Growth Differentiation Factor 9 Is a Germ Cell Regulator of Sertoli Cell Function

Abstract

Oocyte-secreted growth differentiation factor (GDF) 9 and bone morphogenetic protein (BMP) 15 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 localization of both factors are limited to the germ cells of the rat seminiferous epithelium, with GDF9 being principally localized 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 signaling receptors [activin-like kinase (ALK) 5, ALK6, and BMP receptor, type II)]. Individual receptor types were expressed throughout the seminiferous epithelium, but coexpression of ALK5 and BMP receptor, type II 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 localization of the junctional proteins claudin-11, occludin, and zonula occludens-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.

Effects of polymorphisms in the bovine growth differentiation factor 9 gene on sperm quality in Holstein bulls

“…Fitzpatrick et al (1998) and Pennetier et al (2004) detected expression of GDF9 in the testis, and suggested that it could potentially regulate testicular function. This concept is also supported by the dynamic regulation of BMPRII, ALK5, and ALK6 expression throughout the seminiferous tubules, and the fact that Smad signaling pathways are vital for the control of testis development and spermatogenesis (Itman et al, 2006(Itman et al, , 2008Nicholls et al, 2009). However, Dong et al (1996) found that GDF9-knockout males are fertile and show no gross physical or behavioral defects, which indicated that the actions of GDF9 are not essential for the initiation or maintenance of spermatogenesis.…”

“…However, whether the action of GDF9 affects the function of tight junctions, sperm quality, including number, maturation, mobility, and viability, or the circulating concentrations of the key hormones testosterone, FSH, and inhibins has not been analyzed. Furthermore, Nicholls et al (2009) found that GDF9 can modulate key functions of Sertoli cells by affecting the function of tight junctions and the expression of inhibin B. Therefore, in this study, we aimed to elucidate the effects of GDF9 mutations on sperm quality traits.…”

“…Although these two polymorphisms are located in intron 1 of GDF9, they may affect phenotype, gene expression, and consequent function (Van Laere et al, 2003;Krawczak et al, 2007). Thus, these two polymorphisms may have altered the function of tight junctions or the circulating concentrations of the key hormones testosterone, FSH, and inhibins by affecting signal transduction, and finally influenced sperm quality (Nicholls et al, 2009;Fan et al, 2012).…”

“…In males, GDF9 expression has been detected in the testis (Fitzpatrick et al, 1998;Pennetier et al, 2004;Nicholls et al, 2009); however, its role in the testis has not been well elucidated. Itman et al (2006) reported that signals from TGFβ ligands have been implicated in germ cell specification and migration, Sertoli cell proliferation, spermatogonial growth and differentiation, and spermiogenesis.…”

“…However, the effects of GDF9 on the function of tight junctions, sperm quality, including number, maturation, mobility, and viability, or the circulating concentrations of the key hormones testosterone, follicle-stimulating hormone (FSH), and inhibins have not been analyzed in these knockout models, and a change in any of these parameters could affect male fertility. Nicholls et al (2009) reported that GDF9 is germ cell-specific factor in the testis, and demonstrated that GDF9 can modulate key functions of Sertoli cells by affecting the function of tight junctions and the expression of inhibin B. To date, no study has reported the effects of GDF9 on sperm quality.…”