Mitochondrial Genetic Drift after Nuclear Transfer in Oocytes

Mitochondria are energy-producing intracellular organelles containing their own genetic material in the form of mitochondrial DNA (mtDNA), which codes for proteins and RNAs essential for mitochondrial function. Some mtDNA mutations can cause mitochondria-related diseases. Mitochondrial diseases are a heterogeneous group of inherited disorders with no cure, in which mutated mtDNA is passed from mothers to offspring via maternal egg cytoplasm. Mitochondrial replacement (MR) is a genome transfer technology in which mtDNA carrying disease-related mutations is replaced by presumably disease-free mtDNA. This therapy aims at preventing the transmission of known disease-causing mitochondria to the next generation. Here, a proof of concept for the specific removal or editing of mtDNA disease-related mutations by genome editing is introduced. Although the amount of mtDNA carryover introduced into human oocytes during nuclear transfer is low, the safety of mtDNA heteroplasmy remains a concern. This is particularly true regarding donor-recipient mtDNA mismatch (mtDNA–mtDNA), mtDNA-nuclear DNA (nDNA) mismatch caused by mixing recipient nDNA with donor mtDNA, and mtDNA replicative segregation. These conditions can lead to mtDNA genetic drift and reversion to the original genotype. In this review, we address the current state of knowledge regarding nuclear transplantation for preventing the inheritance of mitochondrial diseases.

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Mitochondrial Diseases: Therapeutic Approaches

Bioscience Reports ◽

10.1007/s10540-007-9041-4 ◽

2007 ◽

Vol 27 (1-3) ◽

pp. 125-137 ◽

Cited By ~ 81

Author(s):

Salvatore DiMauro ◽

Michelangelo Mancuso

Keyword(s):

Respiratory Chain ◽

Nuclear Dna ◽

Palliative Therapy ◽

Real Life ◽

Mitochondrial Diseases ◽

Mitochondrial Respiratory Chain ◽

Preventive Therapy ◽

Therapeutic Approaches ◽

Mitochondrial Encephalomyopathies ◽

Mtdna Mutations

Therapy of mitochondrial encephalomyopathies (defined restrictively as defects of the mitochondrial respiratory chain) is woefully inadequate, despite great progress in our understanding of the molecular bases of these disorders. In this review, we consider sequentially several different therapeutic approaches. Palliative therapy is dictated by good medical practice and includes anticonvulsant medication, control of endocrine dysfunction, and surgical procedures. Removal of noxious metabolites is centered on combating lactic acidosis, but extends to other metabolites. Attempts to bypass blocks in the respiratory chain by administration of electron acceptors have not been successful, but this may be amenable to genetic engineering. Administration of metabolites and cofactors is the mainstay of real-life therapy and is especially important in disorders due to primary deficiencies of specific compounds, such as carnitine or coenzyme Q10. There is increasing interest in the administration of reactive oxygen species scavengers both in primary mitochondrial diseases and in neurodegenerative diseases directly or indirectly related to mitochondrial dysfunction. Aerobic exercise and physical therapy prevent or correct deconditioning and improve exercise tolerance in patients with mitochondrial myopathies due to mitochondrial DNA (mtDNA) mutations. Gene therapy is a challenge because of polyplasmy and heteroplasmy, but interesting experimental approaches are being pursued and include, for example, decreasing the ratio of mutant to wild-type mitochondrial genomes (gene shifting), converting mutated mtDNA genes into normal nuclear DNA genes (allotopic expression), importing cognate genes from other species, or correcting mtDNA mutations with specific restriction endonucleases. Germline therapy raises ethical problems but is being considered for prevention of maternal transmission of mtDNA mutations. Preventive therapy through genetic counseling and prenatal diagnosis is becoming increasingly important for nuclear DNA-related disorders. Progress in each of these approaches provides some glimmer of hope for the future, although much work remains to be done.

