Of the 7% of men affected with infertility, about 54% suffer from pre-testicular and/or testicular factor induced azoospermia/ oligospermia. This agenesis of spermatozoa has been the subject of much andrology research over the past 50 years, with a particular focus in the triggers of spermatogenesis. While much of their work is limited to murine populations, researchers have put a lot of emphasis on the spermatogonial stem cell (SSC) niche as the source of the trigger(s). By following physiological patterns exhibited in the seminiferous epithelium, researchers have been able to detect distinct morphological stages that correlate with spermatogonial germ-line action. Different niche cells appear to release different concentrations of active compounds, androgens, and receptors during different stages. Specifically, in the steps leading up to and during SSC differentiation, Sertoli cells and germ line cells release retinoic acid and retinoic acid receptors. Retinoic acid appears to trigger SSCs in vitro as well. Testosterone, released by Leydig cells and potentially testicular macrophages, appears to play an essential role in a spermiation-SSC differentiation axis, as well as a role in GDNF production by peritubular myoid cells, both required for proper maintenance of SSC populations and commitment to meiosis. With new and promising research being done on the whole of the SSC niche, as opposed to just Sertoli cells, scientists are closer than ever to uncovering the secrets of male fertility.
Bibi, M. (2019). Triggers of Spermatogenesis. The Science Journal of the Lander College of Arts and Sciences, 12 (2). Retrieved from https://touroscholar.touro.edu/cgi/viewcontent.cgi?article=1219&context=sjlcas