The expression of
cornifin, a putative cross-linked envelope precursor, was investigated in several squamous differentiating tissues by in situ hybridization and immunohistochemical analysis. Cornifin
mRNA and
protein, which are absent in the normal mucociliary tracheal epithelium, are induced in the suprabasal layers of the squamous metaplastic tracheal epithelium of
vitamin A-deficient hamsters. Similar to the induction of squamous
metaplasia in vivo, culture of rabbit tracheal cells in the absence of
retinoids results in squamous differentiation and expression of cornifin. This induction of cornifin expression is suppressed by
retinoic acid and several of its analogs. Cornifin
mRNA and
protein are also detected in the suprabasal layers of the squamous epithelium of rabbit esophagus and tongue. The distribution of cornifin in human epidermis was compared with that of two other crosslinked envelope precursor
proteins,
involucrin and
loricrin. The localization of cornifin and
involucrin is very similar. Both are induced in the spinous layer and appear at an earlier stage during epidermal differentiation than
loricrin. The expression of cornifin is greatly increased in psoriatic skin. Cornifin
mRNA is barely detectable in normal epidermis, whereas it is present at relatively high levels in the suprabasal layers of psoriatic epidermis. Topical treatment with RA results in thickening of the skin and increases the level of cornifin
mRNA and
protein in the upper spinous layers of mouse skin. Cornifin expression correlates generally with squamous differentiation in a variety of tissues and is abnormally regulated in psoriatic skin and in skin treated topically with
retinoic acid.