scholarly journals Distribution of active forces in the cell cortex

Soft Matter ◽  
2019 ◽  
Vol 15 (35) ◽  
pp. 6952-6966 ◽  
Author(s):  
P. Bohec ◽  
J. Tailleur ◽  
F. van Wijland ◽  
A. Richert ◽  
F. Gallet
Keyword(s):  
Molecular Motors ◽  
Equilibrium Distribution ◽  
Cell Cortex ◽  
Ligand Density ◽  
Actin Cortex ◽  
Stochastic Forces ◽  
Biological Inhibitors

We study the out-of-equilibrium distribution of stochastic forces generated by molecular motors activity, exerted on a probe attached to the actin cortex of premuscular cells, as a function of ligand density, temperature and biological inhibitors.

scholarly journals Vimentin filaments interact with the actin cortex in mitosis allowing normal cell division

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Sofia Duarte ◽  
Álvaro Viedma-Poyatos ◽  
Elena Navarro-Carrasco ◽  
Alma E. Martínez ◽  
María A. Pajares ◽  
...  
Keyword(s):  
Cell Division ◽  
Cell Types ◽  
Hiv Protease ◽  
Cell Cortex ◽  
Tail Domain ◽  
Cellular Functions ◽  
Cortical Actin ◽  
Intrinsically Disordered ◽  
Actin Cortex ◽  
Vimentin Filaments

Abstract The vimentin network displays remarkable plasticity to support basic cellular functions and reorganizes during cell division. Here, we show that in several cell types vimentin filaments redistribute to the cell cortex during mitosis, forming a robust framework interwoven with cortical actin and affecting its organization. Importantly, the intrinsically disordered tail domain of vimentin is essential for this redistribution, which allows normal mitotic progression. A tailless vimentin mutant forms curly bundles, which remain entangled with dividing chromosomes leading to mitotic catastrophes or asymmetric partitions. Serial deletions of vimentin tail domain gradually impair cortical association and mitosis progression. Disruption of f-actin, but not of microtubules, causes vimentin bundling near the chromosomes. Pathophysiological stimuli, including HIV-protease and lipoxidation, induce similar alterations. Interestingly, full filament formation is dispensable for cortical association, which also occurs in vimentin particles. These results unveil implications of vimentin dynamics in cell division through its interplay with the actin cortex.

scholarly journals Cofilin drives rapid turnover and fluidization of entangled F-actin

2019 ◽  
Vol 116 (26) ◽  
pp. 12629-12637 ◽  
Author(s):  
Patrick M. McCall ◽  
Frederick C. MacKintosh ◽  
David R. Kovar ◽  
Margaret L. Gardel
Keyword(s):  
Stress Relaxation ◽  
Molecular Motors ◽  
Atp Hydrolysis ◽  
Low Frequency ◽  
Animal Cells ◽  
Single Filament ◽  
Actin Cortex ◽  
Spatial Reorganization ◽  
Actin Regulatory Proteins

The shape of most animal cells is controlled by the actin cortex, a thin network of dynamic actin filaments (F-actin) situated just beneath the plasma membrane. The cortex is held far from equilibrium by both active stresses and polymer turnover: Molecular motors drive deformations required for cell morphogenesis, while actin-filament disassembly dynamics relax stress and facilitate cortical remodeling. While many aspects of actin-cortex mechanics are well characterized, a mechanistic understanding of how nonequilibrium actin turnover contributes to stress relaxation is still lacking. To address this, we developed a reconstituted in vitro system of entangled F-actin, wherein the steady-state length and turnover rate of F-actin are controlled by the actin regulatory proteins cofilin, profilin, and formin, which sever, recycle, and assemble filaments, respectively. Cofilin-mediated severing accelerates the turnover and spatial reorganization of F-actin, without significant changes to filament length. We demonstrate that cofilin-mediated severing is a single-timescale mode of stress relaxation that tunes the low-frequency viscosity over two orders of magnitude. These findings serve as the foundation for understanding the mechanics of more physiological F-actin networks with turnover and inform an updated microscopic model of single-filament turnover. They also demonstrate that polymer activity, in the form of ATP hydrolysis on F-actin coupled to nucleotide-dependent cofilin binding, is sufficient to generate a form of active matter wherein asymmetric filament disassembly preserves filament number despite sustained severing.

scholarly journals Analysis of the role of microfilaments and microtubules in acquisition of bipolarity and elongation of fibroblasts in hydrated collagen gels.

