Fig. 1.

Model of the actomyosin behavior and experimental setup. (A) Sketch of a transiently cross-linked actin network with myosin bipolar filaments. Unbinding of a cross-linker releases elastic tension locally; the cross-linker will rebind to the network, preserving its elastic properties but causing a loss of stored elastic energy. Myosin power strokes have the effect of modifying the equilibrium length of the adjacent strands $\mathit{R}$, leading to an increase of the tension (SI Text, S2). (B) Transmission image of a cell and setup. (C) Model of the mechanical components of the cell and microplate system. Microplates impose that the vertical force equilibrating the cortical tension is linked to the cell length L with $F=k\left(L_0-L\right)$. Tension along the actomyosin cortex (green surface) is anisotropic and has values σ and ${\sigma }_{\perp }$ along directions ${\mathit{e}}_s$ and ${\mathit{e}}_{\varphi }$. Actin treadmilling provides a boundary condition at the cell leading edge, and the actin cortex undergoes a retrograde flow away from the plates.