Fig. 1. Egfr maintains vnd expression in the medial column. High magnification ventrolateral and ventral views of wild-type (A,C,E) and Egfr (DER; B,D,F) embryos labeled for vnd expression. Insets in E,F show high-magnification lateral views of vnd expression in stage 10 wild-type and Egfr embryos. (A,B) During stage 6, vnd expression becomes detectable in an approx. six-cell-wide column on either side of the ventral midline in wild-type and Egfr embryos. (C) By late stage 8 in wild-type embryos, vnd expression narrows to a three-cell-wide column on either side of the ventral midline. These cells identify the medial column and stage 10 embryos (E) maintain this pattern of vnd expression. Inset in E shows that neuroectodermal cells (arrow) and NBs (arrowhead) express vnd. (D) In Egfr mutant embryos, vnd expression begins to dissipate in the ventral neuroectoderm by stage 8 (arrows) and by stage 10 (F) vnd expression is completely absent from the neuroectoderm. Inset in F shows that NBs (arrowhead) but not neuroectodermal cells (arrow) express vnd in Egfr mutant embryos. Anterior is towards the left and the line indicates the ventral midline.