Antibody:	Anti-Cx40
Detection system:	Secondary antibody coupled to rhodamine
Assay notes:	Data was summarized in Table 2 (including date not shown).

Structure	Level	Pattern	Image	Note
TS15: dorsal aorta	Present	Regionally restricted	4C	Expressed in endothelial cells.

Structure	Level	Pattern	Image	Note
TS15: 1st arch artery	Present	Regionally restricted	4F	Expressed in endothelial cells.

Structure	Level	Pattern	Image	Note
TS15: atrium cardiac muscle	Present		6E
TS15: endocardial lining	Absent		6E

Structure	Level	Pattern	Image	Note
TS17: primitive ventricle cardiac muscle	Present	Regionally restricted	8A/B	Expressed in the myocytes of the trabecular network and the compact free wall of the left ventricle, but no immunoreactivity was detected in the right ventricle. No expression in the interventricular septum.

Structure	Level	Pattern	Image	Note
TS20: ventricle cardiac muscle	Present		9A , 9C	Colocalized with Gja1 in most of the gap junctions of the trabecular network and the free ventricular wall.

Structure	Level	Pattern	Image	Note
TS22: ventricle cardiac muscle	Present	Graded	10A/B	Barely detectable in the compact subepicardial layers, whereas its expression was maintained, if not increased, in the trabecular network.

Structure	Level	Pattern	Image	Note
TS22: ventricle cardiac muscle	Strong	Regionally restricted	10D/E	Highly expressed in the myocytes forming the primitive conduction system. Expressed in the peripheral myocytes. Never observed in the myocytes of the interventricular septum.

Structure	Level	Pattern	Image	Note
TS13: heart	Absent
TS13: vascular system	Absent

Structure	Level	Pattern	Image	Note
TS15: atrioventricular canal	Absent
TS15: primitive ventricle cardiac muscle	Weak	Regionally restricted		Expressed in the left ventricle, not the right ventricle.

Structure	Level	Pattern	Image	Note
TS17: atrioventricular canal	Absent
TS17: outflow tract	Absent
TS17: heart atrium	Strong

Structure	Level	Pattern	Image	Note
TS19: right ventricle cardiac muscle	Present
TS19: atrioventricular canal	Absent
TS19: interventricular septum	Absent
TS19: outflow tract	Absent
TS19: heart atrium	Strong
TS19: heart left ventricle	Strong

Structure	Level	Pattern	Image	Note
TS20: ventricle cardiac muscle	Present	Graded		Barely detectable in the compact subepicardial layers, whereas its expression was maintained, if not increased, in the trabecular network.
TS20: atrioventricular canal	Absent
TS20: outflow tract	Absent
TS20: heart atrium	Strong
TS20: heart left ventricle	Strong
TS20: heart right ventricle	Present

Structure	Level	Pattern	Image	Note
TS21: atrioventricular canal	Absent
TS21: interventricular septum	Absent
TS21: outflow tract	Absent
TS21: impulse conducting system	Present	Regionally restricted		Expressed in bundle branches. Weak expression in His bundle.
TS21: heart atrium	Strong
TS21: heart left ventricle	Strong
TS21: heart right ventricle	Strong

Structure	Level	Pattern	Image	Note
TS22: atrioventricular canal	Absent
TS22: interventricular septum	Absent
TS22: outflow tract	Absent
TS22: heart atrium	Strong
TS22: heart left ventricle	Strong
TS22: heart right ventricle	Strong
TS22: atrioventricular bundle	Present			Expressed in His bundle and bundle branches.

Structure	Level	Pattern	Image	Note
TS28: atrium endocardial lining	Absent
TS28: ventricle endocardial lining	Absent
TS28: ventricle cardiac muscle	Present	Regionally restricted		Expressed in the peripheral myocytes and the myocytes forming the primitive conduction system. Never observed in the myocytes of the interventricular septum.