Zygotic Regulation of Maternal Cyclin A1 and B2 mRNAs

Abstract

At the midblastula transition, the Xenopus laevis embryonic cell cycle is remodeled from rapid alternations between S and M phases to become the complex adult cell cycle. Cell cycle remodeling occurs after zygotic transcription initiates and is accompanied by terminal downregulation of maternal cyclins A1 and B2. We report here that the disappearance of both cyclin A1 and B2 proteins is preceded by the rapid deadenylation of their mRNAs. A specific mechanism triggers this deadenylation. This mechanism depends upon discrete regions of the 3′ untranslated regions and requires zygotic transcription. Together, these results strongly suggest that zygote-dependent deadenylation of cyclin A1 and cyclin B2 mRNAs is responsible for the downregulation of these proteins. These studies also raise the possibility that zygotic control of maternal cyclins plays a role in establishing the adult cell cycle.

ACKNOWLEDGMENTS

We thank J. Sible, H. B. Osborne, and D. L. Weeks for critical reading of the manuscript and H. B Osborne for pGbORF/mosEDEN and Paul Krieg for pGS17.

This work was supported by a Basil O'Connor award (F 498–758) from the March of Dimes Birth Defects Foundation, a DERC Pilot and Feasibility award (DERC-NIH DK252295), and a Carver Trust Medical Research Initiative grant from the Roy J. Carver Charitable Trust.