Mitochondrial enzyme content in the muscles of high-performance fish: evolution and variation among fiber types
Mitochondrial enzyme content in the muscles of high-performance fish: evolution and variation among fiber types
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DOI：
10.1152/ajpregu.00152.2004
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发表时间：
2005-01-01
影响因子：
2.8
通讯作者：
Moyes, CD
中科院分区：
文献类型：
--
作者：
Dalziel, AC;Moore, SE;Moyes, CD
肌肉线粒体含量在纤维类型和种类之间差异很大。我们研究了线粒体酶柠檬酸合成酶（CS）活性变化的起源，这是一种线粒体丰度指数，在纤维类型和高性能鱼类（金枪鱼和长嘴鱼）中。不同肌肉的CS活性差异高达30倍，其中白肌最低，加热器官最高。在物种中，3种金枪鱼的红肌、白肌和心肌的CS活性比2种长嘴鱼的同类肌肉高2倍。由于通过结合PCR方法推断的CS氨基酸序列的比较与进化支特异性催化性能的差异不符，因此CS活性反映了这五个物种之间的CS含量。为了评估这些CS活性差异的基础，我们研究了CS活性（U/g肌）、核含量（DNA/g肌）和CS转录物水平（CS mRNA/g RNA）之间的关系。当每克肌肉表达时，肌肉CS活性相差10到30倍，而当每毫克DNA表达时，仅相差3倍。因此，核DNA含量，而不是纤维类型的差异，在CS基因表达可能是肌肉中CS活性的主要决定因素。相反，CS的进化差异（金枪鱼与长嘴鱼）源于转录后调控的差异，这是基于定量竞争性RT-PCR评估的CS酶水平和CS mRNA之间的关系。这些数据表明，纤维类型的差异可以在CS基因的纤维类型特异性调控没有重大差异的情况下产生，而进化差异可能主要是由于转录后调控。
Muscle mitochondrial content varies widely among fiber types and species. We investigated the origins of variation in the activity of the mitochondrial enzyme citrate synthase (CS), an index of mitochondrial abundance, among fiber types and species of high-performance fish (tunas and billfishes). CS activities varied up to 30-fold among muscles: lowest in billfish white muscle and highest in billfish heater organ. Among species, CS activities of red, white, and cardiac muscles of three tuna species were twofold greater than the homologous muscles of two billfish species. Because comparisons of CS amino acid sequences deduced from a combination of PCR methods argue against clade-specific differences in catalytic properties, CS activity reflects CS content among these five species. To assess the bases of these differences in CS activity, we looked at the relationship between CS activity (U/g muscle), nuclear content (DNA/g muscle), and CS transcript levels (CS mRNA/g RNA). Muscle CS activity differed by 10- to 30-fold when expressed per gram of muscle but only threefold when expressed per milligram of DNA. Thus it is nuclear DNA content, not fiber-type differences, in CS gene expression that may be the main determinant of CS activity in muscle. Conversely, evolutionary (tunas vs. billfishes) differences in CS arise from differences in posttranscriptional regulation, based on relationships between CS enzyme levels and CS mRNA assessed by quantitative competitive RT-PCR. These data argue that fiber-type differences can arise without major differences in fiber-type-specific regulation of the CS gene, whereas evolutionary differences may be largely due to posttranscriptional regulation.