The Role of Progesterone in Oocyte Acquisition of Developmental Competence

It is generally accepted that progesterone (P4) is a key regulator of reproductive function in mammals. In cattle, the primary focus of P4's actions has been uterine receptivity and maintenance of pregnancy. Studies in mammalian laboratory species and ovarian derived cell lines also highlight their role in ovarian function. Extensive research in non-mammalian species has elucidated a critical role for P4 and both its nuclear and membrane-bound receptors in oocyte maturation and ovulation. Until recently, such a role in mammalian oocytes has been disputed. However, as oestrous synchronization regimes are constantly tweaked and revised to maximize pregnancy rates to artificial insemination in cattle, the importance of P4 priming of the dominant ingfollicle is once again tak centre stage. Sequencing of the bovine genome and the development of multiple transcriptomic data mining tools have facilitated an explosion in global transcriptome profiling of immature and matured oocytes and their surrounding cumulus cells. Many of the differentially regulated genes and their associated preferentially populated pathways appear to be P4 regulated in other tissues. Therefore, attention is once again turning to a potential role for P4 in ovulatory follicle development and oocyte maturation in cattle. The current review summarizes the most recent findings in these areas.