Kirby Tyler J, Patel Rooshil M, McClintock Timothy S, Dupont-Versteegden Esther E, Peterson Charlotte A, McCarthy John J
Department of Physiology, College of Medicine, University of Kentucky, Lexington, KT 40536 Center for Muscle Biology, University of Kentucky, Lexington, KT 40536.
Department of Physiology, College of Medicine, University of Kentucky, Lexington, KT 40536.
Mol Biol Cell. 2016 Mar 1;27(5):788-98. doi: 10.1091/mbc.E15-08-0585. Epub 2016 Jan 13.
Myofibers increase size and DNA content in response to a hypertrophic stimulus, thus providing a physiological model with which to study how these factors affect global transcription. Using 5-ethynyl uridine (EU) to metabolically label nascent RNA, we measured a sevenfold increase in myofiber transcription during early hypertrophy before a change in cell size and DNA content. The typical increase in myofiber DNA content observed at the later stage of hypertrophy was associated with a significant decrease in the percentage of EU-positive myonuclei; however, when DNA content was held constant by preventing myonuclear accretion via satellite cell depletion, both the number of transcriptionally active myonuclei and the amount of RNA generated by each myonucleus increased. During late hypertrophy, transcription did not scale with cell size, as smaller myofibers (<1000 μm(2)) demonstrated the highest transcriptional activity. Finally, transcription was primarily responsible for changes in the expression of genes known to regulate myofiber size. These findings show that resident myonuclei possess a significant reserve capacity to up-regulate transcription during hypertrophy and that myofiber transcription is responsive to DNA content but uncoupled from cell size during hypertrophy.
肌纤维会因肥大刺激而增大尺寸并增加DNA含量，从而提供了一个生理模型，用以研究这些因素如何影响整体转录。我们使用5-乙炔基尿苷（EU）对新生RNA进行代谢标记，发现在细胞大小和DNA含量发生变化之前的早期肥大阶段，肌纤维转录增加了七倍。在肥大后期观察到的肌纤维DNA含量的典型增加与EU阳性肌核百分比的显著下降有关；然而，当通过卫星细胞耗竭阻止肌核增加从而使DNA含量保持恒定时，转录活跃的肌核数量以及每个肌核产生的RNA量均增加。在肥大后期，转录并不随细胞大小而变化，因为较小的肌纤维（<1000μm²）表现出最高的转录活性。最后，转录主要负责调节肌纤维大小的已知基因表达的变化。这些发现表明，驻留肌核在肥大过程中具有显著的上调转录的储备能力，并且肌纤维转录对DNA含量有反应，但在肥大过程中与细胞大小解偶联。
