Stage-specific expression of bone morphogenetic protein type I and type II receptor genes: Effects of follicle-stimulating hormone on ovine antral follicles

We investigated the mRNA expression patterns of receptor genes for bone morphogenetic proteins-15 (BMP15) and growth differentiation factor-9 (GDF-9) in granulosa cells of sheep treated with FSH. The effects of FSH and estradiol (E2) on the regulation of BMPRII, BMPRIB and ALK-5 in ovine granulosa cells were also examined. Ovaries were collected on day 16 of the estrous cycle and granulose cells were harvested from follicles of two sizes (3–5 and >5 mm in diameter). For in vitro studies, granulosa cells were obtained from follicles of 3–5 mm in diameter and cultured in serum-free McCoy's 5A medium supplemented with different doses of FSH (0, 1, 5, 10 ng/ml) or a combination of 5 ng/ml FSH with 1 ng/ml E2. Expression of BMPRII, BMPRIB and ALK-5 mRNA was estimated by quantitative real-time PCR. Our results demonstrated that BMPRII, BMPRIB and ALK-5 expression was significantly higher in the granulosa cells of large follicles than of small follicles. Treatment of granulose cells with FSH (1–10 ng/ml) alone down-regulated the expression of BMPRIB (P < 0.05). BMPRII and ALK-5 mRNA expression was not significantly different at an FSH concentration of 5 ng/ml compared to control. A further increase in FSH (10 ng/ml) down-regulated the expression of BMPRII and ALK-5 (P < 0.05). The combination of FSH (5 ng/ml) and E2 (1 ng/ml) up-regulated the expression of BMPRII, BMPRIB and ALK-5 in granulose cells (P < 0.05). Therefore, the present study establishes the expression levels of the receptor genes of BMP15 and GDF-9 and suggests that the expression of BMPRII, BMPRIB and ALK-5 may be regulated by FSH and E2 in ovine granulosa cells.