Structure and dynamics of reconstituted contracting actin networks

Contracting networks of semi-flexible actin filaments and myosin molecular motors have essential roles in many processes in living cells including cell movement and division. To fulfill these functions, the networks must undergo continuous reorganization facilitated by network assembly and disassembly. Despite extensive research, the contractile network behavior in the presence of turnover is still not well understood. To study such networks in a controlled environment, we rely on a reconstituted system based on cell extracts encapsulated into water-in-oil droplets. Thanks to the presence of rapid network turnover, this system exhibits contractile flows that persist for hours and self-organize into a wide array of spatiotemporal patterns.  In my talk, I will focus on a size-dependent transition in the contractile behavior of the system, going from continuous contraction in smaller droplets to periodic contraction in the form of waves and spirals in larger droplets. This transition occurs at a characteristic length scale that is inversely dependent on the network contraction rate. These dynamics are recapitulated by a theoretical model, which considers the coexistence of different density-dependent mechanical states with distinct rheological properties in different regions. The model shows how large-scale contractile behaviors emerge from the interplay between network percolation essential for long-range force transmission and network rearrangements due to advection and turnover. Our findings thus demonstrate how varied contraction patterns can arise from the same microscopic constituents, merely by changing the system geometry.

zoom link: https://technion.zoom.us/j/91744993699