FSH-initiated differentiation of newt spermatogonia to primary spermatocytes in germ-somatic cell reaggregates cultured within a collagen matrix

We previously cultured fragments of newt testes in chemically defined media and showed that mammalian follicle-stimulating hormone (FSH) stimulates pr oliferation of spermatogonia as well as their differentiation into primary spermatocytes (Ji et al., 1992; Abe and Ji, 1994). Next, we indicated in cu ltures composed of spermatogonia and somatic cells (mainly Sertoli cells) t hat FSH stimulates germ cell proliferation via Sertoli cells (Maekawa ef al ., 1995). However, the spermatogonia did not differentiate into primary spe rmatocytes, but instead died. In the present study, we embedded large reagg regates of spermatogonia and somatic cells (mainly Sertoli cells) within a collagen matrix and cultured the reaggregates on a filter that floated on c hemically defined media containing FSH; in this revised culture system, spe rmatogonia proliferated and differentiated into primary spermatocytes. The viability and percentage of germ cells differentiating into primary spermat ocytes were proportional to the percentage of somatic cells in the culture, indicating that differentiation of spermatogonia into primary spermatocyte s is mediated by Sertoli cells.