Molecular cloning of porcine growth differentiation factor 9 (GDF-9) cDNA and its role in early folliculogenesis: direct ovarian injection of GDF-9 gene fragments promotes early folliculogenesis

Growth differentiation factor-9 (GDF-9) is a growth factor secreted by oocytes in growing ovarian follicles. To investigate the ovarian function of GDF-9 in pigs, we first cloned porcine GDF-9 complementary DNA (cDNA), and then injected its gene fragments into the ovary in gilts. Porcine GDF-9 has open reading frame (ORF) homologies of 81.4%, 84.6%, 84.2%, 72.7% and 72.6% with its human, bovine, ovine, rat and mouse counterparts respectively. Regarding the deduced amino-acid sequence of the mature protein, the corresponding homologies reach 92.1%, 97.8%, 97.0%, 89.6% and 88.1% respectively. To investigate the role of GDF-9 in early folliculogenesis, the ovaries of 2-month-old prepubertal gilts were injected with GDF-9 gene fragments. The injection of porcine GDF-9 gene fragments resulted in an increase in the number of primary, secondary and tertiary follicles, concomitant with a decrease in the number of primordial follicles. These results indicated that exogenous GDF-9 can promote early folliculogenesis in the porcine ovary, and that a technique for direct ovarian injection of GFD-9 gene fragments may contribute to a novel therapy for prevention and treatment of infertility associated with ovarian dysfunction.