151
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Ohno T, Umeda S, Hamasaki N, Kang D. Binding of human mitochondrial transcription factor A, an HMG box protein, to a four-way DNA junction. Biochem Biophys Res Commun 2000; 271:492-8. [PMID: 10799324 DOI: 10.1006/bbrc.2000.2656] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mitochondrial transcription factor A (mtTFA), the only known transcription factor in mitochondria, is also implicated in maintenance of mitochondrial genome although little is elucidated about its molecular basis. mtTFA is a member of HMG box proteins family. Some HMG proteins bind with high affinity to four-way DNA junctions that mimic a Holliday structure, a putative intermediate in DNA recombination. To explore possible involvement of a Holliday-like structure in the maintenance of mitochondrial genome, we examine the binding of recombinant human mtTFA to a synthetic four-way DNA junction. The human mtTFA binds to the four-way DNA junction with an approximately 10-fold higher affinity than to the corresponding linear duplex DNA and with essentially the same affinity as to a 40-mer DNA containing the human mitochondrial light strand promoter sequence. The mtTFA binds to the four-way as a monomer. Both of the two HMG box domains of human mtTFA are required for the high affinity binding to the four-way junction.
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Affiliation(s)
- T Ohno
- Department of Clinical Chemistry and Laboratory Medicine, Kyushu University Graduate School of Medical Sciences, Fukuoka, 812-8582, Japan
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152
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Michel U, Stringaris AK, Nau R, Rieckmann P. Differential expression of sense and antisense transcripts of the mitochondrial DNA region coding for ATPase 6 in fetal and adult porcine brain: identification of novel unusually assembled mitochondrial RNAs. Biochem Biophys Res Commun 2000; 271:170-80. [PMID: 10777698 DOI: 10.1006/bbrc.2000.2595] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The mammalian mitochondrial genome is a double-stranded circular DNA molecule, which is transcribed from both strands as polycistronic RNAs, which are further processed to yield the mature polyadenylated mRNAs, rRNAs and tRNAs. We compared the gene expression patterns of foetal and adult porcine brains and identified a sequence tag from the ATPase 6 region of the mitochondrial genome which, in adult brain, was more abundant in the sense (H-strand) form, but, in foetal brain, more abundant in the antisense form (L-strand). By means of solution hybridisation/S1 nuclease protection assay, Northern blotting, and PCR based techniques, we demonstrated that the ATPase 6 region of the porcine mitochondrial genome is transcribed as co-existing, stable sense and antisense RNAs. Furthermore, we identified sense and antisense transcripts from this region consisting of inversely assembled fragments joined together at a direct repeat of 7 nucleotides. Our results suggest that transcription and post-transcriptional processing of mitochondrial RNAs are much more complex than presently thought.
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Affiliation(s)
- U Michel
- Laboratory of Neurobiology, Department of Neurology, University of Göttingen, Robert-Koch-Strasse 40, Göttingen, 37075, Germany
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153
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Affiliation(s)
- A A Morris
- Department of Child Health, Royal Victoria Infirmary, University of Newcastle upon Tyne, UK
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154
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Affiliation(s)
- T Bourgeron
- Laboratoire d'Immunogénétique Humaine, INSERM U276, Institut Pasteur, Paris, France
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155
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Abstract
The organization of the mitochondrial genome is generally very conserved among vertebrates. Because of this, examination of the rare rearrangements which do occur has been suggested as offering a powerful alternative to phylogenetic analyses of mitochondrial DNA sequences. Here, we report on an avian mitochondrial rearrangement in a group of oscine passerines (warblers of the genus Phylloscopus). This rearrangement is identical to the mitochondrial organization recently identified in representatives of four orders of birds, including subsoscine Passeriformes. The rearrangement involves the movement of three genes (tRNA(Pro), NADH6, and tRNA(Glu)) from their normal position in birds between tRNA(Thr) and the control region (CR), to a new location between the CR and a novel, supposedly noncoding (NC), region. Our results suggest that this derived arrangement cannot be used to distinguish between suboscine and oscine passerines, as it has multiple origins both within Passeriformes and within birds as a whole. We found short stretches of DNA with high degrees of similarity between the CR and each NC region, respectively, all of which could be located in the same area of the CR. This suggests that the CR and the NC region are homologous and that the mechanism behind this mitochondrial rearrangement is a tandem duplication followed by multiple deletions. However, the similarities between the control and NC regions of each species were less pronounced than those between the control or NC regions from the different species, supporting the hypothesis of a single basal rearrangement in the Phylloscopus warblers.
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Affiliation(s)
- S Bensch
- Department of Animal Ecology, Lund University, Sweden.
