Regulation of proliferation and differentiation in spermatogonial stem cells: the role of c-kit and its ligand SCF

To study self-renewal and differentiation of spermatogonial stem cells, we have transplanted undifferentiated testicular germ cells of the GFP transge nic mice into seminiferous tubules of mutant mice with male sterility, such as those dysfunctioned at Steel (SE) locus encoding the c-kit ligand or Do minant white spotting (W) locus encoding the receptor c-kit, In the seminif erous tubules of Sl/Sl(d) or Sl(17H)/Sl(17H) mice, transplanted donor germ cells proliferated and formed colonies of undifferentiated c-kit (-) sperma togonia, but were unable to differentiate further. However, these undiffere ntiated but proliferating spermatogonia, retransplanted into Sl(+) seminife rous tubules of W mutant, resumed differentiation, indicating that the tran splanted donor germ cells contained spermatogonial stem cells and that stim ulation of c-kit receptor by its ligand was necessary for maintenance of di fferentiated type A spermatogonia but not for proliferation of undifferenti ated type A spermatogonia, Furthermore, we have demonstrated that their tra nsplantation efficiency in the seminiferous tubules of Sl(17H)/Sl(17H) mice depended upon the stem cell niche on the basement membrane of the recipien t seminiferous tubules and was increased by elimination of the endogenous s permatogonia of mutant mice from the niche by treating them with busulfan.