scholarly journals Liquid behavior of cross-linked actin bundles

2017 ◽  
Vol 114 (9) ◽  
pp. 2131-2136 ◽  
Author(s):  
Kimberly L. Weirich ◽  
Shiladitya Banerjee ◽  
Kinjal Dasbiswas ◽  
Thomas A. Witten ◽  
Suriyanarayanan Vaikuntanathan ◽  
...  
Keyword(s):  
Interfacial Tension ◽  
Actin Cytoskeleton ◽  
Actin Filaments ◽  
Liquid Droplet ◽  
Droplet Shape ◽  
Actin Bundles ◽  
Physiological Processes ◽  
Liquid Behavior ◽  
Capillary Instabilities ◽  
Cross Linker

The actin cytoskeleton is a critical regulator of cytoplasmic architecture and mechanics, essential in a myriad of physiological processes. Here we demonstrate a liquid phase of actin filaments in the presence of the physiological cross-linker, filamin. Filamin condenses short actin filaments into spindle-shaped droplets, or tactoids, with shape dynamics consistent with a continuum model of anisotropic liquids. We find that cross-linker density controls the droplet shape and deformation timescales, consistent with a variable interfacial tension and viscosity. Near the liquid–solid transition, cross-linked actin bundles show behaviors reminiscent of fluid threads, including capillary instabilities and contraction. These data reveal a liquid droplet phase of actin, demixed from the surrounding solution and dominated by interfacial tension. These results suggest a mechanism to control organization, morphology, and dynamics of the actin cytoskeleton.

scholarly journals Regulation of Actin Filament Cross-linking and Bundle Shape in Drosophila Bristles

2000 ◽  
Vol 148 (1) ◽  
pp. 87-99 ◽  
Author(s):  
Lewis G. Tilney ◽  
Patricia S. Connelly ◽  
Kelly A. Vranich ◽  
Michael K. Shaw ◽  
Gregory M. Guild
Keyword(s):  
Plasma Membrane ◽  
Actin Filaments ◽  
Cross Linking ◽  
Limited Area ◽  
Actin Bundles ◽  
Electron Microscopy Analysis ◽  
Section Electron ◽  
Cross Links ◽  
Bundle Size ◽  
Cross Linker

Previous studies demonstrate that in developing Drosophila bristles, two cross-linking proteins are required sequentially to bundle the actin filaments that support elongating bristle cells. The forked protein initiates the process and facilitates subsequent cross-linking by fascin. Using cross-linker–specific antibodies, mutants, and drugs we show that fascin and actin are present in excessive amounts throughout bundle elongation. In contrast, the forked cross-linker is limited throughout bundle formation, and accordingly, regulates bundle size and shape. We also show that regulation of cross-linking by phosphorylation can affect bundle size. Specifically, inhibition of phosphorylation by staurosporine results in a failure to form large bundles if added during bundle formation, and leads to a loss of cross-linking by fascin if added after the bundles form. Interestingly, inhibition of dephosphorylation by okadaic acid results in the separation of the actin bundles from the plasma membrane. We further show by thin section electron microscopy analysis of mutant and wild-type bristles that the amount of material that connects the actin bundles to the plasma membrane is also limited throughout bristle elongation. Therefore, overall bundle shape is determined by the number of actin filaments assembled onto the limited area provided by the connector material. We conclude that assembly of actin bundles in Drosophila bristles is controlled in part by the controlled availability of a single cross-linking protein, forked, and in part by controlled phosphorylation of cross-links and membrane actin connector proteins.

Dynamic control of cell-cell adhesion and membrane-associated actin during food-induced mouth opening in Beroe

1993 ◽  
Vol 106 (1) ◽  
pp. 355-364
Author(s):  
S.L. Tamm ◽  
S. Tamm
Keyword(s):  
Cell Adhesion ◽  
Actin Cytoskeleton ◽  
Actin Filaments ◽  
Dynamic Control ◽  
Mouth Opening ◽  
Cell Junctions ◽  
Dynamic Changes ◽  
Rhodamine Phalloidin ◽  
Rapid Changes ◽  
Muscular Action

We used rhodamine-phalloidin and ultrastructural methods to follow dynamic changes in adhesive cell junctions and associated actin filaments during reversible epithelial adhesion in the mouth of the ctenophore Beroe. A cruising Beroe keeps its mouth closed by interdigitated actin-coated appositions between paired strips of cells lining the lips. The mouth opens rapidly (in 0.2-0.3 s) by muscular action to engulf prey (other ctenophores), then re-seals after ingestion. We found that the interlocking surface architecture of the adhesive cells, including the actin-coated junctions, rapidly disappears after food-induced opening of the mouth. In contrast, forcible separation of the lips in the absence of food rips the junctions, still intact, from the surfaces of the cells. The prey-stimulated loss of adhesive cell junctions and associated actin cytoskeleton is one of the most rapid changes in actin-based junctions yet observed. This system provides unique experimental advantages for investigating the dynamic control of reversible cell adhesions and membrane-associated actin filaments.

