Fig. 5. Ubx control of dally expression in the haltere. (A,A') Wild-type dally-lacZ patterns in wing and haltere discs. AP organizers are indicated by arrows to highlight high dally-lacZ levels in the wing and moderate levels in the haltere. (B,B') Clones in which the Dpp pathway is activated with UAS-tkv^QD (marked by GFP) downregulate dally-lacZ in both the wing and haltere (arrows). (C,C') Driving high tkv levels in the wing converts the wing-like pattern of dally-lacZ into a haltere-like pattern in the A compartment. The moderate dally-lacZ expression level in AP organizer cells is indicated by the arrow. (D,D') dally-lacZ is derepressed in Ubx^- haltere clones (identified by the absence of GFP) in the P compartment, especially within the domain of dally hyper-repression (arrow). (E,E') Clones of cells mutant for en (absence of GFP) in the P compartment derepress dally-lacZ in the haltere (arrow). (F,F') Clones expressing Daughters against Dpp (Dad; marked by GFP), which inhibits Dpp signaling, derepress dally-lacZ in the AP organizer (arrow) and dally hyper-repression (arrowhead) domains. Thus, Dpp represses dally in the medial haltere, and is required for the very low dally levels in the anterior-most cells of the P compartment. (G) Diagrams summarizing the locations and consequences of positive and negative inputs into dally expression (broken red line) in the haltere and wing. In the wing, because peak Dpp and Hh signaling occur in neighboring cells, dally levels are high in the AP organizer owing to Hh activation, but are lower in neighboring cells owing to Dpp repression. In the haltere, because peak Dpp and Hh signaling coincide in the same cells, these two conflicting inputs result in intermediate dally levels in the AP organizer. In addition, dally is hyper-repressed in P cells next to the AP boundary because of Ubx, en and Dpp signaling. Similar effects are also observed for dpp expression (blue dotted line), which, like dally, is activated by Hh and repressed by Dpp (see Crickmore and Mann, 2006). A, anterior compartment; P, posterior compartment.