Non Equilibrium Steady State Dynamics of Contractile Actin Networks

Abstract

The actin cytoskeleton plays a major role during the initial stages of embryonic development. In particular, the actin cytoskeleton can switch, in a cell-cycle dependent manner, into a contractile state and exhibit large scale flows which are essential for the organization and the establishment of polarity in early embryos. For example, myosin-driven contractile flows are essential for the initial cortical polarization in many species, while bulk actin network contraction can drive directional transport in large oocytes. We developed a reconstituted model system to study the onset of contraction in actomyosin networks, and emulate these processes in artificial cells. We encapsulate Xenopus cell extracts in cell-sized water-in-oil emulsions, and introduce different types of actin nucleators at the interface or in bulk, to reconstitute cortical or bulk actin networks, respectively. Importantly, the presence of dynamic turnover in our system allows these networks to attain a dynamic steady state characterized by contractile actin flows which can persist for hours. We add single wall carbon nanotubes as inert fluorescent probes to map the network dynamics at high spatial and temporal resolution, and uncover the self-organized dynamics that lead to the formation of these steady state contractile networks.