Rapid expansion of the spermatogonial stem cell tool box

Abstract

Recently, great technological progress has been achieved in spermatogonial stem cell (SSC) research. In this issue of PNAS, Kanatsu-Shinohara et al. (1) describe yet another important novel use for SSCs. Based on a successful long-term culture protocol for mouse SSCs, this group has designed a way to produce knockout mice from SSCs with an efficiency that is at least comparable with that of embryonic stem (ES) cell-based methods. SSCs were transfected by applying methods used for ES cells and transplanted into recipient mouse testes to produce sperm carrying the desired mutation. This procedure may enable the efficient production of transgenic animals in species from which no ES cells can be made as yet. Before 1994, spermatogonial stem cell numbers could be assessed only by cell counts (2, 3). Then Brinster and colleagues introduced a functional assay for SSCs, the SSC transplantation technique (4, 5). This method has greatly boosted research on SSCs. However, despite efforts by many groups, it remained problematic to culture SSCs and propagate these cells in vitro , hence limiting SSC availability. The breakthrough came when Kanatsu-Shinohara et al. (6) succeeded in culturing SSCs for at least 5 months, achieving a 1014-fold increase in SSC numbers [called germ-line stem (GS) cells by the authors]. These cultured SSCs remained capable of colonizing … *E-mail: d.g.derooij{at}bio.uu.nl