less dynamic F-actin. Spine head enlargement upon application of Tetraethylammonium (TEA, a protocol previously used for the chemical induction of long-term potentiation (cLTP strictly correlated to changes in the dynamics and filament numbers in the different actin filament fractions. Our observations suggest that spine enlargement is governed by a mechanism in which longer filaments are first cut into smaller filaments that cooperate with the second, increasingly dynamic shorter actin filament population to quickly reorganize and expand the actin cytoskeleton within the spine head. This process would allow a fast and efficient spine head enlargement using a major fraction of the actin filament population that was already present before spine head growth.

  8. Blood flow autoregulation in pedicled flaps

    Bonde, Christian T; Holstein-Rathlou, Niels-Henrik; Elberg, Jens J

    2009-01-01

    INTRODUCTION: Clinical work on the blood perfusion in skin and muscle flaps has suggested that some degree of blood flow autoregulation exists in such flaps. An autoregulatory mechanism would enable the flap to protect itself from changes in the perfusion pressure. The purpose of the present study...... was to evaluate if, and to what extent, a tissue flap could compensate a reduction in blood flow due to an acute constriction of the feed artery. Further, we wanted to examine the possible role of smooth muscle L-type calcium channels in the autoregulatory mechanism by pharmacological intervention...... with the L-type calcium channel blocker nimodipine and the vasodilator papaverine. MATERIAL AND METHODS: Pedicled flaps were raised in pigs. Flow in the pedicle was reduced by constriction of the feed artery (n=34). A transit time flow probe measured the effect on blood flow continuously. Following...

  9. Fasciocutaneous flap for vaginal and perineal reconstruction

    A skin and fascia flap from the medial thigh is proposed for vaginal and perineal reconstruction. Dissection, vascular injection, and radiographs of 20 fresh cadaver limbs uniformly demonstrated the presence of a communicating suprafascial vascular plexus in the medial thigh. Three to four nonaxial vessels were consistently found to enter the proximal plexus from within 5 cm of the perineum. Preservation of these vessels permitted reliable elevation of a 9 X 20 cm fasciocutaneous flap without using the gracilis muscle as a vascular carrier. Fifteen flaps in 13 patients were used for vaginal replacement and coverage of vulvectomy, groin, and ischial defects. Depending on the magnitude of the defect, simultaneous and independent elevation of the gracilis muscle provided additional vascularized coverage as needed. Our experience indicates that the medial thigh fasciocutaneous flap is a durable, less bulky, and potentially sensate alternative to the gracilis musculocutaneous flap for vaginal and perineal reconstruction

  10. Fasciocutaneous flap for vaginal and perineal reconstruction

    Wang, T.N.; Whetzel, T.; Mathes, S.J.; Vasconez, L.O.

    1987-07-01

    A skin and fascia flap from the medial thigh is proposed for vaginal and perineal reconstruction. Dissection, vascular injection, and radiographs of 20 fresh cadaver limbs uniformly demonstrated the presence of a communicating suprafascial vascular plexus in the medial thigh. Three to four nonaxial vessels were consistently found to enter the proximal plexus from within 5 cm of the perineum. Preservation of these vessels permitted reliable elevation of a 9 X 20 cm fasciocutaneous flap without using the gracilis muscle as a vascular carrier. Fifteen flaps in 13 patients were used for vaginal replacement and coverage of vulvectomy, groin, and ischial defects. Depending on the magnitude of the defect, simultaneous and independent elevation of the gracilis muscle provided additional vascularized coverage as needed. Our experience indicates that the medial thigh fasciocutaneous flap is a durable, less bulky, and potentially sensate alternative to the gracilis musculocutaneous flap for vaginal and perineal reconstruction.

  11. The clinical application of anterolateral thigh flap.

    Lee, Yao-Chou; Chiu, Haw-Yen; Shieh, Shyh-Jou

    2011-01-01

    The anterolateral thigh flap can provide a large skin paddle nourished by a long and large-caliber pedicle and can be harvested by two-team work. Most importantly, the donor-site morbidity is minimal. However, the anatomic variations decreased its popularity. By adapting free-style flap concepts, such as preoperative mapping of the perforators and being familiar with retrograde perforator dissection, this disadvantage had been overcome gradually. Furthermore, several modifications widen its clinical applications: the fascia lata can be included for sling or tendon reconstruction, the bulkiness could be created by including vastus lateralis muscle or deepithelization of skin flap, the pliability could be increased by suprafascial dissection or primary thinning, the pedicle length could be lengthening by proximally eccentric placement of the perforator, and so forth. Combined with these technical and conceptual advancements, the anterolateral thigh flap has become the workhorse flap for soft-tissue reconstructions from head to toe. PMID:22567234

  12. Facial artery flaps in facial oncoplastic reconstruction.

    Fabrizio, Tommaso

    2013-10-01

    The face is one of the common sites for cutaneous cancer localization. It is well known that the face is the localization of more than 50% of skin cancers. Nowadays, the principles of modern "oncoplasty" recommend the complete excision of the cancer and the reconstruction with respect to cosmetic features of the face in terms of good color, good softness, and good texture of the flaps, utilized in cancer repair. The oncological and cosmetic results of facial reconstruction are strictly linked and the modern plastic and reconstructive surgeon must respect both oncological and cosmetic aspects. For that reason the best solution in facial cancer repair is the utilization of locoregional flaps based on the tributary vessels of the facial artery. In consideration of the dimension of recipient area to repair, the retroangular flap (RAF) or the submental flap could be used. This article is voted to illustrate a very large and long-term casuistry dedicated to these flaps. PMID:24037925

  13. Emerging roles of actin cytoskeleton regulating enzymes in drug addiction: Actin or reactin’?

    Rothenfluh, Adrian; Cowan, Christopher W.

    2013-01-01

    Neurons rely on their cytoskeleton to give them shape and stability, and on cytoskeletal dynamics for growth and synaptic plasticity. Because drug addiction is increasingly seen as the inappropriate learning of strongly reinforcing stimuli, the role of the cytoskeleton in shaping drug memories has been of increasing interest in recent years. Does the cytoskeleton have an active role in shaping these memories, and to what extent do alterations in the cytoskeleton reflect the acute actions of drug exposure, or homeostatic reactions to the chronic exposure to drugs of abuse? Here we will review recent advances in understanding the role of the cytoskeleton in the development of drug addiction, with a focus on actin filaments, as they have been studied in greater detail. PMID:23428655

  14. Exotic wakes of flapping fins

    Schnipper, Teis

    downstream neighbour. When this neighbour is a second flag close by, they synchronise in frequency and the leader experiences a reduced drag compared to that on the lone flag. In case the follower is replaced by a flapping plate, upstream synchronisation and drag reduction is again found over a wide range of...... frequencies. Drag reductions up to a factor 3 are measured. Many results presented are obtained through flow visualisations. A great effort is made to produce visualisations of primarily high scientific quality, but often also with a certain aesthetic appeal....

  15. Laser resurfacing of skin flaps: an experimental comparison

    Srdan Babovic

    2011-05-01

    Full Text Available Objective. The influence of Coherent Ultrapulse, TruPulse and Erbium: YAG laser skin resurfacing on survival of the skin flaps when performed simultaneously was evaluated. Material and methods. We used twelve female Yucatan minipigs in the study. Skin flaps including paniculus carnosus were raised on the animals’ back. The flaps were sutured into the defect under tension. We designed 4 experimental groups: Control-Flaps only, Group 2-Flaps + 4 immediate TruPulse laser passes, Group 3-Flaps + 2 immediate Coherent UltraPulse laser passes, Group 4-Flaps – immediate 50J/cm2 total fluence with Erbium: YAG laser. Results. Flap survival in Control group was 98.8%. There was no flap in Group 2 with complete survival. Survival of the flaps in Group 2 (Tru-Pulse ranged from 75-90%, with average flap survival area of 85.2%. In Group 3 (UltraPulse all 24 flaps had some area of necrosis. Flap survival in Group 3 ranged from 75-95%, with an average of 85.6%. In Group 4 (Erbium: YAG flap survival area ranged from 70-95%, with all 24 flaps with some area of necrosis, with average flap survival area of 87.3%. There is a significant statistical difference in flap survival area between groups 2, 3 and 4 versus Control (p<0.001. Conclusion. The results of our study suggest that laser resurfacing of skin flaps sutured under tension in the same operative session is detrimental for skin flap survival. We also found no significant difference in flap survival area between TruPulse, Coherent UltraPulse and Erbium: YAG laser treated flaps.

  16. A novel algorithm for OSPF link flap damping

    Yang, Yang; Liu, Guangyi; Lin, Xiaokang

    2005-02-01

    Open shortest path first (OSPF) is the most widely used routing protocol in today"s IP networks, and its excellent performance has been proved in wired environments. However, when it is executed under bad channel conditions such as in wireless networks or areas with severe signal interference, links may flap frequently and some terrible problems will appear. This paper proposes a novel algorithm called OSPF link flap damping algorithm (OLFDA). The objective of OLFDA is to reduce the events of link state advertisement (LSA) update and damp the link flap with the precondition that the overall network performance is satisfying. To accomplish this, we can define criteria to identify and dynamically suppress the poorly behaved links. Information of the suppressed links won"t be advertised in OSPF domain and used in calculation of the routing tables. In addition, we can control the maximal number of links suppressed simultaneously by a router to ensure the network connectivity. OLFDA are simulated in many scenarios, and the results indicate that the algorithm has an excellent performance.

  17. Effect of flexibility on flapping wing characteristics under forward flight

    Through two-dimensional numerical simulation and by solving the unsteady incompressible Navier–Stokes (NS) equations, coupled with the structural dynamic equation for the motion of the wing, the effect of flexibility on flapping wing characteristics during forward flight is systematically studied. The flapping wing is considered as a cantilever, which performs the translational and rotational motion at its leading edge, and the other part is passively deformed by the aerodynamic force. The frequency ratio ω* and mass ratio m* are defined and used to characterize the flexibility of the flapping wing. It has been found that an optimal range of the frequency ratio exists in which the flexible wing possesses both a larger propulsive efficiency and lifting efficiency than their rigid counterpart. Also, the flexible wing with the smaller mass ratio may be of benefit to generate thrust, while the larger mass ratio may be of benefit to generate lift. In addition, a stronger leading edge vortex and reattachment vortex are observed around the appropriate flexibility wing’s surface, which therefore leads to better aerodynamic characteristics. (paper)

  18. Effect of flexibility on flapping wing characteristics under forward flight

    Zhu, Jianyang; Jiang, Lin [School of Machinery and Automation, Wuhan University of Science and Technology, Wuhan, 430081, People’s Republic of China (China); Zhou, Chaoying; Wang, Chao, E-mail: cyzhou@hit.edu.cn [Shenzhen Graduate School, Harbin Institute of Technology, Xili Shenzhen University Town, Shenzhen 518055, People’s Republic of China (China)

    2014-10-01

    Through two-dimensional numerical simulation and by solving the unsteady incompressible Navier–Stokes (NS) equations, coupled with the structural dynamic equation for the motion of the wing, the effect of flexibility on flapping wing characteristics during forward flight is systematically studied. The flapping wing is considered as a cantilever, which performs the translational and rotational motion at its leading edge, and the other part is passively deformed by the aerodynamic force. The frequency ratio ω* and mass ratio m* are defined and used to characterize the flexibility of the flapping wing. It has been found that an optimal range of the frequency ratio exists in which the flexible wing possesses both a larger propulsive efficiency and lifting efficiency than their rigid counterpart. Also, the flexible wing with the smaller mass ratio may be of benefit to generate thrust, while the larger mass ratio may be of benefit to generate lift. In addition, a stronger leading edge vortex and reattachment vortex are observed around the appropriate flexibility wing’s surface, which therefore leads to better aerodynamic characteristics. (paper)

  19. Conceptual design of flapping-wing micro air vehicles

    Traditional micro air vehicles (MAVs) are miniature versions of full-scale aircraft from which their design principles closely follow. The first step in aircraft design is the development of a conceptual design, where basic specifications and vehicle size are established. Conceptual design methods do not rely on specific knowledge of the propulsion system, vehicle layout and subsystems; these details are addressed later in the design process. Non-traditional MAV designs based on birds or insects are less common and without well-established conceptual design methods. This paper presents a conceptual design process for hovering flapping-wing vehicles. An energy-based accounting of propulsion and aerodynamics is combined with a one degree-of-freedom dynamic flapping model. Important results include simple analytical expressions for flight endurance and range, predictions for maximum feasible wing size and body mass, and critical design space restrictions resulting from finite wing inertia. A new figure-of-merit for wing structural-inertial efficiency is proposed and used to quantify the performance of real and artificial insect wings. The impact of these results on future flapping-wing MAV designs is discussed in detail. (paper)

  20. Wing rotation and lift in SUEX flapping wing mechanisms

    This research presents detailed modeling and experimental testing of wing rotation and lift in the LionFly, a low cost and mass producible flapping wing mechanism fabricated monolithically from SUEX dry film and powered by piezoelectric bimorph actuators. A flexure hinge along the span of the wing allows the wing to rotate in addition to flapping. A dynamic model including aerodynamics is developed and validated using experimental testing with a laser vibrometer in air and vacuum, stroboscopic photography and high definition image processing, and lift measurement. The 112 mg LionFly produces 46° flap and 44° rotation peak to peak with 12° phase lag, which generates a maximum average lift of 71 μN in response to an applied sinusoidal voltage of 75 V AC and 75 V DC at 37 Hz. Simulated wing trajectories accurately predict measured wing trajectories at small voltage amplitudes, but slightly underpredict amplitude and lift at high voltage amplitudes. By reducing the length of the actuator, reducing the mechanism amplification and tuning the rotational hinge stiffness, a redesigned device is simulated to produce a lift to weight ratio of 1.5. (paper)

  1. The mechanism of body rotation in the flapping flight of butterflies

    Fei, Yueh-Han; Yang, Jing-Tang

    2013-11-01

    The aerodynamic effects of the body rotation on the flapping flying of butterflies are experimentally and numerically investigated. We first observe and record the flying motion of a butterfly (Kallima inachus) in free flight, focusing especially on the body rotation, via two high speed video cameras and PIV. The body rotation is found in phase with wing flapping while the abdomen is out of phase with wing flapping. Further, we establish the model of flexible wings of a butterfly and exploit the fluid dynamics analysis via the dynamic mesh technique to study the contribution of body rotation to the lift. The results reveal that the body rotation is capable of strengthening the vortex ring structure and correspondingly enhancing the efficiency of lift production. Our simulation model shows the body rotation contributes 15% of total lift. The results of this study may serve as a useful guide for designing insect-like MAVs in the future.

  2. Pudendal thigh flap for repair of rectovaginal fistula.

    Sathappan, S; Rica, M A I

    2006-08-01

    The pudendal thigh flap or the Singapore flap is a versatile flap that can be used in the repair of recto-vaginal fistulae. Apart from the potential problem of hair growth, this neurovascular flap proves to be surprisingly simple in technique, robust and has a high potential for normal or near-normal function. PMID:17240589

  3. Total endoscopic free flap harvest of a serratus anterior fascia flap for microsurgical lower leg reconstruction

    Erdmann, Alfons

    2014-04-01

    Full Text Available [english] Background: A tremendous number of free flaps have been developed in the past. As the surgical result depends not only on a successful flap transfer but also on the harvest, this paper details the procedures for undertaking the first total endoscopic harvest of a serratus fascia flap for free flap transplantation to the lower leg. Patient and methods: In September 2012 we performed the first total endoscopic serratus anterior fascia free flap harvest. The incision of 2.5 cm length was made 10 cm in front of anterior muscle border of the latissimus dorsi at level with the midthorax. After insertion of a flexible laparoscopic single port system we started CO gas insufflation. We used this setting to meticulously prepare a neo cavity between atissimus dorsi and M. serratus anterior. The vessels were dissected and the thoraco-dorsal nerve was separated. With a second auxiliary incision we used a clamp to support the raising of the fascia flap from the underlying muscle. Finally we clipped the vessels to the latissimus dorsi muscle and the flap vessels at the Arteria and Vena axillaris. The flap was extracted via the 2.5 cm incision.Results: We were able to perform a total endoscopic harvest of a serratus fascia flap for free flap reconstruction of soft tissues. With this new operative technique we were able to avoid a long skin incision, which in our view lowers the morbidity at the harvest area.Conclusion: We describe a new method for the total endoscopic harvest of the serratus fascia flap for free flap transfer. The flap was harvested within reasonable time and following surgery leaves the patient with minimal donor site morbidity compared to the open technique.

  4. Erbium laser resurfacing for actinic cheilitis.

    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). PMID:24196339

  5. Live cell tracking of symmetry break in actin cytoskeleton triggered by abrupt changes in micromechanical environments.

    Inoue, S; Frank, V; Hörning, M; Kaufmann, S; Yoshikawa, H Y; Madsen, J P; Lewis, A L; Armes, S P; Tanaka, M

    2015-12-01

    With the aid of stimulus-responsive hydrogel substrates composed of ABA triblock copolymer micelles, we monitored the morphological dynamics of myoblast (C2C12) cells in response to an abrupt change in the substrate elasticity by live cell imaging. The remodeling of actin cytoskeletons could be monitored by means of transient transfection with LifeAct-GFP. Dynamic changes in the orientational order of actin filaments were characterized by an order parameter, which enables one to generalize the mechanically induced actin cytoskeletons as a break of symmetry. The critical role that acto-myosin complexes play in the morphological transition was verified by the treatment of cells with myosin II inhibitor (blebbistatin) and the fluorescence localization of focal adhesion contacts. Such dynamically tunable hydrogels can be utilized as in vitro cellular micro-environments that can exert time-dependent stimuli to mechanically regulate target cells. PMID:26347909

  6. Design of Hybrid Passive and Active Mechanisms for Control of Insect-Scale Flapping-Wing Robots

    Teoh, Zhi Ern

    2015-01-01

    Flying insects exhibit a remarkable ability to fly in environments that are small, cluttered and highly dynamic. Inspired by these animals, scientist have made great strides in understanding the aerodynamic mechanisms behind insect-scale flapping-wing flight. By applying these mechanisms together with recent advances in meso-scale fabrication techniques, engineers built an insect-scale flapping-wing robot and demonstrated hover by actively controlling the robot about its roll and pitch axes....

  7. Flow structures around a flapping wing considering ground effect

    Van Truong, Tien; Kim, Jihoon; Kim, Min Jun; Park, Hoon Cheol; Yoon, Kwang Joon; Byun, Doyoung

    2013-07-01

    Over the past several decades, there has been great interest in understanding the aerodynamics of flapping flight, namely the two flight modes of hovering and forward flight. However, there has been little focus on the aerodynamic characteristics during takeoff of insects. In a previous study we found that the Rhinoceros Beetle ( Trypoxylusdichotomus) takes off without jumping, which is uncommon for other insects. In this study we built a scaled-up electromechanical model of a flapping wing and investigated fluid flow around the beetle's wing model. In particular, the present dynamically scaled mechanical model has the wing kinematics pattern achieved from the real beetle's wing kinematics during takeoff. In addition, we could systematically change the three-dimensional inclined motion of the flapping model through each stroke. We used digital particle image velocimetry with high spatial resolution, and were able to qualitatively and quantitatively study the flow field around the wing at a Reynolds number of approximately 10,000. The present results provide insight into the aerodynamics and the evolution of vortical structures, as well as the ground effect experienced by a beetle's wing during takeoff. The main unsteady mechanisms of beetles have been identified and intensively analyzed as the stability of the leading edge vortex (LEV) during strokes, the delayed stall during upstroke, the rotational circulation in pronation periods, and wake capture in supination periods. Due to the ground effect, the LEV was enhanced during half downstroke, and the lift force could thus be increased to lift the beetle during takeoff. This is useful for researchers in developing a micro air vehicle that has a beetle-like flapping wing motion.

  8. Actinic Granuloma with Focal Segmental Glomerulosclerosis

    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. Alix regulates cortical actin and the spatial distribution of endosomes.

    Cabezas, Alicia; Bache, Kristi G; Brech, Andreas; Stenmark, Harald

    2005-06-15

    Alix/AIP1 is a proline-rich protein that has been implicated in apoptosis, endocytic membrane trafficking and viral budding. To further elucidate the functions of Alix, we used RNA interference to specifically suppress its expression. Depletion of Alix caused a striking redistribution of early endosomes from a peripheral to a perinuclear location. The redistribution of endosomes did not affect transferrin recycling or degradation of endocytosed epidermal growth factor receptors, although the uptake of transferrin was mildly reduced when Alix was downregulated. Quantitative immunoelectron microscopy showed that multivesicular endosomes of Alix-depleted cells contained normal amounts of CD63, whereas their levels of lysobisphosphatidic acid were reduced. Alix depletion also caused an accumulation of unusual actin structures that contained clathrin and cortactin, a protein that couples membrane dynamics to the cortical actin cytoskeleton. Our results suggest that Alix functions in the actin-dependent intracellular positioning of endosomes, but that it is not essential for endocytic recycling or for trafficking of membrane proteins between early and late endosomes in non-polarised cells. PMID:15914539

  10. Fibrin glue for Gundersen flap surgery

    Chung HW

    2013-03-01

    Full Text Available Hsi-Wei Chung,1 Jodhbir S Mehta1–31Singapore National Eye Centre, Singapore; 2Tissue Engineering and Stem Cell Group, Singapore Eye Research Institute, Singapore; 3Department of Clinical Sciences, Duke-NUS Graduate Medical School, SingaporePurpose: To evaluate the feasibility of fibrin glue in Gundersen flap surgery.Design: Prospective case series.Study subjects: Seven eyes of seven subjects who had undergone Gundersen flap surgery from 2009 to 2011 at the Singapore National Eye Centre, Singapore.Methods: Review of case records for outcomes after Gundersen flap surgery.Main outcome measures: Surgical success was defined as achieving a stable ocular surface. Complications to be noted included flap retraction or exposure of underlying corneal surface.Results: Surgical success was achieved in all eyes with significant reduction in ocular surface inflammation. No retractions were noted and recovery was uncomplicated.Conclusion: Fibrin glue application is a viable alternative to sutures in Gundersen flap surgery. It reduces surgical downtime, gives faster ocular surface rehabilitation, and offers similar outcomes to conventional conjunctival flap surgery.Keywords: Gundersen, conjunctival flap, fibrin glue

  11. Shape optimisation and performance analysis of flapping wings

    Ghommem, Mehdi

    2012-09-04

    In this paper, shape optimisation of flapping wings in forward flight is considered. This analysis is performed by combining a local gradient-based optimizer with the unsteady vortex lattice method (UVLM). Although the UVLM applies only to incompressible, inviscid flows where the separation lines are known a priori, Persson et al. [1] showed through a detailed comparison between UVLM and higher-fidelity computational fluid dynamics methods for flapping flight that the UVLM schemes produce accurate results for attached flow cases and even remain trend-relevant in the presence of flow separation. As such, they recommended the use of an aerodynamic model based on UVLM to perform preliminary design studies of flapping wing vehicles Unlike standard computational fluid dynamics schemes, this method requires meshing of the wing surface only and not of the whole flow domain [2]. From the design or optimisation perspective taken in our work, it is fairly common (and sometimes entirely necessary, as a result of the excessive computational cost of the highest fidelity tools such as Navier-Stokes solvers) to rely upon such a moderate level of modelling fidelity to traverse the design space in an economical manner. The objective of the work, described in this paper, is to identify a set of optimised shapes that maximise the propulsive efficiency, defined as the ratio of the propulsive power over the aerodynamic power, under lift, thrust, and area constraints. The shape of the wings is modelled using B-splines, a technology used in the computer-aided design (CAD) field for decades. This basis can be used to smoothly discretize wing shapes with few degrees of freedom, referred to as control points. The locations of the control points constitute the design variables. The results suggest that changing the shape yields significant improvement in the performance of the flapping wings. The optimisation pushes the design to "bird-like" shapes with substantial increase in the time

  12. Use of Martius flap in the complex female urethral surgery

    Kasyan, George; Tupikina, Nataliya; Pushkar, Dmitry

    2014-01-01

    Introduction Objectives were to evaluate safety and patient reported perception of the Martius fibroadipose flap for complex female urethra reconstruction. Material and methods Patients operated with a Martius flap were contacted again via telephone to rate their self–perception on cosmetic appearance, pain or numbness of the flap harvest site. Results 37 women (mean age of 46.8 yrs.) were operated with Martius flaps. Complications were limited to bleeding from the flap bed in 19% (7/37); hem...

  13. The plane problem of the flapping wing

    Birnbaum, Walter

    1954-01-01

    In connection with an earlier report on the lifting vortex sheet which forms the basis of the following investigations this will show how the methods developed there are also suitable for dealing with the air forces for a wing with a circulation variable with time. The theory of a propulsive wing flapping up and down periodically in the manner of a bird's wing is developed. This study shows how the lift and its moment result as a function of the flapping motion, what thrust is attainable, and how high is the degree of efficiency of this flapping propulsion unit if the air friction is disregarded.

