Compensatory proliferation induced by cell death Drosophila wing disc requires activity of the apical cell death caspase dronc in a nonapoptotic role requires

Achieving proper organ size requires a balance between proliferation and cell death. For example, at least 40%-60% of cells in the Drosophila wing disc can be lost, yet these discs go onto give rise to normal-looking adult wings as a result of compensatory proliferation [1-3]. The signals that drive this proliferation are unknown. One intriguing possibility is that they derive, at least in part, from the dying cells. To explore this hypothesis, we activated cell death signaling in specific populations of cells in the developing wing but prevented these cells from dying through expression of the baculovirus p35 protein, which inhibits the activity of effector caspases that mediate apoptosis [4]. This allowed us to uncouple the activation steps of apoptosis from death itself. Here we report that stimulation of cell death signaling in the wing disc-in the absence of cell death-results in increased proliferation and ectopic expression of Wingless, a known mitogen in the wing. Activation of the apical cell death caspase Dronc is necessary and sufficient to drive both of these processes. Our results demonstrate an unanticipated function, the nonautonomous induction of proliferation, of an apical cell death caspase. This activity is likely to contribute to tissue homeostasis by promoting local compensatory proliferation in response to cell death. We speculate that dying cells may communicate cell fate or behavior instructions to their neighbors in other contexts as well.