Dissecting the bulge in hair regeneration
Peggy Myung, Mayumi Ito
Peggy Myung, Mayumi Ito
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Dissecting the bulge in hair regeneration

Abstract

The adult hair follicle houses stem cells that govern the cyclical growth and differentiation of multiple cell types that collectively produce a pigmented hair. Recent studies have revealed that hair follicle stem cells are heterogeneous and dynamic throughout the hair cycle. Moreover, interactions between heterologous stem cells, including both epithelial and melanocyte stem cells, within the hair follicle are just now being explored. This review will describe how recent findings have expanded our understanding of the development, organization, and regeneration of hair follicle stem cells. At a basic level, this review is intended to help construct a reference point to integrate the surge of studies on the molecular mechanisms that regulate these cells.

Authors

Peggy Myung, Mayumi Ito

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Figure 3

The genesis of a bulge stem cell population during embryonic hair development.

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The genesis of a bulge stem cell population during embryonic hair develo...
At the placode/germ stage of hair development, cells within the suprabasal layer of the forming germ express some bulge-specific markers, including Sox9 (18). Slow-cycling LRCs, representing HFSCs in the adult hair follicle, can be identified in the upper ORS of developing hair follicles as they grow downward. These are Sox9+ and express other bulge markers (e.g., Tcf3, Lhx2, Nfatc1). They can be traced to the first postnatal telogen bulge/sHG and therefore form the first telogen bulge stem cell population. Sox9-derived cells can be found in the lower ORS and matrix during hair development. Similar to the function of bulge cells during postnatal anagen phases proposed by Greco et al. (35), embryonic Sox9+ putative stem cells are also thought to provide cells to support the matrix during hair growth.