Fig. 5. Increased cell death in Shh mutant brains. TUNEL assay was performed on wild-type (A) and Shh mutant (B) sections at the 15-somite stage. The plane of sections is shown in Fig. 4A,B. Few cells were positive for TUNEL (orange dot) in wild-type embryos, while Shh mutants exhibited increased cell death especially in the diencephalon and anterior midbrain. Bmp4 expression was examined at the 15-somite (C,D) and 19-somite (E,F) stages. At the 15-somite stage, there was no Bmp4 expression in the dorsal midline of the diencephalon and midbrain. At the 19-somite stage, robust expression of Bmp4 was observed in this region in Shh mutants (F). Arrowhead indicates the diencephalon-midbrain boundary. t, telencephalon; d, diencephalon; m, midbrain.

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