Time Dependent Changes in Progesterone Receptor Expression in Cumulus Cells During Meiotic Resumption of Porcine Oocytes

In this study, to investigate the time dependent changes in progesterone receptor (PR) expression in cumulus cells during meiotic resumption of porcine oocytes, each amount of PR-A and PR-B mRNA was analyzed by RT-PCR with primer sets for the PR-B region and the PR-A/B common region. The results showed that the levels of both PR-A/B and PR-B mRNA were very low in cumulus cells immediately recovered from their follicles. The cultivation with FSH and LH significantly increased the level of both PR-A/B and PR- B mRNA in cumulus cell of COCs, whereas the level of PR-B mRNA significantly decreased at 12-hr cultivation. Nevertheless, the higher level of PR-A/B mRNA was maintained up to 20-hr cultivation, suggesting that PR-A was mainly expressed in cumulus cells during cultivation from 12 hr to 20 hr. When COCs were cultured for 10 hr and then further cultured with RU486 for 10 hr, the proportion of oocytes undergoing GVBD significantly decreased in a dose dependent fashion. These results suggest that the high ratios of PR-A to PR-B in cumulus cells of COCs during 12-hr to 20-hr cultivation, are required for meiotic resumption of porcine cumulus-