Ectopic grafting of mammalian testis tissue into mouse hosts

Mammalian spermatogenesis is a highly organized process of cell division and differentiation that requires intimate contact between germ cells and testicular somatic cells. Lack of a suitable in vitro system has caused many aspects of spermatogenesis, especially in nonrodent species, to remain elusive. We describe ectopic grafting of testis tissue from sexually immature males to immunodeficient mouse hosts as an in vivo culture system that allows recapitulation of complete spermatogenesis from diverse mammalian species with the production of fertilization-competent sperm in a mouse host. In this system, the donor species testicular environment is preserved allowing experimentation in a small rodent. The accessibility of the tissue in the mouse host makes it possible to manipulate spermatogenesis and steroidogenesis in a controlled manner that is often not feasible in the donor species. It also allows detailed analysis of the effects of toxins and compounds to enhance or suppress male fertility in an in vivo system without extensive experimentation in the target species. Finally, as it provides a source of male gametes even from immature gonads, grafting of fresh or preserved testis tissue offers an invaluable tool for the conservation of fertility in males if sperm cannot be obtained for cryopreservation.