Fig. 2. rho3 acts independently of slit. (A-D) Slit protein levels are not changed in rho3 mutants. An anti-Slit antibody (in green; red is the tracheal lumen, mAb2A12) detects similar levels of Slit in early (C) and late (D) rho3 stage 16 embryos when compared with wild type (A,B), even in the vicinity of branches that cross the midline in the mutant (D, arrows). A-D are ventral views, anterior towards the left. Scale bar in B: 20 µm. (E-G) A ventral view of late stage 16 embryos stained for the tracheal lumen (by mAb2A12) reveals GB pathfinding defects in slit mutants (F) and slit, rho3 double mutants (G) when compared with wild type (E, anterior is towards the left). (H) Quantification of the midline cross phenotype shows that the effect of the two mutations is additive.