Fos licenses early events in stem cell activation promoting skeletal muscle regeneration [array]. Fos licenses early events in stem cell activation promoting skeletal muscle regeneration [array]

Muscle stem cells, also known as satellite cells, are largely non-proliferative in uninjured skeletal muscle but transition at sites of injury into rapidly dividing progenitors that mediate muscle repair. As early events in satellite cell activation are rate-limiting for recovery from muscle damage, there is substantial interest in discovering their molecular driver(s). Using a comparative transcriptomic approach, we identified a prominent Fos signature in recently activated muscle satellite cells, which was rapidly and transiently induced by muscle damage. Functional interrogation using complementary genetic mouse models revealed that FOS is required for efficiently initiating key stem cell functions, including cell cycle entry, stem/progenitor cell expansion, and regeneration of muscle after injury. Transcriptional profiling further revealed that FOS activates critical gene circuits that stimulate cell migration, proliferation, and differentiation­ while simultaneously repressing quiescence-promoting gene signatures. Pharmacological and genetic disruption of one of these FOS-activated target genes, mono-ADP Ribosyl-Transferase 1 (Art1), in freshly isolated satellite cells substantially diminished cell cycle entry and expansion of the pool of regenerative stem cells. Together, these data implicate FOS as a crucial inducer of early-acting, pro-regenerative gene targets and highlight new transcriptional and post-translational modification events necessary for optimal injury-activated muscle stem cell regenerative responses. Overall design: B1-Integrin+/CXCR4+/CD45-/CD31-/CD11b-/Ter119-/Sca1- Fresh satellite cells (Fresh SCs) were isolated via FACS from resting skeletal muscle (hind-limbs, abdominal, and triceps) of 2-month old C57BL/6J (n=3 mice) adult animals. RNA was extracted from Fresh and Cultured (5-days) SCs and prepared for microarray analysis.

肌干细胞（muscle stem cells），亦称卫星细胞（satellite cells），在未受损伤的骨骼肌中大多处于非增殖状态，但在损伤部位会转化为快速分裂的祖细胞，介导肌肉修复。鉴于卫星细胞激活的早期事件是肌肉损伤修复恢复的限速环节，学界对发掘其分子驱动因子有着浓厚的研究兴趣。本研究采用比较转录组学方法，在新近激活的肌肉卫星细胞中鉴定出显著的Fos特征基因谱，该特征谱可被肌肉损伤快速且瞬时诱导。通过互补遗传小鼠模型开展功能验证实验发现，FOS对于高效启动干细胞核心功能至关重要，这些功能包括细胞周期进入、干/祖细胞扩增以及损伤后肌肉再生。转录谱分析进一步显示，FOS可激活促进细胞迁移、增殖与分化的关键基因调控网络，同时抑制维持细胞静息状态的特征基因谱。对新近分离的卫星细胞施以FOS激活靶基因之一的单ADP核糖基转移酶1（mono-ADP Ribosyl-Transferase 1，Art1）的药理学与遗传学干扰，可显著削弱细胞周期进入以及再生干细胞池的扩增能力。综上，上述数据表明FOS是早期作用的促再生基因靶标的关键诱导因子，并揭示了实现最佳损伤激活肌肉干细胞再生应答所必需的全新转录与翻译后修饰事件。实验设计：从2月龄成年C57BL/6J小鼠（n=3只）的静息骨骼肌（后肢、腹部及肱三头肌）中，通过荧光激活细胞分选术（FACS）分离得到B1-Integrin+/CXCR4+/CD45-/CD31-/CD11b-/Ter119-/Sca1- 新鲜卫星细胞（Fresh SCs）。分别提取新鲜卫星细胞与体外培养5天的卫星细胞的总RNA，制备样本用于基因芯片分析（microarray analysis）。