Fig. 4.

Synergy of Notch and Wingless in Drosophila. Adult eyes (Top) and corresponding larval eye imaginal discs of Drosophila in different genetic backgrounds (see Results for detailed genotypes), stained for BrdU (in red, Middle) to indicate cells in S phase and elav (in green, Bottom) a marker of neuronal differentiation. (B′ and E′) White arrows in indicate ectopic proliferation in the eye imaginal discs. (Bottom) White arrowheads indicate the positions of the morphogenetic furrow. (A–A″) Wild-type animals. (B–B″) Nic-expressing flies show a large-eye phenotype induced by Notch activation. Abnormal, ectopic BrdU incorporation is indicated by the arrow in B′, whereas neuronal differentiation is unaffected in B″. This phenotype is suppressed by expression of dominant-negative Pangolin, the Drosophila homolog of Tcf4. Flies expressing Nic and dominant-negative Pangolin present adult eye morphology, BrdU incorporation, and elav pattern of expression undistinguishable from wild-type flies (compare A–A″ with C–C″). In contrast, the expression of a gain-of-function wingless allele in these flies dramatically enhances the Nic phenotype (compare B–B″ with D–D″). (E–E″) A similar synergy is also observed in flies expressing Nic and harboring a loss-of-function mutation of the Wnt antagonist Apc.