Cloning of the ovine growth and differentiation factor-9 gene and characterization of growth and differentiation factor-9 gene expression

Recently, a novel member of the transforming growth factor-beta (TGF-beta) superfamily, termed growth and differentiation factor-9 (GDF-9) was shown to be expressed in oocytes of mice and humans, and to be essential for normal follicular development beyond the primary (type 2) follicle stage in mice. Taken together, these observations suggest that GDF-9 may play a fundamental role in the initiation of folliculogenesis. Due to the potential regulatory role of GDF-9 in follicular and oocyte growth, the ovine gene for GDF-9 was isolated and characterized, and expression of GDF-9 mRNA in ovaries of domestic ruminants examined. Specific hybridization of GDF-9 35S-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.;Striking phenotypic similarities between GDF-9 deficient mice and sheep homozygous for the Inverdale prolificacy gene (FecXI) suggest a relationship between the FecXI gene and GDF-9 function in the ovary. Therefore, it was hypothesized that two copies of the FecX I gene would lead to inhibition of GDF-9 mRNA expression. To test this hypothesis, in situ hybridization was used to characterize GDF-9 mRNA expression in the ovaries of fetal sheep homozygous and heterozygous for the FecXI gene. Regardless of genotype or stage of development, all oocytes expressed mRNA for GDF-9. On the basis of these results, inhibition of GDF-9 gene expression does not appear to be the mechanism of action by which the FecXI gene alters folliculogenesis.;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. Further, elucidation of the role of GDF-9 in early follicular and oocyte growth may provide information necessary for the development of a practical and efficient method for the culture of preantral follicles in domestic ruminants and other species.