Cells in discs with prior cell death are resistant to IR-induced cell death.

<p>Wing imaginal discs were extirpated from third instar larvae 4(-IR) or 4000 R (+IR) of X-rays, fixed and stained for cleaved Caspase 3. Only the pouch regions are shown. <i>A</i> = Anterior. <i>P</i> = Posterior. (A–B) control discs without GAL4. (B) IR-induced caspase staining was similar in the <i>A</i> and <i>P</i> halves of the pouch in <i>y¹w¹¹¹⁸</i> discs. Cells along the D/V boundary where <i>ban</i> sensor is high, reflecting low <i>ban</i> activity, were more sensitive to IR-induced death (yellow brackets). (C–F) discs from larvae with one copy of <i>ptc-GAL4</i> and one copy of UAS-ds RNA against ATM (C,D) or dE2F1 (E, F). Areas with reduced IR-induced caspase activity (arrows) were found anterior to the domain of cell death induced by <i>ptc-GAL4</i> (between lines). Cells along the D/V boundary were refractory to the protection (yellow brackets in F). (G–J) discs from larvae with one copy of <i>ptc-GAL4</i> and one copy of UAS-<i>rpr</i> (G, H) or UAS-<i>hid</i>, UAS-<i>rpr</i> (I, J). These larvae also carried one copy of <i>tub-GAL80^ts</i>. The protected areas (arrows) included most of the A compartment and parts of the P compartment in (H). The protected area was even greater in (J). We note that death in the <i>ptc</i> domain in Hid/Rpr discs was wider in –IR discs than in +IR discs. These cells seemed to protrude from the disc after irradiation, which could explain the narrowing of the domain. (K) shows the timeline followed. Embryos were collected for 4–6 hours. The duration of incubation at 29°C was 24 hours for ATM or dE2F1 RNAi larvae and 12 hours for Rpr or Hid/Rpr larvae.