Fig. 6. Dominant-negative Ras, but not Raf or activated Yan, can cause GB1 midline crosses. (A-D) SRF driven expression of dominant-negative Egfr and Ras, but not dominant-negative Raf, PI3K or activated Yan produced midline crosses. Ventral views of embryos expressing dominant-negative constructs stained by mAb2A12. Dominant-negative Ras (A), Raf (B) and PI3K (p60, see Materials and methods, C) or activated Yan (Yan^ACT, D) had similar effects on GB migration, causing many GBs to fail to enter the VNC, or to arrest (arrowheads in A-D) or meander inside the VNC (white arrowheads in A,B,D). Only dominant-negative Ras caused midline crosses (arrow in A). In all panels, anterior is towards the left. Scale bars: 20 µm. (E) Quantification of the frequency of midline crosses for the different genotypes.