Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 109, Issue 51, Pages 20820-20825Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1214753109
Keywords
cytoskeleton; active gels; nonequilibrium; myosin II
Categories
Funding
- Burroughs Wellcome Fund
- Packard Foundation
- National Institutes of Health [DP10D00354]
- Materials Research Science and Engineering Center at University of Chicago
- National Science Foundation Institute for Complex Adaptive Matter (ICAM)
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [820054] Funding Source: National Science Foundation
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Here we develop a minimal model of the cell actomyosin cortex by forming a quasi-2D cross-linked filamentous actin (F-actin) network adhered to a model cell membrane and contracted by myosin thick filaments. Myosin motors generate both compressive and tensile stresses on F-actin and consequently induce large bending fluctuations, which reduces their effective persistence length to <1 mu m. Over a large range of conditions, we show the extent of network contraction corresponds exactly to the extent of individual F-actin shortening via buckling. This demonstrates an essential role of buckling in breaking the symmetry between tensile and compressive stresses to facilitate mesoscale network contraction of up to 80% strain. Portions of buckled F-actin with a radius of curvature similar to 300 nm are prone to severing and thus compressive stresses mechanically coordinate contractility with F-actin severing, the initial step of F-actin turnover. Finally, the F-actin curvature acquired by myosin-induced stresses can be further constrained by adhesion of the network to a membrane, accelerating filament severing but inhibiting the long-range transmission of the stresses necessary for network contractility. Thus, the extent of membrane adhesion can regulate the coupling between network contraction and F-actin severing. These data demonstrate the essential role of the nonlinear response of F-actin to compressive stresses in potentiating both myosin-mediated contractility and filament severing. This may serve as a general mechanism to mechanically coordinate contractility and cortical dynamics across diverse actomyosin assemblies in smooth muscle and nonmuscle cells.
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