Morphogenesis during Xenopus gastrulation requires Wee1-mediated inhibition of cell proliferation

Major developmental events in early Xenopus embryogenesis coincide with changes in the length and composition of the cell cycle. These changes are mediated in part through the regulation of CyclinB/Cdc2 and they occur at the first mitotic cell cycle, the mid-blastula transition (MBT) and at gastrulation. In this report, we investigate the contribution of maternal Wee1, a kinase inhibitor of CyclinB/Cdc2, to these crucial developmental transitions. By depleting Wee1 protein levels using antisense morpholino oligonucleotides, we show that Wee1 regulates M-phase entry and Cdc2 tyrosine phosphorylation in early gastrula embryos. Moreover, we find that Weel is required for key morphogenetic movements involved in gastrulation, but is not needed for the induction of zygotic transcription. In addition, Weel is positively regulated by tyrosine autophosphorylation in early gastrula embryos and this upregulation of Weel activity is required for normal gastrulation. We also show that overexpression of Cdc25C, a phosphatase that activates the CyclinB/Cdc2 complex, induces gastrulation defects that can be rescued by Weel, providing additional evidence that cell cycle inhibition is crucial for the gastrulation process. Together, these findings further elucidate the developmental function of Weel and demonstrate the importance of cell cycle regulation in vertebrate morphogenesis.