Antibody:	CD105 (Endoglin) antibody (MJ7/18, #14-1051-85)
Assay notes:	Two Eng antibodies were described, but the one used in this assay was not detailed. Endoglin/CD105 antibody (AF1320) MGI:6730132 may have been used in this assay.

Structure	Level	Pattern	Image	Note
TS19: left atrium endocardial lining	Strong		1A ENG , 1A Merged	Strong expression restricted to endocardium of atria and trabeculated left and right ventricle, co-expressed with CD31 (Pecam1).
TS19: left ventricle endocardial lining	Strong		1A ENG , 1A Merged	Strong expression restricted to endocardium of atria and trabeculated left and right ventricle, co-expressed with CD31 (Pecam1).
TS19: right atrium endocardial lining	Strong		1A ENG , 1A Merged	Strong expression restricted to endocardium of atria and trabeculated left and right ventricle, co-expressed with CD31 (Pecam1).
TS19: right ventricle endocardial lining	Strong		1A ENG , 1A Merged	Strong expression restricted to endocardium of atria and trabeculated left and right ventricle, co-expressed with CD31 (Pecam1).

Structure	Level	Pattern	Image	Note
TS19: ventricle endocardial lining	Present		1B ENG , 1B Merged
TS19: visceral pericardium	Absent		1B ENG , 1B Merged	No expression in epicardial cells.

Structure	Level	Pattern	Image	Note
TS21: left atrium endocardial lining	Strong		2A Merged , 2A ENG	Strong expression in atrial and ventricular endocardium, co-expressed with CD31 (Pecam1).
TS21: left ventricle endocardial lining	Strong		2A Merged , 2A ENG	Strong expression in atrial and ventricular endocardium, co-expressed with CD31 (Pecam1).
TS21: right atrium endocardial lining	Strong		2A Merged , 2A ENG	Strong expression in atrial and ventricular endocardium, co-expressed with CD31 (Pecam1).
TS21: right ventricle endocardial lining	Strong		2A Merged , 2A ENG	Strong expression in atrial and ventricular endocardium, co-expressed with CD31 (Pecam1).

Structure	Level	Pattern	Image	Note
TS21: ventricle endocardial lining	Present		2B ENG , 2B Merged
TS21: myocardium layer	Weak	Regionally restricted	2B ENG , 2B Merged	Low level expression in CD31-negative cells in myocardium, likely corresponding to epicardially derived cells (EPDCs).

Structure	Level	Pattern	Image	Note
TS21: myocardium layer	Weak	Regionally restricted	2B ENG inset , 2B Merged inset	Low level expression in CD31-negative cells in myocardium, likely corresponding to epicardially derived cells (EPDCs).

Structure	Level	Pattern	Image	Note
TS23: left atrium endocardial lining	Strong		3A ENG , 3A Merged	Strong expression throughout atrial and ventricular endocardium, co-expressed with CD31 (Pecam1).
TS23: left ventricle endocardial lining	Strong		3A ENG , 3A Merged	Strong expression throughout atrial and ventricular endocardium, co-expressed with CD31 (Pecam1).
TS23: right atrium endocardial lining	Strong		3A ENG , 3A Merged	Strong expression throughout atrial and ventricular endocardium, co-expressed with CD31 (Pecam1).
TS23: right ventricle endocardial lining	Strong		3A ENG , 3A Merged	Strong expression throughout atrial and ventricular endocardium, co-expressed with CD31 (Pecam1).
TS23: heart blood vessel	Present	Regionally restricted	3A Merged , 3A ENG	Expression in sub-epicardial blood vessels.
TS23: blood vessel endothelium	Present	Regionally restricted	3A Merged , 3A ENG	Expression in vascular endothelium of all coronary blood vessels.

Structure	Level	Pattern	Image	Note
TS23: heart endothelium	Strong	Regionally restricted	3B ENG , 3B Merged	Strong expression in endothelial cells ventricular wall.
TS23: heart blood vessel	Present	Regionally restricted	3B Merged , 3B ENG	Expression in sub-epicardial endothelial cells.
TS23: myocardium layer	Weak	Regionally restricted	3B Merged , 3B ENG	Low level expression in CD31-negative cells in myocardium, likely corresponding to epicardially derived cells (EPDCs).

