Strikingly higher frequency in centenarians and twins of mtDNA mutation causing remodeling of replication origin in leukocytes

The presence of a genetic component in longevity is well known. Here, the association of a mtDNA mutation with a prolonged life span in humans was investigated. Large-scale screening of the mtDNA main control region in leukocytes from subjects of an Italian population revealed a homoplasmic C150T transition near an origin of heavy mtDNA-strand synthesis in approximate to 17% of 52 subjects 99-106 years old, but, in contrast, in only 3.4% of 117 younger individuals (P = 0.0035). Evidence was obtained for the contribution of somatic events, under probable nuclear genetic control, to the striking selective accumulation of the mutation in centenarians. In another study, among leukocyte mtDNA samples from 20 monozygotic and 18 dizygotic twins, 60-75 years old, 30% (P = 0.0007) and 22% (P = 0.011), respectively, of the individuals involved exhibited the homoplasmic C150T mutation. In a different system, i.e., in five human fibroblast longitudinal studies, convincing evidence for the aging-related somatic expansion of the C150T mutation, up to homoplasmy, was obtained. Most significantly, 5' end analysis of nascent heavy mtDNA strands consistently revealed a new replication origin at position 149, substituting for that at 151, only in C150T mutation carrying samples of fibroblasts or immortalized lymphocytes. Considering the aging-related health risks that the centenarians have survived and the developmental risks of twin gestations, it is proposed that selection for a remodeled replication origin, inherited or somatically acquired, provides a survival advantage and underlies the observed high incidence of the C150T mutation in centenarians and twins

Genome wide screen identifies microsatellite markers associated with acute adverse effects following radiotherapy in cancer patients

<p>Abstract</p> <p>Background</p> <p>The response of normal tissues in cancer patients undergoing radiotherapy varies, possibly due to genetic differences underlying variation in radiosensitivity.</p> <p>Methods</p> <p>Cancer patients (n = 360) were selected retrospectively from the RadGenomics project. Adverse effects within 3 months of radiotherapy completion were graded using the National Cancer Institute Common Toxicity Criteria; high grade group were grade 3 or more (n = 180), low grade group were grade 1 or less (n = 180). Pooled genomic DNA (gDNA) (n = 90 from each group) was screened using 23,244 microsatellites. Markers with different inter-group frequencies (Fisher exact test <it>P </it>< 0.05) were analyzed using the remaining pooled gDNA. Silencing RNA treatment was performed in cultured normal human skin fibroblasts.</p> <p>Results</p> <p>Forty-seven markers had positive association values; including one in the <it>SEMA3A </it>promoter region (P = 1.24 × 10^-5). <it>SEMA3A </it>knockdown enhanced radiation resistance.</p> <p>Conclusions</p> <p>This study identified 47 putative radiosensitivity markers, and suggested a role for <it>SEMA3A </it>in radiosensitivity.</p

Aging-dependent large accumulation of muscle-specific point mutations in the transcription/replication control region of human mitochondrial DNA

The aging-dependent large accumulation of specific point mutations, especially the most frequent mutation T414G, in the cultured human skin fibroblast mtDNA transcription/replication regulatory region raised the question of their occurrence in post-mitotic tissues. In the present work, analysis of biopsied or autopsied human skeletal muscle from variously aged individuals revealed the absence or only minimal presence of those skin fibroblast mutations. By contrast, surprisingly, most of 26 individuals 53 to 92 years old, without a known history of neuromuscular disease, exhibited at the same region of human mtDNA in muscle an accumulation of two new point mutations, i.e., A189G and T408A, which were absent or marginally present in the muscle of 19 individuals younger than 34 years. These two mutations were not found in the skin fibroblasts from 22 subjects 64 to 101 years of age (T408A), or were present only in three subjects in very low amounts (A189G). Furthermore, in several older individuals exhibiting an accumulation in muscle of one or both of these mutations, they were nearly absent in other post-mitotic tissues, whereas the most frequent fibroblast-specific mutation (T414G) was present in skin autopsy, but not in muscle. The striking tissue specificity of the aging-dependent mtDNA point mutations and their mapping at critical sites for mtDNA transcription/replication strongly point to the involvement of a specific mutagenic machinery or a specific advantage for the mtDNA replication/transmission and to the functional relevance of these mutations during human aging processes

Experimental determination of individual patient\u27s haplotypes of radiation sensitivity-associated gene

A novel methodology of haplotype determination involving sensitive amplification of single chromosomes was developed. Limited dilution of chromosomes was performed within heated alkaline agarose solution to avoid extensive aggregation during dilution process. Aliquoted and solidified agarose gel pieces were then treated by exogenously provided Phi29 DNA polymerase and random hexamer oligonucleotides, yielding up to 120 000-fold amplification of immobilized chromosomes. The amplified materials were recovered in solution in PCR-ready form by simple heating to melt the gel, making them conveniently available for further applications such as multiple locus genotyping. With this amplification methodology, haplotypes of radiation sensitivity-associated gene were successfully evaluated in individual cancer patients.The 7th International Workshop on Advanced Genomic

Genetic Variation in Individual Sensitivity to Clinical Radiotherapy

KIDS workshop 2009 in NIRS IAEA NIRS Joint Workshop & NIRS Symposium on Radiation Protection for Childre