Stem cells: Prospects for a future therapy of male infertility

Gamete production is a Prerequisite for the recombination of the genome. Distinct types of gametes are not a prerequisite for reproductive success. The need to produce enormous numbers of male gametes in species living in aquatic environments has lead to the introduction of spermatogonial stem cells into the male germline during early evolution of multicellular organisms. Spermatogonial stem cells are able to renew themselves and give rise to only one type of progeny which differentiate into sperm. In contrast to other adult stem cells, spermatogonial stem cells have to be selected for optimal DNA-integrity to ensure adequately low mutation rates during germline transmission. Depletion of spermatogonial stem cells is responsible-for post-therapeutic infertility in oncological patients. Loss or inadequate function of spermatogonial stem cells may also be involved in subfertile or infertile patients or in the decline of spermatogenesis. A depletion of spermatogonia is morphologically detectable as focal or complete Sertoli cell-only syndrome. New tools applied on spermatogonial stem cells have been developed during recent years. Germ cell transplantation showed the potential of spermatogonia to recolonize the testis and refertilize a germ (ell deficient recipient. These and other strategies to culture and store spermatogonial stem cells may be applied in the future to maintain the fertility potential of male patients. Furthermore, the possibility to produce male germline cells from embryonic stem cells has opened fascinating scenarios for the study of gamete formation and might lead to novel in vitro strategies for fertility preservation.