Cytokeratin 7 has been found in columnar and glandular epithelium of the lung, cervix, breast, bile ducts and larger collecting ducts of the kidney. Occasionally staining of blood vessel cell walls, particularly endothelial cells, may be observed. The protein encoded by this gene is a member of the keratin gene family. The type II cytokeratins consist of basic or neutral proteins which are arranged in pairs of heterotypic keratin chains coexpressed during differentiation of simple and stratified epithelial tissues. This type II cytokeratin is specifically expressed in the simple epithelia lining the cavities of the internal organs and in the gland ducts and blood vessels. The genes encoding the type II cytokeratins are clustered in a region of chromosome 12q12-q13. Alternative splicing may result in several transcript variants; however, not all variants have been fully described.