scholarly journals Concerted action of two novel tRNA mtDNA point mutations in chronic progressive external ophthalmoplegia

2008 ◽  
Vol 28 (2) ◽  
pp. 89-96 ◽  
Author(s):  
Cornelia Kornblum ◽  
Gábor Zsurka ◽  
Rudolf J. Wiesner ◽  
Rolf Schröder ◽  
Wolfram S. Kunz
Keyword(s):  
Skeletal Muscle ◽  
Northern Blot ◽  
Phenotypic Expression ◽  
Point Mutations ◽  
Skeletal Muscle Fibre ◽  
Progressive External Ophthalmoplegia ◽  
Chronic Progressive External Ophthalmoplegia ◽  
Mtdna Mutations ◽  
Mtdna Sequence ◽  
Functional Consequences

CPEO (chronic progressive external ophthalmoplegia) is a common mitochondrial disease phenotype in adults which is due to mtDNA (mitochondrial DNA) point mutations in a subset of patients. Attributing pathogenicity to novel tRNA mtDNA mutations still poses a challenge, particularly when several mtDNA sequence variants are present. In the present study we report a CPEO patient for whom sequencing of the mitochondrial genome revealed three novel tRNA mtDNA mutations: G5835A, del4315A, T1658C in tRNATyr, tRNAIle and tRNAVal genes. In skeletal muscle, the tRNAVal and tRNAIle mutations were homoplasmic, whereas the tRNATyr mutation was heteroplasmic. To address the pathogenic relevance, we performed two types of functional tests: (i) single skeletal muscle fibre analysis comparing G5835A mutation loads and biochemical phenotypes of corresponding fibres, and (ii) Northern-blot analyses of mitochondrial tRNATyr, tRNAIle and tRNAVal. We demonstrated that both the G5835A tRNATyr and del4315A tRNAIle mutation have serious functional consequences. Single-fibre analyses displayed a high threshold of the tRNATyr mutation load for biochemical phenotypic expression at the single-cell level, indicating a rather mild pathogenic effect. In contrast, skeletal muscle tissue showed a severe decrease in respiratory-chain activities, a reduced overall COX (cytochrome c oxidase) staining intensity and abundant COX-negative fibres. Northern-blot analyses showed a dramatic reduction of tRNATyr and tRNAIle levels in muscle, with impaired charging of tRNAIle, whereas tRNAVal levels were only slightly decreased, with amino-acylation unaffected. Our findings suggest that the heteroplasmic tRNATyr and homoplasmic tRNAIle mutation act together, resulting in a concerted effect on the biochemical and histological phenotype. Thus homoplasmic mutations may influence the functional consequences of pathogenic heteroplasmic mtDNA mutations.

scholarly journals The costs of being male: are there sex-specific effects of uniparental mitochondrial inheritance?

2014 ◽  
Vol 369 (1646) ◽  
pp. 20130440 ◽  
Author(s):  
Madeleine Beekman ◽  
Damian K. Dowling ◽  
Duur K. Aanen
Keyword(s):  
Maternal Inheritance ◽  
Phenotypic Expression ◽  
Natural Populations ◽  
Mtdna Mutations ◽  
Specific Effects ◽  
Mtdna Sequence ◽  
Multiple Copies ◽  
The One ◽  
Mtdna Variants ◽  
Male Expression

Eukaryotic cells typically contain numerous mitochondria, each with multiple copies of their own genome, the mtDNA. Uniparental transmission of mitochondria, usually via the mother, prevents the mixing of mtDNA from different individuals. While on the one hand, this should resolve the potential for selection for fast-replicating mtDNA variants that reduce organismal fitness, maternal inheritance will, in theory, come with another set of problems that are specifically relevant to males. Maternal inheritance implies that the mitochondrial genome is never transmitted through males, and thus selection can target only the mtDNA sequence when carried by females. A consequence is that mtDNA mutations that confer male-biased phenotypic expression will be prone to evade selection, and accumulate. Here, we review the evidence from the ecological, evolutionary and medical literature for male specificity of mtDNA mutations affecting fertility, health and ageing. While such effects have been discovered experimentally in the laboratory, their relevance to natural populations—including the human population—remains unclear. We suggest that the existence of male expression-biased mtDNA mutations is likely to be a broad phenomenon, but that these mutations remain cryptic owing to the presence of counter-adapted nuclear compensatory modifier mutations, which offset their deleterious effects.

