Fig. 2. Foregut, respiratory tract and skeletal malformations in Foxf1^+/- embryos. (A-C) Hematoxylin and Eosin stained transversal sections showing trachea (Tr) and esophagus (Es) of E18.5 Foxf1^+/- (A,C) and wild-type (B) fetuses. The mutants have variable degrees of narrowing of trachea and esophagus with esophageal atresia and a fistula-like fusion between esophagus and trachea. (D,E) Ventral view of Alcian Blue-stained tracheas from E18.5 Foxf1^+/- (D) and wild-type (E) fetuses. The C-shaped cartilaginous rings, which are segmentally arranged along the trachea (E), are replaced by irregular, hypoplastic patches of cartilage in Foxf1^+/- embryos (D; compare also B with A,C). (F,G) Skeletal malformation in Foxf1^+/- mice shown by Alizarin Red and Alcian Blue staining of E18.5 fetuses. Attachment of the ribs to the sternum is asymmetrical in the mutant, and the ossification centra in the sternebrae (red staining parts of the sternum) are misaligned at the midline (F).