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1
Murrell, Michael, and Margaret L. Gardel. "Actomyosin sliding is attenuated in contractile biomimetic cortices." Molecular Biology of the Cell 25, no. 12 (2014): 1845–53. http://dx.doi.org/10.1091/mbc.e13-08-0450.
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Myosin II motors embedded within the actin cortex generate contractile forces to modulate cell shape in essential behaviors, including polarization, migration, and division. In sarcomeres, myosin II–mediated sliding of antiparallel F-actin is tightly coupled to myofibril contraction. By contrast, cortical F-actin is highly disordered in polarity, orientation, and length. How the disordered nature of the actin cortex affects actin and myosin movements and resultant contraction is unknown. Here we reconstitute a model cortex in vitro to monitor the relative movements of actin and myosin under conditions that promote or abrogate network contraction. In weakly contractile networks, myosin can translocate large distances across stationary F-actin. By contrast, the extent of relative actomyosin sliding is attenuated during contraction. Thus actomyosin sliding efficiently drives contraction in actomyosin networks despite the high degree of disorder. These results are consistent with the nominal degree of relative actomyosin movement observed in actomyosin assemblies in nonmuscle cells.
2
Slabodnick, Mark M., Sophia C. Tintori, Mangal Prakash, et al. "Zyxin contributes to coupling between cell junctions and contractile actomyosin networks during apical constriction." PLOS Genetics 19, no. 3 (2023): e1010319. http://dx.doi.org/10.1371/journal.pgen.1010319.
Full textAbstract:
One of the most common cell shape changes driving morphogenesis in diverse animals is the constriction of the apical cell surface. Apical constriction depends on contraction of an actomyosin network in the apical cell cortex, but such actomyosin networks have been shown to undergo continual, conveyor belt-like contractions before the shrinking of an apical surface begins. This finding suggests that apical constriction is not necessarily triggered by the contraction of actomyosin networks, but rather can be triggered by unidentified, temporally-regulated mechanical links between actomyosin and junctions. Here, we used C. elegans gastrulation as a model to seek genes that contribute to such dynamic linkage. We found that α-catenin and β-catenin initially failed to move centripetally with contracting cortical actomyosin networks, suggesting that linkage is regulated between intact cadherin-catenin complexes and actomyosin. We used proteomic and transcriptomic approaches to identify new players, including the candidate linkers AFD-1/afadin and ZYX-1/zyxin, as contributing to C. elegans gastrulation. We found that ZYX-1/zyxin is among a family of LIM domain proteins that have transcripts that become enriched in multiple cells just before they undergo apical constriction. We developed a semi-automated image analysis tool and used it to find that ZYX-1/zyxin contributes to cell-cell junctions’ centripetal movement in concert with contracting actomyosin networks. These results identify several new genes that contribute to C. elegans gastrulation, and they identify zyxin as a key protein important for actomyosin networks to effectively pull cell-cell junctions inward during apical constriction. The transcriptional upregulation of ZYX-1/zyxin in specific cells in C. elegans points to one way that developmental patterning spatiotemporally regulates cell biological mechanisms in vivo. Because zyxin and related proteins contribute to membrane-cytoskeleton linkage in other systems, we anticipate that its roles in regulating apical constriction in this manner may be conserved.
3
Wirshing, Alison C. E., and Erin J. Cram. "Myosin activity drives actomyosin bundle formation and organization in contractile cells of the Caenorhabditis elegans spermatheca." Molecular Biology of the Cell 28, no. 14 (2017): 1937–49. http://dx.doi.org/10.1091/mbc.e17-01-0029.
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Stress fibers—contractile actomyosin bundles—are important for cellular force production and adaptation to physical stress and have been well studied within the context of cell migration. However, less is known about actomyosin bundle formation and organization in vivo and in specialized contractile cells, such as smooth muscle and myoepithelial cells. The Caenorhabditis elegans spermatheca is a bag-like organ of 24 myoepithelial cells that houses the sperm and is the site of fertilization. During ovulation, spermathecal cells are stretched by oocyte entry and then coordinately contract to expel the fertilized embryo into the uterus. Here we use four-dimensional confocal microscopy of live animals to observe changes to spermathecal actomyosin network organization during cell stretch and contraction. Oocyte entry is required to trigger cell contraction and concomitant production of parallel actomyosin bundles. Actomyosin bundle size, connectivity, spacing, and orientation are regulated by myosin activity. We conclude that myosin drives actomyosin bundle production and that myosin activity is tightly regulated during ovulation to produce an optimally organized actomyosin network in C. elegans spermathecae.
4
Krueger, Daniel, Theresa Quinkler, Simon Arnold Mortensen, Carsten Sachse, and Stefano De Renzis. "Cross-linker–mediated regulation of actin network organization controls tissue morphogenesis." Journal of Cell Biology 218, no. 8 (2019): 2743–61. http://dx.doi.org/10.1083/jcb.201811127.
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Contraction of cortical actomyosin networks driven by myosin activation controls cell shape changes and tissue morphogenesis during animal development. In vitro studies suggest that contractility also depends on the geometrical organization of actin filaments. Here we analyze the function of actomyosin network topology in vivo using optogenetic stimulation of myosin-II in Drosophila embryos. We show that early during cellularization, hexagonally arrayed actomyosin fibers are resilient to myosin-II activation. Actomyosin fibers then acquire a ring-like conformation and become contractile and sensitive to myosin-II. This transition is controlled by Bottleneck, a Drosophila unique protein expressed for only a short time during early cellularization, which we show regulates actin bundling. In addition, it requires two opposing actin cross-linkers, Filamin and Fimbrin. Filamin acts synergistically with Bottleneck to facilitate hexagonal patterning, while Fimbrin controls remodeling of the hexagonal network into contractile rings. Thus, actin cross-linking regulates the spatio-temporal organization of actomyosin contraction in vivo, which is critical for tissue morphogenesis.
5
Martin, Adam C., Michael Gelbart, Rodrigo Fernandez-Gonzalez, Matthias Kaschube, and Eric F. Wieschaus. "Integration of contractile forces during tissue invagination." Journal of Cell Biology 188, no. 5 (2010): 735–49. http://dx.doi.org/10.1083/jcb.200910099.
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Contractile forces generated by the actomyosin cytoskeleton within individual cells collectively generate tissue-level force during epithelial morphogenesis. During Drosophila mesoderm invagination, pulsed actomyosin meshwork contractions and a ratchet-like stabilization of cell shape drive apical constriction. Here, we investigate how contractile forces are integrated across the tissue. Reducing adherens junction (AJ) levels or ablating actomyosin meshworks causes tissue-wide epithelial tears, which release tension that is predominantly oriented along the anterior–posterior (a-p) embryonic axis. Epithelial tears allow cells normally elongated along the a-p axis to constrict isotropically, which suggests that apical constriction generates anisotropic epithelial tension that feeds back to control cell shape. Epithelial tension requires the transcription factor Twist, which stabilizes apical myosin II, promoting the formation of a supracellular actomyosin meshwork in which radial actomyosin fibers are joined end-to-end at spot AJs. Thus, pulsed actomyosin contractions require a supracellular, tensile meshwork to transmit cellular forces to the tissue level during morphogenesis.
6
Yi, Jason, Xufeng S. Wu, Travis Crites, and John A. Hammer. "Actin retrograde flow and actomyosin II arc contraction drive receptor cluster dynamics at the immunological synapse in Jurkat T cells." Molecular Biology of the Cell 23, no. 5 (2012): 834–52. http://dx.doi.org/10.1091/mbc.e11-08-0731.
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Actin retrograde flow and actomyosin II contraction have both been implicated in the inward movement of T cell receptor (TCR) microclusters and immunological synapse formation, but no study has integrated and quantified their relative contributions. Using Jurkat T cells expressing fluorescent myosin IIA heavy chain and F-tractin—a novel reporter for F-actin—we now provide direct evidence that the distal supramolecular activation cluster (dSMAC) and peripheral supramolecular activation cluster (pSMAC) correspond to lamellipodial (LP) and lamellar (LM) actin networks, respectively, as hypothesized previously. Our images reveal concentric and contracting actomyosin II arcs/rings at the LM/pSMAC. Moreover, the speeds of centripetally moving TCR microclusters correspond very closely to the rates of actin retrograde flow in the LP/dSMAC and actomyosin II arc contraction in the LM/pSMAC. Using cytochalasin D and jasplakinolide to selectively inhibit actin retrograde flow in the LP/dSMAC and blebbistatin to selectively inhibit actomyosin II arc contraction in the LM/pSMAC, we demonstrate that both forces are required for centripetal TCR microcluster transport. Finally, we show that leukocyte function–associated antigen 1 clusters accumulate over time at the inner aspect of the LM/pSMAC and that this accumulation depends on actomyosin II contraction. Thus actin retrograde flow and actomyosin II arc contraction coordinately drive receptor cluster dynamics at the immunological synapse.
