Figure 6.

Parasagittal sections of the heart of term wild-type (a), ECE-1–/– (b), and ECE-1–/–; ECE-2–/– (c and d) embryos, and frontal sections of ECE-1–/–; ECE-2–/– embryos (e and f) stained with hematoxylin and eosin. Original magnification is ×11. (a) The interventricular septum (ivs) and aortic outflow (Ao) are seen. (b) Overriding of aorta with a small VSD (arrowhead) is seen in an ECE-1–/– embryo. (c) Persistent truncus arteriosus in an ECE-1–/–; ECE-2–/– embryo. One outflow (arrow) is separated into aortic outflow (Ao) and pulmonary (P) outflows. A large VSD (arrowhead) is shown. Displacement of the left AV valve (asterisk) is seen, opening toward the VSD. (d) Aorticopulmonary window in an ECE-1–/–; ECE-2–/– embryo. Septation of the aortic and pulmonary outflow tracts is incomplete at the base of the outflow tract (arrow). Note that the pulmonary outflow becomes the dorsal aorta (da) via the ductus arteriosus (dc). Pa, pulmonary artery. (e) Pulmonary and aortic outflow tracts originate from the right ventricle (DORV) in an ECE-1–/–; ECE-2–/– embryo. A large conotruncal ridge defect is seen underneath the aortic and pulmonary valves (filled diamond). A large VSD (arrowhead) is also shown. Note that the muscular layers of the pulmonary trunk (P) and aorta (Ao) are hypoplastic, and thin mesenchyme is observed between the two vessels (arrow). (f) DORV in an ECE-1–/–; ECE-2–/– embryo. The conotruncal ridge (filled diamond) is well developed compared with that in e. The arrowhead indicates a VSD.