Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Mutation Accumulation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18Linked to original sources
PubMed2001

Accumulation of mitochondrial DNA deletions in the malignant prostate of patients of different ages.

It has been shown that mitochondrial DNA (mtDNA) deletion mutations accumulate with age in many tissues of the body. However, to date no one has shown that these deletions occur in the malignant prostate. Therefore, we hypothesize that such deletions do occur in the prostate and increasingly so with advanced age. To test this hypothesis, DNA was isolated from 34 radical prostatectomy specimens, and the entire mitochondrial genome (16.5kb) was amplified using long range PCR (LXPCR). The LXPCR products were visualized by gel electrophoresis, and the presence of low molecular weight (<16kb) bands was considered evidence of large mtDNA deletions. In order to show that these lower molecular weight LXPCR bands were not simply PCR artifact, we also digested mtDNA from a subset of the same patients and did Southern analysis with a mtDNA probe. Southern blots confirmed the existence of large deletions in every sample tested. Furthermore, several of the specific deletions identified by LXPCR were also seen in the Southern blots. From the LXPCR data, we found that as the age of the specimen increased, so did the average number of low molecular weight bands (i.e. deletions). In particular, one prominent band was seen at 1.2kb and became more consistent with advanced age.

Adult↗
PubMed2006

Increase of the spontaneous mutation rate in a long-term experiment with Drosophila melanogaster.

In a previous experiment, the effect of 255 generations of mutation accumulation (MA) on the second chromosome viability of Drosophila melanogaster was studied using 200 full-sib MA1 lines and a large C1 control, both derived from a genetically homogeneous base population. At generation 265, one of those MA1 lines was expanded to start 150 new full-sib MA2 lines and a new C2 large control. After 46 generations, the rate of decline in mean viability in MA2 was approximately 2.5 times that estimated in MA1, while the average degree of dominance of mutations was small and nonsignificant by generation 40 and moderate by generation 80. In parallel, the inbreeding depression rate for viability and the amount of additive variance for two bristle traits in C2 were 2-3 times larger than those in C1. The results are consistent with a mutation rate in the line from which MA2 and C2 were derived about 2.5 times larger than that in MA1. The mean viability of C2 remained roughly similar to that of C1, but the rate of MA2 line extinction increased progressively, leading to mutational collapse, which can be ascribed to accelerated mutation and/or synergy after important deleterious accumulation.

Animals↗
PubMed2002

Intraneuronal advanced glycation endproducts in presenilin-1 Alzheimer's disease.

The most frequently mutated gene resulting in dominantly inherited Alzheimer's disease is presenilin-1. We have used antibodies against advanced glycation endproducts (AGE) in brain tissue sections of four patients with three different presenilin I mutations. Accumulation of intracellular AGE was observed in 75-95% of pyramidal neurons in patients with presenilin-1 mutations, far exceeding the percentage of presenilin-1-, tau- or ubiquitin-positive neurons. This high level of AGE-modified proteins in vulnerable neurons is most likely explained by higher levels of their precursors (reactive (di)carbonyl products) or a slower turnover of the participating proteins. These conditions of carbonyl stress may contribute to increased neuronal dysfunction and vulnerability leading to the early disease onset.

Adult↗
PubMed2003

Toward a realistic model of mutations affecting fitness.

Analysis of a recent mutation accumulation (MA) experiment has led to the suggestion that as many as one-half of spontaneous mutations in Arabidopsis are advantageous for fitness. We evaluate this in the light of data from other MA experiments, along with molecular evidence, that suggest the vast majority of new mutations are deleterious.

Animals↗
PubMed1993

p53 protein accumulation and gene mutations in human glioma cell lines.

Mutations in, and aberrant expression of, the p53 tumor suppressor gene were assessed in 17 cell lines derived from human malignant brain tumors (glioblastoma multiforme). Exons 5 through 8 were screened by single strand conformational polymorphism analysis (SSCP), followed by direct DNA sequencing. Mutations were found in 6 of 17 glioma cell lines, i.e., at a frequency similar to that found in primary malignant gliomas. Loss of the wild type allele was observed in 4 of the mutated cell lines. Two cell lines had the same mutation (CGG-->TGG; Arg-->Trp) in codon 248. Five of 6 mutations were transitions, 4 of which occurred at CpG dinucleotides. In one cell line a 10-bp deletion at the intron 4/exon 5 junction was found. Five of 6 glioma cell lines contained a mutation identical to that in the respective primary tumor despite prolonged in vitro culture (140-221 passages). Thus, the acquisition of p53 mutations during culture appears to be infrequent. Two cell lines derived from heterozygous tumors maintained the wild type p53 allele during long term culture. p53 protein levels were assessed by immunofluorescence cytochemistry and immunoprecipitation followed by Western blot analysis and revealed elevated levels of the p53 protein, although to a variable extent, in all cell lines with p53 mutations. A marked p53 protein accumulation was also observed in two cell lines lacking p53 mutations in exons 5 through 8, indicating that a prolonged half life of the gene product is not solely dependent on an aberrant coding sequence. The remaining cell lines had either low levels or no detectable p53 protein; one of the latter contained a gross rearrangement of the p53 gene. Our results suggest that with respect to p53 gene status, glioma cell lines usually resemble the original tumors and may, therefore, be suitable for studying the biological changes associated with p53 mutations in glial tumors.

