Patterns of Expression of Messenger RNAs Encoding GDF9, BMP15, TGFBR1, BMPR1B, and BMPR2 During Follicular Development and Characterization of Ovarian Follicular Populations in Ewes Carrying the Woodlands FecX2W Mutation1

Abstract

Woodlands sheep have a putative genetic mutation (FecX2(W)) that increases ovulation rate. At present, the identity of FecX2(W) is unknown. The trait does not appear to be due to the previously described mutations in bone morphogenetic protein 15 (BMP15), growth differentiation factor 9 (GDF9), or bone morphogenetic protein receptor type 1B (BMPR1B) that affect ovulation rate in sheep. Potentially, FecX2(W) could be an unidentified genetic mutation in BMP15 or in the closely related GDF9, which interacts with BMP15 to control ovarian function. Alternatively, FecX2(W) may affect ovulation rate by changing the expression patterns in the molecular pathways activated by genes known to regulate ovulation rate. The objectives of these experiments were to sequence the complete coding region of the BMP15 and GDF9 genes, determine the patterns of expression of mRNAs encoding GDF9, BMP15, TGFBR1, BMPR1B, and BMPR2 during follicular development, and characterize the follicular populations in ewes heterozygous for the Woodlands mutation and their wild-type contemporaries. No differences in the coding sequences of BMP15 or GDF9 genes were identified that were associated with enhanced ovulation rate. The expression patterns of GDF9 and BMPR2 mRNAs were not different between genotypes. However, expression of BMP15 mRNA was less in oocytes of FecX2(W) ewes in large preantral and antral follicles. Expression of ALK5 mRNA was significantly higher in the oocytes of FecX2(W) ewes, whereas expression of BMPR1B was decreased in both oocytes and granulosa cells of FecX2(W) ewes. FecX2(W) ewes also had increased numbers of antral follicles <1 mm in diameter. These follicles were smaller in average diameter, with the oocytes also being of a smaller mean diameter. Given that a mutation in BMP15 or BMPR1B results in increased ovulation rates in sheep, the differences in expression levels of BMP15 and BMPR1B may play a role in the increase in ovulation rate observed in Woodlands ewes with the FecX2(W) mutation.

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

“…Our findings confirmed observations made in the pig, sheep, goat and cow in which BMPR1A, BMPR1B and BMPR2 mRNA and/or protein were expressed in the oocyte and in both GC and TC of antral follicles (Wilson et al 2001, Souza et al 2002, Glister et al 2004, Quinn et al 2004, Fatehi et al 2005, Silva et al 2005, Feary et al 2007). …”

“…The expression of TGFBR1 mRNA has only been studied in antral follicles of mouse, sheep and cow ovaries, and, consistent with our findings, was expressed in the oocyte, GC and TC (Juneja et al 1996, Juengel et al 2004, Feary et al 2007). Similar to the observations made for the ligands in our study, the oocyte was found to abundantly express BMPR1A, BMPR1B, BMPR2 and TGFBR1 mRNA but little variation in mRNA abundance was observed between the different time points.…”

Using sheep lines with mutations in single genes to better understand ovarian function

“…A possible mechanism for these interactions was identified when it was shown that BMP15 mRNA levels were decreased in animals carrying the Woodlands gene (Feary et al 2007) or homozygous for the Booroola gene (Crawford et al 2011) compared with their wild-type contemporaries. However, BMP15 mutations have also been observed in flocks carrying other putative major genes influencing ovulation rate wherein the effect is additive rather than synergistic.…”

Growth and differentiation factor 9 promotes oocyte growth at the primary but not the early secondary stage in three-dimensional follicle culture

“…Whether GDF9 acts directly on the oocyte to induce follicle growth, indirectly through the granulosa cell or both, is not clear, given that both granulosa cells and oocytes in primary follicles express ALK5 [57][58][59][60][61] and BMPR2 [58,62], the reported type I [63,64] and II receptors for GDF9 [65], respectively. However, it is controversial whether ALK5 is the only type I receptor for GDF9 as Alk5 conditional knockout mice have no defects in follicular development and cumulus expansion [62], which is a distinct phenotype from Gdf9 null mice [17].…”