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156
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Armstrong MR, Blok VC, Phillips MS. A multipartite mitochondrial genome in the potato cyst nematode Globodera pallida. Genetics 2000; 154:181-92. [PMID: 10628979 PMCID: PMC1460896 DOI: 10.1093/genetics/154.1.181] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The mitochondrial genome (mtDNA) of the plant parasitic nematode Globodera pallida exists as a population of small, circular DNAs that, taken individually, are of insufficient length to encode the typical metazoan mitochondrial gene complement. As far as we are aware, this unusual structural organization is unique among higher metazoans, although interesting comparisons can be made with the multipartite mitochondrial genome organizations of plants and fungi. The variation in frequency between populations displayed by some components of the mtDNA is likely to have major implications for the way in which mtDNA can be used in population and evolutionary genetic studies of G. pallida.
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Affiliation(s)
- M R Armstrong
- Department of Nematology, Scottish Crop Research Institute, Dundee, Scotland DD2 5DA.
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157
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Awadalla P, Eyre-Walker A, Smith JM. Linkage disequilibrium and recombination in hominid mitochondrial DNA. Science 1999; 286:2524-5. [PMID: 10617471 DOI: 10.1126/science.286.5449.2524] [Citation(s) in RCA: 218] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The assumption that human mitochondrial DNA is inherited from one parent only and therefore does not recombine is questionable. Linkage disequilibrium in human and chimpanzee mitochondrial DNA declines as a function of the distance between sites. This pattern can be attributed to one mechanism only: recombination.
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Affiliation(s)
- P Awadalla
- Institute of Cell, Animal and Population Biology, University of Edinburgh, Edinburgh EH9 1JT, UK
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158
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Coffey G, Lakshmipathy U, Campbell C. Mammalian mitochondrial extracts possess DNA end-binding activity. Nucleic Acids Res 1999; 27:3348-54. [PMID: 10454643 PMCID: PMC148569 DOI: 10.1093/nar/27.16.3348] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Mammalian mitochondrial protein extracts possess DNA end-binding (DEB) activity. Protein binding to a 394 bp double-stranded DNA molecule was measured using an electrophoretic mobility shift assay. Mitochondrial DEB activity was highly specific for linear DNA. Inclusion of a vast excess of non-radioactive circular DNA did not disrupt binding to radioactive f394. In contrast, binding was abolished by the inclusion of linear competitor DNA. In mammals, nuclear DEB activity is due to Ku, a hetero-dimer composed of the Ku70 and Ku86 proteins. To determine whether mitochondrial DEB activity was also due to Ku, protein extracts were prepared from the Chinese hamster XR-V15B cell line, which lacks this protein. As anticipated, nuclear extracts prepared from these cells lacked DEB activity. In contrast, mitochondrial extracts prepared from these cells had wild-type levels of DEB activity, demonstrating that this latter activity is not a consequence of nuclear contamination. Although the nuclear and mitochondrial DEB activities are independent of each other, they are nevertheless closely related, since mitochondrial DEB activity was 'supershifted' by both anti-Ku70 and anti-Ku86 antisera. The nuclear DEB protein Ku plays an essential role in nuclear DNA double-strand break repair. The DEB activity described herein may therefore play a similar role in mitochondrial DNA repair.
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Affiliation(s)
- G Coffey
- Department of Pharmacology, University of Minnesota Medical School, 3-249 Millard Hall, 435 Delaware Street SE, Minneapolis, MN 55455, USA
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159
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Affiliation(s)
- L A Marcelino
- Center for Environmental Health Sciences, Massachusetts Institute of Technology, Cambridge 02139, USA
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160
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Abstract
DNA repair mechanisms are fairly well characterized for nuclear DNA while knowledge regarding the repair mechanisms operable in mitochondria is limited. Several lines of evidence suggest that mitochondria contain DNA repair mechanisms. DNA lesions are removed from mtDNA in cells exposed to various chemicals. Protein activities that process damaged DNA have been detected in mitochondria. As will be discussed, there is evidence for base excision repair (BER), direct damage reversal, mismatch repair, and recombinational repair mechanisms in mitochondria, while nucleotide excision repair (NER), as we know it from nuclear repair, is not present.
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Affiliation(s)
- D L Croteau
- Laboratory of Molecular Genetics, National Institute on Aging, NIH, Baltimore, MD 21224, USA
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161
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Mansouri A, Gaou I, De Kerguenec C, Amsellem S, Haouzi D, Berson A, Moreau A, Feldmann G, Lettéron P, Pessayre D, Fromenty B. An alcoholic binge causes massive degradation of hepatic mitochondrial DNA in mice. Gastroenterology 1999; 117:181-90. [PMID: 10381926 DOI: 10.1016/s0016-5085(99)70566-4] [Citation(s) in RCA: 138] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
BACKGROUND & AIMS Ethanol causes oxidative stress in the hepatic mitochondria of experimental animals and mitochondrial DNA deletions in alcoholics. We postulated that ethanol intoxication may cause mitochondrial DNA strand breaks. METHODS Effects of an intragastric dose of ethanol (5 g/kg) on hepatic mitochondrial DNA levels, structure, and synthesis were determined by slot blot hybridization, Southern blot hybridization, and in vivo [3H]thymidine incorporation, respectively. RESULTS Two hours after ethanol administration, ethane exhalation (an index of lipid peroxidation) increased by 133%, although hepatic lipids were unchanged. Mitochondrial DNA was depleted by 51%. Its supercoiled form disappeared, whereas linearized forms increased. Long polymerase chain reaction evidenced lesions blocking polymerase progress on the mitochondrial genome. Mitochondrial transcripts decreased. Subsequently, [3H]thymidine incorporation into mitochondrial DNA increased, and mitochondrial DNA levels were restored. In contrast, nuclear DNA was not fragmented and its [3H]thymidine incorporation was unchanged. Liver ultrastructure only showed inconstant mitochondrial lesions. Ethanol-induced mitochondrial DNA depletion was prevented by 4-methylpyrazole, an inhibitor of ethanol metabolism, and attenuated by melatonin, an antioxidant. CONCLUSIONS After an alcoholic binge, ethanol metabolism causes oxidative stress and hepatic mitochondrial DNA degradation in mice. DNA strand breaks may be involved in the development of mitochondrial DNA deletions in alcoholics.
