Filament rigidity and connectivity tune the deformation modes of active biopolymer networks

Stam, Samantha; Freedman, Simon; Banerjee, Shiladitya; Weirich, Kimberly L.; Dinner, Aaron R.; Gardel, Margaret L.

doi:10.1073/pnas.1708625114

Cited by 73 publications

(87 citation statements)

References 62 publications

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“…Our observations of myosin-driven reorganization of branched actin networks on a membrane are in line with previous studies, which also describe a distinct network coarsening upon myosin addition both in solution (Soares e Silva et al, 2011;Backouche et al, 2006;Köhler et al, 2011) and on membranes (Köster et al, 2016;Linsmeier et al, 2016;Murrell and Gardel, 2012;Smith et al, 2007;Stam et al, 2017;Vogel et al, 2013). However, beyond this condensation process, we further observed the subsequent de novo polymerization and redistribution of actin on the membrane (Fig.…”

Section: Discussionsupporting

confidence: 92%

“…Although various reconstitution studies have addressed the mesoscopic effects of myosin contractility on actin network reorganization, a direct investigation of the role of myosin in network turnover has been lacking. The observation of actin turnover has previously been limited either by factors such as stabilized actin filaments, diffusion constraints and restricted polymerization (Köster et al, 2016;Linsmeier et al, 2016;Murrell and Gardel, 2012;Smith et al, 2007;Stam et al, 2017;Vogel et al, 2017Vogel et al, , 2013 or by a focus on macroscopic network-level changes rather than individual network components (Carvalho et al, 2013;Soares e Silva et al, 2011;Köhler et al, 2011;Bussonnier et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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Myosin-II activity generates a dynamic steady state with continuous actin turnover in a minimal actin cortex

Sonal

Ganzinger

Vogel

et al. 2018

Journal of Cell Science

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Dynamic reorganization of the actomyosin cytoskeleton allows fast modulation of the cell surface, which is vital for many cellular functions. Myosin-II motors generate the forces required for this remodeling by imparting contractility to actin networks. However, myosin-II activity might also have a more indirect contribution to cytoskeletal dynamics; it has been proposed that myosin activity increases actin turnover in various cellular contexts, presumably by enhancing disassembly. In vitro reconstitution of actomyosin networks has confirmed the role of myosin in actin network disassembly, but the reassembly of actin in these assays was limited by factors such as diffusional constraints and the use of stabilized actin filaments. Here, we present the reconstitution of a minimal dynamic actin cortex, where actin polymerization is catalyzed on the membrane in the presence of myosin-II activity. We demonstrate that myosin activity leads to disassembly and redistribution in this simplified cortex. Consequently, a new dynamic steady state emerges in which the actin network undergoes constant turnover. Our findings suggest a multifaceted role of myosin-II in the dynamics of the eukaryotic actin cortex. This article has an associated First Person interview with the first author of the paper.

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Section: Discussionsupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Myosin-II activity generates a dynamic steady state with continuous actin turnover in a minimal actin cortex

Sonal

Ganzinger

Vogel

et al. 2018

Journal of Cell Science

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“…Buckling dependent contractility requires the filaments to be highly connected. Therefore, buckling-mediated contractility is promoted by actin filament cross-linkers like ␣-actinin (55) that increase connectivity, but it is suppressed by factors that increase filament rigidity, like tropomyosin (60). Transport-mediated contractility, however, does not require cross-linkers and is not affected by filament rigidity.…”

Section: Discussionmentioning

confidence: 99%

The actin filament bundling protein α-actinin-4 actually suppresses actin stress fibers by permitting actin turnover

Kemp¹,

Brieher

2018

Journal of Biological Chemistry

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Cells organize actin filaments into contractile bundles known as stress fibers that resist mechanical stress, increase cell adhesion, remodel the extracellular matrix, and maintain tissue integrity. α-actinin is an actin filament bundling protein that is thought to be essential for stress fiber formation and stability. However, previous studies have also suggested that α-actinin might disrupt fibers, making the true function of this biomolecule unclear. Here we use fluorescence imaging to show that kidney epithelial cells depleted of α-actinin-4 via shRNA or CRISPR/Cas9, or expressing a disruptive mutant make more massive stress fibers that are less dynamic than those in WT cells, leading to defects in cell motility and wound healing. The increase in stress fiber mass and stability can be explained, in part, by increased loading of the filament component tropomyosin onto stress fibers in the absence of α-actinin, as monitored via immunofluorescence. We show using imaging and cosedimentation that α-actinin and tropomyosin compete for binding to F-actin and that tropomyosin shields actin filaments from cofilin-mediated disassembly and in cells. Perturbing tropomyosin in cells lacking α-actinin-4 results in a complete loss of stress fibers. Our results with α-actinin-4 on stress fiber organization are the opposite of what might have been predicted from previous biochemistry and further highlight how the complex interactions of multiple proteins competing for filament binding lead to unexpected functions for actin-binding proteins in cells.

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“…While architecture has been hypothesized to regulate protein segregation and cellular transport due to motor preference, the effects of architecture on cellular force generation is a nascent field. Mixed polarity architecture in bundles has been shown to promote contractility (49), and the deformations depend on actin bundling (20). Here, we relate the experimentally observed motor dynamics to force generation through agent-based simulations.…”

Section: Discussionmentioning

confidence: 98%

“…Unlike in sarcomeres where the F-actin arranged with opposing polarity supports contractile force generation, in filopodia F-actin are arranged with the same polarity, which may facilitate transport into cellular protrusions (2,14). However, despite evidence that cytoskeletal architecture can impact protein localization and cargo motility generated by transport motor proteins (10,13,(15)(16)(17), and network architecture is critical to myosin-driven contractility (18)(19)(20)the role of F-actin architecture in myosin II force generation remains an open question.…”

Section: Introductionmentioning

confidence: 99%

Actin bundle architecture and mechanics regulate myosin II force generation

Weirich

Stam

Munro

et al. 2020

Preprint

Self Cite

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The actin cytoskeleton is a soft, structural material that underlies biological processes such as cell division, motility, and cargo transport. The cross-linked actin filaments self-organize into a myriad of architectures, from disordered meshworks to ordered bundles, which are hypothesized to control the actomyosin force generation that regulates cell migration, shape, and adhesion. Here, we use fluorescence microscopy and simulations to investigate how actin bundle architectures with varying polarity, spacing, and rigidity impact myosin II dynamics and force generation. Microscopy reveals that mixed polarity bundles formed by rigid cross-linkers support slow, bidirectional myosin II filament motion, punctuated by periods of stalled motion. Simulations reveal that these locations of stalled myosin motion correspond to sustained, high forces in regions of balanced actin filament polarity. By contrast, mixed polarity bundles formed by compliant, large cross-linkers support fast, bidirectional motion with no traps. Simulations indicate that trap duration is directly related to force magnitude, and that the observed increased velocity corresponds to lower forces resulting from both the increased bundle compliance and filament spacing. Our results indicate that the properties of actin structures regulate the dynamics and magnitude of myosin II forces, highlighting the importance of architecture and mechanics in regulating forces in biological materials.

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Filament rigidity and connectivity tune the deformation modes of active biopolymer networks

Cited by 73 publications

References 62 publications

Myosin-II activity generates a dynamic steady state with continuous actin turnover in a minimal actin cortex

Myosin-II activity generates a dynamic steady state with continuous actin turnover in a minimal actin cortex

The actin filament bundling protein α-actinin-4 actually suppresses actin stress fibers by permitting actin turnover

Actin bundle architecture and mechanics regulate myosin II force generation

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