  14. Neural Anatomy of the Anterolateral Thigh Flap

    Luenam, Suriya; Prugsawan, Krit; Kosiyatrakul, Arkaphat; Chotanaphuti, Thanainit; Sriya, Piyanee

    2015-01-01

    The anterolateral thigh (ALT) flap is one of the commonly used sensate flaps for intra-oral, hand, and foot reconstruction. The objective of this study was to describe the anatomic location of the sensory nerves supplying the ALT flap in relation to the surface landmarks and with the vascular pedicles. The dissections were carried out in 28 embalmed specimens. An axial line from the anterior superior iliac spine to the superolateral border of the patella and two circles with radii of 5 and 10...

  15. Short Stop provides an essential link between F-actin and microtubules during axon extension.

    Lee, Seungbok; Kolodziej, Peter A

    2002-03-01

    Coordination of F-actin and microtubule dynamics is important for cellular motility and morphogenesis, but little is known about underlying mechanisms. short stop (shot) encodes an evolutionarily conserved, neuronally expressed family of rod-like proteins required for sensory and motor axon extension in Drosophila melanogaster. We identify Shot isoforms that contain N-terminal F-actin and C-terminal microtubule-binding domains, and that crosslink F-actin and microtubules in cultured cells. The F-actin- and microtubule-binding domains of Shot are required in the same molecule for axon extension, though the length of the connecting rod domain can be dramatically reduced without affecting activity. Shot therefore functions as a cytoskeletal crosslinker in axon extension, rather than mediating independent interactions with F-actin and microtubules. A Ca(2+)-binding motif located adjacent to the microtubule-binding domain is also required for axon extension, suggesting that intracellular Ca(2+) release may regulate Shot activity. These results suggest that Shot coordinates regulated interactions between F-actin and microtubules that are crucial for neuronal morphogenesis. PMID:11874915

  16. Blended Cutout Flap for Reduction of Jet-Flap Interaction Noise

    Czech, Michael J (Inventor); Thomas, Russell H. (Inventor)

    2014-01-01

    An aircraft system includes a wing and a trailing edge device coupled to the wing. The trailing edge device is movable relative to the wing, and includes a leading edge and a trailing edge having a center flap portion and a plurality of outer edge portions integrally combined with the center flap portion such that the center flap portion is shorter in width than that of outer edge portions.

  17. Nuclear actin levels as an important transcriptional switch

    Huet, Guillaume; Skarp, Kari-Pekka; Vartiainen, Maria K.

    2012-01-01

    Nuclear actin levels have recently been linked to different cellular fates, suggesting that actin could act as a switch between altered transcriptional states. Here we discuss our latest results on the mechanisms by which nuclear actin levels are regulated and their implications to the functional significance of nuclear actin.

  18. Nuclear actin levels as an important transcriptional switch

    Huet, Guillaume; Skarp, Kari-Pekka; Vartiainen, Maria K.

    2012-01-01

    Nuclear actin levels have recently been linked to different cellular fates, suggesting that actin could act as a switch between altered transcriptional states. Here we discuss our latest results on the mechanisms by which nuclear actin levels are regulated and their implications to the functional significance of nuclear actin. PMID:22771994

  19. Actin expression in trypanosomatids (Euglenozoa: Kinetoplastea).

    Souza, Ligia Cristina Kalb; Pinho, Rosana Elisa Gonçalves Gonçalves; Lima, Carla Vanessa de Paula; Fragoso, Stênio Perdigão; Soares, Maurilio José

    2013-08-01

    Heteroxenic and monoxenic trypanosomatids were screened for the presence of actin using a mouse polyclonal antibody produced against the entire sequence of the Trypanosoma cruzi actin gene, encoding a 41.9 kDa protein. Western blot analysis showed that this antibody reacted with a polypeptide of approximately 42 kDa in the whole-cell lysates of parasites targeting mammals (T. cruzi, Trypanosoma brucei and Leishmania major), insects (Angomonas deanei, Crithidia fasciculata, Herpetomonas samuelpessoai and Strigomonas culicis) and plants (Phytomonas serpens). A single polypeptide of approximately 42 kDa was detected in the whole-cell lysates of T. cruzi cultured epimastigotes, metacyclic trypomastigotes and amastigotes at similar protein expression levels. Confocal microscopy showed that actin was expressed throughout the cytoplasm of all the tested trypanosomatids. These data demonstrate that actin expression is widespread in trypanosomatids. PMID:23903980

  20. Actin expression in trypanosomatids (Euglenozoa: Kinetoplastea

    Ligia Cristina Kalb Souza

    2013-08-01

    Full Text Available Heteroxenic and monoxenic trypanosomatids were screened for the presence of actin using a mouse polyclonal antibody produced against the entire sequence of the Trypanosoma cruzi actin gene, encoding a 41.9 kDa protein. Western blot analysis showed that this antibody reacted with a polypeptide of approximately 42 kDa in the whole-cell lysates of parasites targeting mammals (T. cruzi, Trypanosoma brucei and Leishmania major, insects (Angomonas deanei, Crithidia fasciculata, Herpetomonas samuelpessoai and Strigomonas culicis and plants (Phytomonas serpens. A single polypeptide of approximately 42 kDa was detected in the whole-cell lysates of T. cruzi cultured epimastigotes, metacyclic trypomastigotes and amastigotes at similar protein expression levels. Confocal microscopy showed that actin was expressed throughout the cytoplasm of all the tested trypanosomatids. These data demonstrate that actin expression is widespread in trypanosomatids.

  1. Chronic actinic damage of facial skin.

    Bilaç, Cemal; Şahin, Mustafa Turhan; Öztürkcan, Serap

    2014-01-01

    Chronic actinic damage of the skin manifests itself as extrinsic skin aging (photoaging) and photocarcinogenesis. During the last decade, substantial progress has been made in understanding cellular and molecular mechanisms of photoaging. DNA photodamage and ultraviolet-generated reactive oxygen species are the initial events that lead to most of the typical histologic and clinical manifestations of chronic photodamage of the skin. Chronic actinic damage affects all layers of the skin. Keratinocytes, melanocytes, fibroblasts, and endothelial cells are altered by ultraviolet radiation and can result in numerous changes in human skin, particularly the skin of fair-skinned individuals. These changes include actinic keratosis, thickening and wrinkling, elastosis, telengiectasia, solar comedones, diffuse or mottled hyperpigmentation, and skin cancers. There are many options in the treatment of changes caused by chronic actinic damage. The most effective measure of prevention of the photoaging and photocarcinogenesis is sun protection. PMID:25441468

  2. The plant actin cytoskeleton responds to signals from microbe-associated molecular patterns.

    Jessica L Henty-Ridilla

    Full Text Available Plants are constantly exposed to a large and diverse array of microbes; however, most plants are immune to the majority of potential invaders and susceptible to only a small subset of pathogens. The cytoskeleton comprises a dynamic intracellular framework that responds rapidly to biotic stresses and supports numerous fundamental cellular processes including vesicle trafficking, endocytosis and the spatial distribution of organelles and protein complexes. For years, the actin cytoskeleton has been assumed to play a role in plant innate immunity against fungi and oomycetes, based largely on static images and pharmacological studies. To date, however, there is little evidence that the host-cell actin cytoskeleton participates in responses to phytopathogenic bacteria. Here, we quantified the spatiotemporal changes in host-cell cytoskeletal architecture during the immune response to pathogenic and non-pathogenic strains of Pseudomonas syringae pv. tomato DC3000. Two distinct changes to host cytoskeletal arrays were observed that correspond to distinct phases of plant-bacterial interactions i.e. the perception of microbe-associated molecular patterns (MAMPs during pattern-triggered immunity (PTI and perturbations by effector proteins during effector-triggered susceptibility (ETS. We demonstrate that an immediate increase in actin filament abundance is a conserved and novel component of PTI. Notably, treatment of leaves with a MAMP peptide mimic was sufficient to elicit a rapid change in actin organization in epidermal cells, and this actin response required the host-cell MAMP receptor kinase complex, including FLS2, BAK1 and BIK1. Finally, we found that actin polymerization is necessary for the increase in actin filament density and that blocking this increase with the actin-disrupting drug latrunculin B leads to enhanced susceptibility of host plants to pathogenic and non-pathogenic bacteria.

  3. Actinic review of EUV masks

    Feldmann, Heiko; Ruoff, Johannes; Harnisch, Wolfgang; Kaiser, Winfried

    2010-04-01

    Management of mask defects is a major challenge for the introduction of EUV for HVM production. Once a defect has been detected, its printing impact needs to be predicted. Potentially the defect requires some repair, the success of which needs to be proven. This defect review has to be done with an actinic inspection system that matches the imaging conditions of an EUV scanner. During recent years, several concepts for such an aerial image metrology system (AIMS™) have been proposed. However, until now no commercial solution exists for EUV. Today, advances in EUV optics technology allow envisioning a solution that has been discarded before as unrealistic. We present this concept and its technical cornerstones.While the power requirement for the EUV source is less demanding than for HVM lithography tools, radiance, floor space, and stability are the main criteria for source selection. The requirement to emulate several generations of EUV scanners demands a large flexibility for the ilumination and imaging systems. New critical specifications to the EUV mirrors in the projection microscope can be satisfied using our expertise from lithographic mirrors. In summary, an EUV AIMS™ meeting production requirements seems to be feasible.

  4. Propeller Flap Reconstruction in Post Oncological Thigh Defect: "The Move in Flap".

    Nambi, G I; Salunke, Abhijeet Ashok

    2015-06-01

    Reconstruction of soft tissue defects of the limb after tumor resection is challenging question for oncosurgeons. The management differs from reconstruction of post traumatic defects due to the complexity of the primary surgery and subsequent radiation. The conventional propeller flap is based on a perforator which is located close to the defect; but in present case the perforator was located far away from the defect. So we describe it as "Move in flap" as the flap rotated a large volume of soft tissue lying between the defect and the perforator. We present a case of post oncological thigh defect with reconstruction using a propeller flap based on distal anteromedial perforator. PMID:26405422

  5. Mechanism of Actin Filament Bundling by Fascin

    Jansen, Silvia; Collins, Agnieszka; Yang, Changsong; Rebowski, Grzegorz; Svitkina, Tatyana; Dominguez, Roberto (UPENN); (UPENN-MED)

    2013-03-07

    Fascin is the main actin filament bundling protein in filopodia. Because of the important role filopodia play in cell migration, fascin is emerging as a major target for cancer drug discovery. However, an understanding of the mechanism of bundle formation by fascin is critically lacking. Fascin consists of four {beta}-trefoil domains. Here, we show that fascin contains two major actin-binding sites, coinciding with regions of high sequence conservation in {beta}-trefoil domains 1 and 3. The site in {beta}-trefoil-1 is located near the binding site of the fascin inhibitor macroketone and comprises residue Ser-39, whose phosphorylation by protein kinase C down-regulates actin bundling and formation of filopodia. The site in {beta}-trefoil-3 is related by pseudo-2-fold symmetry to that in {beta}-trefoil-1. The two sites are {approx}5 nm apart, resulting in a distance between actin filaments in the bundle of {approx}8.1 nm. Residue mutations in both sites disrupt bundle formation in vitro as assessed by co-sedimentation with actin and electron microscopy and severely impair formation of filopodia in cells as determined by rescue experiments in fascin-depleted cells. Mutations of other areas of the fascin surface also affect actin bundling and formation of filopodia albeit to a lesser extent, suggesting that, in addition to the two major actin-binding sites, fascin makes secondary contacts with other filaments in the bundle. In a high resolution crystal structure of fascin, molecules of glycerol and polyethylene glycol are bound in pockets located within the two major actin-binding sites. These molecules could guide the rational design of new anticancer fascin inhibitors.

  6. Sarcomeric pattern formation by actin cluster coalescence.

    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. Periodic and Chaotic Flapping of Insectile Wings

    Huang, Yangyang

    2015-01-01

    Insects use flight muscles attached at the base of the wings to produce impressive wing flapping frequencies. The maximum power output of these flight muscles is insufficient to maintain such wing oscillations unless there is good elastic storage of energy in the insect flight system. Here, we explore the intrinsic self-oscillatory behavior of an insectile wing model, consisting of two rigid wings connected at their base by an elastic torsional spring. We study the wings behavior as a function of the total energy and spring stiffness. Three types of behavior are identified: end-over-end rotation, chaotic motion, and periodic flapping. Interestingly, the region of periodic flapping decreases as energy increases but is favored as stiffness increases. These findings are consistent with the fact that insect wings and flight muscles are stiff. They further imply that, by adjusting their muscle stiffness to the desired energy level, insects can maintain periodic flapping mechanically for a range of operating condit...

  8. Postirradiation flap infection about the oral cavity

    Postirradiation alteration of oral flora is well documented in the literature. Infection as a complication leading to partial or complete loss of a flap used to reconstruct a defect in the oral cavity is a worrisome outcome. We describe how a flap that was judged clinically to be viable became overwhelmingly infected with the Klebsiella oxytoca, an oral cavity pathogen encountered in this patient following irradiation. Local and systemic changes led to detachment of the flap. This complication may be explained, in view of the absence of venous congestion or arterial ischemia both clinically and pathologically, by the proven contamination of the flap by the Klebsiella pathogen. Local factors resulted in lower resistance and subsequent overwhelming infection. Discussion of the case, review of pertinent literature, and proposed solutions are presented

  9. Behind the performance of flapping flyers

    Ramananarivo, Sophie; Thiria, Benjamin

    2010-01-01

    Saving energy and enhancing performance are secular preoccupations shared by both nature and human beings. In animal locomotion, flapping flyers or swimmers rely on the flexibility of their wings or body to passively increase their efficiency using an appropriate cycle of storing and releasing elastic energy. Despite the convergence of many observations pointing out this feature, the underlying mechanisms explaining how the elastic nature of the wings is related to propulsive efficiency remain unclear. Here we use an experiment with a self-propelled simplified insect model allowing to show how wing compliance governs the performance of flapping flyers. Reducing the description of the flapping wing to a forced oscillator model, we pinpoint different nonlinear effects that can account for the observed behavior ---in particular a set of cubic nonlinearities coming from the clamped-free beam equation used to model the wing and a quadratic damping term representing the fluid drag associated to the fast flapping mo...

  10. Colocalization of synapsin and actin during synaptic vesicle recycling

    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...

  11. Internal Motility in Stiffening Actin-Myosin Networks

    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.

  12. Mandibular reconstruction in irradiated patients utilizing myosseous-cutaneous flaps

    Myosseous-cutaneous flaps were used for mandibular reconstruction in 16 irradiated patients. Three of six sternomastoid-clavicle flaps failed (all in conjunction with a neck dissection), as did one of 10 pectoralis major-anterior-fifth rib flaps. One trapezius-scapular flap was used and it succeeded. We found the blood supply of the sternomastoid-clavicle flap too tenuous for use in conjunction with a neck dissection. The trapezius-scapular flap had too short an arc of rotation to be used for defects other than those in the horizontal ramus. In addition, this flap required a change of position and created an undesirable functional deformity. The pectoralis major-fifth rib flap, in contrast, could be used for a variety of defects, in conjunction with a neck dissection, and did not require a change of position during operation. We found it to be the most versatile and dependable of the flaps employed in this series

  13. The Effect of Epigallocatechin Gallate on Flap Viability of Rat Perforator Abdominal Flaps.

    Aksakal, İbrahim Alper; Küçüker, İsmail; Önger, Mehmet Emin; Engin, Murat Sinan; Keleş, Musa Kemal; Demir, Ahmet

    2016-05-01

    Background Epigallocatechin gallate (EGCG) is a substance abundant in green tea. In this study, the effects of EGCG on perforator flap viability were investigated. Methods A total of 40 rats were assigned to four groups of 10 each. In each subject, a 4 × 6 cm abdominal skin flap was raised and adapted back onto its place. In the control group, no further procedures were taken. In the flap group, 40 mg/kg/d EGCG was injected into the flap. In the gavage group, 100 mg/kg/d EGCG was given through a feeding tube. In the intraperitoneal group, 50 mg/kg/d EGCG was injected intraperitoneally. On the 7th postoperative day, flaps were photographed and the viable areas were measured and compared via a one-way analysis of variance. Results The ratios of viable and contracted flap area were 9.15/12.01, 4.59/16.46, 11.56/11.20, and 11.65/10.77 cm(2) for the control, flap group, gavage group, and intraperitoneal group, respectively. While the flap group yielded the worst results in the sense of flap contraction and viability (p < 0.001), the gavage and intraperitoneal groups were significantly better than those of the control group (p = 0.03). Histologically, epidermal, papillary dermal, and capillary tissue volumes were evaluated. In comparison to the control group, the flap group yielded significantly increased epidermal and dermal volumes (p = 0.03), however, these values were significantly decreased (p = 0.04) in the gavage and intraperitoneal groups. Capillary volumes were significantly decreased in EGCG treatment groups (p < 0.01). Conclusion Our experiment has shown that oral and intraperitoneal administration of EGCG increases the perforator flap viability when compared with controls, while direct injection decreases the viability. PMID:26919381

  14. Motion characterization of aortic wall and intimal flap by ECG-gated CT in patients with chronic B-dissection

    Ganten, Maria-Katharina [Department of Radiology, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, 69120 Heidelberg (Germany); Department of Diagnostic Radiology, Ruprecht-Karls-University of Heidelberg (Germany)], E-mail: m.ganten@dkfz-heidelberg.de; Weber, Tim F.; Tengg-Kobligk, Hendrik von [Department of Radiology, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, 69120 Heidelberg (Germany); Boeckler, Dittmar [Department of Vascular and Endovascular Surgery, Ruprecht-Karls-University of Heidelberg (Germany); Stiller, Wolfram [Department of Medical Physics in Radiology, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, 69120 Heidelberg (Germany); Geisbuesch, Philipp [Department of Vascular and Endovascular Surgery, Ruprecht-Karls-University of Heidelberg (Germany); Kauffmann, Guenter W. [Department of Diagnostic Radiology, Ruprecht-Karls-University of Heidelberg (Germany); Delorme, Stefan [Department of Radiology, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, 69120 Heidelberg (Germany); Bock, Michael [Department of Medical Physics in Radiology, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, 69120 Heidelberg (Germany); Kauczor, Hans-Ulrich [Department of Radiology, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, 69120 Heidelberg (Germany)

    2009-10-15

    Rationale and objectives: To evaluate whether dynamic computed tomography (CT)-imaging can provide functional vessel information in patients with chronic aortic dissection type Stanford-B (ADB). Materials and methods: In 32 patients, ECG-gated CT-angiography images were obtained. Cross-sectional area change and wall distensibility were investigated by semiautomatic vessel area segmentation at the end of aortic arch. Significance of distensibility differences was tested with regard to the aortic diameter, and the oscillation of the intimal flap was analyzed. Results: The aorta could be segmented successfully in all patients. These were separated into three subgroups: (A) 6 patients with an aortic diameter <4 cm and without a visible intimal flap, (B) 9 patients with an aortic diameter <4 cm, and (C) 17 individuals with an aortic diameter {>=}4 cm; (B) and (C) having a visible intimal flap. Differences in distensibility between the subgroups were not significant. Overall mean distensibility was D{sub tot} = (1.3 {+-} 0.6) x 10{sup -5} Pa{sup -1}. Analysis of intimal flap oscillation showed a pulsatile short axis diameter decrease of the true lumen of up to 29%. Conclusion: Dynamic, ECG-gated CT-angiography can demonstrate pulsatile changes in aortic area and a highly variable motion of the intimal flap. Aortic distensibility appears independent of diameter or presence of a intimal flap. Follow-up studies may show correlation with possible complications.

  15. The estimation of pressure on the surface of a flapping rigid plate by stereo PIV

    Suryadi, Alexandre; Obi, Shinnosuke [Keio University, Department of Mechanical Engineering, Yokohama, Kanagawa (Japan)

    2011-11-15

    The method to estimate the dynamic load of a flapping wing by the integration of pressure on the wing's surface is discussed. The flapping wing was modeled as a plate flapping sinusoidally in hovering condition. The flow around the flapping plate was measured using stereo PIV on multiple measurement planes along the out-of-plane direction. The phase-averaged velocity field of each measurement plane was calculated so that three-dimensional analyses could be applied. The phase-averaged pressure field was obtained from the integration of the three-dimensional Poisson equation for pressure using the available information acquired from stereo PIV measurements. The pressure field is visualized on the measurement planes. In this study, the estimated load was the torque of the axis of rotation. This torque was compared with the result from strain gauge measurements. The torque estimation, although only on a partial surface of the plate, is within reasonable agreement with the measured torque. The integration of the Poisson equation based on stereo PIV measurements and estimations of the torque shows that an increase in the torque at the start of a flapping stroke is caused by the stagnation on the surface of the plate from the flow that is induced by the leading-edge vortices. (orig.)

  16. Spontaneous polarization in an interfacial growth model for actin filament networks with a rigorous mechanochemical coupling.

    John, Karin; Caillerie, Denis; Misbah, Chaouqi

    2014-11-01

    Many processes in eukaryotic cells, including cell motility, rely on the growth of branched actin networks from surfaces. Despite its central role the mechanochemical coupling mechanisms that guide the growth process are poorly understood, and a general continuum description combining growth and mechanics is lacking. We develop a theory that bridges the gap between mesoscale and continuum limit and propose a general framework providing the evolution law of actin networks growing under stress. This formulation opens an area for the systematic study of actin dynamics in arbitrary geometries. Our framework predicts a morphological instability of actin growth on a rigid sphere, leading to a spontaneous polarization of the network with a mode selection corresponding to a comet, as reported experimentally. We show that the mechanics of the contact between the network and the surface plays a crucial role, in that it determines directly the existence of the instability. We extract scaling laws relating growth dynamics and network properties offering basic perspectives for new experiments on growing actin networks. PMID:25493815

  17. Interaction between Calcium and Actin in Guard Cell and Pollen Signaling Networks

    Dong-Hua Chen

    2013-10-01

    Full Text Available Calcium (Ca2+ plays important roles in plant growth, development, and signal transduction. It is a vital nutrient for plant physical design, such as cell wall and membrane, and also serves as a counter-cation for biochemical, inorganic, and organic anions, and more particularly, its concentration change in cytosol is a ubiquitous second messenger in plant physiological signaling in responses to developmental and environmental stimuli. Actin cytoskeleton is well known for its importance in cellular architecture maintenance and its significance in cytoplasmic streaming and cell division. In plant cell system, the actin dynamics is a process of polymerization and de-polymerization of globular actin and filamentous actin and that acts as an active regulator for calcium signaling by controlling calcium evoked physiological responses. The elucidation of the interaction between calcium and actin dynamics will be helpful for further investigation of plant cell signaling networks at molecular level. This review mainly focuses on the recent advances in understanding the interaction between the two aforementioned signaling components in two well-established model systems of plant, guard cell, and pollen.

  18. Unveiling interactions among mitochondria, caspase-like proteases, and the actin cytoskeleton during plant programmed cell death (PCD.

    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.

  19. Cofilin-induced cooperative conformational changes of actin subunits revealed using cofilin-actin fusion protein

    Umeki, Nobuhisa; Hirose, Keiko; Uyeda, Taro Q. P.

    2016-01-01

    To investigate cooperative conformational changes of actin filaments induced by cofilin binding, we engineered a fusion protein made of Dictyostelium cofilin and actin. The filaments of the fusion protein were functionally similar to actin filaments bound with cofilin in that they did not bind rhodamine-phalloidin, had quenched fluorescence of pyrene attached to Cys374 and showed enhanced susceptibility of the DNase loop to cleavage by subtilisin. Quantitative analyses of copolymers made of different ratios of the fusion protein and control actin further demonstrated that the fusion protein affects the structure of multiple neighboring actin subunits in copolymers. Based on these and other recent related studies, we propose a mechanism by which conformational changes induced by cofilin binding is propagated unidirectionally to the pointed ends of the filaments, and cofilin clusters grow unidirectionally to the pointed ends following this path. Interestingly, the fusion protein was unable to copolymerize with control actin at pH 6.5 and low ionic strength, suggesting that the structural difference between the actin moiety in the fusion protein and control actin is pH-sensitive. PMID:26842224

  20. The dog-ear flap as an alternative for breast reconstruction in patients who have already undergone a DIEAP flap.

    Colebunders, Britt; Depypere, Bernard; Van Landuyt, Koenraad

    2016-05-01

    Breast reconstruction in patients who have previously undergone deep inferior epigastric artery perforator flap (DIEAP) reconstruction or abdominoplasty is often challenging. Depending on patients' body habitus, several second-choice flaps have been described such as the transverse upper gracilis (TUG) flap, profundus femoris artery perforator (PFAP) flap, superior gluteal artery perforator (SGAP) flap, and lumbar artery perforator (LAP) flap. Patients who have undergone a DIEAP flap reconstruction or abdominoplasty occasionally present with dog ears on both sides of the abdominal scar. The adipose tissue and skin of these dog ears are supplied by perforators of the deep circumflex iliac artery (DCIA). The DCIA flap was first described in 1979 by Taylor. We introduce this abdominal "dog-ear" flap for autologous breast reconstruction. PMID:26951847

  1. Dorsal hand coverage with free serratus fascia flap

    Fotopoulos, Peter; Holmer, Per; Leicht, Pernille;

    2003-01-01

    serratus fascia flap, the connective tissue over the serratus muscle, for dorsal hand coverage. The flap consists of thin and well-vascularized pliable tissue, with gliding properties excellent for covering exposed tendons. It is based on the branches of the thoracodorsal artery, which are raised in the...... flap, leaving the long thoracic nerve intact on the serratus muscle. Coverage of the flap with split-thickness skin graft is done immediately. The free serratus fascia flap is an ideal flap for dorsal hand coverage when the extensor tendons are exposed, especially because of low donor-site morbidity....