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Affiliation(s)
- A Mansouri
- INSERM Unité 481 and Centre Claude Bernard de Recherches sur les Hépatites Virales, Hôpital Beaujon, Clichy, France
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162
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163
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Lakshmipathy U, Campbell C. The human DNA ligase III gene encodes nuclear and mitochondrial proteins. Mol Cell Biol 1999; 19:3869-76. [PMID: 10207110 PMCID: PMC84244 DOI: 10.1128/mcb.19.5.3869] [Citation(s) in RCA: 189] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/1998] [Accepted: 02/08/1999] [Indexed: 11/20/2022] Open
Abstract
We provide evidence that the human DNA ligase III gene encodes a mitochondrial form of this enzyme. First, the DNA ligase III cDNA contains an in-frame ATG located upstream from the putative translation initiation start site. The DNA sequence between these two ATG sites encodes an amphipathic helix similar to previously identified mitochondrial targeting peptides. Second, recombinant green fluorescent protein harboring this sequence at its amino terminus was efficiently targeted to the mitochondria of Cos-1 monkey kidney cells. In contrast, native green fluorescent protein distributed to the cytosol. Third, a series of hemagglutinin-DNA ligase III minigene constructs were introduced into Cos-1 cells, and immunocytochemistry was used to determine subcellular localization of the epitope-tagged DNA ligase III protein. These experiments revealed that inactivation of the upstream ATG resulted in nuclear accumulation of the DNA ligase III protein, whereas inactivation of the downstream ATG abolished nuclear localization and led to accumulation within the mitochondrial compartment. Fourth, mitochondrial protein extracts prepared from human cells overexpressing antisense DNA ligase III mRNA possessed substantially less DNA ligase activity than did mitochondrial extracts prepared from control cells. DNA end-joining activity was also substantially reduced in extracts prepared from antisense mRNA-expressing cells. From these results, we conclude that the human DNA ligase III gene encodes both nuclear and mitochondrial enzymes. DNA ligase plays a central role in DNA replication, recombination, and DNA repair. Thus, identification of a mitochondrial form of this enzyme provides a tool with which to dissect mammalian mitochondrial genome dynamics.
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Affiliation(s)
- U Lakshmipathy
- Department of Pharmacology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA
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164
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Abstract
Phylogenetic trees constructed using human mitochondrial sequences contain a large number of homoplasies. These are due either to repeated mutation or to recombination between mitochondrial lineages. We show that a tree constructed using synonymous variation in the protein coding sequences of 29 largely complete human mitochondrial molecules contains 22 homoplasies at 32 phylogenetically informative sites. This level of homoplasy is very unlikely if inheritance is clonal, even if we take into account base composition bias. There must either be 'hypervariable' sites or recombination between mitochondria. We present evidence which suggests that hypervariable sites do not exist in our data. It therefore seems likely that recombination has occurred between mitochondrial lineages in humans.
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Affiliation(s)
- A Eyre-Walker
- Centre for the Study of Evolution, University of Sussex, Brighton, UK.
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165
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Ohsato T, Muta T, Fukuoh A, Shinagawa H, Hamasaki N, Kang D. R-Loop in the replication origin of human mitochondrial DNA is resolved by RecG, a Holliday junction-specific helicase. Biochem Biophys Res Commun 1999; 255:1-5. [PMID: 10082645 DOI: 10.1006/bbrc.1998.0133] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Stable RNA-DNA hybrids (R-loops) prime the initiation of replication in Escherichia coli cells. The R-loops are resolved by Escherichia coli RecG protein, a Holliday junction specific helicase. A stable RNA-DNA hybrid formation in the mitochondrial D-loop region is also implicated in priming the replication of mitochondrial DNA. Consistent with this hypothesis, the 3' ends of the mitochondrial R-loop formed by in vitro transcription are located close to the initiation sites of the mitochondrial DNA replication. This mitochondrial R-loop is resolved by RecG in a dose-dependent manner. Since the resolution by RecG requires ATP, the resolution is dependent on the helicase activity of RecG. A linear RNA-DNA heteroduplex is not resolved by RecG, suggesting that RecG specifically recognizes the higher structure of the mitochondrial R-loop. This is the first example that R-loops of an eukaryotic origin is sensitive to a junction-specific helicase. The resolution of the mitochondrial R-loop by RecG suggests that the replication-priming R-loops have a common structural feature recognized by RecG.
