Active mechanics in cytoskeleton plays crucial roles in several cellular behaviors. A fascinating example is the actin-myosin cytoskeletal network located at the cortical region of the cell, which can generate contractile stress and cause the cellular morphogenetic event, such as cytokinesis. It is known that also reconstituted network gels consisting of actin filaments, myosin filaments, and passive crosslinker proteins, which connect actin filaments with each other, can yield the contractile stress in macroscopic scale [1,2]. Such contractile stress is known to be caused by the activity of myosin as a motor protein [1,2]. However, myosin motor can basically just walk on an actin filament into a definite direction. Hence, contractility of a whole network is not a trivial phenomenon from a mechanical point of view.
In this presentation, I would like to talk about my recent theoretical work on such active stress in an actomyosin network. I have investigated it based on a microscopic model, in which we consider the motion of each filament but the filaments are treated as stiff bars. In the presentation, I will explain my recent finding on a generation mechanism of active contractile stress in this model, and in particular, clarify the significance of sufficient amounts of passive crosslinkers for this mechanism.
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 S. Koehler, and A. R. Bausch, PLoS one 7, e39869 (2012).