  2. Maxillofacial reconstruction with nasolabial and facial artery musculomucosal flaps.

    Braasch, Daniel Cameron; Lam, Din; Oh, Esther S

    2014-08-01

    The nasolabial and facial artery musculomucosal (FAMM) flaps are predictable methods to reconstruct perioral and intraoral defects with vascularized tissue. The nasolabial flap can be harvested as an axial or random patterned flap, whereas the FAMM flap is truly an axial patterned flap, with either a superior or an inferior base. Both flaps have been widely used to provide predictable results, with low morbidity. Future studies are needed to further prove their use in compromised patients, including patients with a history of head and neck radiation and neck dissections. PMID:25086694

  3. The Internal Pudendal Artery Perforator Thigh Flap: A New Freestyle Pedicle Flap for the Ischial Region

    Ichiro Hashimoto, MD

    2014-05-01

    Conclusions: The perforator vessels of the internal pudendal artery are very close to the ischial tuberosity. Blood flow to the flap is reliable when careful debridement of the pressure sore is performed. The iPap thigh flap is a new option for soft-tissue defects in the ischial region, including ischial pressure sores.

  4. Rescue of Primary Incomplete Microkeratome Flap with Secondary Femtosecond Laser Flap in LASIK

    E. A. Razgulyaeva

    2014-01-01

    Full Text Available For laser-assisted in situ keratomileusis (LASIK retreatments with a previous unsuccessful mechanical microkeratome-assisted surgery, some surgical protocols have been described as feasible, such as relifting of the flap or the creation of a new flap and even the change to a surface ablation procedure (photorefractive keratectomy (PRK. This case shows the use of femtosecond technology for the creation of a secondary flap to perform LASIK in a cornea with a primary incomplete flap obtained with a mechanical microkeratome. As we were unable to characterize the interface of the first partial lamellar cut, a thick flap was planned and created using a femtosecond laser platform. As the primary cut was very thick in the nasal quadrant, a piece of loose corneal tissue appeared during flap lifting which was fitted in its position and not removed. Despite this condition and considering the regularity of the new femtosecond laser cut, the treatment was uneventful. This case report shows the relevance of a detailed corneal analysis with an advanced imaging technique before performing a secondary flap in a cornea with a primary incomplete flap. The femtosecond laser technology seems to be an excellent tool to manage such cases successfully.

  5. Lower Extremity Reconstruction Using Vastus Lateralis Myocutaneous Flap versus Anterolateral Thigh Fasciocutaneous Flap

    Min Jae Lee

    2012-07-01

    Full Text Available Background The anterolateral thigh (ALT perforator flap has become a popular option fortreating soft tissue defects of lower extremity reconstruction and can be combined witha segment of the vastus lateralis muscle. We present a comparison of the use of the ALTfasciocutaneous (ALT-FC and myocutaneous flaps.Methods We retrospectively reviewed patients in whom free-tissue transfer was performedbetween 2005 and 2011 for the reconstruction of lower extremity soft-tissue defects. Twentyfourpatients were divided into two groups: reconstruction using an ALT-FC flap (12 cases andreconstruction using a vastus lateralis myocutaneous (VL-MC flap (12 cases. Postoperativecomplications, functional results, cosmetic results, and donor-site morbidities were studied.Results Complete flap survival was 100% in both groups. A flap complication was noted inone case (marginal dehiscence of the ALT-FC group, and no complications were noted in theVL-MC group. In both groups, one case of partial skin graft loss occurred at the donor site,and debulking surgeries were needed for two cases. There were no significant differences inthe mean scores for either functional or cosmetic outcomes in either group.Conclusions The VL-MC flap is able to fill occasional dead space and has comparable survivalrates to ALT-FC with minimal donor-site morbidity. Additionally, the VL-MC flap is easily elevatedwithout myocutaneous perforator injury.

  6. A physics based investigation of Gurney flaps for enhancement of rotorcraft flight characteristics

    Min, Byung-Young

    Helicopters are versatile vehicles that can vertically take off and land, hover, and perform maneuver at very low forward speeds. These characteristics make them unique for a number of civilian and military applications. However, the radial and azimuthal variation of dynamic pressure causes rotors to experience adverse phenomena such as transonic shocks and 3-D dynamic stall. Adverse interactions such as blade vortex interaction and rotor-airframe interaction may also occur. These phenomena contribute to noise and vibrations. Finally, in the event of an engine failure, rotorcraft tends to descend at high vertical velocities causing structural damage and loss of lives. A variety of techniques have been proposed for reducing the noise and vibrations. These techniques include on-board control (OBC) devices, individual blade control (IBC), and higher harmonic control (HHC). Addition of these devices adds to the weight, cost, and complexity of the rotor system, and reduces the reliability of operations. Simpler OBC concepts will greatly alleviate these drawbacks and enhance the operating envelope of vehicles. In this study, the use of Gurney flaps is explored as an OBC concept using a physics based approach. A three dimensional Navier-Stokes solver developed by the present investigator is coupled to an existing free wake model of the wake structure. The method is further enhanced for modeling of Blade-Vortex-Interactions (BVI). Loose coupling with an existing comprehensive structural dynamics analysis solver (DYMORE) is implemented for the purpose of rotor trim and modeling of aeroelastic effects. Results are presented for Gurney flaps as an OBC concept for improvements in autorotation, rotor vibration reduction, and BVI characteristics. As a representative rotor, the HART-II model rotor is used. It is found that the Gurney flap increases propulsive force in the driving region while the drag force is increased in the driven region. It is concluded that the deployable

  7. Incorporation of Cofilin into Rods Depends on Disulfide Intermolecular Bonds: Implications for Actin Regulation and Neurodegenerative Disease

    Bernstein, Barbara W; Alisa E Shaw; Minamide, Laurie S.; Pak, Chi W.; Bamburg, James R.

    2012-01-01

    Rod-shaped aggregates (“rods”), containing equimolar actin and the actin dynamizing protein cofilin, appear in neurons following a wide variety of potentially oxidative stress: simulated microischemia, cofilin overexpression, and exposure to peroxide, excess glutamate, or the dimer/trimer forms of amyloid-β peptide (Aβd/t), the most synaptotoxic Aβ species. These rods are initially reversible and neuroprotective, but if they persist in neurites, the synapses degenerate without neurons dying. ...

  8. The Actin-Severing Protein Cofilin Is Downstream of Neuregulin Signaling and Is Essential For Schwann Cell Myelination

    Sparrow, Nicklaus; Manetti, Maria Elisa; Bott, Marga; Fabianac, Tiffany; Petrilli, Alejandra; Bates, Margaret Longest; Bunge, Mary Bartlett; Lambert, Stephen; Fernandez-Valle, Cristina

    2012-01-01

    Myelination is a complex process requiring coordination of directional motility and an increase in glial cell size to generate a multilamellar myelin sheath. Regulation of actin dynamics during myelination is poorly understood. However, it is known that myelin thickness is related to the abundance of neuregulin-1 (NRG1) expressed on the axon surface. Here we identify cofilin1, an actin depolymerizing and severing protein, as a downstream target of NRG1 signaling in rat Schwann cells (SCs). In...

  9. Simultaneous Tracking of 3D Actin and Microtubule Strains in Individual MLO-Y4 Osteocytes under Oscillatory Flow

    Baik, Andrew D.; Qiu, Jun; Hillman, Elizabeth M. C.; Dong, Cheng; Guo, X. Edward

    2013-01-01

    Osteocytes in vivo experience complex fluid shear flow patterns to activate mechanotransduction pathways. The actin and microtubule (MT) cytoskeletons have been shown to play an important role in the osteocyte’s biochemical response to fluid shear loading. The dynamic nature of physiologically relevant fluid flow profiles (i.e., 1 Hz oscillatory flow) impedes the ability to image and study both actin and MT cytoskeletons simultaneously in the same cell with high spatiotemporal resolution. To ...

  10. Flapping Instability of Two Tandem Flexible Foils in Uniform Axial Flow

    Gurugubelli, Pardha Saradhi; Jaiman, Rajeev Kumar; Chua, Cassey

    2015-11-01

    We present a numerical analysis on the stability and coupled dynamics of two tandem flexible foils clamped at their leading edges in a uniform axial flow. The flexible foils considered for this study correspond to the fixed-point stable regime of the single flexible foil where the flexible foil aligns itself in the flow direction with no significant trailing edge oscillations. A high-order nonlinear coupled solver based on the variational formulation has been considered for analyzing the effects of gap between the foils on the stability and coupled behaviour of both the upstream and downstream foils. As a function of decreasing gap, it is observed that the tandem foil configuration is more prone to flapping instability than its single flexible foil counterpart. The evolution of the instability for the downstream foil shows two distinct dynamical scenarios: (i) only the downstream foil exhibits flapping motion and (ii) both the upstream and the downstream foils perform flapping. With the aid of a rigid foil in the upstream of a flexible foil, we further present a detailed analysis on the effects of the upstream wake and vortex shedding on the stability and flapping dynamics of the downstream foil.

  11. Structural Basis of Actin Filament Nucleation by Tandem W Domains

    Xiaorui Chen

    2013-06-01

    Full Text Available Spontaneous nucleation of actin is very inefficient in cells. To overcome this barrier, cells have evolved a set of actin filament nucleators to promote rapid nucleation and polymerization in response to specific stimuli. However, the molecular mechanism of actin nucleation remains poorly understood. This is hindered largely by the fact that actin nucleus, once formed, rapidly polymerizes into filament, thus making it impossible to capture stable multisubunit actin nucleus. Here, we report an effective double-mutant strategy to stabilize actin nucleus by preventing further polymerization. Employing this strategy, we solved the crystal structure of AMPPNP-actin in complex with the first two tandem W domains of Cordon-bleu (Cobl, a potent actin filament nucleator. Further sequence comparison and functional studies suggest that the nucleation mechanism of Cobl is probably shared by the p53 cofactor JMY, but not Spire. Moreover, the double-mutant strategy opens the way for atomic mechanistic study of actin nucleation and polymerization.

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

    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.

  13. Incorporation of mammalian actin into microfilaments in plant cell nucleus

    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.

  14. Design and experimental results for a turbine with jet flap stator and jet flap

    Bettner, J. L.; Blessing, J. O.

    1973-01-01

    The overall performance and detailed stator performance of a negative hub reaction turbine design featuring a moderately low solidity jet flap stator and a jet flap rotor were determined. Testing was conducted over a range of turbine expansion ratios at design speed. At each expansion ratio, the stator jet flow and rotor jet flow ranged up to about 7 and 8 percent, respectively, of the turbine inlet flow. The performance of the jet flap stator/jet flap rotor turbine was compared with that of a turbine which used the same jet flap rotor and a conventional, high solidity plan stator. The effect on performance of increased axial spacing between the jet stator and rotor was also investigated.

  15. p95-APP1 links membrane transport to Rac-mediated reorganization of actin

    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...

  16. Extended thoracodorsal artery perforator flap for breast reconstruction.

    Angrigiani, Claudio; Rancati, Alberto; Escudero, Ezequiel; Artero, Guillermo

    2015-12-01

    A total of 45 patients underwent partial or total autologous breast reconstruction after skin-sparing mastectomy, skin-reducing mastectomy, and quadrantectomy using a thoracodorsal artery perforator (TDAP) flap. The detailed surgical technique with its variations is explained in this report. The propeller, flip-over, conventional perforator, and muscle-sparing flaps have been described and evaluated. The flaps were partially or completely de-epithelialized. The conventional TDAP can be enlarged or "extended" as the traditional latissimus dorsi musculocutaneous (LD-MC) flap by incorporating the superior and inferior fat compartments. It can be referred to as the "extended TDAP flap". This technique augments the flap volume. In addition, this flap can serve as a scaffold for lipofilling to obtain autologous breast reconstruction in medium to large cases. There were two complete failures due to technical errors during flap elevation. Distal partial tissue suffering was observed in four flaps. These flaps were longer than usual; they reached the midline of the back. It is advisable to discard the distal medial quarter of the flap when it is designed up to the midline to avoid steatonecrosis or fibrosis. A retrospective analysis of the 39 flaps that survived completely revealed a satisfactory result in 82% of the cases. The main disadvantage of this procedure is the final scar. The TDAP flap is a reliable and safe method for partial or total breast autologous reconstruction. PMID:26645006

  17. Viscoelastic cell mechanics and actin remodelling are dependent on the rate of applied pressure.

    Priyanka Pravincumar

    Full Text Available BACKGROUND: Living cells are subjected to external and internal mechanical stresses. The effects of these stresses on the deformation and subsequent biological response of the cells remains unclear. This study tested the hypothesis that the rate at which pressure (or stress is applied influence the viscoelastic properties of the cell associated with differences in the dynamics of the actin cytoskeleton. PRINCIPAL FINDING: Micropipette aspiration was used to determine the instantaneous and equilibrium moduli and the viscosity of isolated chondrocytes based on the standard linear solid (SLS model and a variation of this incorporating Boltzmann superposition. Cells were visualised for 180 seconds following aspiration to 7 cmH(2O at 0.35, 0.70 and 5.48 cmH(2O/sec. Cell recovery was then examined for a further 180 seconds once the pressure had been removed. Reducing the rate of application of pressure reduced the levels of cell deformation and recovery associated with a significant increase in modulus and viscosity. Using GFP transfection and confocal microscopy, we show that chondrocyte deformation involves distortion, disassembly and subsequent reassembly of the cortical actin cytoskeleton. At faster pressure rates, cell deformation produced an increase in cell volume associated with membrane bleb formation. GFP-actin transfection inhibited the pressure rate dependent variation in cell mechanics indicating that this behaviour is regulated by GFP-sensitive actin dynamics. CONCLUSION: We suggest that slower rates of aspiration pressure enable greater levels of cortical actin distortion. This is partially inhibited by GFP or faster aspiration rates leading to membrane bleb formation and an increase in cell volume. Thus the rate of application of pressure regulates the viscoelastic mechanical properties of living cells through pressure rate sensitive differences in actin dynamics. Therefore cells appear softer when aspirated at a faster rate in

  18. A low-cost simulation platform for flapping wing MAVs

    Kok, J. M.; Chahl, J. S.

    2015-03-01

    This paper describes the design of a flight simulator for analysing the systems level performance of a Dragonfly-Inspired Micro Air Vehicle (DIMAV). A quasi-steady blade element model is used to analyse the aerodynamic forces. Aerodynamic and environmental forces are then incorporated into a real world flight dynamics model to determine the dynamics of the DIMAV system. The paper also discusses the implementation of the flight simulator for analysing the manoeuvrability of a DIMAV, specifically several modes of flight commonly found in dragonflies. This includes take-off, roll turns and yaw turns. Our findings with the simulator are consistent with results from wind tunnel studies and slow motion cinematography of dragonflies. In the take-off mode of flight, we see a strong dependence of take-off accelerations with flapping frequency. An increase in wing-beat frequency of 10% causes the maximum vertical acceleration to increase by 2g which is similar to that of dragonflies in nature. For the roll and yaw modes of manoeuvring, asymmetrical inputs are applied between the left and right set of wings. The flapping amplitude is increased on the left pair of wings which causes a time averaged roll rate to the right of 1.76rad/s within two wing beats. In the yaw mode, the stroke plane angle is reduced in the left pair of wings to initiate the yaw manoeuvre. In two wing beats, the time averaged yaw rate is 2.54rad/s.

  19. Chemotactic peptide modulation of actin assembly and locomotion in neutrophils

    1984-01-01

    To determine the relationship between the state of actin polymerization in neutrophils and the formyl-methionyl-leucyl-phenylalanine (fMLP)- induced changes in the locomotive behavior of neutrophils, the mean rate of locomotion (mROL), the percent G-actin, and the relative F- actin content of neutrophils were determined. The mROL was quantified by analysis of the locomotion of individual cells; the percentage of total actin as G-actin was measured by DNase I inhibition; and the F- actin was d...

  20. The interaction between actin and FA fragment of diphtheria toxin

    Ünlü, A.; Bektaş, M.; Şener, S.; Nurten, R.

    2012-01-01

    Actin protein has many other cellular functions such as movement, chemotaxis, secretion and cytodiaresis. Besides, it have structural function. Actin is a motor protein that it has an important role in the movement process of toxin in the cell. It is known that F-actin gives carriage support during the endosomal process. Actin is found in globular (G) and filamentous (F) structure in the cell. The helix of actin occurs as a result of polymerisation of monomeric G-actin molecules through seque...

  1. Control of electrostatic interactions between F-actin and genetically modified lysozyme in aqueous media

    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.

  2. Control of Electrostatic Interactions Between F-Actin And Genetically Modified Lysozyme in Aqueous Media

    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.

  3. Control of electrostatic interactions between F-actin and genetically modified lysozyme in aqueous media

    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.

  4. Control of Electrostatic Interactions Between F-Actin And Genetically Modified Lysozyme in Aqueous Media

    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.

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

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

    2010-07-01

    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. PMID:20442407

  6. DNA segregation by the bacterial actin AlfA during Bacillus subtilis growth and development

    Becker, Eric; Herrera, Nick C; Gunderson, Felizza Q.; Derman, Alan I.; Dance, Amber L; Sims, Jennifer; Larsen, Rachel A.; Pogliano, Joe

    2006-01-01

    We here identify a protein (AlfA; actin like filament) that defines a new family of actins that are only distantly related to MreB and ParM. AlfA is required for segregation of Bacillus subtilis plasmid pBET131 (a mini pLS32-derivative) during growth and sporulation. A 3-kb DNA fragment encoding alfA and a downstream gene (alfB) is necessary and sufficient for plasmid stability. AlfA-GFP assembles dynamic cytoskeletal filaments that rapidly turn over (t1/2

  7. The actin binding protein adseverin regulates osteoclastogenesis.

    Hassanpour, Siavash; Jiang, Hongwei; Wang, Yongqiang; Kuiper, Johannes W P; Glogauer, Michael

    2014-01-01

    Adseverin (Ads), a member of the Gelsolin superfamily of actin binding proteins, regulates the actin cytoskeleton architecture by severing and capping existing filamentous actin (F-actin) strands and nucleating the assembly of new F-actin filaments. Ads has been implicated in cellular secretion, exocytosis and has also been shown to regulate chondrogenesis and megakaryoblastic leukemia cell differentiation. Here we report for the first time that Ads is involved in regulating osteoclastogenesis (OCG). Ads is induced during OCG downstream of RANK-ligand (RANKL) stimulation and is highly expressed in mature osteoclasts. The D5 isoform of Ads is not involved in regulating OCG, as its expression is not induced in response to RANKL. Three clonal Ads knockdown RAW264.7 (RAW) macrophage cell lines with varying degrees of Ads expression and OCG deficiency were generated. The most drastic OCG defect was noted in the clonal cell line with the greatest degree of Ads knockdown as indicated by a lack of TRAcP staining and multinucleation. RNAi mediated knockdown of Ads in osteoclast precursors resulted in distinct morphological changes characterized by altered F-actin distribution and increased filopodia formation. Ads knockdown precursor cells experienced enhanced migration while fusion of knockdown precursors cells was limited. Transient reintroduction of de novo Ads back into the knockdown system was capable of rescuing TRAcP expression but not osteoclast multinucleation most likely due to the transient nature of Ads expression. This preliminary study allows us to conclude that Ads is a RANKL induced early regulator of OCG with a potential role in pre-osteoclast differentiation and fusion. PMID:25275604

  8. The actin binding protein adseverin regulates osteoclastogenesis.

    Siavash Hassanpour

    Full Text Available Adseverin (Ads, a member of the Gelsolin superfamily of actin binding proteins, regulates the actin cytoskeleton architecture by severing and capping existing filamentous actin (F-actin strands and nucleating the assembly of new F-actin filaments. Ads has been implicated in cellular secretion, exocytosis and has also been shown to regulate chondrogenesis and megakaryoblastic leukemia cell differentiation. Here we report for the first time that Ads is involved in regulating osteoclastogenesis (OCG. Ads is induced during OCG downstream of RANK-ligand (RANKL stimulation and is highly expressed in mature osteoclasts. The D5 isoform of Ads is not involved in regulating OCG, as its expression is not induced in response to RANKL. Three clonal Ads knockdown RAW264.7 (RAW macrophage cell lines with varying degrees of Ads expression and OCG deficiency were generated. The most drastic OCG defect was noted in the clonal cell line with the greatest degree of Ads knockdown as indicated by a lack of TRAcP staining and multinucleation. RNAi mediated knockdown of Ads in osteoclast precursors resulted in distinct morphological changes characterized by altered F-actin distribution and increased filopodia formation. Ads knockdown precursor cells experienced enhanced migration while fusion of knockdown precursors cells was limited. Transient reintroduction of de novo Ads back into the knockdown system was capable of rescuing TRAcP expression but not osteoclast multinucleation most likely due to the transient nature of Ads expression. This preliminary study allows us to conclude that Ads is a RANKL induced early regulator of OCG with a potential role in pre-osteoclast differentiation and fusion.

  9. Modified cup flap for volar oblique fingertip amputations

    Ahmadli, A.

    2016-02-01

    Full Text Available We describe a modified volar “V-Y cup” flap for volar fingertip defects that do not exceed more than half of the distal phalanx for better aesthetic and functional outcome. In seven cases out of eight, the flap was elevated with a subdermal pedicle, whereas in one case, the flap was elevated as an island on the bilateral neurovascular bundle. The fingertips have been evaluated for sensibility using standard tests, hook nail deformity and patient satisfaction. Seven flaps have survived completely. The flap with skeletonized bilateral digital neurovascular bundle has shown signs of venous insufficiency on the 5 postoperative day with consecutive necrosis. Suturing the distal edges of the flap in a “cupping” fashion provided a normal pulp contour. The modified flap can be used for defects as mentioned above. Subdermally dissected pedicle-based flap is safe and easy to elevate. The aesthetic and functional outcomes have been reported to be satisfactory.

  10. Kinematic control of aerodynamic forces on an inclined flapping wing with asymmetric strokes

    In the present study, we conduct an experiment using a one-paired dynamically scaled model of an insect wing, to investigate how asymmetric strokes with different wing kinematic parameters are used to control the aerodynamics of a dragonfly-like inclined flapping wing in still fluid. The kinematic parameters considered are the angles of attack during the mid-downstroke (αmd) and mid-upstroke (αmu), and the duration (Δτ) and time of initiation (τp) of the pitching rotation. The present dragonfly-like inclined flapping wing has the aerodynamic mechanism of unsteady force generation similar to those of other insect wings in a horizontal stroke plane, but the detailed effect of the wing kinematics on the force control is different due to the asymmetric use of the angle of attack during the up- and downstrokes. For example, high αmd and low αmu produces larger vertical force with less aerodynamic power, and low αmd and high αmu is recommended for horizontal force (thrust) production. The pitching rotation also affects the aerodynamics of a flapping wing, but its dynamic rotational effect is much weaker than the effect from the kinematic change in the angle of attack caused by the pitching rotation. Thus, the influences of the duration and timing of pitching rotation for the present inclined flapping wing are found to be very different from those for a horizontal flapping wing. That is, for the inclined flapping motion, the advanced and delayed rotations produce smaller vertical forces than the symmetric one and the effect of pitching duration is very small. On the other hand, for a specific range of pitching rotation timing, delayed rotation requires less aerodynamic power than the symmetric rotation. As for the horizontal force, delayed rotation with low αmd and high αmu is recommended for long-duration flight owing to its high efficiency, and advanced rotation should be employed for hovering flight for nearly zero horizontal force. The present study

  11. The forked flap repair for hypospadias

    Anil Chadha

    2012-01-01

    Full Text Available Context: Despite the abundance of techniques for the repair of Hypospadias, its problems still persist and a satisfactory design to correct the penile curvature with the formation of neourethra from the native urethral tissue or genital or extragenital tissues, with minimal postoperative complications has yet to evolve. Aim: Persisting with such an endeavor, a new technique for the repair of distal and midpenile hypospadias is described. Materials and Methods: The study has been done in 70 cases over the past 11 years. The "Forked-Flap" repair is a single stage method for the repair of such Hypospadias with chordee. It takes advantage of the rich vascular communication at the corona and capitalizes on the established reliability of the meatal based flip-flap. The repair achieves straightening of the curvature of the penis by complete excision of chordee tissue from the ventral surface of the penis beneath the urethral plate. The urethra is reconstructed using the native plate with forked flap extensions and genital tissue relying on the concept of meatal based flaps. Water proofing by dartos tissue and reinforcement by Nesbit′s prepucial tissue transfer completes the one stage procedure. Statistical Analysis: An analysis of 70 cases of this single stage technique of repair of penile hypospadias with chordee, operated at 3 to 5 years of age over the past 11 years is presented. Results and Conclusion: The Forked Flap gives comparable and replicable results; except for a urethrocutaneous fistula rate of 4% no other complications were observed.

