Fig. 2. Extrusion of cpa mutant cells is independent of programmed cell death. All panels show third instar wing imaginal discs. (A-C) Optical cross-sections of discs stained with anti-Dlg (blue in A,B'',C) to outline apical cell membranes and anti-Caspase 3 (red in A,B',B'') or anti-ß-Galactosidase to reveal puc-lacZ expression (red in C). Anti-Caspase 3 antibody gives a non-specific background staining seen at the apical surface of the discs. (A) T155-Gal4; UAS-flp induced cpa^69E mutant clones marked by the absence of GFP (green). (B-C) hs>flp induced cpa^69E (B) or cpa^107E (C) mutant clones, positively labeled with GFP (green). (A,B'',C) The overlay of all three channels. cpa mutant clones express Caspase 3 and puc-lacZ cell autonomously. Cell death is seen when FLP is induced either by heat shock or by the epithelial driver T155-GAL4, and is therefore not due to stressed conditions induced by heat shock, as described for clones mutant for the Dpp receptor thickveins (tkv) (Gibson and Perrimon, 2005). (D-I) Standard confocal sections (D-F) or optical cross sections (G-I) of clones positively labelled with GFP (green) and stained with anti-Dlg (red) and anti-Arm (blue). (D,G) cpa^107E mutant clones; (E,H) clones overexpressing th; (F,I) cpa^107E mutant clones overexpressing th. th overexpression promotes survival of cpa mutant cells, but fails to prevent their extrusion. The white arrows define the wing blade region.