Fig. 7. Dlp overexpression blunts the Wingless gradient while loss of dlp sharpens it. (A) Overexpression of Dlp with engrailed-gal4 eliminates expression of senseless (a `high Wingless target') in the posterior compartment (on the right of the broken line where engrailed-gal4 is expressed). (B) At the same time, expression of distal-less, a `low Wingless target' is broadened (arrowhead) specifically in the posterior compartment. (C,D) A similar broadening of distal-less expression is seen in large Dlp misexpression clones (right-hand clone, marked with GFP in C). There is slight upregulation of distal-less at the edge of the clone within its normal domain of expression (arrowhead in D) consistent with increased presentation activity as a result of Dlp overexpression. (E,F) Mutant dlp cells have reduced levels of Wingless protein. Mutant clones are marked by the absence of GFP (green in E). Reduction of Wingless protein (shown in F) is subtle but unambiguous [see, for example, the reduction in the number of vesicles in the mutant area (arrowhead)]. (G,H) Reduction of Wingless protein at the surface of dlp mutant cells. Extracellular staining (shown in H) was performed as described previously (Strigini and Cohen, 2000). Again, mutant cells are marked by the absence of GFP (green in G). (I,J) Expression of distal-less in wild type (I) and homozygous dlp (J) discs. Both panels are from discs processed and photographed under identical conditions. The domain of distal-less expression is clearly narrower in wing discs obtained from dlp homozygous larvae than in the wild type. Thus, in dlp mutants, a low level target is activated over a reduced range. (K,L) Expression of senseless in wild-type (K) and homozygous dlp (L) discs. Again, both panels are from discs processed and photographed under identical conditions. The domain of senseless expression is slightly wider in the dlp mutant, consistent with the formation of ectopic bristles near the adult wing margin.