Evidence for a molecular complex consisting of Fyb/SLAP, SLP-76, Nck, VASP and WASP that links the actin cytoskeleton to Fcγ receptor signalling during phagocytosis

2001 ◽  
Vol 114 (23) ◽  
pp. 4307-4318
Author(s):  
Marc G. Coppolino ◽  
Matthias Krause ◽  
Petra Hagendorff ◽  
David A. Monner ◽  
William Trimble ◽  
...  
Keyword(s):  
Actin Cytoskeleton ◽  
Molecular Complex ◽  
Actin Filaments ◽  
Sh2 Domain ◽  
Fcγ Receptors ◽  
Receptor Signalling ◽  
Src Homology 2 ◽  
Src Homology ◽  
Particle Ingestion ◽  
Syndrome Protein

Phagocytosis by macrophages and neutrophils involves the spatial and temporal reorganisation of the actin-based cytoskeleton at sites of particle ingestion. Local polymerisation of actin filaments supports the protrusion of pseudopodia that eventually engulf the particle. Here we have investigated in detail the cytoskeletal events initiated upon engagement of Fc receptors in macrophages. Ena/vasodilator-stimulated phosphoprotein (VASP) proteins were recruited to phagosomes forming around opsonised particles in both primary and immortalised macrophages. Not only did the localisation of Ena/VASP proteins coincide, spatially and temporally, with the phagocytosis-induced reorganisation of actin filaments, but their recruitment to the phagocytic cup was required for the remodelling of the actin cytoskeleton, extension of pseudopodia and efficient particle internalisation. We also report that SLP-76, Vav and profilin were recruited to forming phagosomes. Upon induction of phagocytosis, a large molecular complex, consisting in part of Ena/VASP proteins, the Fyn-binding/SLP-76-associated protein (Fyb/SLAP), Src-homology-2 (SH2)-domain-containing leukocyte protein of 76 kDa (SLP-76), Nck, and the Wiskott-Aldrich syndrome protein (WASP), was formed. Our findings suggest that activation of Fcγ receptors triggers two signalling events during phagocytosis: one through Fyb/SLAP that leads to recruitment of VASP and profilin; and another through Nck that promotes the recruitment of WASP. These converge to regulate actin polymerisation, controlling the assembly of actin structures that are essential for the process of phagocytosis.

Involvement of actin cytoskeleton in modulation of apical K channel activity in rat collecting duct

1994 ◽  
Vol 267 (4) ◽  
pp. F592-F598 ◽  
Author(s):  
W. H. Wang ◽  
A. Cassola ◽  
G. Giebisch
Keyword(s):  
Actin Cytoskeleton ◽  
Actin Filaments ◽  
Cytochalasin B ◽  
Collecting Duct ◽  
K Channel ◽  
Cortical Collecting Duct ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Channel Inhibition ◽  
Inside Out

We have employed the patch-clamp technique to investigate the role of the actin cytoskeleton in the modulation of the low-conductance K+ channel in the apical membrane of the rat cortical collecting duct (CCD). This K+ channel is inactivated by application of cytochalasin B or D, both compounds known to disrupt actin filaments. The effect of both cytochalasins, B and D, was fully reversible in cell-attached patches, but channel activity could not be fully restored in excised membrane patches. The effect of cytochalasins on channel activity was specific and resulted from depolymerization of the actin cytoskeleton, since application of 10 microM chaetoglobosin C, a cytochalasin analogue that does not depolymerize the actin filaments, had no effect on channel activity in inside-out patches. Addition of either actin monomers or of the polymerizing actin filaments in inside-out patches to the cytosolic medium had no effect on channel activity. This suggests that cytochalasin B- or D-induced inactivation of apical K+ channels is not caused by obstruction of the channel pore by actin. We also observed that channel inhibition by cytochalasin B or D could be blocked by pretreatment with 5 microM phalloidin, a compound that stabilizes actin filaments. We conclude that apical K+ channel activity depends critically on the integrity of the actin cytoskeleton.

scholarly journals Force-mediated cellular anisotropy and plasticity dictate the elongation dynamics of embryos