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Case Report: Mitochondrial Encephalomyopathy Presents as Epilepsy, Ataxia, and Dystonia With a Rare Mutation in MT-TW

Frontiers in Neurology ◽

10.3389/fneur.2021.679302 ◽

2021 ◽

Vol 12 ◽

Author(s):

Shuang Wang ◽

Jing Miao ◽

Jiachun Feng

Keyword(s):

Muscle Biopsy ◽

Nuclear Dna ◽

Genetic Test ◽

Mitochondrial Diseases ◽

Internal Capsule ◽

Mitochondrial Encephalomyopathy ◽

Normal Brain ◽

Inherited Disorders ◽

Rare Mutation ◽

Test Result

Mitochondrial diseases are a group of common inherited disorders caused by mutations in nuclear DNA or mitochondrial DNA (mtDNA); the clinical phenotype of diseases caused by mutant mtDNA is challenging owing to heteroplasmy of mtDNA and may delay diagnosis and treatment. Herein, we report the case of an adult male who slowly developed epilepsy, ataxia, dystonia, impaired cognition, and hearing impairment over 14 years in the absence of clinical myopathy. His lactate level was normal. Brain computed tomography showed calcifications of the bilateral basal ganglia, thalamus, and cerebellar dentate nuclei. Magnetic resonance imaging revealed multiple lesions in the bilateral internal capsule and periventricular areas, which were hypointense on T1-weighted images and hyperintense on T2-weighted images. The first blood genetic test result was negative. Two years later, a muscle biopsy was performed. Succinate dehydrogenase (SDH) staining showed several ragged blue fibers and atypical strongly SDH-reactive vessels. Cytochrome C oxidase (COX) staining revealed abundant COX-deficient fibers. mtDNA testing of blood and muscle revealed a rare m.5549G>A mutation in the MT-TW gene. It was heteroplasmic, with 5.4% mutant mtDNA in the blood and 61.5% in the muscle. The patient was diagnosed with mitochondrial encephalomyopathy and treated with levetiracetam instead of valproate to reduce possible mitochondrial toxicity. After receiving anti-epileptic drugs and mitochondrial supplements, the patient remained clinically stable. For mitochondrial disease, when mutant mtDNA is not detected in blood, muscle biopsy should be performed in routine analysis, and it should be genetically tested, even if there are no manifestations of myopathy.

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Human Mitochondrial RNA Processing and Modifications: Overview

International Journal of Molecular Sciences ◽

10.3390/ijms22157999 ◽

2021 ◽

Vol 22 (15) ◽

pp. 7999

Author(s):

Marta Jedynak-Slyvka ◽

Agata Jabczynska ◽

Roman J. Szczesny

Keyword(s):

Rna Processing ◽

Mitochondrial Diseases ◽

Mitochondrial Rna ◽

Mtdna Mutations ◽

Current State ◽

Substantial Progress ◽

Eukaryotic Organisms ◽

Almost All ◽

Adenosine Triphosphate Production ◽

Made In

Mitochondria, often referred to as the powerhouses of cells, are vital organelles that are present in almost all eukaryotic organisms, including humans. They are the key energy suppliers as the site of adenosine triphosphate production, and are involved in apoptosis, calcium homeostasis, and regulation of the innate immune response. Abnormalities occurring in mitochondria, such as mitochondrial DNA (mtDNA) mutations and disturbances at any stage of mitochondrial RNA (mtRNA) processing and translation, usually lead to severe mitochondrial diseases. A fundamental line of investigation is to understand the processes that occur in these organelles and their physiological consequences. Despite substantial progress that has been made in the field of mtRNA processing and its regulation, many unknowns and controversies remain. The present review discusses the current state of knowledge of RNA processing in human mitochondria and sheds some light on the unresolved issues.

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Cryobanking of Amphibian Genetic Recourses in Russia: Past and Future

Russian Journal of Herpetology ◽

10.30906/1026-2296-2019-26-6-319-324 ◽

2019 ◽

Vol 26 (6) ◽

pp. 319-324

Author(s):

Victor K. Uteshev ◽

Edith N. Gakhova ◽

Ludmila I. Kramarova ◽

Natalia V. Shishova ◽

Svetlana A. Kaurova ◽

...

