Cortical Actomyosin Flows are Generated by Actomyosin Cluster Vibrations in Vitro

Cortical actomyosin dynamics and flows play pivotal roles in eukaryotic cells, e.g. for cell motility, cell division and chiral morphogenesis during early embryogenesis of multicellular organisms. For many model systems myosin motors have been proposed to play a key role in the generation of cortical actomyosin dynamics and flows. However, little is known about the mechanisms behind these actomyosin flows. We reconstituted and confined minimal actin cortices inside water in oil droplets. These spherically confined actomyosin cortices exhibit directional actomyosin flow-like motions upon ATP induced contractility of the myosin motors. By combining our experiments with a theoretical description, we found that the observed direct motion of the actomyosin clusters arises from vibrations within the individual actomyosin clusters. By tracking actin clusters, we detected fingerprints of vibrational states driving their directed motions in the spherical confinement. These vibrations may provide a mechanism driving cortical actomyosin dynamics and flows in living systems.