Coexpression of keratins characteristic of skin and hair differentiation in nail cells.

To further investigate the differentiation of nail, this study examined the composition and expression patterns of nail keratin by using monoclonal antibodies specific for keratins characteristic of skin or hair differentiation. Immunoblotting studies revealed that bovine hoof plate contains skin and hair differentiation-specific keratins, whereas immunofluorescence staining also showed that both keratins were present in the suprabasal cells in the bovine nail matrix. Skin differentiation-specific keratins were found to be expressed in the apical and dorsal nail matrices, whereas the hair differentiation-specific keratins were expressed mainly in the ventral nail matrix and partially in the apical and dorsal nail matrices. Moreover, the localization of the two types of keratins partially overlapped. Double-label immunofluorescence showed that unusual keratinocytes that co-express skin and hair differentiation-specific keratins exist in the nail matrix. These results indicate that the nail matrix consists of both skin-type and hair-type differentiating cells and, additionally, intermediate keratinocytes that may be progressing the pathways of both skin and hair differentiation.