线粒体DNA与DNA甲基化

线粒体是除细胞核之外唯一携带遗传物质的细胞器,其线粒体DNA（mitochondrial DNA,mtDNA）控制着线粒体一些最基本的性质,对细胞功能有着重要影响.DNA甲基化是调节基因表达的重要方式之一.研究表明mtDNA存在CpG位点的低甲基化,并且mtDNA基因的表达受核DNA（nuclear DNA,nDNA）及线粒体自身DNA甲基化的调控,mtDNA和nDNA协同作用参与机体代谢调节和疾病发生发展过程.就近年来mtDNA与DNA甲基化的关系作一综述.     

线粒体DNA突变与肿瘤发生的关系

线粒体DNA（mitochondrial DNA,mtDNA）是真核细胞内的核外遗传物质。事实证明,由于线粒体特殊的生物学结构与功能,和核基因（nDNA）相比,mtDNA更容易发生突变和氧化损伤。目前研究已经发现许多肿瘤组织中mtDNA结构和拷贝量发生了变化。文章主要对mtDNA突变、整合和不稳定性与肿瘤发生的关系以及可能的机理进行了综述。     

线粒体DNA突变与肿瘤发生

线粒体是哺乳动物细胞内唯一含有核外遗传物质的细胞器。由于其自身的特征以及所处的环境等因素,较之于nDNA,mtDNA更容易受到损伤因子的攻击。mtDNA突变,mtDNA片段整合入核基因组等可能与肿瘤的发生以及肿瘤表型的产生有较为密切的关系。深入研究线粒体及其基因组的结构和表达调控,探讨核质关系,对于阐明细胞癌变的机制可能具有重要意义。     

线粒体DNA修复系统相关酶的研究进展

线粒体DNA（mtDNA）编码线粒体电子传递系统的亚单位以及构建翻译机器所需的各种rRAN和tRNA。mtDNA编码的每一个亚单位都是线粒体完成正常的氧化磷酸化过程所必需的,因此,线粒体DNA的完整性对于生物体的生存十分重要。长期以来,人们一直认为线粒体中不存在DNA的修复。近年来在线粒体提取物中却检测到了一定数量的修复因子,提示线粒体中存在DNA的修复。主要对线粒体修复系统中相关酶的研究进展进行综述。Abstract: Mitochondrial DNA（mtDNA） encodes subunits of the mitochondrial electron transport system and the rRNAs and tRNAs required for constructing the mitochondrial tranlational machinery.Each subunit encoded by mtDNA is essential for normal oxidative phosphorylation.Thus,integrity of the mtDNA is crucial for the survival of organisms.It has long been held that there is no DNA repair in mitochondria.But in recent years,a number of repair factors have been found in mitochondrial extracts,suggesting the presence of DNA repair in mitochondria.This review summarized recent progress of enzyme in mitochondrial DNA repair processes.     

DNA甲基转移酶

DNA甲基化在基因调节和动物发育中起着重要作用。负责DNA甲基化作用的酶尔为DNA甲基转移酶（Dnmts）。到目前为止,在哺乳动物细胞中已经鉴定了三种DNA甲基转移酶基因家族,即Dnmt1、Dnmt2和Dnmt3。鉴定和研究DNA甲基转移酶对阐明DNA甲基化机制起着关键的作用。     

线粒体DNA异质性

线粒体 DNA（mitochondrial DNA,mtDNA）是线粒体内最重要的遗传物质。mtDNA 突变普 遍存在,突变型 mtDNA 与野生型 mtDNA 共存的现象被称为 mtDNA 异质性。mtDNA 异质性与衰老和多种疾病密切相关。mtDNA异质性特性、mtDNA 异质性与衰老和疾病相关性以及线粒体疾病的治疗等都是近年来遗传学研究的热点。本文从 mtDNA 异质性的动态变化、组织特异性、mtDNA 异质性与疾病以及线粒体疾病的治疗等方面对 mtDNA 异质性进行综述。     

线粒体DNA拷贝量降低诱发人支气管上皮细胞钙信号失调

采用溴化乙锭（EtBr）诱导线粒体DNA（mitochondrial DNA,mtDNA）拷贝量降低的人支气管上皮细胞株（ρ-HBE）;Real—timePCR与共聚焦成像表明,经EtBr诱导60d并挑取的单克隆细胞株,其mtDNA拷贝量下降为正常细胞的24％,成功构建了ρ-HBE。与母本细胞相比,ρ-HBE群体倍增时间延长,生长速度减慢。流式细胞术检测细胞线粒体膜电位（△ψm）下降,以Fura-2标记胞浆内游离钙,ρ-HBE[Ca2＋]i升高;线粒体解耦联剂FccP刺激细胞后,激光共聚焦扫描显微镜动态监测单个活细胞[Ca2＋]i变化,发现[ca2＋]i水平波动幅度小。提示mtDNA拷贝数降低可导致细胞内钙信号调节紊乱。     

