title: F-actin buckling coordinates contractility and severing in a biomimetic actomyosin cortex.
abstract: 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 μm. 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 ~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.
authors.affiliation: Institute for Biophysical Dynamics, James Franck Institute, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Murrell
authors.forename: Margaret L
authors.initials: ML
authors.lastname: Gardel
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D000205:Actomyosin / Q000737:chemistry*; D000818:Animals; D032701:Biomimetics; D002448:Cell Adhesion; D002645:Chickens; D019245:Compressive Strength; D003599:Cytoskeleton / Q000378:metabolism; D019281:Dimerization; D008051:Lipid Bilayers / Q000737:chemistry; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology; D024462:Myosin Type II / Q000378:metabolism; D010063:Ovum; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013314:Stress, Mechanical
chemical_list: D000199:Actins; D008051:Lipid Bilayers; D000205:Actomyosin; D024462:Myosin Type II