Dynamic Balance between Force Generation and Relaxation Facilitates Pulsatile Contraction of Actomyosin

Actomyosin contractility regulates various biological processes including cell migration, muscle contraction, and tissue morphogenesis. Cell cortex underlying a membrane, which is a representative actomyosin network in eukaryote cells, exhibits dynamic contractile behaviors. Interestingly, the cell cortex shows reversible aggregation of actin and myosin called pulsatile contraction in diverse cellular phenomena. While contractile behaviors of actomyosin machinery have been studied extensively in several in vitro experiments and computational studies, the pulsatile contraction of actomyosin networks observed in vivo has not been recapitulated well. Here, we employed an agent-based computational model based on Brownian dynamics to identify critical factors facilitating the pulsatile contraction of actomyosin networks. We found that the strong pulsatile contraction of actomyosin networks only occurs when there is subtle balance between force generation from motors, global force relaxation via actin turnover, and local force relaxation via angle-dependent actin severing. Our study provides critical insights into understanding the mechanisms and roles of the pulsatile contraction observed in cells.