MRE11-independent effects of Mirin on mitochondrial DNA integrity and cellular immune responses.

Mirin, a chemical inhibitor of MRE11, has been recently reported to suppress immune response triggered by mitochondrial DNA (mtDNA) breakage and release during replication stalling. We show that while Mirin reduces mitochondrial replication fork breakage in mitochondrial 3´-exonuclease MGME1 deficient cells, this effect occurs independently of MRE11. We also discovered that Mirin directly inhibits cellular immune responses, as shown by its suppression of STAT1 phosphorylation in Poly(I:C)-treated cells.

Overactive mitochondrial DNA replication disrupts perinatal cardiac maturation.

High mitochondrial DNA (mtDNA) amount has been reported to be beneficial for resistance and recovery of metabolic stress, while increased mtDNA synthesis activity can drive aging signs. The intriguing contrast of these two mtDNA boosting outcomes prompted us to jointly elevate mtDNA amount and frequency of replication in mice. We report that high activity of mtDNA synthesis inhibits perinatal metabolic maturation of the heart.

Species-specific variation in mitochondrial genome tandem repeat polymorphisms in hares (Lepus spp., Lagomorpha, Leporidae) provides insight into their evolution.

The non-coding regions of the mitochondrial DNAs (mtDNAs) of hares, rabbits, and pikas (Lagomorpha) contain short (∼20 bp) and long (130-160 bp) tandem repeats, absent in related mammalian orders. In the presented study, we provide in-depth analysis for mountain hare (Lepus timidus) and brown hare (L. europaeus) mtDNA non-coding regions, together with a species- and population-level analysis of tandem repeat variation.

Uncharacterized protein C17orf80 - a novel interactor of human mitochondrial nucleoids.

Molecular functions of many human proteins remain unstudied, despite the demonstrated association with diseases or pivotal molecular structures, such as mitochondrial DNA (mtDNA). This small genome is crucial for the proper functioning of mitochondria, the energy-converting organelles. In mammals, mtDNA is arranged into macromolecular complexes called nucleoids that serve as functional stations for its maintenance and expression.

Enhanced mitochondrial G-quadruplex formation impedes replication fork progression leading to mtDNA loss in human cells.

Mitochondrial DNA (mtDNA) replication stalling is considered an initial step in the formation of mtDNA deletions that associate with genetic inherited disorders and aging. However, the molecular details of how stalled replication forks lead to mtDNA deletions accumulation are still unclear. Mitochondrial DNA deletion breakpoints preferentially occur at sequence motifs predicted to form G-quadruplexes (G4s), four-stranded nucleic acid structures that can fold in guanine-rich regions.

Analysis of Mitochondrial DNA Replication by Two-Dimensional Agarose Gel Electrophoresis.

Two-dimensional neutral/neutral agarose gel electrophoresis (2D-AGE) has been employed for nearly two decades in the analysis of replication and maintenance processes of animal mitochondrial DNA, but the method's potential has not been fully exploited. Here, we describe the various steps involved in this technique, from DNA isolation, to two-dimensional neutral/neutral agarose gel electrophoresis (2D-AGE), Southern hybridization and interpretation. We also provide examples of the applicability of 2D-AGE to investigate the different features of mtDNA maintenance and regulation.

Molecular phenotyping uncovers differences in basic housekeeping functions among closely related species of hares (Lepus spp., Lagomorpha: Leporidae).

Speciation is a fundamental evolutionary process, which results in genetic differentiation of populations and manifests as discrete morphological, physiological and behavioural differences. Each species has travelled its own evolutionary trajectory, influenced by random drift and driven by various types of natural selection, making the association of genetic differences between the species with the phenotypic differences extremely complex to dissect. In the present study, we have used an in vitro model to analyse in depth the genetic and gene regulation differences between fibroblasts of two closely related mammals, the arctic/subarctic mountain hare (Lepus timidus Linnaeus) and the temperate steppe-climate adapted brown hare (Lepus europaeus Pallas).

Top3α is the replicative topoisomerase in mitochondrial DNA replication.

Mitochondrial DNA has been investigated for nearly fifty years, but many aspects of the maintenance of this essential small genome remain unknown. Like any genome, mammalian mitochondrial DNA requires the function of topoisomerases to counter and regulate the topological tension arising during replication, transcription, segregation, and repair. However, the functions of the different mitochondrial topoisomerases are poorly understood.

Heterozygous p.Y955C mutation in DNA polymerase γ leads to alterations in bioenergetics, complex I subunit expression, and mtDNA replication.

In human cells, ATP is generated using oxidative phosphorylation machinery, which is inoperable without proteins encoded by mitochondrial DNA (mtDNA). The DNA polymerase gamma (Polγ) repairs and replicates the multicopy mtDNA genome in concert with additional factors. The Polγ catalytic subunit is encoded by the POLG gene, and mutations in this gene cause mtDNA genome instability and disease.

Adaptive and Pathological Outcomes of Radiation Stress-Induced Redox Signaling.

Ionizing radiation can damage cells either directly or through oxidative damage caused by ionization. Although radiation exposure from natural sources is very limited, ionizing radiation in nuclear disaster zones and long spaceflights causes inconspicuous, yet measurable physiological effects in men and animals, whose significance remains poorly known. Understanding the physiological impacts of ionizing radiation has a wide importance due to the increased use of medical imaging and radiotherapy.

MRE11-dependent instability in mitochondrial DNA fork protection activates a cGAS immune signaling pathway.

