Review Article
Yoko Sato, Masayasu Taniguc
Abstract
Several experimental systems are available for inducing spermatogenesis outside the endogenous testis. These systems have been developed as tools for studying spermatogenesis and as an option for preserving genetic material obtained from males when sperm recovery is not possible. Two in vivo systems are available for this purpose: tissue grafting and cell transplantation. Ectopic grafting of immature testicular tissues into immunodeficient mouse hosts is a type of in vivo system that allows the immature testicular tissue from many types of animals to undergo complete spermatogenesis. The other in vivo system is germ cell transplantation into the recipient testis, which induces colonization of spermatogonial stem cells from many types of animals and allows the stem cells to differentiate into spermatozoa in some cases. Furthermore, 2 in vitro systems are available: tissue culture and 3-dimensional (3D) cell culture. The tissue culture system and the combination of tissue culture and germ cell transplantation system were developed recently; this made it possible to perform complete spermatogenesis by using mouse spermatogonial stem cells. Isolated immature mouse testicular cells can differentiate into spermatozoa when the 3D culture system is used. All these systems have advantages and disadvantages with respect to studying spermatogenesis and preserving fertility in many types of animals. Therefore, it is necessary to consider many factors that might affect the results of spermatogenesis in order to use these experimental systems appropriately. Herein, we have discussed the advantages and disadvantages of these systems, especially in connection with several factors that may affect spermatogenesis.