Polo-like kinase family members function in the formation of bipolar spindles, and in yeast the polo-like kinase
plo1+ (Ohkura et al. 1995) has been shown to be necessary for cytokinesis. Additionally, human Plk1 is able to phosphorylate the kinesin-like protein MKLP1 in vitro (Lee et al. 1995). The C. elegans MKLP1 homolog
zen-4 is of interest to our lab as a null mutation results in a zygotic hypodermal enclosure defect. Furthermore, the
zen-4 germline mosaic and RNA interference phenotypes demonstrate a late cytokinesis defect (see abstract by Raich et al.). We are interested in molecules that interact with
zen-4, and C. elegans polo-like kinase is a likely candidate. A C. elegans polo-like kinase was identified by GeneFinder on cosmid K06H7. This putative polo homolog contains a catalytic domain which is 51% identical to the Drosophila polo kinase domain. C. elegans polo also contains a conserved region in the C-terminus called the Polo Domain (PD). This domain is 29 amino acids long, of which 15 amino acids are strictly conserved. C. elegans polo is 100% identical in those 15 amino acids and similar in the remaining 14. There are several Kohara clones corresponding to the predicted polo-like kinase, and RNA was transcribed in vitro using
yk206c10 and
yk383e2. RNA injection results in a variable phenotype, with most embryos showing defects in cell division, formation of the spindle poles, polar body extrusion, and completion of cytokinesis. Some of these defects are reminiscent of defects seen in
zen-4 RNA(i) embryos. Interestingly, the first few embryos produced from animals injected with lowered concentrations of RNA display enclosure defects similar to zygotic
zen-4 mutants. Further analysis will be conducted to determine the primary defect in RNA interference embryos and to determine if C. elegans polo and
zen-4 physically interact.