Base Sequence↗
PubMedDate not supplied

Mitochondria harbouring mutant mtDNA--a cuckoo in the nest?

Mutations of the mitochondrial DNA (mtDNA) are associated with a number of human diseases. To become relevant in terms of pathology, a mutation must generally affect at least 50-70% of mtDNA molecules in a tissue. One way to reach this level is by inheritance. Mitotic segregation of mtDNA in the female germline can result in large increases in the percentage of mutant mtDNA between generations. A different explanation is required if a particular mtDNA mutation accumulates over time in somatic cells. We discuss the possibility that mutant mtDNA, by causing deficient oxidative phosphorylation, may become preferentially replicated and may thus thrive in the cell like a cuckoo in the nest. However, despite preferential replication, a de novo mtDNA mutation will be confined to that particular cell or a small clone of daughter cells. Significant accumulation can only occur if the cell harbouring the mutant mtDNA undergoes malignant transformation and therefore starts proliferating continuously. This type of amplification of mutant mtDNA has recently been demonstrated in certain bone marrow disorders (myelodysplastic syndromes) and in colon cancer cell lines. Finally, in postmitotic tissues, an inherited mutation which is present in virtually all cells of the tissue, may accumulate through replicative advantage. This may contribute to the development of degenerative diseases.

Cell Division↗
PubMed1995

Evolution of mouse hepatitis virus (MHV) during chronic infection: quasispecies nature of the persisting MHV RNA.

Coronavirus infection of mice has been used extensively as a model for the study of acute encephalitis and chronic demyelination. To examine the evolution of coronavirus RNA during chronic demyelinating infection, we isolated RNA from intracerebrally inoculated mice at 4, 6, 8, 13, 20, and 42 days postinfection and used reverse transcription-polymerase chain reaction amplification methods (RT-PCR) to detect viral sequences. RNA sequences from two viral structural genes, the spike gene and the nucleocapsid gene, were detected throughout the chronic infection. In contrast, infectious virus was not detectable from brain homongenates beyond 13 days postinfection. These results indicate that coronavirus RNA persists in the brain at times when infectious virus is not detected. To determine if genetic changes were occurring during viral replication in the host, we cloned and sequenced the RT-PCR products from the spike and nucleocapsid regions and analyzed the sequences for mutations. Sequencing of the cloned products revealed that a variety of mutant forms of viral RNA persisted in the CNS, including point mutants, deletion mutants, and termination mutants. The mutations accumulated during persistent infection in both the spike and the nucleocapsid sequences, with greater than 65% of the mutations encoding amino acid changes. These results show that a diverse population or quasispecies consisting of mutant and deletion variant viral RNAs (which may not be capable of producing infectious virus particles) persists in the central nervous system of mice during chronic demyelinating infection. The implications of these results for the role of persistent viral genetic information in the pathogenesis of chronic demyelination are discussed.

Amino Acid Sequence↗
PubMed1995

Genotypic selection of mitochondrial and oncogenic mutations in human tissue suggests mechanisms of age-related pathophysiology.

The invention of the polymerase chain reaction (PCR) has facilitated the development of a new class of assays to quantify human somatic mutations in vivo, based on genotypic selection of mutants at the DNA level rather than phenotypic selection of mutants at the cell level. Use of these assays has provided new perspectives on the timing, location and distribution of somatic mutagenesis in mitochondrial genes and in oncogenes of the aging human body. This descriptive information has led to the inference and development of new models for age-related pathophysiology and oncogenesis. Mutations of mitochondrial genes rise rapidly with age to frequencies a thousand fold higher than those of nuclear genes. Genotypic selection analysis has revealed that mitochondrial mutations accumulate predominantly in non-mitotic cells whose age-dependent loss is associated with pathology. Random mitochondrial mutation is most likely to inactive Complex I, a deficiency of which induces mitochondrial superoxide formation and cell death. Genotypic selection of oncogenic mutations at the BCL2 and p53 loci has revealed that the cell specificity of oncogenic mutations in persons without cancer correlates well with sites of tumor origin, indicating that cells bearing such mutations are the likely precursors of future tumors. Quantitative variation in human BCL2 mutation frequency is extensive, and BCL2 mutation frequency rises with age, concordant with increased risk for lymphoma. The clonality and persistence of BCL2 mutations suggests two specific testable mechanisms of lymphomagenesis. BCL2 mutation frequency rises in persons exposed to cigarette smoke, and more p53 mutations occur in skin exposed to sunlight than in unexposed skin. Thus, in addition to their likely relevance to future cancer risk, the dose-response relationship between exposure and oncogenic mutations indicates promise for their future use as in vivo biodosimeters of human exposure to carcinogens.

