(W393) ACCUMULATION OF CYCLIN-DEPENDENT KINASE-1 AT THE ACQUISITION OF MEIOTIC COMPETENCE BY OOCYTES IS POST-TRANSCRIPTIONALLY REGULATED BY A MECHANISM DEPENDENT ON THE GRANULOSA CELLS.
Clarke, Hugh1, Cui, Shanjin1, Allard, Patrick1, Gauthier, France1, 1 McGill University, Montreal, QC, Canada
ABSTRACT- During growth, prophase-arrested oocytes acquire the ability to undergo meiotic maturation, which is a transition to M-phase of the cell cycle. Such oocytes are termed meiotically competent. Previous work has shown that fully grown meiotically competent oocytes of the mouse contain more cyclin-dependent kinase (cdk)-1 and cyclin B than do small meiotically incompetent oocytes. Here, we examined growing oocytes specifically during the transition from incompetence to competence. Cdk-1 protein increased 4.5-fold during this 2-day interval, whereas p42/p44 ERK and tubulin increased less than 1.5-fold. In contrast, cdk-1 mRNA increased only 1.5-fold during the same period, which was similar to the increase in other tested mRNAs. Thus, the increase in cdk-1 protein cannot be attributed to increased mRNA template. To identify mechanisms responsible for the increase in cdk-1, we obtained incompetent oocytes and cultured them for four days in the presence or absence of the surrounding granulosa cells. Cdk-1 increased 2.3-fold in granulosa-enclosed oocytes, but only 1.1-fold in granulosa-free oocytes. Moreover, the granulosa-enclosed oocytes acquired meiotic competence at a higher frequency than the granulosa-free oocytes. We propose that signals sent by the surrounding granulosa cells trigger translational activation in oocytes of mRNAs encoding cdk-1 and possibly other proteins required for entry into M-phase, and that this confers meiotic competence. Supported by the Program in Oocyte Health of the Canadian Institutes of Health Research and the Fonds de la recherche en santé du Québec.
KEY WORDS: oogenesis, cell cycle, translational control, granulosa