ABSTRACT
Spermatogonial transplantation from mouse-to-mouse was first reported by Brinster and colleagues in 1994. Since then, many important developments in this fascinating methodology such as interspecies transplants, transplants from cryopreserved and cultured spermatogonial stem cells have been made. This technique has been shown a valuable tool to study the biology of spermatogonial stem cells. Also, important functional questions regarding Sertoli-germ cell interactions and the role of the Sertoli cell and germ cells during spermatogenesis have now been answered. Transplantation of cultured spermatogonial stem cells is now opening exciting possibilities for in vitro multiplication and manipulation of male germ line cells. Spermatogonial stem cells can be considered "immortal". By freezing and storing testicular tissue, it should be possible to preserve indefinitely the genetic stocks of valuable farm animals, endangered species and uniqueexperimental animals, until a suitable recipient can be found that will maintain the germ line. Transplantation of spermatogonia has also potential clinical application to address human infertility. Overall, spermatogonial transplantation has been proved to be an extraordinary and powerful technique to investigate reproductive biology.