Progenitor cells expressing nestin, a neural crest stem cell marker, differentiate into outer root sheath keratinocytes.

Background: Nestin, which was originally described as a neural crest stem cell marker, is known to be expressed in bulge follicle cells of human, canine and murine anagen hairs. However, the capacity of nestin-expressing cells to differentiate into the components of the hair follicle or the epidermis has been insufficiently investigated.

Hypothesis/objectives: To determine whether nestin-expressing cells are capable of differentiating into keratinocytes.

Animals/materials: A double-transgenic mouse line Nes-Cre/CAG-CAT-EGFP, in which enhanced green fluorescent protein (EGFP) is expressed upon Cre-based recombination driven by the nestin promoter.

Methods And Materials: The tissue distribution of EGFP and nestin cells in the skin of the mouse line was analysed by immunofluorescence and immunohistochemical analyses.

Results: EGFP cells were recognized in the outer epithelial cell layers of anagen and telogen hair follicles, but rarely seen in the interfollicular epidermis. The EGFP cells in the outer layers of the hair follicles coexpressed keratin 14, a marker of the outer root sheath (ORS) keratinocytes, but not trichohyalin granules, an inner root sheath keratinocyte cell marker. Immunostaining for nestin failed to detect its expression in the majority of hair follicle epithelial cells, suggesting that the EGFP cells in the ORS were derived from nestin-expressing progenitor cells that had become further committed along the epithelial cell lineage, where nestin is no longer expressed.

Conclusions And Clinical Importance: These results suggest that progenitor cells that differentiate into ORS keratinocytes are distinct from those for other hair follicle or epidermal components and provide implications for regenerative medicine and the molecular classification of hair follicle tumours.