Expression of involucrin in normal, hyperproliferative and neoplastic mouse keratinocytes

Involucrin is a protein precursor of the epidermal cornified envelope. Alth ough expression of the human protein has been documented extensively, studi es in the mouse have been hampered by a shortage of good antibodies. We des cribe the production of recombinant mouse involucrin and preparation of rab bit antisera to the protein that work well by immunohistochemistry and West ern blotting. We confirm that in normal mouse epidermis the onset of involu crin expression is in the upper spinous layers and inner root sheath of the hair follicle. Involucrin was also detected in the differentiating epithel ial cells of normal tongue, oesophagus and bladder. Involucrin was expresse d in a subpopulation of mouse keratinocytes cultured in standard or low cal cium medium and the proportion of involucrin-positive cells increased durin g suspension-induced terminal differentiation. Western blotting of keratino cytes from several inbred mouse strains revealed a remarkable heterogeneity in the electrophoretic mobility of involucrin, reflecting inter-strain var iation in the number of tandem repeats in the protein. In the hyperprolifer ative epidermis of healing wounds involucrin was expressed in most of the s uprabasal layers. In epidermal papillomas and carcinomas involucrin express ion correlated well with degree of histological differentiation. The sites of expression of the mouse protein were thus the same as those previously r eported for human involucrin. With the development of the new antibodies we anticipate that involucrin will become as widely used a marker of keratino cyte differentiation in the mouse as it is in the human.