2021 ◽  
Vol 7 (27) ◽  
pp. eabg3264
Author(s):  
Chao Fang ◽  
Xi Wei ◽  
Xueying Shao ◽  
Yuan Lin
Keyword(s):  
Plastic Deformation ◽  
Caenorhabditis Elegans ◽  
Muscle Contraction ◽  
Dynamic Model ◽  
Actin Filaments ◽  
Actin Bundles ◽  
Abnormal Embryo ◽  
Intracellular Forces ◽  
Kinetics Of ◽  
Good Agreement

We developed a unified dynamic model to explain how cellular anisotropy and plasticity, induced by alignment and severing/rebundling of actin filaments, dictate the elongation dynamics of Caenorhabditis elegans embryos. It was found that the gradual alignment of F-actins must be synchronized with the development of intracellular forces for the embryo to elongate, which is then further sustained by muscle contraction–triggered plastic deformation of cells. In addition, we showed that preestablished anisotropy is essential for the proper onset of the process while defects in the integrity or bundling kinetics of actin bundles result in abnormal embryo elongation, all in good agreement with experimental observations.

scholarly journals Regulated Actin Cytoskeleton Assembly at Filopodium Tips Controls Their Extension and Retraction

1999 ◽  
Vol 146 (5) ◽  
pp. 1097-1106 ◽  
Author(s):  
Aneil Mallavarapu ◽  
Tim Mitchison
Keyword(s):  
Actin Cytoskeleton ◽  
Growth Cone ◽  
Actin Filaments ◽  
Neuroblastoma Cell ◽  
Initial Step ◽  
Growth Cones ◽  
Neuroblastoma Cell Line ◽  
Dominant Factor ◽  
Retrograde Flow ◽  
Assembly Rate

The extension and retraction of filopodia in response to extracellular cues is thought to be an important initial step that determines the direction of growth cone advance. We sought to understand how the dynamic behavior of the actin cytoskeleton is regulated to produce extension or retraction. By observing the movement of fiduciary marks on actin filaments in growth cones of a neuroblastoma cell line, we found that filopodium extension and retraction are governed by a balance between the rate of actin cytoskeleton assembly at the tip and retrograde flow. Both assembly and flow rate can vary with time in a single filopodium and between filopodia in a single growth cone. Regulation of assembly rate is the dominant factor in controlling filopodia behavior in our system.

Design of a microfluidic device for the measurement of the elastic modulus of deformable particles

Soft Matter ◽  
2019 ◽  
Vol 15 (5) ◽  
pp. 880-889 ◽  
Author(s):  
Massimiliano M. Villone ◽  
Janine K. Nunes ◽  
Yankai Li ◽  
Howard A. Stone ◽  
Pier Luca Maffettone
Keyword(s):  
Elastic Modulus ◽  
Interfacial Tension ◽  
Continuous Flow ◽  
Liquid Droplet ◽  
Flow Process ◽  
Deformable Particles ◽  
Soft Particles ◽  
Continuous Flow Process ◽  
Microfluidic Technique

A microfluidic technique recently proposed in the literature to measure the interfacial tension between a liquid droplet and an immiscible suspending liquid [Hudson et al., Appl. Phys. Lett., 2005, 87, 081905], [Cabral and Hudson, Lab Chip, 2006, 6, 427] is suitably adapted to the characterization of the elastic modulus of soft particles in a continuous-flow process.

Dynamics of actin filaments during tension-dependent formation of actin bundles

2007 ◽  
Vol 1770 (8) ◽  
pp. 1115-1127 ◽  
Author(s):  
Hiroaki Hirata ◽  
Hitoshi Tatsumi ◽  
Masahiro Sokabe
Keyword(s):  
Actin Filaments ◽  
Actin Bundles

Nuclear ion channel activity is regulated by actin filaments

1996 ◽  
Vol 270 (5) ◽  
pp. C1532-C1543 ◽  
Author(s):  
A. G. Prat ◽  
H. F. Cantiello
Keyword(s):  
Ion Channels ◽  
Actin Cytoskeleton ◽  
Nuclear Envelope ◽  
Ion Channel ◽  
Actin Filaments ◽  
Actin Binding ◽  
Bathing Solution ◽  
Channel Activity ◽  
Nuclear Ion Channels ◽  
Inside Out

