ABSTRACT
In this chapter, the authors introduce spermatogonial stem cells (SSC), which lie at the heart of male reproductive capacity, and the controversy surrounding the existence of an equivalent stem cell in the female gonads. They also introduce the embryonic ancestor to the adult germ line stem cells, the primordial germ cell. The developmental origins of germ stem cells have been characterized in both invertebrates and vertebrates, and there are a remarkable number of similarities, as there are in the structures and mechanisms that maintain them in the adult. The main constituents of the SSC niche are Sertoli cells, which reside within the seminiferous epithelium and provide essential cues for the maintenance and coordination of spermatogenesis. Transplantation assays have been developed that enable a true test of stem cell capacity for several stem cell types, including those from testicular tissue. Embryogenesis is characterized by a number of transient cell types that have stem cell-like properties, especially if placed in cell culture.