7
Lippincott, J., K. B. Shannon, W. Shou, R. J. Deshaies, and R. Li. "The Tem1 small GTPase controls actomyosin and septin dynamics during cytokinesis." Journal of Cell Science 114, no. 7 (2001): 1379–86. http://dx.doi.org/10.1242/jcs.114.7.1379.
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Cytokinesis in budding yeast involves an actomyosin-based ring which assembles in a multistepped fashion during the cell cycle and constricts during cytokinesis. In this report, we have investigated the structural and regulatory events that occur at the onset of cytokinesis. The septins, which form an hour-glass like structure during early stages of the cell cycle, undergo dynamic rearrangements prior to cell division: the hourglass structure splits into two separate rings. The contractile ring, localized between the septin double rings, immediately undergoes contraction. Septin ring splitting is independent of actomyosin ring contraction as it still occurs in mutants where contraction fails. We hypothesize that septin ring splitting may remove a structural barrier for actomyosin ring to contract. Because the Tem1 small GTPase (Tem1p) is required for the completion of mitosis, we investigated its role in regulating septin and actomyosin ring dynamics in the background of the net1-1 mutation, which bypasses the anaphase cell cycle arrest in Tem1-deficient cells. We show that Tem1p plays a specific role in cytokinesis in addition to its function in cell cycle progression. Tem1p is not required for the assembly of the actomyosin ring but controls actomyosin and septin dynamics during cytokinesis.
8
Szymanski, P. T., J. D. Strauss, G. Doerman, J. DiSalvo, and R. J. Paul. "Polylysine activates smooth muscle actin-myosin interaction without LC20 phosphorylation." American Journal of Physiology-Cell Physiology 262, no. 6 (1992): C1446—C1455. http://dx.doi.org/10.1152/ajpcell.1992.262.6.c1446.
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Phosphorylation/dephosphorylation of the 20-kDa light chain of smooth muscle myosin is a major regulator of actin-myosin interaction. Phosphatase inhibitors have thus been shown to enhance contraction in smooth muscle. The activity of type II phosphatase against phosphorylated myosin light chains is inhibited by polylysine. Thus we studied the effects of polylysine (10-13 kDa) on actin-myosin interaction in permeabilized guinea pig taenia coli fibers and in bovine aortic actomyosin. Addition of polylysine (10-20 microM) to Ca-ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid buffered solution ([Ca2+] less than 0.01 microM) elicited a contraction in fibers of 40 +/- 8% (n = 6) of maximally stimulated contractions ([Ca2+] congruent to 1.5 microM). Untreated fibers did not generate any significant force in parallel control experiments. Similarly, polylysine stimulated the ATPase activity both in fibers and actomyosin in a dose-dependent manner. This stimulation could be completely inhibited and abolished upon addition of heparin, a negatively charged heteropolysaccharide. In actomyosin previously phosphorylated with ATP gamma S, polylysine in a concentration range of 2-13 microM did not further stimulate enzyme activity. These increases in activity were not connected with significant changes in the phosphorylation of 20-kDa myosin light chain nor could any incorporation of 32P associated with polylysine stimulation be detected in both skinned fibers and actomyosin by autoradiography of SDS gels. Our data indicate that polylysine increases actin-myosin interaction in both smooth muscle model systems by directly influencing contractile proteins. As such, polylysine may be a useful probe for the mechanism of activation of smooth muscle.
9
Chew, Ting Gang, Junqi Huang, Saravanan Palani, et al. "Actin turnover maintains actin filament homeostasis during cytokinetic ring contraction." Journal of Cell Biology 216, no. 9 (2017): 2657–67. http://dx.doi.org/10.1083/jcb.201701104.
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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.
10
VerPlank, Lynn, and Rong Li. "Cell Cycle-regulated Trafficking of Chs2 Controls Actomyosin Ring Stability during Cytokinesis." Molecular Biology of the Cell 16, no. 5 (2005): 2529–43. http://dx.doi.org/10.1091/mbc.e04-12-1090.
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Cytokinesis requires the coordination of many cellular complexes, particularly those involved in the constriction and reconstruction of the plasma membrane in the cleavage furrow. We have investigated the regulation and function of vesicle transport and fusion during cytokinesis in budding yeast. By using time-lapse confocal microscopy, we show that post-Golgi vesicles, as well as the exocyst, a complex required for the tethering and fusion of these vesicles, localize to the bud neck at a precise time just before spindle disassembly and actomyosin ring contraction. Using mutants affecting cyclin degradation and the mitotic exit network, we found that targeted secretion, in contrast to contractile ring activation, requires cyclin degradation but not the mitotic exit network. Analysis of cells in late anaphase bearing exocyst and myosin V mutations show that both vesicle transport and fusion machineries are required for the completion of cytokinesis, but this is not due to a delay in mitotic exit or assembly of the contractile ring. Further investigation of the dynamics of contractile rings in exocyst mutants shows these cells may be able to initiate contraction but often fail to complete the contraction due to premature disassembly during the contraction phase. This phenotype led us to identify Chs2, a transmembrane protein targeted to the bud neck through the exocytic pathway, as necessary for actomyosin ring stability during contraction. Chs2, as the chitin synthase that produces the primary septum, thus couples the assembly of the extracellular matrix with the dynamics of the contractile ring during cytokinesis.
11
Darenfed, Hassina, and Craig A. Mandato. "Wound-induced contractile ring: a model for cytokinesis." Biochemistry and Cell Biology 83, no. 6 (2005): 711–20. http://dx.doi.org/10.1139/o05-164.
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The actomyosin-based contractile ring is required for several biological processes, such as wound healing and cytokinesis of animal cells. Despite progress in defining the roles of this structure in both wound closure and cell division, we still do not fully understand how an actomyosin ring is spatially and temporally assembled, nor do we understand the molecular mechanism of its contraction. Recent results have demonstrated that microtubule-dependent local assembly of F-actin and myosin-II is present in wound closure and is similar to that in cytokinesis in animal cells. Furthermore, signalling factors such as small Rho GTPases have been shown to be involved in the regulation of actin dynamics during both processes. In this review we address recent findings in an attempt to better understand the dynamics of actomyosin contractile rings during wound healing as compared with the final step of animal cell division.Key words: actomyosin ring, microtubules, cytokinesis, wound healing.
12
Horowitz, A., O. Clement-Chomienne, M. P. Walsh, T. Tao, H. Katsuyama, and K. G. Morgan. "Effects of calponin on force generation by single smooth muscle cells." American Journal of Physiology-Heart and Circulatory Physiology 270, no. 5 (1996): H1858—H1863. http://dx.doi.org/10.1152/ajpheart.1996.270.5.h1858.
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Although the actin-binding and actomyosin adenosinetriphosphatase (ATPase) inhibitory properties of calponin are well documented in vitro, its function in the smooth muscle cell has not been elucidated. To address this question, we utilized the ferret aortic smooth muscle cell, which shows a protein kinase C-dependent contraction even at pCa (-log [Ca2+]) 9.0 in the absence of a change in myosin light chain phosphorylation. Force was recorded from single, briefly permeabilized cells stimulated via a Ca(2+)-independent pathway by either phenylephrine or the epsilon isoenzyme of protein kinase C. Treatment of stimulated cells with wild-type recombinant calponin reduced steady-state contractile force by 45-60%. When calponin application preceded protein kinase C epsilon treatment, contraction was completely suppressed. On the other hand, calponin phosphorylated at Ser175 or mutant calponin with a Ser175 ⇢ Ala replacement had no effect on contractile force. A peptide corresponding to Leu166-Gly194 of calponin, which included an actin-binding domain but excluded the actomyosin ATPase inhibitory region, was synthesized. Treatment of aortic smooth muscle cells with this peptide triggered a concentration-dependent contraction, presumably by alleviating the inhibitory effect of endogenous calponin. A control peptide with a scrambled sequence of the same residues produced no detectable contractile response. Although other interpretations are possible, these results are consistent with the view that calponin participates in thin filament-mediated regulation of smooth muscle contraction and that it may be part of a Ca(2+)-independent pathway downstream of protein kinase C epsilon.
13
Hai, Chi-Ming, and Hak Rim Kim. "An expanded latch-bridge model of protein kinase C-mediated smooth muscle contraction." Journal of Applied Physiology 98, no. 4 (2005): 1356–65. http://dx.doi.org/10.1152/japplphysiol.00834.2004.
