Long-range self-organization of cytoskeletal myosin II filament stacks

Hu, Shiqiong; Dasbiswas, Kinjal; Guo, Zhenhuan; Tee, Yee-Han; Thiagarajan, Visalatchi; Hersen, Pascal; Chew, Teng‐Leong; Safran, S. A.; Zaidel-Bar, Ronen; Bershadsky, Alexander D.

doi:10.1038/ncb3466

Cited by 196 publications

(251 citation statements)

References 48 publications

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“…Since transverse deformations were never seen in experiments, it is clear that the stress fibres must be the predominant contractile elements observable at this resolution that respond to local RhoA-induced contractions. Furthermore, this result illustrates that it is appropriate to think of a stress fibre as a 1D contractile element with viscous and elastic components embedded in a passive viscoelastic network, which is consistent with recently published image-based observations26.…”

Section: Resultssupporting

confidence: 91%

“…In contrast, at longer timescales, it is thought that dynamic processes make the cytoskeleton behave predominately like a viscous fluid, enabling cytoskeletal flows and remodelling. These dynamic processes, including exchange of proteins from the cytosol, are typically on the order of tens of seconds in structures like the cortex2425 and on the order of a minute in stress fibres26. The molecular regulation underlying the competition between elastic and viscous processes in cells is not well understood.…”

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confidence: 99%

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Optogenetic control of RhoA reveals zyxin-mediated elasticity of stress fibres

et al. 2017

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Cytoskeletal mechanics regulates cell morphodynamics and many physiological processes. While contractility is known to be largely RhoA-dependent, the process by which localized biochemical signals are translated into cell-level responses is poorly understood. Here we combine optogenetic control of RhoA, live-cell imaging and traction force microscopy to investigate the dynamics of actomyosin-based force generation. Local activation of RhoA not only stimulates local recruitment of actin and myosin but also increased traction forces that rapidly propagate across the cell via stress fibres and drive increased actin flow. Surprisingly, this flow reverses direction when local RhoA activation stops. We identify zyxin as a regulator of stress fibre mechanics, as stress fibres are fluid-like without flow reversal in its absence. Using a physical model, we demonstrate that stress fibres behave elastic-like, even at timescales exceeding turnover of constituent proteins. Such molecular control of actin mechanics likely plays critical roles in regulating morphodynamic events.

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Section: Resultssupporting

confidence: 91%

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confidence: 99%

Optogenetic control of RhoA reveals zyxin-mediated elasticity of stress fibres

et al. 2017

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“…Recent research, using superresolution light-microscopic imaging of living cells by which individual myosin filaments could be discerned, have shown that myosin filaments are very dynamic (32)(33)(34). Myosins tagged with fluorescent fusion proteins were imaged as closely spaced "dumbbells" corresponding to the ∼300-nm-long bipolar filaments assembled in vitro.…”

Section: Discussionmentioning

confidence: 99%

Effect of ATP and regulatory light-chain phosphorylation on the polymerization of mammalian nonmuscle myosin II

