Proliferation of spermatogonial stem cells and spermatogenesis in vitro.

Detection of spermatogonial stem cells (SSC) became possible 10 years ago, with the transplantation of germ cells into the seminiferous tubules of mice. Using this assay system, attempts to maintain and expand SSC in vitro finally bore fruit. Gonocytes from neonatal mice and spermatogonial stem cells from adult mice were plated on feeder cells in a medium supplemented with Glial cell line-derived neurotrophic factor (GDNF) along with certain other factors. The germ cells that emerged under such conditions, named germline stem (GS) cells, proliferated exponentially through self-renewing division. GS cells in vitro show features of differentiation as well. Some expressed c-kit, which is a cell surface marker of differentiating spermatogonia. Therefore, it seems that GS cells undergo both self-renewing and differentiating cell divisions in vitro. There is a century of history behind attempts to reproduce spermatogenesis in vitro and significant progress has been made. Nonetheless, there are few established culture-based protocols for recreating spermatogenesis in vitro. GS cells would be an ideal starting material in this regard. (Reprod Med Biol 2006; 5: 169-174).