Abnormal heart development in VE-PTP mutant embryos. (A-B) E9.5 embryos immunostained as whole mounts for PECAM-1 show normal trabeculation (arrows) in wild-type hearts (A), and impaired ventricular trabeculation (arrows) in VE-PTP mutant hearts (B). (C-D) Cryosections through the heart regions of E9.5 wt (C) and VE-PTP homozygous mutant embryos (D). The myocardium was stained for N-cadherin (red) and the endocardium (arrow) for VE-cadherin (green). Whereas multiple attachment points between endocardium and myocardium are apparent in the atria of wt hearts (a) and trabeculation has started in the ventricular region (v) marked by arrowheads, the heart of mutant embryos showed alterations in endocardial cell morphology and failure of the endocardium to attach to the myocardium. Note the impaired myocardial trabeculation (arrowhead on the right). a indicates atrium of the heart; v, ventricle of the heart. Bars represent 100 μm. Objectives used: (A-B) Plan S 1 ×/0.085 NA; (C-D) Fluar 20 ×/0.75 NA.