Gonadotropins affect Oct-4 gene expression during mouse oocyte growth

The transcription factor Oct-4 is required for the maintenance of stem cells pluripotency and is involved in the regulation of the expression of a number of developmental genes. Oct-4 is also expressed in the female gamete during folliculogenesis, but the role it plays is largely unknown. Its upstream and promoter regions have some characteristic features that make this gene a possible target of hormonal regulation. To further our understanding of Oct-4 gene expression during oocyte growth, we tested whether changes to the hormonal milieu of the ovary may affect its transcription. Using a semi-quantitative single-cell-sensitive reverse transcription-polymerase chain reaction (RT-PCR) assay, we investigated the pattern of Oct-4 expression during mouse oocyte growth in females intraperitoneally injected with pregnant mare serum gonadotropin (PMSG) alone or PMSG followed by human chorionic gonadotropin (hCG). The results of this study show that gonadotropins induced two major increases in Oct-4 expression during folliculogenesis: (1) 48 hr after PMSG injection, in oocytes isolated from primordial follicles; and (2) following a surge of hCG, in preovulatory antral oocytes. These results suggest a potential twofold role for this gene in the recruitment of oocytes for initiating growth and in the selection of oocytes for ovulation. Also, they may contribute to our knowledge of the molecular bases of oocyte growth, meiosis resumption, and acquisition of a developmental competence.