Fig. 5. Dpp signaling pathway is activated during squamous morphogenesis in the wing disc. Color images show p-MAD (red) and -spectrin (green). Black and white images (A'-D') show p-MAD and (D'') -spectrin alone. Wing discs are from larvae at 67 hours AED (A,A'), 72 hours AED (B,B') and 96 hours AED (C,C'). (A,A') Prior to squamous morphogenesis, p-MAD is present in a ventral wedge in the PE. (B,B') Early in squamous morphogenesis, a stripe of p-MAD expression appears in the PE (yellow arrowhead). (C,C') During the third instar, p-MAD expression broadens and is observed in the majority of squamous cells of the posterior compartment in the PE. (D-D'') Enlargement of region boxed in C. (D-D'') p-MAD is observed only in squamous cells of the posterior compartment and is absent from margin cells (C,D') in both A and P compartments of the PE. (E) hh-lacZ expression in the wing PE from a wandering third instar larva. Scale bar in A: 50 µm.