Temporal regulation of BMP2, BMP6, BMP15, GDF9, BMPR1A, BMPR1B, BMPR2 and TGFBR1 mRNA expression in the oocyte, granulosa and theca cells of developing preovulatory follicles in the pig

Abstract

This study aimed to describe the abundance and localization ofBMP2,BMP6,BMP15,GDF9,BMPR1A,BMPR1B,BMPR2andTGFBR1mRNA during pig preovulatory follicular development and to evaluate their implication in improving follicular maturity in the preovulatory period preceding the second versus first post-weaning oestrus. Oocytes, granulosa (GC) and theca cells (TC) were recovered from antral follicles of primiparous sows at day 1, 2 and 4 after weaning and at day 14, 16 and 20 of their subsequent oestrous cycle. Real-time PCR analysis revealed that with the exception ofBMP6mRNA, which was absent in GC, all genes were expressed in every cell type. AlthoughBMP6,BMP15andGDF9mRNA were most abundant in the oocyte, their expression remained relatively constant during follicular development. By contrast, receptorBMPR1BandTGFBR1expressions in the GC and TC were temporally regulated.BMPR1BmRNA abundance was positively correlated with plasma oestradiol (E2) suggesting that its regulation by oestrogen may be implicated in normal folliculogenesis. Interestingly, the increase inBMPR1BmRNA and protein abundance during the periovulatory period in GC and TC suggests a role for bone morphogenetic protein (BMP) 15 in the ovulatory process. Finally, expression of these ligands and receptors was not associated with potential differences in follicle maturity observed during the second versus first post-weaning preovulatory follicular wave. In conclusion, our results clearly demonstrate the presence of a complex signalling system within the pig follicle involving the transforming growth factor-β superfamily and their receptors, and provide evidence to support a role for BMP15 and BMPR1B during ovulation.