Expression and biological effects of bone morphogenetic protein-15 in the hen ovary

The bone morphogenetic protein 15 (Bmp15) and growth differentiation factor 9 (Gdf9) genes are two members of the transforming growth factor-beta superfamily. In mammals, these genes are known to be specifically expressed in oocytes and to be essential for female fertility. However, potential ovarian roles of BMPs remain unexplored in birds. The aim of the present work was to study for the first time the expression of Bmp15 in the hen ovary, to compare its expression pattern with that of Gdf9, and then to investigate the effects of BMP15 on granulosa cell (GC) proliferation and steroidogenesis. We found that chicken Bmp15 and Gdf9 genes were preferentially expressed in the ovary. We showed using in situ hybridization that Bmp15 and Gdf9 mRNAs were specifically localized in oocytes of all ovarian follicles examined. We also demonstrated using real-time quantitative RT-PCR that Bmp15 and Gdf9 expression was maintained during hierarchical follicular maturation in the gerrminal disc region and then progressively declined after ovulation. BMP15 was able to activate Smad1 (mothers against decapentaplegichomolog1) signaling pathway in hen GCs. Moreover, we showed a strong inhibitory effect of BMP15 on gonadotropin-induced progesterone production in hen GCs. This inhibitory effect was associated with a decrease in steroidogenic acute regulatory protein (STAR) level. Taken together, our results suggest that BMP15 may have a key role in the female fertility of birds.