Schematic representation of shaft cell development and DIAP1 protein dynamics. DIAP1 degradation is sustained during SOP cell division (phase I) and induced again just before bristle elongation (phase III). In the middle phase (phase II), Dronc could be activated in the absence of DIAP1, indicating that DIAP1 functions as a cell death inhibitor to suppress caspase activation and maintain the cellular integrity. In phase III, DIAP1 needs to be degraded with specific timing to regulate shaft cell morphogenesis appropriately. PRAP expression dynamics are shown in green and bristle length as a magenta line.