Distribution and threshold expression of the tRNA(Lys) mutation in skeletal muscle of patients with myoclonic epilepsy and ragged-red fibers (MERRF).
Distribution and threshold expression of the tRNA(Lys) mutation in skeletal muscle of patients with myoclonic epilepsy and ragged-red fibers (MERRF).
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发表时间：
1992-12
影响因子：
9.8
通讯作者：
L. Boulet;George Karpati;E. Shoubridge
中科院分区：
文献类型：
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作者：
L. Boulet;George Karpati;E. Shoubridge
我们研究了4例肌阵挛性癫痫和破碎红纤维（MERRF）患者骨骼肌中携带tRNA（Lys）基因第8344位A-G突变的突变型mtDNA的分布和表达。在所有患者的肌肉样本中，突变基因组的比例大于总mtDNA的80%，并且与细胞色素c氧化酶（考克斯）活性的降低相关。绝大多数的成肌细胞，克隆自卫星细胞群在同一肌肉，同质的突变。在这个人口中的突变体mtDNA的总体比例是类似的分化的肌肉，这表明骨骼肌中的突变体与野生型mtDNA的比例是在卵子或早期发育过程中确定的，并随年龄变化不大。所有mtDNA编码基因的翻译在同质突变成肌细胞克隆中受到严重抑制，但在异质或野生型克隆中没有。在通过不同比例的突变体和野生型成肌细胞融合形成的异质肌管中确定突变的生化表达的阈值。在含有突变mtDNA的肌管中，翻译减少的幅度是蛋白质特异性的。复合体I和IV亚基比复合体V亚基受到更大的影响，并且与蛋白质大小和赖氨酸残基数目粗略相关。大约15%的野生型线粒体DNA将翻译和考克斯活性恢复到接近正常水平。这些结果表明，在tRNA（赖氨酸）的A到G的取代是一种功能隐性突变，可以拯救细胞器内互补与野生型mtDNA的一小部分，并解释了陡峭的阈值表达的MERRF临床表型。
We investigated the distribution and expression of mutant mtDNAs carrying the A-to-G mutation at position 8344 in the tRNA(Lys) gene in the skeletal muscle of four patients with myoclonus epilepsy and ragged-red fibers (MERRF). The proportion of mutant genomes was greater than 80% of total mtDNAs in muscle samples of all patients and was associated with a decrease in the activity of cytochrome c oxidase (COX). The vast majority of myoblasts, cloned from the satellite-cell population in the same muscles, were homoplasmic for the mutation. The overall proportion of mutant mtDNAs in this population was similar to that in differentiated muscle, suggesting that the ratio of mutant to wild-type mtDNAs in skeletal muscle is determined either in the ovum or during early development and changes little with age. Translation of all mtDNA-encoded genes was severely depressed in homoplasmic mutant myoblast clones but not in heteroplasmic or wild-type clones. The threshold for biochemical expression of the mutation was determined in heteroplasmic myotubes formed by fusion of different proportions of mutant and wild-type myoblasts. The magnitude of the decrease in translation in myotubes containing mutant mtDNAs was protein specific. Complex I and IV subunits were more affected than complex V subunits, and there was a rough correlation with both protein size and number of lysine residues. Approximately 15% wild-type mtDNAs restored translation and COX activity to near normal levels. These results show that the A-to-G substitution in tRNA(Lys) is a functionally recessive mutation that can be rescued by intraorganellar complementation with a small proportion of wild-type mtDNAs and explain the steep threshold for expression of the MERRF clinical phenotype.