The major goal of this proposal is to understand the posttranscriptional control of vertebrate oocyte meiosis. Using Xenopus material, it is now established that several mRNAs that are dormant in prophase I arrested oocytes undergo cytoplasmic polyadenylation-induced translational activation during meiotic maturation. A particular sequence, the cytoplasmic polyadenylation element (CPE), which resides in the 3' untranslated region of responding mRNAs, directs the timing and extent of polyadenylation. The CPE is bound by CPEB, a protein that is essential for polyadenylation, translation, and oocyte maturation. During oocyte maturation, CPEB is phosphorylated by two different kinases, one that acts early and one that acts late. The early phosphorylation appears to be important for the activation of polyadenylation while the late phosphorylation is closely correlated with the eventual destruction of CPEB. Each of these events will be examined in detail. A new CPEB associated factor, CAF-1, has been isolated and cloned. Aside from interacting with CPEB, CAF-1 also binds components of the translation machinery, where it seems to play a critical role in mRNA masking prior to the onset of polyadenylation. A detailed analysis of CAF-1 and its interactions with CPEB and other proteins will be undertaken. A dominant negative mutant form of CPEB inhibits polyadenylation and translation in injected Xenopus oocytes. This mutant fails to bind a newly identified CPEB associated protein, suggesting that this protein is involved in polyadenylation. This new CPEB-associated protein will be isolated, cloned, and characterized. Finally, CPEB does not appear to be uniformly distributed in oocytes, but instead is concentrated locally in the animal hemisphere. The mechanism responsible for, and the biological significance of, this localization will be investigated.
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