Encapsulated Actomyosin Patterns Drive Cell-Like Membrane Shape Changes

Abstract

Cell shape changes from locomotion to cytokinesis are, to a large extent, driven by myosin-driven remodeling of cortical actin patterns. Passive crosslinkers such as α-actinin and fascin as well actin nucleator Arp2/3 complex largely determine the architecture and connectivity of actin network patterns; consequently, they regulate network remodeling and membrane shape changes. Membrane constriction in animal cell cytokinesis proceeds by assembly and contraction of a contractile ring pattern rich in α-actinin and myosin at the equator of the cell cortex, with which the ring is contiguous. Here we reconstitute actomyosin networks inside cell-sized lipid bilayer vesicles and show that, depending on vesicle size and concentrations of α-actinin and fascin, actomyosin networks assemble into ring and aster-like patterns. Anchoring actin to the membrane enhances the interaction of the contractile networks with lipid membrane but does not change the architecture of the patterns. A membrane-bound actomyosin ring exerts force and constricts the membrane. An Arp2/3 complex-mediated actomyosin cortex is shown to assemble a ring-like pattern at the equatorial cortex and contribute to myosin-driven clustering of the cortex and consequently membrane deformation. An active gel theory unifies a model for the observed membrane constriction and protrusion induced by the membrane-bound actomyosin networks.