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A thin-filament-regulated latch-bridge model of smooth muscle contraction is proposed to integrate thin-filament-based inhibition of actomyosin ATPase activity with myosin phosphorylation in the regulation of smooth muscle mechanics. The model included two latch-bridge cycles, one of which was identical to the four-state model as proposed by Hai and Murphy ( Am J Physiol Cell Physiol 255: C86–C94, 1988), whereas the ultraslow cross-bridge cycle has lower cross-bridge cycling rates. The model-fitted phorbol ester induced slow contractions at constant myosin phosphorylation and predicted steeper dependence of force on myosin phosphorylation in phorbol ester-stimulated smooth muscle. By shifting cross bridges between the two latch-bridge cycles, the model predicts that a smooth muscle cell can either maintain force at extremely low-energy cost or change its contractile state rapidly, if necessary. Depending on the fraction of cross bridges engaged in the ultraslow latch-bridge cycle, the model predicted biphasic kinetics of smooth muscle mechanics and variable steady-state dependencies of force and shortening velocity on myosin phosphorylation. These results suggest that thin-filament-based regulatory proteins may function as tuners of actomyosin ATPase activity, thus allowing a smooth muscle cell to have two discrete cross-bridge cycles with different cross-bridge cycling rates.
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Freundt, Johanna K., and Wolfgang A. Linke. "Titin as a force-generating muscle protein under regulatory control." Journal of Applied Physiology 126, no. 5 (2019): 1474–82. http://dx.doi.org/10.1152/japplphysiol.00865.2018.
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Titin has long been recognized as a mechanical protein in muscle cells that has a main function as a molecular spring in the contractile units, the sarcomeres. Recent work suggests that the titin spring contributes to muscle contraction in a more active manner than previously thought. In this review, we highlight this property, specifically the ability of the immunoglobulin-like (Ig) domains of titin to undergo unfolding-refolding transitions when isolated titin molecules or skeletal myofibrils are held at physiological force levels. Folding of titin Ig domains under force is a hitherto unappreciated, putative source of work production in muscle cells, which could work in synergy with the actomyosin system to maximize the energy delivered by a stretched, actively contracting muscle. This review also focuses on the mechanisms shown to modulate titin-based viscoelastic forces in skeletal muscle cells, including chaperone binding, titin oxidation, phosphorylation, Ca2+ binding, and interaction with actin filaments. Along the way, we discuss which of these modulatory mechanisms might contribute to the phenomenon of residual force enhancement relevant for eccentric muscle contractions. Finally, a brief perspective is added on the potential for the alterations in titin-based force to dynamically alter mechano-chemical signaling pathways in the muscle cell. We conclude that titin from skeletal muscle is a determinant of both passive and active tension and a bona fide mechanosensor, whose stiffness is tuned by various independent mechanisms.
15
Stephens, Newman L. "Smooth Muscle Contraction: Recent Advances." Canadian Journal of Physiology and Pharmacology 72, no. 11 (1994): 1317–19. http://dx.doi.org/10.1139/y94-189.
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Research in smooth muscle contraction has shown remarkable progress over the last 5 years. Striking advances have been made in the areas of biochemical regulation of contraction, centering on myosin light chain kinase activity, and of biophysical delineation of the contractile process at the actomyosin level by use of the newly developed motility assay. The purpose of the symposium held at Minaki, Ont., was to obtain a comprehensive reporting of the recent advances made in the area of smooth muscle contraction. Specifically, advances in the areas of biophysics of contraction, energetics, and contractile and regulator proteins (including the interesting newcomers caldesmon and calponin) and the changes that occur in pathophysiological entities such as asthma, hypertension, anaphylactic shock, high-altitude hypoxia, and persistent pulmonary hypertension of the newborn were presented.Key words: smooth muscle biophysics, smooth muscle biochemistry, energetics of smooth muscle, pathophysiology of smooth muscle.
16
Staddon, Michael F., Edwin M. Munro, and Shiladitya Banerjee. "Pulsatile contractions and pattern formation in excitable actomyosin cortex." PLOS Computational Biology 18, no. 3 (2022): e1009981. http://dx.doi.org/10.1371/journal.pcbi.1009981.
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The actin cortex is an active adaptive material, embedded with complex regulatory networks that can sense, generate, and transmit mechanical forces. The cortex exhibits a wide range of dynamic behaviours, from generating pulsatory contractions and travelling waves to forming organised structures. Despite the progress in characterising the biochemical and mechanical components of the actin cortex, the emergent dynamics of this mechanochemical system is poorly understood. Here we develop a reaction-diffusion model for the RhoA signalling network, the upstream regulator for actomyosin assembly and contractility, coupled to an active actomyosin gel, to investigate how the interplay between chemical signalling and mechanical forces regulates stresses and patterns in the cortex. We demonstrate that mechanochemical feedback in the cortex acts to destabilise homogeneous states and robustly generate pulsatile contractions. By tuning active stress in the system, we show that the cortex can generate propagating contraction pulses, form network structures, or exhibit topological turbulence.
17
Fernandez-Gonzalez, Rodrigo, and Jennifer A. Zallen. "Wounded cells drive rapid epidermal repair in the early Drosophila embryo." Molecular Biology of the Cell 24, no. 20 (2013): 3227–37. http://dx.doi.org/10.1091/mbc.e13-05-0228.
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Epithelial tissues are protective barriers that display a remarkable ability to repair wounds. Wound repair is often associated with an accumulation of actin and nonmuscle myosin II around the wound, forming a purse string. The role of actomyosin networks in generating mechanical force during wound repair is not well understood. Here we investigate the mechanisms of force generation during wound repair in the epidermis of early and late Drosophila embryos. We find that wound closure is faster in early embryos, where, in addition to a purse string around the wound, actomyosin networks at the medial cortex of the wounded cells contribute to rapid wound repair. Laser ablation demonstrates that both medial and purse-string actomyosin networks generate contractile force. Quantitative analysis of protein localization dynamics during wound closure indicates that the rapid contraction of medial actomyosin structures during wound repair in early embryos involves disassembly of the actomyosin network. By contrast, actomyosin purse strings in late embryos contract more slowly in a mechanism that involves network condensation. We propose that the combined action of two force-generating structures—a medial actomyosin network and an actomyosin purse string—contributes to the increased efficiency of wound repair in the early embryo.
18
Spriet, Lawrence L., Karin Soderlund, and Eric Hultman. "Energy cost and metabolic regulation during intermittent and continuous tetanic contractions in human skeletal muscle." Canadian Journal of Physiology and Pharmacology 66, no. 1 (1988): 134–39. http://dx.doi.org/10.1139/y88-024.
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Muscle ATP turnover, glycogenolytic, and glycolytic rates were estimated to compare the energy cost and glycolytic regulation of 102.4 s of continuous and intermittent stimulation. Quadriceps femoris muscles of male subjects were stimulated at 20 Hz for one continuous contraction (n = 6) or a series of 64 contractions (1.6 s on, 1.6 s off; n = 6). Leg blood flow was occluded and muscle biopsies were obtained at rest and following 51.2 and 102.4 s of contraction time in both conditions. Isometric force production by the activated knee extensors decreased to 55% of initial contraction force with intermittent and 80% of initial contraction force with continuous stimulation following 51.2 s of contraction time. Corresponding ATP turnover rates were 4.49 ± 0.39 and 3.80 ± 0.44 mmol∙kg dry muscle−1∙s−1.When normalized for tension production the respective energy costs of intermittent and continuous contractions were 3.66 ± 0.47 and 2.64 ± 0.36 mmol ATP∙kg−1∙100 N−1.Glycogenolytic rates were identical during the first 51.2 s of stimulation but glycolysis was higher in the intermittent group (1.05 ± 0.10 vs. 0.86 ± 0.11 mmol∙kg−1∙s−1). We suggest that the increased ATP utilization of intermittent contractions is associated with enhanced Ca2+-transport ATPase activity during relaxation and enhanced actomyosin ATPase activity during the early portion of each contraction. Glycolytic rate is dependent on ATP demand and regulated by allosteric modulators of phosphofructokinase and pyruvate kinase which are released or consumed in the reactions associated with contraction.
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Pinar, Mario, Pedro M. Coll, Sergio A. Rincón, and Pilar Pérez. "Schizosaccharomyces pombe Pxl1 Is a Paxillin Homologue That Modulates Rho1 Activity and Participates in Cytokinesis." Molecular Biology of the Cell 19, no. 4 (2008): 1727–38. http://dx.doi.org/10.1091/mbc.e07-07-0718.
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Schizosaccharomyces pombe Rho GTPases regulate actin cytoskeleton organization and cell integrity. We studied the fission yeast gene SPBC4F6.12 based on its ability to suppress the thermosensitivity of cdc42-1625 mutant strain. This gene, named pxl1+, encodes a protein with three LIM domains that is similar to paxillin. Pxl1 does not interact with Cdc42 but it interacts with Rho1, and it negatively regulates this GTPase. Fission yeast Pxl1 forms a contractile ring in the cell division region and deletion of pxl1+ causes a delay in cell–cell separation, suggesting that it has a function in cytokinesis. Pxl1 N-terminal region is required and sufficient for its localization to the medial ring, whereas the LIM domains are necessary for its function. Pxl1 localization requires actin polymerization and the actomyosin ring, but it is independent of the septation initiation network (SIN) function. Moreover, Pxl1 colocalizes and interacts with Myo2, and Cdc15, suggesting that it is part of the actomyosin ring. Here, we show that in cells lacking Pxl1, the myosin ring is not correctly assembled and that actomyosin ring contraction is delayed. Together, these data suggest that Pxl1 modulates Rho1 GTPase signaling and plays a role in the formation and contraction of the actomyosin ring during cytokinesis.
