Overexpression of GFP-Smash PM or Shrm leads to reduced lumen diameter of the embryonic dorsal tracheal trunk. (A–F) αCatenin-GFP (A and D), GFP-Smash PM (B and E), or Shrm (C and F) together with αCatenin-GFP were overexpressed in the tracheal system of stage 16 embryos using breathless::Gal4 as driver. A–C are confocal images of GFP fluorescence in three adjacent segments of the dorsal tracheal trunk of living embryos of the indicated genotypes. Fusion points are indicated by red arrowheads. D–F are higher-magnification images of the AJs of ring-like fusion cells viewed from the side; right panels are the same junctions seen in cross section reconstructed from z-stacks. Lumen diameter in right panels is indicated by red double-headed arrows. (G) Quantification of lumen diameter measured at the fusion point between tracheal metameres 6 and 7 (red asterisks in A–C in the three genotypes indicated at the bottom). ***, P < 0,001; ns, not significant; Student’s t test. n = 11 for btl>αCat-GFP; n = 10 for btl>GFP-Smash PM and btl>Shrm, αCat-GFP. Bars: (A–C) 20 µm; (D–F) 5 µm. Error bars show mean ± SEM.