Fig. 3. Rescue of tracheal cell migration in the absence of dof. Whole-mount antibody staining for the tracheal lumen of stage 15 embryos using the 2A12 antibody (green, A,B,D,E,G,H,J,K; red, C,F,I,L) and for the terminal cells using the anti-DSRF antibody (green, C,F,I,L). Embryos from crosses described in the Materials and Methods were collected at 18°C and 25°C. (A) Tracheal system of a homozygous dof mutant embryo upon the expression of a dof transgene driven by btl-Gal4. Apart from defects that are due to the malformation of the mesoderm in dof mutant embryos (for example, truncation of visceral branches), the tracheal system was fully rescued. (B) The Btl wild-type receptor construct was not able to rescue tracheal cell migration in btl,dof double mutant embryos. (C) DSRF/bs expression was not induced in any tracheal cell in btl,dof mutant embryos expressing the btl transgene. (D,E) The Btl-Htl chimeric receptor construct was not able to rescue tracheal cell migration in btl,dof mutant embryos. (F) DSRF/bs expression was not induced in the tracheal cells of btl,dof mutant embryos expressing Btl-Htl. (G,H) In contrast to Btl and Htl, the Btl-Tor fusion protein was able to rescue tracheal cell migration in btl,dof mutants. The general pattern of the tracheal system was rescued. Dorsal trunk fusion occurred efficiently but some dorsal branches failed to form (dorsal arrowheads). The lateral trunk did not fuse (arrows) and depending on the embryo, one or two ganglionic branches failed to form (ventral arrowhead). (I) Expression of the Btl-Tor construct led to ectopic activation of DSRF/bs and terminal cell formation in btl,dof mutant embryos (arrow). (J,K) The Btl-EGFR construct was able to rescue tracheal cell migration in btl,dof mutant embryos to a certain extent. General tracheal patterning was rescued, although the tracheal tree was more affected. In some embryos the dorsal trunk was disrupted, some dorsal branches were missing (dorsal arrowheads) or misguided (dorsal arrow) and the lateral trunk failed to fuse (ventral arrows). In contrast to the rescue by Btl-Tor, some of the ganglionic branches failed to form and did not migrate in proper direction (ventral arrowhead). (L) DSRF/bs expression was strongly reduced in btl,dof mutant embryos expressing Btl-EGFR (arrow).