The simplicity of the stem cell niche in the Drosophila testis makes it an ideal model for understanding niche-stem cell interactions. It is composed of 10-15 hubs cells, which are surrounded by germline stem cells (GSCs) and somatic cyst stem cells (CySCs). Following ablation of all the CySCs, the quiescent hub cells are able to proliferate and leave the hub to replace the lost CySCs, but whether lost hub cells can be replaced was not known. Now, Erika Matunis and colleagues discover that lost hub cells are not replaced by either proliferation of remaining hub cells or by CySCs. First, they find that genetic ablation of all hub cells results in a complete loss of the niche. However, when using elegant GeneSwitch experiments to remove some of the hub cells, they observe that while the niche remains functional, the lost hub cells are not replaced. Furthermore, they detect no proliferating cells in the hub during ablation or in the following 24 hours. Together, these data demonstrate that lost hub cells in the Drosophila testis cannot be replaced either by remaining hub cells or by conversion of another cell type.
