Stem cells depend on intrinsic and local factors to maintain their identity and activity but they also respond to external conditions. For example, Drosophila germline stem cells (GSCs) and follicle stem cells (FSCs) respond to diet via insulin signals. Now, Daniela Drummond-Barbosa and colleagues reveal that the nutrient sensor Target of rapamycin (TOR) controls the stem cells in the Drosophila ovary in numerous ways (see ). TOR, they show, promotes GSC proliferation and maintenance independently of insulin signalling and is required for the proliferation, growth and survival of differentiating germ cells. By contrast, although TOR controls the proliferation of FSCs, it is not required for their maintenance or for the proliferation of their differentiating progeny. Instead, TOR controls follicle cell numbers by promoting their growth and survival independently of apoptosis or autophagy. The researchers speculate, therefore, that TOR is part of a conserved mechanism that ties stem cell maintenance and function, and the survival, proliferation and growth of their descendants, to diet-dependent factors.
