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processing of clustered DNA damageShikazono, Naoya; Akamatsu, Ken; Takahashi, Momoko*; Noguchi, Miho; Urushibara, Ayumi; O'Neill, P.*; Yokoya, Akinari
Mutation Research; Fundamental and Molecular Mechanisms of Mutagenesis, 749(1-2), p.9 - 15, 2013/09
Times Cited Count：12 Percentile：36.83(Biotechnology & Applied Microbiology)We examined the biological consequences of bi-stranded clustered damage sites, consisting of a combination of DNA lesions using a bacterial plasmid-based assay. The transformation efficiencies were significantly lower for the bi-stranded clustered GAP/AP lesions than for either a single GAP or a single AP site. When the two lesions were separated by 10-20 bp, the transformation efficiencies were comparable with those of the single lesions. This recovery of transformation efficiency for separated lesions requires DNA polymerase I (Pol I) activity. Analogously, the mutation frequency was enhanced in a bi-stranded cluster containing a GAP and an 8-oxoG, and Pol I was found to play an important role in minimising mutations induced as a result of clustered lesions. These results indicate that the biological consequences of clustered DNA damage strongly depend on Pol I activity.
-rays in 
Toyoshima, Yoshiyuki*; Takahashi, Akemi*; Tanaka, Hisaki*; Watanabe, Jun*; Mogi, Yoshinobu*; Yamazaki, Tatsuo*; Hamada, Ryoko*; Iwashita, Kazuhiro*; Sato, Katsuya; Narumi, Issei
Mutation Research; Fundamental and Molecular Mechanisms of Mutagenesis, 740(1-2), p.43 - 49, 2012/12
Times Cited Count：18 Percentile：49.23(Biotechnology & Applied Microbiology)Noguchi, Miho; Urushibara, Ayumi; Yokoya, Akinari; O'Neill, P.*; Shikazono, Naoya
Mutation Research; Fundamental and Molecular Mechanisms of Mutagenesis, 732(1-2), p.34 - 42, 2012/04
Times Cited Count：16 Percentile：45.3(Biotechnology & Applied Microbiology)The effect of a single strand break associated with base lesion(s) in vivo remains largely unknown. In the present study we determined the mutagenicities of two- and three-lesion clustered damage sites containing a 1-nucleotide gap (GAP) and 8-oxo-7,8-dihydroguanine(s) (8-oxoG(s)). The mutation frequencies (MFs) of bi-stranded two-lesion clusters (GAP/8-oxoG), especially in mutY-deficient strains, were high and were similar to those for bi-stranded clusters with 8-oxoG and base lesions/AP sites, suggesting that the GAP is processed with an efficiency similar to the efficiency of processing a base lesion or an AP site within a cluster. The MFs of tandem two-lesion clusters comprised of a GAP and an 8-oxoG were comparable to or less than the MF of a single 8-oxoG. The mutagenic potential of three-lesion clusters, which were comprised of a tandem lesion (a GAP and an 8-oxoG) and an opposing single 8-oxoG, was higher than that of a single 8-oxoG, but was no more than that of a bi-stranded 8-oxoGs. We suggest that incorporation of a nucleotide opposite 8-oxoG is less mutagenic when a GAP is present in a cluster than when a GAP is absent. Our observations indicate that the repair of a GAP is retarded by an opposing 8-oxoG, but not by a tandem 8-oxoG, and that the extent of GAP repair determines the biological consequences.
Hase, Yoshihiro; Yoshihara, Ryohei; Nozawa, Shigeki; Narumi, Issei
Mutation Research; Fundamental and Molecular Mechanisms of Mutagenesis, 731(1-2), p.41 - 47, 2012/03
Times Cited Count：33 Percentile：72.04(Biotechnology & Applied Microbiology)To gain insight into the mutagenic effects of accelerated heavy ions in plants, the mutagenic effects of carbon ions near the range end (mean LET: 425 keV/
m) were compared with the effects of carbon ions penetrating the seeds (mean LET: 113 keV/m). Mutational analysis by plasmid rescue of 
from irradiated Arabidopsis plants showed a 2.7-fold increase in mutant frequency for 113 keV/m carbon ions, whereas no enhancement of mutant frequency was observed for carbon ions near the range end. This suggested that carbon ions near the range end induced mutations that were not recovered by plasmid rescue. An Arabidopsis DNA ligase IV mutant, deficient in non-homologous end-joining repair, showed hyper-sensitivity to both types of carbon-ion irradiation. The difference in radiation sensitivity between the wild type and the repair-deficient mutant was greatly diminished for carbon ions near the range end, suggesting that these ions induce irreparable DNA damage. Mutational analysis of the Arabidopsis 
locus showed that while the frequency of generation of glabrous mutant sectors was not different between the two types of carbon-ion irradiation, large deletions (
30 kb) were six times more frequently induced by carbon ions near the range end. This suggests that the proportion of large deletions increases with LET in plants.
-ray-irradiated tobacco cells; Evidence for radiation-induced genomic instability in plant cellsYokota, Yuichiro; Funayama, Tomoo; Hase, Yoshihiro; Hamada, Nobuyuki*; Kobayashi, Yasuhiko; Tanaka, Atsushi; Narumi, Issei
Mutation Research; Fundamental and Molecular Mechanisms of Mutagenesis, 691(1-2), p.41 - 46, 2010/09
Times Cited Count：9 Percentile：28.46(Biotechnology & Applied Microbiology)Ionizing radiation-induced genomic instability has been documented in various end points such as chromosomal aberrations and mutations, which arises in the descendants of irradiated mammalian or yeast cells many generations after the initial insult. This study aimed at addressing radiation-induced genomic instability in higher plant tobacco cells. We thus investigated micronucleus (MN) formation and cell proliferation in tobacco cells irradiated with -rays and their descendants. The descendants that have undergone at least 22 generations after irradiation still showed a two-fold MN frequency compared to sham-irradiated cells. This is the direct evidence for radiation-induced genomic instability in tobacco cells.
