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

2018 ◽  
Vol 132 (4) ◽  
pp. jcs219899 ◽  
Author(s):  
Sonal ◽  
Kristina A. Ganzinger ◽  
Sven K. Vogel ◽  
Jonas Mücksch ◽  
Philipp Blumhardt ◽  
...  
Keyword(s):  
Steady State ◽  
Myosin Ii ◽  
Actin Cortex ◽  
Actin Turnover

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

2018 ◽  
Author(s):  
Sonal ◽  
Kristina A. Ganzinger ◽  
Sven K. Vogel ◽  
Jonas Mücksch ◽  
Philipp Blumhardt ◽  
...  
Keyword(s):  
Steady State ◽  
Actin Polymerization ◽  
Myosin Ii ◽  
Fine Tuning ◽  
Cellular Functions ◽  
Actin Cortex ◽  
Actin Turnover ◽  
Cytoskeletal Dynamics

ABSTRACTDynamic reorganization of the actomyosin cytoskeleton allows a fine-tuning of cell shape that is vital to many cellular functions. It is well established that myosin-II motors generate the forces required for remodeling the cell surface by imparting contractility to actin networks. An additional, less understood, role of myosin-II in cytoskeletal dynamics is believed to be in the regulation of actin turnover; it has been proposed that myosin activity increases actin turnover in various cellular contexts, presumably by contributing to disassembly. In vitro reconstitution of actomyosin networks has confirmed the role of myosin in actin network disassembly, but factors such as diffusional constraints and the use of stabilized filaments have thus far limited the observation of myosin-assisted actin turnover in these networks. 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 actin filaments undergo constant turnover. Our findings suggest a multi-faceted role of myosin-II in fast remodeling of the eukaryotic actin cortex.

scholarly journals Myosin IIA drives membrane bleb retraction

2019 ◽  
Vol 30 (9) ◽  
pp. 1051-1059 ◽  
Author(s):  
Nilay Taneja ◽  
Dylan T. Burnette
Keyword(s):  
Mammalian Cells ◽  
Myosin Ii ◽  
Cross Linking ◽  
Nonmuscle Myosin ◽  
Final Phase ◽  
Biophysical Properties ◽  
Actin Cortex ◽  
Nonmuscle Myosin Ii ◽  
Membrane Blebs ◽  
Ability To Drive

Membrane blebs are specialized cellular protrusions that play diverse roles in processes such as cell division and cell migration. Blebbing can be divided into three distinct phases: bleb nucleation, bleb growth, and bleb retraction. Following nucleation and bleb growth, the actin cortex, comprising actin, cross-linking proteins, and nonmuscle myosin II (MII), begins to reassemble on the membrane. MII then drives the final phase, bleb retraction, which results in reintegration of the bleb into the cellular cortex. There are three MII paralogues with distinct biophysical properties expressed in mammalian cells: MIIA, MIIB, and MIIC. Here we show that MIIA specifically drives bleb retraction during cytokinesis. The motor domain and regulation of the nonhelical tailpiece of MIIA both contribute to its ability to drive bleb retraction. These experiments have also revealed a relationship between faster turnover of MIIA at the cortex and its ability to drive bleb retraction.

scholarly journals Directional Transport of a Bead Bound to Lamellipodial Surface Is Driven by Actin Polymerization

2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Daisuke Nobezawa ◽  
Sho-ichi Ikeda ◽  
Eitaro Wada ◽  
Takashi Nagano ◽  
Hidetake Miyata
Keyword(s):  
Actin Polymerization ◽  
Cancer Metastasis ◽  
Myosin Ii ◽  
Optical Trap ◽  
Cell Movement ◽  
Cytochalasin D ◽  
The Other ◽  
Other Hand ◽  
Latrunculin A ◽  
Actin Turnover