1984 ◽  
Vol 99 (2) ◽  
pp. 536-549 ◽  
Author(s):  
J J Tomasek ◽  
E D Hay
Keyword(s):  
Actin Cytoskeleton ◽  
Shape Change ◽  
Cell Cortex ◽  
Collagen Gels ◽  
Actin Cortex ◽  
Microtubule Disruption ◽  
Corneal Fibroblasts ◽  
Fourth Step ◽  
Collagenous Stroma

Fibroblasts in situ reside within a collagenous stroma and are elongate and bipolar in shape. If isolated and grown on glass, they change from elongate to flat shape, lose filopodia, and acquire ruffles. This shape change can be reversed to resemble that in situ by suspending the cells in hydrated collagen gels. In this study of embryonic avian corneal fibroblasts grown in collagen gels, we describe for the first time the steps in the acquisition of the elongate shape and analyze the effect of cytoskeleton-disrupting drugs on filopodial activity, assumption of bipolarity, and cell elongation within extracellular matrix. We have previously shown by immunofluorescence that filopodia contain actin but not myosin and are free of organelles. The cell cortex is rich in actin and the cytosol, in myosin. By using antitubulin, we show in the present study that microtubules are aligned along the long axis of the bipolar cell body. The first step in assumption of the elongate shape is extension of filopodia by the round cells suspended in collagen, and this is not significantly affected by the drugs we used: taxol to stabilize microtubules; nocodazole to disassemble microtubules; and cytochalasin D to disrupt microfilaments. The second step, movement of filopodia to opposite ends of the cell, is disrupted by cytochalasin, but not by taxol or nocodazole. The third step, extension of pseudopodia and acquisition of bipolarity similarly requires intact actin, but not microtubules. If fibroblasts are allowed to become bipolar before drug treatment, moreover, they remain so in the presence of the drugs. To complete the fourth step, extensive elongation of the cell, both intact actin and microtubules are required. Retraction of the already elongated cell occurs on microtubule disruption, but retraction requires an intact actin cytoskeleton. We suggest that the cell interacts with surrounding collagen fibrils via its actin cytoskeleton to become bipolar in shape, and that microtubules interact with the actin cortex to bring about the final elongation of the fibroblast.

scholarly journals Dictyostelium myosin IK is involved in the maintenance of cortical tension and affects motility and phagocytosis

2000 ◽  
Vol 113 (4) ◽  
pp. 621-633 ◽  
Author(s):  
E.C. Schwarz ◽  
E.M. Neuhaus ◽  
C. Kistler ◽  
A.W. Henkel ◽  
T. Soldati
Keyword(s):  
Class I ◽  
Actin Binding ◽  
Cell Cortex ◽  
Tail Domain ◽  
Cortical Actin ◽  
Cortical Tension ◽  
Actin Cortex ◽  
Significant Enrichment ◽  
Motor Velocity ◽  
Distinctive Role

Dictyostelium discoideum myosin Ik (MyoK) is a novel type of myosin distinguished by a remarkable architecture. MyoK is related to class I myosins but lacks a cargo-binding tail domain and carries an insertion in a surface loop suggested to modulate motor velocity. This insertion shows similarity to a secondary actin-binding site present in the tail of some class I myosins, and indeed a GST-loop construct binds actin. Probably as a consequence, binding of MyoK to actin was not only ATP- but also salt-dependent. Moreover, as both binding sites reside within its motor domain and carry potential sites of regulation, MyoK might represent a new form of actin crosslinker. MyoK was distributed in the cytoplasm with a significant enrichment in dynamic regions of the cortex. Absence of MyoK resulted in a drop of cortical tension whereas overexpression led to significantly increased tension. Absence and overexpression of MyoK dramatically affected the cortical actin cytoskeleton and resulted in reduced initial rates of phagocytosis. Cells lacking MyoK showed excessive ruffling, mostly in the form of large lamellipodia, accompanied by a thicker basal actin cortex. At early stages of development, aggregation of myoK null cells was slowed due to reduced motility. Altogether, the data indicate a distinctive role for MyoK in the maintenance and dynamics of the cell cortex.

