Fig. 4. Posterior expansion of prospective telencephalic tissue. Dorsal views and sections of normal and VAD whole-mount quail embryos hybridized with the markers indicated. (A,B) The general fore- and midbrain marker Otx2 shows an expanded anterior expression in VAD embryos (see arrows), whereas (C,D) the Pax6-negative region indicates that the affected expanded territory corresponds to the future telencephalon (compare AP length of region marked with red lines in C,D). Note that the Pax-6-positive domain is not changed between normal and VAD embryos. (E-H) The markers Nkx2.1 and Bf1 confirm that the expansion of anterior territories corresponds to the presumptive ventral telencephalon, which is maintained until stage 11+ (arrow in F and red lines in G,H). Note that only the posterior Nkx2.1 expression border is shifted (arrowheads in mid-sagittal sections E',F'), whereas the anterior boundary has not changed. In VAD embryos, ectopic expression of Nkx2.1 is also detected in the ventral foregut (asterisk in F'). Arrows in insets in G,H indicate a caudal shift of Bf1 expression in horizontal section at ventral levels. The asterisks (A,B) indicate the position of the node. Note that the embryos in B and F are slightly older than the embryos in A and E. s, somite; t, telencephalon; di, diencephalon; mes, mesencephalon; e, eye. Scale bars: 100 µm in A,B; 200 µm in C-H.

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