The force driving the retrograde flow of actin cytoskeleton is important in the cellular activities involving cell movement (e.g., growth cone motility in axon guidance, wound healing, or cancer metastasis). However, relative importance of the forces generated by actin polymerization and myosin II in this process remains elusive. We have investigated the retrograde movement of the poly-D-lysine-coated bead attached with the optical trap to the edge of lamellipodium of Swiss 3T3 fibroblasts. The velocity of the attached bead drastically decreased by submicromolar concentration of cytochalasin D, latrunculin A, or jasplakinolide, indicating the involvement of actin turnover. On the other hand, the velocity decreased only slightly in the presence of 50 μM (−)-blebbistatin and Y-27632. Comparative fluorescence microscopy of the distribution of actin filaments and that of myosin II revealed that the inhibition of actin turnover by cytochalasin D, latrunculin A, or jasplakinolide greatly diminished the actin filament network. On the other hand, inhibition of myosin II activity by (−)-blebbistatin or Y-27632 little affected the actin network but diminished stress fibers. Based on these results, we conclude that the actin polymerization/depolymerization plays the major role in the retrograde movement, while the myosin II activity is involved in the maintenance of the dynamic turnover of actin in lamellipodium.

scholarly journals Cortical F-Actin, the Exocytic Mode, and Neuropeptide Release in Mouse Chromaffin Cells Is Regulated by Myristoylated Alanine-rich C-Kinase Substrate and Myosin II

2009 ◽  
Vol 20 (13) ◽  
pp. 3142-3154 ◽  
Author(s):  
Bryan W. Doreian ◽  
Tiberiu G. Fulop ◽  
Robert L. Meklemburg ◽  
Corey B. Smith
Keyword(s):  
Chromaffin Cells ◽  
Myosin Ii ◽  
Splanchnic Nerve ◽  
Cortical Actin ◽  
Kinase Substrate ◽  
Actin Cortex ◽  
Collapse Mode ◽  
Associated Proteins ◽  
Intact Cortex ◽  
Activity Dependent

Adrenal medullary chromaffin cells are innervated by the sympathetic splanchnic nerve and translate graded sympathetic firing into a differential hormonal exocytosis. Basal sympathetic firing elicits a transient kiss-and-run mode of exocytosis and modest catecholamine release, whereas elevated firing under the sympathetic stress response results in full granule collapse to release catecholamine and peptide transmitters into the circulation. Previous studies have shown that rearrangement of the cell actin cortex regulates the mode of exocytosis. An intact cortex favors kiss-and-run exocytosis, whereas disrupting the cortex favors the full granule collapse mode. Here, we investigate the specific roles of two actin-associated proteins, myosin II and myristoylated alanine-rich C-kinase substrate (MARCKS) in this process. Our data demonstrate that MARCKS phosphorylation under elevated cell firing is required for cortical actin disruption but is not sufficient to elicit peptide transmitter exocytosis. Our data also demonstrate that myosin II is phospho-activated under high stimulation conditions. Inhibiting myosin II activity prevented disruption of the actin cortex, full granule collapse, and peptide transmitter release. These results suggest that phosphorylation of both MARCKS and myosin II lead to disruption of the actin cortex. However, myosin II, but not MARCKS, is required for the activity-dependent exocytosis of the peptide transmitters.

scholarly journals Mechanosensitivity of Actin Turnover Allows Cells to Maintain Homeostasis against Myosin-II Contractile Fluctuations in the Cytoskeleton

2016 ◽  
Vol 110 (3) ◽  
pp. 620a
Author(s):  
Shuyuan Wang ◽  
Sathish Thiyagarajan ◽  
Mark A. Smith ◽  
Elizabeth Blankman ◽  
Laura M. Chapin ◽  
...  
Keyword(s):  
Myosin Ii ◽  
Actin Turnover

Enhancement of myosin II/actin turnover at the contractile ring induces slower furrowing in dividing HeLa cells

2011 ◽  
Vol 435 (3) ◽  
pp. 569-576 ◽  
Author(s):  
Tomo Kondo ◽  
Kozue Hamao ◽  
Keiju Kamijo ◽  
Hiroshi Kimura ◽  
Makiko Morita ◽  
...  
Keyword(s):  
Hela Cells ◽  
Fluorescence Recovery After Photobleaching ◽  
Kinase Inhibitor ◽  
Myosin Ii ◽  
Rho Kinase ◽  
Filamentous Actin ◽  
Contractile Ring ◽  
Rho Kinase Inhibitor ◽  
Actin Turnover ◽  
Dividing Cells