Mitochondrial DNA (mtDNA) instability activates cGAS-dependent innate immune signaling by unknown mechanisms. Here, we find that Fanconi anemia suppressor genes are acting in the mitochondria to protect mtDNA replication forks from instability. Specifically, Fanconi anemia patient cells show a loss of nascent mtDNA through MRE11 nuclease degradation.

TFAM knockdown-triggered mtDNA-nucleoid aggregation and a decrease in mtDNA copy number induce the reorganization of nucleoid populations and mitochondria-associated ER-membrane contacts.

The correct organization of mitochondrial DNA (mtDNA) in nucleoids and the contacts of mitochondria with the ER play an important role in maintaining the mitochondrial genome distribution within the cell. Mitochondria-associated ER membranes (MAMs) consist of interacting proteins and lipids located in the outer mitochondrial membrane and ER membrane, forming a platform for the mitochondrial inner membrane-associated genome replication factory as well as connecting the nucleoids with the mitochondrial division machinery. We show here that knockdown of a core component of mitochondrial nucleoids, TFAM, causes changes in the mitochondrial nucleoid populations, which subsequently impact ER-mitochondria membrane contacts.

The Type and Source of Reactive Oxygen Species Influences the Outcome of Oxidative Stress in Cultured Cells.

Oxidative stress can be modeled using various different experimental approaches, such as exposing the cells or organisms to oxidative chemicals. However, the actual effects of these chemicals, outside of the immediate measured effect, have attracted relatively little attention. We show here that three commonly used oxidants, menadione, potassium bromate, and hydrogen peroxide, while known to function differently, also elicit different types of responses in HEK293T cells.

Author Correction: Defects in mtDNA replication challenge nuclear genome stability through nucleotide depletion and provide a unifying mechanism for mouse progerias.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Defects in mtDNA replication challenge nuclear genome stability through nucleotide depletion and provide a unifying mechanism for mouse progerias.

Mitochondrial DNA (mtDNA) mutagenesis and nuclear DNA repair defects are considered cellular mechanisms of ageing. mtDNA mutator mice with increased mtDNA mutagenesis show signs of premature ageing. However, why patients with mitochondrial diseases, or mice with other forms of mitochondrial dysfunction, do not age prematurely remains unknown.

Replication fork rescue in mammalian mitochondria.

Replication stalling has been associated with the formation of pathological mitochondrial DNA (mtDNA) rearrangements. Yet, almost nothing is known about the fate of stalled replication intermediates in mitochondria. We show here that replication stalling in mitochondria leads to replication fork regression and mtDNA double-strand breaks.

Twist and Turn-Topoisomerase Functions in Mitochondrial DNA Maintenance.

Like any genome, mitochondrial DNA (mtDNA) also requires the action of topoisomerases to resolve topological problems in its maintenance, but for a long time, little was known about mitochondrial topoisomerases. The last years have brought a closer insight into the function of these fascinating enzymes in mtDNA topology regulation, replication, transcription, and segregation. Here, we summarize the current knowledge about mitochondrial topoisomerases, paying special attention to mammalian mitochondrial genome maintenance.

Ciprofloxacin impairs mitochondrial DNA replication initiation through inhibition of Topoisomerase 2.

Maintenance of topological homeostasis is vital for gene expression and genome replication in all organisms. Similar to other circular genomes, also mitochondrial DNA (mtDNA) is known to exist in various different topological forms, although their functional significance remains unknown. We report here that both known type II topoisomerases Top2α and Top2β are present in mammalian mitochondria, with especially Top2β regulating the supercoiling state of mtDNA.

Known Unknowns of Mammalian Mitochondrial DNA Maintenance.

Mammalian mitochondrial DNA (mtDNA) replication and repair have been studied intensively for the last 50 years. Although recently advances in elucidating the molecular mechanisms of mtDNA maintenance and the proteins involved in these have been made, there are disturbing gaps between the existing theoretical models and experimental observations. Conflicting data and hypotheses exist about the role of RNA and ribonucleotides in mtDNA replication, but also about the priming of replication and the formation of pathological rearrangements.

ATAD3 controls mitochondrial cristae structure in mouse muscle, influencing mtDNA replication and cholesterol levels.

Mutations in the mitochondrial inner membrane ATPase result in neurological syndromes in humans. In mice, the ubiquitous disruption of (also known as ) was embryonic lethal, but a skeletal muscle-specific conditional knockout (KO) was viable. At birth, ATAD3 muscle KO mice had normal weight, but from 2 months onwards they showed progressive motor-impaired coordination and weakness.

Preclinical Efficacy and Safety Evaluation of Hematopoietic Stem Cell Gene Therapy in a Mouse Model of MNGIE.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disorder caused by thymidine phosphorylase (TP) deficiency resulting in systemic accumulation of thymidine (d-Thd) and deoxyuridine (d-Urd) and characterized by early-onset neurological and gastrointestinal symptoms. Long-term effective and safe treatment is not available. Allogeneic bone marrow transplantation may improve clinical manifestations but carries disease and transplant-related risks.

Tissue specific differences in mitochondrial DNA maintenance and expression.

The different cell types of multicellular organisms have specialized physiological requirements, affecting also their mitochondrial energy production and metabolism. The genome of mitochondria is essential for mitochondrial oxidative phosphorylation (OXHPOS) and thus plays a central role in many human mitochondrial pathologies. Disorders affecting mitochondrial DNA (mtDNA) maintenance are typically resulting in a tissue-specific pattern of mtDNA deletions and rearrangements.