Initiation and stimulation of spermatogenesis in vitro by mammalian follicle-stimulating hormone in the Japanese newt, Cynops pyrrhogaster.

In order to elucidate the molecular mechanisms by which spermatogenesis is regulated, especially the roles of hormones and somatic cells in the initiation and promotion of spermatogenesis, we developed an organ culture system with a chemically defined medium. When newt testes fragments rich in secondary spermatogonia were cultured in control medium for three weeks, most of the testicular cysts still remained as secondary spermatogonia. On the other hand, in the medium supplemented with follicle-stimulating hormone (FSH) alone, DNA syntheses in secondary spermatogonia and Sertoli cells were stimulated and secondary spermatogonia differentiated into primary spermatocytes (zygotene-pachytene) in more than half of the cysts by the second week. When newt testes fragments rich in primary spermatocytes were cultured in a control medium for three weeks only round spermatids were observed at the most advanced stage. On the other hand, in the medium supplemented with FSH alone, elongated spermatids appeared by the second week. Neither the addition of luteinizing hormone (LH) nor androgens (testosterone and 5 alpha-dihydrotestosterone) to the control medium stimulated differentiation for either step. Consistent with these findings was the fact that radioreceptor assays revealed high affinity specific binding sites for FSH but none for LH for either stage of the testes (secondary spermatogonia and primary spermatocytes). Preliminary results indicate that FSH does not bind to germ cells but to somatic cells (most probably Sertoli cells). These and our unpublished data suggest that FSH triggers proliferation and differentiation of spermatogonia into elongated spermatids by acting on Sertoli cells which in turn act on germ cells.