Circular RNAs (circRNAs) have been recognized as critical regulators of skeletal muscle development. Myocyte enhancer factor 2A (MEF2A) is an evolutionarily conserved transcriptional factor that regulates myogenesis. However, it remains unclear whether MEF2A produces functional circRNAs. In this study, we identified two evolutionarily conserved circular MEF2A RNAs (circMEF2As), namely circMEF2A1 and circMEF2A2, in chicken and mouse muscle stem cells. Our findings revealed that circMEF2A1 promotes myogenesis by regulating the miR-30a-3p/PPP3CA/NFATC1 axis, whereas circMEF2A2 facilitates myogenic differentiation by targeting the miR-148a-5p/SLIT3/ROBO2/β-catenin signaling pathway. Furthermore, in vivo experiments demonstrated that circMEF2As both promote skeletal muscle growth. We also discovered that the linear MEF2A mRNA-derived MEF2A protein binds to its own promoter region, accelerating the transcription of MEF2A and upregulating the expression of both linear MEF2A and circMEF2As, forming a MEF2A autoregulated positive feedback loop. Moreover, circMEF2As positively regulate the expression of linear MEF2A by adsorbing miR-30a-3p and miR-148a-5p, which directly contribute to the MEF2A autoregulated feedback loop. Importantly, we found that mouse circMEF2As are essential for the myogenic differentiation of C2C12 cells. Collectively, our results demonstrated the evolution, function, and underlying mechanisms of circMEF2As in animal myogenesis, which may provide novel insight for both the farm animal meat industry and human medicine.

中文翻译：

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进化保守的环状 MEF2A RNA 调节肌原分化和骨骼肌发育。

环状 RNA (circRNA) 已被认为是骨骼肌发育的关键调节因子。肌细胞增强因子 2A (MEF2A) 是一种进化上保守的转录因子，可调节肌生成。然而，目前尚不清楚 MEF2A 是否产生功能性 circRNA。在这项研究中，我们在鸡和小鼠肌肉干细胞中鉴定了两种进化上保守的环状 MEF2A RNA (circMEF2As)，即 circMEF2A1 和 circMEF2A2。我们的研究结果表明，circMEF2A1 通过调节 miR-30a-3p/PPP3CA/NFATC1 轴促进肌生成，而 circMEF2A2 通过靶向 miR-148a-5p/SLIT3/ROBO2/β-catenin 信号通路促进肌生成分化。此外，体内实验表明 circMEF2As 均能促进骨骼肌生长。我们还发现，线性MEF2A mRNA衍生的MEF2A蛋白与其自身的启动子区域结合，加速MEF2A的转录并上调线性MEF2A和circMEF2A的表达，形成MEF2A自动调节的正反馈环。此外，circMEF2As通过吸附miR-30a-3p和miR-148a-5p正向调节线性MEF2A的表达，这直接有助于MEF2A自动调节反馈环。重要的是，我们发现小鼠 circMEF2As 对于 C2C12 细胞的肌原性分化至关重要。总的来说，我们的结果证明了 circMEF2As 在动物肌肉生成中的进化、功能和潜在机制，这可能为农场动物肉类工业和人类医学提供新的见解。