Fig. 5. Invagination defects in EGFR-related mutants. Tracheal invagination phenotypes in stage 14 embryos. (A) All of the btl-GFP- expressing cells were internal except for the spiracle cells (arrow). (B-D) Many of the btl-GFP- expressing cells remained external in the rho (B), Egfr (C), and pnt (D) mutants. (E,F) The tracheal placode expanded 1.5 fold in the Egfr^-/- (F) compared with Egf^r+/- (E) embryos. (G) In the Egfr mutants, the invagination position (arrows) was variable and sometimes duplicated. (H-K) Position of invagination sites (% position measured from the dorsal edge) and the number of sites in controls, and in Egfr, Dsor1 and pnt mutants. The incidence of double invagination observed in Egfr and Dsor1 embryos was counted separately, without reference to their position. Scale bars: 10 µm.