Fig. 2. wg expression and XC enhancer activity depends on Dpp and Wg signaling. (A,B) wg transcripts revealed by in situ hybridization. Arrowheads indicate PS8, the site of wg midgut expression in wild-type embryos (A). wg expression is completely abolished in the midgut of dpp^s13 homozygous-mutant embryos (B). (C-L) Regulation of XC or XC([Hox/Pbx2-3-4]) enhancer activity by AbdA, Dpp and Wg visualized by in situ hybridization to lacZ transcripts. All panels show magnifications of lateral views of the midgut of stage 14 embryos, except panel F, which is from a stage 15 embryo. Embryos in C,J,K and L have been processed in the same conditions and the length of staining time was identical. Arrows indicate sites of ectopic enhancer activity. The embryo in C bears a wild-type copy of the XC enhancer and serves as a reference for the activity of XC variants. With respect to wg expression, XC enhancer activity in the wild type (C) is lost in dpp^s13 homozygous-mutant embryos (D). The embryo in D has been overstained to ensure the absence of lacZ staining. Mesodermal ubiquitous expression of Dpp in 24B-Gal4/UAS-dpp embryos induces ectopic activity of the XC enhancer posterior to PS8 (E) in cells where AbdA is present. At stage 15, ectopic sites of XC activity coincide with the sites of extra constrictions that form in this genotype (F). Mesodermal ubiquitous expression of AbdA in 24B-Gal4/UAS-abdA embryos weakly induces ectopic activity of the XC enhancer anterior to PS8 (G), in close proximity to the PS7 Dpp source. In 24B-Gal4/UAS-abdA embryos, ectopic XC([Hox/Pbx2-3-4]) enhancer activity is stronger than XC enhancer activity, and is also detected more anteriorly, close the source of Dpp in VM cells close to PS3-4 (H). Simultaneous expression of AbdA and Dpp in 24B-Gal4/UAS-dpp/UAS-abdA embryos induces ectopic XC enhancer activity anterior and posterior to PS8 (I). XC activity is diminished in wg^IL114 homozygous embryos shifted to restrictive temperature at 7 hours of development at 25°C (J) or in 24B-Gal4/UAS-Tcf(DN) embryos expressing the dominant-negative form of the Wg transcriptional effector Drosophila Tcf (K). In wg^ILL114 homozygous mutants grown at 29°C, ectopic Dpp signaling provided by 24B-Gal4/UAS-dpp still induces, although at lower levels, ectopic XC enhancer activity (L).

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