  12. Deltopectoral Flap in the Era of Microsurgery

    R. C. L. Chan

    2014-01-01

    Full Text Available Background. Our study aimed to review the role of deltopectoral (DP flap as a reconstructive option for defects in the head and neck region in the microvascular era. Methods. All patients who received DP flap reconstruction surgery at the Department of Surgery, Queen Mary Hospital, between 1999 and 2011 were recruited. Demographic data, indications for surgery, defect for reconstruction, and surgical outcomes were analyzed. Results. Fifty-four patients were included. All but two patients were operated for reconstruction after tumour resection. The remaining two patients were operated for necrotizing fasciitis and osteoradionecrosis. The majority of DP flaps were used to cover neck skin defect (63.0%. Other reconstructed defects included posterior pharyngeal wall (22.2%, facial skin defect (11.1%, and tracheal wall (3.7%. All donor sites were covered with partial thickness skin graft. Two patients developed partial flap necrosis at the tip and were managed conservatively. The overall flap survival rate was 96.3%. Conclusions. Albeit the technical advancements in microvascular surgery, DP still possesses multiple advantages (technical simplicity, reliable axial blood supply, large size, thinness, and pliability which allows it to remain as a useful, reliable, and versatile surgical option for head and neck reconstruction.

  13. Topology optimization of pressure adaptive honeycomb for a morphing flap

    Vos, Roelof; Scheepstra, Jan; Barrett, Ron

    2011-03-01

    The paper begins with a brief historical overview of pressure adaptive materials and structures. By examining avian anatomy, it is seen that pressure-adaptive structures have been used successfully in the Natural world to hold structural positions for extended periods of time and yet allow for dynamic shape changes from one flight state to the next. More modern pneumatic actuators, including FAA certified autopilot servoactuators are frequently used by aircraft around the world. Pneumatic artificial muscles (PAM) show good promise as aircraft actuators, but follow the traditional model of load concentration and distribution commonly found in aircraft. A new system is proposed which leaves distributed loads distributed and manipulates structures through a distributed actuator. By using Pressure Adaptive Honeycomb (PAH), it is shown that large structural deformations in excess of 50% strains can be achieved while maintaining full structural integrity and enabling secondary flight control mechanisms like flaps. The successful implementation of pressure-adaptive honeycomb in the trailing edge of a wing section sparked the motivation for subsequent research into the optimal topology of the pressure adaptive honeycomb within the trailing edge of a morphing flap. As an input for the optimization two known shapes are required: a desired shape in cruise configuration and a desired shape in landing configuration. In addition, the boundary conditions and load cases (including aerodynamic loads and internal pressure loads) should be specified for each condition. Finally, a set of six design variables is specified relating to the honeycomb and upper skin topology of the morphing flap. A finite-element model of the pressure-adaptive honeycomb structure is developed specifically tailored to generate fast but reliable results for a given combination of external loading, input variables, and boundary conditions. Based on two bench tests it is shown that this model correlates well

  14. 14 CFR 25.1511 - Flap extended speed.

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Flap extended speed. 25.1511 Section 25... Limitations § 25.1511 Flap extended speed. The established flap extended speed V FE must be established so that it does not exceed the design flap speed V F chosen under §§ 25.335(e) and 25.345, for...

  15. Pharyngo oesophageal strictures and its reconstruction by delto pectoral flaps

    Guha, Goutam; S Gupta; Chakraborty, S

    2005-01-01

    Delto pectoral flap is a thin and pliable cutaneous axial flap suitable for the reconstruction of pharynx and upper oesophagus. Corrosive stricture of the pharyngo oesophageal area can very well be reconstructed by deltopectoral flap. Oesophageal reconstruction by viscera like stomach or colon often produces anastomic stricture at the upper anastomic site with hypopharynx or upper oesophagus. Delto pectoral flap can also be used to reconstruct this anastomotic stricture. Postoperative swallow...

  16. The Use of the Juri Temporo-Parieto-Occipital Flap

    Juri, Jose; Valotta, Marìa Fernanda

    2005-01-01

    The temporo-parieto-occipital flap, introduced in 1969, was the first large monopedicled flap performed in the scalp for reconstructive and aesthetic purposes. Its versatility for correction of many areas of the scalp relies on its wide arch of rotation, based in the flap's pedicle, which is the superficial temporal artery and vein. The axial pattern of the flap is explained by the unique kind of vascularization present in the scalp, based on a profuse intraparietal blood flow with multiple a...

  17. The submental island flap for reconstruction of facial defects.

    Prabhune K; Patni S; Gomes D.; Bhathena H; Kavarana N

    1998-01-01

    The procedure of facial resurfacing dictates that there should be an excellent colour and texture match between the facial and the transposed skin. Cervical flaps e.g. platysma flap are commonly used for reconstruction of facial defects but, with disadvantages like limited mobility, unacceptable donor site and unpredictable outcomes. The submental island flap is a new addition to the armamentorium of the Plastic Surgeon. It is an axial pattern flap based on the submental branch of facial arte...

  18. Perforator plus flaps: Optimizing results while preserving function and esthesis

    Mehrotra Sandeep

    2010-01-01

    Full Text Available Background: The tenuous blood supply of traditional flaps for wound cover combined with collateral damage by sacrifice of functional muscle, truncal vessels, or nerves has been the bane of reconstructive procedures. The concept of perforator plus flaps employs dual vascular supply to flaps. By safeguarding perforators along with supply from its base, robust flaps can be raised in diverse situations. This is achieved while limiting collateral damage and preserving nerves, vessels, and functioning muscle with better function and aesthesis. Materials and Methods: The perforator plus concept was applied in seven different clinical situations. Functional muscle and fasciocutaneous flaps were employed in five and adipofascial flaps in two cases, primarily involving lower extremity defects and back. Adipofascial perforator plus flaps were employed to provide cover for tibial fracture in one patients and chronic venous ulcer in another. Results: All flaps survived without any loss and provided long-term stable cover, both over soft tissue and bone. Functional preservation was achieved in all cases where muscle flaps were employed with no clinical evidence of loss of power. There was no sensory loss or significant oedema in or distal to the flap in both cases where neurovascular continuity was preserved during flap elevation. Fracture union and consolidation were satisfactory. One patient had minimal graft loss over fascia which required application of stored grafts with subsequent take. No patient required re-operation. Conclusions: Perforator plus concept is holistic and applicable to most flap types in varied situations. It permits the exercise of many locoregional flap options while limiting collateral functional damage. Aesthetic considerations are also addressed while raising adipofascial flaps because of no appreciable donor defects. With quick operating times and low failure risk, these flaps can be a better substitute to traditional flaps and at

  19. The aerodynamic and structural study of flapping wing vehicles

    Zhou, Liangchen

    2013-01-01

    This thesis reports on the aerodynamic and structural study carried out on flapping wings and flapping vehicles. Theoretical and experimental investigation of aerodynamic forces acting on flapping wings in simple harmonic oscillations is undertaken in order to help conduct and optimize the aerodynamic and structural design of flapping wing vehicles. The research is focused on the large scale ornithopter design of similar size and configuration to a hang glider. By means of Theodorsen’s th...

  20. F-actin mechanics control spindle centring in the mouse zygote

    Chaigne, Agathe; Campillo, Clément; Voituriez, Raphaël; Gov, Nir S.; Sykes, Cécile; Verlhac, Marie-Hélène; Terret, Marie-Emilie

    2016-01-01

    Mitotic spindle position relies on interactions between astral microtubules nucleated by centrosomes and a rigid cortex. Some cells, such as mouse oocytes, do not possess centrosomes and astral microtubules. These cells rely only on actin and on a soft cortex to position their spindle off-centre and undergo asymmetric divisions. While the first mouse embryonic division also occurs in the absence of centrosomes, it is symmetric and not much is known on how the spindle is positioned at the exact cell centre. Using interdisciplinary approaches, we demonstrate that zygotic spindle positioning follows a three-step process: (1) coarse centring of pronuclei relying on the dynamics of an F-actin/Myosin-Vb meshwork; (2) fine centring of the metaphase plate depending on a high cortical tension; (3) passive maintenance at the cell centre. Altogether, we show that F-actin-dependent mechanics operate the switch between asymmetric to symmetric division required at the oocyte to embryo transition.

  1. Direct visualization of flow-induced conformational transitions of single actin filaments in entangled solutions

    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...

  2. Myopathy-inducing mutation H40Y in ACTA1 hampers actin filament structure and function.

    Chan, Chun; Fan, Jun; Messer, Andrew E; Marston, Steve B; Iwamoto, Hiroyuki; Ochala, Julien

    2016-08-01

    In humans, more than 200 missense mutations have been identified in the ACTA1 gene. The exact molecular mechanisms by which, these particular mutations become toxic and lead to muscle weakness and myopathies remain obscure. To address this, here, we performed a molecular dynamics simulation, and we used a broad range of biophysical assays to determine how the lethal and myopathy-related H40Y amino acid substitution in actin affects the structure, stability, and function of this protein. Interestingly, our results showed that H40Y severely disrupts the DNase I-binding-loop structure and actin filaments. In addition, we observed that normal and mutant actin monomers are likely to form distinctive homopolymers, with mutant filaments being very stiff, and not supporting proper myosin binding. These phenomena underlie the toxicity of H40Y and may be considered as important triggering factors for the contractile dysfunction, muscle weakness and disease phenotype seen in patients. PMID:27112274

  3. Femtosecond pump-probe studies of actinic-wavelength dependence in aqueous chlorine dioxide photochemistry

    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 (2A2 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.

  4. Dynamin-Actin Cross Talk Contributes to Phagosome Formation and Closure.

    Marie-Anaïs, Florence; Mazzolini, Julie; Herit, Floriane; Niedergang, Florence

    2016-05-01

    Phagocytosis is a mechanism used by macrophages to internalize and eliminate microorganisms or cellular debris. It relies on profound rearrangements of the actin cytoskeleton that is the driving force allowing plasma membrane extension around the particle. The closure step of phagocytosis, however, remains poorly defined. We used a dedicated experimental setup with Total Internal Reflection Fluorescence Microscopy (TIRFM) to monitor phagosome formation and closure in three dimensions in living cells. We show that dynamin-2, which mediates the scission of endocytic vesicles, was recruited early and concomitantly with actin during phagosome formation. Dynamin-2 accumulated at the site of phagosome closure in living macrophages. Inhibition of its activity with dominant negative mutants or drugs demonstrated that dynamin-2 is implicated in actin dynamics and pseudopod extension. Depolymerization of actin led to impaired dynamin-2 recruitment or activity. Finally, we show that dynamin-2 plays a critical role in the effective scission of the phagosome from the plasma membrane. Thus, we establish that a cross talk between actin and dynamin takes place for phagosome formation and closure before dynamin functions for scission. PMID:26847957

  5. Shear-induced reorganization of renal proximal tubule cell actin cytoskeleton and apical junctional complexes.

    Duan, Yi; Gotoh, Nanami; Yan, Qingshang; Du, Zhaopeng; Weinstein, Alan M; Wang, Tong; Weinbaum, Sheldon

    2008-08-12

    In this study, we demonstrate that fluid shear stress (FSS)-induced actin cytoskeletal reorganization and junctional formation in renal epithelial cells are nearly completely opposite the corresponding changes in vascular endothelial cells (ECs) [Thi MM et al. (2004) Proc Natl Acad Sci USA 101:16483-16488]. Mouse proximal tubule cells (PTCs) were subjected to 5 h of FSS (1 dyn/cm(2)) to investigate the dynamic responses of the cytoskeletal distribution of filamentous actin (F-actin), ZO-1, E-cadherin, vinculin, and paxillin to FSS. Immunofluorescence analysis revealed that FSS caused basal stress fiber disruption, more densely distributed peripheral actin bands (DPABs), and the formation of both tight junctions (TJs) and adherens junctions (AJs). A dramatic reinforcement of vinculin staining was found at the cell borders as well as the cell interior. These responses were abrogated by the actin-disrupting drug, cytochalasin D. To interpret these results, we propose a "junctional buttressing" model for PTCs in which FSS enables the DPABs, TJs, and AJs to become more tightly connected. In contrast, in the "bumper-car" model for ECs, all junctional connections were severely disrupted by FSS. This "junctional buttressing" model explains why a FSS of only 1/10 of that used in the EC study can cause a similarly dramatic, cytoskeletal response in these tall, cuboidal epithelial cells; and why junctional buttressing between adjacent cells may benefit renal epithelium in maximizing flow-activated, brush border-dependent, transcellular salt and water reabsorption. PMID:18685100

  6. Cations Stiffen Actin Filaments by Adhering a Key Structural Element to Adjacent Subunits.

    Hocky, Glen M; Baker, Joseph L; Bradley, Michael J; Sinitskiy, Anton V; De La Cruz, Enrique M; Voth, Gregory A

    2016-05-26

    Ions regulate the assembly and mechanical properties of actin filaments. Recent work using structural bioinformatics and site-specific mutagenesis favors the existence of two discrete and specific divalent cation binding sites on actin filaments, positioned in the long axis between actin subunits. Cation binding at one site drives polymerization, while the other modulates filament stiffness and plays a role in filament severing by the regulatory protein, cofilin. Existing structural methods have not been able to resolve filament-associated cations, and so in this work we turn to molecular dynamics simulations to suggest a candidate binding pocket geometry for each site and to elucidate the mechanism by which occupancy of the "stiffness site" affects filament mechanical properties. Incorporating a magnesium ion in the "polymerization site" does not seem to require any large-scale change to an actin subunit's conformation. Binding of a magnesium ion in the "stiffness site" adheres the actin DNase-binding loop (D-loop) to its long-axis neighbor, which increases the filament torsional stiffness and bending persistence length. Our analysis shows that bound D-loops occupy a smaller region of accessible conformational space. Cation occupancy buries key conserved residues of the D-loop, restricting accessibility to regulatory proteins and enzymes that target these amino acids. PMID:27146246

  7. Actin filaments target the oligomeric maturation of the dynamin GTPase Drp1 to mitochondrial fission sites.

    Ji, Wei-ke; Hatch, Anna L; Merrill, Ronald A; Strack, Stefan; Higgs, Henry N

    2015-01-01

    While the dynamin GTPase Drp1 plays a critical role during mitochondrial fission, mechanisms controlling its recruitment to fission sites are unclear. A current assumption is that cytosolic Drp1 is recruited directly to fission sites immediately prior to fission. Using live-cell microscopy, we find evidence for a different model, progressive maturation of Drp1 oligomers on mitochondria through incorporation of smaller mitochondrially-bound Drp1 units. Maturation of a stable Drp1 oligomer does not forcibly lead to fission. Drp1 oligomers also translocate directionally along mitochondria. Ionomycin, a calcium ionophore, causes rapid mitochondrial accumulation of actin filaments followed by Drp1 accumulation at the fission site, and increases fission rate. Inhibiting actin polymerization, myosin IIA, or the formin INF2 reduces both un-stimulated and ionomycin-induced Drp1 accumulation and mitochondrial fission. Actin filaments bind purified Drp1 and increase GTPase activity in a manner that is synergistic with the mitochondrial protein Mff, suggesting a role for direct Drp1/actin interaction. We propose that Drp1 is in dynamic equilibrium on mitochondria in a fission-independent manner, and that fission factors such as actin filaments target productive oligomerization to fission sites. PMID:26609810

  8. Dipteran wing motor-inspired flapping flight versatility and effectiveness enhancement.

    Harne, R L; Wang, K W

    2015-03-01

    Insects are a prime source of inspiration towards the development of small-scale, engineered, flapping wing flight systems. To help interpret the possible energy transformation strategies observed in Diptera as inspiration for mechanical flapping flight systems, we revisit the perspective of the dipteran wing motor as a bistable click mechanism and take a new, and more flexible, outlook to the architectural composition previously considered. Using a representative structural model alongside biological insights and cues from nonlinear dynamics, our analyses and experimental results reveal that a flight mechanism able to adjust motor axial support stiffness and compression characteristics may dramatically modulate the amplitude range and type of wing stroke dynamics achievable. This corresponds to significantly more versatile aerodynamic force generation without otherwise changing flapping frequency or driving force amplitude. Whether monostable or bistable, the axial stiffness is key to enhance compressed motor load bearing ability and aerodynamic efficiency, particularly compared with uncompressed linear motors. These findings provide new foundation to guide future development of bioinspired, flapping wing mechanisms for micro air vehicle applications, and may be used to provide insight to the dipteran muscle-to-wing interface. PMID:25608517

  9. Unique Flap Conformation in an HIV-1 Protease with High-Level Darunavir Resistance.

    Nakashima, Masaaki; Ode, Hirotaka; Suzuki, Koji; Fujino, Masayuki; Maejima, Masami; Kimura, Yuki; Masaoka, Takashi; Hattori, Junko; Matsuda, Masakazu; Hachiya, Atsuko; Yokomaku, Yoshiyuki; Suzuki, Atsuo; Watanabe, Nobuhisa; Sugiura, Wataru; Iwatani, Yasumasa

    2016-01-01

    Darunavir (DRV) is one of the most powerful protease inhibitors (PIs) for treating human immunodeficiency virus type-1 (HIV-1) infection and presents a high genetic barrier to the generation of resistant viruses. However, DRV-resistant HIV-1 infrequently emerges from viruses exhibiting resistance to other protease inhibitors. To address this resistance, researchers have gathered genetic information on DRV resistance. In contrast, few structural insights into the mechanism underlying DRV resistance are available. To elucidate this mechanism, we determined the crystal structure of the ligand-free state of a protease with high-level DRV resistance and six DRV resistance-associated mutations (including I47V and I50V), which we generated by in vitro selection. This crystal structure showed a unique curling conformation at the flap regions that was not found in the previously reported ligand-free protease structures. Molecular dynamics simulations indicated that the curled flap conformation altered the flap dynamics. These results suggest that the preference for a unique flap conformation influences DRV binding. These results provide new structural insights into elucidating the molecular mechanism of DRV resistance and aid to develop PIs effective against DRV-resistant viruses. PMID:26870021

  10. Actin filaments growing against a barrier with fluctuating shape

    Sadhu, Raj Kumar; Chatterjee, Sakuntala

    2016-06-01

    We study force generation by a set of parallel actin filaments growing against a nonrigid obstacle, in the 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 nonrigid 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 affect 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 calculations within mean-field theory show reasonable agreement with our simulation results.

  11. Actin filaments growing against a barrier with fluctuating shape

    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.

  12. 14 CFR 23.1511 - Flap extended speed.

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Flap extended speed. 23.1511 Section 23.1511 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT... Information § 23.1511 Flap extended speed. (a) The flap extended speed V FE must be established so that it...

  13. Peroperative evaluation of vascularity of various flaps by fluorescein technique

    Bhattacharya V

    2006-01-01

    Full Text Available Background: The viability of any pedicled flap depends upon its vascularity. When a flap is dissected it becomes relatively ischaemic. Ultimately, the viability of the flap depends on the vessels incorporated in the pedicle and their perfusion capacity. There are different techniques to evaluate the blood supply of a flap. Aims: This study deals with experimental and clinical efficiency of fluorescein dye technique to evaluate the vascularity of flaps of various compositions. Materials and Methods: The experimental study was conducted on rats to standardize the technique. Thereafter clinical evaluation was conducted for different flaps namely fasciocutaneous, skeletonized perforator based fasciocutaneous, adipofascial, fasciocutaneous flap with adipofascial extension, fasciocutaneous flap with fascial extension and fasciocutaneous flap with split fascial extension. Conclusions: The paper deals in detail with the technique and method of documentation of a fluorescein study on flaps both experimentally and clinically. The appearance of fluorescein on both the surfaces and distal margin of the flap confirmed the adequacy of vascularity soon after dissection of the flaps. It was found to be an easy, safe and reliable objective method.

  14. Fibula free flap splitting for mandible reconstruction: A technical note

    López-Arcas, José María; M. Burgueño; Del Castillo, J. L.

    2009-01-01

    Conformation of the fibula flap to passively adapt to the remaining mandible may be indeed challenging. A review of the ‘axial splitting’ technique for fibula free flaps is presented with a novel method of osteosynthesis. Adequate mandibular angle shape is achieved by performing this type of osteotomy with a minimal use of titanium hardware for flap insetting.

  15. Unilateral Breast Reconstruction Using Bilateral Inferior Gluteal Artery Perforator Flaps

    Toshihiko Satake, MD

    2015-03-01

    Conclusions: Use of bilateral IGAP flaps for breast reconstruction helps to avoid asymmetry of the inferior buttock volume and shape. Bilateral flaps provide sufficient tissue volume and allow for reconstruction of a breast comparable to the unaffected side. In patients with moderate-to-high projection breast whose abdominal tissue cannot be used for reconstruction, IGAP flaps may be a suitable alternative.

  16. Prospective evaluation of outcome measures in free-flap surgery.

    Kelly, John L

    2004-08-01

    Free-flap failure is usually caused by venous or arterial thrombosis. In many cases, lack of experience and surgical delay also contribute to flap loss. The authors prospectively analyzed the outcome of 57 free flaps over a 28-month period (January, 1999 to April, 2001). The setting was a university hospital tertiary referral center. Anastomotic technique, ischemia time, choice of anticoagulant, and the grade of surgeon were recorded. The type of flap, medications, and co-morbidities, including preoperative radiotherapy, were also documented. Ten flaps were re-explored (17 percent). There were four cases of complete flap failure (6.7 percent) and five cases of partial failure (8.5 percent). In patients who received perioperative systemic heparin or dextran, there was no evidence of flap failure (p = .08). The mean ischemia time was similar in flaps that failed (95 +\\/- 29 min) and in those that survived (92 +\\/- 34 min). Also, the number of anastomoses performed by trainees in flaps that failed (22 percent), was similar to the number in flaps that survived (28 percent). Nine patients received preoperative radiotherapy, and there was complete flap survival in each case. This study reveals that closely supervised anastomoses performed by trainees may have a similar outcome to those performed by more senior surgeons. There was no adverse effect from radiotherapy or increased ischemia time on flap survival.

  17. Continuous-Wave Stimulated Emission Depletion Microscope for Imaging Actin Cytoskeleton in Fixed and Live Cells

    Bhanu Neupane

    2015-09-01

    Full Text Available Stimulated emission depletion (STED microscopy provides a new opportunity to study fine sub-cellular structures and highly dynamic cellular processes, which are challenging to observe using conventional optical microscopy. Using actin as an example, we explored the feasibility of using a continuous wave (CW-STED microscope to study the fine structure and dynamics in fixed and live cells. Actin plays an important role in cellular processes, whose functioning involves dynamic formation and reorganization of fine structures of actin filaments. Frequently used confocal fluorescence and STED microscopy dyes were employed to image fixed PC-12 cells (dyed with phalloidin- fluorescein isothiocyante and live rat chondrosarcoma cells (RCS transfected with actin-green fluorescent protein (GFP. Compared to conventional confocal fluorescence microscopy, CW-STED microscopy shows improved spatial resolution in both fixed and live cells. We were able to monitor cell morphology changes continuously; however, the number of repetitive analyses were limited primarily by the dyes used in these experiments and could be improved with the use of dyes less susceptible to photobleaching. In conclusion, CW-STED may disclose new information for biological systems with a proper characteristic length scale. The challenges of using CW-STED microscopy to study cell structures are discussed.

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

    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

  19. Double papilla flap technique for dual purpose

    P Mohan Kumar

    2012-01-01

    Full Text Available Marginal tissue recession exposes the anatomic root on the teeth, which gives rise to -common patient complaints. It is associated with sensitivity, tissue irritation, cervical abrasions, and esthetic concerns. Various types of soft tissue grafts may be performed when recession is deep and marginal tissue health cannot be maintained. Double papilla flap is an alternative technique to cover isolated recessions and correct gingival defects in areas of insufficient attached gingiva, not suitable for a lateral sliding flap. This technique offers the advantages of dual blood supply and denudation of interdental bone only, which is less susceptible to permanent damage after surgical exposure. It also offers the advantage of quicker healing in the donor site and reduces the risk of facial bone height loss. This case report presents the advantages of double papilla flap in enhancing esthetic and functional outcome of the patient.

