Fig. 4. Foxp1^–/– embryos have severe defects in outflow tract development. H+E staining of embryonic sections of wild-type (A-C,G-I) and Foxp1^–/– (D-F,J-L) were performed to characterize defects in outflow tract development. Foxp1 null embryos show PTA at E11.5 (E, arrow) and at E14.5 (F, arrow). Of Foxp1 null embryos, 20% have DORV, with both aorta and pulmonary artery arising from the right ventricle (J-L), whereas wild-type littermates exhibit the correct septation of these vessels, with the aorta arising from the left ventricle and the pulmonary artery arising from the right ventricle (G-I). RV, right ventricle; LV, left ventricle; AO, aorta; PA, pulmonary artery. Scale bars: 400 µm in A-F; 600 µm in G-L.