Fig. 5. Slit signaling is required for the outgrowth of tracheal branches outside the CNS. Lateral view of stage 16 embryos carrying one copy of the 1-eve-1 lacZ marker stained to visualize tracheal cells and lumen. In robo2 (B) and slit (C) mutant embryos outgrowth of the dorsal branches (DBs) is disrupted, resulting in missing (asterisks) or short DBs. In robo mutants (A), DB outgrowth is not affected. Several of the GBs in robo2 (E) and slit (F) mutants are shorter and misrouted (asterisks) In robo mutants (D), GBs migrate ventrally as in wild-type embryos (arrow in D). Scale bar: 20 µm in A-F.