Characterization of polo-like kinase 1 during meiotic maturation of the mouse oocyte

We have characterized plk1 in mouse oocytes during meiotic maturation and a fter parthenogenetic activation until entry into the first mitotic division . Plk1 protein expression remains unchanged during maturation. However, two different isoforms can be identified by SDS-PAGE. A fast migrating form, p resent in the germinal vesicle, seems characteristic of interphase. A slowe r form appears as early as 30 min before germinal vesicle breakdown (GVBD), is maximal at GVBD, and is maintained throughout meiotic maturation. This form gradually disappears after exit from meiosis. The slow form correspond s to a phosphorylation since it disappears after alkaline phosphatase treat ment. Plk1 activation, therefore, takes place before GVBD and MAPK activati on since plk1 kinase activity correlates with its slow migrating phosphoryl ated form. However, plk1 phosphorylation is inhibited after treatment with two specific p34(cdc2) inhibitors, roscovitine and butyrolactone, suggestin g plk1 involvement in the MPF autoamplification loop. During meiosis plk1 u ndergoes a cellular redistribution consistent with its putative targets. At the germinal vesicle stage, plk1 is found diffusely distributed in the cyt oplasm and enriched in the nucleus and during prometaphase is localized to the spindle poles. At anaphase it relocates to the equatorial plate and is restricted to the postmitotic bridge at telophase. After parthenogenetic ac tivation, plk1 becomes dephosphorylated and its activity drops progressivel y. Upon entry into the first mitotic M-phase at nuclear envelope breakdown plk1 is phosphorylated and there is an increase in its kinase activity. At the two-cell stage, the fast migrating form with weak kinase activity is pr esent. In this work we show that plk1 is present in mouse oocytes during me iotic maturation and the first mitotic division. The variation of plk1 acti vity and subcellular localization during this period suggest its implicatio n in the organization and progression of M-phase. (C) 2000 Academic Press.