Fig. 1. Coronary artery defects in Cx431 knockout mouse hearts. (A) Transverse sections through the base of the heart of an E17.5 Cx431^–/– embryo stained with an antibody to -cardiac myosin. A large pouch (Po) breached the pulmonary valve ring. Note the myosin-free subendocardial layer in the wall of the pouch. The right coronary artery stem was absent in this animal (not shown). (B) In this E14.5 Cx431^–/– mouse heart, the mouth of the coronary artery (arrowhead) is narrowed and the stem of the coronary artery is continuous with a large thin-walled sinus (s) that empties into numerous intertrabecular sinusoids. Note the base of the right ventricle is filled with trabecula that obscures the right ventricular outflow. The lacZ-positive cells (blue) represent neural crest cells labeled with a Cx431 promoter driven lacZ transgene (Lo et al., 1997). (C-E) A caudal-to-cranial sequence of an E17.5 Cx431^–/– heart stained with an antibody to -cardiac myosin. The left coronary artery exits the aorta normally (arrow in E) but the right coronary artery exits a sinus of the pulmonary trunk rather than the aorta. In C, the mouth of the right coronary artery (RCA) is just opening into the coronary sinus of the pulmonary trunk, seen more clearly in D (asterisk). (F-H) E17.5 Cx431^–/– heart stained with an antibody to myosin. In a caudal-to-cranial sequence, a branch of the left coronary artery (arrow) empties into and becomes continuous with an enlarged intertrabecular sinusoid that is in the early stages of forming a pouch in the right ventricle. Ao, aorta; Av, aortic valve; PI, pulmonary infundibulum (right ventricular outflow tract); Po, pouch; Pv, pulmonary valve; OFS, remnant of the outflow tract septum; RV, right ventricle; RCA, right coronary artery. Scale bars: 100 µm.