Integrin distribution during heart development in the long ‐ tailed macaque (M. fascicularis)

Background: Cardiogenesis appears to require cellular and extracellular matrix interactions for normal development. Although numerous matrix components have been identified within embryonic heart tissue, the distribution, and function of their respective integrin receptors, implicated as mediators of cell‐matrix interaction, remain unknown in primates. Methods: Using immunocytochemistry, the localization of integrin subunits α1, α5, α6, and β1 were examined in hearts of macaque embryos during early septation and trabeculation, and compared to the distribution of the integrin ligands laminin, collagen IV, and fibronectin. Results: At stage 11, α5 reactivity was limited to endothelial cells in the primitive heart. At stage 13, α1 and α5 were additionally detected on mesenchymal cells within the endocardial cushions. On myocardial cells at this stage, α5 stained weakly in all regions, but α1 was not expressed. The α6 subunit appeared more prominent in both stages, being present on myocardial cells throughout the heart, particularly on the basal surface of myocardial cells adjacent to the myocardial basement membrane. Inconsistent reactivity occurred on endothelial cells however, and no staining for α6 was detected on cushion mesenchymal cells. At both stages, β1 reactivity was present on all cardiac cell population and overlapped that of the α‐subunits examined. Laminin, collagen IV, and fibronectin were detected at each stage and their distribution correlated with that described for the subunits. Conclusions: These results show specific selective patterns of expression for the subunits which are comparable to the localization of their known glycoprotein ligands and suggest defined roles for individual integrins during heart development in primates. © 1995 Wiley‐Liss, Inc.