Karim Nayernia of the University of Newcastle, UK, and his colleagues treated male embryonic stem cells (ESCs) with a range of substances, which converted them first into germline stem cells and then into spermatogonial stem cells. (newscientist.com)
A few months later, the researchers injected each monkey's own spermatogonial stem cells back into its testes. (newscientist.com)
They come from a pool of self - renewing spermatogonial stem cells that are present at birth. (sciencedaily.com)