Cytoplasmic and nuclear phospholipase C-β1 relocation:: Role in resumption of meiosis in the mouse oocyte

The location of the phospholipase C beta1-isoform (PLC-beta1) in the mouse oocyte and its role in the resumption of meiosis were examined. We used specific monoclonal antibodies to monitor the in vitro dynamics of the subcellular distribution of the enzyme from the release of the oocyte from the follicle until breakdown of the germinal vesicle (GVBD) by Western blotting, electron microscope immunohistochemistry, and confocal microscope immunofluorescence. PLC-beta1 became relocated to the oocyte cortex and the nucleoplasm during the G2/M transition, mainly in the hour preceding GVBD. The enzyme was a 150-kDa protein, corresponding to PLC-beta 1a. Its synthesis in the cytoplasm increased during this period, and it accumulated in the nucleoplasm. GVBD was dramatically inhibited by the microinjection of anti-PLC-beta1 monoclonal antibody into the germinal vesicle (GV) only when this accumulation was at its maximum. In contrast, PLC-gamma1 was absent from the GV from the time of release from the follicle until 1 h later, and microinjection of anti-PLC-gamma1 into the GV did not affect GVBD. Our results demonstrate a relationship between the relocation of PLC-beta1 and its role in the first step of meiosis.