Fig. 3. Six3 confers the anterior competence for Fgf8. Dissected brains from HH19 embryos that had been electroporated at HH8 with GFP (control; A) and Fgf8b (B) were in situ hybridized for Bf1. (C) Normal expression of Six3 in a HH19 dissected brain. Ectopic Bf1-expressing domains are detected in the hypothalamic region (arrow in B). Dissected brains from HH13 embryos were stained for Bf1 (D, control; E, Six3-misexpressed) and for Fgf8 (F, normal embryo). Note an ectopic Bf1-expressing domain at the mid-hindbrain boundary where Fgf8 is expressed (arrows in E,F). Embryos were cultured by New’s method and electroporation was done at HH5. Note the efficient introduction of exogenous genes into the entire brain (E'). (G,H) HH25 dissected brain to which Six3 with constitutively active Fgfr1 (G,G') or Fgfr3 (H) were introduced at HH10, stained for Bf1 (G,G') and Emx2 (H). The specimen was flat-mounted to expose the anterior hindbrain region, showing the experimental side on the left (H). Ectopic Bf1- or Emx2-expressing cells are detected (arrows in G,G',H). Bars, 0.5 mm. is, isthmus; me, mesencephalon; ov, optic vesicle; pr, prosencephalon; rh, rhombencephalon; vm, ventral midline.