Involvement of Polo-like kinase 1 in MEK1/2-regulated spindle formation during mouse oocyte meiosis.

Our recent studies have shown that MEK1/2 is a critical regulator of microtubule organization and spindle formation during oocyte meiosis. In the present study, we found that Plk1 colocalized with p-MEK1/2 at various meiotic stages after GVBD when microtubule began to organize. Also, Plk1 was able to coimmunoprecipitate with p-MEK1/2 in metaphase I stage mouse oocyte extracts, further confirming their physical interaction. Taxol-treated oocytes exhibited a number of cytoplasmic asters, in which both Plk1 and p-MEK1/2 were present, indicating that they might be complexed to participate in the acentrosomal spindle formation at the MTOCs during oocyte meiosis. Depolymerization of microtubules by nocodazole resulted in the complete disassembly of spindles, but Plk1 remained associated with p-MEK1/2, accumulating in the vicinity of chromosomes. More importantly, when p-MEK1/2 activity was blocked by U0126, Plk1 lost its normal localization at the spindle poles, which might be one of the most vital factors causing the abnormal spindles in MEK1/2-inhibited oocytes. Taken together, these data indicate that Plk1 and MEK1/2 regulate the spindle formation in the same pathway and that Plk1 is involved in MEK1/2-regulated spindle assembly during mouse oocyte meiotic maturation.