Fig. 5. Involvement of the Drosophila EXT genes in Dpp signalling. All discs are oriented anterior left, dorsal up. (A-D') p-Mad staining in a wild-type wing disc (A), and in discs carrying mutant clones of ttv⁶³ (B,B'), sotv⁴⁴ (C,C') and botv¹⁰³ (D,D'). The mutant clones are marked by the absence of GFP and are outlined with dots. (E-H') UAS-GFP-dpp under the control of dpp^Gal4 in an otherwise wild-type wing disc (E) and in discs carrying mutant clones of ttv⁶³ (F,F'), sotv⁴⁴ (G,G') and botv¹⁰³ (H,H'). The mutant clones are marked by the absence of DsRed and are outlined with dots. The distribution of GFP-Dpp outside the Dpp expression domain in the wild-type background appears to be a gradient extending towards the A and P compartments. Within the mutant clones of ttv⁶³, sotv⁴⁴ and botv¹⁰³, the ranges of the GFP-Dpp gradient are greatly reduced.