Individual skeletal muscles have evolved to perform specific tasks based on their molecular composition. In general, muscle fibers are characterized as either fast-twitch or slow-twitch based on their myosin heavy chain isoform profiles. This approach made sense in the early days of muscle studies when SDS-PAGE was the primary tool for mapping fiber type. However, Next Generation Sequencing tools permit analysis of the entire muscle transcriptome in a single sample, which allows for more precise characterization of differences among fiber types, including distinguishing between different isoforms of specific proteins. We demonstrate the power of this approach by comparing the differential gene expression patterns of extensor digitorum longus (EDL), psoas, and soleus from mice using high throughput RNA sequencing. EDL and psoas are typically classified as fast-twitch muscles based on their myosin expression pattern, while soleus is considered a slow-twitch muscle. The majority of the transcriptomic variability aligns with the fast-twitch and slow-twitch characterization. However, psoas and EDL exhibit unique expression patterns associated with the genes coding for extracellular matrix, myofibril, transcription, translation, striated muscle adaptation, mitochondrion distribution, and metabolism. Furthermore, significant expression differences between psoas and EDL were observed in genes coding for myosin light chain, troponin, tropomyosin isoforms, and several genes encoding the constituents of the Z-disk. The observations highlight the intricate molecular nature of skeletal muscles and demonstrate the importance of utilizing transcriptomic information as a tool for skeletal muscle characterization.

中文翻译：

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小鼠EDL，腰肌和比目鱼肌转录组的比较分析

各个骨骼肌已经进化为根据其分子组成执行特定任务。通常，基于肌纤维的肌球蛋白重链同工型，肌纤维被表征为快肌或慢肌。在SDS-PAGE是绘制纤维类型的主要工具时，这种方法在肌肉研究的早期是有意义的。但是，下一代测序工具可以分析单个样品中的整个肌肉转录组，从而可以更精确地表征纤维类型之间的差异，包括区分特定蛋白质的不同同工型。我们通过使用高通量RNA测序比较来自小鼠的趾长伸肌（EDL），腰大肌和比目鱼肌的差异基因表达模式，证明了这种方法的力量。EDL和腰肌通常根据其肌球蛋白表达模式被分类为快肌，而比目鱼肌则被视为慢肌。大部分转录组变异性与快发和慢发特征一致。然而，腰大肌和EDL表现出与细胞外基质，肌原纤维，转录，翻译，横纹肌适应，线粒体分布和代谢相关的基因的独特表达模式。此外，在编码肌球蛋白轻链，肌钙蛋白，原肌球蛋白同工型的基因和编码Z盘成分的几个基因中，观察到腰大肌和EDL之间存在明显的表达差异。