Anchoring of epithelia to underlying connective tissue: evidence of frayed ends of collagen fibrils directly merging with meshwork of lamina densa.

We examined the epithelial-subepithelial junction of mouse pancreas, human placenta and monkey oral mucosa. In mouse pancreas, in quick-freeze, deep-etch, rotary-replicated micrographs, collagen fibrils ran close to the lamina densa and frayed out into two or three subfibrils merging with lamina densa meshwork. In placental villi, some collagen fibrils ran toward trophoblasts and probably merging with lamina densa. In oral mucosa, some collagen fibrils curved to epithelial cells, passed through the anchoring fibril network and apparently merged with the basal surface of lamina densa. Together with the morphology of reconstituted collagen fibrils from type V collagen and hybrid fibrils from type V and type I collagen and the results presented here, we propose that a direct connection of collagen fibrils with lamina densa could be a ubiquitous anchoring system to stabilize epithelial tissues.