Lilja Karin C, Zhang Nan, Magli Alessandro, Gunduz Volkan, Bowman Christopher J, Arpke Robert W, Darabi Radbod, Kyba Michael, Perlingeiro Rita, Dynlacht Brian D
Department of Pathology, New York University Cancer Institute, New York University School of Medicine, New York, New York, United States of America.
Lillehei Heart Institute, University of Minnesota, Minneapolis, MN, United States of America.
PLoS One. 2017 Apr 25;12(4):e0176190. doi: 10.1371/journal.pone.0176190. eCollection 2017.
Pluripotent stem cells (PSC) hold great promise for the treatment of human skeletal muscle diseases. However, it remains challenging to convert PSC to skeletal muscle cells, and the mechanisms by which the master regulatory transcription factor, Pax7, promotes muscle stem (satellite) cell identity are not yet understood. We have taken advantage of PSC-derived skeletal muscle precursor cells (iPax7), wherein the induced expression of Pax7 robustly initiates the muscle program and enables the in vitro generation of precursors that seed the satellite cell compartment upon transplantation. Remarkably, we found that chromatin accessibility in myogenic precursors pre-figures subsequent activation of myogenic differentiation genes. We also found that Pax7 binding is generally restricted to euchromatic regions and excluded from H3K27 tri-methylated regions in muscle cells, suggesting that recruitment of this factor is circumscribed by chromatin state. Further, we show that Pax7 binding induces dramatic, localized remodeling of chromatin characterized by the acquisition of histone marks associated with enhancer activity and induction of chromatin accessibility in both muscle precursors and lineage-committed myoblasts. Conversely, removal of Pax7 leads to rapid reversal of these features on a subset of enhancers. Interestingly, another cluster of Pax7 binding sites is associated with a durably accessible and remodeled chromatin state after removal of Pax7, and persistent enhancer accessibility is associated with subsequent, proximal binding by the muscle regulatory factors, MyoD1 and myogenin. Our studies provide new insights into the epigenetic landscape of skeletal muscle stem cells and precursors and the role of Pax7 in satellite cell specification.
多能干细胞(PSC)在治疗人类骨骼肌疾病方面具有巨大潜力。然而,将PSC转化为骨骼肌细胞仍然具有挑战性,并且主要调控转录因子Pax7促进肌肉干细胞(卫星细胞)特性的机制尚未明确。我们利用了PSC来源的骨骼肌前体细胞(iPax7),其中Pax7的诱导表达有力地启动了肌肉程序,并能够在体外产生移植后可植入卫星细胞区室的前体细胞。值得注意的是,我们发现成肌前体细胞中的染色质可及性预示着随后成肌分化基因的激活。我们还发现,Pax7的结合通常局限于常染色质区域,在肌肉细胞中被排除在H3K27三甲基化区域之外,这表明该因子的募集受到染色质状态的限制。此外,我们表明Pax7的结合会诱导染色质发生显著的局部重塑,其特征是获得与增强子活性相关的组蛋白标记,并在肌肉前体细胞和定向分化的成肌细胞中诱导染色质可及性。相反,去除Pax7会导致这些特征在一部分增强子上迅速逆转。有趣的是,另一簇Pax7结合位点在去除Pax7后与持久可及且重塑的染色质状态相关,并且持续的增强子可及性与随后肌肉调节因子MyoD1和肌细胞生成素的近端结合有关。我们的研究为骨骼肌干细胞和前体细胞的表观遗传景观以及Pax7在卫星细胞特化中的作用提供了新的见解。