Palms and soles differ from other body sites in terms of clinical and histologic appearance, response to mechanical stress, and the distribution of
keratin 9. Because
keratin 9 is exclusively expressed in the palmoplantar suprabasal keratinocyte layers, it is considered a
differentiation marker of palms and soles. We studied palmoplantar mesenchymal influences on
keratin 9 induction in nonpalmoplantar epidermis. Although palmoplantar keratinocytes when cultured alone continued to express
keratin 9 mRNA in 12 (100%) of 12 cultures, nonpalmoplantar keratinocytes did not express it in 16 of 17 cultures. Although nonpalmoplantar keratinocytes did not express
keratin 9 mRNA when cultured with nonpalmoplantar fibroblasts, they did express it within 2 h in cocultures with palmoplantar fibroblasts derived from papillary dermis. Grafting of these coculture sheets on severe combined immunodeficient mice resulted in an epidermis, which histologically showed hyperkeratosis and acanthosis and immunohistochemically expressed
keratin 9. Furthermore, pure epidermal sheets from nonpalmoplantar skin grafted on the human sole
wounds due to
burn, injury, and the resection of acral lentiginous
melanoma, demonstrated adoption of palmoplantar phenotype and expressed
keratin 9. Our report indicates extrinsic
keratin 9 regulation by signals from dermal fibroblasts. This is also the first to suggest the possibility of treating palmoplantar
wounds with nonpalmoplantar epidermis, which is much easier to obtain and harvest.