N-cadherin/catenin-based costameres in cultured chicken cardiomyocytes

N-cadherin is a member of the Ca²⁺-dependent cell adhesion molecules and plays an important role in the assembly of the adherens junction in chicken cardiomyocytes. In addition to being present at the cell-cell junction, N-cadherin is associated with costameres in extrajunctional regions. The significance of the N-cadherin-associated costameres and whether catenins are components of costameres in chicken cardiomyocytes are not known. In this study, double-labeling immunofluorescence microscopy was used to determine the extrajunctional distribution of both N-cadherin and its cytoplasmic associated proteins, α- and β-catenins, and their relationship to myofibrillar Z-disc α-actinin. N-cadherin, α-, and β-catenins were all found to be present at the extrajunctional region and, in some cases, were codistributed with myofibrillar α-actinin exhibiting a periodic staining pattern. Confocal microscopy confirmed that both N-cadherin and β-catenin colocalized with peripheral myofibrillar α-actinin on the dorsal surface of cardiomyocytes as components of the costameres. Intracellular application of antibodies specific for the cytoplasmic portions of N-cadherin, α-, and β- catenin, either by electroporation or microinjection, resulted in myofibril disorganization and disassembly. These results suggest the existence of N- cadherin/catenin-based costameres in the dorsal surface of cultured chicken cardiomyocytes in addition to the integrin/vinculin-based costameres found in the ventral surface and indicate that the former set of costameres is essential for cardiac myofibrillogenesis.