Size-dependent transition from steady contraction to waves in actomyosin networks with turnover

Abstract

Actomyosin networks play essential roles in many cellular processes including intracellular transport, cell division, and cell motility, exhibiting a myriad of spatiotemporal patterns. Despite extensive research, how the interplay between network mechanics, turnover and geometry leads to these different patterns is not well understood. We focus on the size-dependent behavior of contracting actomyosin networks in the presence of turnover, using a reconstituted system based on cell extracts encapsulated in water-in-oil droplets. We find that the system can self-organize into different global contraction patterns, exhibiting persistent contractile flows in smaller droplets and periodic contractions in the form of waves or spirals in larger droplets. The transition between continuous and periodic contraction 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 local density-dependent mechanical states with distinct rheological properties. The model shows how large-scale contractile behaviors emerge from the interplay between network percolation essential for long-range force transmission and rearrangements due to advection and turnover. Our findings thus demonstrate how varied contraction patterns can arise from the same microscopic constituents, without invoking specific biochemical regulation, merely by changing the systems geometry.