Production of functional spermatids from mouse germline stem cells in ectopically reconstituted seminiferous tubules

Testicular germ cell transplantation into the seminiferous tubules is at present the only way to induce spermatogenesis from a given source of spermatogonial stem cells. Here we show an alternative method that harnesses the self-organizing ability of testicular somatic cells. The testicular cells of embryonic or neonatal mice or rats and of newborn pigs were dissociated into single cells. Each of them reorganized into a tubular structure following implantation into the subcutis of immunodeficient mice. When mouse germline stem (GS) cells derived from spermatogonial stem cells and expanded in culture were intermingled with testicular cells of rodents, they were integrated in the reconstituted tubules and differentiated beyond meiosis into spermatids. Normal offspring were produced by the microinjection of those spermatids into oocytes. This method could be applicable to various mammalian species and useful for producing functional gametes from GS cells in a xenoectopic environment.