On page 1391, Jantsch-Plunger et al. describe a protein that regulates both the structure of the late mitotic spindle and the function of the contractile ring. CYK-4, therefore, conceptually links microtubules to actin, and mitosis to cytokinesis.
Worms with a cyk4ts mutation were isolated in an embryonic-lethal screen. In the first embryonic division, the mutant cells form a cleavage furrow that ingresses but then regresses. The central spindle, a set of microtubule bundles that normally lies between the separating genomes, is reduced and disorganized. In wild-type cells, both CYK-4 and the kinesin-like protein ZEN-4 localize to the central spindle, and they rely on each other for their localization. CYK-4 may help to cluster multiple copies of ZEN-4 so the ZEN-4 can assemble anti-parallel microtubules into a central spindle.
Although CYK-4 is required for organizing the central spindle,...