Actin filaments are novel second messengers involved in ion channel regulation. Because cytoskeletal components interact with the nuclear envelope, the actin cytoskeleton may also control nuclear membrane function. In this report, the patch-clamp technique was applied to isolated nuclei from amphibian A6 epithelial cells to assess the role of actin filaments on nuclear ion channel activity under nucleus-attached or -excised conditions. The most prevalent spontaneous nuclear ion channel species, 76% (n = 46), was cation selective and had a maximal single-channel conductance of approximately 420 pS. Nuclear ion channels also displayed multiple subconductance states, including channel activity of 26 pS that was frequently observed. Nuclear ion channel activity on otherwise quiescent patches was induced by either addition of the actin cytoskeleton disrupter cytochalasin D (CD; 5 micrograms/ml, 60%, 3 of 5 patches) or actin (10-1,000 micrograms/ml) to the bathing solution of nucleus-attached patches (59%, 13 of 22 patches). Actin also induced ion channel activity in quiescent excised inside-out patches from the nuclear envelope (80%, 4 of 5 patches). In contrast, addition of bovine serum albumin (10-1,000 micrograms/ml) to the bathing solution of nucleus-attached patches was without effect on nuclear ion channel activity (5 of 5 patches). The monoclonal antibody MAb414, specific for nuclear pore complex proteins, completely prevented either spontaneous or cytosolic actin-induced nuclear ion channels under nucleus-attached conditions (4 of 4 patches) but not intranuclear actin-induced nuclear ion channels under excised inside-out conditions (3 of 3 patches). In nucleus-attached patches, channel activity was readily activated by addition of the G-actin-binding protein deoxyribonuclease I to nucleus-attached patches (56%, 5 of 9 patches) or further addition of the actin-cross-linker filamin in the presence of actin (57%, 4 of 7 patches). The data indicate that dynamic changes in actin filament organization may represent a novel mechanism to control nuclear function.

scholarly journals Bundling of actin filaments by alpha-actinin depends on its molecular length.

1990 ◽  
Vol 110 (6) ◽  
pp. 2013-2024 ◽  
Author(s):  
R K Meyer ◽  
U Aebi
Keyword(s):  
Smooth Muscle ◽  
Actin Filament ◽  
Actin Filaments ◽  
Actin Binding ◽  
Molar Ratio ◽  
Cross Linking ◽  
Actin Bundle ◽  
Actin Bundles ◽  
Chicken Gizzard ◽  
Molecular Length

Cross-linking of actin filaments (F-actin) into bundles and networks was investigated with three different isoforms of the dumbbell-shaped alpha-actinin homodimer under identical reaction conditions. These were isolated from chicken gizzard smooth muscle, Acanthamoeba, and Dictyostelium, respectively. Examination in the electron microscope revealed that each isoform was able to cross-link F-actin into networks. In addition, F-actin bundles were obtained with chicken gizzard and Acanthamoeba alpha-actinin, but not Dictyostelium alpha-actinin under conditions where actin by itself polymerized into disperse filaments. This F-actin bundle formation critically depended on the proper molar ratio of alpha-actinin to actin, and hence F-actin bundles immediately disappeared when free alpha-actinin was withdrawn from the surrounding medium. The apparent dissociation constants (Kds) at half-saturation of the actin binding sites were 0.4 microM at 22 degrees C and 1.2 microM at 37 degrees C for chicken gizzard, and 2.7 microM at 22 degrees C for both Acanthamoeba and Dictyostelium alpha-actinin. Chicken gizzard and Dictyostelium alpha-actinin predominantly cross-linked actin filaments in an antiparallel fashion, whereas Acanthamoeba alpha-actinin cross-linked actin filaments preferentially in a parallel fashion. The average molecular length of free alpha-actinin was 37 nm for glycerol-sprayed/rotary metal-shadowed and 35 nm for negatively stained chicken gizzard; 46 and 44 nm, respectively, for Acanthamoeba; and 34 and 31 nm, respectively, for Dictyostelium alpha-actinin. In negatively stained preparations we also evaluated the average molecular length of alpha-actinin when bound to actin filaments: 36 nm for chicken gizzard and 35 nm for Acanthamoeba alpha-actinin, a molecular length roughly coinciding with the crossover repeat of the two-stranded F-actin helix (i.e., 36 nm), but only 28 nm for Dictyostelium alpha-actinin. Furthermore, the minimal spacing between cross-linking alpha-actinin molecules along actin filaments was close to 36 nm for both smooth muscle and Acanthamoeba alpha-actinin, but only 31 nm for Dictyostelium alpha-actinin. This observation suggests that the molecular length of the alpha-actinin homodimer may determine its spacing along the actin filament, and hence F-actin bundle formation may require "tight" (i.e., one molecule after the other) and "untwisted" (i.e., the long axis of the molecule being parallel to the actin filament axis) packing of alpha-actinin molecules along the actin filaments.

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