(A and B) In situ hybridizations for Jag1 in control embryos. (A) Jag1 expression in pharyngeal endoderm (arrows, E10.5 embryo). (B) Jag1 expression in pharyngeal mesenchyme (arrow), OFT (arrowheads), and aortic arch arteries (asterisks, E11.5 embryo). (C and D) Jag1 immunostaining through E11.5 control (C) and mutant (D) embryos demonstrated loss of Jag1 expression in pharyngeal mesenchyme (arrow) and OFT (black arrowheads) of the mutant. Expression was maintained in the aortic arch arteries (white arrowheads). (E–G) Photographs and diagrams of hearts from E18.5 control (E) and mutant (F and G) embryos. (E) Arrows indicate pulmonary artery and aorta. (F) Double outlet right ventricle (arrows). (G) Double outlet right ventricle (arrows) and an interrupted aortic arch. (H–K) H&E-stained sections of E18.5 control (H and J) and mutant (I and K) hearts, demonstrating a double outlet right ventricle and a ventricular septal defect (arrow). (L–O) In situ hybridization of E10.5 control (L and N) and mutant (M and O) embryos. Control sections (L and N) demonstrated normal neural crest expression of Sema3C (L) and PlexinA2 (N) in the 2 clusters of cells in the center of the developing OFT cushions (dotted circles in N), while mutants (M and O) demonstrated reduced expression. Original magnification, ×30 (E–G). Scale bars: 250 μm (A, C, D, H, and I), 500 μm (B, J, and K), 100 μm (L–O).