A,B, D–G) Stage 16 embryos stained for the 2A12 luminal antigen showing the tracheal tree (upper panels) or a close up of a dorsal trunk of the same embryo (lower panels). Moderate overexpression of Crb lengthens and widens dorsal trunks (A). Reducing crb dosage rescues tube size defects in yrt mutant embryos (B), but not in verm (D,E) or sinu (F,G) mutant embryos. C) Staining showing Verm (green) and 2A12 (red) in a dorsal trunk of an embryo overexpressing Crb. Overexpression of Crb does not interfere with Verm secretion. Scale bars: A,B,D–G, 100 μm; C, 30 μm; A′,B′,D′-G′, 30 μm.