Fig. 7. Fgf8, Fgf17 and En1 are expressed normally in En2^-/- and En1^-/+;En2^-/- mutant E11.5 mouse embryos. RNA in situ hybridization of Fgf8 (A-C'), Fgf17 (D-F') and En1 (G-I') on sagittal sections of En1^-/+ (A,D,G), En2^-/- (B,E,H) and En1^-/+;En2^-/- (C,F,I) E11.5 mutant embryos. Upper (A-I) and lower (A'-I') panels show medial and lateral sections, respectively. The Fgf8/17 expression domains are positioned normally but are slightly reduced in size in mutants (C,F). En1 is expressed normally in mutants (H,I). The isthmus corresponds to the Fgf8 expression domain and is outlined in red. Red asterisks indicate truncation of the isthmus/inferior colliculus. r1, rhombomere 1; Ist, isthmus, mes, mesencephalon.