MicroRNA-205 promotes hair regeneration by modulating mechanical properties of hair follicle stem cells

Stiffness and actomyosin contractility are intrinsic mechanical properties of animal cells required for the shaping of tissues. However, whether tissue stem cells (SCs) and progenitors located within SC niche have different mechanical properties that govern their size and functions remains unclear. We show that hair follicle SCs in the bulge are stiff with high actomyosin contractility and resistant to size change, whereas hair germ (HG) progenitors are soft and periodically enlarge and contract during quiescence. During activation, HGs reduce contraction and more frequently enlarge, a process that is associated with weakening of the actomyosin network, nuclear YAP accumulation and cell cycle re-entry. Induction of miR-205, a novel regulator of the actomyosin cytoskeleton, reduces actin contractility, decreases the stiffness of the bulge and HG, and activates hair regeneration in young and old mice. This study reveals the control of tissue SC size and activities by spatiotemporally compartmentalized mechanical properties and demonstrates the possibility to stimulate tissue regeneration by fine-tuning cell mechanics. ### Competing Interest Statement The authors have declared no competing interest.