CONNEXIN EXPRESSION IN THE DEVELOPING AVIAN CARDIOVASCULAR-SYSTEM

Recent observations have suggested that the patterns of expression of the gap junction protein connexin43 in the developing cardiovascular s ystem of the avian embryo diverge significantly from the patterns prev iously seen in mammalian species. Therefore, a detailed analysis of co nnexin43 expression in the chicken embryo was performed by use of immu nofluorescent localization with two different connexin43-specific anti peptide antibodies as well as Western and Northern blot analysis. Conn exin43 protein was not detected in the avian myocardium, the venous sy stem, or the smaller vessels of the arterial system. Rather, it was li mited exclusively to the vessels of the arterial outflow tract in a co ncentric pattern that became evident by embryonic day 8. Double staini ng with anti-alpha-smooth muscle actin and connexin43 demonstrated col ocalization in the media of outflow tract vessel walls. The developmen tal expression of connexin43 was found to mirror the spatial patternin g 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 immun ostaining in the avian outflow tract. Double staining with anti-connex in42 and anti-A-cell adhesion molecule (specific for avian intercalate d discs) demonstrated colocalization between cardiac myocytes, indicat ing that connexin42 is a constituent of avian myocardial gap junctions . In light of these findings, developmental expression of differing my ocardial connexins may reconcile previous studies showing different ph ysiological properties of avian and mammalian cardiac gap junctions.