Keyword(s):

Genetic Material ◽

Reproductive Technologies ◽

Cell Biophysics ◽

Amphibian Species ◽

Modern Biology ◽

Rare And Endangered Species ◽

Long Term Storage ◽

Current State ◽

Rare And Endangered ◽

Academy Of Sciences

In modern biology, a search for efficient and safe ways of long-term storage of animal genomes is vital for the survival of rare and endangered species. To date, the only reliable method of prolonging the preservation of genome is deep freezing of somatic and reproductive cells, including spermatozoa. Here we overview the current state of reproductive technologies and present the cryopresevation strategies of genetic material of selected amphibian species. These strategies were developed at the Institute of Cell Biophysics, Russian Academy of Sciences, Pushchino, Russia. Cryopreservation could help managing the threatened populations of amphibian species through genome storage and mediate the production of healthy animals from the stored material.

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Treatment for mitochondrial diseases

Reviews in the Neurosciences ◽

10.1515/revneuro-2020-0034 ◽

2020 ◽

Vol 0 (0) ◽

Author(s):

Tongling Liufu ◽

Zhaoxia Wang

Keyword(s):

Clinical Trials ◽

Nuclear Dna ◽

Mitochondrial Diseases ◽

Cochrane Collaboration ◽

Potential Bias ◽

Leber Hereditary Optic Neuropathy ◽

Pharmacological Agents ◽

Unpublished Studies ◽

New Treatment ◽

Allotopic Expression

AbstractMitochondrial diseases are predominantly caused by mutations of mitochondrial or nuclear DNA, resulting in multisystem defects. Current treatments are largely supportive, and the disorders progress relentlessly. Nutritional supplements, pharmacological agents and physical therapies have been used in different clinical trials, but the efficacy of these interventions need to be further evaluated. Several recent reviews discussed some of the interventions but ignored bias in those trials. This review was conducted to discover new studies and grade the original studies for potential bias with revised Cochrane Collaboration guidelines. We focused on seven published studies and three unpublished studies; eight of these studies showed improvement in outcome measurements. In particular, two of the interventions have been tested in studies with strict design, which we believe deserve further clinical trials with a large sample. Additionally, allotopic expression of the ND4 subunit seemed to be an effective new treatment for patients with Leber hereditary optic neuropathy.

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Genetic variation in recombination rate in the pig

Genetics Selection Evolution ◽

10.1186/s12711-021-00643-0 ◽

2021 ◽

Vol 53 (1) ◽

Author(s):

Martin Johnsson ◽

Andrew Whalen ◽

Roger Ros-Freixedes ◽

Gregor Gorjanc ◽

Ching-Yi Chen ◽

...

Keyword(s):

Genetic Variation ◽

Recombination Rate ◽

Large Scale ◽

Genome Wide Association Study ◽

Genetic Material ◽

A Genome ◽

Pig Genome ◽

Genetic Length ◽

Trait Locus ◽

Genomic Regions

Abstract Background Meiotic recombination results in the exchange of genetic material between homologous chromosomes. Recombination rate varies between different parts of the genome, between individuals, and is influenced by genetics. In this paper, we assessed the genetic variation in recombination rate along the genome and between individuals in the pig using multilocus iterative peeling on 150,000 individuals across nine genotyped pedigrees. We used these data to estimate the heritability of recombination and perform a genome-wide association study of recombination in the pig. Results Our results confirmed known features of the recombination landscape of the pig genome, including differences in genetic length of chromosomes and marked sex differences. The recombination landscape was repeatable between lines, but at the same time, there were differences in average autosome-wide recombination rate between lines. The heritability of autosome-wide recombination rate was low but not zero (on average 0.07 for females and 0.05 for males). We found six genomic regions that are associated with recombination rate, among which five harbour known candidate genes involved in recombination: RNF212, SHOC1, SYCP2, MSH4 and HFM1. Conclusions Our results on the variation in recombination rate in the pig genome agree with those reported for other vertebrates, with a low but nonzero heritability, and the identification of a major quantitative trait locus for recombination rate that is homologous to that detected in several other species. This work also highlights the utility of using large-scale livestock data to understand biological processes.

