Ultrastructural Localization of Hair Keratins in Human Scalp Hair Shafts as Revealed by Rapid-Freezing Immunocytochemistry.

The study examined the expression of keratin K14 in human skin, particularly in the epidermis and hair follicles, using monospecific antisera and cRNA probes. It was found that K14 expression and filament organization differed significantly between the hair follicle and epidermis. In the outer root sheath (ORS) cells, which are mitotically active, K14 expression was low, and keratin filaments were fewer and more loosely organized compared to basal epidermal cells. As ORS cells differentiated, they increased K14 expression and formed denser keratin bundles. In contrast, matrix cells, which can differentiate into the inner root sheath, cuticle, and hair shaft, did not express K14 or form keratin filaments. Instead, they produced hair-specific keratins and dense filament bundles without inducing K14 expression. The study suggested that the patterns of K14 expression and filament organization in skin epithelial cells were linked to their pluripotency and highlighted the distinct differentiation programs of hair follicles compared to other stratified squamous epithelia.