FIG. 1.

Effect of GDNF withdrawal on SSC colonization. A) Cultures of rat EPCAM⁺ clump-forming germ cells contain both SSCs and proliferating daughter spermatogonia that form tightly connected clumps (arrows) that loosely adhere to the feeder layer. Bar = 100 μm. B) True SSCs and their proliferating daughter spermatogonia are indistinguishable from each other unless assayed for using germ cell transplantation. After transplantation to the testes of busulphan-treated recipient nude mice, cultured rat SSCs form colonies of spermatogenesis that are easily visualized by using transgenic donor cells. In this case, the donor was transgenic for the mt-LacZ gene. Bar = 1.5 mm. C) Overnight withdrawal (18 h) of GDNF from cultured rat EPCAM⁺ clump-forming germ cells does not significantly influence the population of SSCs within the culture, as indicated by the lack of difference between colony numbers before and after GDNF withdrawal. Error bars represent the SEM.