Fig. 3. Posterior Dally levels influence Dpp signaling and compartment size. (A,A') An en-Gal4; UAS-GFP haltere disc stained for P-Mad. The AP boundary is traced in yellow. Little P-Mad staining is found in the P compartment of the haltere. (B,B') An en-Gal4; UAS-lacZ, UAS-dally^weak haltere disc stained for P-Mad. Boosting dally levels in the P compartment of the haltere increases the intensity and extent of posterior P-Mad staining. This genotype also causes a reduction in P-Mad staining in the A cells abutting the AP compartment boundary (arrow). (C,C') Driving a stronger version of UAS-dally (UAS-dally^strong) ith en-Gal4 causes most of the P-Mad signal to shift into the P compartment, non-autonomously reducing P-Mad levels in adjacent A-compartment cells to near basal levels (arrow). (D) en-Gal4; UAS-dally^weak haltere discs have a larger P:A ratio (in the Nubbin-marked, appendage-forming domain) than control (en-Gal4; UAS-lacZ) haltere discs. (E) Expressing UAS-dally^weak in the haltere P compartment increases overall adult haltere size by 5% as compared with control (en-Gal4; UAS-lacZ) halteres. A, anterior compartment; P, posterior compartment.