Localization of growth differentiation factor-9 (GDF-9) mRNA and protein in rat ovaries and cDNA cloning of rat GDF-9 and its novel homolog GDF-9B

Although targeted gene disruption of GDF-9, an oocyte derived growth factor , leads to an arrest of folliculogenesis and causes infertility in female m ice, little is known on the expression of GDF-9 protein in the ovary. We sh ow that GDF-9 protein is expressed in rat oocytes during folliculogenesis f rom the early primary follicle stage onwards but the most intensive immunos taining,was seen in primary and preantral follicles. Northern blot analyses of the ontogeny of GDF-9 gene expression in postnatal rat ovaries showed t hat the GDF-9 transcript levels are clearly increased on the second postnat al day concomitant with the appearance of primary follicles. Interestingly, Northern blot and in situ hybridization analyses indicate a similar expres sion pattern for GDF-9B, the rat ortholog of a mouse GDF-9 like factor for which we recently reported the partial amino acid sequence. The polypeptide sequences deduced from isolated ovarian cDNAs indicate that the rat GDF-9 prepropeptide is 440 amino acids (aa) in length and the putative mature pep tide is 135 aa:whereas rat GDF-9B is 391 aa long and the mature region is 1 25 aa. We conclude that (1) the GDF-9 protein is highly expressed in the oo cytes of primary follicles of rat ovaries suggesting that it plays a role m ainly in early folliculogenesis and that (2) the full-length polypeptide se quence of GDF-9B suggests that this novel TGF-beta family member is likely to be a secreted growth factor that may regulate folliculogenesis at simila r developmental stages as GDF-9. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.