Figure 4. Cardiovascular defects in D1^ECKO embryos are evident at mid-gestation.

(A, B) H&E staining of cross sections from control and D1^ECKO E11.5 hearts shows condensed and discontinuous atrial myocardium in the mutant (B, arrow), which also displays truncus arteriosus (TA), while the aorta (Ao) and pulmonary artery (P) are separated in the Tie2-cre control heart (A). (C, D) Sections adjacent to those shown in (A,B) were stained for Foxp4 (green) and MF20 (red), markers of epicardium and myocardium, respectively. (E, F) H&E stained sections of ventricular regions show abnormal blood islands in D1^ECKO embryos (arrows) and abnormal thickened regions of compact myocardium (brackets). (G, H) Whole-mount PECAM staining of E12.5 wild type (WT) and D1^ECKO hearts shows coronary vessel plexus defects in mutants (H). The base of the outflow trunk in the D1^ECKO embryo is covered with PECAM-positive cells (arrow, H), while the corresponding region of the wild type is not (arrow, G). (I,J) Higher magnification of the boxes in (G) and (H), showing large clusters of PECAM positive cells are apparent in the ventricular surface of the D1^ECKO heart (arrowheads, J). Scale bars equal to 50 μm in A, B, E, F and 100 μm in C, D.