Timely translation during the mouse oocyte-to-embryo transition

In the mouse, completion of oocyte maturation and the initiation of preimpl antation development occur during transcriptional silence and depend on the presence and translation of stored mRNAs transcribed in the growing oocyte . The Spin gene has three transcripts, each with an identical open reading frame and a different 3' untranslated region (UTR). beta-galactosidase-tagg ed reporter transcripts containing each of the different Spin 3'UTRs were i njected into oocytes and zygotes and beta-galactosidase activity was monito red. Results from these experiments suggest that differential polyadenylati on and translation occurs at two critical points in the oocyte-to-embryo tr ansition - upon oocyte maturation and fertilization - and is dependent on s equences in the 3'UTR, The stability and mobility shifts of ten other mater nal transcripts were monitored by reprobing a northern blot of oocytes and embryos collected at 12 hour intervals after fertilization. Some are more s table than others and the upward mobility shift associated with polyadenyla tion correlates with the presence of cytoplasmic polyadenylation elements ( CPEs) within about 120 nucleotides of the nuclear polyadenylation signal, A survey of the 3' UTRs of expressed sequence tag clusters from a mouse 2-ce ll stage cDNA library indicates that about one third contain CPEs. We sugge st that differential transcript stability and a translational control progr am can supply the diversity of protein products necessary for oocyte matura tion and the initiation of development.