Biology and manipulation technologies of male germline stem cells in mammals

BACKGROUND: Spermatogonial stem cells (SSCs) are the origin of sperm and defined by their functions of “colonization in the testis” and “spermatogenesis”. In vitro manipulation techniques of SSCs contribute to a wide variety of fields including reproductive medicine and molecular breeding. This review presents the recent progress of the biology and manipulation technologies of SSCs. METHODS: Research articles regarding SSC biology and technologies were collected and summarized. MAIN FINDINGS: Dr. Ralph Brinster developed the spermatogonial transplantation technique that enables SSC detection by functional markers. Using this technique, cultured SSCs, termed germline stem (GS) cells, were established from the mouse. GS cells provide the opportunity to produce genome‐edited animals without using zygotes. In vitro spermatogenesis allows production of haploid germ cells from GS cells without spermatogonial transplantation. The recent advancement of pluripotent stem cell culture techniques has also achieved production of functional GS‐like cells in addition to male/female germ cells. CONCLUSION: Although in vitro manipulation techniques of GS cells have been developed for the mouse, it appears to be difficult to apply these techniques to other species. Understanding and control of interspecies barriers are required to extend this technology to nonrodent mammals.