Fig. 3. Cardiac outflow tract defects in Msx1/2 mutant embryos. Histological analysis of E12.5 (A,B) and E15.5 (C-H) control (A,C-E) and Msx1/2 mutant (B,F-H) embryo hearts. (A,B) At E12.5, the septation of the pulmonary trunk (PT) and the ascending aorta (Ao) is evident in the control (A), but not in the mutant (arrow in B). (C-H) Serial transverse sections from caudal to rostral show the aorta and pulmonary trunk arising from the right ventricle in the mutant (double outlet right ventricle). Msx1/2 mutants also exhibit dysmorphogenesis of the ventricular wall and myocardium. The location of the thymus (TH) was abnormal. RV, right ventricle; LV, left ventricle. Scale bars: in B, 0.5 mm for A,B; in E, 0.5 mm for C-H.