Active elasticity of cells

The mechanics of animal cells is determined strongly by contractility of the actomyosin system, which in turn is regulated mainly through the small GTPase Rho. We first discuss the case of strongly adherent cells with stress fibers, whose forces can be measured with traction force microscopy on soft elastic substrate. Using optogenetics to locally activate Rho and a simple model for active viscoelasticity, we find that stress fibers respond mainly elastically and transmit forces quickly over large distances, despite the rapid turnover of their molecular constituents. We then discuss cortical contraction waves in starfish oocytes, where Rho is activated after degradation of a cell cycle kinase. We find that the resulting wave depends on cell mechanics and shape, as described by a chemo-mechanical model.