Nuclear Gene Involvement in Cytochrome Oxidase Deficiency

细胞色素c氧化酶(COX)又称线粒体呼吸链复合体IV，由13个亚基组成，其中3个由线粒体DNA(MtDNA)编码，10个由核DNA(NDNA)编码。许多COX缺乏症与线粒体DNA编码的COX亚基的点突变有关，但关于孟德尔遗传性COX缺乏症的分子基础知之甚少，表现出广泛不同的表型，包括全身性和组织特异性的临床表现。特别是，尚未在10个nDNA编码的COX亚基中发现任何突变。 然而，在过去的四年中，已经在四个COX组装基因-COX10、SC01、SC02和SURF1-中发现了突变。我们认为存在其他类似的基因，并建议通过筛选我们从COX缺乏症患者中收集的大量成纤维细胞来鉴定它们。我们建议首先，在已知的COX结构和组装基因中筛选“明显的”候选基因。在第一次筛选中存活下来的细胞系中，我们将使用啮齿动物-人类单染色体杂交和微细胞介导的染色体转移相结合的功能互补来确定互补组和候选染色体位点。这些基因座上的罪魁祸首基因将通过组合 微卫星和缺失图谱，再加上对该区域候选基因的明智测序。由此确定的任何新基因都将被描述为其在COX结构、功能和组织特异性表达中的作用。 揭示COX缺乏症的分子基础将有助于为这些通常致命且无法治愈的疾病的诊断和治疗指明方向。此外，这些错误将对理解基本的生物学现象非常有用，如COX全酶组装、COX功能、线粒体输入以及能量利用和产生。在高等真核生物中，除了引起上述疾病的那些突变外，没有自然发生的COX突变。因此，阐明COX缺陷的分子基础将从临床和科学的角度为我们提供新的有用的见解。

Cytochrome c oxidase (COX), or complex IV of the mitochondrial respiratory chain, is a copper- and hemecontaining metalloprotein composed of 13 subunits, 3 encoded by mitochondrial DNA (mtDNA) and 10 by nuclear DNA (nDNA). A number of COX-deficiency disorders are associated with point mutations in mtDNAencoded COX subunits, but very little is known regarding the molecular basis of mendelian-inherited COX deficiency disorders, which display widely varying phenotypes, including both generalized and tissuespecific clinical presentations. In particular, no mutation in any of the 10 nDNA-encoded COX subunits has yet been found. In the last four years, however, mutations have been found in four COX assembly genes - COX10 , SC01, SC02, and SURF1. We believe that other such genes exist, and propose to identify them by screening our large collection of fibroblasts from patients with COX deficiency. We propose to first, screen for "obvious" candidate genes among the known COX structural and assembly genes. Among those cell lines which survive this first screen, we will use functional complementation by a combination of rodent-human monochromosomal hybrids and microcell-mediated chromosomal transfer to identify complementation groups and candidate chromosomal loci. The culprit genes at these loci will be identified by a combination of microsatelle and deletion mapping, coupled with a judicious sequencing of candidate genes in the region. Any new gene thus identified will be characterized as to its role in COX structure, function, and tissue-specific expression. Uncovering the molecular basis of COX deficiency will be useful in terms of pointing the way to diagnosis and treatment of these generally fatal and untreatable disorders. Moreover, these errors will be extremely useful in understanding fundamental biological phenomena, such as COX holoenzyme assembly, COX function, mitochondrial importation, and energy utilization and production. There are no naturally occurring COX mutants in higher eukaryotes other than those causing the diseases outlined above. Thus, elucidating the molecular basis of the COX deficiencies will afford us new and useful insights from both a clinical and scientific standpoint.