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Affiliation(s)
- T Ohsato
- Department of Clinical Chemistry and Laboratory Medicine, Kyushu University Faculty of Medicine, Fukuoka, 812-8582, Japan
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166
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Abstract
Living organisms are constantly exposed to oxidative stress from environmental agents and from endogenous metabolic processes. The resulting oxidative modifications occur in proteins, lipids and DNA. Since proteins and lipids are readily degraded and resynthesized, the most significant consequence of the oxidative stress is thought to be the DNA modifications, which can become permanent via the formation of mutations and other types of genomic instability. Many different DNA base changes have been seen following some form of oxidative stress, and these lesions are widely considered as instigators for the development of cancer and are also implicated in the process of aging. Several studies have documented that oxidative DNA lesions accumulate with aging, and it appears that the major site of this accumulation is mitochondrial DNA rather than nuclear DNA. The DNA repair mechanisms involved in the removal of oxidative DNA lesions are much more complex than previously considered. They involve base excision repair (BER) pathways and nucleotide excision repair (NER) pathways, and there is currently a great deal of interest in clarification of the pathways and their interactions. We have used a number of different approaches to explore the mechanism of the repair processes, to examine the repair of different types of oxidative lesions and to measure different steps of the repair processes. Furthermore, we can measure the DNA damage processing in the nuclear DNA and separately, in the mitochondrial DNA. Contrary to widely held notions, mitochondria have efficient DNA repair of oxidative DNA damage.
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Affiliation(s)
- V A Bohr
- Laboratory of Molecular Genetics, National Institute on Aging, NIH, Baltimore, MD 21224, USA
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167
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Abstract
Interest in the role of mitochondria in aging has intensified in recent years. This focus on mitochondria originated in part from the free radical theory of aging, which argues that oxidative damage plays a key role in degenerative senescence. Among the numerous mechanisms known to generate oxidants, leakage of the superoxide anion and hydrogen peroxide from the mitochondrial electron transport chain are of particular interest, due to the correlation between species-specific metabolic rate ("rate of living") and life span. Phenomenological studies of mitochondrial function long ago noted a decline in mitochondrial function with age, and on-going research continues to add to this body of knowledge. The extranuclear somatic mutation theory of aging proposes that the accumulation of mutations in the mitochondrial genome may be responsible in part for the mitochondrial phenomenology of aging. Recent studies of mitochondrial DNA (mtDNA) deletions have shown that they increase with age in humans and other mammals. Currently, there exist numerous important and fundamental questions surrounding mitochondria and aging. Among these are (1) How important are mitochondrial oxidants in determining overall cellular oxidative stress? (2) What are the mechanisms of mitochondrial oxidant generation? (3) How are lesions and mutations in mtDNA formed? (4) How important are mtDNA lesions and mutations in causing mitochondrial dysfunction? (5) How are mitochondria regulated, and how does this regulation change during aging? (6) What are the dynamics of mitochondrial turnover? (7) What is the relationship between mitochondrial damage and lipofuscinogenesis? (8) What are the relationships among mitochondria, apopotosis, and aging? and (9) How can mitochondrial function (ATP generation and the establishment of a membrane potential) and dysfunction (oxidant generation) be modulated and degenerative senescence thereby treated?
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Affiliation(s)
- K B Beckman
- Department of Molecular and Cell Biology, University of California, Berkeley 94720-3202, USA.
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168
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Howell N. Human mitochondrial diseases: answering questions and questioning answers. INTERNATIONAL REVIEW OF CYTOLOGY 1998; 186:49-116. [PMID: 9770297 DOI: 10.1016/s0074-7696(08)61051-7] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Since the first identification in 1988 of pathogenic mitochondrial DNA (mtDNA) mutations, the mitochondrial diseases have emerged as a major clinical entity. The most striking feature of these disorders is their marked heterogeneity, which extends to their clinical, biochemical, and genetic characteristics. The major mitochondrial encephalomyopathies include MELAS (mitochondrial encephalopathy with lactic acidosis and stroke-like episodes), MERRF (myoclonic epilepsy with ragged red fibers), KSS/CPEO (Kearns-Sayre syndrome/chronic progressive external ophthalmoplegia), and NARP/MILS (neuropathy, ataxia, and retinitis pigmentosum/maternally inherited Leigh syndrome) and they typically present highly variable multisystem defects that usually involve abnormalities of skeletal muscle and/or the CNS. The primary emphasis here is to review recent investigations of these mitochondrial diseases from the standpoint of how the complexities of mitochondrial genetics and biogenesis might determine their varied features. In addition, the mitochondrial encephalomyopathies are compared and contrasted to Leber hereditary optic neuropathy, a mitochondrial disease in which the pathogenic mtDNA mutations produce a more uniform and focal neuropathology. All of these disorders involve, at some level, a mitochondrial respiratory chain dysfunction. Because mitochondrial genetics differs so strikingly from the Mendelian inheritance of chromosomes, recent research on the origin and subsequent segregation and transmission of mtDNA mutations is reviewed.
