A mutation in the tRNA Leu(UUR) gene associated with the MELAS subgroup of mitochondrial encephalomyopathies
TL;DR: An A-to-G transition mutation at nucleotide pair 3,243 in the dihydrouridine loop of mitochondrial tRNALeu(UUR) that is specific to patients with MELAS is reported, which creates an Apal restriction site and could perform a simple molecular diagnostic test for the disease.
Abstract: MITOCHONDRIAL encephalomyopathies are usually divided into three distinct clinical subgroups: (1) mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS); (2) myoclonus epilepsy associated with ragged-red fibres (MERRF); and (3) chronic progressive external ophthalmoplegia (CPEO) including Kearns-Sayre syndrome1–5. Large deletions of human mitochondrial DNA and a transition mutation at the mitochondrial transfer RNAlys gene give rise to CPEO including Kearns–Sayre syndrome6–8 and MERRF9,10, respectively. Here we report an A-to-G transition mutation at nucleotide pair 3,243 in the dihydrouridine loop of mitochondrial tRNALeu(UUR) that is specific to patients with MELAS. Because this mutation creates an Apal restriction site, we could perform a simple molecular diagnostic test for the disease. The mutation was present in 26 out of 31 independent MELAS patients and 1 out of 29 CPEO patients, but absent in the 5 MERRF and 50 controls tested. Southern blot analysis confirmed that the mutant DNA always coexists with the wild-type DNA (heteroplasmy).
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TL;DR: The mitochondria provide a direct link between the authors' environment and their genes and the mtDNA variants that permitted their forbears to energetically adapt to their ancestral homes are influencing their health today.
Abstract: Life is the interplay between structure and energy, yet the role of energy deficiency in human disease has been poorly explored by modern medicine. Since the mitochondria use oxidative phosphorylation (OXPHOS) to convert dietary calories into usable energy, generating reactive oxygen species (ROS) as a toxic by-product, I hypothesize that mitochondrial dysfunction plays a central role in a wide range of age-related disorders and various forms of cancer. Because mitochondrial DNA (mtDNA) is present in thousands of copies per cell and encodes essential genes for energy production, I propose that the delayed-onset and progressive course of the agerelated diseases results from the accumulation of somatic mutations in the mtDNAs of post-mitotic tissues. The tissue-specific manifestations of these diseases may result from the varying energetic roles and needs of the different tissues. The variation in the individual and regional predisposition to degenerative diseases and cancer may result from the interaction of modern dietary caloric intake and ancient mitochondrial genetic polymorphisms. Therefore the mitochondria provide a direct link between our environment and our genes and the mtDNA variants that permitted our forbears to energetically adapt to their ancestral homes are influencing our health today.
3,016 citations
TL;DR: The essential role of mitochondrial oxidative phosphorylation in cellular energy production, the generation of reactive oxygen species, and the initiation of apoptosis has suggested a number of novel mechanisms for mitochondrial pathology.
Abstract: Over the past 10 years, mitochondrial defects have been implicated in a wide variety of degenerative diseases, aging, and cancer. Studies on patients with these diseases have revealed much about the complexities of mitochondrial genetics, which involves an interplay between mutations in the mitochondrial and nuclear genomes. However, the pathophysiology of mitochondrial diseases has remained perplexing. The essential role of mitochondrial oxidative phosphorylation in cellular energy production, the generation of reactive oxygen species, and the initiation of apoptosis has suggested a number of novel mechanisms for mitochondrial pathology. The importance and interrelationship of these functions are now being studied in mouse models of mitochondrial disease.
2,950 citations
TL;DR: This review explores the advances that have been made and the areas in which future progress is likely in understanding basic mitochondrial genetics and the relationship between inherited mutations and disease phenotypes, and in identifying acquired mtDNA mutations in both ageing and cancer.
Abstract: The human mitochondrial genome is extremely small compared with the nuclear genome, and mitochondrial genetics presents unique clinical and experimental challenges. Despite the diminutive size of the mitochondrial genome, mitochondrial DNA (mtDNA) mutations are an important cause of inherited disease. Recent years have witnessed considerable progress in understanding basic mitochondrial genetics and the relationship between inherited mutations and disease phenotypes, and in identifying acquired mtDNA mutations in both ageing and cancer. However, many challenges remain, including the prevention and treatment of these diseases. This review explores the advances that have been made and the areas in which future progress is likely.
1,525 citations
TL;DR: The extent of size reduction within metazoan mitochondrial-transfer RNA (mt-tRNA) gene sets strongly correlates with the degree to which the more variable secondary structure element-forming regions of mt-rRNA genes are lost.
