Prepubertal rat Sertoli cells secrete a mitogenic factor(s) that stimulates germ and somatic cell proliferation

Sertoli cells were isolated from prepubertal 6- and 12-day-old rats. The Sertoli cell-conditioned media (SCCM-6 and SCCM-12) can markedly stimulate the proliferation of somatic cells and quiescent rat prespermatogonia in a dose-dependent and an age-related manner. SCCM-12 stimulated cell proliferation of BALB/c 3T3 fibroblasts up to 7-fold over control values, but did not stimulate to the same degree the germ cell mitotic activity. SCCM-6 stimulated proliferation of prespermatogonia up to 5-10-fold over controls. The mitogenic factor(s) in SCCM-6 appears to be more specific to prespermatogonia than to somatic cells which is consistent with the in vivo stimulation of mitosis in germ cells 5-6 days after birth and with the action of 'mitosis inducing substance'. The mitogenic factor(s) appears to be protein with a molecular weight over 8000 and sensitive to heat and trypsin treatment. These results suggest that the different mitogenicity of prepubertal rat SCCM on germ and somatic cells may be due to secretion of multiple mitogens by Sertoli cells in an age-dependent manner.