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Affiliation(s)
- N Howell
- Department of Radiation Oncology, University of Texas Medical Branch, Galveston 77555, USA.
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169
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Kumazawa Y, Ota H, Nishida M, Ozawa T. The complete nucleotide sequence of a snake (Dinodon semicarinatus) mitochondrial genome with two identical control regions. Genetics 1998; 150:313-29. [PMID: 9725849 PMCID: PMC1460336 DOI: 10.1093/genetics/150.1.313] [Citation(s) in RCA: 168] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The 17,191-bp mitochondrial DNA (mtDNA) of a Japanese colubrid snake, akamata (Dinodon semicarinatus), was cloned and sequenced. The snake mtDNA has some peculiar features that were found in our previous study using polymerase chain reaction: duplicate control regions that have completely identical sequences over 1 kbp, translocation of tRNALeu(UUR) gene, shortened TpsiC arm for most tRNA genes, and a pseudogene for tRNAPro. Phylogenetic analysis of amino acid sequences of protein genes suggested an unusually high rate of molecular evolution in the snake compared to other vertebrates. Southern hybridization experiments using mtDNAs purified from multiple akamata individuals showed that the duplicate state of the control region is not a transient or unstable feature found in a particular individual, but that it stably occurs in mitochondrial genomes of the species. This may, therefore, be regarded as an unprecedented example of stable functional redundancy in animal mtDNA. However, some of the examined individuals contain a rather scanty proportion of heteroplasmic mtDNAs with an organization of genes distinct from that of the major mtDNA. The gene organization of the minor mtDNA is in agreement with one of models that we present to account for the concerted evolution of duplicate control regions.
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Affiliation(s)
- Y Kumazawa
- Department of Earth and Planetary Sciences, Nagoya University, Nagoya 464-8602, Japan.
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170
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Yowe DL, Ames BN. Quantitation of age-related mitochondrial DNA deletions in rat tissues shows that their pattern of accumulation differs from that of humans. Gene X 1998; 209:23-30. [PMID: 9524209 DOI: 10.1016/s0378-1119(97)00628-8] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Three age-related mtDNA deletions were identified, and the competitive polymerase chain reaction (PCR) was used to quantitate their levels in different Fisher 344 rat tissues. Deletions that removed 4834; 13273; or 13415nt of the mitochondrial genome were shown to be associated with 16 (mtDNA4834), nine (mtDNA13273), or five (mtDNA13415) nt direct repeats, respectively. The mtDNA4834 deletion was detected in an age-related manner in all tissues screened; the mtDNA13415 deletion was detected in old heart, and in both young and old brain; and the mtDNA13273 deletion was only detected in old brain tissues. The mtDNA4834 deletion was found to be at its highest level in the liver (1.88x10-2%), followed by the brain (0.22x10-2%) and kidney (0.40x10-2%) of old animals. Much lower levels were observed in old heart (0.07x10-2%) and lung (0. 04x10-2%). This distribution of mtDNA deletions in old rat tissues is in contrast to work done in humans where age-related deletions are present at the highest levels in post-mitotic tissues with much lower levels in more mitotic tissues. An inverse relationship was observed between the level of mtDNA deletions and the size of the deleted region, since the mtDNA13415 deletion was present at about a 100-fold lower level (0.53x10-5%) than the smaller mtDNA4834 deletion in old heart tissue.
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Affiliation(s)
- D L Yowe
- Barker Hall, Department of Molecular, Cell Biology, Division of Biochemistry, Molecular Biology, University of California, Berkeley, CA 94720, USA
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171
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Zastawny TH, Dabrowska M, Jaskolski T, Klimarczyk M, Kulinski L, Koszela A, Szczesniewicz M, Sliwinska M, Witkowski P, Olinski R. Comparison of oxidative base damage in mitochondrial and nuclear DNA. Free Radic Biol Med 1998; 24:722-5. [PMID: 9586801 DOI: 10.1016/s0891-5849(97)00331-6] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The levels of endogenous pig liver cells mitochondrial DNA oxidative base damage have been investigated using isotope dilution gas chromatography mass spectrometry (GC/MS). Higher levels of five measured bases were found in mtDNA in relation to nuclear DNA. We have also detected large differences in the modified base ratios of mitochondrial versus nuclear DNA. These ratios for the bases with promutagenic properties as 8OHGua and 5OHCyt are much lower than for other bases (5OHHyd, 5OHMeHyd, 5OHMeUra).
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Affiliation(s)
- T H Zastawny
- Department of Clinical Biochemistry, University School of Medical Sciences, Bydgoszcz, Poland.
