Expression of Growth Differentiation Factor-9 In the Developing Ovary and In Nonovarian Tissues

INTRODUCTION During mammalian ovarian organogenesis, the massive loss of oogonia via apoptosis is attenuated by the association of germ cells with somatic mesoepithelial cells of the gonadal ridge to form primordial follicles. It is suspected that the germ cell actively participates in this process via the production of local regulatory factors. Growth differentiation factor-9 (GDF-9), a member of the TGF-ß superfamily, has been shown to be essential for normal follicular development beyond the primary follicle stage in rodents and humans and a key factor for primordial follicle formation in sheep, bovine, and hamsters [1-4]. Several TGF-β family members have been shown to have highly specific and restrictive tissue distributions; most likely reflecting their roles as developmental regulators. GDF-9 has long been reported as an oocytespecific factor since it was first identified by the use of degenerate primers in 1992 [5]. Early analysis of GDF9 mRNA demonstrated the exclusive nature of its expression in the mammalian ovary, specifically in the oocyte. Furthermore, GDF-9 has been shown to mimic oocytes by stimulating cumulus expansion and development in vitro [6]. GDF-9 is essential for the normal progression and development of follicle development in the mammalian ovary. Few studies have addressed the possibility of GDF-9 expression in non-ovarian tissues [7]. Our lab discovered postreproductive (>60 weeks of age) transcriptional expression of GDF-9 in the hamster ovary. The appearance of this oocyte-specific factor at a period following follicle exhaustion within the hamster ovary, lead us to examine non-ovarian tissues for expression of GDF-9.