Aging↗
PubMed1997

A novel germ line p53 mutation in intron 6 in diverse childhood malignancies.

Screening for p53 mutations in exons 5 to 8 in 124 pediatric malignancies identified 18 abnormal shifts using single strand conformation polymorphism: 12 were missense mutations and in 6, no mutation was detected in the exon or in the splice donor acceptor sequences. Sequencing was then performed in the adjacent introns, revealing a G to A base substitution at 39 base pairs upstream to exon 7. This mutation was identified in the germ line of five of the patients, and also in the father of one, whose parents were available. For comparison, of the 184 normal controls similarly screened, only one had this mutation (P=0.036). Positive staining of p53 protein was observed in three of the paraffin embedded tissues that were available: brain tumor, rhabdomyosarcoma, and lymphocytes from a normal lymph node from the rhabdomyosarcoma patient. All tumors with the identified intron mutation were Li-Fraumeni syndrome tumors. Sequencing of all exons including splice sites was performed and revealed no mutation. We suggest that this mutation in intron 6 of the p53 gene stabilizes the wild type p53 protein, resulting in its abnormal accumulation. Mutations in the noncoding region of p53 should be further studied.

Brain Neoplasms↗
PubMed1998

Bottleneck effect on genetic variance. A theoretical investigation of the role of dominance.

The phenomenon that the genetic variance of fitness components increase following a bottleneck or inbreeding is supported by a growing number of experiments and is explained theoretically by either dominance or epistasis. In this article, diffusion approximations under the infinite sites model are used to quantify the effect of dominance, using data on viability in Drosophila melanogaster. The model is based on mutation parameters from mutation accumulation experiments involving balancer chromosomes (set I) or inbred lines (set II). In essence, set I assumes many mutations of small effect, whereas set II assumes fewer mutations of large effect. Compared to empirical estimates from large outbred populations, set I predicts reasonable genetic variances but too low mean viability. In contrast, set II predicts a reasonable mean viability but a low genetic variance. Both sets of parameters predict the changes in mean viability (depression), additive variance, between-line variance and heritability following bottlenecks generally compatible with empirical results, and these changes are mainly caused by lethals and deleterious mutants of large effect. This article suggests that dominance is the main cause for increased genetic variances for fitness components and fitness-related traits after bottlenecks observed in various experiments.

Genetic Variation↗
PubMed2005

Role of RpoS and MutS in phase variation of Pseudomonas sp. PCL1171.

Pseudomonas sp. strain PCL1171 undergoes reversible colony phase variation between opaque phase I and translucent phase II colonies, which is dependent on spontaneous mutations in the regulatory genes gacA and gacS. Mutation of the mutS gene and constitutive expression of rpoS increases the frequency at which gac mutants appear 1000- and 10-fold, respectively. Experiments were designed to study the relationship between gacS, rpoS and mutS. These studies showed that (i) a functional gac system is required for the expression of rpoS, (ii) RpoS suppresses the expression of mutS and therefore increases the frequency of gac mutants, and (iii) upon mutation of rpoS and gacS, the expression of mutS is increased. Mutation of gacS abolishes suppression of mutS expression in stationary growth, suggesting that additional gac-dependent factors are involved in this suppression. In conclusion, inefficient mutation repair via MutS, of which the expression is influenced by gacA/S itself and by rpoS in combination with other factors, contributes to the high frequency of mutations accumulating in gacA/S. The role of RpoS in the growth advantage of a gac mutant was analysed, and mutation of rpoS only reduced the length of the lag phase, but did not affect the growth rate, suggesting a role for both RpoS and a reduction of metabolic load in the growth advantage of a gac mutant.

Adenosine Triphosphatases↗
PubMed2025

Experimental Test of Evolutionary Safety of a CRISPR-Cas9 Gene-Drive Element.

