Biological & Soft Matter Seminar: Scaling behavior in steady-state contractile actomyosin network flow

Abstract:

Contractile actomyosin networks have an essential role in many cellular processes including cell division, intracellular transport and cell motility. While the molecular components involved are largely known, we still do not understand what controls the large scale properties of these networks. Synthetic, cell-free systems offer a valuable platform to explore cytoskeletal dynamics over a broad range of parameters, detached from the complexity of the living cell. Here, we generate contractile actomyosin networks with rapid turnover in vitro, by encapsulating cytoplasmic Xenopus egg extracts into cell-sized ‘water-in-oil’ droplets. Within minutes, the networks reach a dynamic steady-state with continuous inward flow. The networks exhibit homogenous, density-independent contraction for a wide range of physiological conditions, indicating that the myosin-generated stress driving contraction is proportional to the effective network viscosity. We further find that the contraction rate approximately scales with the network turnover rate, but this relation breaks down in the presence of excessive crosslinking or branching. Our findings suggest that cells use diverse biochemical mechanisms to generate robust, yet tunable, actin flows by regulating two parameters: turnover rate and network geometry.