Fig. 5. Anteriorly localized upd expression is required for hindgut elongation. When upd is expressed throughout the hindgut (using bynGAL4) in an upd^os1A mutant background, the hindgut is shorter and more deformed (A) and has as many or more cells in transverse section (B) than that seen in upd^os1A embryos (compare with Fig. 3B,F). When upd is expressed only in the small intestine (using drmGAL4) in an upd^os1A mutant background, the length of the hindgut and number of cells in transverse section is almost indistinguishable from that seen in wild-type (C,D; compare with Fig. 3A,E). The drm³/drm⁶ hindgut is short and wide (E) and has an excessive number of cells in its circumference (F). When upd is expressed only in the small intestine (using drmGAL4) in a drm³/drm⁶ mutant background, the hindgut is more elongated (G), and has fewer cells in its circumference (H) than seen in drm³/drm⁶. This phenotype is similar to the rescue of the drm³/drm⁶ hindgut that is seen when drmGAL4 is used to drive UAS-drm (R. B. Green, PhD thesis, UCLA, 2002). Hindgut apical surfaces are outlined by anti-Crb staining; embryos are stage 16; GAL4-driven expression patterns are shown on the right of each pair of panels. Length measurements and circumference counts are summarized in I.