Reproduction Abstracts

After the resumption of meiosis and fertilization, differentiated oocytes dramatically change their nature to generate totipotent zygotes. However, since transcription does not occur in oocytes and early 1-cell stage embryos, gene expression is controlled only by post-transcriptional regulation. There are huge mRNAs stored in full-grown oocytes (FGO). A part of them is not translated in FGO and MII stage oocytes, and become translated after the resumption of meiosis and fertilization, respectively. Generally, translation of mRNA is regulated by its untranslated regions (UTRs). In the present study, we examined that the role of UTRs in the alteration of cyclin A2 (CcnA2) translation after the resumption of meiosis and fertilization.

FGO and MII stage oocytes were microinjected with cRNA encoding luciferase with 5’UTR and/or 3’UTR of CcnA2. They were allowed to resume meiosis and fertilized in vitro and examined for luciferase activity.

Both of 5’UTR and 3’UTR decreased the translation of Luc cRNA in FGO. However, when meiosis was resumed, 3’UTR increased the translation, while 5’UTR decreased it. The Luc cRNA with both of two UTRs increased the translation. After fertilization, the up-regulation by 3’UTR was also observed, whereas 5’UTR showed no significant effect. These results suggest that UTRs of CcnA2 bear time-specific translational regulation, and that this regulation is largely dependent on 3’UTR.