Fig. 7. Ubx-mediated repression of Vg in non-DV cells is downstream to Arm and upstream to Vg-autoregulation. (A,B) dpp-GAL4/UAS-N^intra-haltere discs stained for Vg (A) and Wg (B). Unlike in wing discs, activation of Vg by ectopic N^intra is cell autonomous and Wg is not activated in haltere discs. (C,D) dpp-GAL4/UAS-activated Arm-haltere discs stained for Vg (C) and Wg (D). No activation of Vg and Wg was observed. Compare this with Fig. 3E, which shows cell-autonomous activation of Vg in wing discs by ectopic Arm. (E,F) Wild-type (E) and vg¹/vg¹- (F) haltere discs showing the expression pattern of N23-GAL4. As in wing discs, the GAL4 driver is expressed in non-DV cells of haltere discs, but only in the posterior compartment. (G,H) N23-GAL4/UAS-vg- (G) and vg¹/vg¹; N23-GAL4/UAS-vg- (H) haltere discs stained for vg-QE (red) and Wg (green). Note that Vg is capable of activating its quadrant enhancer in both wild-type and vg¹/vg¹ backgrounds. This suggests that downregulation of Vg by Ubx in non-DV cells in wild-type haltere discs is upstream of Vg-autoregulation.