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172
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Abstract
Variation in mtDNA has been used extensively to draw inferences in phylogenetics and population biology. In the majority of eukaryotes investigated, transmission of mtDNA is uniparental and clonal, with genotypic diversity arising from mutation alone. In other eukaryotes, the transmission of mtDNA is biparental or primarily uniparental with the possibility of "leakage" from the minority parent. In these cases, heteroplasmy carries the potential for recombination between mtDNAs of different descent. In fungi, such mtDNA recombination has long been documented but only in laboratory experiments and only under conditions in which heteroplasmy is ensured. Despite this experimental evidence, mtDNA recombination has not been to our knowledge documented in a natural population. Because evidence from natural populations is prerequisite to understanding the evolutionary impact of mtDNA recombination, we investigated the possibility of mtDNA recombination in an organism with the demonstrated potential for heteroplasmy in laboratory matings. Using nucleotide sequence data, we report here that the genotypic structure of mtDNA in a natural population of the basidiomycete fungus Armillaria gallica is inconsistent with purely clonal mtDNA evolution and is fully consistent with mtDNA recombination.
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Affiliation(s)
- B J Saville
- Department of Botany, University of Toronto at Mississauga, Mississauga, Ontario, Canada L5L 1C6
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173
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Anson RM, Croteau DL, Stierum RH, Filburn C, Parsell R, Bohr VA. Homogenous repair of singlet oxygen-induced DNA damage in differentially transcribed regions and strands of human mitochondrial DNA. Nucleic Acids Res 1998; 26:662-8. [PMID: 9421531 PMCID: PMC147305 DOI: 10.1093/nar/26.2.662] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Photoactivated methylene blue was used to damage purified DNA and the mitochondrial DNA (mtDNA) of human fibroblasts in culture. The primary product of this reaction is the DNA lesion 7-hydro-8-oxo-deoxyguanosine (8-oxo-dG). The DNA damage was quantitated using Escherichia coli formamidopyrimidine DNA glycosylase (Fpg) in a gene-specific damage and repair assay. Assay conditions were refined to give incision at all enzyme-sensitive sites with minimal non-specific cutting. Cultured fibroblasts were exposed to photoactivated methylene blue under conditions that would produce an average of three oxidative lesions per double-stranded mitochondrial genome. Within 9 h, 47% of this damage had been removed by the cells. This removal was due to repair rather than to replication, cell loss or degradation of damaged genomes. The rate of repair was measured in both DNA strands of the frequently transcribed ribosomal region of the mitochondrial genome and in both strands of the non-ribosomal region. Fpg-sensitive alkali-resistant oxidative base damage was efficiently removed from human mtDNA with no differences in the rate of repair between strands or between two different regions of the genome that differ substantially with regard to transcriptional activity.
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Affiliation(s)
- R M Anson
- Laboratory of Molecular Genetics and Laboratory of Biological Chemistry, National Institute on Aging, Baltimore, MD, USA
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174
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Wise CA, Sraml M, Easteal S. Departure from neutrality at the mitochondrial NADH dehydrogenase subunit 2 gene in humans, but not in chimpanzees. Genetics 1998; 148:409-21. [PMID: 9475751 PMCID: PMC1459762 DOI: 10.1093/genetics/148.1.409] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
To test whether patterns of mitochondrial DNA (mtDNA) variation are consistent with a neutral model of molecular evolution, nucleotide sequences were determined for the 1041 bp of the NADH dehydrogenase subunit 2 (ND2) gene in 20 geographically diverse humans and 20 common chimpanzees. Contingency tests of neutrality were performed using four mutational categories for the ND2 molecule: synonymous and nonsynonymous mutations in the transmembrane regions, and synonymous and nonsynonymous mutations in the surface regions. The following three topological mutational categories were also used: intraspecific tips, intraspecific interiors, and interspecific fixed differences. The analyses reveal a significantly greater number of nonsynonymous polymorphisms within human transmembrane regions than expected based on interspecific comparisons, and they are inconsistent with a neutral equilibrium model. This pattern of excess nonsynonymous polymorphism is not seen within chimpanzees. Statistical tests of neutrality, such as TAJIMA's D test, and the D and F tests proposed by FU and LI, indicate an excess of low frequency polymorphisms in the human data, but not in the chimpanzee data. This is consistent with recent directional selection, a population bottleneck or background selection of slightly deleterious mutations in human mtDNA samples. The analyses further support the idea that mitochondrial genome evolution is governed by selective forces that have the potential to affect its use as a "neutral" marker in evolutionary and population genetic studies.
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Affiliation(s)
- C A Wise
- The John Curtin School of Medical Research, The Australian National University, Canberra, ACT.
