Gene Targeting of Envoplakin, a Cytoskeletal Linker Protein and Precursor of the Epidermal Cornified Envelope

Abstract

Envoplakin, a member of the plakin family of cytoskeletal linker proteins, is localized in desmosomes of stratified epithelial cells and is a component of the epidermal cornified envelope. Gene targeting in mouse embryonic stem cells was used to generate a null allele of envoplakin. No envoplakin transcripts from the targeted allele could be detected in the skin of newborn mice. Mice homozygous for the targeted allele were born in the normal Mendelian ratio and were fertile. They did not develop any discernible pathological phenotype up to the age of 1 year. The ultrastructural appearance of cornified envelopes from adult epidermis was indistinguishable between wild-type and knockout mice, and there was no evidence that the absence of envoplakin affected the subcellular distribution of periplakin or desmoplakin, two other plakins found in desmosomes. The proportion of immature cornified envelopes in the epidermis of newborn mice was greater in envoplakin-null animals than in heterozygous littermates or wild-type mice, and the envelopes had a larger surface area. This correlated with a slight delay in barrier acquisition during embryonic development. We conclude that although envoplakin is part of the scaffolding on which the cornified envelope is assembled, it is not essential for envelope formation or epidermal barrier function.

ACKNOWLEDGMENTS

We are grateful to Ian Rosewell for blastocyst injections, Mike Owen for embryonic stem cells, Eddie Wang for practical advice on ES cell cultures, Jill Williamson for karyotyping the ES cell clones, and George Elia and the members of the ICRF Histopathology Laboratory for their help in preparing and sectioning paraffin blocks. We thank the personnel of the Biological Resources Unit for their expert technical assistance.

The research was funded by the Imperial Cancer Research Fund, and by an EU Network grant to F.M.W. by an EMBO Long-Term Fellowship to A.M.