Spermatogonial stem cells (SSCs) undergo self-renewal division and support spermatogenesis. Whilst various cytokines coordinate to drive SSC self-renewal, small make it clear is identified regarding the mechanisms underlying this approach. We investigated the molecular mechanism by reconstructing SSC self-renewal in vitro with no exogenous cytokines. Activation Hypoxia-inducible factors(HIF) of Ras or overexpression of cyclins D2 and E1, each of which were induced by Ras; enabled long-term self-renewal of cultured spermatogonia. SSCs with activated Ras responded effectively to differentiation signals and underwent spermatogenesis, whereas differentiation was abrogated in cyclin transfectants just after spermatogonial transplantation. Both Ras- and cyclin-transfected cells produced seminomatous tumors, suggesting that excessive self-renewing stimulus induces oncogenic transformation. In contrast, cells that overexpressed cyclin D1 or D3 failed to produce germ cell colonies soon after transplantation, which indicated that cyclin expression pattern is definitely an vital determinant to long-term SSC recolonization. Therefore, the Ras-cyclin D2 pathway regulates the balance involving tissue upkeep and tumorigenesis inside the SSC population.