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175
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Lightowlers RN, Chinnery PF, Turnbull DM, Howell N. Mammalian mitochondrial genetics: heredity, heteroplasmy and disease. Trends Genet 1997; 13:450-5. [PMID: 9385842 DOI: 10.1016/s0168-9525(97)01266-3] [Citation(s) in RCA: 325] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Mammalian mitochondrial DNA (mtDNA) is present at high copy number (10(3)-10(4) copies) in virtually all cells of the body. The mitochondrial genome shows strict maternal inheritance and the vast majority of copies are identical at birth (homoplasmy). Occasionally, a subpopulation of mtDNA molecules carry a pathogenic mutation. When this heteroplasmic mtDNA is present during embryogenesis, it can lead to a variety of clinical symptoms predominantly affecting muscle and nerve, but also affecting other tissues. While the importance of mitochodrial heteroplasmy in human disease is unquestioned, we remain largely ignorant of many fundamental aspects of mitochondrial genetics. How do mutations arise and can they be repaired, what influences the segregation and fixation of heteroplasmic mtDNA, do levels of heteroplasmy fluctuate during life, is it possible to modulate these levels by external intervention and, finally, can we predict the segregation and transmission of a mutant genome? The aim of this article is to summarize and discuss recent observations that have addressed several of these fundamental issues and to reiterate how much we still have to learn about mitochondrial genetics.
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Affiliation(s)
- R N Lightowlers
- Department of Neurology, Medical School, University of Newcastle upon Tyne, UK.
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176
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White MF, Lilley DM. Characterization of a Holliday junction-resolving enzyme from Schizosaccharomyces pombe. Mol Cell Biol 1997; 17:6465-71. [PMID: 9343409 PMCID: PMC232499 DOI: 10.1128/mcb.17.11.6465] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The rearrangement and repair of DNA by homologous recombination involves the creation of Holliday junctions, which are cleaved by a class of junction-specific endonucleases to generate recombinant duplex DNA products. Only two cellular junction-resolving enzymes have been identified to date: RuvC in eubacteria and CCE1 from Saccharomyces cerevisiae mitochondria. We have identified a protein from Schizosaccharomyces pombe which has 28% sequence identity to CCE1. The YDC2 protein has been cloned and overexpressed in Escherichia coli, and the purified recombinant protein has been shown to be a Holliday junction-resolving enzyme. YDC2 has a high degree of specificity for the structure of the four-way junction, to which it binds as a dimer. The enzyme exhibits a sequence specificity for junction cleavage that differs from both CCE1 and RuvC, and it cleaves fixed junctions at the point of strand exchange. The conservation of the mechanism of Holliday junction cleavage between two organisms as diverse as S. cerevisiae and S. pombe suggests that there may be a common pathway for mitochondrial homologous recombination in fungi, plants, protists, and possibly higher eukaryotes.
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Affiliation(s)
- M F White
- Department of Biochemistry, University of Dundee, United Kingdom
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177
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Croteau DL, ap Rhys CM, Hudson EK, Dianov GL, Hansford RG, Bohr VA. An oxidative damage-specific endonuclease from rat liver mitochondria. J Biol Chem 1997; 272:27338-44. [PMID: 9341184 DOI: 10.1074/jbc.272.43.27338] [Citation(s) in RCA: 125] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Reactive oxygen species have been shown to generate mutagenic lesions in DNA. One of the most abundant lesions in both nuclear and mitochondrial DNA is 7,8-dihydro-8-oxoguanine (8-oxoG). We report here the partial purification and characterization of a mitochondrial oxidative damage endonuclease (mtODE) from rat liver that recognizes and incises at 8-oxoG and abasic sites in duplex DNA. Rat liver mitochondria were purified by differential and Percoll gradient centrifugation, and mtODE was extracted from Triton X-100-solubilized mitochondria. Incision activity was measured using a radiolabeled double-stranded DNA oligonucleotide containing a unique 8-oxoG, and reaction products were separated by polyacrylamide gel electrophoresis. Gel filtration chromatography predicts mtODE's molecular mass to be between 25 and 30 kDa. mtODE has a monovalent cation optimum between 50 and 100 mM KCl and a pH optimum between 7.5 and 8. mtODE does not require any co-factors and is active in the presence of 5 mM EDTA. It is specific for 8-oxoG and preferentially incises at 8-oxoG:C base pairs. mtODE is a putative 8-oxoG glycosylase/lyase enzyme, because it can be covalently linked to the 8-oxoG oligonucleotide by sodium borohydride reduction. Comparison of mtODE's activity with other known 8-oxoG glycosylases/lyases and mitochondrial enzymes reveals that this may be a novel protein.