Myosin II ATPase activity is enhanced by the phosphorylation of MRLC (myosin II regulatory light chain) in non-muscle cells. It is well known that pMRLC (phosphorylated MRLC) co-localizes with F-actin (filamentous actin) in the CR (contractile ring) of dividing cells. Recently, we reported that HeLa cells expressing non-phosphorylatable MRLC show a delay in the speed of furrow ingression, suggesting that pMRLC plays an important role in the control of furrow ingression. However, it is still unclear how pMRLC regulates myosin II and F-actin at the CR to control furrow ingression during cytokinesis. In the present study, to clarify the roles of pMRLC, we measured the turnover of myosin II and actin at the CR in dividing HeLa cells expressing fluorescent-tagged MRLCs and actin by FRAP (fluorescence recovery after photobleaching). A myosin II inhibitor, blebbistatin, caused an enhancement of the turnover of MRLC and actin at the CR, which induced a delay in furrow ingression. Furthermore, only non-phosphorylatable MRLC and a Rho-kinase inhibitor, Y-27632, accelerated the turnover of MRLC and actin at the CR. Interestingly, the effect of Y-27632 was cancelled in the cell expressing phosphomimic MRLCs. Taken together, these results reveal that pMRLC reduces the turnover of myosin II and also actin at the CR. In conclusion, we show that the enhancement of myosin II and actin turnover at the CR induced slower furrowing in dividing HeLa cells.

scholarly journals The interplay of stiffness and force anisotropies drives embryo elongation

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Thanh Thi Kim Vuong-Brender ◽  
Martine Ben Amar ◽  
Julien Pontabry ◽  
Michel Labouesse
Keyword(s):  
Experimental Data ◽  
Material Properties ◽  
Myosin Ii ◽  
Mechanical Forces ◽  
Cell Behaviour ◽  
Cortical Tension ◽  
Actin Cortex ◽  
Stiffness Anisotropy ◽  
Spatiotemporal Changes ◽  
Tissue Material

The morphogenesis of tissues, like the deformation of an object, results from the interplay between their material properties and the mechanical forces exerted on them. The importance of mechanical forces in influencing cell behaviour is widely recognized, whereas the importance of tissue material properties, in particular stiffness, has received much less attention. Using Caenorhabditis elegans as a model, we examine how both aspects contribute to embryonic elongation. Measuring the opening shape of the epidermal actin cortex after laser nano-ablation, we assess the spatiotemporal changes of actomyosin-dependent force and stiffness along the antero-posterior and dorso-ventral axis. Experimental data and analytical modelling show that myosin-II-dependent force anisotropy within the lateral epidermis, and stiffness anisotropy within the fiber-reinforced dorso-ventral epidermis are critical in driving embryonic elongation. Together, our results establish a quantitative link between cortical tension, material properties and morphogenesis of an entire embryo.

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 Actin turnover maintains actin filament homeostasis during cytokinetic ring contraction

2017 ◽  
Vol 216 (9) ◽  
pp. 2657-2667 ◽  
Author(s):  
Ting Gang Chew ◽  
Junqi Huang ◽  
Saravanan Palani ◽  
Ruth Sommese ◽  
Anton Kamnev ◽  
...  
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Actin Polymerization ◽  
Myosin Ii ◽  
Contractile Ring ◽  
Ring Contraction ◽  
Actin Turnover ◽  
Exogenous Addition ◽  
Turn Over

Cytokinesis in many eukaryotes involves a tension-generating actomyosin-based contractile ring. Many components of actomyosin rings turn over during contraction, although the significance of this turnover has remained enigmatic. Here, using Schizosaccharomyces japonicus, we investigate the role of turnover of actin and myosin II in its contraction. Actomyosin ring components self-organize into ∼1-µm-spaced clusters instead of undergoing full-ring contraction in the absence of continuous actin polymerization. This effect is reversed when actin filaments are stabilized. We tested the idea that the function of turnover is to ensure actin filament homeostasis in a synthetic system, in which we abolished turnover by fixing rings in cell ghosts with formaldehyde. We found that these rings contracted fully upon exogenous addition of a vertebrate myosin. We conclude that actin turnover is required to maintain actin filament homeostasis during ring contraction and that the requirement for turnover can be bypassed if homeostasis is achieved artificially.

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