  20. Collective Flow Enhancement by Tandem Flapping Wings

    Gravish, Nick; Peters, Jacob M.; Combes, Stacey A.; Wood, Robert J.

    2015-10-01

    We examine the fluid-mechanical interactions that occur between arrays of flapping wings when operating in close proximity at a moderate Reynolds number (Re ≈100 - 1000 ). Pairs of flapping wings are oscillated sinusoidally at frequency f , amplitude θM, phase offset ϕ , and wing separation distance D*, and outflow speed v* is measured. At a fixed separation distance, v* is sensitive to both f and ϕ , and we observe both constructive and destructive interference in airspeed. v* is maximized at an optimum phase offset, ϕmax, which varies with wing separation distance, D*. We propose a model of collective flow interactions between flapping wings based on vortex advection, which reproduces our experimental data.

  1. Numerical linearized MHD model of flapping oscillations

    Korovinskiy, D. B.; Ivanov, I. B.; Semenov, V. S.; Erkaev, N. V.; Kiehas, S. A.

    2016-06-01

    Kink-like magnetotail flapping oscillations in a Harris-like current sheet with earthward growing normal magnetic field component Bz are studied by means of time-dependent 2D linearized MHD numerical simulations. The dispersion relation and two-dimensional eigenfunctions are obtained. The results are compared with analytical estimates of the double-gradient model, which are found to be reliable for configurations with small Bz up to values ˜ 0.05 of the lobe magnetic field. Coupled with previous results, present simulations confirm that the earthward/tailward growth direction of the Bz component acts as a switch between stable/unstable regimes of the flapping mode, while the mode dispersion curve is the same in both cases. It is confirmed that flapping oscillations may be triggered by a simple Gaussian initial perturbation of the Vz velocity.

  2. Dorso-palmar triangular finger flap-A new advancement flap for cover of finger amputations-A preliminary report

    Mishra Satyanarayan

    2001-01-01

    Full Text Available A triangular V-Y type advancement flap on the finger has been designed, which advances skin from over the whole circumference of the finger, which includes both palmar and dorsal skin. The flap is sensate too. It is indicated for finger and thumb amputations proximal to the body of the nail. Six flaps were raised with five successes and one partial necrosis. This is a preliminary report on a new flap.

  3. Regulation of the actin cytoskeleton in Helicobacter pylori-induced migration and invasive growth of gastric epithelial cells

    Rieder Gabriele

    2011-11-01

    Full Text Available Abstract Dynamic rearrangement of the actin cytoskeleton is a significant hallmark of Helicobacter pylori (H. pylori infected gastric epithelial cells leading to cell migration and invasive growth. Considering the cellular mechanisms, the type IV secretion system (T4SS and the effector protein cytotoxin-associated gene A (CagA of H. pylori are well-studied initiators of distinct signal transduction pathways in host cells targeting kinases, adaptor proteins, GTPases, actin binding and other proteins involved in the regulation of the actin lattice. In this review, we summarize recent findings of how H. pylori functionally interacts with the complex signaling network that controls the actin cytoskeleton of motile and invasive gastric epithelial cells.

  4. Activator-inhibitor coupling between Rho signalling and actin assembly makes the cell cortex an excitable medium.

    Bement, William M; Leda, Marcin; Moe, Alison M; Kita, Angela M; Larson, Matthew E; Golding, Adriana E; Pfeuti, Courtney; Su, Kuan-Chung; Miller, Ann L; Goryachev, Andrew B; von Dassow, George

    2015-11-01

    Animal cell cytokinesis results from patterned activation of the small GTPase Rho, which directs assembly of actomyosin in the equatorial cortex. Cytokinesis is restricted to a portion of the cell cycle following anaphase onset in which the cortex is responsive to signals from the spindle. We show that shortly after anaphase onset oocytes and embryonic cells of frogs and echinoderms exhibit cortical waves of Rho activity and F-actin polymerization. The waves are modulated by cyclin-dependent kinase 1 (Cdk1) activity and require the Rho GEF (guanine nucleotide exchange factor), Ect2. Surprisingly, during wave propagation, although Rho activity elicits F-actin assembly, F-actin subsequently inactivates Rho. Experimental and modelling results show that waves represent excitable dynamics of a reaction-diffusion system with Rho as the activator and F-actin the inhibitor. We propose that cortical excitability explains fundamental features of cytokinesis including its cell cycle regulation. PMID:26479320

  5. Actin protofilament orientation in deformation of the erythrocyte membrane skeleton.

    Picart, C.; Dalhaimer, P.; Discher, D. E.

    2000-01-01

    The red cell's spectrin-actin network is known to sustain local states of shear, dilation, and condensation, and yet the short actin filaments are found to maintain membrane-tangent and near-random azimuthal orientations. When calibrated with polarization results for single actin filaments, imaging of micropipette-deformed red cell ghosts has allowed an assessment of actin orientations and possible reorientations in the network. At the hemispherical cap of the aspirated projection, where the ...

  6. Dendritic Actin Filament Nucleation Causes Traveling Waves and Patches

    Carlsson, Anders E

    2010-01-01

    The polymerization of actin via branching at a cell membrane containing nucleation-promoting factors is simulated using a stochastic-growth methodology. The polymerized-actin distribution displays three types of behavior: a) traveling waves, b) moving patches, and c) random fluctuations. Increasing actin concentration causes a transition from patches to waves. The waves and patches move by a treadmilling mechanism which does not require myosin II. The effects of downregulation of key proteins on actin wave behavior are evaluated.

  7. Dendritic Actin Filament Nucleation Causes Traveling Waves and Patches

    Carlsson, Anders E.

    2010-06-01

    The polymerization of actin via branching at a cell membrane containing nucleation-promoting factors is simulated using a stochastic-growth methodology. The polymerized-actin distribution displays three types of behavior: (a) traveling waves, (b) moving patches, and (c) random fluctuations. Increasing actin concentration causes a transition from patches to waves. The waves and patches move by a treadmilling mechanism not involving myosin II. The effects of downregulation of key proteins on actin wave behavior are evaluated.

  8. Measurement and Analysis of in vitro Actin Polymerization

    Doolittle, Lynda K.; Rosen, Michael K.; Padrick, Shae B.

    2013-01-01

    The polymerization of actin underlies force generation in numerous cellular processes. While actin polymerization can occur spontaneously, cells maintain control over this important process by preventing actin filament nucleation and then allowing stimulated polymerization and elongation by several regulated factors. Actin polymerization, regulated nucleation and controlled elongation activities can be reconstituted in vitro, and used to probe the signaling cascades cells use to control when ...

  9. Force Generation by Endocytic Actin Patches in Budding Yeast

    Carlsson, Anders E.; Bayly, Philip V.

    2014-01-01

    Membrane deformation during endocytosis in yeast is driven by local, templated assembly of a sequence of proteins including polymerized actin and curvature-generating coat proteins such as clathrin. Actin polymerization is required for successful endocytosis, but it is not known by what mechanisms actin polymerization generates the required pulling forces. To address this issue, we develop a simulation method in which the actin network at the protein patch is modeled as an active gel. The def...

  10. Daylight photodynamic therapy for actinic keratosis

    Wiegell, Stine; Wulf, H C; Szeimies, R-M;

    2011-01-01

    Photodynamic therapy (PDT) is an attractive therapy for non-melanoma skin cancers including actinic keratoses (AKs) because it allows treatment of large areas; it has a high response rate and results in an excellent cosmesis. However, conventional PDT for AKs is associated with inconveniently lon...

  11. Competition of two distinct actin networks for actin defines a bistable switch for cell polarization

    Lomakin, Alexis J.; Lee, Kun-Chun; Han, Sangyoon J.; Bui, D A.; Davidson, Michael; Mogilner, Alex; Danuser, Gaudenz

    2015-01-01

    Symmetry-breaking polarization enables functional plasticity of cells and tissues and is yet not well understood. Here we show that epithelial cells, hard-wired to maintain a static morphology and to preserve tissue organization, can spontaneously switch to a migratory polarized phenotype upon relaxation of the actomyosin cytoskeleton. We find that myosin-II engages actin in the formation of cortical actomyosin bundles and thus makes it unavailable for deployment in the process of dendritic growth normally driving cell motility. At low contractility regimes epithelial cells polarize in a front-back manner due to emergence of actin retrograde flows powered by dendritic polymerization of actin. Coupled to cell movement, the flows transport myosin-II from the front to the back of the cell, where the motor locally “locks” actin in contractile bundles. This polarization mechanism could be employed by embryonic and cancer epithelial cells in microenvironments where high contractility-driven cell motion is inefficient. PMID:26414403

  12. The transversely split gracilis twin free flaps

    Upadhyaya Divya

    2010-01-01

    Full Text Available The gracilis muscle is a Class II muscle that is often used in free tissue transfer. The muscle has multiple secondary pedicles, of which the first one is the most consistent in terms of position and calibre. Each pedicle can support a segment of the muscle thus yielding multiple small flaps from a single, long muscle. Although it has often been split longitudinally along the fascicles of its nerve for functional transfer, it has rarely been split transversely to yield multiple muscle flaps that can be used to cover multiple wounds in one patient without subjecting him/her to the morbidity of multiple donor areas .

  13. Salvage of Intraoperative Deep Inferior Epigastric Perforator Flap Venous Congestion with Augmentation of Venous Outflow: Flap Morbidity and Review of the Literature

    Oscar Ochoa, MD

    2013-10-01

    Conclusions: Arterial and venous anatomies play unique roles in flap reliability. DIEP flap venous congestion must be treated expeditiously with venous augmentation to relieve venous congestion and mitigate flap morbidity.

  14. [The gracilis muscle as musculocutaneous flap. Evaluation of 20 cases].

    Gholam, D; Trevidic, P; Kleimann, P; Hautefeuille, P; Nicoletis, C

    1991-01-01

    The use of gracilis as muscular or myocutaneous flap is very well-known. The authors report 20 cases of gracilis flap including 13 reconstructions of the vaginal cavity following extended abdomino-perineal resection. Some technical points concerning the localization of the cutaneous part of the flap and the pedicle dissection are discussed. The use of gracilis flap is still limited in surgical teams following extended abdomino-perineal resection, nevertheless it is a very useful flap because of its low morbidity, the shortening of patient hospitalization and the very satisfying aesthetic result of the neo-vaginal cavity. PMID:1726389

  15. Aged insulin granules display reduced microtubule-dependent mobility and are disposed within actin-positive multigranular bodies

    Hoboth, Peter; Müller, Andreas; Ivanova, Anna; Mziaut, Hassan; Dehghany, Jaber; Sönmez, Anke; Lachnit, Martina; Meyer-Hermann, Michael; Kalaidzidis, Yannis; Solimena, Michele

    2015-01-01

    Insulin secretion is key for glucose homeostasis. Insulin secretory granules (SGs) exist in different functional pools, with young SGs being more mobile and preferentially secreted. However, the principles governing the mobility of age-distinct SGs remain undefined. Using the time-reporter insulin-SNAP to track age-distinct SGs we now show that their dynamics can be classified into three components: highly dynamic, restricted, and nearly immobile. Young SGs display all three components, whereas old SGs are either restricted or nearly immobile. Both glucose stimulation and F-actin depolymerization recruit a fraction of nearly immobile young, but not old, SGs for highly dynamic, microtubule-dependent transport. Moreover, F-actin marks multigranular bodies/lysosomes containing aged SGs. These data demonstrate that SGs lose their responsiveness to glucose stimulation and competence for microtubule-mediated transport over time while changing their relationship with F-actin. PMID:25646459

  16. Propeller thoracodorsal artery perforator flap for breast reconstruction

    Angrigiani, Claudio; Escudero, Ezequiel; Artero, Guillermo; Gercovich, Gustavo; Deza, Ernesto Gil

    2014-01-01

    Background The thoracodorsal artery perforator (TDAP) flap has been described for breast reconstruction. This flap requires intramuscular dissection of the pedicle. A modification of the conventional TDAP surgical technique for breast reconstruction is described, utilizing instead a propeller TDAP flap. The authors present their clinical experience with the propeller TDAP flap in breast reconstruction alone or in combination with expanders or permanent implants. Methods From January 2009 to February 2013, sixteen patients had breast reconstruction utilizing a propeller TDAP flap. Retrospective analysis of patient characteristics, clinical indications, procedure and outcomes were performed. The follow-up period ranged from 4 to 48 months. Results Sixteen patients had breast reconstruction using a TDAP flap with or without simultaneous insertion of an expander or implant. All flaps survived, while two cases required minimal resection due to distal flap necrosis, healing by second intention. There were not donor-site seromas, while minimal wound dehiscence was detected in two cases. Conclusions The propeller TDAP flap appears to be safe and effective for breast reconstruction, resulting in minimal donor site morbidity. The use of this propeller flap emerges as a true alternative to the traditional TDAP flap. PMID:25207210

  17. The double opposing myomucosal cheek flap in hard palate reconstruction.

    Pabiszczak, Maciej; Banaszewski, Jacek; Pastusiak, Tomasz; Buczkowska, Agata; Wierzbicka, Małgorzata

    2015-01-01

    Limited defects in the oral cavity can be treated with local and pedicled cheek flaps. It allows to preserve the functions of the resected organ. Large defects in the midline of the hard palate can be reconstructed with double opposing myomucosal cheek flaps. The aim of this study was to discuss the methodology of the flap harvest and to show our experiences of treatment in a group of 15 patients with oral cavity cancer. In 1 patient the double opposing myomucosal cheek flap was harvested due to the wider local defect. The small size of the flap with ability to use the double opposing cheek flap in more extended defects as well as short duration of the surgery procedure can lead to reduced risk of postoperative complications. Finally, cheek flaps form an effective method of treatment of defects in the oral cavity. PMID:26388355

  18. Capping complex formation at the slow-growing end of the actin filament.

    Kostyukova, A S

    2008-12-01

    Actin filaments are polar; their barbed (fast-growing) and pointed (slow-growing) ends differ in structure and dynamic properties. The slow-growing end is regulated by tropomodulins, a family of capping proteins that require tropomyosins for optimal function. There are four tropomodulin isoforms; their distributions vary depending on tissue type and change during development. The C-terminal half of tropomodulin contains one compact domain represented by alternating alpha-helices and beta-structures. The tropomyosin-independent actin-capping site is located at the C-terminus. The N-terminal half has no regular structure; however, it contains a tropomyosin-dependent actin-capping site and two tropomyosin-binding sites. One tropomodulin molecule can bind two tropomyosin molecules. Effectiveness of tropomodulin binding to tropomyosin depends on the tropomyosin isoform. Regulation of tropomodulin binding at the pointed end as well as capping effectiveness in the presence of specific tropomyosins may affect formation of local cytoskeleton and dynamics of actin filaments in cells. PMID:19216712

  19. First dorsal metacarpal artery islanded flap: A useful flap for reconstruction of thumb pulp defects

    Satish Chetan

    2009-01-01

    Full Text Available Thumb pulp defects are commonly due to avulsion injuries. It is very important to reconstruct these defects using sensate flaps as the thumb pulp needs to be sensate for implementing the various functions of the thumb. A very good option for coverage of these defects is the islanded first dorsal metacarpal artery flap. Our study was done over a period of 2 years and involved 9 consecutive cases of thumb pulp defects treated at our institution. The patients included 8 males and 1 female, ranging in age from 16 to 51 years old. The flap size ranged from 2 x 1.5 cm to 5 x 3 cm. We had only one complication in the form of partial flap necrosis, which fortunately healed following debridement without the need for a secondary procedure. All our cases were done under local anesthesia with tourniquet control. All the patients had good fine touch and average two-point discrimination of 6 mm, which was satisfactory. Our good results further reinforce the islanded first dorsal metacarpal artery flap as one the best flaps for sensate reconstruction of thumb pulp defects. It replaces the soft tissue loss at the thumb pulp with minimal donor site morbidity and with good return of thumb pulp sensation.

  20. The "open book" flap: a heterodigital cross-finger skin flap and adipofascial flap for coverage of a circumferential soft tissue defect of a digit.

    Tadiparthi, S; Akali, A; Felberg, L

    2009-02-01

    A case of circumferential digital skin loss with exposed tendons from the proximal phalanx to the distal interphalangeal joint is presented. This was treated with a two-layer heterodigital cross-finger ("open book") flap from the adjacent digit, utilising a skin-only cross-finger flap to cover the palmar defect and an adipofascial flap to cover the dorsal defect. PMID:19129359

  1. Self-organization of stress patterns drives state transitions in actin cortices

    Tan, Tzer Han; Abu-Shah, Enas; Li, Junang; Sharma, Abhinav; MacKintosh, Fred C; Keren, Kinneret; Schmidt, Christoph F; Fakhri, Nikta

    2016-01-01

    Biological functions rely on ordered structures and intricately controlled collective dynamics. In contrast to systems in thermodynamic equilibrium, order is typically established and sustained in stationary states by continuous dissipation of energy. Non-equilibrium dynamics is a necessary condition to make the systems highly susceptible to signals that cause transitions between different states. How cellular processes self-organize under this general principle is not fully understood. Here, we find that model actomyosin cortices, in the presence of rapid turnover, display distinct steady states, each distinguished by characteristic order and dynamics as a function of network connectivity. The different states arise from a subtle interaction between mechanical percolation of the actin network and myosin-generated stresses. Remarkably, myosin motors generate actin architectures, which in turn, force the emergence of ordered stress patterns. Reminiscent of second order phase transitions, the emergence of order...

  2. Clinical application of free omental flap transfer

    Harii, K.

    1978-04-01

    In the field of reconstruction surgery, the greater omentum has been used as a transposed flap for the treatment of chronic lymphedema, radionecrosis, and so forth. Its transferable range was limited by the length of its pedicle. Microvascular anastomosis allows for free transplantation of this organ and has vastly expanded its usefulness.

  3. Neural Anatomy of the Anterolateral Thigh Flap.

    Luenam, Suriya; Prugsawan, Krit; Kosiyatrakul, Arkaphat; Chotanaphuti, Thanainit; Sriya, Piyanee

    2015-06-01

    The anterolateral thigh (ALT) flap is one of the commonly used sensate flaps for intra-oral, hand, and foot reconstruction. The objective of this study was to describe the anatomic location of the sensory nerves supplying the ALT flap in relation to the surface landmarks and with the vascular pedicles. The dissections were carried out in 28 embalmed specimens. An axial line from the anterior superior iliac spine to the superolateral border of the patella and two circles with radii of 5 and 10 cm centered on the midpoint of the former line were used for the surface landmarks. At the intersection point of the axial line and the 10-cm circle, the main lateral femoral cutaneous nerve (LFCN) and its anterior branch were located within 1 and 2.4 cm, respectively. At the intersection point of the axial line and the 5-cm circle, the anterior branch of the LFCN was located within 2.8 cm. The anterior branch of the LFCN can be detected within 3 cm from the central perforator pedicle in all specimens. The posterior branch of the LFCN, superior perforator nerve, and median perforator nerve were found in more variable locations. The findings from our study provide additional information for clinical use in the planning of sensate ALT flap harvest. PMID:26078503

  4. Aerohydrodynamics of flapping-wing propulsors

    Rozhdestvensky, K.V.; Ryzhov, V.A. [Saint-Petersburg State Marine Technical University (Russian Federation). Dept. of Applied Mathematics and Mathematical Modeling

    2003-11-01

    It is the objective of this survey to review research and development results of flapping-wing propulsors and of vehicles equipped with them. Given the complex and multi-disciplinary character of the problem, a wide range of questions is considered in order to provide a general idea of the state-of-the-art. The main attention is directed at the aerohydrodynamics of flapping-wing propulsors. The major relevant mathematical models and the corresponding numerical results are presented together with the experimental data obtained up to the present time. Also, the physical and the design factors are discussed, which affect the aerohydrodynamic characteristics of flapping wings and that therefore have to be accounted for in the modem mathematical models. Experimental data and numerical modeling results are compared to determine domains of validity of the latter for the aerohydrodynamic design of full-scale air and marine vehicles. Also, existing engineering solutions for vehicles with flapping-wing propulsors are presented and prospective directions for future investigations are outlined. (author)

  5. Late complication of Boari bladder flap

    Berzeg, Semin; Beyersdorff, Dirk; Kopka, Lars [Department of Radiology, Charite Campus Mitte, Schumannstrasse 20/21, 10117 Berlin (Germany); Baumgart, Egbert; Lenk, Severin [Department of Urology, Charite Campus Mitte, Schumannstrasse 20/21, 10117 Berlin (Germany)

    2003-07-01

    A very rare late complication of Boari bladder flap repair with development of pseudodiverticulum and recurrent genitourinary tract infection secondary to vesicoureteral reflux is presented. Radiologic evaluation of the patient comprised intravenous pyelography (IVP), micturating cystourethrogram, cystoscopy, and multislice computed tomography (MSCT). (orig.)

  6. Late complication of Boari bladder flap

    A very rare late complication of Boari bladder flap repair with development of pseudodiverticulum and recurrent genitourinary tract infection secondary to vesicoureteral reflux is presented. Radiologic evaluation of the patient comprised intravenous pyelography (IVP), micturating cystourethrogram, cystoscopy, and multislice computed tomography (MSCT). (orig.)

  7. Periodic and chaotic flapping of insectile wings

    Huang, Y.; Kanso, E.

    2015-11-01

    Insects use flight muscles attached at the base of the wings to produce impressive wing flapping frequencies. The maximum power output of these flight muscles is insufficient to maintain such wing oscillations unless there is good elastic storage of energy in the insect flight system. Here, we explore the intrinsic self-oscillatory behavior of an insectile wing model, consisting of two rigid wings connected at their base by an elastic torsional spring. We study the wings behavior as a function of the total energy and spring stiffness. Three types of behavior are identified: end-over-end rotation, chaotic motion, and periodic flapping. Interestingly, the region of periodic flapping decreases as energy increases but is favored as stiffness increases. These findings are consistent with the fact that insect wings and flight muscles are stiff. They further imply that, by adjusting their muscle stiffness to the energy level at which they are operating, insects can maintain periodic flapping mechanically for a range of operating conditions.

  8. How actin/myosin crosstalks guide the adhesion, locomotion and polarization of cells.

    Sackmann, Erich

    2015-11-01

    Cell-tissue-tissue interaction is determined by specific short range forces between cell adhesion molecules (CAMs) and ligands of the tissue, long range repulsion forces mediated by cell surface grafted macromolecules and adhesion-induced elastic stresses in the cell envelope. This interplay of forces triggers the rapid random clustering of tightly coupled linkers. By coupling of actin gel patches to the intracellular domains of the CAMs, these clusters can grow in a secondary process resulting in the formation of functional adhesion microdomains (ADs). The ADs can act as biochemical steering centers by recruiting and activating functional proteins, such as GTPases and associated regulating proteins, through electrostatic-hydrophobic forces with cationic lipid domains that act as attractive centers. First, I summarize physical concepts of cell adhesion revealed by studies of biomimetic systems. Then I describe the role of the adhesion domains as biochemical signaling platforms and force transmission centers promoting cellular protrusions, in terms of a shell string model of cells. Protrusion forces are generated by actin gelation triggered by molecular machines (focal adhesion kinase (FAK), Src-kinases and associated adaptors) which assemble around newly formed integrin clusters. They recruit and activate the GTPases Rac-1 and actin gelation promoters to charged membrane domains via electrostatic-hydrophobic forces. The cell front is pushed forward in a cyclic and stepwise manner and the step-width is determined by the dynamics antagonistic interplay between Rac-1 and RhoA. The global cell polarization in the direction of motion is mediated by the actin-microtubule (MT) crosstalk at adhesion domains. Supramolecular actin-MT assemblies at the front help to promote actin polymerization. At the rear they regulate the dismantling of the ADs through the Ca(++)-mediated activation of the protease calpain and trigger their disruption by RhoA mediated contraction via

  9. The roles of aerodynamic and inertial forces on maneuverability in flapping flight

    Vejdani, Hamid; Boerma, David; Swartz, Sharon; Breuer, Kenneth

    2015-11-01

    We investigate the relative contributions of aerodynamic and the whole-body dynamics in generating extreme maneuvers. We developed a 3D dynamical model of a body (trunk) and two rectangular wings using a Lagrangian formulation. The trunk has 6 degrees of freedom and each wing has 4 degrees of actuation (flapping, sweeping, wing pronation/supination and wing extension/flexion) and can be massless (like insect wings) or relatively massive (like bats). To estimate aerodynamic forces, we use a blade element method; drag and lift are calculated using a quasi-steady model. We validated our model using several benchmark tests, including gliding and hovering motion. To understand the roles of aerodynamic and inertial forces, we start the investigation by constraining the wing motion to flapping and wing length extension/flexion motion. This decouples the trunk degrees of freedom and affects only roll motion. For bats' dynamics (massive wings), the model is much more maneuverable than the insect dynamics case, and the effect of inertial forces dominates the behavior of the system. The role of the aerodynamic forces increases when the wings have sweeping and flapping motion, which affects the pitching motion of the body. We also analyzed the effect of all wing motions together on the behavior of the model in the presence and in the absence of aerodynamic forces.

