Fig. 6. Cell interactions at the boundary of vg-expressing cells drive the expression of the IR enhancer. (A-G) dpp-GAL4/UAS-hth removes vg expression (A), but does not affect expression of rn (B) or nub (C) (arrows). Note that the activation of the N-dependent vg BE is not repressed (arrowheads in A). wg is ectopically expressed within the Dpp domain in two stripes of cells that abut vg-expressing cells (D-F, arrows). In second instar larvae, the two stripes of Wg are more apparent (D). In third instar larvae, only one stripe is seen because of a fold in the epithelium (F). (G,H) Two results indicate that the new Wg stripe corresponds to the activation of the IR enhancer: Dll expression is missing (G); and n N^ts; dpp-GAL4/UAS-hth (H), wg expression in the wing margin is missing (arrowheads) but the IR and the new stripe of wg is not affected (red arrow). (I) hth is unable to directly activate wg expression: in en-GAL4/UAS-hth only posterior cells in the AP boundary activate the IR (red arrow), indicating that cell interactions with vg-expressing cells are required.