Phase diagrams of membrane skeletons based on liquid crystal elastomer simulations

Summary form only given. Spectrin and actin filaments form membrane cytoskeletons in many cell-types, including red blood cell (RBC) and outer hair cells of the ear (OHC). To address principles of cytoskeleton self-organization, actin filaments are simulated as stiff rods in 2D interconnected by a soft network of spectrin. The phase behavior of this system under compression is qualitatively identical to that of a 2D fluid of hard rods, in which, short rods (typical of actin filaments in the red cell) show no order and long rods form a nematic phase. Networks with long actin filaments in the isotropic density regime can also be sheared into a nematic phase. Actin filaments that approximate the length of spectrin cross-linkers form a quenched nematic phase at zero external pressure. Consistent with this model, the OHC cytoskeleton exhibits locked in nematic behavior due to its large actin filament length relative to to spectrin. Tension studies of this quenched nematic state reveal a soft response in the direction perpendicular to the filaments-the direction of sound propagation through the OHC. Differing mechanical responses of cells to external stimuli highlight the importance of varied self-assembly mechanisms for cell cytoskeletons made of the same major components.