Fig. 7. (A,B) hth expression detected with antibody to ß-galactosidase in hth-lacZ wing discs. hth is expressed in the wing hinge in two rings (A). The inner ring (red arrow) and the outer ring (red arrowhead) overlap with the IR and the OR of Wg. (B) In spd^fg discs, the hth expression in the inner ring is missing but the outer ring is not affected. (C) rn lineage tracing. Expression of rn visualised by rn-lacZ (red) and by rn-GAL4/UAS-FLP Act>>GAL4/UAS-GFP (green), which labels all the cells that expressed rn at any time during the development of the disc. Note that the green channel shows a broader domain, indicating cells that have lost rn expression. This result suggests that in the border of Rn domain, cells have a tendency to lose rn expression. (D,E) hth^P2 clones, revealed by the absence of GFP (green), remove wg expression (red) in the IR (white arrows) when observed in mature wing discs (D), but do not do so when observed in earlier discs (E). This indicates that the maintenance, but not the initiation, of wg expression requires Hth function. (F-H) wg expression in the IR is required to maintain sharp borders in the vg expression domain. Expression of vg QE-lacZ in wild-type (F), spd^fg (G) and N^ts (H) [at restrictive temperature (30°C)] wing discs detected with antibody to ß-galactosidase. The border of the Vg domain (black arrows) is sharp in wild-type larvae or when wg is removed from the wing margin (H), but less well defined when wg is removed from the IR (G).