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Affiliation(s)
- D L Croteau
- Laboratory of Molecular Genetics, NIA, National Institutes of Health, Baltimore, Maryland 21224, USA
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178
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Croteau DL, Bohr VA. Repair of oxidative damage to nuclear and mitochondrial DNA in mammalian cells. J Biol Chem 1997; 272:25409-12. [PMID: 9325246 DOI: 10.1074/jbc.272.41.25409] [Citation(s) in RCA: 366] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Affiliation(s)
- D L Croteau
- Laboratory of Molecular Genetics, NIA, National Institutes of Health, Baltimore, Maryland 21224, USA
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179
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Thyagarajan B, Campbell C. Elevated homologous recombination activity in fanconi anemia fibroblasts. J Biol Chem 1997; 272:23328-33. [PMID: 9287344 DOI: 10.1074/jbc.272.37.23328] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
It is widely believed that Fanconi anemia cells possess a reduced ability to repair inter-strand DNA cross-links. While the mechanism through which inter-strand DNA cross-links are removed from mammalian chromosomes is unknown, these lesions are repaired via homologous recombination in lower eukaryotes and bacteria. Based on the hypothesis that a similar mechanism of DNA repair functions in mammalian somatic cells, we measured homologous recombination activity in diploid fibroblasts from healthy donors, and Fanconi anemia patients. Somewhat surprisingly, homologous recombination levels in nuclear protein extracts prepared from Fanconi anemia cells were nearly 100-fold higher than in extracts prepared from control cells. We observed a similar increase in the activity of a 100-kDa homologous DNA pairing protein in extracts from Fanconi anemia cells. Transfection studies confirmed that plasmid homologous recombination levels in intact Fanconi anemia cells were substantially elevated, compared with control cells. These results suggest that inappropriately elevated levels of homologous recombination activity may contribute to the genomic instability and cancer predisposition that characterize Fanconi anemia.
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Affiliation(s)
- B Thyagarajan
- Department of Pharmacology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA
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180
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Henle ES, Linn S. Formation, prevention, and repair of DNA damage by iron/hydrogen peroxide. J Biol Chem 1997; 272:19095-8. [PMID: 9235895 DOI: 10.1074/jbc.272.31.19095] [Citation(s) in RCA: 389] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Affiliation(s)
- E S Henle
- Division of Biochemistry and Molecular Biology, University of California, Berkeley, California 94720-3202, USA
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181
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182
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Börner GV, Yokobori S, Mörl M, Dörner M, Pääbo S. RNA editing in metazoan mitochondria: staying fit without sex. FEBS Lett 1997; 409:320-4. [PMID: 9224682 DOI: 10.1016/s0014-5793(97)00357-8] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
RNA editing subsumes a number of functionally different mechanisms which have in common that they change the nucleotide sequence of RNA transcripts such that they become different from what would conventionally be predicted from their gene sequences. RNA editing has now been found in the organelles of numerous organisms as well as in a few nuclear transcripts. Most recently, it was shown to affect tRNAs in the mitochondria of several animals. The occurrence and evolutionary persistence of RNA editing is perplexing since backmutations in the genes might be assumed rapidly to eliminate the need for 'correction' of the gene sequences at the post-transcriptional level. Here, we review the recent RNA editing systems discovered in animal mitochondria and propose that they have arisen as a mechanism counteracting the accumulation of mutations that occurs in asexual genetic system.
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Affiliation(s)
- G V Börner
- Institute of Zoology, University of Munich, Germany
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183
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Bidooki SK, Johnson MA, Chrzanowska-Lightowlers Z, Bindoff LA, Lightowlers RN. Intracellular mitochondrial triplasmy in a patient with two heteroplasmic base changes. Am J Hum Genet 1997; 60:1430-8. [PMID: 9199564 PMCID: PMC1716139 DOI: 10.1086/515460] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
We report the clinical, biochemical, and genetic investigation of a patient with a severe mitochondrial encephalomyopathy. Genetic studies identified a novel, heteroplasmic tRNA mutation at nt 10010. This T-->C transition is located in the DHU loop of mitochondrial tRNA(Gly). In skeletal muscle, it was present at lower levels in cytochrome c oxidase (COX)-normal (87.2% +/- 11%) compared with COX-deficient fibers (97.3% +/- 2.6%); it was found in skin fibroblasts and blood cells, but at lower levels of heteroplasmy (15% +/- 6% and 17% +/- 10%, respectively). A second, heteroplasmic transition (A-->G), at nt 5656, showed a different distribution than the tRNA(Gly) mutation, with very low levels in skeletal muscle (< 3%) but higher levels in blood (22.7% +/- 3%) and skin fibroblasts (21% +/- 2%). These transitions were followed both in vivo, by repeat biopsy and blood sampling, and in vitro, by establishing primary cultures of myoblasts and skin fibroblasts. Repeat muscle biopsy showed a dramatic increase in COX-deficient fibers, but not of the tRNAGly mutation. Indeed, no significant change in heteroplasmy was measured for either substitution in muscle or blood. In vitro analysis gave very different results. The T10010C was not found in cultured myoblasts, even at early passage. In uncloned fibroblasts, the T10010C was stable (approximately 10%) for several passages but then gradually was lost. In contrast, the A5656G rose progressively from 27% to 91%. In cloned fibroblasts, different combinations of both base-pair changes and wild type could be identified, confirming the presence of clonal, intracellular triplasmy.
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Affiliation(s)
- S K Bidooki
- Department of Neurology, Medical School, University of Newcastle upon Tyne, United Kingdom
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