Spatiotemporal expression pattern of neuroepithelial stem cell marker nestin suggests a role in dermal homeostasis, neovasculogenesis, and tumor stroma development: a study on embryonic and adult human skin.

Whereas keratinocytic bulge stem cells are well characterized, comparably little is known about cutaneous mesenchymal stem cells. The follicular connective tissue sheath is proposed as a niche for dermal stem cells. Because the neuroepithelial stem cell marker nestin represents a marker for mesenchymal stem cells in various tissues, our aim was to characterize its spatiotemporal expression pattern in the skin with special reference to the follicular mesenchyme. We studied immunohistochemically nestin expression over the course of human cutaneous embryogenesis, in postnatal skin, in scalp wounds, and in the peritumoral stroma of basal cell carcinomas and compared its expression with that of other known mesenchymal markers. Nestin is expressed throughout the entire early embryonic dermis but confined later during development to the follicular connective tissue sheath, where it can also be found in postnatal human hair follicles. Its expression is up-regulated in scalp wounds and the nestin-positive cells seem to originate from the follicular mesenchyme. Nestin is also expressed in a thin layer of fibroblasts in the immediate vicinity of basal cell carcinomas. The examination for nestin expression of scalp wounds is considered preliminary, because we examined scalp wounds representing re-excisions of previously diagnosed neoplasms from which we had no exact time table available as to when the original excision took place. We propose that nestin functions as a stem cell marker of the follicular mesenchyme and has a major regulatory role in dermal homeostasis, cutaneous neovasculogenesis, and tumor stroma development.