Entropy Production and Cytoskeletal Avalanches in Cytoskeletal Networks

Cells of higher organisms contain a dynamically remodeling filamentous network, called cytoskeleton, comprised of actin, myosin and many other molecules. The cytoskeleton endues cells with their instantaneous shapes, providing a machinery for cells to move around, generate forces and also integrate both chemical and mechanical signaling. To investigate the fundamental principles behind the self-organization of these networks, we have developed a detailed physico-chemical, stochastic model (MEDYAN, http://medyan.org) of the cytoskeletal dynamics, where the mechanical rigidity of filaments and their corresponding deformations under internally and externally generated forces are taken into account. We used MEDYAN to investigate the recently observed phenomenon of cytoquakes, where unusually large cytoskeletal remodeling processes intermittently occur. We devised an algorithm for quantifying dissipation in cytoskeletal dynamics, uncovering earthquake-like processes of gradual stress accumulation followed by sudden rupture and subsequent network remodeling. Predictions from our computer simulations are put in the context of in vitro and vivo experimental measurements.