EHC mutants display defects in cardiac development.

A: Heterozygous littermate control at E11.5 showing developing heart in pericardial sac. B: EHC mutant has pericardial effusion and blood visible in pericardial sac (arrow). C: Transverse section of control littermate at E11.5. The boxed region indicates the segment shown in panel C’. C’: Note the absence of blood cells on the cardiac surface and in the pericardial space. D: Transverse section of EHC mutant at E11.5 showing enlarged atria. The boxed region indicates the segment shown in panel D’. D’: Blood cells are present on the surface of the EHC heart (black arrow) and in the pericardial space (orange arrow). E: In heterozygous littermates at E14.5 the ventricular chamber is surrounded by a thick compact myocardium, which is highly organised. F: At E14.5, EHC mutants show a reduced compact ventricular myocardium (indicated by asterisk), accompanied by a thinning of the ventricular septal tissue (arrow). Note the abnormal atrial morphology and different localisation of the atria with respect to the ventricle compared to control (E). G: Heterozygous heart at E16.5 shows expected ventricular vascular connections and also coronary vessels on the cardiac surface (arrow). H: EHC mutant heart shows double-outlet right ventricle (DORV) (asterisk) as well as an absence of surface coronary vessels (arrow). Note the vesicle-like structures present on the ventricular surface. I: EHC/Myh10∆ and J: Myh10∆/Myh10∆ hearts at E16.5 similarly show DORV (asterisks) and ventricular vesicles (arrows). Scale bar = 200 μm (E, F), 1mm (A-D, G-J). Abbreviations: Het: heterozygote; lb: limb bud; LA: left atria, LV: left ventricle, RA: right atria, RV: right ventricle, VS: ventricular septum, ∆: Myh10∆.