Mouse polo-like kinase 1 associates with the acentriolar spindle poles, meiotic chromosomes and spindle midzone during oocyte maturation

We have examined the dynamics of the localisation of the polo-like kinase 1 (Plk1) during maturation of the mouse oocyte. Levels of Plk1 protein incre ase following germinal vesicle breakdown, at which time the enzyme begins t o accumulate at discrete positions on the condensing chromosomes and, subse quently, at the poles of the meiotic spindle, which moves towards the corte x of the egg. interestingly, at metaphase in both meiotic divisions, PIk1 s hows a punctate localisation along the broad spindle poles. Moreover, the p unctate distribution of Plk1 on the meiotic chromosomes appears at early an aphase to correspond to the centromeric regions. The protein relocates to t he spindle midzone during late anaphase and then associates with the midbod y at telophase. We have confirmed the specific pattern of immune-localisati on seen in fixed preparations by observing the distribution of Plk1 tagged with green fluorescent protein in living oocytes. We discuss the localisati on of the enzyme in light of the structure of the spindle poles, which are known to lack centrioles, and the highly asymmetric nature of the meiotic d ivisions.