Anchoring filaments of the amphibian epidermal-dermal junction traverse the basal lamina entirely from the plasma membrane of hemidesmosomes to the dermis

An electron microscopical study of the epidermal-dermal junction in the axolotl and adult Rana pipiens has been carried out. This shows that filaments of about 12nm in diameter, known as anchoring filaments, pass from the hemidesmosomes at the base of the epidermal cells across the basal lamina to the dermis. There they may unite to form broader fibres, known as anchoring fibrils, or may simply form bundles. In the axolotl, particularly, the anchoring fibrils or bundles of anchoring filaments, enmesh with the collagen fibres of the dermis. Removal of epidermal cells with EDTA results in separation along a plane in the lamina rara of the basal lamina, i.e. between the plasma membrane of the cells and the lamina densa. The anchoring filaments remain inserted into the lamina densa. Hemidesmosomal plaques are no longer visible in regions of the plasma membrane that have been separated from the basal lamina by EDTA, and no evidence was found that plaques are engulfed by the cells. It is proposed that the hemidesmosome-anchoring filament system provides a structural link between the collagenous filament system of the dermis and the intracellular cytokeratin filament system of the epidermis, which, in turn, is linked between cells by desmosomes.