Expression in in-vivo and in-vitro growing and maturing oocytes: focus on regulation of expression at the translational level.

Studies of expression in in-vivo and in-vitro maturing oocytes have the potential to elucidate signalling pathways involved in the intricate crosstalk between the oocyte and its somatic compartment during differentiation and morphogenetic processes, and the origin of disturbances in oocyte maturation possibly involved in reduced fertility. This review summarizes data on expression studies with focus on regulation of expression at the translational level in the maturing oocyte. The regulation of gene expression at the translational level as analysed in in-vitro maturing oocytes is complex and highly conserved between different species. It is characterized by differential degradation, and by storage and recruitment of distinct maternal mRNAs involving conserved consensus sequences in the 5' or 3' untranslated regions (UTRs) of mRNAs. Proteins interacting with such sequences affect the temporal 3' polyadenylation, and bring the 5' and 3' UTRs of mRNAs into close proximity for efficient initiation of translation. Post-translational modifications of mRNA-associated proteins contribute to maturation- and developmentally controlled and to cell cycle-dependent expression. New methodologies for analysis of ovary-specific gene expression and function of genes in oogenesis are also reviewed, e.g. RT-PCR, SAGE-PCR, real-time rapid cycle fluorescence monitored RT-PCR, differential display techniques, and microinjection of anti-sense RNA, double-stranded RNAs or mRNAs expressing green fluorescent protein-tagged proteins into maturing oocytes.