Desmoglein isotype expression in the hair follicle and its cysts correlates with type of keratinization and degree of differentiation

Within stratified squamous epithelia, such as the epidermis, desmogleins are generally expressed in a differentiation-specific manner. Similar to the epidermis, the hair follicle is compartmentalized into a hierarchy of cell types based on their level of differentiation. Relatively undifferentiated stem cells in the bulge can generate epidermis, sebaceous gland, and hair bulb matrix cells. The latter give rise to at least six different cell types that keratinize as they move up the hair shaft and inner root sheath. Here, we examined expression patterns of the desmoglein isotypes, desmogleins 1, 2, and 3 in the cutaneous epithelium, and discovered that desmoglein 1 and 2 expression correlated with the state of differentiation of defined populations within the hair follicle. Desmoglein 2 was highly expressed by the least differentiated cells of the cutaneous epithelium, including the hair follicle bulge of the fetus and adult, bulb matrix cells, and basal layer of the outer root sheath. In contrast, desmoglein 1 defined more differentiated cell populations, and was expressed in epidermal suprabasal cells, the inner root sheath, and the innermost layers of the outer root sheath. We found that the expression pattern of desmoglein 3 correlated with different types of keratinization. In areas of trichilemmal keratinization in the follicle, and in cysts arising from these areas, desmoglein 3 was expressed throughout all layers of the outer root sheath and cyst wall. In areas of epidermal-like keratinization, such as in the infundibulum and in epidermal inclusion cysts, desmoglein 3 expression was limited mainly to the basal layer. We conclude that desmoglein expression patterns define compartments of cells in similar states of differentiation within the cutaneous epithelium, and reveal a hierarchy of differentiation among these compartments.