Nestin as a Marker of Unipotent Epithelial Progenitor Cell Differentiation into Outer Root Sheath Keratinocytes in Embryonic and Adult Hair Follicles

Nestin, an intermediate filament protein known for its expression in neural stem/progenitor cells, is also found in the outer root sheath (ORS) keratinocytes of hair follicles (HFs). This study aimed to identify when nestin-expressing cells or their descendants first appear during hair follicle development and in adult hair follicles. Using genetically modified mice that express green fluorescent protein (EGFP) under the control of the nestin promoter, the researchers discovered that nestin-positive cells are present in the epithelial layer of embryonic hair follicles at the peg stage and express keratin 5, but not other markers like vimentin or Sox2. In adult hair follicles, these nestin-positive cells do not express keratin 15, a marker for multipotent stem cells. However, after hair depilation to induce hair growth, most ORS keratinocytes in the regenerating follicles were EGFP-positive. This suggests that nestin marks unipotent progenitor cells that can differentiate into ORS keratinocytes in both embryonic and adult hair follicles.