Figure 1.

Stem cell niche organization and signalling. (a) In the proximal arm of the male gonad of C. elegans, the DTC provides the necessary cues for stem cell maintenance to the closest germline stem cells. The outline on the right indicates the signalling molecules involved. (b) In the Drosophila testis, a somatic cluster of cells called the hub acts as stem cell niche for the closely associated germline and somatic stem cells. The signalling pathways involved in the decision between self-renewal and differentiation are outlined on the right. (c) In the mouse testis, the stem cell niche comprises different factors; Sertoli cells, Leydig cells and vascularization seem to play a role. The outline on the right depicts the factors promoting self-renewal of the germline stem cells.