Fig. 6.

Formation of myocardium, smooth muscle and an elastic matrix in the outflow vessels of Sp^2H embryos and fetuses. (A,B) MF20 labelling of the cardiac muscle (brown) shows that this extends only to the pericardial reflections (arrows in A,B) in Sp^2H/+ embryos, but ectopically into the aortic sac (red arrows in B) in Sp^2H/Sp^2H embryos. NCC are marked by their expression of βgal (blue). (C,D,G,H) αSMA immunostaining of E13.5 fetuses shows reduced staining within the arterialized walls of the common trunk in the Sp^2H/Sp^2H fetus (D) compared with the septated aorta and pulmonary trunk of the Sp^2H/+ fetus (C). There were similar patterns of staining in the aortic arches of Sp^2H/Sp^2H embryos and stage matched controls (G,H). (E,F,I,J) Miller's elastin staining of E13.5 fetuses reveals similar patterns of elastin deposition in the proximal region of the arterialized vessels (arrows in E,F), although the layers are more disorganized in the Sp^2H/Sp^2H fetus. Elastin deposition is much reduced in the aortic arch of Sp^2H/Sp^2H compared to Sp^2H/+ fetuses (arrows in I,J). aa, aortic arch; ao, aorta; as, aortic sac; cat, common arterial trunk; oft, outflow tract.