Lomax M I, Coucouvanis E, Schon E A, Barald K F
Department of Anatomy and Cell Biology, University of Michigan Medical School, Ann Arbor 48109.
Muscle Nerve. 1990 Apr;13(4):330-7. doi: 10.1002/mus.880130409.
Recent studies of patients with mitochondrial myopathies suggest the existence of both muscle-specific and developmentally regulated isoforms of cytochrome c oxidase (COX), the terminal enzyme complex of the electron transport chain. To investigate the temporal pattern of gene expression of nuclear genes for COX in developing muscle, the steady-state levels of COX mRNA in total RNA from a satellite cell-derived mouse muscle cell line, C2C12, were analyzed and compared with COX mRNA levels in mature rat skeletal muscle. Undifferentiated myoblasts, myotubes just after fusion (early myotubes), and fully differentiated, contractile, striated myotubes (late myotubes) were analyzed for mRNA levels for four of the 10 different nuclear-encoded COX subunits: IV, Vb, Vlc and VIII-liver. Of these, IV, Vb and Vlc are identical in both bovine heart and liver, whereas subunit VIII has heart and liver isoforms. In C2C12 myoblasts, the level of mRNA for subunits IV, Vb, and VIII-liver is equal to or greater than the level in tissues such as brain, skeletal muscle, and liver. As myoblasts fuse and differentiate into myotubes, the levels of mRNA for these subunits undergo radically different changes. Transcripts for subunits IV and Vb accumulate to higher levels during myogenesis. The level of subunit VIII transcripts decreases during myogenesis, providing additional evidence that subunit VIII has tissue-specific isoforms in the rat. Little mRNA for COX Vlc was detected in either the C2C12 cell line or in primary embryonic rat myoblasts or myotubes in culture in spite of high levels in adult skeletal muscles, suggesting that subunit Vlc may have both fetal and adult isoforms in rodents.
近期针对线粒体肌病患者的研究表明，电子传递链的终端酶复合物细胞色素c氧化酶（COX）存在肌肉特异性和发育调控的同工型。为了研究COX核基因在发育中的肌肉中的基因表达时间模式，对卫星细胞衍生的小鼠肌肉细胞系C2C12的总RNA中COX mRNA的稳态水平进行了分析，并与成熟大鼠骨骼肌中的COX mRNA水平进行了比较。分析了未分化的成肌细胞、融合后不久的肌管（早期肌管）以及完全分化、可收缩的横纹肌管（晚期肌管）中10种不同核编码COX亚基中的4种的mRNA水平：IV、Vb、Vlc和VIII-肝脏。其中，IV、Vb和Vlc在牛心脏和肝脏中是相同的，而亚基VIII有心脏和肝脏同工型。在C2C12成肌细胞中，亚基IV、Vb和VIII-肝脏的mRNA水平等于或高于脑、骨骼肌和肝脏等组织中的水平。当成肌细胞融合并分化为肌管时，这些亚基的mRNA水平发生了截然不同的变化。亚基IV和Vb的转录本在肌生成过程中积累到更高水平。亚基VIII转录本的水平在肌生成过程中下降，这为亚基VIII在大鼠中有组织特异性同工型提供了额外证据。尽管在成年骨骼肌中水平很高，但在C2C12细胞系或培养的原代胚胎大鼠成肌细胞或肌管中均未检测到COX Vlc的mRNA，这表明亚基Vlc在啮齿动物中可能同时存在胎儿和成年同工型。
