Figure 7

Single subepicardial EC contributes to both coronary arteries and veins. (A, B) E10.5-labeled subepicardial ECs give rise to arterial cells (NOTCH1⁺, red arrowheads) and venous cells (COUP TFII⁺, green arrowheads) at E15.5. White arrowheads indicate COUP TFII⁺ endocardial cells. (C) Schematic representation of clones recovered from Apln^CreERT2/+;Rosa26^Rainbow/+ embryos with low-efficiency recombination. (D, E) Representative coronary vessel clone in an E15.5 Apln^CreERT2/+;Rosa26^Rainbow/+ heart shown in whole mount (D) and section (E). (F) Coronary ECs in one clone were positive for both arterial (NOTCH1) and venous (COUP TFII) markers. Yellow arrowheads indicate subepicardial venous EC (RFP⁺;COUP TFII⁺); white arrowheads point to intramyocardial arterial ECs (RFP⁺;NOTCH1⁺). (G) Percentage of intramyocardial and subepicardial coronary ECs within single Apln^CreERT2/+;Rosa26^Rainbow/+ clone compared with the distribution of total vessels. *P < 0.05; n = 5 for all vessels; n = 28 for clonal vessels. (H) VE-Cad-CreERT2-induced coronary clones (white) containing sister cells within the AV junction are distributed throughout the thickness of the heart (double yellow arrow). White dotted line indicates epicardium; red dotted line indicates border between trabecular and compact myocardium. (I) Quantification of the percentage of subepicardial (Subepi., blue) and intramyocardial (Intramyo., red) ECs within each clone at E13.5. A similar graph demonstrating the distribution of total vessels in E13.5 left ventricle (10×) is shown for comparison. n = 3-6. LV, left ventricle; RV, right ventricle; VS, ventricular septum. Yellow bar = 100 μm; white bar = 0.5 mm.