BACKGROUND & AIMS - The role of cell adhesion molecules in colonic organogenesis remains poorly understood. This study examined the expression of alpha-integrin subunits and extracellular matrix ligands during human colonic development.
METHODS - Standard immunohistochemistry was used to characterize extracellular matrix and alpha-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 alpha 2, alpha 3, alpha 5, and alpha 8, and, by 11 weeks, alpha 9. alpha 3, alpha 6, and alpha 8 expression was accentuated at the basal membrane. During transition from pseudostratified to simple columnar epithelium, a vertical alpha 2 gradient formed. Mesenchymal cells expressed alpha 5 and alpha 8 by 9 weeks. The developing muscularis (propria and mucosae) showed accentuated alpha 5 expression. By 16 weeks, alpha 8 expression localized to the muscularis mucosae and villus core. Mesenchymal vascular elements stained strongly with anti-alpha 2 and alpha 6 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.