The role of dynamic gene expression in myogenic stem cells

发育中的肌肉形成并维持一个肌源性干细胞库。这些常驻干细胞是成肌细胞的来源，在发育期间用于肌肉生长，并在围产期产生卫星细胞。肌肉干细胞的维持、增殖和分化缺陷在遗传性肌肉疾病中起重要作用。新出现的证据表明，调控分子的表达动态及其波动控制干细胞的维持和分化，从而控制干细胞的命运。我们未发表的工作表明，转录因子Hes 1和MyoD在增殖的肌肉干细胞中显示振荡表达。振荡周期约为3小时，比细胞周期或昼夜节律的振荡短得多。此外，振荡是异步的，并且相邻小区异相振荡。Hes 1的振荡表达驱动MyoD的振荡表达。Hes 1振荡器的消融抑制MyoD振荡，导致持续的MyoD表达，并增加细胞的分化趋势。这会导致肌肉干细胞的维持明显不足，导致肌肉生长和修复受损。该提案的总体目标是定义肌肉干细胞中振荡基因的网络，评估MyoD/Hes 1振荡在机制水平上的后果，并将此信息应用于识别肌肉发育障碍患者这些网络中的致病变体。我们将使用光遗传学工具来同步转录因子（TF）振荡，并在振荡周期的不同阶段定义基因表达。这将揭示以振荡方式表达的基因网络。将使用光遗传学工具来评估MyoD/Hes 1的持续或振荡表达是否直接影响基因表达和染色质状态。深入了解干细胞维持和分化过程中的这种振荡周期，了解它们的表观遗传调控，以及它们的计算建模，将有助于我们识别先天性肌病和其他人类肌肉发育障碍中的突变基因。

The developing muscle forms and maintains a pool of myogenic stem cells. These resident stem cells are the source of myoblasts for muscle growth during development and generate satellite cells in the perinatal period. Deficits in the maintenance, proliferation, and differentiation of muscle stem cells play an important role in inherited muscle disorders. Emerging evidence indicates that the expression dynamics of regulatory molecules and their fluctuation control the maintenance and differentiation of stem cells, thereby controlling stem cell fate. Our unpublished work shows that the transcription factors Hes1 and MyoD display oscillatory expression in proliferating muscle stem cells. The oscillatory period is around 3 hours, much shorter than the oscillations of the cell cycle or the circadian rhythm. Moreover, oscillations are asynchronous and neighboring cells oscillate out of phase. Oscillatory expression of Hes1 drives the oscillatory expression of MyoD. Ablation of the Hes1 oscillator dampens MyoD oscillations, causes sustained MyoD expression, and increases a cell’s tendency to differentiate. This leads to marked deficits in the maintenance of muscle stem cells, resulting in impaired muscle growth and repair. The overarching goal of this proposal is to define the network of oscillatory genes in muscle stem cells, to assess the consequences of MyoD/Hes1 oscillations on a mechanistic level, and to apply this information to the identification of disease-causing variants in these networks in patients with disorders of muscle development. We will use optogenetic tools to synchronize transcription factor (TF) oscillations and define gene expression during different phases of the oscillatory cycle. This will reveal the network of genes that are expressed in an oscillatory manner. Optogenetic tools will be used to assess whether sustained or oscillatory expression of MyoD/Hes1 directly influences gene expression and the chromatin state. Insight into such oscillatory cycles during stem cell maintenance and differentiation, into their epigenetic regulation, and their computational modeling will help us identify genes mutated in congenital myopathies and other disorders of human muscle development.