Melanocyte stem cells (McSCs) are key components of the hair follicle (HF) stem cell system that are derived from neural crest during embryogenesis and are responsible for regeneration of differentiated melanocytes during successive HF cycles. Our previous research has shown that two subsets of phenotypically and functionally distinct McSCs exist in murine telogen HFs, CD34+ McSCs in the bulge/lower permanent portion (LPP) and CD34- McSCs in the secondary hair germ (SHG). Whether these subsets are maintained independently or exist in a developmental hierarchy is not yet known. Using Dct-H2BGFP mice, we analyzed the quiescent and proliferative properties of McSCs and melanocytes in anagen and telogen. We found unexpectedly that Kit+Nestin- quiescent melanocytes are maintained outside of the bulge/LPP region throughout anagen in addition to the Kit+Nestin+ quiescent melanocytes of the bulge/LPP. Both subpopulations express lower levels of melanocyte differentiation markers Mitf, Pax3, Dct, Tyrp1 and Tyr compared to differentiated melanocytes of the HF bulb/matrix. These results suggest that quiescent melanocytes localized in the outer root sheath, both in and below the bulge/LPP) retain the stem cell phenotype observed in quiescent McSCs during telogen. This finding has implications for maintenance of distinct subsets of McSCs throughout successive HF cycles.

中文翻译：

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补充体内方法揭示毛囊隆起外的生长期中的静态黑素细胞

黑色素细胞干细胞（McSCs）是毛囊（HF）干细胞系统的关键组成部分，它们在胚胎发生过程中源自神经c，并在连续的HF循环中负责分化的黑色素细胞的再生。我们以前的研究表明，表型和功能上不同的McSCs的两个子集存在于小鼠端粒细胞HF，凸起/下永久部分（LPP）中的CD34 + McSCs和次生发芽（SHG）中的CD34- McSCs。这些子集是独立维护还是存在于开发层次结构中尚不清楚。使用Dct-H2BGFP小鼠，我们分析了McSCs和黑色素细胞在生长期和端生期中的静止和增殖特性。我们出乎意料地发现，除了凸起/ LPP的Kit + Nestin +静态黑素细胞外，Kit + Nestin-静态黑素细胞在整个生长期都保持在凸起/ LPP区域之外。与HF灯泡/基质的分化的黑素细胞相比，两个亚群均表达了较低水平的黑素细胞分化标记物Mitf，Pax3，Dct，Tyrp1和Tyr。这些结果表明，定位于外部根鞘中，在凸起/ LPP之内和之下的静态黑素细胞保留了在静止期McSCs中观察到的干细胞表型。这一发现对于在连续的HF周期中维持McSCs的不同子集具有影响。