Regular bottlenecks and restrictions to somatic fusion prevent the accumulation of mitochondrial defects in
            Neurospora

The replication and segregation of multi-copy mitochondrial DNA (mtDNA) are not under strict control of the nuclear DNA. Within-cell selection may thus favour variants with an intracellular selective advantage but a detrimental effect on cell fitness. High relatedness among the mtDNA variants of an individual is predicted to disfavour such deleterious selfish genetic elements, but experimental evidence for this hypothesis is scarce. We studied the effect of mtDNA relatedness on the opportunities for suppressive mtDNA variants in the fungus Neurospora carrying the mitochondrial mutator plasmid pKALILO. During growth, this plasmid integrates into the mitochondrial genome, generating suppressive mtDNA variants. These mtDNA variants gradually replace the wild-type mtDNA, ultimately culminating in growth arrest and death. We show that regular sequestration of mtDNA variation is required for effective selection against suppressive mtDNA variants. First, bottlenecks in the number of mtDNA copies from which a ‘ Kalilo ’ culture started significantly increased the maximum lifespan and variation in lifespan among cultures. Second, restrictions to somatic fusion among fungal individuals, either by using anastomosis-deficient mutants or by generating allotype diversity, prevented the accumulation of suppressive mtDNA variants. We discuss the implications of these results for the somatic accumulation of mitochondrial defects during ageing.

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An mtDNA mutant mouse demonstrates that mitochondrial deficiency can result in autism endophenotypes

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2021429118 ◽

2021 ◽

Vol 118 (6) ◽

pp. e2021429118

Author(s):

Tal Yardeni ◽

Ana G. Cristancho ◽

Almedia J. McCoy ◽

Patrick M. Schaefer ◽

Meagan J. McManus ◽

...

Keyword(s):

Nuclear Dna ◽

Copy Number Variants ◽

Autism Spectrum ◽

Repetitive Behaviors ◽

Seizure Threshold ◽

Loss Of Function ◽

Restricted Interests ◽

Mtdna Mutations ◽

Mitochondrial Defects ◽

Mtdna Variants

Autism spectrum disorders (ASDs) are characterized by a deficit in social communication, pathologic repetitive behaviors, restricted interests, and electroencephalogram (EEG) aberrations. While exhaustive analysis of nuclear DNA (nDNA) variation has revealed hundreds of copy number variants (CNVs) and loss-of-function (LOF) mutations, no unifying hypothesis as to the pathophysiology of ASD has yet emerged. Based on biochemical and physiological analyses, it has been hypothesized that ASD may be the result of a systemic mitochondrial deficiency with brain-specific manifestations. This proposal has been supported by recent mitochondrial DNA (mtDNA) analyses identifying both germline and somatic mtDNA variants in ASD. If mitochondrial defects do predispose to ASD, then mice with certain mtDNA mutations should present with autism endophenotypes. To test this prediction, we examined a mouse strain harboring an mtDNA ND6 gene missense mutation (P25L). This mouse manifests impaired social interactions, increased repetitive behaviors and anxiety, EEG alterations, and a decreased seizure threshold, in the absence of reduced hippocampal interneuron numbers. EEG aberrations were most pronounced in the cortex followed by the hippocampus. Aberrations in mitochondrial respiratory function and reactive oxygen species (ROS) levels were also most pronounced in the cortex followed by the hippocampus, but absent in the olfactory bulb. These data demonstrate that mild systemic mitochondrial defects can result in ASD without apparent neuroanatomical defects and that systemic mitochondrial mutations can cause tissue-specific brain defects accompanied by regional neurophysiological alterations.

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Wild-type IDH2 protects nuclear DNA from oxidative damage and is a potential therapeutic target in colorectal cancer

Oncogene ◽

10.1038/s41388-021-01968-2 ◽

2021 ◽

Author(s):

Shuang Qiao ◽

Wenhua Lu ◽

Christophe Glorieux ◽

Jiangjiang Li ◽

Peiting Zeng ◽

...