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Epilepsy in Mitochondrial Diseases—Current State of Knowledge on Aetiology and Treatment

Children ◽

10.3390/children8070532 ◽

2021 ◽

Vol 8 (7) ◽

pp. 532

Author(s):

Dorota Wesół-Kucharska ◽

Dariusz Rokicki ◽

Aleksandra Jezela-Stanek

Keyword(s):

Oxidative Phosphorylation ◽

Mitochondrial Dysfunction ◽

Mitochondrial Disease ◽

Clinical Picture ◽

Poor Prognosis ◽

Treatment Options ◽

Mitochondrial Diseases ◽

Energy Deficit ◽

Atp Production ◽

Current State

Mitochondrial diseases are a heterogeneous group of diseases resulting from energy deficit and reduced adenosine triphosphate (ATP) production due to impaired oxidative phosphorylation. The manifestation of mitochondrial disease is usually multi-organ. Epilepsy is one of the most common manifestations of diseases resulting from mitochondrial dysfunction, especially in children. The onset of epilepsy is associated with poor prognosis, while its treatment is very challenging, which further adversely affects the course of these disorders. Fortunately, our knowledge of mitochondrial diseases is still growing, which gives hope for patients to improve their condition in the future. The paper presents the pathophysiology, clinical picture and treatment options for epilepsy in patients with mitochondrial disease.

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Mitochondrial DNA Replacement Techniques to Prevent Human Mitochondrial Diseases

International Journal of Molecular Sciences ◽

10.3390/ijms22020551 ◽

2021 ◽

Vol 22 (2) ◽

pp. 551

Author(s):

Luis Sendra ◽

Alfredo García-Mares ◽

María José Herrero ◽

Salvador F. Aliño

Keyword(s):

Mitochondrial Dna ◽

Nuclear Dna ◽

Genetic Disorders ◽

Mitochondrial Diseases ◽

Legal Regulation ◽

Donor Oocyte ◽

Legal Position ◽

Ethical And Legal Issues ◽

Mitochondrial Replacement Techniques ◽

Do So

Background: Mitochondrial DNA (mtDNA) diseases are a group of maternally inherited genetic disorders caused by a lack of energy production. Currently, mtDNA diseases have a poor prognosis and no known cure. The chance to have unaffected offspring with a genetic link is important for the affected families, and mitochondrial replacement techniques (MRTs) allow them to do so. MRTs consist of transferring the nuclear DNA from an oocyte with pathogenic mtDNA to an enucleated donor oocyte without pathogenic mtDNA. This paper aims to determine the efficacy, associated risks, and main ethical and legal issues related to MRTs. Methods: A bibliographic review was performed on the MEDLINE and Web of Science databases, along with searches for related clinical trials and news. Results: A total of 48 publications were included for review. Five MRT procedures were identified and their efficacy was compared. Three main risks associated with MRTs were discussed, and the ethical views and legal position of MRTs were reviewed. Conclusions: MRTs are an effective approach to minimizing the risk of transmitting mtDNA diseases, but they do not remove it entirely. Global legal regulation of MRTs is required.

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Abstract 17097: Non-Synonymous Mitochondrial DNA Variants Are Common in Myocardial Tissue of Heart Failure Patients

Circulation ◽

10.1161/circ.142.suppl_3.17097 ◽

2020 ◽

Vol 142 (Suppl_3) ◽

Author(s):

Pappu Ananya ◽

Michael Binder ◽

Yang Wanjun ◽

Rebecca McClellan ◽

Brittney Murray ◽

...

Keyword(s):

