Fig. 2. Mislocalization of E-Cadherin in tracheal cells that have reduced Rac activity. (A-B) Wild-type embryonic trachea at stage 12 (A) and stage 14 (B). Cell nuclei are marked with nuclear localized ß-galactosidase expressed by btl-Gal4 (green in A,B). The apical cell surface is labeled with anti-Crumbs (purple in A,B). Grayscale images of anti-Crumb are shown in A' and B'. Tracheal branches migrate toward the positions labeled with broken circles in which Bnl/FGF is expressed (Sutherland et al., 1996). While tracheal branches extend, cells of the dorsal branch (DB) and dorsal trunk (DT) rearrange their relative positions and form thinner tubules. (C,D) Wild-type (C) and btl-Gal4/+; btl-Gal4/UAS-DRac1N17 (D) embryos were stained with monoclonal antibody 2A12, which labels the tracheal lumen. In Rac1N17-expressing trachea, phenotypes of zigzagged and/or truncated DT were similar to those of Rac1, 2 mutants (compare D with G). (E-H,I) Wild-type (E,F), Rac1, 2 mutant (G,H) and btl-Gal4/+; btl-Gal4/UAS-DRac1N17 (I) embryos were stained with anti-E-Cadherin (purple), and tracheal cells were marked with GFP-moesin (green) to reveal F-actin. Grayscale images of anti-E-Cadherin are shown separately. F and H are high-magnification images of the broken frames shown in E and G. Arrows and arrowheads indicate basal and apical cell membranes of tracheal cells, respectively (F,H). E-Cadherin have accumulated at the apical side of the lateral membrane in wild-type trachea (E,F). In Rac1, 2 mutant and btl-Gal4/+; btl-Gal4/UAS-DRac1N17 embryos, E-Cadherin has abnormally accumulated at the basal membrane of tracheal cells (G-I). In I, E-Cadherin accumulation in cell protrusions is also evident (arrows). Scale bars: 20 µm in B,E,G,I; 5 µm in F,H; 40 µm in C.