Actomyosin ring

The actomyosin ring operates in contractile motion,[3] although the mechanism on how or what triggers the constriction is still an evolving topic.

[8] Activation of the cell-cycle kinase (e.g. Rho-kinases) during telophase initiates constriction of the actomyosin ring by creating a groove that migrates in an inward motion.

Rho-kinases such as ROCK1 has been found to regulate actomyosin contraction through phosphorylation of the myosin light chain (MLC).

In animals, the ring forms along the cleavage furrow on the inside of the plasma membrane then splits by abscission.

These structures are not made out of actomyosin, but serve a similar role in constricting and permitting cytokinesis.

Fig.1. Cell cycle showing the formation of the actomyosin ring during telophase or early cytokinesis stage.
Fig. 2. The actomyosin ring induces formation of the cleavage furrow (4th from top) to assist cell cleavage.