Niche relocated by muscle contraction Regulation of adult stem cells by their microenvironment, or niche, is essential for tissue homeostasis and for regeneration after injury and during aging. Normal regression of hair follicles during the hair cycle poses a particular challenge for maintaining a functional proximity of stem cells to their niche, especially the specialized mesenchymal cells of the dermal papilla. Using mice as a model organism, Heitman et al. demonstrate that the follicle dermal sheath is an active smooth muscle that drives tissue remodeling through coordinated cell contraction, enabling renewed contact between the dermal papilla and hair follicle stem cells during hair follicle regression. This biomechanical mechanism of niche relocation may be utilized in other stem cell niche systems. Science, this issue p. 161 In mice, the hair follicle stem cell niche is relocated by the muscle-like contraction of the dermal sheath. Tissue homeostasis requires the balance of growth by cell production and regression through cell loss. In the hair cycle, during follicle regression, the niche traverses the skin through an unknown mechanism to reach the stem cell reservoir and trigger new growth. Here, we identify the dermal sheath that lines the follicle as the key driver of tissue regression and niche relocation through the smooth muscle contractile machinery that generates centripetal constriction force. We reveal that the calcium-calmodulin–myosin light chain kinase pathway controls sheath contraction. When this pathway is blocked, sheath contraction is inhibited, impeding follicle regression and niche relocation. Thus, our study identifies the dermal sheath as smooth muscle that drives follicle regression for reuniting niche and stem cells in order to regenerate tissue structure during homeostasis.

中文翻译：

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在毛发周期回归期间，真皮鞘收缩为干细胞生态位重新定位提供动力

通过肌肉收缩重新定位的生态位 成体干细胞的微环境或生态位的调节对于组织稳态以及损伤后和衰老过程中的再生至关重要。毛发周期期间毛囊的正常退化对维持干细胞与其生态位的功能接近提出了特殊挑战，尤其是真皮乳头的特化间充质细胞。Heitman 等人使用小鼠作为模型生物。证明毛囊真皮鞘是一种活跃的平滑肌，通过协调的细胞收缩来驱动组织重塑，从而在毛囊退化过程中使真皮乳头和毛囊干细胞之间重新接触。这种生态位重新定位的生物力学机制可用于其他干细胞生态位系统。科学，本期第 3 页。161 在老鼠身上，毛囊干细胞生态位因真皮鞘的肌肉样收缩而重新定位。组织稳态需要通过细胞产生的生长和通过细胞损失的消退来平衡。在毛发周期中，在毛囊退化期间，生态位通过一种未知的机制穿过皮肤到达干细胞库并引发新的生长。在这里，我们通过产生向心收缩力的平滑肌收缩机制确定了排列毛囊的真皮鞘是组织退化和生态位重新定位的关键驱动因素。我们揭示了钙-钙调蛋白-肌球蛋白轻链激酶通路控制鞘收缩。当这条通路被阻断时，鞘收缩被抑制，阻碍卵泡退化和生态位重新定位。因此，