Identification of differentially expressed mRNAs in bovine preimplantation embryos.

We have characterised the changes in preimplantation embryos that occur in the mRNA population during the transition from maternal to zygotic control of embryogenesis. We connected the mRNA differential display method and RT-PCR based method that allows amplification of the whole population of messengers. In the early stages of development we have further characterised the level of individual mRNAs with the help of semiquantitative RT-PCR used with specific primers. This report concerns four of 12 cDNA fragments that appeared to be differentially expressed between the 4- and late 8-cell stages. A transcript corresponding to fragment no. 1/12 appears to be analogous to the maternal mRNA since it is abundant in 1-, 2-, 4- and 8-cell embryos and rapidly decreases in the later stages. A similar pattern of expression was revealed in the transcript corresponding to fragment no. 8/9. A transcript corresponding to fragment no. 20/8 is newly synthesised from the embryonic genome at the late 8-cell stage and its amount rapidly increases during the following stages. This messenger shows a 91.7% identity with mRNA for human S3A ribosomal protein and 92.2% identity with mRNA for Felis domesticus S3A ribosomal protein. A transcript corresponding to fragment no. 8/19 is stage-specific, being newly synthesised from an embryonic genome at the late 8-cell stage and decreasing in the later stages. This messenger shows 86.6% identity with a mouse mRNA for proline-rich protein and 91.6% identity with human mRNA for KIAA-0058 gene. A complex of these molecular markers represents a suitable tool for answering questions concerning the molecular control of major gene activation during bovine embryogenesis.

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 mitotic cell cycles that follow fertilization. This means that the regulation of gene expression in early embryos heavily relies on the translational activation or inactivation of maternal mRNAs. In mammals, the mechanisms that control the translation of maternal mRNAs have been mainly studied in the mouse when maternal to zygotic transition occurs after the first mitotic division. In other mammalian species, however, this transition occurs later after several cell cycles, and little is known concerning the regulation of maternal information during this period. To address this question, we have used rabbit pre-implantation embryos to analyze the translational activation and stability of two maternal mRNAs, mm 41 and mm61. During the cleavage period, these mRNAs exhibit distinct kinetics for both their translational activation and degradation. In addition, these mRNAs both undergo cytoplasmic polyadenylation but with different efficiencies. This polyadenylation was functionally correlated with the translational activation of these mRNAs; inhibiting polyadenylation prevented translational activation. The differential 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 species.