Zygotic regulation of maternal cyclin A1 and B2 mRNAs

At the midblastula transition? the Xenopus laevis embryonic cell cycle is r emodeled from rapid alternations between S and M phases to become the compl ex adult cell cycle, Cell cycle remodeling occurs after zygotic transcripti on initiates and is accompanied by terminal downregulation of maternal cycl ins A1 and BZ. We report here that the disappearance of both cyclin A1 and B2 proteins is preceded by the rapid deadenylation of their mRNAs. A specif ic mechanism triggers this deadenylation, This mechanism depends upon discr ete regions of the 3' untranslated regions and requires zygotic transcripti on, Together, these results strongly suggest that zygote-dependent deadenyl ation of cyclin A1 and cyclin BZ mRNAs is responsible for the downregulatio n of these proteins. These studies also raise the possibility that zygotic control of maternal cyclins plays a role in establishing the adult cell cyc le.