Contraction Mechanisms in Composite Active Actin Networks

Köhler, Simone; Bausch, Andreas R.

doi:10.1371/journal.pone.0039869

Cited by 50 publications

(65 citation statements)

References 29 publications

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“…2 i and ii and Fig. 4, right bar), consistent with previous observations in bulk networks (22)(23)(24)(25)33). The striking finding is that actin-membrane anchoring governs the outcome of cortex contraction.…”

Section: Cortex Connectivity and Membrane Attachment Govern Contractionsupporting

confidence: 90%

“…We find that crushing is slower than peeling because osmotic pressure works against it. In cells, where the geometry is inside-out, cortical tension is also opposed by osmotic pressure (33). Although cells likely have additional machineries to avoid failure, actomyosin contractility can under some conditions lead to tissue tear-off at the scale of a cell layer in developing fly embryos (47).…”

Section: Force Analysis and Estimates Of Characteristic Times And Crimentioning

confidence: 99%

See 1 more Smart Citation

Cell-sized liposomes reveal how actomyosin cortical tension drives shape change

Carvalho

Tsai

Lees

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

106

111

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Significance Animal cells continuously move, divide, and transmit forces by actively reorganizing their internal scaffold or cytoskeleton. Molecular motors pull actin filaments together and generate contraction of the cytoskeleton underneath the cell membrane. We address the detailed mechanism of contraction by using a minimal in vitro assay: a liposome membrane to which we attach actin filaments and molecular motors in a controlled manner. We reproduce contraction like in cells. We show that the scaffold needs to be tightly attached to the membrane for efficient contraction, but, under some conditions, efficient contraction can lead to liposome destruction. These results suggest that cells must precisely control their contractility to remain intact during cellular events.

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Section: Cortex Connectivity and Membrane Attachment Govern Contractionsupporting

confidence: 90%

Section: Force Analysis and Estimates Of Characteristic Times And Crimentioning

confidence: 99%

Cell-sized liposomes reveal how actomyosin cortical tension drives shape change

Carvalho

Tsai

Lees

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

106

111

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“…116,155,220,255,292,327,339). This was initially reported for actin filament bundles stabilized by fascin during an in vitro filament gliding assay (133).…”

Section: Myosin-induced Disassemblymentioning

confidence: 77%

“…The velocity of contraction depends on filament architecture: contraction is faster for antiparallel filaments compared with branched networks. The orientation of the actin filaments in the contracting network is thus a major determinant for controlling the rate of contraction (155,255). Moreover, the dynamics of actin polymerization and depolymerization have to be taken into account in addition to myosin activity for explaining phenomena such as actin ring contraction during cytokinesis (354).…”

mentioning

confidence: 99%

Actin Dynamics, Architecture, and Mechanics in Cell Motility

Blanchoin

Boujemaa-Paterski

Sykes

et al. 2014

Physiological Reviews

1,165

1,145

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Tight coupling between biochemical and mechanical properties of the actin cytoskeleton drives a large range of cellular processes including polarity establishment, morphogenesis, and motility. This is possible because actin filaments are semi-flexible polymers that, in conjunction with the molecular motor myosin, can act as biological active springs or "dashpots" (in laymen's terms, shock absorbers or fluidizers) able to exert or resist against force in a cellular environment. To modulate their mechanical properties, actin filaments can organize into a variety of architectures generating a diversity of cellular organizations including branched or crosslinked networks in the lamellipodium, parallel bundles in filopodia, and antiparallel structures in contractile fibers. In this review we describe the feedback loop between biochemical and mechanical properties of actin organization at the molecular level in vitro, then we integrate this knowledge into our current understanding of cellular actin organization and its physiological roles. I. PREFACE ON ACTIN ORGANIZATION AND CELL MECHANICSAnimal cells (i.e., those without a cell wall) have the ability to change their shape to adapt to their environment, move through narrow spaces, divide, or allow exo-and endocytosis. The machinery of these shape changes relies on the assembly of proteins, in particular actin, a globular protein that polymerizes into filaments of different types of organization: branched and crosslinked networks, parallel bundles, and anti-parallel contractile structures (FIGURE 1A). These different architectures can be envisioned as a series of interconnected active springs and dashpots (green and red symbols in FIGURE 1B, respectively) that act as mechanical elements to drive cell shape changes and motility. The purpose of this review is to correlate recent progress in our understanding of the interplay between biochemical elements and mechanical properties. Instead of describing biochemical and mechanical properties separately, our main goal here is to address piece by piece the integrated feedback loop between biochemistry and mechanics.At the front of the cell, branched and crosslinked networks in a quasi two-dimensional sheet make up the lamellipodium, and are the major engine of cell movement since they push the cell membrane by polymerizing against it (FIGURE 1A, iii). Aligned bundles underlie filopodia that are the fingerlike structures at the front of the cell, important for directional response of the cell (FIGURE 1A, iv). A thin layer of actin, called the cell cortex, coats the plasma membrane at the back and sides of the cell, important for cell shape maintenance and changes (FIGURE 1A, i). The rest of the cell contains a three-dimensional network of crosslinked filaments interspersed with contractile bundles, including stress fibers that connect the cell cytoskeleton to the extracellular matrix via focal adhesion sites (FIGURE 1A, ii). Contraction in the cell is produced by the molecular motor protein myosin. Myosin assembles into anti...

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“…Active media often exhibit superdiffusion with mean-squared displacements (MSD) r 2 that vary superlinearly with time, r 2 ∝ t a with 1 < a 2, as observed in intracellular transport [47][48][49], in vitro experiments [30,45,50], and models of self-propelled particles [34][35][36]. Conversely, 0 < a < 1 is referred to as subdiffusion.…”

Section: A Dynamics Of Weakly Bound Statesmentioning

confidence: 99%

Nonequilibrium structure and dynamics in a microscopic model of thin-film active gels

2014

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In the presence of adenosine triphosphate, molecular motors generate active force dipoles that drive suspensions of protein filaments far from thermodynamic equilibrium, leading to exotic dynamics and pattern formation. Microscopic modeling can help to quantify the relationship between individual motors plus filaments to organization and dynamics on molecular and supramolecular length scales. Here, we present results of extensive numerical simulations of active gels where the motors and filaments are confined between two infinite parallel plates. Thermal fluctuations and excluded-volume interactions between filaments are included. A systematic variation of rates for motor motion, attachment, and detachment, including a differential detachment rate from filament ends, reveals a range of nonequilibrium behavior. Strong motor binding produces structured filament aggregates that we refer to as asters, bundles, or layers, whose stability depends on motor speed and differential end detachment. The gross features of the dependence of the observed structures on the motor rate and the filament concentration can be captured by a simple one-filament model. Loosely bound aggregates exhibit superdiffusive mass transport, where filament translocation scales with lag time with nonunique exponents that depend on motor kinetics. An empirical data collapse of filament speed as a function of motor speed and end detachment is found, suggesting a dimensional reduction of the relevant parameter space. We conclude by discussing the perspectives of microscopic modeling in the field of active gels.

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Contraction Mechanisms in Composite Active Actin Networks

Cited by 50 publications

References 29 publications

Cell-sized liposomes reveal how actomyosin cortical tension drives shape change

Cell-sized liposomes reveal how actomyosin cortical tension drives shape change

Actin Dynamics, Architecture, and Mechanics in Cell Motility

Nonequilibrium structure and dynamics in a microscopic model of thin-film active gels

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