Liu

Billington

Shu

et al. 2017

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

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Addition of 1 mM ATP substantially reduces the light scattering of solutions of polymerized unphosphorylated nonmuscle myosin IIs (NM2s), and this is reversed by phosphorylation of the regulatory light chain (RLC). It has been proposed that these changes result from substantial depolymerization of unphosphorylated NM2 filaments to monomers upon addition of ATP, and filament repolymerization upon RLC-phosphorylation. We now show that the differences in myosin monomer concentration of RLC-unphosphorylated and -phosphorylated recombinant mammalian NM2A, NM2B, and NM2C polymerized in the presence of ATP are much too small to explain their substantial differences in light scattering. Rather, we find that the decrease in light scattering upon addition of ATP to polymerized unphosphorylated NM2s correlates with the formation of dimers, tetramers, and hexamers, in addition to monomers, an increase in length, and decrease in width of the bare zones of RLC-unphosphorylated filaments. Both effects of ATP addition are reversed by phosphorylation of the RLC. Our data also suggest that, contrary to previous models, assembly of RLCphosphorylated NM2s at physiological ionic strength proceeds from folded monomers to folded antiparallel dimers, tetramers, and hexamers that unfold and polymerize into antiparallel filaments. This model could explain the dynamic relocalization of NM2 filaments in vivo by dephosphorylation of RLC-phosphorylated filaments, disassembly of the dephosphorylated filaments to folded monomers, dimers, and small oligomers, followed by diffusion of these species, and reassembly of filaments at the new location following rephosphorylation of the RLC.C lass II myosins, the first of 37 known myosin classes (1, 2) to be discovered and originally thought to be specific for muscle, are now known to occur widely in nonmuscle cells in numerous species. Human nonmuscle cells express three different myosin 2 paralogs: nonmuscle myosins (NM) NM2A, NM2B, and NM2C. Like all class II myosins (3, 4), NM2 monomers are hexapeptides of two identical heavy chains (HC), two essential light chains (ELC), and two regulatory light chains (RLC). The HCs of NM2A, NM2B, and NM2C are encoded by different genes, have 60-80% sequence similarity, and isoforms of each are derived from alternative splicing (4).Each HC has an N-terminal globular motor domain with an ATPase site and an actin-binding site, followed by a lever arm that binds one ELC and one RLC, and a long tail that homodimerizes to form a coiled-coil α-helix. The HC ends with a short C-terminal nonhelical tailpiece (5). Like most class II myosins, NM2 monomers assemble into bipolar filaments by antiparallel association of their elongated coiled-coil helical tails. The filaments of NM2s are appreciably smaller than filaments of muscle myosins, with lengths of about 300 nm, consisting of ∼30 monomers for filaments of NM2A and NM2B and ∼14 monomers for filaments of NM2C (5).As described originally for smooth muscle myosin based on light-scattering data (6-8), filaments of unphosp...

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“…The dynamics underlying changes in NMII reorganization are just beginning to be understood (Beach et al, 2017;Hu et al, 2017). EMT, the process by which static, well-ordered and apical-basal polarized epithelial cells transform into dynamically migrating mesenchymal cells associated with extensive reorganization of the actomyosin cytoskeleton is of major interest and is important for cardiac development.…”

Section: Nmiib Function In Myocardial Growthmentioning

confidence: 99%

Nonmuscle myosin IIB regulates epicardial integrity and epicardium-derived mesenchymal cell maturation

Sung

Yang

et al. 2017

Journal of Cell Science

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Nonmuscle myosin IIB (NMIIB; heavy chain encoded by MYH10) is essential for cardiac myocyte cytokinesis. The role of NMIIB in other cardiac cells is not known. Here, we show that NMIIB is required in epicardial formation and functions to support myocardial proliferation and coronary vessel development. Ablation of NMIIB in epicardial cells results in disruption of epicardial integrity with a loss of E-cadherin at cell-cell junctions and a focal detachment of epicardial cells from the myocardium. NMIIB-knockout and blebbistatin-treated epicardial explants demonstrate impaired mesenchymal cell maturation during epicardial epithelial-mesenchymal transition. This is manifested by an impaired invasion of collagen gels by the epicardium-derived mesenchymal cells and the reorganization of the cytoskeletal structure. Although there is a marked decrease in the expression of mesenchymal genes, there is no change in Snail (also known as Snai1) or E-cadherin expression. Studies from epicardiumspecific NMIIB-knockout mice confirm the importance of NMIIB for epicardial integrity and epicardial functions in promoting cardiac myocyte proliferation and coronary vessel formation during heart development. Our findings provide a novel mechanism linking epicardial formation and epicardial function to the activity of the cytoplasmic motor protein NMIIB.

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Long-range self-organization of cytoskeletal myosin II filament stacks

Cited by 196 publications

References 48 publications

Optogenetic control of RhoA reveals zyxin-mediated elasticity of stress fibres

Optogenetic control of RhoA reveals zyxin-mediated elasticity of stress fibres

Effect of ATP and regulatory light-chain phosphorylation on the polymerization of mammalian nonmuscle myosin II

Nonmuscle myosin IIB regulates epicardial integrity and epicardium-derived mesenchymal cell maturation

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