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 spermatogenesi s 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 fra gments rich in secondary spermatogonia were cultured in control medium for three weeks, most of the testicular cysts still remained as secon dary 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 spermato gonia differentiated into primary spermatocytes (zygotene-pachytene) i n more than half of the cysts by the second week. When newt testes fra gments rich in primary spermatocytes were cultured in a control medium for three weeks only round spermatids were observed at the most advan ced stage. On the other hand, in the medium supplemented with FSH alon e, elongated spermatids appeared by the second week. Neither the addit ion of luteinizing hormone (LH) nor androgens (testosterone and 5alpha -dihydrotestosterone) to the control medium stimulated differentiation for either step. Consistent with these findings was the fact that rad ioreceptor assays revealed high affinity specific binding sites for FS H but none for LH for either stage of the testes (secondary spermatogo nia and primary spermatocytes). Preliminary results indicate that FSH does not bind to germ cells but to somatic cells (most probably Sertol i cells). These and our unpublished data suggest that FSH triggers pro liferation and differentiation of spermatogonia into elongated spermat ids by acting on Sertoli cells which in turn act on germ cells.