Growth differentiation factor 9 is a germ cell regulator of sertoli cell function

Oocyte-secreted Growth Differentiation Factor 9 (GDF9) and Bone Morphogenetic Protein 15 (BMP15) are critical regulatory factors in female reproduction. Together, they promote granulosa cell proliferation and stimulate the maturation of preovulatory follicles. Despite their importance in female fertility, GDF9 and BMP15 expression patterns and function during spermatogenesis have not been investigated. In this study, we show that the expression and stage-specific localisation of both factors are limited to the germ cells of the rat seminiferous epithelium; with GDF9 being principally localised in round spermatids and BMP15 in gonocytes and pachytene spermatocytes. To identify potential cellular targets for GDF9 actions, cells of the seminiferous tubule were isolated and screened for the expression of signalling receptors (ALK5, ALK6, and BMPRII). Individual receptor types were expressed throughout the seminiferous epithelium, but co-expression of ALK5 and BMPRII was limited to Sertoli cells and round spermatids. Based on the reproductive actions of related TGFbeta ligands in the ovary and testis, GDF9 was assessed for its ability to regulate tight junction function and inhibin B production in rat Sertoli cell cultures. When recombinant mouse GDF9 was added to immature Sertoli cell cultures, it inhibited membrane localisation of the junctional proteins claudin-11, occludin and ZO-1, thereby disrupting tight junction integrity. Concomitantly, GDF9 up-regulated inhibin subunit expression and significantly stimulated dimeric inhibin B protein production. Together these results demonstrate that GDF9 and BMP15 are germ cell specific factors in the rat testis, and that GDF9 can modulate key Sertoli cell functions.