20
Lehman, W., V. Hatch, M. Rosol, et al. "Troponin-Tropomyosin Control of Thin Filament Activity Revealed by Electron Microscopy and 3-D Reconstruction." Microscopy and Microanalysis 6, S2 (2000): 88–89. http://dx.doi.org/10.1017/s1431927600032931.
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Muscle contraction and the actomyosin ATPase that drives the contractile process are switched on and off by changes in sarcoplasmic free Ca2+ -concentration. In skeletal and cardiac muscles, on-off switching is mediated by the actinassociated protein tropomyosin and by the troponin complex. While the details of this mechanism are still subject to debate, it is well-accepted that tropomyosin strands move to sterically block and unblock myosin binding sites on actin, thereby controlling actomyosin ATPase and consequently contraction. It is also well known that the Ca2+- dependency of the movement of tropomyosin on actin is governed by troponin.As a means of studying tropomyosin movement and the influence of troponin, we have used cryo-EM, negative staining and 3-dimensional helical reconstruction to define the positions of tropomyosin and troponin on thin filaments. We examined various preparations of native isolated filaments and filaments reconstituted with wild-type and mutant proteins.
21
Månsson, Alf. "Hypothesis: Single Actomyosin Properties Account for Ensemble Behavior in Active Muscle Shortening and Isometric Contraction." International Journal of Molecular Sciences 21, no. 21 (2020): 8399. http://dx.doi.org/10.3390/ijms21218399.
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Muscle contraction results from cyclic interactions between myosin II motors and actin with two sets of proteins organized in overlapping thick and thin filaments, respectively, in a nearly crystalline lattice in a muscle sarcomere. However, a sarcomere contains a huge number of other proteins, some with important roles in muscle contraction. In particular, these include thin filament proteins, troponin and tropomyosin; thick filament proteins, myosin binding protein C; and the elastic protein, titin, that connects the thin and thick filaments. Furthermore, the order and 3D organization of the myofilament lattice may be important per se for contractile function. It is possible to model muscle contraction based on actin and myosin alone with properties derived in studies using single molecules and biochemical solution kinetics. It is also possible to reproduce several features of muscle contraction in experiments using only isolated actin and myosin, arguing against the importance of order and accessory proteins. Therefore, in this paper, it is hypothesized that “single molecule actomyosin properties account for the contractile properties of a half sarcomere during shortening and isometric contraction at almost saturating Ca concentrations”. In this paper, existing evidence for and against this hypothesis is reviewed and new modeling results to support the arguments are presented. Finally, further experimental tests are proposed, which if they corroborate, at least approximately, the hypothesis, should significantly benefit future effective analysis of a range of experimental studies, as well as drug discovery efforts.
22
Zhang, Shi-Jin, Daniel C. Andersson, Marie E. Sandström, Håkan Westerblad, and Abram Katz. "Cross bridges account for only 20% of total ATP consumption during submaximal isometric contraction in mouse fast-twitch skeletal muscle." American Journal of Physiology-Cell Physiology 291, no. 1 (2006): C147—C154. http://dx.doi.org/10.1152/ajpcell.00578.2005.
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It is generally believed that cross bridges account for >50% of the total ATP consumed by skeletal muscle during contraction. We investigated the effect of N-benzyl- p-toluene sulfonamide (BTS), an inhibitor of myosin ATPase, on muscle force production and energy metabolism under near-physiological conditions (50-Hz stimulation frequency at 30°C results in 35% of maximal force). Extensor digitorum longus muscles from mice were isolated and stimulated to perform continuous isometric tetanic contractions. Metabolites of energy metabolism were analyzed with fluorometric techniques. ATP turnover was estimated from the changes in phosphocreatine (PCr), ATP, and lactate (−2ΔATP − ΔPCr + [1.5Δlactate]). During contractions (2–10 s), BTS decreased force production to ∼5% of control. Under these conditions, BTS inhibited ATP turnover by only 18–25%. ATP turnover decreased markedly and similarly with and without BTS as the duration of contraction progressed. In conclusion, cross bridges (i.e., actomyosin ATPase) account for only a small fraction (∼20%) of the ATP consumption during contraction in mouse fast-twitch skeletal muscle under near-physiological conditions, suggesting that ion pumping is the major energy-consuming process.
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Tamada, Masako, Tomas D. Perez, W. James Nelson, and Michael P. Sheetz. "Two distinct modes of myosin assembly and dynamics during epithelial wound closure." Journal of Cell Biology 176, no. 1 (2007): 27–33. http://dx.doi.org/10.1083/jcb.200609116.
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Actomyosin contraction powers the sealing of epithelial sheets during embryogenesis and wound closure; however, the mechanisms are poorly understood. After laser ablation wounding of Madin–Darby canine kidney cell monolayers, we observed distinct steps in wound closure from time-lapse images of myosin distribution during resealing. Immediately upon wounding, actin and myosin II regulatory light chain accumulated at two locations: (1) in a ring adjacent to the tight junction that circumscribed the wound and (2) in fibers at the base of the cell in membranes extending over the wound site. Rho-kinase activity was required for assembly of the myosin ring, and myosin II activity was required for contraction but not for basal membrane extension. As it contracted, the myosin ring moved toward the basal membrane with ZO-1 and Rho-kinase. Thus, we suggest that tight junctions serve as attachment points for the actomyosin ring during wound closure and that Rho-kinase is required for localization and activation of the contractile ring.
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Kscheschinski, Bjoern, Mirna Kramar, and Karen Alim. "Calcium regulates cortex contraction in Physarum polycephalum." Physical Biology 21, no. 1 (2023): 016001. http://dx.doi.org/10.1088/1478-3975/ad0a9a.
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Abstract The tubular network-forming slime mold Physarum polycephalum is able to maintain long-scale contraction patterns driven by an actomyosin cortex. The resulting shuttle streaming in the network is crucial for the organism to respond to external stimuli and reorganize its body mass giving rise to complex behaviors. However, the chemical basis of the self-organized flow pattern is not fully understood. Here, we present ratiometric measurements of free intracellular calcium in simple morphologies of Physarum networks. The spatiotemporal patterns of the free calcium concentration reveal a nearly anti-correlated relation to the tube radius, suggesting that calcium is indeed a key regulator of the actomyosin activity. We compare the experimentally observed phase relation between the radius and the calcium concentration to the predictions of a theoretical model including calcium as an inhibitor. Numerical simulations of the model suggest that calcium indeed inhibits the contractions in Physarum, although a quantitative difference to the experimentally measured phase relation remains. Unraveling the mechanism underlying the contraction patterns is a key step in gaining further insight into the principles of Physarum’s complex behavior.
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Harden, Nicholas, Michael Ricos, Kelly Yee, et al. "Drac1 and Crumbs participate in amnioserosa morphogenesis during dorsal closure in Drosophila." Journal of Cell Science 115, no. 10 (2002): 2119–29. http://dx.doi.org/10.1242/jcs.115.10.2119.
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Dorsal closure of the Drosophila embryo involves morphological changes in two epithelia, the epidermis and the amnioserosa, and is a popular system for studying the regulation of epithelial morphogenesis. We previously implicated the small GTPase Drac1 in the assembly of an actomyosin contractile apparatus, contributing to cell shape change in the epidermis during dorsal closure. We now present evidence that Drac1 and Crumbs, a determinant of epithelial polarity, are involved in setting up an actomyosin contractile apparatus that drives amnioserosa morphogenesis by inducing apical cell constriction. Expression of constitutively active Drac1 causes excessive constriction of amnioserosa cells and contraction of the tissue, whereas expression of dominant-negative Drac1 impairs amnioserosa morphogenesis. These Drac1 transgenes may be acting through their effects on the amnioserosa cytoskeleton, as constitutively active Drac1 causes increased staining for F-actin and myosin, whereas dominant-negative Drac1 reduces F-actin levels. Overexpression of Crumbs causes premature cell constriction in the amnioserosa, and dorsal closure defects are seen in embryos homozygous for hypomorphic crumbs alleles. The ability of constitutively active Drac1 to cause contraction of the amnioserosa is impaired in a crumbsmutant background. We propose that amnioserosa morphogenesis is a useful system for studying the regulation of epithelial morphogenesis by Drac1.