Abstract: Publisher Summary This chapter describes structural features and evolution of metazoan mitochondrial DNA (mtDNA) molecules. Throughout the evolution of metazoa, gene content of mitochondria-genomes is highly conserved, as has the close packing of genes. Most of the occasional sequence expansions that have occurred, by way of either repeated or noncoding unique sequences, are found in the control or putative control region, rather than being dispersed between genes. Of the 13 open reading frames recognized in the human mtDNA molecules, four (COI, COII, COIII, and Cyt b) are originally identified in regard to the proteins they encode, from similarities of their predicted amino acid sequences to known amino acid sequences of bovine proteins, and predicted amino acid sequences of yeast mt-protein genes. Among mtDNAs of vertebrates and higher invertebrates, there are genes that overlap. Some overlaps are among the 3′ ends of two genes that are encoded in opposite strands of the molecule. The extent of size reduction within metazoan mitochondrial-transfer RNA (mt-tRNA) gene sets strongly correlates with the degree to which the more variable secondary structure element-forming regions of mt-rRNA genes are lost.
1,478 citations
TL;DR: It is expected that cell cultures of patients with mitochondrial diseases will increasingly be used to address fundamental questions about mtDNA expression, and several key enzymes involved in mtDNA replication, transcription and protein synthesis have now been biochemically identified and some have been cloned.
1,337 citations
References
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TL;DR: A new method for determining nucleotide sequences in DNA is described, which makes use of the 2',3'-dideoxy and arabinon nucleoside analogues of the normal deoxynucleoside triphosphates, which act as specific chain-terminating inhibitors of DNA polymerase.
Abstract: A new method for determining nucleotide sequences in DNA is described. It is similar to the “plus and minus” method [Sanger, F. & Coulson, A. R. (1975) J. Mol. Biol. 94, 441-448] but makes use of the 2′,3′-dideoxy and arabinonucleoside analogues of the normal deoxynucleoside triphosphates, which act as specific chain-terminating inhibitors of DNA polymerase. The technique has been applied to the DNA of bacteriophage ϕX174 and is more rapid and more accurate than either the plus or the minus method.
62,728 citations
TL;DR: A thermostable DNA polymerase was used in an in vitro DNA amplification procedure, the polymerase chain reaction, which significantly improves the specificity, yield, sensitivity, and length of products that can be amplified.
Abstract: A thermostable DNA polymerase was used in an in vitro DNA amplification procedure, the polymerase chain reaction. The enzyme, isolated from Thermus aquaticus, greatly simplifies the procedure and, by enabling the amplification reaction to be performed at higher temperatures, significantly improves the specificity, yield, sensitivity, and length of products that can be amplified. Single-copy genomic sequences were amplified by a factor of more than 10 million with very high specificity, and DNA segments up to 2000 base pairs were readily amplified. In addition, the method was used to amplify and detect a target DNA molecule present only once in a sample of 10(5) cells.
17,663 citations
09 Apr 1981
TL;DR: The complete sequence of the 16,569-base pair human mitochondrial genome is presented and shows extreme economy in that the genes have none or only a few noncoding bases between them, and in many cases the termination codons are not coded in the DNA but are created post-transcriptionally by polyadenylation of the mRNAs.
Abstract: The complete sequence of the 16,569-base pair human mitochondrial genome is presented. The genes for the 12S and 16S rRNAs, 22 tRNAs, cytochrome c oxidase subunits I, II and III, ATPase subunit 6, cytochrome b and eight other predicted protein coding genes have been located. The sequence shows extreme economy in that the genes have none or only a few noncoding bases between them, and in many cases the termination codons are not coded in the DNA but are created post-transcriptionally by polyadenylation of the mRNAs.
8,783 citations
TL;DR: Observations demonstrate that mtDNA heteroplasmy can occur in man and that human disease may be associated with defects of the mitochondrial genome.
Abstract: In vitro studies of muscle mitochondrial metabolism in patients with mitochondrial myopathy have identified a variety of functional defects of the mitochondrial respiratory chain, predominantly affecting complex I (NADH-CoQ reductase) or complex III (ubiquinol-cytochrome c reductase) in adult cases. These two enzymes consist of approximately 36 subunits, eight of which are encoded by mitochondrial DNA (mtDNA). The increased incidence of maternal, as opposed to paternal, transmission in familial mitochondrial myopathy suggests that these disorders may be caused by mutations of mtDNA. Multiple restriction endonuclease analysis of leukocyte mtDNA from patients with the disease, and their relatives, showed no differences in cleavage patterns between affected and unaffected individuals in any single maternal line. When muscle mtDNA was studied, nine of 25 patients were found to have two populations of muscle mtDNA, one of which had deletions of up to 7 kilobases in length. These observations demonstrate that mtDNA heteroplasmy can occur in man and that human disease may be associated with defects of the mitochondrial genome.
1,700 citations
TL;DR: The mouse mitochondrial DNA genome is highly homologous in overall sequence and in gene organization to human mitochondrial DNA, with the descending order of conserved regions being tRNA genes; origin of light-strand replication; r RNA genes; knownprotein-coding genes; unidentified protein-c coding genes; displacement-loop region.
1,617 citations