Fig. 5. Conditional ablation of Smo using Mef2C-AHF-Cre results in AVSD. E14.5 transverse sections of (A) WT (Mef2C-AHF-Cre; R26R) and (B) Mef2C-AHF-Cre; R26R; Smo^flox/- mutant embryos. Loss of Hh receptiveness results in loss of the DMP (arrowhead in B). The central mesenchymal mass on the ventricular septum (asterisk) is more rounded with less distinct AV septal valve leaflets in mutants. (C,D) The disparity in septal valve development becomes more pronounced by E16.5. Mural leaflets (arrows in D) appear unaffected in mutants, while septal leaflets (asterisks in D) are missing. Multiple views of wild type (E,E') and conditional mutant (F,F') MRM renderings demonstrate loss of the DMP in addition to a single OFT vessel in mutants (purple). Atrial walls have been subtracted in E and F to allow visualization of wedge-shaped DMP (green). A section of the dorsal wall has been subtracted in E' and F' to demonstrate relative size of DMP to other septal structures. Ao, aorta; LA, left atria; LV, left ventricle; MV, mitral valve; Pa, pulmonary artery; PAS, primary atrial septum; RA, right atria; RV, right ventricle; TV, tricuspid valve. Color scheme: red, aorta; brown, ventricles; yellow, AV cushion tissue; blue, pulmonary artery; purple, atria; DMP, green.