Figure 5.

Active viscous membrane shell model for cortical polarization. (Left) Schematics of the mechanical parameters involved in the model depicted on the initial spherical state of the cell: the myosin activity (ςΔμ) generates an active tension τ^a = ςΔμe₀/2 in the viscous cortex of thickness e₀ and viscosity η under permanent actomyosin turnover. The cortical tension balances the pressure difference across the cell according to Laplace’s law: P_int-P_ext = 2 τ^a/R₀. (Right) Result of the numerical simulation is represented here. Stationary polarized state of the cell is obtained numerically by locally weakening the active tension at the bead location. The perturbation generates a cortical flow toward the opposite pole, whose normalized amplitude V is rendered using a color gradient. The cortical flow perturbs the cortical actomyosin thickness, as evidenced by the variation in the shell thickness, and polarizes the cell shape.