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Webber, Sandra, and Dean Kriellaars. "Neuromuscular factors contributing to in vivo eccentric moment generation." Journal of Applied Physiology 83, no. 1 (1997): 40–45. http://dx.doi.org/10.1152/jappl.1997.83.1.40.
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Webber, Sandra, and Dean Kriellaars. Neuromuscular factors contributing to in vivo eccentric moment generation. J. Appl. Physiol. 83(1): 40–45, 1997.—Muscle series elasticity and its contribution to eccentric moment generation was examined in humans. While subjects [male, n = 30; age 26.3 ± 4.8 (SD) yr; body mass 78.8 ± 13.1 kg] performed an isometric contraction of the knee extensors at 60° of knee flexion, a quick stretch was imposed with a 12°-step displacement at 100°/s. The test was performed at 10 isometric activation levels ranging from 1.7 to 95.2% of maximal voluntary contraction (MVC). A strong linear relationship was observed between the peak imposed eccentric moment derived from quick stretch and the isometric activation level ( y = 1.44 x + 7.08; r = 0.99). This increase in the eccentric moment is consistent with an actomyosin-dependent elasticity located in series with the contractile element of muscle. By extrapolating the linear relationship to 100% MVC, the predicted maximum eccentric moment was found to be 151% MVC, consistent with in vitro data. A maximal voluntary, knee extensor strength test was also performed (5–95°, 3 repetitions, ±50, 100, 150, 200, and 250°/s). The predicted maximum eccentric moment was 206% of the angle- and velocity-matched, maximal voluntary eccentric moments. This was attributed to a potent neural regulatory mechanism that limits the recruitment and/or discharge of motor units during maximal voluntary eccentric contractions.
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Somara, Sita, and Khalil N. Bitar. "Phosphorylated HSP27 modulates the association of phosphorylated caldesmon with tropomyosin in colonic smooth muscle." American Journal of Physiology-Gastrointestinal and Liver Physiology 291, no. 4 (2006): G630—G639. http://dx.doi.org/10.1152/ajpgi.00350.2005.
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Thin-filament regulation of smooth muscle contraction involves phosphorylation, association, and dissociation of contractile proteins in response to agonist stimulation. Phosphorylation of caldesmon weakens its association with actin leading to actomyosin interaction and contraction. Present data from colonic smooth muscle cells indicate that acetylcholine induced a significant association of caldesmon with PKCα and sustained phosphorylation of caldesmon at ser789. Furthermore, acetylcholine induced significant and sustained increase in the association of phospho-caldesmon with heat-shock protein (HSP)27 with concomitant increase in the dissociation of phospho-caldesmon from tropomyosin. At the thin filament level, HSP27 plays a crucial role in acetylcholine-induced association of contractile proteins. Present data from colonic smooth muscle cells transfected with non-phospho-HSP27 mutant cDNA indicate that the absence of phospho-HSP27 inhibits acetylcholine-induced caldesmon phosphorylation. Our results further indicate that the presence of phospho-HSP27 significantly enhances acetylcholine-induced sustained association of phospho-caldesmon with HSP27 with a concomitant increase in acetylcholine-induced dissociation of phospho-caldesmon from tropomyosin. We thus propose a model whereby upon acetylcholine-induced phosphorylation of caldesmon at ser789, the association of phospho-caldesmon (ser789) with phospho-HSP27 results in an essential conformational change leading to dissociation of phospho-caldesmon from tropomyosin. This leads to the sliding of tropomyosin on actin thus exposing the myosin binding sites on actin for actomyosin interaction.
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Rieu, Jean-Paul, Hélène Delanoë-Ayari, Seiji Takagi, Yoshimi Tanaka, and Toshiyuki Nakagaki. "Periodic traction in migrating large amoeba of Physarum polycephalum." Journal of The Royal Society Interface 12, no. 106 (2015): 20150099. http://dx.doi.org/10.1098/rsif.2015.0099.
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The slime mould Physarum polycephalum is a giant multinucleated cell exhibiting well-known Ca 2+ -dependent actomyosin contractions of its vein network driving the so-called cytoplasmic shuttle streaming. Its actomyosin network forms both a filamentous cortical layer and large fibrils. In order to understand the role of each structure in the locomotory activity, we performed birefringence observations and traction force microscopy on excised fragments of Physarum . After several hours, these microplasmodia adopt three main morphologies: flat motile amoeba, chain types with round contractile heads connected by tubes and motile hybrid types. Each type exhibits oscillations with a period of about 1.5 min of cell area, traction forces and fibril activity (retardance) when fibrils are present. The amoeboid types show only peripheral forces while the chain types present a never-reported force pattern with contractile rings far from the cell boundary under the spherical heads. Forces are mostly transmitted where the actomyosin cortical layer anchors to the substratum, but fibrils maintain highly invaginated structures and contribute to forces by increasing the length of the anchorage line. Microplasmodia are motile only when there is an asymmetry in the shape and/or the force distribution.
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Dasanayake, Nilushi L., and Anders E. Carlsson. "General Mechanism of Actomyosin Contraction." Biophysical Journal 102, no. 3 (2012): 349a. http://dx.doi.org/10.1016/j.bpj.2011.11.1913.
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Sutherland, Ann, and Alyssa Lesko. "Pulsed actomyosin contractions in morphogenesis." F1000Research 9 (February 25, 2020): 142. http://dx.doi.org/10.12688/f1000research.20874.1.
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Cell and tissue shape changes are the fundamental elements of morphogenesis that drive normal development of embryos into fully functional organisms. This requires a variety of cellular processes including establishment and maintenance of polarity, tissue growth and apoptosis, and cell differentiation, rearrangement, and migration. It is widely appreciated that the cytoskeletal networks play an important role in regulating many of these processes and, in particular, that pulsed actomyosin contractions are a core cellular mechanism driving cell shape changes and cell rearrangement. In this review, we discuss the role of pulsed actomyosin contractions during developmental morphogenesis, advances in our understanding of the mechanisms regulating actomyosin pulsing, and novel techniques to probe the role of pulsed actomyosin processes in in vivo model systems.
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Mucha, David R., Carter L. Myers, and Richard C. Schaeffer. "Endothelial contraction and monolayer hyperpermeability are regulated by Src kinase." American Journal of Physiology-Heart and Circulatory Physiology 284, no. 3 (2003): H994—H1002. http://dx.doi.org/10.1152/ajpheart.00862.2002.
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Endothelial monolayer hyperpermeability is regulated by a myosin light chain phosphorylation (MLCP)-dependent contractile mechanism. In this study, we tested the role of Src-dependent tyrosine phosphorylation to modulate endothelial contraction and monolayer barrier function with the use of the myosin phosphatase inhibitor calyculin A (CalA) to directly elevate MLCP with the Src family tyrosine kinase inhibitor herbimycin A (HA) in bovine pulmonary artery endothelial cells (EC). CalA stimulated an increase in MLCP, Src kinase activity, an increase in the tyrosine phosphorylation of paxillin and focal adhesion (FA) kinase (p125FAK), and monolayer hyperpermeability. Microscopic examination of CalA-treated EC revealed a contractile morphology characterized by peripheral contractile bands of actomyosin filaments and stress fibers linked to phosphotyrosine-containing FAs. These CalA-dependent events were HA sensitive. HA alone stimulated an improvement in monolayer barrier formation by reducing the levels of MLCP and phosphotyrosine-containing proteins and the number of large paracellular holes. These data show that Src kinase plays an important role in regulating monolayer hyperpermeability through adjustments in tyrosine phosphorylation, MLCP, and EC contraction.
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Saadaoui, Mehdi, Didier Rocancourt, Julian Roussel, Francis Corson, and Jerome Gros. "A tensile ring drives tissue flows to shape the gastrulating amniote embryo." Science 367, no. 6476 (2020): 453–58. http://dx.doi.org/10.1126/science.aaw1965.
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Tissue morphogenesis is driven by local cellular deformations that are powered by contractile actomyosin networks. How localized forces are transmitted across tissues to shape them at a mesoscopic scale is still unclear. Analyzing gastrulation in entire avian embryos, we show that it is driven by the graded contraction of a large-scale supracellular actomyosin ring at the margin between the embryonic and extraembryonic territories. The propagation of these forces is enabled by a fluid-like response of the epithelial embryonic disk, which depends on cell division. A simple model of fluid motion entrained by a tensile ring quantitatively captures the vortex-like “polonaise” movements that accompany the formation of the primitive streak. The geometry of the early embryo thus arises from the transmission of active forces generated along its boundary.
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Itoh, Katsuhiko, Takahiro Ebata, Hiroaki Hirata, et al. "DMPK is a New Candidate Mediator of Tumor Suppressor p53-Dependent Cell Death." Molecules 24, no. 17 (2019): 3175. http://dx.doi.org/10.3390/molecules24173175.