Shikazono, Naoya; O'Neill, P.*
Mutation Research; Fundamental and Molecular Mechanisms of Mutagenesis, 669(1-2), p.162 - 168, 2009/11
Times Cited Count：17 Percentile：44.68(Biotechnology & Applied Microbiology)Iwakawa, Mayumi*; Hamada, Nobuyuki*; Imadome, Kaori*; Funayama, Tomoo; Sakashita, Tetsuya; Kobayashi, Yasuhiko; Imai, Takashi*
Mutation Research; Fundamental and Molecular Mechanisms of Mutagenesis, 642(1-2), p.57 - 67, 2008/07
Times Cited Count：34 Percentile：66.2(Biotechnology & Applied Microbiology)Hamada, Nobuyuki*; Ni, M.*; Funayama, Tomoo; Sakashita, Tetsuya; Kobayashi, Yasuhiko
Mutation Research; Fundamental and Molecular Mechanisms of Mutagenesis, 639(1-2), p.35 - 44, 2008/03
Times Cited Count：47 Percentile：77.48(Biotechnology & Applied Microbiology)To characterize the energetic heavy ion-induced bystander response, we employed precise microbeams of C and Ne ions for targeting only a very small fraction of cells in confluent fibroblast cultures. Conventional broad field irradiation was conducted in parallel to see the effects in irradiated cells. Exposure of 0.00026% of cells led to nearly 10% reductions in the clonogenic survival and twofold rises in the apoptotic incidence regardless of ion species. Whilst apoptotic frequency increased with time up to 72 h post irradiation in irradiated cells, its frequency escalated up to 24 h post irradiation but declined at 48 h post irradiation in bystander cells, indicating that bystander cells exhibit transient commitment to apoptosis. C and Ne-ion microbeam irradiation similarly caused almost twofold increments in the levels of serine 15-phosphorylated p53 proteins, irrespective of whether 0.00026, 0.0013 or 0.0066% of cells were targeted. Whereas the levels of phosphorylated p53 were elevated and remained unchanged at 2 and 6 h post irradiation in irradiated cells, its levels rose at 6 h post irradiation but not at 2 h post irradiation in bystander cells, suggesting that bystander cells manifest delayed p53 phosphorylation.
Hamada, Nobuyuki*; Hara, Takamitsu*; Funayama, Tomoo; Sakashita, Tetsuya; Kobayashi, Yasuhiko
Mutation Research; Fundamental and Molecular Mechanisms of Mutagenesis, 637(1-2), p.190 - 196, 2008/01
Times Cited Count：22 Percentile：49.95(Biotechnology & Applied Microbiology)Dependence of ionizing radiation-induced genomic instability on the linear energy transfer (LET) of the radiation is incompletely characterized; however, our previous work has shown that delayed reductions in clonogenicity can be most pronounced at LET of 108 keV/m. To gain insight into potential cellular mechanisms involved in LET-dependent delayed loss of clonogenicity, we investigated morphological changes in colonies arising from normal human diploid fibroblasts exposed to -rays or energetic carbon ions (108 keV/m). Exposure of confluent cultures to carbon ions was 4-fold more effective at inactivating cellular clonogenic potential and produced more abortive colonies containing reduced number of cells per colony than -rays. Second, colonies were assessed for clonal morphotypic heterogeneity. The yield of differentiated cells was elevated in a dose- and LET-dependent fashion in clonogenic colonies, whereas differentiated cells predominated to a comparable extent irrespective of radiation type or dose in abortive colonies.
Matsuo, Yuichiro*; Nishijima, Shigehiro*; Hase, Yoshihiro; Sakamoto, Ayako; Tanaka, Atsushi; Shimizu, Kikuo*
Mutation Research; Fundamental and Molecular Mechanisms of Mutagenesis, 602(1-2), p.7 - 13, 2006/12
Times Cited Count：29 Percentile：58.31(Biotechnology & Applied Microbiology)no abstracts in English
PprA proteinSato, Katsuya*; Wada, Seiichi; Kikuchi, Masahiro; Funayama, Tomoo; Narumi, Issei; Kobayashi, Yasuhiko
Mutation Research; Fundamental and Molecular Mechanisms of Mutagenesis, 596(1-2), p.36 - 42, 2006/04
Times Cited Count：4 Percentile：10.91(Biotechnology & Applied Microbiology)In a previous study we identified the novel protein PprA that plays a critical role in the radiation resistance of . In this study, we focussed on the ability of PprA protein to recognize and bind to double-stranded DNA carrying strand breaks, and attempted to visualize radiation-induced DNA strand breaks in mammalian cultured cells by employing PprA protein using an immunofluorescence technique. Increased PprA protein binding to CHO-K1 nuclei immediately following irradiation suggests the protein is binding to DNA strand breaks. By altering the cell permeabilization conditions, PprA protein binding to CHO-K1 mitochondria, which is probably resulted from DNA strand break immediately following irradiation, was also detected. The method developed and detailed in this study will be useful in evaluating DNA damage responses in cultured cells, and could also be applicable to genotoxic tests in the environmental and pharmaceutical fields.
