All panels show third instar wing imaginal discs. (A, B, D–F) standard confocal sections. (C) optical cross section, stained with anti-Arm to outline the apical membrane. Clones are positively labeled with GFP (green in D’,E’, F’). (A, C, D, D’; E, E’) cpa anti-sense probe to reveal cpa mRNA expression (white in A,C,D,E and magenta in D’,E’) in wildtype (A, C) or in clones overexpressing vg (white arrow in D, D’) or in clones overexpressing Nintra (white arrow in E, E’). Since cpa mRNA accumulates on the basal surface of the wing disc epithelium, standard confocal sections fail to reveal cpa accumulation in all vg and N-overexpressing clones. (B) cpa sense probe. Note that the background level is very low. (F) clones overexpressing Nintra, stained with anti-Vg (white in F or magenta in F’). Vg is misexpressed.