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Tumor suppressor p53 plays an integral role in DNA-damage induced apoptosis, a biological process that protects against tumor progression. Cell shape dramatically changes when cells undergo apoptosis, which is associated with actomyosin contraction; however, it remains entirely elusive how p53 regulates actomyosin contraction in response to DNA-damaging agents. To identify a novel p53 regulating gene encoding the modulator of myosin, we conducted DNA microarray analysis. We found that, in response to DNA-damaging agent doxorubicin, expression of myotonic dystrophy protein kinase (DMPK), which is known to upregulate actomyosin contraction, was increased in a p53-dependent manner. The promoter region of DMPK gene contained potential p53-binding sequences and its promoter activity was increased by overexpression of the p53 family protein p73, but, unexpectedly, not of p53. Furthermore, we found that doxorubicin treatment induced p73 expression, which was significantly attenuated by downregulation of p53. These data suggest that p53 induces expression of DMPK through upregulating p73 expression. Overexpression of DMPK promotes contraction of the actomyosin cortex, which leads to formation of membrane blebs, loss of cell adhesion, and concomitant caspase activation. Taken together, our results suggest the existence of p53-p73-DMPK axis which mediates DNA-damage induced actomyosin contraction at the cortex and concomitant cell death.
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Mandato, Craig A., and William M. Bement. "Contraction and polymerization cooperate to assemble and close actomyosin rings around Xenopus oocyte wounds." Journal of Cell Biology 154, no. 4 (2001): 785–98. http://dx.doi.org/10.1083/jcb.200103105.
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Xenopus oocytes assemble an array of F-actin and myosin 2 around plasma membrane wounds. We analyzed this process in living oocytes using confocal time-lapse (four-dimensional) microscopy. Closure of wounds requires assembly and contraction of a classic “contractile ring” composed of F-actin and myosin 2. However, this ring works in concert with a 5–10-μm wide “zone” of localized actin and myosin 2 assembly. The zone forms before the ring and can be uncoupled from the ring by inhibition of cortical flow and contractility. However, contractility and the contractile ring are required for the stability and forward movement of the zone, as revealed by changes in zone dynamics after disruption of contractility and flow, or experimentally induced breakage of the contractile ring. We conclude that wound-induced contractile arrays are provided with their characteristic flexibility, speed, and strength by the combined input of two distinct components: a highly dynamic zone in which myosin 2 and actin preferentially assemble, and a stable contractile actomyosin ring.
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Ratz, Paul H., and John E. Speich. "Evidence that actomyosin cross bridges contribute to “passive” tension in detrusor smooth muscle." American Journal of Physiology-Renal Physiology 298, no. 6 (2010): F1424—F1435. http://dx.doi.org/10.1152/ajprenal.00635.2009.
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Contraction of detrusor smooth muscle (DSM) at short muscle lengths generates a stiffness component we termed adjustable passive stiffness (APS) that is retained in tissues incubated in a Ca2+-free solution, shifts the DSM length-passive tension curve up and to the left, and is softened by muscle strain and release (strain softened). In the present study, we tested the hypothesis that APS is due to slowly cycling actomyosin cross bridges. APS and active tension produced by the stimulus, KCl, displayed similar length dependencies with identical optimum length values. The myosin II inhibitor blebbistatin relaxed active tension maintained during a KCl-induced contraction and the passive tension maintained during stress-relaxation induced by muscle stretch in a Ca2+-free solution. Passive tension was attributed to tension maintaining rather than tension developing cross bridges because tension did not recover after a rapid 10% stretch and release as it did during a KCl-induced contraction. APS generated by a KCl-induced contraction in intact tissues was preserved in tissues permeabilized with Triton X-100. Blebbistatin and the actin polymerization inhibitor latrunculin-B reduced the degree of APS generated by a KCl-induced contraction. The degree of APS generated by KCl was inhibited to a greater degree than was the peak KCl-induced tension by rhoA kinase and cyclooxygenase inhibitors. These data support the hypothesis that APS is due to slowly cycling actomyosin cross bridges and suggest that cross bridges may play a novel role in DSM that uniquely serves to ensure proper contractile function over an extreme working length range.
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Ali, Farah, Peter D. Paré, and Chun Y. Seow. "Models of contractile units and their assembly in smooth muscle." Canadian Journal of Physiology and Pharmacology 83, no. 10 (2005): 825–31. http://dx.doi.org/10.1139/y05-052.
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It is believed that the contractile filaments in smooth muscle are organized into arrays of contractile units (similar to the sarcomeric structure in striated muscle), and that such an organization is crucial for transforming the mechanical activities of actomyosin interaction into cell shortening and force generation. Details of the filament organization, however, are still poorly understood. Several models of contractile filament architecture are discussed here. To account for the linear relationship observed between the force generated by a smooth muscle and the muscle length at the plateau of an isotonic contraction, a model of contractile unit is proposed. The model consists of 2 dense bodies with actin (thin) filaments attached, and a myosin (thick) filament lying between the parallel thin filaments. In addition, the thick filament is assumed to span the whole contractile unit length, from dense body to dense body, so that when the contractile unit shortens, the amount of overlap between the thick and thin filaments (i.e., the distance between the dense bodies) decreases in exact proportion to the amount of shortening. Assembly of the contractile units into functional contractile apparatus is assumed to involve a group of cells that form a mechanical syncytium. The contractile apparatus is assumed malleable in that the number of contractile units in series and in parallel can be altered to accommodate strains on the muscle and to maintain the muscle's optimal mechanical function.Key words: contraction model, ultrastructure, length adaptation, plasticity.
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Ishigami, M., K. Kuroda, and S. Hatano. "Dynamic aspects of the contractile system in Physarum plasmodium. III. Cyclic contraction-relaxation of the plasmodial fragment in accordance with the generation-degeneration of cytoplasmic actomyosin fibrils." Journal of Cell Biology 105, no. 1 (1987): 381–86. http://dx.doi.org/10.1083/jcb.105.1.381.
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Plasmodial fragments of Physarum polycephalum, excised from anterior regions of a thin-spread plasmodium, contracted-relaxed cyclicly with a period of 3-5 min. The area of the fragments decreased approximately 10% during contraction. In most cases, there was little endoplasmic streaming which indicates that contractions were synchronized throughout the fragment. By both polarized light and fluorescence microscopy, the organization and distribution of the cytoplasmic actomyosin fibrils in the fragments changed in synchrony with the contraction cycle. The fibrils formed during the contraction phase, and finally became a highly organized framework consisting of a three-dimensional network of numerous fibrils with many converging points (the nodes). During relaxation, the fibrils degenerated and disappeared almost completely, though some very weak fibrils remained near the nodes and the periphery. The results obtained by fluorometry of the fragments, stained with rhodamine-phalloidin, suggested that the G-F transformation of actin is not the main underlying process of the fibrillar formation.
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Gavara, Núria, Raimon Sunyer, Pere Roca-Cusachs, Ramon Farré, Mar Rotger, and Daniel Navajas. "Thrombin-induced contraction in alveolar epithelial cells probed by traction microscopy." Journal of Applied Physiology 101, no. 2 (2006): 512–20. http://dx.doi.org/10.1152/japplphysiol.00185.2006.
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Contractile tension of alveolar epithelial cells plays a major role in the force balance that regulates the structural integrity of the alveolar barrier. The aim of this work was to study thrombin-induced contractile forces of alveolar epithelial cells. A549 alveolar epithelial cells were challenged with thrombin, and time course of contractile forces was measured by traction microscopy. The cells exhibited basal contraction with total force magnitude 55.0 ± 12.0 nN (mean ± SE, n = 12). Traction forces were exerted predominantly at the cell periphery and pointed to the cell center. Thrombin (1 U/ml) induced a fast and sustained 2.5-fold increase in traction forces, which maintained peripheral and centripetal distribution. Actin fluorescent staining revealed F-actin polymerization and enhancement of peripheral actin rim. Disruption of actin cytoskeleton with cytochalasin D (5 μM, 30 min) and inhibition of myosin light chain kinase with ML-7 (10 μM, 30 min) and Rho kinase with Y-27632 (10 μM, 30 min) markedly depressed basal contractile tone and abolished thrombin-induced cell contraction. Therefore, the contractile response of alveolar epithelial cells to the inflammatory agonist thrombin was mediated by actin cytoskeleton remodeling and actomyosin activation through myosin light chain kinase and Rho kinase signaling pathways. Thrombin-induced contractile tension might further impair alveolar epithelial barrier integrity in the injured lung.
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Cheffings, Thomas H., Nigel J. Burroughs, and Mohan K. Balasubramanian. "Actin turnover ensures uniform tension distribution during cytokinetic actomyosin ring contraction." Molecular Biology of the Cell 30, no. 8 (2019): 933–41. http://dx.doi.org/10.1091/mbc.e18-08-0511.
