Differential regulation of the translation and the stability of two maternal transcripts in preimplantation rabbit embryos

In most species, transcription is essentially silent during the first mitot ic cell cycles that follow fertilization. This means that the regulation of gene expression in early embryos heavily relies on the translational activ ation or inactivation of maternal mRNAs. In mammals, the mechanisms that co ntrol the translation of maternal mRNAs have been mainly studied in the mou se when maternal to zygotic transition occurs after the first mitotic divis ion. In other mammalian species, however, this transition occurs later afte r several cell cycles, and little is known concerning the regulation of mat ernal information during this period. To address this question, we have use d rabbit preimplantation embryos to analyze the translational activation an d stability of two maternal mRNAs, mm 41 and mm61. During the cleavage peri od, these mRNAs exhibit distinct kinetics for both their translational acti vation and degradation. In addition, these mRNAs both undergo cytoplasmic p olyadenylation but with different efficiencies. This polyadenylation was fu nctionally correlated with the translational activation of these mRNAs; inh ibiting polyadenylation prevented translational activation. The differentia l efficiency of cytoplasmic polyadenylation, driven by cis-elements in the 3' untranslated region of these mRNAs, was also observed in Xenopus laevis embryos, which emphasizes the high conservation of this mechanism between s pecies. (C) 2000 Wiley-Liss, Inc.