CRISPR-Cas9 gene drives (CCGDs) are powerful tools for genetic control of wild populations, with applications from disease eradication to species conservation. However, Cas9 alone and in a complex with gRNA can cause double-stranded DNA breaks at off-target sites, which could increase the mutational load and lead to unintended loss-of-heterozygosity (LOH) events. These undesired effects raise potential concerns about the long-term evolutionary safety of CCGDs, but the magnitude of these effects is unknown. To measure how the presence of a CCGD or a Cas9 alone in the genome affects the rates of LOH events and de novo mutations, we carried out a mutation accumulation experiment in yeast Saccharomyces cerevisiae. We found no detectable effects on the genome-wide rates of mutations or LOH events. Our power calculations suggest that CCGD or Cas9 affect these rates by less than 30%, which is much less than natural variation for these traits in yeast. A more detailed examination shows that CCGD or Cas9 may alter the lengths and genomic distributions of LOH events, but the statistical support for these effects is weak. Thus, our results demonstrate that CCGDs impose at most a weak additional mutational burden in the yeast model. Although mutagenic effects of gene drives need to be further evaluated in other systems, our results add credence to the proposition that the evolutionary risks posed by well designed gene drives are likely acceptable.

Journal Article↗
PubMed2006

Mitochondrial DNA deletion mutations in articular chondrocytes of cartilage affected by osteoarthritis.

OBJECTIVE: To detect the changes of mitochondrion DNA (mtDNA) sequence in articular chondrocytes of cartilage affected by osteoarthritis and to clarified the pathogenetic mechanism of osteoarthritis. METHODS: We analyzed the mtDNA 4,977 bp deletion mutations of articular chondrocytes in 10 patients with osteoarthritis and 3 normal cartilages using the gap-PCR amplification method. We designed a two round PCR detection method, in which total DNA was isolated from articular chondrocytes as the template of the first round PCR reaction and products from the first round were the template in the second round reaction. RESULTS: The results of the first rounds of PCR reaction showed the mtDNA 524 bp amplified products in the osteoarthritis group and in the corresponding peripheral blood samples were not detected, but the 533 bp products were detected. However,the results of the second round reaction revealed that the 524 bp zones were detected in 2 of the 10 osteoarthritis patients and the corresponding peripheral blood samples were not detected. The 533 bp products were detected in all specimens. The mtDNA 524 bp amplified products in all the normal articular chondrocytes and the corresponding peripheral white blood cells contrast were not detected in both rounds PCR. CONCLUSION: This was the first study to evaluate the mtDNA 4799 bp large fragment deletion mutational accumulation between nt8,470 - nt13,447 of articular chondrocytes in osteoarthritic cartilage. Osteoarthritis may be related to mtDNA mutation of articular chondrocytes.

Adult↗
PubMed1986

A new yeast mutation in the glucosylation steps of the asparagine-linked glycosylation pathway. Formation of a novel asparagine-linked oligosaccharide containing two glucose residues.

We have isolated and characterized a new yeast mutation in the glucosylation steps of lipid-linked oligosaccharide biosynthesis, alg8-1. Cells carrying the alg8-1 mutation accumulate Glc1Man9GlcNAc2-lipid both in vivo and in vitro. We present evidence showing that the alg8-1 mutation blocks addition of the second alpha 1,3-linked glucose. alg8-1 cells transfer Glc1Man9GlcNAc2 to protein instead of the wild type oligosaccharide, Glc3Man9GlcNAc2. Pulse-chase studies indicate that the Glc1Man9GlcNAc2 transferred is processed more slowly than the wild type oligosaccharide. The yeast mutation gls1-1 lacks glucosidase I activity (Esmon, B., Esmon, P.C., and Schekman, R. (1984) J. Biol. Chem. 259, 10322-10327), the enzyme responsible for removing the alpha 1,2-linked glucose residues from protein-linked oligosaccharides. We demonstrate that gls1-1 cells contain glucosidase II activity (which removes alpha 1,3-linked glucose residues) and have constructed the alg8-1 gls1-1 haploid double mutant. The Glc1Man9GlcNAc2 oligosaccharide was trimmed normally in these cells, demonstrating that the alg8-1 oligosaccharide contained an alpha 1,3-linked glucose residue. A novel Glc2 compound was probably produced by the action of the biosynthetic enzyme that normally adds the alpha 1,2-linked glucose to lipid-linked Glc2Man9GlcNAc2. This enzyme may be able to slowly add alpha 1,2-linked glucose residue to protein-bound Glc1Man9GlcNAc2. The relevance of these findings to similar observations in other systems where glucose residues are added to asparagine-linked oligosaccharides and the possible significance of the reduced rate of oligosaccharide trimming in the alg mutants are discussed.