scholarly journals Myosin motors fragment and compact membrane-bound actin filaments

eLife ◽  
2013 ◽  
Vol 2 ◽  
Author(s):  
Sven K Vogel ◽  
Zdenek Petrasek ◽  
Fabian Heinemann ◽  
Petra Schwille
Keyword(s):  
Cell Division ◽  
Compressive Stress ◽  
Actin Filaments ◽  
Cell Cortex ◽  
Tirf Microscopy ◽  
Actin Cortex ◽  
Actin Turnover ◽  
Membrane Bound ◽  
Myosin Motors

Cell cortex remodeling during cell division is a result of myofilament-driven contractility of the cortical membrane-bound actin meshwork. Little is known about the interaction between individual myofilaments and membrane-bound actin filaments. Here we reconstituted a minimal actin cortex to directly visualize the action of individual myofilaments on membrane-bound actin filaments using TIRF microscopy. We show that synthetic myofilaments fragment and compact membrane-bound actin while processively moving along actin filaments. We propose a mechanism by which tension builds up between the ends of myofilaments, resulting in compressive stress exerted to single actin filaments, causing their buckling and breakage. Modeling of this mechanism revealed that sufficient force (∼20 pN) can be generated by single myofilaments to buckle and break actin filaments. This mechanism of filament fragmentation and compaction may contribute to actin turnover and cortex reorganization during cytokinesis.

scholarly journals Adhesion of active cytoskeletal vesicles

2018 ◽  
Author(s):  
R. Maan ◽  
E. Loiseau ◽  
A. R. Bausch
Keyword(s):  
Molecular Motors ◽  
Building Blocks ◽  
Membrane Area ◽  
Actin Cortex ◽  
Rigidity Sensing ◽  
Solid Substrates ◽  
Strong Adhesion ◽  
Glass Surfaces ◽  
Synthetic Biology Approach

AbstractRegulation of adhesion is a ubiquitous feature of living cells, observed during processes such as motility, antigen recognition or rigidity sensing. At the molecular scale, a myriad of mechanisms are necessary to recruit and activate the essential proteins, while at the cellular scale efficient regulation of adhesion relies on the cell’s ability to adapt its global shape. To understand the role of shape remodeling during adhesion, we use a synthetic biology approach to design a minimal model, starting with a limited number of building blocks. We assemble cytoskeletal vesicles whose size, reduced volume, and cytoskeleton contractility can be independently tuned. We are able to show that these cytoskeletal vesicles can sustain strong adhesion to solid substrates only if molecular motors are able to actively remodel the actin cortex. When the cytoskeletal vesicles are deformed under hypertonic osmotic pressure, they develop a crumpled geometry with huge deformations. In the presence of molecular motors, these deformations are dynamic in nature and can compensate for an absence of excess membrane area needed for adhesion to take place. When the cytoskeletal deformations are able to compensate for lack of excess membrane area, the cytoskeletal vesicles are able to attach to the rigid glass surfaces even under strong adhesive forces. The balance of deformability and adhesion strength is identified to be key to enable cytoskeletal vesicles to adhere to solid substrates.

scholarly journals Actin and Myosin in Non-Neuronal Exocytosis

Cells ◽  
2020 ◽  
Vol 9 (6) ◽  
pp. 1455 ◽  
Author(s):  
Pika Miklavc ◽  
Manfred Frick
Keyword(s):  
Molecular Motors ◽  
Molecular Mechanisms ◽  
Current Knowledge ◽  
Cell Cortex ◽  
Secretory Cells ◽  
Secretory Vesicles ◽  
Cortical Actin ◽  
Myosin V ◽  
Myosin I

