Targeted inactivation of the type VII collagen gene (Col7a1) in mice results in severe blistering phenotype: a model for recessive dystrophic epidermolysis bullosa.

Dystrophic forms of epidermolysis bullosa (DEB) are associated with mutations in the type VII collagen gene (Col7a1) which encodes the major component of anchoring fibrils. To develop a DEB animal model, type VII collagen deficient mice were generated by targeted homologous recombination. The targeting vector replaced exons 46-69 of Col7a1 with the neomycin-resistance gene, in reverse transcriptional orientation, resulting in elimination of most of the collagenous domain 1. Col7a1 heterozygous (+/-) mice were phenotypically normal. Mating of Col7a1 +/- mice revealed that Col7a1 null (-/-) mice, which were born with extensive cutaneous blistering, died during the first two weeks of life probably due to complications arising from the blistering. Transmission electron microscopy revealed subepidermal blistering below the lamina densa and absence of anchoring fibrils. Immunohistochemical staining with anti-human type VII collagen antibody stained the dermal-epidermal junction in control mice, but did not stain the skin of Col7a1 null mice. Collectively, the DEB mice recapitulate the clinical, genetic, immunohistochemical and ultrastructural characteristics of recessive DEB in humans. These mice provide an animal model to study the pathomechanisms of DEB and serve as a system to test therapeutic approaches, including gene replacement, towards the cure of this devastating skin disease.