REPRODUCTION RESEARCH 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 Francois Paradis, Susan Novak, Gordon K Murdoch 1 , Michael K Dyck, Walter T Dixon and George R Foxcroft Swine Reproduction-Development Program, Department of Agricultural, Food and Nutritional Science, 4-10 Agriculture-Forestry Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2P5 and 1 Department of Animal and Veterinary Science, College of Agricultural and Life Sciences, University of Idaho, Moscow, Idaho 83844-2010, USA Correspondence should be addressed to F Paradis; Email: fparadis@ualberta.ca Abstract This study aimed to describe the abundance and localization of BMP2, BMP6, BMP15, GDF9, BMPR1A, BMPR1B, BMPR2 and TGFBR1 mRNA 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 of BMP6 mRNA, which was absent in GC, all genes were expressed in every cell type. Although BMP6, BMP15 and GDF9 mRNA were most abundant in the oocyte, their expression remained relatively constant during follicular development. By contrast, receptor BMPR1B and TGFBR1 expressions in the GC and TC were temporally regulated. BMPR1B mRNA abundance was positively correlated with plasma oestradiol (E 2 ) suggesting that its regulation by oestrogen may be implicated in normal folliculogenesis. Interestingly, the increase in BMPR1B mRNA 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-b superfamily and their receptors, and provide evidence to support a role for BMP15 and BMPR1B during ovulation. Reproduction (2009) 138 115–129 Introduction Ovarian follicular development in large domestic mammals is a long and intricate process that ultimately results in the ovulation of a subset of one or more oocytes potentially competent to support fertilization and embryonic development. Since ovulation rate and oocyte quality can be important determinants of reproductive efficiency, it is essential to understand the regulation of follicular growth leading to ovulation. It is now widely accepted that during the later phases of follicular growth, the processes of recruitment and selection establish a preovulatory follicle population characteristic of each species (Hunter et al. 2004). At the onset of the follicular phase in the pig, a pool of w50 follicles are recruited to actively grow, from which the preovulatory population of 12–20 follicles will be selected for ovulation (Foxcroft & Hunter 1985, Hunter et al. 2004). These processes are closely regulated by endocrine and paracrine factors, including the gonadotrophins, metabolic factors and several local growth factors. Nutritional manipulations modify sow fertility and increased lactational catabolism in primiparous sows has detrimental consequences for embryonic survival by day 30 of gestation in the subsequent litter (Foxcroft 1997). Nutritional restriction during the last week of lactation was also shown to exert detrimental effects on follicle and oocyte quality (Zak et al. 1997). Using in vitro techniques, these authors demonstrated that 1) the oocytes recovered from the presumptive preovula- tory follicles of feed-restricted sows were less capable of q 2009 Society for Reproduction and Fertility DOI: 10.1530/REP-08-0538 ISSN 1470–1626 (paper) 1741–7899 (online) Online version via www.reproduction-online.org