Enrichment and transplantation of spermatogonial stem cells.

Spermatogenesis is a complex, highly organized process originated from stem cell spermatogonia. Because there are very few stem cells and they can only be defined by their function, the identification and isolation of these cells has been very difficult. By using a spermatogonial transplantation assay system, we have identified alpha6-and beta1-integrin expression on stem cells, and cells isolated with these antigens were significantly enriched in stem cells. This is the first demonstration of spermatogonial stem cell-associated antigens. Analysis of two infertile mouse models, Steel/SteelDickie (Sl/Sld) and experimental cryptorchidism, showed that the number of stem cells is reduced in Sl/Sld testis. Whereas cryptorchid testes are greatly enriched for stem cells, and one in 200 cells is a stem cell. These techniques will provide an important starting point for further purification and characterization of spermatogonial stem cells.