Fig. 6. Anterior neural patterning of Smad4 mutants. Whole-mount in situ hybridization of (A,C,E,G,I) control and (B,D,F,H,J) mutant embryos. (A-D) Otx2 expression marks the anterior epiblast of both wild-type and mutant embryos at E7.5, but by E8.5 normal expression within the fore- and midbrain is confined to a small patch of rostral neuroepithelium in Smad4 mutants. (E,F) Similarly, Six3 expression within the anterior forebrain is reduced in mutant embryos. (G,H) Fgf8 transcripts identify the anterior neural ridge (ANR; red arrows) and midbrain/hindbrain junction (black arrows) in wild-type embryos. ANR expression is lost in Smad4 mutants, while expression probably corresponding to the midbrain/hindbrain junction is observed (arrows). (I,J) Evidence of partial hindbrain formation is demonstrated by Krox20 expression. (I) Control, lateral view; (J) mutant, ventral view.