Constriction mechanism of the actomyosin ring

Cytokinesis in most eukaryotic cells is orchestrated by a contractile actomyosin ring. While many of the proteins involved are known, the mechanism of constriction remains unclear. Based on the current literature and new 3D molecular details from electron cryotomography, here we developed 3D coarse‐grained models of actin filaments, unipolar and bipolar myosins, actin crosslinkers, and membranes and simulated their interactions. Exploring a matrix of possible actomyosin configurations showed that node‐based architectures like those presently described for ring assembly result in membrane puckers not seen in EM images of real cells. Instead, actin and myosin are more likely uniformly distributed around the ring. In the model that best matches data from fluorescence microscopy, electron cryotomography, and biochemical experiments, ring tension is generated by interactions between bipolar myosins and actin, and transmitted to the membrane via unipolar myosins.