The Initiator Caspase Dronc Drives Compensatory Proliferation of Apoptosis-Resistant Cells During Epithelial Tissue Regeneration After Ionizing Radiation
Caspases, well-known for their role in executing apoptosis, also participate in various non-apoptotic processes. Despite this, their involvement in promoting compensatory proliferation - a key aspect of tissue regeneration following extensive cell death - has been a subject of ongoing ambiguity. In our study, we investigate compensatory proliferation in the Drosophila wing imaginal disc following ionizing radiation, a model epithelial tissue that has been a pioneering system for studying this regenerative response. Using a delayed genetic reporter to monitor the activity of the initiator caspase-2/9 ortholog, Dronc, we identified two populations of apoptosis-resistant epithelial cells involved in compensatory proliferation: those that activate Dronc (termed DARE cells) and those that do not (NARE cells). We show that DARE cells pass their apoptosis-resistance trait to their daughter cells, suggesting a molecular memory. We demonstrate that Dronc in DARE cells, but not the apoptosome adapter Dark and the effector caspases, promotes compensatory proliferation both within these cells and in NARE cells through a non-cell-autonomous mechanism. We found that Myo1D, an unconventional myosin interacting with Dronc, is essential for the survival of DARE cells by preventing the lethal activation of effector caspases and subsequent apoptosis. In contrast, Myo7A/Crinkled, another unconventional myosin that interacts with Dronc, promotes effector caspase activation in DARE cells. We demonstrate that the TNFR>JNK signaling pathway in DARE cells directly regulates their proliferation, which in turn influences NARE cell proliferation. Consequently, we show that maintaining proliferative homeostasis between DARE and NARE cells is vital for balanced tissue regeneration. Given the widespread use of ionizing irradiation in cancer treatment and prevention, our findings have potential implications for understanding treatment-resistant cells and cancer recurrence.