scholarly journals Origins and functional consequences of somatic mitochondrial DNA mutations in human cancer

eLife ◽  
2014 ◽  
Vol 3 ◽  
Author(s):  
Young Seok Ju ◽  
Ludmil B Alexandrov ◽  
Moritz Gerstung ◽  
Inigo Martincorena ◽  
Serena Nik-Zainal ◽  
...  
Keyword(s):  
Human Cancer ◽  
Missense Mutations ◽  
Mtdna Mutations ◽  
Dna Mutations ◽  
Mtdna Sequence ◽  
Sequencing Studies ◽  
Functional Consequences ◽  
Somatic Alterations ◽  
Mtdna Replication ◽  
Tumor Types

Recent sequencing studies have extensively explored the somatic alterations present in the nuclear genomes of cancers. Although mitochondria control energy metabolism and apoptosis, the origins and impact of cancer-associated mutations in mtDNA are unclear. In this study, we analyzed somatic alterations in mtDNA from 1675 tumors. We identified 1907 somatic substitutions, which exhibited dramatic replicative strand bias, predominantly C > T and A > G on the mitochondrial heavy strand. This strand-asymmetric signature differs from those found in nuclear cancer genomes but matches the inferred germline process shaping primate mtDNA sequence content. A number of mtDNA mutations showed considerable heterogeneity across tumor types. Missense mutations were selectively neutral and often gradually drifted towards homoplasmy over time. In contrast, mutations resulting in protein truncation undergo negative selection and were almost exclusively heteroplasmic. Our findings indicate that the endogenous mutational mechanism has far greater impact than any other external mutagens in mitochondria and is fundamentally linked to mtDNA replication.

scholarly journals Mitochondrial DNA spectra of single human CD34+ cells, T cells, B cells, and granulocytes

Blood ◽  
2005 ◽  
Vol 106 (9) ◽  
pp. 3271-3284 ◽  
Author(s):  
Yoji Ogasawara ◽  
Kazutaka Nakayama ◽  
Magdalena Tarnowka ◽  
J. Philip McCoy ◽  
Sachiko Kajigaya ◽  
...  
Keyword(s):  
T Cells ◽  
Mitochondrial Dna ◽  
B Cells ◽  
Single Cells ◽  
Point Mutations ◽  
Isolated Cells ◽  
Mtdna Mutations ◽  
Human Cd34 ◽  
Cd34 Cells ◽  
Mtdna Sequence

Abstract Previously, we described the age-dependent accumulation of mitochondrial DNA (mtDNA) mutations, leading to a high degree of mtDNA heterogeneity among normal marrow and blood CD34+ clones and in granulocytes. We established a method for sequence analysis of single cells. We show marked, distinct mtDNA heterogeneity from corresponding aggregate sequences in isolated cells of 5 healthy adult donors—37.9% ± 3.6% heterogeneity in circulating CD34+ cells, 36.4% ± 14.1% in T cells, 36.0% ± 10.7% in B cells, and 47.7% ± 7.4% in granulocytes. Most heterogeneity was caused by poly-C tract variability; however, base substitutions were also prevalent, as follows: 14.7% ± 5.7% in CD34+ cells, 15.2% ± 9.0% in T cells, 15.4% ± 6.7% in B cells, and 32.3% ± 2.4% in granulocytes. Many poly-C tract length differences and specific point mutations seen in these same donors but assayed 2 years earlier were still present in the new CD34+ samples. Additionally, specific poly-C tract differences and point mutations were frequently shared among cells of the lymphoid and myeloid lineages. Secular stability and lineage sharing of mtDNA sequence variability suggest that mutations arise in the lymphohematopoietic stem cell compartment and that these changes may be used as a natural genetic marker to estimate the number of active stem cells.

