Expression, Regulation, and Function of Progesterone Receptors in Bovine Cumulus Oocyte Complexes During In Vitro Maturation1

Abstract

Progesterone (P4) exerts its effects by binding to specific genomic (nPR-A/B) and non-genomic (mPRalpha/beta, PGRMC1/2) receptors. P4 has a role in the regulation of the ovulatory cycle, but its participation in oocyte maturation in mammals has not yet been clarified. Therefore, the aim of the present study was to characterize the protein expression of P4 receptors (PRs) in bovine oocytes and cumulus cells during in vitro maturation (IVM) and to study the effect of P4 and its receptors on oocyte developmental competence. Cumulus-oocyte complexes (COCs) were subjected to IVM, in vitro fertilization, and in vitro culture. IVM was performed for 24 h in the presence or absence of P4, luteinizing hormone (LH), follicle-stimulating hormone (FSH), trilostane, promegestone (R5020), mifepristone (RU 486), or antibodies against mPRalpha or mPRbeta. Protein expression of PRs was studied by Western blotting and immunofluorescence. The results demonstrate the presence of both genomic and nongenomic PRs in bovine COCs. The dynamic changes observed in the protein expression of PRs following IVM or in response to supplementation with LH, FSH, or P4 suggest an important role during bovine oocyte maturation. Inhibition of P4 synthesis by cumulus cells or blocking of nPR and mPR alpha activity produced a decrease in bovine embryo development, indicating that P4 intracellular signaling is mediated by its interaction with nuclear and membrane PRs and is important for oocyte developmental competence.