Galectin-7, a marker of all types of stratified epithelia

Galectin-7 is a 14-kDA member of the lectin family we have previously cloned in the human. Its expression was found at all stages of differentiation of the human epidermis and was reduced but not suppressed when oral metaplasia of reconstructed epidermis was induced by retinoic acid. This suggested that galectin-7 could be a marker of both keratinized and non-keratinized stratified epithelia. To ascertain this hypothesis, we cloned the rat and the mouse cDNAs and produced a specific antiserum raised against a synthetic peptide. The distribution of galectin-7 mRNAs and protein was studied by in situ hybridization and immunolabelling of various human, rat and mouse epithelia. Galectin-7 was found to be expressed in interfollicular epidermis and in the outer root sheath of the hair follicle, but not in the hair matrix, nor in the sebaceous glands. It was present in esophagus and oral epithelia, cornea, Hassal's corpuscles of the thymus, but not in simple and transitional epithelia. Galectin-7 can thus be considered as a marker of all subtypes of keratinocytes. In that respect it differs from both "basal-specific" keratins K5-K14 and from "suprabasal-specific" markers such as keratins K1-K10 and involucrin. Galectin-7 also differs from some desmosomal proteins, which are present in all types of epithelia and in myocardium. Galectin-7 was absent from cultured carcinoma cell lines and was reduced both in human carcinomas and in murine tumors produced with the two-stage carcinogenesis protocol.