Asparagine↗
PubMed2002

Mitochondrial DNA mutations in the parotid gland of cigarette smokers and non-smokers.

It has previously been demonstrated that mitochondrial DNA (mtDNA) mutations accumulate in the lung and increase in frequency with age. It has also been shown that the level of mtDNA mutations including deletions and base substitutions are elevated in lung tissue of smokers relative to non-smokers. We have previously shown that the 'common' 4977 bp mtDNA deletion is present in the parotid (salivary) gland of smokers and non-smokers and that there is a significant increase in the level of this deletion in Warthins tumour, an oncocytoma of the parotid gland. In this study we used semi-quantitative PCR to confirm the presence of 4977 bp mtDNA deletion in the parotid gland of non-smokers and smokers. Importantly, we show that the deletion accumulates with age regardless of smoking status and that there was no significant difference in the level of the 4977 bp deletion in parotid tissue of smokers and non-smokers. Using strand conformational polymorphism (SSCP) and direct sequencing we also found 5/23 smokers had parotid tissue specific base substitutions: either an A/T to G/C transition at A4767 or a G/C to A/T transition at G4853. These results are evidence of age related increase in the 4977 bp deletion and a higher level of mutations, probably due to oxidative damage, in the parotid gland of smokers.

Adenolymphoma↗
PubMed2006

Low impact of germline transposition on the rate of mildly deleterious mutation in Caenorhabditis elegans.

Little is known about the role of transposable element (TE) insertion in the production of mutations with mild effects on fitness, the class of mutations thought to be central to the evolution of many basic features of natural populations. We propagated mutation-accumulation (MA) lines of two RNAi-deficient strains of Caenorhabditis elegans that exhibit germline transposition. We show here that the impact of TE activity was to raise the level of mildly deleterious mutation by 2- to 8.5-fold, as estimated from fecundity, longevity, and body length measurements, compared to that observed in a parallel MA experiment with a control strain characterized by a lack of germline transposition. Despite this increase, the rate of mildly deleterious mutation was between one and two orders of magnitude lower than the rate of TE accumulation, which was approximately two new insertions per genome per generation. This study suggests that high rates of TE activity do not necessarily translate into high rates of detectable nonlethal mutation.

Animals↗
PubMed1994

Genotype-environment interactions and the estimation of the genomic mutation rate in Drosophila melanogaster.

We have studied the relative fitnesses of three genotypes of Drosophila melanogaster in 50 environments. Two genotypes, the MA lines, had accumulated mutations in the absence of natural selection over 62 generations. The third was a related strain where selection had continued to act. The environments differed in three factors: parental density, dilution of the medium, and the temperature régime and medium composition. Our measure of fitness assessed fecundity and viability relative to a reference genotype. Both MA lines always had lower fitnesses than the selected line, but the difference increased dramatically with dilution of the medium and, especially, crowding. Under the most severe conditions, the performance of the MA lines approached 0. This increased difference in harsh conditions may be caused both by a uniform increase in the magnitude of deleterious effects of all mutations and by the exposure of mutations which are essentially neutral under benign conditions. If the second cause is important, previous experiments are likely to have underestimated the genomic deleterious mutation rate in Drosophila melanogaster more than previously thought.

Animals↗
PubMed1994

Selection against deleterious mutations and the maintenance of biparental sex.

The mutational deterministic hypothesis postulates an advantage to sexual over asexual reproduction when mutation rates are on the order of 1.0 per genome per generation, provided that selection takes the form of a synergistic epistasis. While the efficacy of this mechanism has been investigated for infinite populations, its ability to protect sex in finite populations exhibiting stochastic dynamics remains untested. Stochastic processes have the potential to undermine protection for sex in two ways: (1) asexual lineages derived from sexual ancestors may, by chance, be founded by individuals bearing fewer than the equilibrium mean number of mutations, and (2) once established, such lineages will undergo random perturbations in the rates at which they grow and accumulate mutations. In the present study, I show using computer simulation that sexual populations of as many as 10,000 individuals are susceptible to invasion by asexual lineages for mutation rates higher than predicted under the mutational deterministic hypothesis. My simulations differ from previous investigations in that they model the progress of asexual lineages into sexual populations as both stochastic and deterministic processes for various mutation rates, selection regimes, and population sizes. It is suggested that ecological factors, such as parasitism or release from competition, could interact with selection against deleterious mutations to protect sex. To provide the sole explanation for sex, however, may require that selection against deleterious mutations be accompanied by mutation rates on the order of 2.0 per genome per generation.

Animals↗