Chuzhoi mutants exhibit defects in cardiovascular development. Transverse sections through the thoracic region of wild-type (A, C, E) and chuzhoi homozygous mutant (B, D, F) E17.5 fetuses, stained with haematoxylin and eosin. In control hearts at E17.5, the aorta arises from the left ventricle (A) and the pulmonary trunk arises from the right ventricle (C). In the hearts of chuzhoi mutant littermates, the aorta (B) and pulmonary trunk (D) arise from the right ventricle, with the vessels rising parallel to one another (B). Whereas the right and left ventricles are separated in the control heart (E), a peri-membranous ventricular septal defect (arrow in F) can be seen in the chuzhoi mutant heart. Ao, aorta; lv, left ventricle; rv, right ventricle; pt, pulmonary trunk.