RNA-Seq of Myf6-knockout versus Wild-type satellite cells

In metazoans, skeletal muscle evolved to contract and produce force. Recent experimental evidence, however, suggests that skeletal muscle has also acquired endocrine functions and produces a vast array of muscle-derived cytokines and growth factors, collectively called myokines. The mechanisms that regulate myokine production and their effect on the resident stem cell population inskeletal muscle remain unknown. Here, we report that in adult skeletal muscle, Myf6/MRF4 is a major regulator of myokine expression. Genetic deletion of Myf6 in skeletal muscle leads to reduction of the muscle stem cell (MuSCs) pool in adult mice in a myokine-dependent manner but, surprisingly, does not disrupt muscle differentiation. Using ChIP-Seq and gene expression analyses of myogenic factors, we show that Myf6/MRF4 is a direct regulator of many myokines and muscle-secreted proteins, including ligands for canonical signaling pathways such as EGFR and VEGFR. Consequently, in Myf6-deficient animals,MuSCs increasingly break quiescence, but can nevertheless undergo differentiation. Lastly, we show that Myf6 and its gene network rapidly respondto aerobic and anaerobic exercise. Together, these findings indicate that control of myokine signaling by Myf6 is critical to maintain muscle stem cell pool and skeletal muscle function via myokine signaling. Satellite cells from two 10 month-old female wild-type mice, two 10 month-old female Myf6-knockout mice and three 4 week-old male wild-type mice were analyzed.在后生动物中，骨骼肌的演化核心功能为收缩并产生肌力。然而近期的实验证据表明，骨骼肌还获得了内分泌功能，可分泌大量肌源性细胞因子与生长因子，这类物质统称为肌因子（myokines）。目前，调控肌因子生成的具体机制，以及其对骨骼肌内驻留干细胞群的影响仍未明确。本研究发现，在成年骨骼肌中，Myf6/MRF4是肌因子表达的核心调控因子。通过遗传学手段敲除骨骼肌中的Myf6基因，会以肌因子依赖的方式减少成年小鼠的肌肉干细胞（MuSCs）库，但令人意外的是，该操作并不会破坏肌肉分化过程。通过对肌源性因子进行染色质免疫沉淀测序（ChIP-Seq）与基因表达分析，我们证实Myf6/MRF4可直接调控多种肌因子及肌分泌蛋白的表达，其中包括表皮生长因子受体（EGFR）、血管内皮生长因子受体（VEGFR）等经典信号通路的配体。因此，在Myf6基因敲除的动物体内，MuSCs会愈发频繁地退出静息状态，但仍可正常完成分化过程。最后，我们证实Myf6及其基因调控网络可快速响应有氧与无氧运动刺激。综合以上研究结果，我们认为Myf6通过调控肌因子信号通路，可维持肌肉干细胞库稳态与骨骼肌功能，该调控机制至关重要。本研究分析了2只10月龄雌性野生型小鼠、2只10月龄雌性Myf6基因敲除小鼠以及3只4周龄雄性野生型小鼠的肌卫星细胞。