Fig. 1. dally expression and Dpp signaling are reduced in the posterior haltere. (A-A'') Comparison of dally-lacZ and P-Mad staining in the wing and haltere. In the wing, dally-lacZ is expressed similarly on both sides of the AP organizer (A'). In the haltere, dally-lacZ expression is low in the P compartment, especially in P cells abutting the AP boundary (arrow). P-Mad staining in the wing is detected in two slopes that peak at either side of the AP organizer, whereas in the haltere, P-Mad is detected in a single stripe (A''). (B) dally-lacZ intensity traces for the wing and haltere discs shown in A. The approximate position of the AP boundary is indicated here (and in D,F) by an arrow. Note the symmetry in dally expression in the wing with respect to the AP organizer (just left of the arrow), as compared with the asymmetry in the haltere. Also note the generally lower dally levels in AP organizer cells and the hyper-repressed levels in the P cells abutting the AP boundary in the haltere. (C-C'') The repression of dally-lacZ in the haltere correlates with very low P-Mad staining in the P compartment. The yellow line marks the AP compartment boundary. Note that strong P-Mad labeling is detected for only one or two cell diameters posterior to the AP boundary, and that the basal level of P-Mad staining is higher in the A compartment (compare levels at asterisks in C''). (D) Intensity plots of P-Mad and dally-lacZ stainings from the pouch region of the wild-type haltere disc shown in C. In the P compartment, P-Mad staining drops off rapidly, coinciding with a sharp drop in dally-lacZ. P-Mad staining persists much further away from the AP organizer in the A compartment (arrow). The blue dotted line marks the low point of the P-Mad signal. (E-E'') ptc-Gal4 UAS-dpp::GFP wing and haltere discs stained for P-Mad (blue) and for GFP using an extracellular staining protocol (red). The green channel shows GFP autofluorescence. In the haltere (enlarged in E' and E''), extracellular Dpp::GFP and P-Mad detection stop a few cell boundaries posterior to the AP boundary (white arrow), whereas these signals decay more gradually in the A compartment (compare staining around asterisks). (F) Intensity plots of extracellular-GFP, P-Mad and GFP autofluorescence for the haltere disc shown in (E'). P-Mad and extracellular-GFP staining extend further anteriorly than posteriorly from the site of Dpp::GFP production (approximated by GFP autofluorescence). W, wing; H, haltere; A, anterior compartment; P, posterior compartment.