Immunolocalization of α-integrin subunits and extracellular matrix components during human colonic organogenesis

Background and Aims: The role of cell adhesion molecules in colonic organogenesis remains poorly understood. This study examined the expression of α-integrin subunits and extracellular matrix ligands during human colonic development. Methods: Standard immunohistochemistry was used to characterize extracellular matrix and α-integrin subunit expression during development. Results: At 9 weeks, type-IV collagen and laminin were present underlying epithelium, around vascular structures, and surrounding inner circular muscle layer fibers. Fibronectin was uniformly expressed in the mesenchyme. Tenascin distribution was restricted to the presumptive muscle layer and, later, to the villus core and muscularis mucosae. The 9-week epithelium expressed α₂, α₃, α₅, and α₈, and, by 11 weeks, α₉, α₃, α₆, and α₈ expression was accentuated at the basal membrane. During transition from pseudostratified to simple columnar epithelium, a vertical α₂ gradient formed. Mesenchymal cells expressed α₅ and α₈ by 9 weeks. The developing muscularis (propria and mucosae) showed accentuated α₅ expression. By 16 weeks, α₈ expression localized to the muscularis mucosae and villus core. Mesenchymal vascular elements stained strongly with anti-α₂ and α₆ by 9 weeks. Conclusions: These observations show the complexity and overlap of adhesive receptor expression and ligands during development and reveal early cell commitment to the formation of specific structures.