Fig. 7. Egfr pathway overactivation in GB1 causes premature turns. (A-E) Ventral views of late stage 16 embryos stained for tracheal lumen (mAb2A12) and double-stained for lumen and longitudinal fascicles (B, by mAb2A12 in black and anti-Fas2 in brown, respectively). SRF driven expression of Rho1 (A,B), two different forms of activated Egfr (C,D) and activated Ras (E) caused GBs to turn posteriorly prematurely, before reaching the midline (arrowheads in A-E). (F) The overall frequency of early turns for each genotype (black bar) and the fraction of affected branches that was classified as early turns (white bar). As an example, dominant-negative Egfr had a strong effect on GB migration but only about 10% of the affected branches classified as early turns (F). We interpret those early turns as a result of randomised migration. By contrast, close to 30% of the branches affected by activated Egfr were early turns (F). In SRF-Rho1 50% of the GBs were turning prematurely (F), yet the longitudinal fascicles appear unaffected (B, anti-Fas2 in brown).