Keyword(s):

Colorectal Cancer ◽

Oxidative Damage ◽

Therapeutic Target ◽

Nuclear Dna ◽

Wild Type ◽

Potential Therapeutic Target

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Somatic deficiency causes reproductive parasitism in a fungus

Nature Communications ◽

10.1038/s41467-021-21050-5 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Alexey A. Grum-Grzhimaylo ◽

Eric Bastiaans ◽

Joost van den Heuvel ◽

Cristina Berenguer Millanes ◽

Alfons J. M. Debets ◽

...

Keyword(s):

Neurospora Crassa ◽

Experimental Evolution ◽

Evolutionary Dynamics ◽

Genetic Load ◽

Wild Type ◽

Fusion Frequency ◽

Somatic Fusion ◽

Extensive Variation ◽

Reproductive Parasitism ◽

Multicellular Organisms

AbstractSome multicellular organisms can fuse because mergers potentially provide mutual benefits. However, experimental evolution in the fungus Neurospora crassa has demonstrated that free fusion of mycelia favours cheater lineages, but the mechanism and evolutionary dynamics of this exploitation are unknown. Here we show, paradoxically, that all convergently evolved cheater lineages have similar fusion deficiencies. These mutants are unable to initiate fusion but retain access to wild-type mycelia that fuse with them. This asymmetry reduces cheater-mutant contributions to somatic substrate-bound hyphal networks, but increases representation of their nuclei in the aerial reproductive hyphae. Cheaters only benefit when relatively rare and likely impose genetic load reminiscent of germline senescence. We show that the consequences of somatic fusion can be unequally distributed among fusion partners, with the passive non-fusing partner profiting more. We discuss how our findings may relate to the extensive variation in fusion frequency of fungi found in nature.

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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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Host Insect Inhibitor-of-Apoptosis SfIAP Functionally Replaces Baculovirus IAP but Is Differentially Regulated by Its N-Terminal Leader

Journal of Virology ◽

10.1128/jvi.01311-10 ◽

2010 ◽

Vol 84 (21) ◽

pp. 11448-11460 ◽

Cited By ~ 20

Author(s):

Rebecca J. Cerio ◽

Rianna Vandergaast ◽

Paul D. Friesen

Keyword(s):

Selective Advantage ◽

Biochemical Properties ◽

Inhibitor Of Apoptosis ◽

Loss Of Function ◽

Wild Type ◽

Host Insect ◽

Orgyia Pseudotsugata ◽

Induced Apoptosis ◽

Lepidopteran Host ◽

Maximal Stability

ABSTRACT The inhibitor-of-apoptosis (IAP) proteins encoded by baculoviruses bear a striking resemblance to the cellular IAP homologs of their invertebrate hosts. By virtue of the acquired selective advantage of blocking virus-induced apoptosis, baculoviruses may have captured cellular IAP genes that subsequently evolved for virus-specific objectives. To compare viral and host IAPs, we defined antiapoptotic properties of SfIAP, the principal cellular IAP of the lepidopteran host Spodoptera frugiperda. We report here that SfIAP prevented virus-induced apoptosis as well as viral Op-IAP3 (which is encoded by the Orgyia pseudotsugata nucleopolyhedrovirus) when overexpressed from the baculovirus genome. Like Op-IAP3, SfIAP blocked apoptosis at a step prior to caspase activation. Both of the baculovirus IAP repeats (BIRs) were required for SfIAP function. Moreover, deletion of the C-terminal RING motif generated a loss-of-function SfIAP that interacted and dominantly interfered with wild-type SfIAP. Like Op-IAP3, wild-type SfIAP formed intracellular homodimers, suggesting that oligomerization is a functional requirement for both cellular and viral IAPs. SfIAP possesses a ∼100-residue N-terminal leader domain, which is absent among all viral IAPs. Remarkably, deletion of the leader yielded a fully functional SfIAP with dramatically increased protein stability. Thus, the SfIAP leader contains an instability motif that may confer regulatory options for cellular IAPs that baculovirus IAPs have evolved to bypass for maximal stability and antiapoptotic potency. Our findings that SfIAP and viral IAPs have common motifs, share multiple biochemical properties including oligomerization, and act at the same step to block apoptosis support the hypothesis that baculoviral IAPs were derived by acquisition of host insect IAPs.

