a, Homozygous wg[KO; NRT-Wg] flies and one control (wg[KO; NRT-Wg]/GlaBC) fly. b, Wings from a control (wg[KO; NRT-Wg]/GlaBC, and a homozygous wg[KO; NRT-Wg] fly (see size information and details of the wing margin in Extended Data Figure 1i-l). c, d, Expression of Frizzled3-GFP and Distalless in control and homozygous wg[KO; NRT-Wg] imaginal discs. e, f, Fluorescence intensity profile along lines connecting red arrowheads. g, h, Wingless immunoreactivity in a control (wild type) and a homozygous wg[KO; NRT-Wg] disc, with corresponding transverse sections (along line connecting white marks). i, Excision of HA-tagged NRT-Wingless (red and white arrows) from wg[KO; FRT.NRT-Wg.FRT QF] with Flp produced from hedgehog-gal4 tubulin-gal80ts UAS-flp at 29°C. Low magnification frontal view and high magnification transverse section along line defined by white marks are shown.