  10. Thrust augmentation in tandem flapping foils by foil-wake interaction

    Anderson, Erik; Lauder, George

    2006-11-01

    Propulsion by pitching and heaving airfoils and hydrofoils has been a focus of much research in the field of biologically inspired propulsion. Organisms that use this sort of propulsion are self-propelled, so it is difficult to use standard experimental metrics such as thrust and drag to characterize performance. We have constructed a flapping foil robot mounted in a flume on air-bearings that allows for the determination of self-propelled speed as a metric of performance. We have used a pair of these robots to examine the impact of an upstream flapping foil on a downstream flapping foil as might apply to tandem fins of a swimming organism or in-line swimming of schooling organisms. Self-propelled speed and a force transducer confirmed significant thrust augmentation for particular foil-to-foil spacings, phase differences, and flapping frequencies. Flow visualization shows the mechanism to be related to the effective angle of attack of the downstream foil due to the structure of the wake of the upstream foil. This confirms recent computational work and the hypotheses by early investigators of fish fluid dynamics.

  11. Pneumatic artificial muscles for trailing edge flap actuation: a feasibility study

    In this study a novel aircraft trailing edge flap actuation system was developed and tested. Pneumatic artificial muscles (PAMs) were used as the driving elements of this system to demonstrate their feasibility and utility as an alternative aerospace actuation technology. A prototype flap/actuator system was integrated into a model wing section and tested on the bench-top under simulated airloads for flight at 100 m s−1 (M = 0.3) and in an open-jet wind tunnel at free stream velocities ranging up to 45 m s−1 (M = 0.13). Testing was performed for actuator pressures ranging from 0.069 to 0.62 MPa (10–90 psi) and actuation frequencies from 0.1 to 31 Hz. Results show that the PAM-driven trailing edge flap system can generate substantial and sustainable dynamic deflections, thereby proving the feasibility of using pneumatic artificial muscle actuators in a trailing edge flap system. Key issues limiting system performance are identified, that should be resolved in future research

  12. The Retrograde Ulnar Dorsal Flap: Surgical Technique and Experience as Island Flap in Coverage of Hand Defects.

    Vergara-Amador, Enrique

    2015-09-01

    Flaps from the forearm are often used to reconstruct soft-tissue defects in the hand. The retrograde ulnar dorsal flap has the advantage that it does not sacrifice a major vascular axis. The anatomic bases of this flap are the proximal and distal branch of the ulnar dorsal artery. The distal branch is partially accompanied with the dorsal branch of the ulnar nerve, and arrives under the abductor digiti quinti muscle making anastomoses with the deep branch of the ulnar artery. The proximal branch reaching the proximal third of the forearm, and anastomose with perforating branches of the ulnar artery. I used this island flap in 12 patients with coverage defects on the hand. The biggest flap was 13×6 cm. Only 1 flap had partial necrosis which did not lead to problems. The retrograde ulnar dorsal flap is a flap designed with reverse flow from the distal branch of the ulnar dorsal artery, and which does not sacrifice the ulnar artery. The donor defect on the forearm ulnar side had a greater esthetic acceptance. Knowing other distal anastomoses, described by other authors later, dorsal at the base of the fourth interdigital space grant greater security to the retrograde ulnar dorsal flap. It is worth highlighting the importance of preserving the adipofascial tissue around the pedicle. Experience with this flap permits us to state that it is a safe and reproducible flap to cover any defect on the dorsal of the hand as well as the first web space. PMID:26079665

  13. The Structural Basis of Actin Organization by Vinculin and Metavinculin.

    Kim, Laura Y; Thompson, Peter M; Lee, Hyunna T; Pershad, Mihir; Campbell, Sharon L; Alushin, Gregory M

    2016-01-16

    Vinculin is an essential adhesion protein that links membrane-bound integrin and cadherin receptors through their intracellular binding partners to filamentous actin, facilitating mechanotransduction. Here we present an 8.5-Å-resolution cryo-electron microscopy reconstruction and pseudo-atomic model of the vinculin tail (Vt) domain bound to F-actin. Upon actin engagement, the N-terminal "strap" and helix 1 are displaced from the Vt helical bundle to mediate actin bundling. We find that an analogous conformational change also occurs in the H1' helix of the tail domain of metavinculin (MVt) upon actin binding, a muscle-specific splice isoform that suppresses actin bundling by Vt. These data support a model in which metavinculin tunes the actin bundling activity of vinculin in a tissue-specific manner, providing a mechanistic framework for understanding metavinculin mutations associated with hereditary cardiomyopathies. PMID:26493222

  14. Assessing safety of negative-pressure wound therapy over pedicled muscle flaps: A retrospective review of gastrocnemius muscle flap.

    Lance, Samuel; Harrison, Lindsey; Orbay, Hakan; Boudreault, David; Pereira, Gavin; Sahar, David

    2016-04-01

    The use of negative-pressure wound therapy (NPWT) for management of open wounds and immobilization of split-thickness skin grafts (STSGs) over wounds has been well described. However, there is a concern for potential compromise of flap viability when NPWT is used for skin grafts over pedicled muscle flaps. We have used NPWT to immobilize STSGs in eight patients who underwent a pedicled gastrocnemius muscle flap operation in our department. We applied a negative pressure of -75 mmHg on the muscle flaps for 5 days postoperatively. All wounds healed successfully, with a 97.5 ± 5.5% mean STSG uptake. No flap necrosis was observed. In our series, the use of NPWT for fixation of STSGs over pedicled gastrocnemius muscle flap was effective and had no negative impact on flap viability. PMID:26732293

  15. Actin filaments at the leading edge of cancer cells are characterized by a high mobile fraction and turnover regulation by profilin I.

    Gisela Lorente

    Full Text Available Cellular motility is the basis for cancer cell invasion and metastasis. In the case of breast cancer, the most common type of cancer among women, metastasis represents the most devastating stage of the disease. The central role of cellular motility in cancer development emphasizes the importance of understanding the specific mechanisms involved in this process. In this context, tumor development and metastasis would be the consequence of a loss or defect of the mechanisms that control cytoskeletal remodeling. Profilin I belongs to a family of small actin binding proteins that are thought to assist in actin filament elongation at the leading edge of migrating cells. Traditionally, Profilin I has been considered to be an essential control element for actin polymerization and cell migration. Expression of Profilin I is down-regulated in breast and various other cancer cells. In MDA-MB-231 cells, a breast cancer cell line, further inhibition of Profilin I expression promotes hypermotility and metastatic spread, a finding that contrasts with the proposed role of Profilin in enhancing polymerization. In this report, we have taken advantage of the fluorescence recovery after photobleaching (FRAP of GFP-actin to quantify and compare actin dynamics at the leading edge level in both cancer and non-cancer cell models. Our results suggest that (i a high level of actin dynamics (i.e., a large mobile fraction of actin filaments and a fast turnover is a common characteristic of some cancer cells; (ii actin polymerization shows a high degree of independence from the presence of extracellular growth factors; and (iii our results also corroborate the role of Profilin I in regulating actin polymerization, as raising the intracellular levels of Profilin I decreased the mobile fraction ratio of actin filaments and slowed their polymerization rate; furthermore, increased Profilin levels also led to reduced individual cell velocity and directionality.

  16. Actin-mediated bacterial propulsion: comet profile, velocity pulsations

    The propulsion of bacteria under the action of an actin gel network is examined in terms of gel concentration dynamics. The model includes the elasticity of the network, the gel–bacterium interaction, the bulk and interface polymerization. A formula for the cruise velocity is obtained where the contributions to bacterial motility arising from elasticity and polymerization are made explicit. Higher velocities correspond to lower concentration peaks and longer tails, in agreement with experimental results. The condition for the onset of motion is explicitly given. The behavior of the system is explored by varying the growth rates and the gel elasticity. At steady state two regimes are found, respectively, of constant and pulsating velocity; in the latter case, the velocity undergoes sudden accelerations and subsequent recoveries. The transition to the pulsating regime is obtained by increasing the elastic response of the gel

  17. Recurrent squamous cell carcinoma of the scalp treated with serial free flaps

    Ikander, Peder; Sørensen, Jens Ahm

    2015-01-01

    dorsi flaps and one anterolateral thigh flap. No total flap loss was seen, but partial flap necrosis called for secondarily reconstruction. The final result was cosmetically acceptable and the patient is of good health. In conclusion, serial free microvascular flaps may be used with good results when...

  18. Pedicle versus free flap reconstruction in patients receiving intraoperative brachytherapy.

    Geiger, Erik J; Basques, Bryce A; Chang, Christopher C; Son, Yung; Sasaki, Clarence T; McGregor, Andrew; Ariyan, Stephan; Narayan, Deepak

    2016-08-01

    Introduction This study compared complication rates between pedicle flaps and free flaps used for resurfacing of intraoperative brachytherapy (IOBT) implants placed following head and neck tumour extirpation to help clarify the ideal reconstructive procedure for this scenario. Patients and methods A retrospective review of reconstructions with IOBT at our institution was conducted. Patient and treatment details were recorded, as were the number and type of flap complications, including re-operations. Logistic regressions compared complications between flap groups. Results Fifty free flaps and 55 pedicle flaps were included. On multivariate analysis, free flap reconstruction with IOBT was significantly associated with both an increased risk of having any flap complication (OR = 2.9, p = 0.037) and with need for operative revision (OR = 3.5, p = 0.048) compared to pedicle flap reconstruction. Conclusions In the setting of IOBT, free flaps are associated with an increased risk of having complications and requiring operative revisions. PMID:26983038

  19. STUDY OF VARIOUS MODIFICATIONS OF REVERSE SURAL ARTERY FLAP

    Jainath

    2013-10-01

    Full Text Available A BS T R ACT : Soft tissue reconstruction of distal third leg, heel and ankle reg ion is a challenging problem because of poor vascularity and limited mobility of skin. The reverse sural artery with ideal flap thickness, minimal donor site morbidity, lack of functional muscle loss, short recovery time, wide arc of rotation and safe vasc ularity makes it a preferable flap for covering such defects. AIMS A N D OBJECTIVES : To study various modifications of distally based reverse sural artery flap to suit the defects and for better survival of flaps. RESULTS : It is a retrospective study conduct ed in our institute to cover the distal leg and foot defects.60 cases of distal leg defects exposing vital structure who underwent reverse sural artery flap coverage were included in the study .5 of the 60 flaps had complete flap necrosis and another11 fla ps had partial necrosis.73.4% of the flaps survived during the follow up period of 1 years with good functional outcome. CONCLUSIONS : Reverse sural artery flap with its modifications is a good flap for the defects of distal leg, heel and ankle defects

  20. Robot-Assisted Free Flap in Head and Neck Reconstruction

    Han Gyeol Song

    2013-07-01

    Full Text Available Background  Robots have allowed head and neck surgeons to extirpate oropharyngealtumors safely without the need for lip-split incision or mandibulotomy. Using robots inoropharyngealreconstruction is newbut essentialfor oropharyngeal defectsthatresultfromrobotic tumor excision. We report our experience with robotic free-flap reconstruction ofhead and neck defectsto exemplify the necessity forrobotic reconstruction.Methods  We investigated head and neck cancer patients who underwent ablation surgeryand free-flap reconstruction by robot. Between July 1, 2011 andMarch 31, 2012, 5 caseswereperformed and patient demographics, location of tumor, pathologic stage, reconstructionmethods, flap size, recipient vessel, necessary pedicle length, and operation time wereinvestigated.Results  Among five free-flap reconstructions, four were radial forearm free flaps and onewas an anterolateral thigh free-flap. Four flaps used the superior thyroid artery and oneflap used a facial artery as the recipient vessel. The average pedicle length was 8.8 cm. Flapinsetting and microanastomosis were achieved using a specially manufactured roboticinstrument. The total operation timewas 1,041.0 minutes(range, 814 to 1,132 minutes, andcomplicationsincluding flap necrosis, hematoma, andwound dehiscence did not occur.Conclusions  Thisstudy demonstratesthe clinically applicable use ofrobotsin oropharyngealreconstruction, especially using a free flap. A robot can assist the operator in insettingthe flap at a deep portion of the oropharynx without the need to perform a traditionalmandibulotomy. Robot-assisted reconstruction may substitute for existing surgical methodsand is accepted asthemost up-to-datemethod.

  1. Effect of flapping trajectories on the dragonfly aerodynamics

    2006-01-01

    The effects of translational, figure-eight and double-figure-eight flapping trajectories on the dragonfly aerodynamics were numerically studied by solving the Navier-Stokes equations. There is a common characteristic regarding the lift/drag force coefficients that the downstroke flapping provides the lift forces while the upstroke flapping creates the thrust forces for different flapping trajectories. The maximum lift force coefficient exceeds five for the translational trajectory. It is greater than six for the figure-eight and double-figure-eight flapping trajectories, which is sufficiently larger than unity under the steady state flight condition. The ellipse and double-figure-eight flapping trajectories yield the decrease of the lift force, while the figure-eight flapping trajectory yields higher lift force as well as the thrust force than the translational flapping one. During the insect flight, the wing flapping status should be changed instantaneously to satisfy various requirements. Study of the flapping trajectories on the insect aerodynamics is helpful for the design of the Micro-air-vehicles (MAVs).

  2. Reconstruction of the Lower Extremity Using Free Flaps

    Min Jo Kang

    2013-09-01

    Full Text Available Background The aim of lower-extremity reconstruction has focused on wound coverage andfunctional recovery. However, there are limitations in the use of a local flap in cases of extensivedefects of the lower-extremities. Therefore, free flap is a useful option in lower-extremityreconstruction.Methods We performed a retrospective review of 49 patients (52 cases who underwentlower-extremity reconstruction at our institution during a 10-year period. In these patients,we evaluated causes and sites of defects, types of flaps, recipient vessels, types of anastomosis,survival rate, and complications.Results There were 42 men and 10 women with a mean age of 32.7 years (range, 3-72years. The sites of defects included the dorsum of the foot (19, pretibial area (17, ankle(7, heel (5 and other sites (4. The types of free flap included latissimus dorsi muscle flap(10, scapular fascial flap (6, anterolateral thigh flap (6, and other flaps (30. There werefour cases of vascular complications, out of which two flaps survived after intervention. Theoverall survival of the flaps was 96.2% (50/52. There were 19 cases of other complications atrecipient sites such as partial graft loss (8, partial flap necrosis (6 and infection (5. However,these complications were not notable and were resolved with skin grafts.Conclusions The free flap is an effective method of lower-extremity reconstruction. Goodoutcomes can be achieved with complete debridement and the selection of appropriaterecipient vessels and flaps according to the recipient site.

  3. Towards the Structure Determination of a Modulated Protein Crystal: The Semicrystalline State of Profilin:Actin

    Borgstahl, G.; Lovelace, J.; Snell, E. H.; Bellamy, H.

    2003-01-01

    One of the remaining challenges to structural biology is the solution of modulated structures. While small molecule crystallographers have championed this type of structure, to date, no modulated macromolecular structures have been determined. Modulation of the molecular structures within the crystal can produce satellite reflections or a superlattice of reflections in reciprocal space. We have developed the data collection methods and strategies that are needed to collect and analyze these data. If the macromolecule's crystal lattice is composed of physiologically relevant packing contacts, structural changes induced under physiological conditions can cause distortion relevant to the function and biophysical processes of the molecule making up the crystal. By careful measurement of the distortion, and the corresponding three-dimensional structure of the distorted molecule, we will visualize the motion and mechanism of the biological macromolecule(s). We have measured the modulated diffraction pattern produced by the semicrystalline state of profilin:actin crystals using highly parallel and highly monochromatic synchrotron radiation coupled with fine phi slicing (0.001-0.010 degrees) for structure determination. These crystals present these crystals present a unique opportunity to address an important question in structural biology. The modulation is believed to be due to the formation of actin helical filaments from the actin beta ribbon upon the pH-induced dissociation of profilin. To date, the filamentous state of actin has resisted crystallization and no detailed structures are available. The semicrystalline state profilin:actin crystals provides a unique opportunity to understand the many conformational states of actin. This knowledge is essential for understanding the dynamics underlying shape changes and motility of eukaryotic cells. Many essential processes, such as cytokinesis, phagocytosis, and cellular migration depend upon the capacity of the actin

  4. Gelsolin mediates calcium-dependent disassembly of Listeria actin tails

    Larson, Laura; Arnaudeau, Serge; Gibson, Bruce; Li, Wei; Krause, Ryoko; Hao, Binghua; Bamburg, James R.; Lew, Daniel P.; Demaurex, Nicolas; Southwick, Frederick

    2005-01-01

    The role of intracellular Ca2+ in the regulation of actin filament assembly and disassembly has not been clearly defined. We show that reduction of intracellular free Ca2+ concentration ([Ca2+]i) to <40 nM in Listeria monocytogenes-infected, EGFP–actin-transfected Madin–Darby canine kidney cells results in a 3-fold lengthening of actin filament tails. This increase in tail length is the consequence of marked slowing of the actin filament disassembly rate, without a significant change in assembly rate. The Ca2+-sensitive actin-severing protein gelsolin concentrates in the Listeria rocket tails at normal resting [Ca2+]i and disassociates from the tails when [Ca2+]i is lowered. Reduction in [Ca2+]i also blocks the severing activity of gelsolin, but not actin-depolymerizing factor (ADF)/cofilin microinjected into Listeria-infected cells. In Xenopus extracts, Listeria tail lengths are also calcium-sensitive, markedly shortening on addition of calcium. Immunodepletion of gelsolin, but not Xenopus ADF/cofilin, eliminates calcium-sensitive actin-filament shortening. Listeria tail length is also calcium-insensitive in gelsolin-null mouse embryo fibroblasts. We conclude that gelsolin is the primary Ca2+-sensitive actin filament recycling protein in the cell and is capable of enhancing Listeria actin tail disassembly at normal resting [Ca2+]i (145 nM). These experiments illustrate the unique and complementary functions of gelsolin and ADF/cofilin in the recycling of actin filaments. PMID:15671163

  5. Tropomyosin - master regulator of actin filament function in the cytoskeleton.

    Gunning, Peter W; Hardeman, Edna C; Lappalainen, Pekka; Mulvihill, Daniel P

    2015-08-15

    Tropomyosin (Tpm) isoforms are the master regulators of the functions of individual actin filaments in fungi and metazoans. Tpms are coiled-coil parallel dimers that form a head-to-tail polymer along the length of actin filaments. Yeast only has two Tpm isoforms, whereas mammals have over 40. Each cytoskeletal actin filament contains a homopolymer of Tpm homodimers, resulting in a filament of uniform Tpm composition along its length. Evidence for this 'master regulator' role is based on four core sets of observation. First, spatially and functionally distinct actin filaments contain different Tpm isoforms, and recent data suggest that members of the formin family of actin filament nucleators can specify which Tpm isoform is added to the growing actin filament. Second, Tpms regulate whole-organism physiology in terms of morphogenesis, cell proliferation, vesicle trafficking, biomechanics, glucose metabolism and organ size in an isoform-specific manner. Third, Tpms achieve these functional outputs by regulating the interaction of actin filaments with myosin motors and actin-binding proteins in an isoform-specific manner. Last, the assembly of complex structures, such as stress fibers and podosomes involves the collaboration of multiple types of actin filament specified by their Tpm composition. This allows the cell to specify actin filament function in time and space by simply specifying their Tpm isoform composition. PMID:26240174

  6. A CFD-informed quasi-steady model of flapping wing aerodynamics

    Nakata, Toshiyuki; Liu, Hao; Bomphrey, Richard J.

    2016-01-01

    Aerodynamic performance and agility during flapping flight are determined by the combination of wing shape and kinematics. The degree of morphological and kinematic optimisation is unknown and depends upon a large parameter space. Aimed at providing an accurate and computationally inexpensive modelling tool for flapping-wing aerodynamics, we propose a novel CFD (computational fluid dynamics)-informed quasi-steady model (CIQSM), which assumes that the aerodynamic forces on a flapping wing can be decomposed into the quasi-steady forces and parameterised based on CFD results. Using least-squares fitting, we determine a set of proportional coefficients for the quasi-steady model relating wing kinematics to instantaneous aerodynamic force and torque; we calculate power with the product of quasi-steady torques and angular velocity. With the quasi-steady model fully and independently parameterised on the basis of high-fidelity CFD modelling, it is capable of predicting flapping-wing aerodynamic forces and power more accurately than the conventional blade element model (BEM) does. The improvement can be attributed to, for instance, taking into account the effects of the induced downwash and the wing tip vortex on the force generation and power consumption. Our model is validated by comparing the aerodynamics of a CFD model and the present quasi-steady model using the example case of a hovering hawkmoth. It demonstrates that the CIQSM outperforms the conventional BEM while remaining computationally cheap, and hence can be an effective tool for revealing the mechanisms of optimization and control of kinematics and morphology in flapping-wing flight for both bio-flyers and unmanned air systems.

  7. Performance Analysis of the Flapping Wing Propulsion Based on a New Experimentally Validated Aeroelastic Model

    Pourtakdoust, Seid H.; Aliabadi, Saeed Karimain

    Flapping micro air vehicle (FMAV) is considered to exhibit much better performance at low speeds and small sizes compared to fixed-wing MAVs. To maximize the potential and capabilities of FMAVs also to produce adequate design implications, a new aeroelastic model of a typical flexible FMAV is being developed utilizing Euler-Bernoulli torsion beam and quasi steady aerodynamic model. The new model accounts for all natural existing complex interactions between the mass, inertia, elastic properties, aerodynamic loading, flapping amplitude and frequency of the FMAV as well as the effects of several geometric and design parameters. To validate the proposed theoretical model, a typical FMAV as well as instrumented test stand for the online measurement of forces, flapping angle and power consumption have been constructed. The experimental results are initially utilized to validate the flight dynamic model, and several appropriate conclusions are drawn. The model is subsequently used to demonstrate the flapping propulsion characteristics of the FMAV via simulation. Using dimensionless parameters, a set of new generalized curves have been deduced. The results indicate that by proper adjustment of the wing stiffness parameter as a function of the reduced frequency, the FMAV will attain its optimum propulsive efficiency. This fact raises additional new ideas for further research in this area by utilizing intelligent variable stiffness materials and/or or active morphing technology for the sustained, high-performance flight of FMAVs. The generalized model can also be used to conduct a performance and stability analysis of FMAVs and to design and optimize flapping-wing structures.

  8. Fibroblast-mediated contraction in actinically exposed and actinically protected aging skin

    The changes in skin morphology over time are a consequence of both chronologic aging and the accumulation of environmental exposure. Through observation, we know that actinic radiation intensifies the apparent aging of skin. We have investigated the effects of aging and actinic radiation on the ability of fibroblasts to contract collagen-fibroblast lattices. Preauricular and postauricular skin samples were obtained from eight patients aged 49 to 74 undergoing rhytidectomy. The samples were kept separate, and the fibroblasts were grown in culture. Lattices constructed with preauricular fibroblasts consistently contracted more than lattices containing postauricular fibroblasts. The difference in amount of contraction in 7 days between sites was greatest for the younger patients and decreased linearly as donor age increased (r = -0.96). This difference may be due to preauricular fibroblasts losing their ability to contract a lattice as aging skin is exposed to more actinic radiation

  9. Isolation of a 5-kilodalton actin-sequestering peptide from human blood platelets.

    Safer, D; Golla, R; Nachmias, V T

    1990-01-01

    Resting human platelets contain approximately 0.3 mM unpolymerized actin. When freshly drawn and washed platelets are treated with saponin, 85-90% of the unpolymerized actin diffuses out. Analysis by polyacrylamide gel electrophoresis under nondenaturing conditions shows that the bulk of this unpolymerized actin migrates with a higher mobility than does pure G-actin, profilactin, or actin-gelsolin complex. When muscle G-actin is added to fresh or boiled saponin extract, the added muscle actin...

