Regulation of spontaneous meiosis resumption in mouse oocytes by various conventional PKC isozymes depends on cellular compartmentalization

In this study, we investigated the spatio-temporal distribution of conventional protein kinases C (cPKC) isoforms PKC-, PKC-I, PKC-II and PKC- in mouse oocytes. The cPKCs were present in the cytoplasm at the start of the process and migrated to the nucleus (or germinal vesicle) before germinal vesicle breakdown, except for PKC- which remained cytoplasmic. In both compartments, the fully phosphorylated form corresponding to the 'mature' enzyme was revealed for PKC-, PKC-I and PKC-II. Microinjection of specific antibodies against each isozyme in one or the other cell compartment at different times of the meiotic process, permitted us to observe the following: (1) when located in the cytoplasm at the beginning of the process, PKC- is not implicated in germinal vesicle breakdown, PKC-I and PKC- are involved in maintaining the meiotic arrest, and PKC-II plays a role in meiosis reinitiation. Furthermore, just before germinal vesicle breakdown, these cytoplasmic cPKCs were no longer implicated. (2) When located in the germinal vesicle, PKC-, PKC-I and PKC-II are involved in meiosis reinitiation. Our data highlight not only the importance of the nuclear pathways in the cell cycle progression, but also their independence of the cytoplasmic ones. Further investigations are however necessary to discover the molecular targets of these cPKCs to better understand the links with the cell cycle progression.