Reproducing Spermatogenesis V. NeriQueenie 2017 Germ cells isolated from testicular tissue or derived from embryonic stem cells represent a possible treatment option for children who have survived cancer and for azoospermic men. Self-renewal of spermatogonia stem cells is the foundation for sustaining spermatogenesis throughout life. In recent years, spermatogonia transplantation in mammals has been carried out successfully and, more recently, the appearance of germ cell lines derived from embryonic stem cells has rendered the treatment or prevention of azoospermia conceivable. In our laboratory, we have identified and labeled human spermatogenic cells at various steps of differentiation and carried out their xenogeneic transplantation into recipient gonads. In addition, by appropriately modifying culture conditions, we have been able to propagate mouse spermatogonia stem cells in vitro.