Fig. 4. Elevated Rac activity disrupts tracheal cell adhesion. (A-D) Time-lapse observations of a btl-Gal4, UAS-GFP-moesin/UAS-DRac1V12 embryo. By stage 12, tracheal branching is already delayed (A), and in the next 4 hours many of the tracheal cells are expelled in clusters of one to five cells. (E-H) High-magnification images of a btl-Gal4, UAS-GFP-moesin/UAS-DRac1V12 embryo. Tracheal cells have become spherical and detached from the tracheal cell cluster. Arrows follow the same tracheal cell. The thin arrow in H indicates a thin stalk of cytoplasm. (I,J) Activated Rac1 transforms the tracheal epithelium into a mesenchymal state. gfp-moesin-labeled cells (green) form large cell aggregates in which expression of apical cell marker Crumbs (purple in I, grayscale in I') and E-Cadherin (purple in J, grayscale in J') were greatly reduced. In J, E-Cadherin is undetectable in the trachea, although its expression in the malpighian tubule appears to be normal (arrows). Scale bars: in A,I,J, 40 µm for A-D,I,J; in E, 5 µm for E-H.