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In many eukaryotes, cytokinesis is facilitated by the contraction of an actomyosin ring (AMR). The exact mechanisms that lead to this contractility are unknown, although some models posit that actin turnover in the AMR is essential. The effect of reduced actin dynamics during AMR formation has been well studied in Schizosaccharomyces pombe; however, the corresponding effects on AMR contraction are not well understood. By using mutants of the fission yeast actin severing protein Adf1, we observed that contracting AMRs display a “peeling” phenotype, where bundles of actin and myosin peel off from one side of the AMR, and are pulled across to the opposite side. This occurs multiple times during cytokinesis and is dependent on the activity of myosins Myo2, Myp2, and Myo51. We found that the distribution of Myo2 in the AMR anticorrelates with the location of peeling events, suggesting that peeling is caused by a nonuniform tension distribution around the AMR, and that one of the roles of actin turnover is to maintain a uniform tension distribution around the AMR.
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Lippincott, John, and Rong Li. "Dual Function of Cyk2, a cdc15/PSTPIP Family Protein, in Regulating Actomyosin Ring Dynamics and Septin Distribution." Journal of Cell Biology 143, no. 7 (1998): 1947–60. http://dx.doi.org/10.1083/jcb.143.7.1947.
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We previously showed that the budding yeast Saccharomyces cerevisiae assembles an actomyosin-based ring that undergoes a contraction-like size change during cytokinesis. To learn more about the biochemical composition and activity of this ring, we have characterized the in vivo distribution and function of Cyk2p, a budding yeast protein that exhibits significant sequence similarity to the cdc15/PSTPIP family of cleavage furrow proteins. Video microscopy of cells expressing green fluorescent protein (GFP)-tagged Cyk2p revealed that Cyk2p forms a double ring that coincides with the septins through most of the cell cycle. During cytokinesis, however, the Cyk2 double ring merges with the actomyosin ring and exhibits a contraction-like size change that is dependent on Myo1p. The septin double ring, in contrast, does not undergo the contraction-like size change but the separation between the two rings increases during cytokinesis. These observations suggest that the septin-containing ring is dynamically distinct from the actomyosin ring and that Cyk2p transits between the two types of structures. Gene disruption of CYK2 does not affect the assembly of the actomyosin ring but results in rapid disassembly of the ring during the contraction phase, leading to incomplete cytokinesis, suggesting that Cyk2p has an important function in modulating the stability of the actomyosin ring during contraction. Overexpression of Cyk2p also blocks cytokinesis, most likely due to a loss of the septins from the bud neck, indicating that Cyk2p may also play a role in regulating the localization of the septins.
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Warren, Gordon L., Jay H. Williams, Christopher W. Ward, et al. "Decreased contraction economy in mouse EDL muscle injured by eccentric contractions." Journal of Applied Physiology 81, no. 6 (1996): 2555–64. http://dx.doi.org/10.1152/jappl.1996.81.6.2555.
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Warren III, Gordon L., Jay H. Williams, Christopher W. Ward, Hideki Matoba, Christopher P. Ingalls, Karl M. Hermann, and R. B. Armstrong. Decreased contraction economy in mouse EDL muscle injured by eccentric contractions. J. Appl. Physiol. 81(6): 2555–2564, 1996.—The objective of this study was to find out whether basal and/or active energy metabolism are altered in isolated mouse extensor digitorum longus muscle injured by eccentric (Ecc) contractions. Measurements of basal O2 consumption and isometric tetanus O2 recovery cost were made at 25°C on muscles that had done either 10 Ecc, 10 isometric (Iso), or no contractions (No). In parallel experiments, rates of lactate and pyruvate production were measured to estimate the anaerobic contribution. Basal O2 consumption was unaffected by the type of protocol performed ( P = 0.07). However, the tetanus O2 cost per force-time integral was elevated by 30–36% for the Ecc protocol muscles over that for the Iso and No protocol muscles. When including the increased lactate production by the Ecc protocol muscles, the total energetic cost per force-time integral was 53% higher than that for the Iso protocol muscles [2.35 ± 0.17 vs. 1.54 ± 0.18 μmol O2/(N ⋅ m ⋅ s)]. The decreased economy was attributed to two factors. First, in skinned fibers isolated from the injured muscles, the ratio of maximal actomyosin adenosinetriphosphatase activity to force production was up by 37.5%, suggesting uncoupling of ATP hydrolysis from force production. Second, increased reliance on anaerobic metabolism along with the fluorescent microscopic study of mitochondrial membrane potential and histochemical study of ATP synthase suggested an uncoupling of oxidative phosphorylation in the injured muscles.
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Sechi, Stefano, Anna Frappaolo, Roberta Fraschini, et al. "Rab1 interacts with GOLPH3 and controls Golgi structure and contractile ring constriction during cytokinesis in Drosophila melanogaster." Open Biology 7, no. 1 (2017): 160257. http://dx.doi.org/10.1098/rsob.160257.
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Cytokinesis requires a tight coordination between actomyosin ring constriction and new membrane addition along the ingressing cleavage furrow. However, the molecular mechanisms underlying vesicle trafficking to the equatorial site and how this process is coupled with the dynamics of the contractile apparatus are poorly defined. Here we provide evidence for the requirement of Rab1 during cleavage furrow ingression in cytokinesis. We demonstrate that the gene omelette ( omt ) encodes the Drosophila orthologue of human Rab1 and is required for successful cytokinesis in both mitotic and meiotic dividing cells of Drosophila melanogaster . We show that Rab1 protein colocalizes with the conserved oligomeric Golgi (COG) complex Cog7 subunit and the phosphatidylinositol 4-phosphate effector GOLPH3 at the Golgi stacks. Analysis by transmission electron microscopy and 3D-SIM super-resolution microscopy reveals loss of normal Golgi architecture in omt mutant spermatocytes indicating a role for Rab1 in Golgi formation. In dividing cells, Rab1 enables stabilization and contraction of actomyosin rings. We further demonstrate that GTP-bound Rab1 directly interacts with GOLPH3 and controls its localization at the Golgi and at the cleavage site . We propose that Rab1, by associating with GOLPH3, controls membrane trafficking and contractile ring constriction during cytokinesis.
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Vallen, Elizabeth A., Juliane Caviston, and Erfei Bi. "Roles of Hof1p, Bni1p, Bnr1p, and Myo1p in Cytokinesis inSaccharomyces cerevisiae." Molecular Biology of the Cell 11, no. 2 (2000): 593–611. http://dx.doi.org/10.1091/mbc.11.2.593.
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Cytokinesis in Saccharomyces cerevisiae occurs by the concerted action of the actomyosin system and septum formation. Here we report on the roles of HOF1,BNI1, and BNR1 in cytokinesis, focusing on Hof1p. Deletion of HOF1 causes a temperature-sensitive defect in septum formation. A Hof1p ring forms on the mother side of the bud neck in G2/M, followed by the formation of a daughter-side ring. Around telophase, Hof1p is phosphorylated and the double rings merge into a single ring that contracts slightly and may colocalize with the actomyosin structure. Upon septum formation, Hof1p splits into two rings, disappearing upon cell separation. Hof1p localization is dependent on septins but not Myo1p. Synthetic lethality suggests that Bni1p and Myo1p belong to one functional pathway, whereas Hof1p and Bnr1p belong to another. These results suggest that Hof1p may function as an adapter linking the primary septum synthesis machinery to the actomyosin system. The formation of the actomyosin ring is not affected by bni1Δ, hof1Δ, orbnr1Δ. However, Myo1p contraction is affected bybni1Δ but not by hof1Δ orbnr1Δ. In bni1Δ cells that lack the actomyosin contraction, septum formation is often slow and asymmetric, suggesting that actomyosin contraction may provide directionality for efficient septum formation.
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Mehta, Dolly, Dale D. Tang, Ming-Fang Wu, Simon Atkinson, and Susan J. Gunst. "Role of Rho in Ca2+-insensitive contraction and paxillin tyrosine phosphorylation in smooth muscle." American Journal of Physiology-Cell Physiology 279, no. 2 (2000): C308—C318. http://dx.doi.org/10.1152/ajpcell.2000.279.2.c308.
