Reservoirs for repair? Damage-responsive stem cells and adult tissue regeneration in Drosophila.

Adult stem cells in mammals are important for normal tissue renewal (homeostasis) and regeneration after injury. In the past ten years, different types of homeostatic adult stem cells have also been identified in the genetically accessible fruit fly (Drosophila melanogaster), among which intestinal stem cells have taken centre stage. Recent studies provide evidence that adult fly tissues may also harbor quiescent stem cells, which can enter cell cycle upon injury to regenerate compromised tissue. Such damage-responsive stem cells have been described in flight muscles, the adult brain and in a narrow region of the fly hindgut. Strikingly, many mammalian tissues have also been shown to maintain quiescent, but regeneration-competent, stem cells. However, little is known about the injury-induced signals that lead to their activation. Here, we provide a brief overview of active and damage-responsive adult stem cells in the fruit fly and focus on injury-dependent signalling events. We highlight the potential of Drosophila to model damage-induced stem cell activation to deepen our molecular understanding of how dormant stem cells can be efficiently recruited for tissue repair after injury.