线粒体疾病小鼠模型的建立及病理生理学研究

线粒体疾病是机体ATP合成障碍、供能不足引起的多系统疾病。近十年来,随着线粒体疾病小鼠模型的不断建立和完善,发现核DNA（nuclear DNA,nDNA）或（和）线粒体DNA（mitochondrial DNA,mtDNA）突变造成线粒体氧化磷酸化功能缺陷是其发病的主要原因。将着重介绍线粒体氧化磷酸化功能缺陷导致线粒体疾病的小鼠模型的建立及其病理生理学特点。     

香菇栽培种线粒体DNA和核糖体DNA多态性研究初探

本文应用RFLP技术研究了10个香菇主栽品种的线粒体DNA（mtDNA）和核糖体DNA（rDNA）的部分小区段,利用PCR技术扩增了rDNA5．8＋ITS区段及mtDNA的小区段,分析这些片段的限制性酸切图谱,并进行菌株间的遗传相似系数的估算。结果显示：菌株间的rDNA在5．8＋ITS区段差异很小,表明同一种内菌株间的rDNA具有相对的遗传稳定性;不同菌株间未检出mtDNA的差异,表明菌株间在所研究的区段具有很高的遗传相似性。     

Methylation pattern of mouse mitochondrial DNA.

The pattern of methylation of mouse mitochondrial DNA (mtDNA) was studied using several techniques. By employing a sensitive analytical procedure it was possible to show that this DNA contains the modified base 5-methylcytosine (m5Cyt). This residue occurred exclusively at the dinucleotide sequence CpG at a frequency of 3 to 5%. The pattern of methylation was further investigated by determining the state of methylation of several MspI (HpaII) sites. Different sites were found to be methylated to a different extent, implying that methylation of mtDNA is nonrandom. Based on the known base composition and nucleotide sequence of mouse mtDNA, the dinucleotide sequence CpG was found to be underrepresented in this DNA. The features of mtDNA methylation (CpG methylation, partial methylation of specific sites and CpG underrepresentation) are also characteristic of vertebrate nuclear DNA. This resemblance may reflect functional relationship between the mitochondrial and nuclear genomes.     

Loss of CpG dinucleotides from DNA. VI. Methylation of mitochondrial and chloroplast genes

From nucleotide sequences of mitochondrial and chloroplast genes the probable frequency of the CpG----TpG + CpA substitutions was determined. These substitutions may indicate the level of prior DNA methylation. It was found that the level of this methylation is significantly lower in mitochondrial DNA (mtDNA) and chloroplast DNA (chDNA) than in nuclear DNA (nDNA) of the same species. The species (taxon) specificity of mtDNA and chDNA methylation was revealed. A correlation was found between the level of CpG methylation in nDNA, and mtDNA and chDNA in different organisms. It is shown that cytosine residues in CpG were not subjected to significant methylation in the fungi and invertebrate mtDNA and also in the algae chDNA. In contrast, the vertebrate mtDNA bears the impress of CpG-supression, which is confirmed by direct data on methylation of these DNA. Here the first data on the possible enzymatic methylation of the plant mtDNA and chDNA were obtained. It was shown that the degree of CpG-suppression in the 5S rRNA nuclear genes of lower and higher plants is significantly higher in the chloroplast genes of 4,5S and 5S rRNA. From data on pea chDNA hydrolysis with MspI and HpaII it was established that in CCGG sequences this DNA is not methylated. The role of DNA methylation in increasing the mutation rate and in accelerating the evolutionary rates of vertebrate mtDNA is discussed.     

The Most Redundant Sequences in Human CpG Island Library Are Derived from Mitochondrial Genome

An altered pattern of epigenetic modifications, such as DNA methylation and histone modification, is critical to many common human diseases, including cancer. Recently, mitochondrial DNA (mtDNA) was reported to be associated with tumorigenesis through epigenetic regulation of methylation patterns. One of the promising approaches to study DNA methylation and CpG islands (CGIs) is sequencing and analysis of clones derived from the physical library generated by methyl-CpG-binding domain proteins and restriction enzyme MseI. In this study, we observed that the most redundant sequences of 349 clones in a human CGI library were all generated from the human mitochondrial genome. Further analysis indicated that there was a 5,845-bp DNA transfer from mtDNA to chromosome 1, and all the clones should be the products of a 510-hp MseI fragment, which contained a putative CGI of 270 bp. The 510-bp fragment was annotated as part of cytochrome c oxidase subunit Ⅱ (COXⅡ), and phylogenetic analysis of homologous sequences containing COXII showed three DNA transfer events from mtDNA to nuclear genome, one of which underwent secondary transfer events between different chromosomes. These results may further our understanding of how the mtDNA regulates DNA methylation in the nucleus.