Oral Presentation Annual Meetings of the Endocrine Society of Australia and Society for Reproductive Biology and Australia and New Zealand Bone and Mineral Society 2016

Maturational events in ovarian follicles from ewes having heterozygous mutations in both the BMP15 (I+) and BMPRIB (B+) genes (I+B+) with high ovulation rates (OR) compared to wild-types (++) with low OR (#61)

Zaramasina Clark 1 , Kenneth McNatty 1 , Derek Heath 1 , Jenny Juengel 2 , Janet Pitman 1
  1. School of Biological Sciences, Victoria University of Wellington, Wellington
  2. Invermay Agricultural Centre, AgResearch, Mosgiel, Otago, New Zealand

Maturational events in ovarian follicles that lead to the attainment of developmentally-competent oocytes are not fully understood. To investigate these events in low OR species is problematic as normally, only 1-2 follicles ovulate each reproductive cycle. To overcome this, we investigated the morphological and molecular characteristics of granulosa cells (GC), cumulus cells (CC) and oocytes in both growing and ‘presumptive pre-ovulatory’ follicles in ewes with normal (++) and high (I+B+) OR. We hypothesised that follicles with expanded CC-oocyte complexes were ‘presumptive pre‑ovulatory’ follicles and that functional similarities in these follicles between the genotypes signify some of the key events involved during the final maturational stages. Ewes (++: N=10, OR=1-3; I+B+: N=9, OR=4-8) had CIDRs inserted for 10 days. Prostaglandin F2α was administered 24h before, and ovaries were collected 52h after, CIDR removal. From each individual follicle ≥1mm in diameter, CC and denuded oocytes, as well as GC were collected for analyses of gene expression and cAMP responses to gonadotrophins, respectively. The diameters of pre-ovulatory follicles were smaller (P<0.0001) in I+B+ (3.5±0.1mm) compared to ++ (5.7±0.6mm) ewes. In pre-ovulatory follicles, cAMP responses of GC to gonadotrophins were not different between genotypes when standardised for GC number, but total cAMP was increased (P<0.0001) in ++ ewes, due to greater GC numbers/follicle. Expression of key genes involved in late maturational events (e.g. HAS2, VCAN, PGR) was increased in expanded, compared to non-expanded, CC and were similar between genotypes. Expression of a regulatory gene involved in protein processing (HSP90B1) was decreased (P<0.0001) in non-expanded, compared to expanded, CC in I+B+ ewes, but was similar between genotypes in expanded CC, and between expanded and non-expanded CC in ++ ewes. In summary, the genes involved in key maturational events were similar in pre-ovulatory follicles regardless of genotypic differences in OR and pre-ovulatory follicle size.