Stem cell dynamics in the hair follicle niche

• Hair follicles are mammalian skin appendages that have the capacity to periodically and stereotypically regenerate.
• Hair follicle regeneration is fueled by adult epithelial stem cells that reside in a specialized tissue niche.
• The hair follicle niche constitutes a complex tissue microenvironment, consisting of neighboring cells, molecular signals and extracellular material.
• Stem cell behavior and contribution to regeneration are influenced by the niche microenvironment.
• Changes in the niche microenvironment due to injury or other pathological conditions may alter stem cell fate.

Hair follicles are appendages of the mammalian skin that have the ability to periodically and stereotypically regenerate in order to continuously produce new hair over our lifetime. The ability of the hair follicle to regenerate is due to the presence of stem cells that along with other cell populations and non-cellular components, including molecular signals and extracellular material, make up a niche microenvironment. Mounting evidence suggests that the niche is critical for regulating stem cell behavior and thus the process of regeneration. Here, we review the literature concerning past and current studies that have utilized mouse genetic models, combined with other approaches to dissect the molecular and cellular composition of the hair follicle niche. We also discuss our current understanding of how stem cells operate within the niche during the process of tissue regeneration and the factors that regulate their behavior.