  10. Freestyle-Like V-Y Flaps of the Eyebrow: A New Outlook and Indication of an Historical Technique

    Angelo Alberto Leto Barone

    2013-01-01

    Full Text Available The eyebrow region is of utmost importance for facial movement, symmetry, and the overall cosmetic appearance of the face. Trauma or tumor resection often leave scars that may dislocate the eyebrow producing an alteration both in static symmetry of the face and in the dynamic expressivity. The authors present a technique for eyebrow’s defects repair using the remaining eyebrow advancement by means of a “freestyle-like” V-Y flap. In the past two years a total of eight consecutive patients underwent excision of skin lesions in the superciliary region and immediate reconstruction with this technique. On histology, six patients were affected from basal cell carcinomas, one from squamous cell carcinoma, and one from congenital intradermal melanocytic nevus. The pedicle of the flap included perforators from the supratrochlear, supraorbital, or superficial temporalis artery. Advancement of the entire aesthetic subunit that includes the eyebrow using a V-Y perforator flap was performed successfully in all cases achieving full, tension-free closure of defects up to 3.0 cm. “Freestyle-like” V-Y flaps should be considered as a first-line choice for partial defects of the eyebrow. The greater mobility compared to random subcutaneous flaps allows to reconstruct large defects providing an excellent cosmetic result.

  11. Temporal-based pericranial flaps for orbitofrontal Dural repair: A technical note and Review of the literature

    Esther Dupépé

    2016-03-01

    Conclusions: A temporal-based pericranial flap represents an alternative vascularized pedicle flap to the classic frontal-based pericranial flap used in orbitofrontal dural repair. In certain clinical settings, the temporal-based flap may be preferable.

  12. The Cortical Actin Determines Different Susceptibility of Naïve and Memory CD4+ T Cells to HIV-1 Cell-to-Cell Transmission and Infection

    Permanyer, Marc; Pauls, Eduardo; Badia, Roger; Esté, José A; Ballana, Ester

    2013-01-01

    Memory CD4+ T cells are preferentially infected by HIV-1 compared to naïve cells. HIV-1 fusion and entry is a dynamic process in which the cytoskeleton plays an important role by allowing virion internalization and uncoating. Here, we evaluate the role of the cortical actin in cell-to-cell transfer of virus antigens and infection of target CD4+ T cells. Using different actin remodeling compounds we demonstrate that efficiency of HIV-internalization was proportional to the actin polymerization...

  13. The pathogen-actin connection: A platform for defense signaling in plants

    Day, B; Henty, Jessica L; Porter, K J; Staiger, Chris J

    2011-09-08

    The cytoskeleton, a dynamic network of cytoplasmic polymers, plays a central role in numerous fundamental processes, such as development, reproduction, and cellular responses to biotic and abiotic stimuli. As a platform for innate immune responses in mammalian cells, the actin cytoskeleton is a central component in the organization and activation of host defenses, including signaling and cellular repair. In plants, our understanding of the genetic and biochemical responses in both pathogen and host that are required for virulence and resistance has grown enormously. Additional advances in live-cell imaging of cytoskeletal dynamics have markedly altered our view of actin turnover in plants. In this review, we outline current knowledge of host resistance following pathogen perception, both in terms of the genetic interactions that mediate defense signaling, as well as the biochemical and cellular processes that are required for defense signaling.

  14. Treatment of lumbosacral decubitus ulcers by Lymberg flap

    The lymberg flap was used for the treatment of lumbosacral decubitus and irradiation-induced ulcer successfully in 6 lesion of 5 cases. The results were evaluated, and characteristics and indication of the method were discussed. The procedure of the method: A rhomboid flap with a side lenghth, equal to that of the lesion and with an angle of 600, was cut out, and transplanted to cover the lesion. The wound of a donor was sutured by extending the surrounding area. Of characteristics of this method, a flap can be produced in a desired shape; tension lies little on the flap; and a small area is needed for the flap. However, in recurrence, the first wound may cause circulation disturbance in a flap. Large wounds of donors sometimes cannont be closed. Therefore, a fresh case with relatively small lesions is an indication to this method. (Ueda, J.)

  15. Structure of the F-actin-tropomyosin complex.

    von der Ecken, Julian; Müller, Mirco; Lehman, William; Manstein, Dietmar J; Penczek, Pawel A; Raunser, Stefan

    2015-03-01

    Filamentous actin (F-actin) is the major protein of muscle thin filaments, and actin microfilaments are the main component of the eukaryotic cytoskeleton. Mutations in different actin isoforms lead to early-onset autosomal dominant non-syndromic hearing loss, familial thoracic aortic aneurysms and dissections, and multiple variations of myopathies. In striated muscle fibres, the binding of myosin motors to actin filaments is mainly regulated by tropomyosin and troponin. Tropomyosin also binds to F-actin in smooth muscle and in non-muscle cells and stabilizes and regulates the filaments there in the absence of troponin. Although crystal structures for monomeric actin (G-actin) are available, a high-resolution structure of F-actin is still missing, hampering our understanding of how disease-causing mutations affect the function of thin muscle filaments and microfilaments. Here we report the three-dimensional structure of F-actin at a resolution of 3.7 Å in complex with tropomyosin at a resolution of 6.5 Å, determined by electron cryomicroscopy. The structure reveals that the D-loop is ordered and acts as a central region for hydrophobic and electrostatic interactions that stabilize the F-actin filament. We clearly identify map density corresponding to ADP and Mg(2+) and explain the possible effect of prominent disease-causing mutants. A comparison of F-actin with G-actin reveals the conformational changes during filament formation and identifies the D-loop as their key mediator. We also confirm that negatively charged tropomyosin interacts with a positively charged groove on F-actin. Comparison of the position of tropomyosin in F-actin-tropomyosin with its position in our previously determined F-actin-tropomyosin-myosin structure reveals a myosin-induced transition of tropomyosin. Our results allow us to understand the role of individual mutations in the genesis of actin- and tropomyosin-related diseases and will serve as a strong foundation for the targeted

  16. Pumping by flapping in a viscoelastic fluid

    Pak, On Shun

    2010-01-01

    In a world without inertia, Purcell's scallop theorem states that in a Newtonian fluid a time-reversible motion cannot produce any net force or net flow. Here we consider the extent to which the nonlinear rheological behavior of viscoelastic fluids can be exploited to break the constraints of the scallop theorem in the context of fluid pumping. By building on previous work focusing on force generation, we consider a simple, biologically-inspired geometrical example of a flapper in a polymeric (Oldroyd-B) fluid, and calculate asymptotically the time-average net fluid flow produced by the reciprocal flapping motion. The net flow occurs at fourth order in the flapping amplitude, and suggests the possibility of transporting polymeric fluids using reciprocal motion in simple geometries even in the absence of inertia. The induced flow field and pumping performance are characterized and optimized analytically. Our results may be useful in the design of micro-pumps handling complex fluids.

  17. CATERPILLAR ADVANCEMENT FOR PARTIALLY NECROSED DELTOPECTORAL FLAP

    Anand Narayan

    2015-04-01

    Full Text Available Development of electric lamp by Thomas Elva Edison had significant impact on human civilization. With increasing production of electrical energy to meet ongoing demands of increased frequency of electrical injuries. Despite increased awareness of potential dangers, elect ricity is responsible for many fatalities all over the world. Electrical burn accounts for ~3% of all burn related injuries. Estimated 3, 000 annual admittions to burn units. Electrical burn have bimodal distribution ~1/3 children <6 yrs ( E lectric cords & wall outlets ~2/3 miners, construction, & electrical workers. Our case is one that of a 12 year old male child having electrical injury over face and neck with exposed angle of mandible which was covered by Deltopectoral flap with caterpillar advancement of flap.

  18. Stability investigation of an airfoil section with active flap control

    Bergami, Leonardo; Gaunaa, Mac

    2010-01-01

    This work presents a method to determine flutter and divergence instability limits for a two-dimensional (2-D) airfoil section fitted with an actively controlled trailing edge flap. This flap consists of a deformable trailing edge, which deformation is governed by control algorithms based on measurements of either heave displacement, local angle of attack or aerodynamic pressure difference measured over the airfoil. The purpose of the controlled deformable flap is to reduce fluctuations in th...

  19. USB noise reduction by nozzle and flap modifications

    Hayden, R. E.

    1976-01-01

    The development of concepts for reducing upper surface blown flap noise at the source through flap modifications and special nozzles is reviewed. In particular, recent results obtained on the aerodynamic and acoustic performance of flaps with porous surfaces near the trailing edge and multi-slotted nozzles are reviewed. Considerable reduction (6-10 db) of the characteristic low frequency peak is shown. The aerodynamic performance is compared with conventional systems, and prospects for future improvements are discussed.

  20. Medial circumflex femoral artery flap for ischial pressure sore

    Palanivelu S

    2009-01-01

    A new axial pattern flap based on the terminal branches of the medial circumflex femoral artery is described for coverage of ischial pressure sore. Based on the terminal branches of the transverse branch of medial circumflex femoral artery, which exit through the gap between the quadratus femoris muscle above and the upper border of adductor magnus muscle below, this fascio cutaneous flap is much smaller than the posterior thigh flap but extremely useful to cover ischeal pressure sores. The s...

  1. Fenestration of bone flap during decompressive craniotomy for subdural hematoma

    Ha Son Nguyen; Ninh Doan; Christopher Wolfla; Glen Pollock

    2016-01-01

    Background: Persistent/recurrent extra-axial hemorrhage may occur after decompression of a subdural hematoma (SDH) followed by an immediate replacement of bone flap. A fenestration of the bone flap may encourage extra-axial fluid absorption; however, the literature has not explored this technique. Methods: Forty-four consecutive patients who underwent surgical decompression of SDH with immediate replacement of bone flap were divided into two groups: Fenestration (F), n = 33, and no fenest...

  2. Acetylcysteine in random skin flap in rats

    Abla Luiz Eduardo Felipe

    2005-01-01

    Full Text Available PURPOSE: Analyze the ability of Acetylcysteine to reduce distal necrosis in a random skin flap, in the rat. METHODS: The present study utilized 28 adult male Wistar-EPM rats distributed, at random, in two groups of 14 animals. Control group rats (CG received distilled water and Acetylcysteine group animals (NACG received NAC (300 mg/kg by oral infusion, 15 minutes before flap elevation. On the seventh postoperative day, percentage of distal necrosis was determined and skin samples collected in order to allow determination of MDA levels. RESULTS: The mean necrotic area in CG group (control was 66 % and in NACG group (Acetylcysteine 52 %, a statistically significant difference according to the Mann-Whitney test (U calc = 25; U crit = 45. MDA levels were lower in the CG flap skin samples than in the NACG samples (U calc = 24; U crit = 45, the oposite being true in the normal skin samples (U calc = 10; U crit = 45. CONCLUSION: Acetylcysteine was effective, according to the model used, reducing the percentage of distal necrosis in NACG rats.

  3. Design and performance prediction of swashplateless helicopter rotors with trailing edge flaps and tabs

    Falls, Jaye

    This work studies the design of trailing edge controls for swashplateless helicopter primary control, and examines the impact of those controls on the performance of the rotor. The objective is to develop a comprehensive aeroelastic analysis for swashplateless rotors in steady level flight. The two key issues to be solved for this swashplateless control concept are actuation of the trailing edge controls and evaluating the performance of the swashplateless rotor compared to conventionally controlled helicopters. Solving the first requires simultaneous minimization of trailing flap control angles and hinge moments to reduce actuation power. The second issue requires not only the accurate assessment of swashplateless rotor power, but also similar or improved performance compared to conventional rotors. The analysis consists of two major parts, the structural model and the aerodynamic model. The inertial contributions of the trailing edge flap and tab are derived and added to the system equations in the structural model. Two different aerodynamic models are used in the analysis, a quasi-steady thin airfoil theory that includes arbitrary hinge positions for the flap and the tab, and an unsteady lifting line model with airfoil table lookup based on wind tunnel test data and computational fluid dynamics simulation. The design aspect of the problem is investigated through parametric studies of the trailing edge flap and tab for a Kaman-type conceptual rotor and a UH-60A swashplateless variant. The UH-60A model is not changed except for the addition of a trailing edge flap to the rotor blade, and the reduction of pitch link stiffness to imitate a soft root spring. Study of the uncoupled blade response identifies torsional stiffness and flap hinge stiffness as important design features of the swashplateless rotor. Important trailing edge flap and tab design features including index angle, aerodynamic overhang, chord and length are identified through examination of coupled

  4. Pedicled and free TRAM flaps in breast reconstructions : a comparative study

    Edsander-Nord, Åsa

    2000-01-01

    The transverse rectus abdominis musculocutaneous (TRAM) flap is frequently used when autologous tissue is desired for breast reconstruction, and it can be transferred pedicled or free. The pedicled TRAM flap is elevated as a lower transverse abdominal flap with the rectus abdominis muscle attached in the epigastric area, by which means the deep superior epigastric vessels nourish the flap. The flap is tunneled to its new position on the thoracic wall. The free TRAM flap c...

  5. Propeller Perforator Flaps in Distal Lower Leg:Evolution and Clinical Applications

    Georgescu, Alexandru V.

    2012-01-01

    Simple or complex defects in the lower leg, and especially in its distal third, continue to be a challenging task for reconstructive surgeons. A variety of flaps were used in the attempt to achieve excellence in form and function. After a long evolution of the reconstructive methods, including random pattern flaps, axial pattern flaps, musculocutaneous flaps and fasciocutaneous flaps, the reappraisal of the works of Manchot and Salmon by Taylor and Palmer opened the era of perforator flaps. T...

  6. Reverse actin sliding triggers strong myosin binding that moves tropomyosin

    Bekyarova, T. I.; Reedy, M C; Baumann, B. A. J.; Tregear, R T; Ward, A; Krzic, U.; Prince, K.M.; Perz-Edwards, R. J.; Reconditi, M.; Gore, D.; Irving, T C; Reedy, M K

    2008-01-01

    Actin/myosin interactions in vertebrate striated muscles are believed to be regulated by the “steric blocking” mechanism whereby the binding of calcium to the troponin complex allows tropomyosin (TM) to change position on actin, acting as a molecular switch that blocks or allows myosin heads to interact with actin. Movement of TM during activation is initiated by interaction of Ca2+ with troponin, then completed by further displacement by strong binding cross-bridges. We report x-ray evidence...

  7. Actin gene expression in developing sea urchin embryos.

    Crain, W R; Durica, D S; Van Doren, K

    1981-01-01

    We show that the synthesis of actin is regulated developmentally during early sea urchin embryogenesis and that the level of synthesis of this protein parallels the steady-state amounts of the actin messenger ribonucleic acids (RNA). An in vitro translation and RNA blotting analysis of embryo RNA from several stages of early development indicated that during the first 8 h after fertilization there was a low and relatively constant level of actin messenger RNA in the embryo. Between 8 and 13 h...

  8. Myosin phosphorylation triggers actin polymerization in vascular smooth muscle

    Chen, Xuesong; Pavlish, Kristin; Benoit, Joseph N.

    2008-01-01

    A variety of contractile stimuli increases actin polymerization, which is essential for smooth muscle contraction. However, the mechanism(s) of actin polymerization associated with smooth muscle contraction is not fully understood. We tested the hypothesis that phosphorylated myosin triggers actin polymerization. The present study was conducted in isolated intact or β-escin-permeabilized rat small mesenteric arteries. Reductions in the 20-kDa myosin regulatory light chain (MLC20) phosphorylat...

  9. Calcium-Actin Waves and Oscillations of Cellular Membranes

    Veksler, Alex; Gov, Nir S.

    2009-01-01

    We propose a mechanism for the formation of membrane oscillations and traveling waves, which arise due to the coupling between the actin cytoskeleton and the calcium flux through the membrane. In our model, the fluid cell membrane has a mobile but constant population of proteins with a convex spontaneous curvature, which act as nucleators of actin polymerization and adhesion. Such a continuum model couples the forces of cell-substrate adhesion, actin polymerization, membrane curvature, and th...

  10. Design, Fabrication and Testing Of Flapping Wing Micro Air Vehicle

    K. P. Preethi Manohari Sai

    2016-01-01

    Full Text Available Flapping flight has the potential to revolutionize micro air vehicles (MAVs due to increased aerodynamic performance, improved maneuverability and hover capabilities. The purpose of this project is to design and fabrication of flapping wing micro air vehicle. The designed MAV will have a wing span of 40cm. The drive mechanism will be a gear mechanism to drive the flapping wing MAV, along with one actuator. Initially, a preliminary design of flapping wing MAV is drawn and necessary calculation for the lift calculation has been done. Later a CAD model is drawn in CATIA V5 software. Finally we tested by Flying.

  11. Thoracodorsal artery perforator flap for upper limb reconstruction

    Thoracodorsal artery perforator flap (TAP) is a feasible option to reconstruct defects in upper limb where only skin and subcutaneous tissue is required. Methods: This case series was carried out at department of Plastic and Reconstructive Surgery Combined Military Hospital Rawalpindi. A total of 5 patients with upper limb defects were reconstructed with thoracodorsal artery musculocutaneous perforator flaps. Among them, 3 were pedicled and two free TAP flaps. All flaps except one pedicled flap were raised on a single perforator pedicle. Recipient sites were one axilla, two shoulder regions and two hands. The soft tissue defects in the patients had resulted from burns, trauma, wide local excision of synovial sarcoma and surgery for hidradenitis suppurativa. Preoperative hand held Doppler ultrasound was used to locate and mark the perforator. Results: All flaps survived without significant complications. All flaps were hyperemic in the immediate postoperative period. We designed and raised all the five flaps on eccentrically placed perforators. All the raised perforators originated from the descending branch of the thoracodorsal artery. The donor sites were closed primarily with linear scars in all cases except one, in which partial closure was accomplished with split thickness skin grafting (STSG). Conclusion: The thoracodorsal artery perforator flap has great potential for reconstructing large, relatively shallow, defects of upper limb because of its suitable skin quality, texture and appropriate thickness, as well as hidden donor site, a reliable pedicle and sparing of muscle unit. (author)

  12. Medial circumflex femoral artery flap for ischial pressure sore

    Palanivelu S

    2009-01-01

    Full Text Available A new axial pattern flap based on the terminal branches of the medial circumflex femoral artery is described for coverage of ischial pressure sore. Based on the terminal branches of the transverse branch of medial circumflex femoral artery, which exit through the gap between the quadratus femoris muscle above and the upper border of adductor magnus muscle below, this fascio cutaneous flap is much smaller than the posterior thigh flap but extremely useful to cover ischeal pressure sores. The skin redundancy below the gluteal fold allows a primary closure of the donor defect. It can also be used in combination with biceps femoris muscle flap.

  13. Monocortical Deep Circumflex Iliac Artery Flap in Jaw Reconstruction.

    Moon, Seong-Yong

    2015-06-01

    Conventionally deep circumflex iliac artery (DCIA) flap had been harvested as bicortical form. However, several complications and adverse effects occurred such as abnormal hip contour, hernia, severe bleeding tendency, gait disturbance, and hypoesthesia. All the 9 patients required reconstruction of the jaw with microvascular free flaps after radical resection. Monocortical bone segment was harvested from the anterior iliac crest, and the amount of bone harvested was from 47 to 90 mm (mean, 63 ± 14.6). Monocortical deep circumflex iliac artery flap has sufficient advantages in donor-site morbidity, which is one of the factors to choose flap. PMID:26080179

  14. Cervicopectoral flap in head and neck cancer surgery

    Sivrioglu Nazan S

    2003-12-01

    Full Text Available Abstract Background Reconstruction of the head and neck after adequate resection of primary tumor and neck dissection is a challenge. It should be performed at one sitting in advanced tumors. Defects caused by the resection should be closed with flaps which match in color, texture and hair bearing characteristics with the face. Cervicopectoral flap is a one such flap from chest and neck skin mainly used to cover the cheek defects. Methods This study included twelve patients presenting with cancer of the head and neck to Izmir Ataturk Training Hospital and Adnan Menderes University Hospital. Tumor resection and neck dissection was performed in one session by the same surgeon. A single incision was made and a medially based cervicopectoral fascio-cutaneous flap was used for surgical exposure in neck dissection and for closure of defects after tumor resection. Results There was no major complication. Two flaps had partial superficial epidermolysis at the suture line. Good aesthetic and functional results were achieved. Conclusion The cervicopectoral flap is an excellent alternative for the reconstruction of head and neck. Harvesting and application of the flap is rapid and safe. Only a single incision is sufficient for dissection and flap elevation. This flap achieves perfect surgical exposure, makes neck dissection easy and allows one to perform both tumor resection and neck dissection in one session.

  15. Oropharyngeal reconstruction with a pedicled submandibular gland flap.

    Mashrah, Mubarak A; Zhou, Shang-Hui; Abdelrehem, Ahmed; Ma, Chunyue; Xu, Liqun; He, Yue; Zhang, Chen-Ping

    2016-05-01

    Locoregional flaps are widely used for reconstruction of small and medium defects in the oral cavity. The submandibular gland flap is a pedicled flap, which derives its blood supply from the facial artery, based on the submandibular gland. We describe the use of the flap in 20 patients who required oropharyngeal reconstruction with a pedicled submandibular gland flap after resection of a tumour between July 2012 and October 2014. Patients with squamous cell carcinoma were excluded. All flaps were pedicled on the facial vessels (inferiorly in 17 patients and superiorly in 3). The indications were: reconstruction of intraoral mucosal defects (n=13), filling the parapharyngeal dead space (n=6), and obliteration of the mastoid (n=1). All the flaps atrophied, but with no clinical effect. One patient developed partial loss of the flap, and one early leakage. There were no cases of xerostomia, and no signs of recurrence during the postoperative follow-up period of 3-26 months. The flap is useful, as it is simple and reliable for reconstruction of small to medium oropharyngeal defects in carefully selected cases, and gives good cosmetic and functional results. PMID:26388070

  16. Angiographic findings before and after transplantation of split myocutaneous flaps

    Prerequisite for successful split-skin flap transplants of myocutaneous flaps is the presence of adequate adjacent afferent and efferent vessels, thus making an arteriography of the receiving region mandatory during surgery preparation. In 20 or 29 patients in whom a split myocutaneous flap was transplanted to the lower leg, angiography revealed 22 pathological or other therapy-relevant findings. Besides the afferent vessels it is basically necessary to visualise the peripheral efferent pathways in order to prevent that vascular anastomosis to the split-skin flap obstructs the blood supply of the leg. (orig.)

  17. Development of a morphing flap using shape memory alloy actuators: the aerodynamic characteristics of a morphing flap

    The discontinuous contour of a wing with conventional flaps diminishes the aerodynamic performance of an aircraft. A wing with a continuous contour does not experience extreme flow stream fluctuations during flight, and consequently has good aerodynamic characteristics. In this study, a morphing flap using shape memory alloy actuators is proposed, designed and fabricated, and its aerodynamic characteristics are investigated using aerodynamic analyses and wind tunnel tests. The ribs of the morphing flap are designed and fabricated with multiple elements joined together in a way that allows relative rotations of adjacent elements and forms a smooth contour of the morphing flap. The aerodynamic analyses of this multiple-element morphing-flap wing are performed using XFLR pro; its aerodynamic performance is compared with that of a mechanical-flap wing, and is measured through wind-tunnel tests. (papers)

  18. Progressive hearing loss and gradual deterioration of sensory hair bundles in the ears of mice lacking the actin-binding protein Eps8L2

    Furness, David N.; Johnson, Stuart L.; Manor, Uri; Rüttiger, Lukas; Tocchetti, Arianna; Offenhauser, Nina; Olt, Jennifer; Goodyear, Richard J.; Vijayakumar, Sarath; Dai, Yuhai; Hackney, Carole M.; Franz, Christoph; Di Fiore, Pier Paolo; Masetto, Sergio; Jones, Sherri M.

    2013-01-01

    Mechanotransduction in the mammalian auditory system depends on mechanosensitive channels in the hair bundles that project from the apical surface of the sensory hair cells. Individual stereocilia within each bundle contain a core of tightly packed actin filaments, whose length is dynamically regulated during development and in the adult. We show that the actin-binding protein epidermal growth factor receptor pathway substrate 8 (Eps8)L2, a member of the Eps8-like protein family, is a newly i...

  19. Immunocytochemical identification of actin in mitochondria of Physarum polycephalum

    2003-01-01

    Mitochondria isolated from the plasmodia of Physarum polycephalum Schw. are reacted with rabbit anti-actin antibody, and detected with FITC-conjugated sheep anti-rabbit IgG antibody. The results of indirect immunofluorescence show that actin exists in the mitochondria. Western blot analysis confirms the existence of actin in the protein preparation of the mitochondria. The indirect immunoelectron microscopic observation using the same antibodies verifies further that actin is the constituents of mitochondria, and it is dispersively distributed in the mitochondria of P. polycephalum.

  20. Actin polymerisation at the cytoplasmic face of eukaryotic nuclei

    David-Watine Brigitte

    2006-05-01

    Full Text Available Abstract Background There exists abundant molecular and ultra-structural evidence to suggest that cytoplasmic actin can physically interact with the nuclear envelope (NE membrane system. However, this interaction has yet to be characterised in living interphase cells. Results Using a fluorescent conjugate of the actin binding drug cytochalasin D (CD-BODIPY we provide evidence that polymerising actin accumulates in vicinity to the NE. In addition, both transiently expressed fluorescent actin and cytoplasmic micro-injection of fluorescent actin resulted in accumulation of actin at the NE-membrane. Consistent with the idea that the cytoplasmic phase of NE-membranes can support this novel pool of perinuclear actin polymerisation we show that isolated, intact, differentiated primary hepatocyte nuclei support actin polymerisation in vitro. Further this phenomenon was inhibited by treatments hindering steric access to outer-nuclear-membrane proteins (e.g. wheat germ agglutinin, anti-nesprin and anti-nucleoporin antibodies. Conclusion We conclude that actin polymerisation occurs around interphase nuclei of living cells at the cytoplasmic phase of NE-membranes.

