Figure 9.

PRC1 forms a central spindle matrix directing kinesin function during cytokinesis. PRC1 is a master regulator of the central spindle interacting with multiple motor proteins that are involved in cytokinesis. Centralspindlin, shown as MKlp1 for simplicity, controls Rho activation and inactivation, whereas KIF14 is needed for citron kinase localization to the central spindle, midbody, and, thus, its site of activity. One function of Rho is to control the activation state of citron kinase. MKlp2 is needed for both the targeting of Plk1 and the chromosomal passenger complex and, thus, for spatial control of both Plk1 and Aurora B. These kinases phosphorylate proteins required for cytokinesis, including components of the centralspindlin complex. The molecular function of KIF4 is less clear, but it too appears to be required for cytokinesis. In the absence of MKlp1 and MKlp2, early events in central spindle and cleavage furrow formation are abnormal. This leads to defects in furrow positioning and contractility. KIF14 and citron kinase are not required for these early events or late events such as midbody formation but are needed for efficient cytokinesis.