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Interplay of population genetics and dynamics in the genetic control of mosquitoes

Journal of The Royal Society Interface ◽

10.1098/rsif.2013.1071 ◽

2014 ◽

Vol 11 (93) ◽

pp. 20131071 ◽

Cited By ~ 38

Author(s):

Nina Alphey ◽

Michael B. Bonsall

Keyword(s):

Population Genetics ◽

Overlapping Generations ◽

Large Scale ◽

Genetic Model ◽

Homing Endonuclease ◽

Wild Type ◽

Larval Competition ◽

Selfish Genetic Elements ◽

Fitness Effects ◽

Ecological Aspects

Some proposed genetics-based vector control methods aim to suppress or eliminate a mosquito population in a similar manner to the sterile insect technique. One approach under development in Anopheles mosquitoes uses homing endonuclease genes (HEGs)—selfish genetic elements (inherited at greater than Mendelian rate) that can spread rapidly through a population even if they reduce fitness. HEGs have potential to drive introduced traits through a population without large-scale sustained releases. The population genetics of HEG-based systems has been established using discrete-time mathematical models. However, several ecologically important aspects remain unexplored. We formulate a new continuous-time (overlapping generations) combined population dynamic and genetic model and apply it to a HEG that targets and knocks out a gene that is important for survival. We explore the effects of density dependence ranging from undercompensating to overcompensating larval competition, occurring before or after HEG fitness effects, and consider differences in competitive effect between genotypes (wild-type, heterozygotes and HEG homozygotes). We show that population outcomes—elimination, suppression or loss of the HEG—depend crucially on the interaction between these ecological aspects and genetics, and explain how the HEG fitness properties, the homing rate (drive) and the insect's life-history parameters influence those outcomes.

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An estimate of heterosis in Drosophila melanogaster

Genetics Research ◽

10.1017/s0016672300012453 ◽

1971 ◽

Vol 18 (1) ◽

pp. 97-105 ◽

Cited By ~ 54

Author(s):

J. A. Sved

Keyword(s):

Drosophila Melanogaster ◽

High Frequency ◽

Marker Chromosome ◽

Selective Advantage ◽

Wild Type ◽

Set Up

SUMMARYTwenty-five population cages of D. melanogaster were set up, each containing a different wild-type second chromosome and the marker chromosome Cy. In all but one case where contamination apparently occurred, the Cy chromosome persisted in the population at high frequency, showing a selective advantage of Cy/ + heterozygotes over wild-type homozygotes. Overall, the results indicate that homozygosity of the entire second chromosome causes a depression in fitness of the order of 85%.

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Escape of mitochondrial DNA to the nucleus in yme1 yeast is mediated by vacuolar-dependent turnover of abnormal mitochondrial compartments

Journal of Cell Science ◽

10.1242/jcs.111.16.2455 ◽

1998 ◽

Vol 111 (16) ◽

pp. 2455-2464 ◽

Cited By ~ 3

Author(s):

C.L. Campbell ◽

P.E. Thorsness

Keyword(s):

