Fig. 2. knk and rtv functions in the chitin-mediated pathway of tube-size control. (A-F) Mutations in knk and rtv do not enhance the tracheal phenotypes of chitin-deficient embryos. Wild-type embryos laid by Nikkomycin-fed parents (1 mg/ml) (D) develop full kkv tracheal phenotype with local dilations and cysts, compared with wild type (A). This phenotype is similar to that of knk^7A69 mutants (B) and to knk^7A69 mutant embryos laid by Nikkomycin-fed parents (E). Also chitin-deficient rtv¹¹ mutant embryos laid by Nikkomycin-fed parents (F) develop tracheal phenotypes indistinguishable from that of chitin-deficient embryos, but the untreated rtv¹¹ mutant embryos (C) display less severe tube dilations. (G,H) When wild-type flies are fed with a low Nikkomycin dose (0.5 mg/ml) (G), their embryonic offspring display tracheal phenotypes reminiscent of the rtv¹¹ mutant phenotypes (H). Scale bars: 15 µm in A-F; 20 µm in G,H.