Polo-like kinases: a team that plays throughout mitosis

When the first mutant allele of the Drosophila genepolo was first characterized over 10 years ago, attention focused on the defects that centrosome behavior exhibited at various stages of development (Sunkel and Glover 1988). The subsequent realization that the serine-threonine kinase it encodes is highly conserved from yeasts to humans has provoked a flurry of investigation into the function of the enzyme. A role for the polo-like kinases (plks) in regulating centrosome behavior has been borne out in several organisms, and the enzymes have attracted further attention recently with the realization that they regulate multiple stages of mitotic progression. In this article we review the current status of our understanding of the functions of plks from the time of commitment to M phase in the activation of Cdc25, through the activation of the anaphase promoting complex (APC), to the regulation of late mitotic events essential for cytokinesis. We discuss how to reconcile the sometimes apparently disparate observations made upon plk function in different organisms.