Fig. 3. Reconstruction of the isthmus after mouse Fgf8b misexpression. (A) In situ hybridization for Otx2 (purple), in situ hybridization for mouse Fgf8 (red): A, part e and inlet of A, parts b and c. Arrowhead indicates the posterior limit of the Otx2 expression domain. Photos of A, parts c-f are from the same embryo. (B) in situ hybridization for Gbx2 (purple), in situ hybridizaition for mouse Fgf8 (red): B, part e and inlet of B, parts b and c. Arrowhead indicates anterior limit of Gbx2 expression domain. Photos of B, parts c-f are from the same embryo. (C) Double in situ hybridization with chick Fgf8 probe (purple), and with mouse Fgf8 probe (red). Arrowheads on C, part f indicate chick Fgf8 (endogenous) expression line. (D) in situ hybridization for Lmxb1 (purple), in situ hybridization for mouse Fgf8 (red): D, part d and inlet of D, parts b and c. Arrowheads on D, part g indicate Limx1b expression line. Otx2 expression in the mesencephalon retreats (A), and complementarily, Gbx2 expression extends rostrally (B). Fgf8 expression in the isthmus, that is expression from the embryonic gene (purple on C), disappears, and a new expression line appears by 36 hours after electroporation. Interaction of among Fgf8, Lmx1b and Wnt1 may be involved in reconstruction of the isthmus as indicated by Matsunaga et al. (Matsunaga et al., 2003). mes, mesencephalon; is, isthmus; met, metencephalon; exp, experimental side; cont, control side. Scale bar: 200 µm.