Fig. 4. Enhanced degradation of Arm in haltere discs. (A-D) Wild-type expression of Arm in wing (A,B) and haltere (C,D) discs. (A1,C1) Higher magnification images of wing (A1) and haltere pouch (C1). In wing discs, cells surrounding Wg-expressing DV boundary cells show higher levels of Arm (A,A1,B). In haltere discs, levels of Arm at the DV boundary are indistinguishable from those of non-DV cells (C,C1,D). In a few haltere discs, we observed somewhat higher levels of Arm in the cells that intersect the A/P and DV boundaries (D). (E) vg-GAL4/UAS-Ubx-wing disc. Ectopic Ubx downregulates Arm levels in the DV cells of the wing disc. (F,G) omb-GAL4/UAS-arm^S10-wing (F) and -haltere (G) discs. Wing and haltere discs show comparable levels of degradation-resistant Arm expressed from UAS-arm^S10. (H,I) omb-GAL4/UAS-arm^S2-wing (H) and -haltere (I) discs. In wing discs, overexpression of wild-type Arm from UAS-arm^S2 leads to accumulation of Arm only in the presumptive DV boundary and hinge cells. However, no significant accumulation of wild-type Arm (from arm^S2) is seen in the DV boundary of haltere discs, although, as in wing discs, hinge cells accumulate large amounts of wild-type Arm. This suggests that Ubx enhances degradation of Arm in the haltere pouch.