Dynamic mechanisms for membrane skeleton transitions.

The plasma membrane and the underlying skeleton form a protective barrier for eukaryotic cells. The molecular players forming this complex composite material constantly rearrange under mechanical stress. One of those molecules, spectrin, is ubiquitous in the membrane skeleton and linked by short actin filaments. In this work, we developed a generalized network model for the membrane skeleton integrated with myosin contractility and membrane mechanics to investigate the response of the spectrin meshwork to mechanical loading. We observed that the force generated by membrane bending is important to maintain a regular skeletal structure suggesting that the membrane is not just supported by the skeleton, but has an active contribution to the stability of the cell structure. We found that spectrin and myosin turnover are necessary for the transition between stress and rest states in the skeleton. Simulations of a fully connected network representing a whole cell show that the surface area constraint of the plasma membrane and volume restriction of the cytoplasm enhance the stability of the membrane skeleton. Furthermore, we showed that cell attachment through adhesions promotes cell shape stabilization.