Connexin expression in the developing avian cardiovascular system.

ABSTRACT

Recent observations have suggested that the patterns of expression of the gap junction protein connexin43 in the developing cardiovascular system of the avian embryo diverge significantly from the patterns previously seen in mammalian species. Therefore, a detailed analysis of connexin43 expression in the chicken embryo was performed by use of immunofluorescent localization with two different connexin43-specific antipeptide antibodies as well as Western and Northern blot analysis. Connexin43 protein was not detected in the avian myocardium, the venous system, or the smaller vessels of the arterial system. Rather, it was limited exclusively to the vessels of the arterial outflow tract in a concentric pattern that became evident by embryonic day 8. Double staining with anti-alpha-smooth muscle actin and connexin43 demonstrated colocalization in the media of outflow tract vessel walls. The developmental expression of connexin43 was found to mirror the spatial patterning of secondary actin; connexin43, however, preceded the expression of secondary actin by a period of 1-2 days. In contrast, antibodies to a related gap junction protein (connexin42) revealed an absence of immunostaining in the avian outflow tract. Double staining with anti-connexin42 and anti-A-cell adhesion molecule (specific for avian intercalated discs) demonstrated colocalization between cardiac myocytes, indicating that connexin42 is a constituent of avian myocardial gap junctions. In light of these findings, developmental expression of differing myocardial connexins may reconcile previous studies showing different physiological properties of avian and mammalian cardiac gap junctions.