The Hair Follicle Stem Cell Niche: The Bulge and Its Environment

Abstract

The hair follicle (HF) is a dynamic miniorgan that has become one of the best understood models of tissue stem cell (SC) behavior. Distinct temporal orchestration of HF SC self-renewal, differentiation, and quiescence makes the HF an ideal system for studying regulation in a SC niche during normal homeostasis of a tissue. The HF bulge structure acts as the SCs' maintenance niche, and houses a heterogeneous collection of SCs that promote HF growth and contribute to epidermal wound repair. Bulge-neighboring cells contribute to the niche environment and are important for regulating HFSC activation, quiescence and differentiation. This review will explore the HFSC behavior within their niche, and the mechanisms that contribute to the homeostasis and maintenance of HFSCs in adult skin.