Fig. 1. Vg expression, QE activity and wing development in wild-type, vg^b and vg⁰ wing discs. (A,A') 1XQE-lacZ (A, ß-gal, red) and Vg (A', blue) expression define the wing primordium of the mature Drosophila wing disc (also delimited by a characteristic fold, white dots). The surrounding rotund (rn)-only domain (unlabeled) is circumscribed by the inner of two rings of Wg expression [green; inner ring (IR), yellow arrowhead and yellow dots in A-C,E; outer ring (OR), purple arrowhead]. (B,C) Vg and 1XQE-lacZ expression and the wing primordium are absent, and the rn-only domain is reduced or eliminated in vg^b (B) and vg⁰ (C) discs. (D-E') Vg and 1XQE-lacZ expression and wing development are rescued in rp49-vg vg^b discs (D,D'), but not in rp49-vg vg⁰ discs (E,E'; except for a few patches of weak 1XQE-lacZ expression visible in the overexposed image in E'). The rn-only domain appears rescued in both rp49-vg vg^b and rp49-vg vg⁰ discs. Vg expression is also restored in D-V border cells of rp49-vg vg^b discs (albeit only in the wing pouch), indicating additional BE(s) in the vg^b gene. (F-G') Tub1>vg clones (black by the absence of GFP, green) autonomously rescue 1XQE-lacZ expression and wing development in vg^b (F,F') and vg⁰ (G,G') discs. 1XQE-lacZ is expressed in a quadrant pattern in both cases, presumably in response to Wg-expressing (faint green) D-V border cells. Vg expression (bright blue) appears normal in the wing pouch of the vg^b disc (F'), indicating a normal QE response by the vg^b allele superimposed on the uniform, moderate level of exogenous Vg (dull blue, compare F',G'). Here, and in the remaining figures, clones were induced during the first larval instar (unless otherwise stated), discs are from mature third instar larvae, anterior is left, dorsal is up, protein or reporter gene stains are indicated by color, and relevant genotypes are indicated either above the images or, in the case of clones, indicated by outlined ovals filled in red, blue or black, as marked in the experiment.