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We investigated whether Rho activation is required for Ca2+-insensitive paxillin phosphorylation, myosin light chain (MLC) phosphorylation, and contraction in tracheal muscle. Tyrosine-phosphorylated proteins have been implicated in the Ca2+-insensitive contractile activation of smooth muscle tissues. The contractile activation of tracheal smooth muscle increases tyrosine phosphorylation of the cytoskeletal proteins paxillin and focal adhesion kinase. Paxillin is implicated in integrin-mediated signal transduction pathways that regulate cytoskeletal organization and cell motility. In fibroblasts and other nonmuscle cells, paxillin tyrosine phosphorylation depends on the activation of Rho and is inhibited by cytochalasin, an inhibitor of actin polymerization. In permeabilized muscle strips, we found that ACh induced Ca2+-insensitive contraction, MLC phosphorylation, and paxillin tyrosine phosphorylation. Ca2+-insensitive contraction and MLC phosphorylation induced by ACh were inhibited by C3 transferase, an inhibitor of Rho activation; however, C3 transferase did not inhibit paxillin tyrosine phosphorylation. Ca2+-insensitive paxillin tyrosine phosphorylation was also not inhibited by the Rho kinase inhibitor Y-27632, by cytochalasin D, or by the inhibition of MLC phosphorylation. We conclude that, in tracheal smooth muscle, Rho mediates Ca2+-insensitive contraction and MLC phosphorylation but that Rho is not required for Ca2+-insensitive paxillin tyrosine phosphorylation. Paxillin phosphorylation also does not require actomyosin activation, nor is it inhibited by the actin filament capping agent cytochalasin D.
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Yoshinaga, Natsuhiko, and Philippe Marcq. "Contraction of cross-linked actomyosin bundles." Physical Biology 9, no. 4 (2012): 046004. http://dx.doi.org/10.1088/1478-3975/9/4/046004.
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Julien, Jean-Daniel, and Karen Alim. "Oscillatory fluid flow drives scaling of contraction wave with system size." Proceedings of the National Academy of Sciences 115, no. 42 (2018): 10612–17. http://dx.doi.org/10.1073/pnas.1805981115.
Full textAbstract:
Flows over remarkably long distances are crucial to the functioning of many organisms, across all kingdoms of life. Coordinated flows are fundamental to power deformations, required for migration or development, or to spread resources and signals. A ubiquitous mechanism to generate flows, particularly prominent in animals and amoebas, is actomyosin cortex-driven mechanical deformations that pump the fluid enclosed by the cortex. However, it is unclear how cortex dynamics can self-organize to give rise to coordinated flows across the largely varying scales of biological systems. Here, we develop a mechanochemical model of actomyosin cortex mechanics coupled to a contraction-triggering, soluble chemical. The chemical itself is advected with the flows generated by the cortex-driven deformations of the tubular-shaped cell. The theoretical model predicts a dynamic instability giving rise to stable patterns of cortex contraction waves and oscillatory flows. Surprisingly, simulated patterns extend beyond the intrinsic length scale of the dynamic instability—scaling with system size instead. Patterns appear randomly but can be robustly generated in a growing system or by flow-generating boundary conditions. We identify oscillatory flows as the key for the scaling of contraction waves with system size. Our work shows the importance of active flows in biophysical models of patterning, not only as a regulating input or an emergent output, but also as a full part of a self-organized machinery. Contractions and fluid flows are observed in all kinds of organisms, so this concept is likely to be relevant for a broad class of systems.
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Schmidt, Martin, Blair Bowers, Archana Varma, Dong-Hyun Roh, and Enrico Cabib. "In budding yeast, contraction of the actomyosin ring and formation of the primary septum at cytokinesis depend on each other." Journal of Cell Science 115, no. 2 (2002): 293–302. http://dx.doi.org/10.1242/jcs.115.2.293.
Full textAbstract:
Saccharomyces cerevisiae chs2 mutants are unable to synthesize primary septum chitin, and myo1 mutants cannot construct a functional contractile ring. The morphology of the two mutants, as observed by electron microscopy, is very similar. In both cases, neither an invagination of the plasma membrane, which normally results from contraction of the actomyosin ring, nor generation of a chitin disc, the primary septum, is observed. Rather, both mutants are able to complete cytokinesis by an abnormal process in which lateral walls thicken gradually and finally meet over an extended region, giving rise to a thick septum lacking the normal trilaminar structure and often enclosing lacunae. Defects in chs2 or myo1 strains were not aggravated in a double mutant, an indication that the corresponding proteins participate in a common process. In contrast, in a chs3 background the chs2 mutation is lethal and the myo1 defect is greatly worsened, suggesting that the synthesis of chitin catalyzed by chitin synthase III is necessary for the functionality of the remedial septa. Both chs2 and myo1 mutants show abnormalities in budding pattern and a decrease in the level of certain proteins associated with budding, such as Bud3p, Bud4p and Spa2p. The possible reasons for these phenotypes and for the interdependence between actomyosin ring contraction and primary septum formation are discussed.
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Wirshing, Alison C. E., and Erin J. Cram. "Spectrin regulates cell contractility through production and maintenance of actin bundles in theCaenorhabditis elegansspermatheca." Molecular Biology of the Cell 29, no. 20 (2018): 2433–49. http://dx.doi.org/10.1091/mbc.e18-06-0347.
Full textAbstract:
Disruption to the contractility of cells, including smooth muscle cells of the cardiovascular system and myoepithelial cells of the glandular epithelium, contributes to the pathophysiology of contractile tissue diseases, including asthma, hypertension, and primary Sjögren’s syndrome. Cell contractility is determined by myosin activity and actomyosin network organization and is mediated by hundreds of protein–protein interactions, many directly involving actin. Here we use a candidate RNA interference screen of more than 100 Caenorhabditis elegans genes with predicted actin-binding and regulatory domains to identify genes that contribute to the contractility of the somatic gonad. We identify the spectrin cytoskeleton composed of SPC-1/α-spectrin, UNC-70/β-spectrin, and SMA-1/β heavy-spectrin as required for contractility and actin organization in the myoepithelial cells of the C. elegans spermatheca. We use imaging of fixed and live animals as well as tissue- and developmental-stage-specific disruption of the spectrin cytoskeleton to show that spectrin regulates the production of prominent central actin bundles and is required for maintenance of central actin bundles throughout successive rounds of stretch and contraction. We conclude that the spectrin cytoskeleton contributes to spermathecal contractility by promoting maintenance of the robust actomyosin bundles that drive contraction.
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Vogel, Sven K., Christian Wölfer, Diego A. Ramirez-Diaz, Robert J. Flassig, Kai Sundmacher, and Petra Schwille. "Symmetry Breaking and Emergence of Directional Flows in Minimal Actomyosin Cortices." Cells 9, no. 6 (2020): 1432. http://dx.doi.org/10.3390/cells9061432.
Full textAbstract:
Cortical actomyosin flows, among other mechanisms, scale up spontaneous symmetry breaking and thus play pivotal roles in cell differentiation, division, and motility. According to many model systems, myosin motor-induced local contractions of initially isotropic actomyosin cortices are nucleation points for generating cortical flows. However, the positive feedback mechanisms by which spontaneous contractions can be amplified towards large-scale directed flows remain mostly speculative. To investigate such a process on spherical surfaces, we reconstituted and confined initially isotropic minimal actomyosin cortices to the interfaces of emulsion droplets. The presence of ATP leads to myosin-induced local contractions that self-organize and amplify into directed large-scale actomyosin flows. By combining our experiments with theory, we found that the feedback mechanism leading to a coordinated directional motion of actomyosin clusters can be described as asymmetric cluster vibrations, caused by intrinsic non-isotropic ATP consumption with spatial confinement. We identified fingerprints of vibrational states as the basis of directed motions by tracking individual actomyosin clusters. These vibrations may represent a generic key driver of directed actomyosin flows under spatial confinement in vitro and in living systems.
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Descovich, Carlos Patino, Daniel B. Cortes, Sean Ryan, et al. "Cross-linkers both drive and brake cytoskeletal remodeling and furrowing in cytokinesis." Molecular Biology of the Cell 29, no. 5 (2018): 622–31. http://dx.doi.org/10.1091/mbc.e17-06-0392.
Full textAbstract:
Cell shape changes such as cytokinesis are driven by the actomyosin contractile cytoskeleton. The molecular rearrangements that bring about contractility in nonmuscle cells are currently debated. Specifically, both filament sliding by myosin motors, as well as cytoskeletal cross-linking by myosins and nonmotor cross-linkers, are thought to promote contractility. Here we examined how the abundance of motor and nonmotor cross-linkers affects the speed of cytokinetic furrowing. We built a minimal model to simulate contractile dynamics in the Caenorhabditis elegans zygote cytokinetic ring. This model predicted that intermediate levels of nonmotor cross-linkers are ideal for contractility; in vivo, intermediate levels of the scaffold protein anillin allowed maximal contraction speed. Our model also demonstrated a nonlinear relationship between the abundance of motor ensembles and contraction speed. In vivo, thorough depletion of nonmuscle myosin II delayed furrow initiation, slowed F-actin alignment, and reduced maximum contraction speed, but partial depletion allowed faster-than-expected kinetics. Thus, cytokinetic ring closure is promoted by moderate levels of both motor and nonmotor cross-linkers but attenuated by an over-abundance of motor and nonmotor cross-linkers. Together, our findings extend the growing appreciation for the roles of cross-linkers in cytokinesis and reveal that they not only drive but also brake cytoskeletal remodeling.