Galectin-7, a new marker of mammalian stratified epithelia

Galectin-7 is a 14 kDA member of the lectin family recently cloned in the human. In human epidermis galectin-7 mRNA and protein were found to be present in all viable cell layers of the epithelium, showing that the expression of this marker was independant of the stage of differentiation of the keratinocyte. Studies with cultured keratinocytes showed that galectin-7 expression was not influenced by the calcium concentration and the resulting modulation of stratification, a result correlating with its pan-epidermal expression. Moreover, a model of reconstructed epidermis allowed us to show that galectin-7 expression is reduced but not suppressed when the metaplasia of epidermis into oral epithelium is induced by retinoic acid. This result suggested to us that galectin-7 could be a marker of both keratinized and non-keratinized stratified epithelia. To check this hypothesis the distribution of galectin-7 in human, rat and mouse epithelia was studied with a specific antiserum raised against a synthetic peptide. Moreover the rat cDNA was cloned and the distribution of galectin-7 mRNA was also studied in the rat. Galectin-7 was found to be expressed in interfollicular epidermis and the outer root sheath of the hair follicle, but not in the hair matrix, nor in the sebaceous glands. It was also present in esophagus and oral epithelia, cornea, Hassal 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. Moreover this marker does not seem to be influenced by the stage of differentiation. In that respect it differs from keratins K5-K14 which are transcribed only in the basal layer and from involucrin which is synthesized only in the suprabasal layers. Galectin-7 also differs from desmosomal proteins, which are present in all types of epithelia and in myocardium.