Alkaline Phosphatase ◽

Mitochondrial Dna ◽

High Rate ◽

Wild Type ◽

Yeast Saccharomyces Cerevisiae ◽

Mitochondrial Defects ◽

Proteinase A ◽

Abnormal Mitochondria ◽

Wild Type Yeast

Inactivation of Yme1p, a mitochondrially-localized ATP-dependent metallo-protease in the yeast Saccharomyces cerevisiae, causes a high rate of DNA escape from mitochondria to the nucleus as well as pleiotropic functional and morphological mitochondrial defects. The evidence presented here suggests that the abnormal mitochondria of a yme1 strain are degraded by the vacuole. First, electron microscopy of Yme1p-deficient strains revealed mitochondria physically associated with the vacuole via electron dense structures. Second, disruption of vacuolar function affected the frequency of mitochondrial DNA escape from yme1 and wild-type strains. Both PEP4 or PRC1 gene disruptions resulted in a lower frequency of mitochondrial DNA escape. Third, an in vivo assay that monitors vacuole-dependent turnover of the mitochondrial compartment demonstrated an increased rate of mitochondrial turnover in yme1 yeast when compared to the rate found in wild-type yeast. In this assay, vacuolar alkaline phosphatase, encoded by PHO8, was targeted to mitochondria in a strain bearing disruption to the genomic PHO8 locus. Maturation of the mitochondrially localized alkaline phosphatase pro-enzyme requires proteinase A, which is localized in the vacuole. Therefore, alkaline phosphatase activity reflects vacuole-dependent turnover of mitochondria. This assay reveals that mitochondria of a yme1 strain are taken up by the vacuole more frequently than mitochondria of an isogenic wild-type strain when these yeast are cultured in medium necessitating respiratory growth. Degradation of abnormal mitochondria is one pathway by which mitochondrial DNA escapes and migrates to the nucleus.

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Abstract 80: Accumulation of Mitochondrial DNA in Autolysosome Causes Inflammation and Heart Failure Through Toll-Like Receptor 9 (TLR9) Signaling

Circulation Research ◽

10.1161/res.111.suppl_1.a80 ◽

2012 ◽

Vol 111 (suppl_1) ◽

Author(s):

Takafumi Oka ◽

Osamu Yamaguchi ◽

Issei Komuro ◽

Kinya Otsu

Keyword(s):

Heart Failure ◽

Mitochondrial Dna ◽

Nuclear Dna ◽

Apoptotic Cell ◽

Pressure Overload ◽

Wild Type ◽

Dnase Ii ◽

Cardiac Phenotype ◽

Deficient Mice ◽

Tlr9 Signaling

Backgrounds Nuclear DNA in apoptotic cell is digested by lysosomal deoxyribonuclease II (DNase II) in macrophages. Improper DNA digestion can lead to inflammation. We previously reported that cardiac-specific DNase II-deficient mice (CKO) exhibited heart failure after transverse aortic constriction (TAC). We observed inflammatory response and DNA accumulation in autolysosome in TAC-operated CKO heart. They were considered to be mitochondrial DNA (mtDNA). In present study, we elucidated the mechanism of inflammation integrated by DNA accumulation in TAC-operated CKO hearts. Furthermore we investigated the pathogenesis of inflammation and heart failure in wild-typeTAC-operated mice. Methods & Results First, we identified the origin of accumulated DNA in lysosome. To label cardiac mtDNA, EdU (5-ethynyl 2’ deoxyuridine) were injected into mice before TAC. In TAC-operated CKO mice, EdU- and LAMP2a (lysosomal marker) or LC3 (autophagosome marker) positive deposits were observed, indicating that mtDNA accumulated in autolysosome. Then, we examined the mechanism how the mtDNA accumulation leads to inflammation. mtDNA has similarities to bacterial DNA, which contains inflammatogenic unmethylated CpG motif. TLR9, localized in the endolysosome, senses DNA with unmethylated CpG motifs. Therefore, we hypothesized that undigested mtDNA is sensed by TLR9. We administrated the inhibitory oligodeoxynucleotides against TLR9 to TAC-operated CKO mice. They attenuated the development of cardiomyopathy in CKO mice. Ablation of Tlr9 also canceled the cardiac phenotype of CKO mice. Next, we examined the involvement of DNA accumulation and TLR9 signaling in wild-type TAC-operated mice. DNase II activity was up-regulated in hypertrophied hearts, but not in failing hearts. LAMP2a- or LC3- positive DNA accumulation was observed in failing hearts. To determine the significance of TLR9 signaling pathway in the pathogenesis of heart failure, we subjected TLR9-deficient mice to TAC. They showed significant resistance to pressure-overload. TLR9-inhibitory oligodeoxynucleotides also improved the mortality in wild-type TAC-operated mice. Conclusion mtDNA-TLR9 axis is involved in inflammation in failing hearts in response to pressure overload.

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