Fig. 4. Wg, Hh and Egfr signalling are required in spiracular chamber and stigmatophore cells for posterior spiracle organogenesis. (A-D) ems-Gal4 or sal-Gal4 promote expression at late stage 11. ems-Gal4/UAS-GFP (A,B) and sal-Gal4/UAS-GFP embryos (C,D), immunostained in red for GFP, and in green for Cut (A,B) and Sal (C,D) at early (A,C) or late (B,D) stage 11. GFP is detected in late stage 11 embryos, roughly 1 hour after the onset of Sal and Cut protein accumulation in the dorsal A8 ectoderm.(E-J) Effects of DN-TCF (E,H), DN-Egfr (F,I) and DN-Ci (G,J) expression driven by ems-Gal4 or sal-Gal4. Blocking either signalling by ems-Gal4 impairs filzkörper formation, and not that of stigmatophore (E-G). Reciprocally, blocking either signalling by sal-Gal4 impairs stigmatophore development, leaving filzkörper differentiation unaffected (H-J). The stigmatophore phenotype resulting from the loss of Hh signalling (J) is weaker than those resulting from the loss of Wg and Egfr signalling (H,I).