Location, location, location: How does a spermatogonium know it is a spermatogonial stem cell (SSC)?

摘要

Like stem cells in other systems, SSCs are rare members of the spermatogonial population, and there are no definitive markers for their identification. The models for spermatogonial development came initially from painstaking kinetic studies based on cell morphology and staging of the spermatogenic cycle. Later studies used [3H]-thymidine to label S-phase spermatogonia to follow their kinetics and fate; more recent studies used transgenic mice expressing beta-galactosidase or green fluorescent protein in spermatogonia. A key observation that helped to propel the field forward was that SSCs are not randomly distributed over the basal lamina of the seminiferous epithelium, but rather are concentrated in the areas adjacent to vascularized interstitial tissue [2, 3]. Stem cells of other tissues, such as hair follicles (reviewed in [4]) or the intestinal epithelium (reviewed in [5]), localize to specific regions, referred to as stem cell niches, that provide a microenvironment beneficial for stem cell self-renewal.