Regulation of germ cell and Sertoli cell development by activin, follistatin, and FSH

We have demonstrated a role for activin A, follistatin, and FSH in male germ cell differentiation at the time when spermatogonial stem cells and committed spermatogonia first appear in the developing testis. Testis fragments from 3-day-old rats were cultured for 1 or 3 days with various combinations of these factors, incubated with bromodeoxyuridine (BrdU) to label proliferating cells, and then processed for stereological analysis and detection of BrdU incorporation. Gonocyte numbers were significantly elevated in cultures treated with activin, while the combination of FSH and the activin antagonist, follistatin, increased the proportion of spermatogonia in the germ cell population after 3 days. All fragment groups treated with FSH contained a significantly higher proportion of proliferating Sertoli cells, while activin and follistatin each reduced Sertoli cell division. In situ hybridization and immunohistochemistry on normal rat testes demonstrated that gonocytes, but not spermatogonia, contain the activin beta(A) subunit mRNA and protein. In contrast, gonocytes first expressed follistatin mRNA and protein at 3 days after birth, concordant with the transition of gonocytes to spermatogonia. Collectively, these data demonstrate that germ cells have the potential to regulate their own maturation through production of endogenous activin A and follistatin. Sertoli cells were observed to produce the activin/inhibin beta(A) subunit, the inhibin alpha subunit, and follistatin, demonstrating that these cells have the potential to regulate germ cell maturation as well as their own development. These findings indicate that local regulation of activin bioactivity may underpin the coordinated development of germ cells and somatic cells at the onset of spermatogenesis.