Spermatogonial Stem Cells and Spermatogenesis

Spermatogonial stem cells and spermatogenesis in mice, monkeys and men

“…Collectively, A s , A pr and A al make up the population of undifferentiated spermatogonia that comprises 0.3% of germ cells in the rodent testis; A s make up 10% of undifferentiated spermatogonia (0.03% of germ cells; Fig. 2A) (Phillips et al, 2010; Huckins, 1971; Oakberg, 1971a; Valli et al, 2015; Oakberg, 1971b). Larger clones of A al spermatogonia differentiate to A1 spermatogonia.…”

“…Thus, through a series of transit amplifying mitotic and meiotic divisions, a relatively small pool of stem cells in the rodent testis produces 40 million sperm per gram of testis parenchyma each day (Figs. 1A and 2A) (Tegelenbosch & de Rooij, 1993; Valli et al, 2015; Thayer et al, 2001). …”

“…However, the broader pool of stem & transit amplifying progenitors in rodents is understood to include A s , A pr and A al spermatogonia with a cKIT negative phenotype. Similarly, the precise definition of functional stem cells in primate testes are subject to debate (Valli et al, 2015; Hermann et al, 2009), but the broader pool of stem/progenitor spermatogonia resides in the population of A dark and A pale spermatogonia with a cKIT negative phenotype. In rodents, the population of A s , A pr and A al un-differentiated spermatogonia comprises 0.3% of germ cells in the testis (Fig.…”

Stem Cell Therapies for Male Infertility: Where Are We Now and Where Are We Going?

“…The challenge with the human studies is that it is not possible to test the function of the putative germ cells by transplantation or fertilization, which are the gold standards in animal studies. Spermatogenic lineage development and testicular anatomy in nonhuman primates is similar to humans [ 5 ], and this may serve as a platform for safety and feasibility studies in which putative germ cells can be tested by transplantation and the resulting gametes and be tested by fertilization [ 58 ], embryo transfer, and production of live offspring. Perhaps one day it will be possible to build a human testis in vitro or in vivo, and this will provide the ultimate platform to test the spermatogenic potential of putative human therapeutic stem cells.…”

Experimental methods to preserve male fertility and treat male factor infertility

“…These adult tissue stem cells (designated Adark and Apale spermatogonia in humans) balance self-renewing divisions that maintain the stem cell pool with differentiating divisions that insure continuous sperm production (Fig. 1) 6–8 . Therefore, SSCs are essential for spermatogenesis and male fertility.…”