Molecular Cloning of the Ovine Growth/Differentiation Factor-9 Gene and Expression of Growth/Differentiation Factor-9 in Ovine and Bovine Ovaries

Recently a novel member of the transforming growth factor β (TGFβ) superfamily termed growth/differentiation factor-9 (GDF-9) was shown to be expressed in ovaries of mice and humans, and to be essential for normal follicular development beyond the primary (type 2) follicle stage in mice. In the present study, the gene for ovine GDF-9 was isolated and characterized, and expression of GDF-9 mRNA in ovaries of domestic ruminants was examined. The predicted amino acid sequence of ovine GDF-9 is 77% and 66% homologous to human and mouse GDF-9, respectively. Specific hybridization using homologous 35 S-antisense probes was restricted to oocytes. In contrast to similar studies in mice in which GDF-9 was first detected beginning at the primary (type 2) follicle stage, in ovine and bovine ovaries GDF-9 mRNA was expressed beginning at the primordial (type 1) follicle stage. The observed timing and pattern of GDF-9 expression in oocytes of domestic ruminants is consistent with a role for GDF-9 in the initiation and maintenance of folliculogenesis in these species, and supports the general concept that early stages of follicular growth and development are regulated by intraovarian factors.