CELL CYCLE CONTROL IN EARLY DEVELOPMENT

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In this research project, we obtained the-following results using the amphibian Xenopus system. (1) Contrary to the generally accepted view, nuclear material is essential for the activation of MPF during oocyte maturation. (2) Cyclin B2, but not cyclin B1, is required for bipolar spindle formation during oocyte maturation. (3) The checkpoint kinase Chk1 is required for G2 arrest of oocytes and contains an autoinhibitory region at its C-terminus. (4) Wee1 kinase is absent in meiosis I oocytes and this lack of Weel is essential for entry into meiosis II. (5) The AUUUA motif present in the 3'UTR is essential for translational arrest of Mos mRNA upon fertilization. (6) Nek2 kinase is essential for the formation and maintenance of centrosomes in cleaving embryos. .(7) Two distinct Weel isoforms, maternal Wee1A and zygotic Wee1B, exist in early embryos and are involved in the maternal/zygotic transition of the cell cycle. (8) Chk1 kinase is activated transiently at a physiological replication checkpoint at the midblastula transition and directly targets Cdc25A for degradation at this transition.