Fig. 1. knk and rtv are required for uniform tracheal tube expansion. The developing tracheal lumen of wild-type, knk and rtv mutant embryos was visualized with the lumen-specific antibody 2A12. (A-C) Stage 16 knk^7A69 (B) and rtv¹¹ (C) mutant embryos display irregular tracheal tube shapes, but no defects in branch patterning, compared with wild-type embryos (A). The box in A depicts the dorsal trunk (DT) region in D-L. (D-F) At stage 14, the 2A12 antigen begins to accumulate in the wild-type DT lumen (D), but is reduced in the lumen of knk^7A69 (E) and rtv¹¹ (F) mutants. (G-I) During stage 15, the wild-type DT lumen (G) expands uniformly, whereas the DT lumen of knk^7A69 (H) and rtv¹¹ (I) mutants remain constricted at branch fusions (arrows), and the tube between fusion junctions becomes excessively overgrown. (J-L) During stage 16, the knk^7A69 (K) and rtv¹¹ (L) mutant DTs in addition become extensively elongated compared with the wild-type trunk (J). (M-O) The lumen of the narrower multicellular ganglionic branches (GB) is discontinuous in knk^7A69 (N) and rtv¹¹ (O) mutants at the border of the ventral nerve cord (arrowheads), compared with wild type GB (M). (P) Illustration of tracheal cell shape changes during DT expansion at stage 15. The DT lumen is encircled by three to five cuboidal cells (pale grey) attached to each other by intercellular junctions, apart from the branch fusion lumens, which are surrounded by two toroidal cells (dark grey). Lumen expansion from stage 14 to 15 does not involve cell division and relies on coordinated growth of the apical cell surfaces. (Q) The GB branches are made by rows of single cells folding over themselves, and the arrowhead points to where lumen discontinuities are observed in knk^7A69 and rtv¹¹ mutants. Different shades of grey are used to distinguish neighbouring cells in the row. Scale bars: 25 µm. DT, dorsal trunk.