Mammalian spermatogenesis is maintained by stemInterleukin-2 receptor cell capacity inside undifferentiated spermatogonial subpopulation. Right here, applying a blend of surface markers, we describe a purification technique for undifferentiated spermatogonia. Flow cytometric analysis revealed that this population is composed of Plzf-positive cells and exhibits Blebbistatin mw quiescence and also the side population phenotype, fulfilling standard stem cell criteria. We then applied this technique to analyze undifferentiated spermatogonia and stem cell action of Atm(-/-) mice. Atm(-/-) testis shows progressive depletion of undifferentiated spermatogonia accompanied by cell-cycle arrest. In Atm(-/-) undifferentiated spermatogonia, a self-renewal defect was observed in vitro and in vivo. Accumulation of DNA damage and activation in the p19(Arf)-p53-p21(Cip1/Waf1) pathway were observed in Atm(-/-) undifferentiated spermatogonia. Furthermore, suppression of p21(Cip1/Waf1) in an Atm(-/-) background restored transplantation ability of undifferentiated spermatogonia, indicating that ATM plays an vital role in servicing of undifferentiated spermatogonia and their stem cell capability by suppressing PDE inhibitor DNA damage-induced cell-cycle arrest.