ABSTRACT
INTRODUCTION The preservation of spermatogenesis throughout a human’s adult reproductive life depends on one cell type only: the adult spermatogonial stem cell (SSC). SSCs are undifferentiated cells that give rise to the spermatogenic cells and, finally, the spermatozoa. Even though there is a continual loss of differentiated cells, the spermatogenic cell lineage maintains its cell number thanks to the adult SSCs, which produce both new stem cells (self-renewal) and differentiating cells.
