Stem cell factor protects germ cells from apoptosis in vitro

Stem cell factor (SCF) plays an important role in migration, adhesion, prol iferation, and survival of primordial germ cells and spermatogonia during t esticular development. However, the function of SCF in the adult testis is poorly described. We have previously shown that, in the presence of SCF, th ere were more type A spermatogonia incorporating thymidine at stage XII of rat seminiferous tubules cultured in vitro than in the absence of SCF, impl ying that the increased DNA synthesis might result from enhanced survival o f spermatogonia, To explore the potential pro-survival function of SCF duri ng spermatogenesis, the seminiferous tubules from stage XII were cultured i n the presence or absence of SCF (100 ng/ml) for 8, 24, 48, and 72 hours, r espectively, and apoptosis was analyzed by DNA laddering and in situ 3'-end labeling (ISEL) staining. Surprisingly, not only spermatogonia, but also s permatocytes and spermatids, were protected from apoptosis in the presence of SCF, Apoptosis took place much later and was less severe in the SCF-trea ted tubules than in the controls. Based on previous studies showing that FS H prevents germ cells from undergoing apoptosis in vitro, and that SCF leve l is increased dramatically in response to FSH stimulation, we also tested if the pro-survival effect of FSH is mediated through SCF by using a functi on-blocking monoclonal antibody, ACK-2, to block SCF/c-kit interaction. Aft er 24 hours of blockade, the protective effect of FSH was partially abolish ed, as manifested by DNA laddering and ISEL analyses. The present study dem onstrates that SCF acts as an important survival factor for germ cells in t he adult rat testis and FSH pro-survival effect on germ cells is mediated p artially through the SCF/c-kit pathway.