Germinal vesicle material is dispensable for oscillations in cdc2 and MAP kinase activities, cyclin B degradation and synthesis during meiosis in Xenopus oocytes

We have investigated at a molecular level the requirements for germinal vesicle (nuclear) material during the course of meiosis in Xenopus oocytes. We present the localization of some cell cycle proteins in stage VI oocytes; most of those analyzed are cytoplasmic, although some (MAD, 26S proteasome) are distributed between the cytoplasm and the germinal vesicle. By analyzing changes in individual oocytes, we find that the unphosphorylated form of cyclin B2 disappears and the phosphorylated form is then degraded in both nucleated and enucleated oocytes. Enucleated oocytes are also capable of resynthesizing both cyclin B1 and cyclin B2 after the initial degradation and of reactivating cdc2 kinase. Synthesis of mos protein and activation of MAP kinase concomitant with cdc2-cyclin B reactivation are also unaffected by prior removal of the germinal vesicle.