Fig. 2. drl and Wnt5 are required for proper positioning of the tip of the salivary gland. (A-A'') Wild-type Drosophila embryos were hybridized in situ with fkh and drl probes. Ventral view of a stage 11 embryo. The drl receptor is expressed in the dorsoposterior of the salivary placode (arrow), which later corresponds to the salivary gland cells that lead invagination into the embryo. (B-B'') Lateral view of stage 15 embryo with an enhancer trap insertion at the drl locus. ß-galactosidase expression at the salivary gland is confined to the distal tip. Arrows denote the location of drl expression in the salivary gland. (C-H) Lateral view of stage 15-16 embryos stained for FKH and the apical cell marker CRB. (I) Graphical representation of phenotypic penetrance in embryos scored for salivary gland migration defects at stages 14-16. (C) Wild-type control. (D,I) In drl-null embryos, the salivary glands curve ventromedially. (E,I) The drl^R343 mutant phenotype can be rescued by UAS-drl using a salivary-gland-specific GAL4 driver, fkh-GAL4. (F,I) The intracellular domain of drl is important for drl function, as UAS-drlⁱ does not rescue the salivary gland migration phenotype in drl^R343 mutant embryos. (G,I) In embryos lacking Wnt5 the tip of the salivary gland is bent toward the CNS. (H) Lateral view of a stage 15 embryo stained with the salivary gland marker SG2 in green, the mesodermal marker Titin in red and the CVM marker FASIII also in green. The salivary glands of drl^R343 mutant embryos do not maintain contact with LVM (compare with Fig. 1K).