Connexin 43 is Localized in Gizzard Smooth Muscle Cells during Chicken Development

Smooth muscle cells are widely distributed in the digestive organs of chickens. They exist as single cells, but adhere to each other to function synchronously. In this study, the expression of the gap junction protein connexin 43 (Cx43) in chicken gizzards was investigated at embryonic days (E) 10, E15, and E18. Gizzards have an abundance of smooth muscle cells because of their thick muscle layers, which enable easy analysis of the cells. Morphological observations and expression patterns of smooth muscle markers were confirmed. Next, we observed where the markers were localized in the gizzard tissue at E10, E15, and E18. Finally, the expression pattern of Cx43 in primary cultured smooth muscle cells from E15 gizzards was investigated. The analysis revealed the expression and localization of Cx43 and calponin 1 in the smooth muscle layers, and 3D analysis revealed dynamic changes in the localization pattern of Cx43 from E10 to E15. Cultured smooth muscle cells confirmed that Cx43 was expressed in the cell membrane and cytosol. In conclusion, Cx43 expression was identified in chicken gizzards at E10, E15, and E18, which was localized differently during development. The expression was broad at E10, and became restricted at E15 and E18. Primary culture of smooth muscle cells showed that Cx43 was present in the cell membrane and cytosol. This suggests that Cx43 is actively translated into the cytosol at E10, forming a hexamer, and shuttling the cell membrane to function as a gap junction.