  1. Shape Changes of Self-Assembled Actin Bilayer Composite Membranes

    Hackl, W; Sackmann, E

    1997-01-01

    We report the self-assembly of thin actin shells beneath the membranes of giant vesicles. Ion-carrier mediated influx of Mg2+ induces actin polymerization in the initially spherical vesicles. Buckling of the vesicles and the formation of blisters after thermally induced bilayer expansion is demonstrated. Bilayer flickering is dominated by tension generated by its coupling to the actin cortex. Quantitative flicker analysis suggests the bilayer and the actin cortex are separated by 0.4 \\mum to 0.5 \\mum due to undulation forces.

  2. An unconventional form of actin in protozoan hemoflagellate, Leishmania.

    Kapoor, Prabodh; Sahasrabuddhe, Amogh A; Kumar, Ashutosh; Mitra, Kalyan; Siddiqi, Mohammad Imran; Gupta, Chhitar M

    2008-08-15

    Leishmania actin was cloned, overexpressed in baculovirus-insect cell system, and purified to homogeneity. The purified protein polymerized optimally in the presence of Mg2+ and ATP, but differed from conventional actins in its following properties: (i) it did not polymerize in the presence of Mg2+ alone, (ii) it polymerized in a restricted range of pH 7.0-8.5, (iii) its critical concentration for polymerization was found to be 3-4-fold lower than of muscle actin, (iv) it predominantly formed bundles rather than single filaments at pH 8.0, (v) it displayed considerably higher ATPase activity during polymerization, (vi) it did not inhibit DNase-I activity, and (vii) it did not bind the F-actin-binding toxin phalloidin or the actin polymerization disrupting agent Latrunculin B. Computational and molecular modeling studies revealed that the observed unconventional behavior of Leishmania actin is related to the diverged amino acid stretches in its sequence, which may lead to changes in the overall charge distribution on its solvent-exposed surface, ATP binding cleft, Mg2+ binding sites, and the hydrophobic loop that is involved in monomer-monomer interactions. Phylogenetically, it is related to ciliate actins, but to the best of our knowledge, no other actin with such unconventional properties has been reported to date. It is therefore suggested that actin in Leishmania may serve as a novel target for design of new antileishmanial drugs. PMID:18539603

  3. Calcium and actin in the saga of awakening oocytes

    Santella, Luigia, E-mail: santella@szn.it; Limatola, Nunzia; Chun, Jong T.

    2015-04-24

    The interaction of the spermatozoon with the egg at fertilization remains one of the most fascinating mysteries of life. Much of our scientific knowledge on fertilization comes from studies on sea urchin and starfish, which provide plenty of gametes. Large and transparent, these eggs have served as excellent model systems for studying egg activation and embryo development in seawater, a plain natural medium. Starfish oocytes allow the study of the cortical, cytoplasmic and nuclear changes during the meiotic maturation process, which can also be triggered in vitro by hormonal stimulation. These morphological and biochemical changes ensure successful fertilization of the eggs at the first metaphase. On the other hand, sea urchin eggs are fertilized after the completion of meiosis, and are particularly suitable for the study of sperm–egg interaction, early events of egg activation, and embryonic development, as a large number of mature eggs can be fertilized synchronously. Starfish and sea urchin eggs undergo abrupt changes in the cytoskeleton and ion fluxes in response to the fertilizing spermatozoon. The plasma membrane and cortex of an egg thus represent “excitable media” that quickly respond to the stimulus with the Ca{sup 2+} swings and structural changes. In this article, we review some of the key findings on the rapid dynamic rearrangements of the actin cytoskeleton in the oocyte/egg cortex upon hormonal or sperm stimulation and their roles in the modulation of the Ca{sup 2+} signals and in the control of monospermic fertilization. - Highlights: • Besides microtubules, microfilaments may anchor the nucleus to oocyte surface. • The cortical Ca{sup 2+} flash and wave at fertilization mirror electrical membrane change. • Artificial egg activation lacks microvilli extension in the perivitelline space. • Calcium is necessary but not sufficient for cortical granules exocytosis. • Actin cytoskeleton modulates Ca{sup 2+} release at oocyte maturation

  4. Calcium and actin in the saga of awakening oocytes

    The interaction of the spermatozoon with the egg at fertilization remains one of the most fascinating mysteries of life. Much of our scientific knowledge on fertilization comes from studies on sea urchin and starfish, which provide plenty of gametes. Large and transparent, these eggs have served as excellent model systems for studying egg activation and embryo development in seawater, a plain natural medium. Starfish oocytes allow the study of the cortical, cytoplasmic and nuclear changes during the meiotic maturation process, which can also be triggered in vitro by hormonal stimulation. These morphological and biochemical changes ensure successful fertilization of the eggs at the first metaphase. On the other hand, sea urchin eggs are fertilized after the completion of meiosis, and are particularly suitable for the study of sperm–egg interaction, early events of egg activation, and embryonic development, as a large number of mature eggs can be fertilized synchronously. Starfish and sea urchin eggs undergo abrupt changes in the cytoskeleton and ion fluxes in response to the fertilizing spermatozoon. The plasma membrane and cortex of an egg thus represent “excitable media” that quickly respond to the stimulus with the Ca2+ swings and structural changes. In this article, we review some of the key findings on the rapid dynamic rearrangements of the actin cytoskeleton in the oocyte/egg cortex upon hormonal or sperm stimulation and their roles in the modulation of the Ca2+ signals and in the control of monospermic fertilization. - Highlights: • Besides microtubules, microfilaments may anchor the nucleus to oocyte surface. • The cortical Ca2+ flash and wave at fertilization mirror electrical membrane change. • Artificial egg activation lacks microvilli extension in the perivitelline space. • Calcium is necessary but not sufficient for cortical granules exocytosis. • Actin cytoskeleton modulates Ca2+ release at oocyte maturation and fertilization

  5. Free combined composite flaps using the lateral circumflex femoral system for repair of massive defects of the head and neck regions: an introduction to the chimeric flap principle.

    Koshima, I; Yamamoto, H; Hosoda, M; Moriguchi, T; Orita, Y; Nagayama, H

    1993-09-01

    Chimeric composite flaps combined using microanastomoses consist of two or more flaps or tissues, each with an isolated pedicle and a single vascular source. Free combined chimeric flaps using the lateral circumflex femoral system were used to treat massive composite defects of the head and neck in 10 cases. A combined anterolateral thigh flap and vascularized iliac bone graft based on the lateral circumflex femoral system and the deep circumflex iliac system was the most commonly used combination. An anteromedial thigh flap and a paraumbilical perforator-based flap were also combined with this principal combination. The advantages of this chimeric flap over other osteocutaneous flaps are: (1) The flap is relatively thin and the pedicle vessels are up to 10 cm longer and are wider than those of other flaps for easier harvesting of the flap. (2) It is unnecessary to reposition the patient. (3) The vascular pedicle to the skin can be separated from that of the bone. (4) The donor site is not close to the recipient site. (5) The donor scar is in an unexposed area. (6) The skin territory of this flap is extremely wide. (7) A combined anterolateral and anteromedial thigh flap and vascularized iliac bone graft can be easily obtained as an extended combined osteocutaneous flap. (8) Other neighboring skin flaps, such as a groin flap, a paraumbilical perforator-based flap, or a medial thigh flap, can be combined with this chimeric flap because several major muscle branches to be anastomosed derive from the lateral circumflex femoral system. Chimeric composite flaps using the lateral circumflex femoral system are considered suitable for the repair of massive composite defects of the head and neck. PMID:8341739

  6. Aerodynamics of a bio-inspired flexible flapping-wing micro air vehicle

    MAVs (micro air vehicles) with a maximal dimension of 15 cm and nominal flight speeds of around 10 m s−1, operate in a Reynolds number regime of 105 or lower, in which most natural flyers including insects, bats and birds fly. Furthermore, due to their light weight and low flight speed, the MAVs' flight characteristics are substantially affected by environmental factors such as wind gust. Like natural flyers, the wing structures of MAVs are often flexible and tend to deform during flight. Consequently, the aero/fluid and structural dynamics of these flyers are closely linked to each other, making the entire flight vehicle difficult to analyze. We have recently developed a hummingbird-inspired, flapping flexible wing MAV with a weight of 2.4–3.0 g and a wingspan of 10–12 cm. In this study, we carry out an integrated study of the flexible wing aerodynamics of this flapping MAV by combining an in-house computational fluid dynamic (CFD) method and wind tunnel experiments. A CFD model that has a realistic wing planform and can mimic realistic flexible wing kinematics is established, which provides a quantitative prediction of unsteady aerodynamics of the four-winged MAV in terms of vortex and wake structures and their relationship with aerodynamic force generation. Wind tunnel experiments further confirm the effectiveness of the clap and fling mechanism employed in this bio-inspired MAV as well as the importance of the wing flexibility in designing small flapping-wing MAVs.

  7. Duplication in the microtubule-actin cross-linking factor 1 gene causes a novel neuromuscular condition

    Jørgensen, Louise H; Mosbech, Mai-Britt; Færgeman, Nils J;

    2014-01-01

    Spectrins and plakins are important communicators linking cytoskeletal components to each other and to cellular junctions. Microtubule-actin cross-linking factor 1 (MACF1) belongs to the spectraplakin family and is involved in control of microtubule dynamics. Complete knock out of MACF1 in mice is...

  8. Identification of Flap Motion Parameters for Vibration Reduction in Helicopter Rotors with Multiple Active Trailing Edge Flaps

    Uğbreve;ur Dalli

    2011-01-01

    Full Text Available An active control method utilizing the multiple trailing edge flap configuration for rotorcraft vibration suppression and blade loads control is presented. A comprehensive model for rotor blade with active trailing edge flaps is used to calculate the vibration characteristics, natural frequencies and mode shapes of any complex composite helicopter rotor blade. A computer program is developed to calculate the system response, rotor blade root forces and moments under aerodynamic forcing conditions. Rotor blade system response is calculated using the proposed solution method and the developed program depending on any structural and aerodynamic properties of rotor blades, structural properties of trailing edge flaps and properties of trailing edge flap actuator inputs. Rotor blade loads are determined first on a nominal rotor blade without multiple active trailing edge flaps and then the effects of the active flap motions on the existing rotor blade loads are investigated. Multiple active trailing edge flaps are controlled by using open loop controllers to identify the effects of the actuator signal output properties such as frequency, amplitude and phase on the system response. Effects of using multiple trailing edge flaps on controlling rotor blade vibrations are investigated and some design criteria are determined for the design of trailing edge flap controller that will provide actuator signal outputs to minimize the rotor blade root loads. It is calculated that using the developed active trailing edge rotor blade model, helicopter rotor blade vibrations can be reduced up to 36% of the nominal rotor blade vibrations.

  9. Comparative study of visual acuity and aberrations after intralase femtosecond LASIK: small corneal flap versus big corneal flap

    Ya-Li; Zhang; Lei; Liu; Chang-Xia; Cui; Ming; Hu; Zhao-Na; Li; Li-Jun; Cao; Xiu-Hua; Jing; Guo-Ying; Mu

    2014-01-01

    AIM:To study the effects of different flap sizes on visual acuity, refractive outcomes, and aberrations after femtosecond laser for laser keratomileusis (LASIK). ·METHODS: In each of the forty patients enrolled, 1 eye was randomly assigned to receive treatment with a 8.1mm diameter corneal flap, defined as the small flap, while the other eye was treated with a 8.6mm diameter corneal flap, defined as the big flap. Refractive errors, visual acuity, and higher -order aberrations were compared between the two groups at week 1, month 1 and 3 postoperatively. · RESULTS: The postoperative refractive errors and visual acuity all conformed to the intended goal. Postoperative higher -order aberrations were increased, especially in spherical aberration (Z12) and vertical coma (Z7). There were no statistically significant differences between the two groups in terms of postoperative refractive errors, visual acuity, root mean square of total HOAs (HO -RMS), trefoil 30° (Z6), vertical coma (Z7), horizontal coma (Z8), trefoil 0° (Z9), and spherical aberration (Z12) at any point during the postoperative follow-up. ·CONCLUSION: Both the small and big flaps are safe and effective procedures to correct myopia, provided the exposure stroma meets the excimer laser ablations. The personalized size corneal flap is feasible, as we can design the size of corneal flap based on the principle that the corneal flap diameter should be equal to or greater than the sum of the maximum ablation diameter and apparatus error.

  10. A propeller flap for single-stage nose reconstruction in selected patients: supratrochlear artery axial propeller flap.

    Cordova, Adriana; D'Arpa, Salvatore; Massimiliano, Tripoli; Toia, Francesca; Moschella, Francesco

    2014-06-01

    The paramedian forehead flap is the gold standard technique for nose reconstruction. It requires two different surgical operations which prolonged the postoperative dressing and care. We present our 5-year experience with a propeller flap based on the supratrochlear artery, which allows one-stage transfer of the forehead skin to the nose without the need for pedicle division. This technique is indicated in a selected group of patients who are not suitable for multiple-stage reconstructions because they have concurrent medical conditions, reduced mobility, or live far away from specialized medical centers. We have renamed this procedure as supratrochlear artery axial propeller flap, from the acronym STAAP flap, to stress the axial, well known and constant, vascularization of the flap. In the past 5 years, we have been performing 25 STAAP flaps; full-thickness nasal reconstruction was performed in 11 cases. The patients were 16 males and 9 females, with a mean age of 79.5 years. All patients had multiple comorbidities. Complete flap survival was observed in 23 cases and healing was complete in 7 days. In two cases, there was a partial distal necrosis of the flap treated conservatively. Cosmetic results were good and the patient's satisfaction was significant. These results indicate that the STAAP flap is a reliable and useful technique in selected cases, as old or noncompliant patients who benefit from a one-stage technique of nose reconstruction. PMID:24918712

  11. The F-actin bundler α-actinin Ain1 is tailored for ring assembly and constriction during cytokinesis in fission yeast.

    Li, Yujie; Christensen, Jenna R; Homa, Kaitlin E; Hocky, Glen M; Fok, Alice; Sees, Jennifer A; Voth, Gregory A; Kovar, David R

    2016-06-01

    The actomyosin contractile ring is a network of cross-linked actin filaments that facilitates cytokinesis in dividing cells. Contractile ring formation has been well characterized in Schizosaccharomyces pombe, in which the cross-linking protein α-actinin SpAin1 bundles the actin filament network. However, the specific biochemical properties of SpAin1 and whether they are tailored for cytokinesis are not known. Therefore we purified SpAin1 and quantified its ability to dynamically bind and bundle actin filaments in vitro using a combination of bulk sedimentation assays and direct visualization by two-color total internal reflection fluorescence microscopy. We found that, while SpAin1 bundles actin filaments of mixed polarity like other α-actinins, SpAin1 has lower bundling activity and is more dynamic than human α-actinin HsACTN4. To determine whether dynamic bundling is important for cytokinesis in fission yeast, we created the less dynamic bundling mutant SpAin1(R216E). We found that dynamic bundling is critical for cytokinesis, as cells expressing SpAin1(R216E) display disorganized ring material and delays in both ring formation and constriction. Furthermore, computer simulations of initial actin filament elongation and alignment revealed that an intermediate level of cross-linking best facilitates filament alignment. Together our results demonstrate that dynamic bundling by SpAin1 is important for proper contractile ring formation and constriction. PMID:27075176

  12. A study of a three-dimensional self-propelled flying bird with flapping wings

    Zhu, LinLin; Guan, Hui; Wu, ChuiJie

    2015-09-01

    In this paper, a study of a three-dimensional (3D) self-propelled bionic flying bird in a viscous flow is carried out. This bionic bird is propelled and lifted through flapping and rotating wings, and better flying can be achieved by adjusting the flapping and rotation motion of wings. In this study, we found that the bird can fly faster forward and upward with appropriate center of rotation and oscillation without more energy consumption and have perfect flight performance at a certain angle of attack by adjusting the center of oscillation. The study utilizes a 3D computational fluid dynamics package which constitutes combined immersed boundary method and the volume of fluid method. In addition, it includes adaptive multigrid finite volume method and control strategy of swimming and flying.

  13. Early Venous Occlusion Detection in a Free Flap Using Real-time Laser Doppler Imaging

    Héba Alkhashnam, MD

    2013-04-01

    Full Text Available Summary: Early detection of venous occlusion in free flaps is particularly difficult to identify, and its duration is known to be directly proportional to flap mortality. Here, we report a case of deep inferior epigastric perforator based breast reconstruction in which the intraoperative use of a perfusion camera enabled identifying a venous occlusion based on microcirculatory pulsation dynamics in real time. The sensitivity of our proposed method suggests that in certain cases in which the onset of venous occlusion begins in the operating room we can detect and treat occlusion before sending the patient to recovery. Further development of this technique will allow for earlier and more objective decision making with regard to venous occlusion detection in free tissue transfer.

  14. VISCOELASTIC CONSTITUTIVE MODEL RELATED TO DEFORMATION OF INSECT WING UNDER LOADING IN FLAPPING MOTION

    BAO Lin; HU Jin-song; YU Yong-liang; CHENG Peng; XU Bo-qing; TONG Bing-gang

    2006-01-01

    Flexible insect wings deform passively under the periodic loading during flapping flight. The wing flexibility is considered as one of the specific mechanisms on improving insect flight performance. The constitutive relation of the insect wing material plays a key role on the wing deformation, but has not been clearly understood yet. A viscoelastic constitutive relation model was established based on the stress relaxation experiment of a dragonfly wing (in vitro). This model was examined by the finite clement analysis of the dynamic deformation response for a model insect wing under the action of the periodical inertial force in flapping. It is revealed that the viscoelastic constitutive relation is rational to characterize the biomaterial property of insect wings in contrast to the elastic one. The amplitude and form of the passive viscoelastic deformation of the wing is evidently dependent on the viscous parameters in the constitutive relation.

  15. Effects of structural flexibility of wings in flapping flight of butterfly

    The objective of this paper is to clarify the effects of structural flexibility of wings of a butterfly in flapping flight. For this purpose, a dynamics model of a butterfly is derived by Lagrange’s method, where the butterfly is considered as a rigid multi-body system. The panel method is employed to simulate the flow field and the aerodynamic forces acting on the wings. The mathematical model is validated by the agreement of the numerical result with the experimentally measured data. Then, periodic orbits of flapping-of-wings flights are parametrically searched in order to fly the butterfly models. Almost periodic orbits are found, but they are unstable. Deformation of the wings is modeled in two ways. One is bending and its effect on the aerodynamic forces is discussed. The other is passive wing torsion caused by structural flexibility. Numerical simulations demonstrate that flexible torsion reduces the flight instability. (paper)

  16. Interactions between the Yeast SM22 Homologue Scp1 and Actin Demonstrate the Importance of Actin Bundling in Endocytosis* S⃞

    Gheorghe, Dana M.; Aghamohammadzadeh, Soheil; Rooij, Iwona I. Smaczynska-de; Allwood, Ellen G.; Winder, Steve J.; Ayscough, Kathryn R.

    2008-01-01

    The yeast SM22 homologue Scp1 has previously been shown to act as an actin-bundling protein in vitro. In cells, Scp1 localizes to the cortical actin patches that form as part of the invagination process during endocytosis, and its function overlaps with that of the well characterized yeast fimbrin homologue Sac6p. In this work we have used live cell imaging to demonstrate the importance of key residues in the Scp1 actin interface. We have defined two actin binding domains within Scp1 that all...

  17. Elbow Reconstruction Using Island Flap for Burn Patients

    Gi Yeun Hur

    2012-11-01

    Full Text Available Background Deep burns of the elbow lead to soft tissue necrosis and infection, with exposureof deep structures. Adequate wound coverage of this area requires thin, pliable, and durabletissue, while optimal functional recovery requires early coverage and functional rehabilitation.We have found 3 types of island flaps that provide reliable coverage for the elbow.Methods A retrospective study was performed on all patients who underwent flap coverageof an elbow defect at our hospital. The patients’ data including age, sex, cause of injury, wounddimensions, timing of flap coverage, postoperative elbow motion, and complications wereinvestigated.Results Between 2001 and 2012, 16 patients were treated at our hospital. The mean agewas 53.3 years. Three kinds of flaps were performed: 9 latissimus dorsi flaps, 4 lateral armflaps, and 4 radial forearm flaps. The average defect size was 183.5 cm2 (range, 28 to 670cm2. Wound coverage was performed at mean duration of 45.9 days (range, 14 to 91 days.The mean postoperative active elbow flexion was 98° (range, 85° to 115°. Partial flap failureoccurred in 1 latissimus dorsi flap. Minor complications included partial flap loss (11.8%,hematoma (23.5%, seroma (35.3%, and wound infection (5.9%.Conclusions Flap selection for elbow reconstruction is determined by the defect size andthe extent of the adjacent tissue injury. Elbow reconstruction using an island flap is a singlestaged,reliable, and relatively simple procedure that permits initiation of early rehabilitation,thereby improving a patient’s functional outcome.

  18. The cortical actin determines different susceptibility of naïve and memory CD4+ T cells to HIV-1 cell-to-cell transmission and infection.

    Permanyer, Marc; Pauls, Eduardo; Badia, Roger; Esté, José A; Ballana, Ester

    2013-01-01

    Memory CD4+ T cells are preferentially infected by HIV-1 compared to naïve cells. HIV-1 fusion and entry is a dynamic process in which the cytoskeleton plays an important role by allowing virion internalization and uncoating. Here, we evaluate the role of the cortical actin in cell-to-cell transfer of virus antigens and infection of target CD4+ T cells. Using different actin remodeling compounds we demonstrate that efficiency of HIV-internalization was proportional to the actin polymerization of the target cell. Naïve (CD45RA+) and memory (CD45RA-) CD4+ T cells could be phenotypically differentiated by the degree of cortical actin density and their capacity to capture virus. Thus, the higher cortical actin density of memory CD4+ T cells was associated to increased efficiency of HIV-antigen internalization and the establishment of a productive infection. Conversely, the lower cortical actin density in naïve CD4+ T cells restricted viral antigen transfer and consequently HIV-1 infection. In conclusion, the cortical actin density differentially affects the susceptibility to HIV-1 infection in naïve and memory CD4+ T cells by modulating the efficiency of HIV antigen internalization. PMID:24244453

  19. Kinetics of the Formation and Dissociation of Actin Filament Branches Mediated by Arp2/3 Complex

    Mahaffy, Rachel E.; Pollard, Thomas D.

    2006-01-01

    The actin filament network at the leading edge of motile cells relies on localized branching by Arp2/3 complex from “mother” filaments growing near the plasma membrane. The nucleotide bound to the mother filaments (ATP, ADP and phosphate, or ADP) may influence the branch dynamics. To determine the effect of the nucleotide bound to the subunits of the mother filament on the formation and stability of branches, we compared the time courses of actin polymerization in bulk samples measured using ...

  20. Plasmin enzymatic activity in the presence of actin

    Yusova E. I.

    2015-10-01

    Full Text Available Aim. To study the changes in the plasmin activity towards substrates with high and low molecular mass in the presence of actin. Methods. The proteins used for this investigation were obtained by affinity chromatography and gel-filtration. The plasmin enzymatic activity was determined by a turbidimetric assay and a chromogenic substrate-based assay. The enzyme linked immunosorbent assay and biotin-avidin-phosphatase system were used to study the interaction of plasminogen and its fragments with actin. Results. It was shown that G-actin causes 1.5-fold decrease in the rate of polymeric fibrin hydrolysis by plasmin and Glu-plasminogen activated by the tissue plasminogen activator. However, actin did not impede plasmin autolysis and had no influence on its amidase activity. We have studied an interaction of biotinylated Glu-plasminogen and its fragments (kringle 1-3, kringle 4 and mini-plasminogen with immobilized G-actin. Glu-plasminogen and kringle 4 had a high affinity towards actin (C50 is 113 and 117 nM correspondingly. Mini-plasminogen and kringe 4 did not bind to actin. A similar affinity of Glu-plasminogen and kringle 1-3 towards actin proves the involvement of the kringle 1-3 lysine-binding sites of the native plasminogen form in the actin interaction. Conclusions. Actin can modulate plasmin specificity towards high molecular mass substrates through its interaction with lysine-binding sites of the enzyme kringle domains. Actin inhibition of the fibrinolytic activity of plasmin is due to its competition with fibrin for thelysine binding sites of plasminogen/plasmin.