Cellular secretion depends on exocytosis of secretory vesicles and discharge of vesicle contents. Actin and myosin are essential for pre-fusion and post-fusion stages of exocytosis. Secretory vesicles depend on actin for transport to and attachment at the cell cortex during the pre-fusion phase. Actin coats on fused vesicles contribute to stabilization of large vesicles, active vesicle contraction and/or retrieval of excess membrane during the post-fusion phase. Myosin molecular motors complement the role of actin. Myosin V is required for vesicle trafficking and attachment to cortical actin. Myosin I and II members engage in local remodeling of cortical actin to allow vesicles to get access to the plasma membrane for membrane fusion. Myosins stabilize open fusion pores and contribute to anchoring and contraction of actin coats to facilitate vesicle content release. Actin and myosin function in secretion is regulated by a plethora of interacting regulatory lipids and proteins. Some of these processes have been first described in non-neuronal cells and reflect adaptations to exocytosis of large secretory vesicles and/or secretion of bulky vesicle cargoes. Here we collate the current knowledge and highlight the role of actomyosin during distinct phases of exocytosis in an attempt to identify unifying molecular mechanisms in non-neuronal secretory cells.

scholarly journals Generation of stress fibers through myosin-driven re-organization of the actin cortex

2020 ◽  
Author(s):  
JI Lehtimäki ◽  
EK Rajakylä ◽  
S Tojkander ◽  
P Lappalainen
Keyword(s):  
De Novo ◽  
Myosin Ii ◽  
Focal Adhesions ◽  
Stress Fibers ◽  
Cell Cortex ◽  
Cortical Actin ◽  
Cellular Processes ◽  
Actin Cortex ◽  
Muscle Myosin ◽  
Subsequent Stabilization

SummaryContractile actomyosin bundles, stress fibers, govern key cellular processes including migration, adhesion, and mechanosensing. Stress fibers are thus critical for developmental morphogenesis. The most prominent actomyosin bundles, ventral stress fibers, are generated through coalescence of pre-existing stress fiber precursors. However, whether stress fibers can assemble through other mechanisms has remained elusive. We report that stress fibers can also form without requirement of pre-existing actomyosin bundles. These structures, which we named cortical stress fibers, are embedded in the cell cortex and assemble preferentially underneath the nucleus. In this process, non-muscle myosin II pulses orchestrate the reorganization of cortical actin meshwork into regular bundles, which promote reinforcement of nascent focal adhesions, and subsequent stabilization of the cortical stress fibers. These results identify a new mechanism by which stress fibers can be generated de novo from the actin cortex, and establish role for stochastic myosin pulses in the assembly of functional actomyosin bundles.

scholarly journals Generation of stress fibers through myosin-driven reorganization of the actin cortex

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Jaakko I Lehtimäki ◽  
Eeva Kaisa Rajakylä ◽  
Sari Tojkander ◽  
Pekka Lappalainen
Keyword(s):  
De Novo ◽  
Myosin Ii ◽  
Focal Adhesions ◽  
Stress Fibers ◽  
Cell Cortex ◽  
Cortical Actin ◽  
Cellular Processes ◽  
Actin Cortex ◽  
Muscle Myosin ◽  
Subsequent Stabilization

Contractile actomyosin bundles, stress fibers, govern key cellular processes including migration, adhesion, and mechanosensing. Stress fibers are thus critical for developmental morphogenesis. The most prominent actomyosin bundles, ventral stress fibers, are generated through coalescence of pre-existing stress fiber precursors. However, whether stress fibers can assemble through other mechanisms has remained elusive. We report that stress fibers can also form without requirement of pre-existing actomyosin bundles. These structures, which we named cortical stress fibers, are embedded in the cell cortex and assemble preferentially underneath the nucleus. In this process, non-muscle myosin II pulses orchestrate the reorganization of cortical actin meshwork into regular bundles, which promote reinforcement of nascent focal adhesions, and subsequent stabilization of the cortical stress fibers. These results identify a new mechanism by which stress fibers can be generated de novo from the actin cortex and establish role for stochastic myosin pulses in the assembly of functional actomyosin bundles.

Sign in / Sign up

Export Citation Format

Share Document