Structure	Level	Pattern	Image	Note
TS23: myocardium layer	Weak	Regionally restricted	3B ENG inset , 3B Merged inset	Low level expression in CD31-negative cells in myocardium, likely corresponding to epicardially derived cells (EPDCs).

Structure	Level	Pattern	Image	Note
TS25: heart blood vessel	Present	Regionally restricted	4A ENG , 4A Merged	Authors report higher expression in vascular endothelium of coronary veins compared with arteries.

Structure	Level	Pattern	Image	Note
TS25: heart blood vessel	Present	Regionally restricted	4B Merged , 4B ENG	Expression in sub-epicardial vein.
TS25: coronary artery	Weak	Regionally restricted	4B ENG , 4B Merged	Lower expression in small muscularized artery in mid-myocardium of ventricular wall.

Structure	Level	Pattern	Image	Note
TS25: vein endothelium	Strong	Regionally restricted	5A Merged , 5A ENG	Strong expression in vascular endothelium of coronary veins.

Structure	Level	Pattern	Image	Note
TS25: heart blood vessel	Strong	Regionally restricted	5B ENG , 5B Merged	Strong expression in sub-epicardial veins of ventricular wall.

Structure	Level	Pattern	Image	Note
TS21: tricuspid valve	Weak	Regionally restricted	6A ENG , 6A Merged	Reduced expression in tricuspid valve mesenchymal cells compared to adjacent endocardium.
TS21: endocardial lining	Present	Regionally restricted	6A ENG , 6A Merged

Structure	Level	Pattern	Image	Note
TS23: tricuspid valve	Weak	Regionally restricted	6B ENG , 6B Merged	Reduced expression in tricuspid valve mesenchymal cells compared to adjacent endocardium.
TS23: endocardial lining	Present	Regionally restricted	6B ENG , 6B Merged

Structure	Level	Pattern	Image	Note
TS25: tricuspid valve	Weak	Regionally restricted	6C ENG , 6C Merged	Reduced expression in tricuspid valve mesenchymal cells compared to adjacent endocardium.
TS25: endocardial lining	Present	Regionally restricted	6C Merged , 6C ENG

Structure	Level	Pattern	Image	Note
TS25: heart blood vessel	Present	Regionally restricted	7A Merged , 7A ENG	Stronger expression in venous endothelial cells than in arterial endothelial cells.

Structure	Level	Pattern	Image	Note
TS28: cardiac vein	Strong	Regionally restricted	8A Vein Merged , 8A Vein ENG	Higher expression in vascular endothelium of coronary veins compared with arteries.

Structure	Level	Pattern	Image	Note
TS28: coronary artery	Weak	Regionally restricted	8A Artery ENG , 8A Artery Merged	Higher expression in vascular endothelium of coronary veins compared with arteries.

Structure	Level	Pattern	Image	Note
TS28: cardiac vein	Strong		8B Vein Merged , 8B Vein ENG

Structure	Level	Pattern	Image	Note
TS28: coronary artery	Weak	Regionally restricted	8B Artery ENG , 8B Artery Merged	Approximately two-fold lower expression in arterial endothelium than in venous endothelium.

Structure	Level	Pattern	Image	Note
TS28: cardiac vein	Strong		9A Vein ENG , 9A Vein Merged

Structure	Level	Pattern	Image	Note
TS28: coronary artery	Weak	Regionally restricted	9A Artery ENG , 9A Artery Merged	Approximately two-fold lower expression in arterial endothelium than in venous endothelium.

Structure	Level	Pattern	Image	Note
TS28: cardiac vein	Strong		9B Vein Merged , 9B Vein ENG

Structure	Level	Pattern	Image	Note
TS28: coronary artery	Weak	Regionally restricted	9B Artery ENG , 9B Artery Merged	Approximately two-fold lower expression in arterial endothelium than in venous endothelium.