Heart Failure ◽

Mitochondrial Dna ◽

Nuclear Dna ◽

Left Ventricular ◽

Individual Risk ◽

Myocardial Tissue ◽

Mtdna Mutation ◽

Mtdna Mutations ◽

Ventricular Tissue ◽

Mtdna Variants

Introduction: Mitochondrial heart disease due to pathogenic mitochondrial DNA (mtDNA) mutations can present as hypertrophic or dilated cardiomyopathy, ventricular arrhythmias and conduction disease. It is estimated that the mutation rate of mtDNA is 10 to 20-fold higher than that of nuclear DNA genes due to damage from reactive oxygen species released as byproducts during oxidative phosphorylation. When a new mtDNA mutation arises, it creates an intracellular heteroplasmic mixture of mutant and normal mtDNAs, called heteroplasmy. Heteroplasmy levels can vary in various tissues and examining mtDNA variants in blood may not be representative for the heart. The frequency of pathogenic mtDNA variants in myocardial tissues in unknown. Hypothesis: Human ventricular tissue may contain mtDNA mutations which can lead to alterations in mitochondrial function and increase individual risk for heart failure. Methods: Mitochondrial DNA was isolated from 61 left ventricular myocardial samples obtained from failing human hearts at the time of transplantation. mtDNA was sequenced with 23 primer pairs. In silico prediction of non-conservative missense variants was performed via PolyPhen-2. Heteroplasmy levels of variants predicted to be pathogenic were quantified using allele-specific ARMS-PCR. Results: We identified 21 mtDNA non-synonymous variants predicted to be pathogenic in 17 hearts. Notably, one heart contained four pathogenic mtDNA variants (ATP6: p.M104; ND5: p.P265S; ND4: p.N390S and p.L445F). Heteroplasmy levels exceeded 90% for all four variants in myocardial tissue and were significantly lower in blood. No pathogenic mtDNA variants were identified in 44 hearts. Hearts with mtDNA mutations had higher levels of myocardial GDF-15 (growth differentiation factor-15; 6.2±2.3 vs. 1.3±0.18, p=0.045), an established serum biomarker in various mitochondrial diseases. Conclusions: Non-synonymous mtDNA variants predicted to be pathogenic are common in human left ventricular tissue and may be an important modifier of the heart failure phenotype. Future studies are necessary to correlate myocardial mtDNA mutations with cardiovascular outcomes and to assess whether serum GDF-15 allows identifying patients with myocardial mtDNA mutations.

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Abstract 206: Accumulation of Mitochondrial DNA Mutations Impairs Survival, Proliferation, and Differentiation of Cardiac Progenitor Cells

Circulation Research ◽

10.1161/res.115.suppl_1.206 ◽

2014 ◽

Vol 115 (suppl_1) ◽

Author(s):

Amabel M Orogo ◽

Dieter A Kubli ◽

Anne N Murphy ◽

Åsa B Gustafsson

Keyword(s):

Mitochondrial Dna ◽

Progenitor Cells ◽

Mitochondrial Biogenesis ◽

Nuclear Dna ◽

Critical Role ◽

Chemotherapeutic Agents ◽

Cardiac Progenitor Cells ◽

Mtdna Mutations ◽

Differentiation Medium ◽

Proliferation And Differentiation

Activation and participation of cardiac progenitor cells (CPCs) in regeneration are critical for effective repair in the wake of pathologic injury. Stem cell activation and commitment involve increased energy demand and mitochondrial biogenesis. To date, little attention has been paid to the importance of mitochondria in CPC survival, proliferation and differentiation. CPC function is reduced with age but the underlying mechanism is still unclear. Mitochondrial DNA (mtDNA) is more susceptible to oxidative attacks than nuclear DNA due to its proximity to the mitochondrial respiratory chain and lack of protective histone-like proteins. With age, mtDNA accumulates mutations that can impair mitochondrial respiration and increase ROS production. In this study, we examined the effects of accumulating mtDNA mutations on CPC proliferation and survival. We have found that incubation of uncommitted c-kit+ CPCs in differentiation medium increased mitochondrial mass and expansion of the mitochondrial network, which correlated with increased cell size and expression of cardiac lineage commitment markers. Differentiation activated mitochondrial biogenesis, increased mtDNA copy number, and enhanced oxidative capacity and cellular ATP levels in CPCs. To investigate the effect of mtDNA mutations and aging on CPC survival and function, we utilized a mouse model in which a mutation in the mtDNA polymerase γ (POLG m/m ) leads to accumulation of mtDNA mutations, mitochondrial dysfunction, and accelerated aging. Isolated CPCs from hearts of 2-month old POLG m/m mice had reduced proliferation and were more susceptible to oxidative stress and chemotherapeutic agents compared to WT CPCs. The majority of POLG m/m CPCs contained fragmented mitochondria as shown by immunostaining. Incubation in differentiation medium resulted in fewer GATA-4 positive POLG m/m CPCs compared to WT CPCs. The reduced differentiation in these POLG m/m CPCs correlated with reduced PGC-1α expression and OXPHOS protein levels, suggesting that mitochondrial biogenesis is impaired. These data demonstrate that mitochondria play a critical role in CPC function, and accumulation of mtDNA mutations impairs CPC function and reduces their repair potential.

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