Identification and propagation of human spermatogonial stem cells

Spermatogonial stem cells (SSCs) are a self-renewing population of adult stem cells. These cells could restors reproduction throughout the life of the male by sperm production. In non-primate mammals, spermatogonial stem cells named A-single (As), and the A-paired (Apr) and A-aligned (Aal) are the progenitor spermatogonial population. In human, very little findings is available about SSCs. there are two different types of A spermatogonia, the Adark and Apale spermatogonia. The Adark spermatogonia were referred to as the reserve stem cells, whereas the Apale were considered the renewing stem cells. Regulation of the SSC population includes establishment and maintenance of a niche microenvironment in the seminiferous tubules of the testis. Signaling from somatic cells within the niche determines the fate of SSCs by either supporting self-renewal or initiating differentiation to spermatozoa. Although numerous expression markers have been helpful in isolating and enriching spermatogonial stem cells, no specific marker for this cell type has yet been identified. Culture of testicular cells on various feeder cells has made it possible to culture and expansion of spermatogonial stem cells for a long period of time and hormones and growth factors are investigated for their role in the process of proliferation of spermatogonial stem cells.