Contractile ring formation

During cytokinesis the actin–myosin contractile ring forms between two daughter cells, pinching them apart. On page 391, Wu et al. demonstrate that the contractile ring in fission yeast arises from a band of nodes rather than from one single spot, as previously proposed.

Previous experiments yielded two countervailing views of how the actin–myosin ring forms. In one scenario, an actin cable was thought to extend from a single progenitor spot that contained Mid1p/anillin, a large adaptor protein known to be involved in ring formation. In the alternate scenario, Mid1p was thought to accumulate in multiple nodes that then coalesced into a ring.

Using a series of fluorescently tagged proteins, Wu et al. found that myosin-II appeared around the equator of the cell before anaphase and was concentrated in a large number of...