Cytoplasmic and nuclear phospholipase C-beta 1 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 spe cific monoclonal antibodies to monitor the in vitro dynamics of the subcell ular distribution of the enzyme from the release of the oocyte from the fol licle until breakdown of the germinal vesicle (GVBD) by Western blotting, e lectron microscope immunohistochemistry, and confocal microscope immunofluo rescence. PLC-beta1 became relocated to the oocyte cortex and the nucleopla sm during the G2/M transition, mainly in the hour preceding GVBD. The enzym e was a 150-kDa protein, corresponding to PLC-beta 1a. Its synthesis in the cytoplasm increased during this period, and it accumulated in the nucleopl asm. GVBD was dramatically inhibited by the microinjection of anti-PLC-beta 1 monoclonal antibody into the germinal vesicle (GV) only when this accumul ation was at its maximum. In contrast, PLC-gamma1 was absent from the GV fr om the time of release from the follicle until 1 h later, and microinjectio n of anti-PLC-gamma1 into the GV did not affect GVBD. Our results demonstra te a relationship between the relocation of PLC-beta1 and its role in the f irst step of meiosis.