Muscle fibres: applications for the study of the metabolic consequences of enzyme deficiencies in skeletal muscle

2000 ◽  
Vol 28 (2) ◽  
pp. 159-164 ◽  
Author(s):  
S. Vielhaber ◽  
A. Kudin ◽  
R. Schröder ◽  
C. E. Elger ◽  
W. S. Kunz
Keyword(s):  
Skeletal Muscle ◽  
Large Scale ◽  
Citrate Synthase ◽  
Quantitative Estimation ◽  
Phenotypic Expression ◽  
Metabolic Effects ◽  
Progressive External Ophthalmoplegia ◽  
Muscle Fibres ◽  
Control Analysis ◽  
Mitochondrial Enzymes

Mitochondrial function in saponin-permeabilized muscle fibres can be studied by high-resolution respirometry, laser-excited fluorescence spectroscopy and fluorescence microscopy. We applied these techniques to study metabolic effects of changes in the pattern of mitochondrial enzymes in skeletal muscle of patients with chronic progressive external ophthalmoplegia or Kearns-Sayre syndrome harbouring large-scale deletions of mitchondrial DNA (mtDNA). In all patients combined deficiencies of respiratory chain enzymes containing mitochondrially encoded subunits were observed. The citrate synthase-normalized activity ratios of these enzymes decreased linearly with increasing mtDNA heteroplasmy. This indicates the absence of any well-defined mutation thresholds for mitochondrial enzyme activities in the entire skeletal muscle. We applied metabolic control analysis to perform a quantitative estimation of the metabolic influence of the observed enzyme deficiencies. For patients with degrees of mtDNA heteroplasmy below about 60% we observed at almost normal maximal rates of respiration an increase in flux control coefficients of complexes I and IV. Permeabilized skeletal-muscle fibres of patients with higher degrees of mtDNA heteroplasmy and severe enzyme deficiencies exhibited additionally decreased maximal rates of respiration. This finding indicates the presence of a ‘metabolic threshold’ which can be assessed by functional studies of muscle fibres providing the link to the phenotypic expression of the mtDNA mutation in skeletal muscle.

Disorders Affecting the Extraocular Muscles

2008 ◽  
Author(s):  
Agnes Wong
Keyword(s):  
Mitochondrial Dna ◽  
Lactic Acidosis ◽  
Clinical Features ◽  
Point Mutations ◽  
Extraocular Muscles ◽  
Progressive External Ophthalmoplegia ◽  
Chronic Progressive External Ophthalmoplegia ◽  
Ragged Red Fibers ◽  
Parking Lot ◽  
A3243g Mutation

Chronic progressive external ophthalmoplegia (CPEO) occurs in 90% of patients with mitochondrial myopathy. It is characterized by a slowly progressive ptosis and ophthalmoplegia. The ophthalmoplegia is usually preceded by ptosis for months to years, and downgaze is usually intact. Kearns-Sayre Syndrome is a subtype of chronic progressive external ophthalmoplegia. Most cases are sporadic and associated with single deletions of mitochondrial DNA. Ragged-red fibers are seen on light microscopy (using modified Gomori trichrome stain). ■ Due to accumulation of enlarged mitochondria under the sarcolemma of affected muscles ■ Found in skeletal muscles, orbicularis, and extraocular muscles ■ On electron microscopy, the mitochondria contain paracrystalline (“parking lot”) inclusions and disorganized cristae that are sometimes arranged concentrically. 1. Muscle biopsy (e.g., deltoid) 2. ERG 3. Electrocardiogram (EKG) 4. Genetic testing There is no effective treatment for CPEO. Maintaining a high-lipid, low-carbohydrate diet, taking co-enzyme Q10, biotin, or thiamine, and avoiding medications such as valproate and phenobarbital may be helpful. ■ MELAS stands for mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes. ■ Maternally inherited; caused by point mutations of mitochondrial DNA (A3243G mutation accounts for about 80% of all cases) ■ Clinical features 1. Strokelike episodes before age 40 (hallmark feature) 2. Encephalopathy characterized by developmental delay, seizures, or dementia 3. Mitochondrial dysfunction manifested as lactic acidosis or ragged-red fibers 4. Ophthalmoplegia 5. Optic atrophy and pigmentary retinopathy 6. Diabetes mellitus and hearing loss ■ MNGIE stands for mitochondrial neuro-gastrointestinal encephalomyopathy. ■ Autosomal recessive; caused by mutations in the nuclear gene ECGF1, resulting in thymidine phosphorylase deficiency, which in turn causes deletions, duplications, and depletion of mitochondrial DNA ■ Clinical features: ophthalmoplegia, peripheral neuropathy, leukoencephalopathy, and gastrointestinal symptoms (recurrent nausea, vomiting, or diarrhea) with intestinal dysmotility SANDO stands for sensory ataxic neuropathy, dysarthria, and ophthalmoplegia. It is sporadic and is caused by multiple deletions of mitochondrial DNA.

Sign in / Sign up

Export Citation Format

Share Document