Active tension and membrane friction mediate cortical flows and blebbing in a model actomyosin cortex

Abstract

Blebs, spherical membrane bulges of the cell membrane, are ubiquitous structures observed in various biological phenomena, including apoptosis, cell division, to bleb-based cell migration. The mechanics of blebbing have been characterized in terms of the actin cytoskeleton beneath the cell membrane. However, how changes in cortical mechanics relate to changes in the physical behaviors of the cell remains unclear. Here, we reconstitute a minimal model of the actomyosin cortex within liposomes. Upon laser ablation of the cortex, myosin-induced mechanical stresses are relaxed by different mechanisms - either cortical flows or membrane blebbing. For cortical flows, the cortex-membrane composite behaves as a viscoelastic fluid. By contrast, for ablation-induced blebbing, elastic stresses are accumulated, and the cortex behaves as a solid with a stress yield. These results highlight pivotal roles for membrane elasticity, cytoskeleton, and pressure in the mechanical responses of the actomyosin cortex.