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Volume 50, Issue 2
Displaying 1-9 of 9 articles from this issue
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Award Review Article
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Hiroshi YASUDA2009 Volume 50 Issue 2 Pages 89-96
Published: 2009
Released on J-STAGE: April 02, 2009
Advance online publication: February 07, 2009JOURNAL FREE ACCESSThe biggest concern about the health risk to astronauts is how large the stochastic effects (cancers and hereditary effects) of space radiation could be. The practical goal is to determine the "effective dose" precisely, which is difficult for each crew because of the complex transport processes of energetic secondary particles. The author and his colleagues thus attempted to measure an effective dose in space using a life-size human phantom torso in the STS-91 Shuttle-Mir mission, which flew at nearly the same orbit as that of the International Space Station (ISS). The effective dose for about 10-days flight was 4.1 mSv, which is about 90% of the dose equivalent (H) at the skin; the lowest H values were seen in deep, radiation-sensitive organs/tissues such as the bone marrow and colon. Succeeding measurements and model calculations show that the organ dose equivalents and effective dose in the low Earth orbit mission are highly consistent, despite the different dosimetry methodologies used to determine them.View full abstractDownload PDF (638K)
Review
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Ken-ichi YANO, Keiko MOROTOMI-YANO, Noritaka ADACHI, Hidenori AKIYAMA2009 Volume 50 Issue 2 Pages 97-108
Published: 2009
Released on J-STAGE: April 02, 2009
JOURNAL FREE ACCESSNon-homologous end-joining (NHEJ) is the major repair pathway for DNA double-strand breaks (DSBs) in mammalian species. Upon DSB induction, a living cell quickly activates the NHEJ pathway comprising of multiple molecular events. However, it has been difficult to analyze the initial phase of DSB responses in living cells, primarily due to technical limitations. Recent advances in real-time imaging and site-directed DSB induction using laser microbeam allow us to monitor the spatiotemporal dynamics of NHEJ factors in the immediate-early phase after DSB induction. These new approaches, together with the use of cell lines deficient in each essential NHEJ factor, provide novel mechanistic insights into DSB recognition and protein assembly on DSBs in the NHEJ pathway. In this review, we provide an overview of recent progresses in the imaging analyses of the NHEJ core factors. These studies strongly suggest that the NHEJ core factors are pre-assembled into a large complex on DSBs prior to the progression of the biochemical reactions in the NHEJ pathway. Instead of the traditional step-by-step assembly model from the static view of NHEJ, a novel model for dynamic protein assembly in the NHEJ pathway is proposed. This new model provides important mechanistic insights into the protein assembly at DSBs and the regulation of DSB repair.View full abstractDownload PDF (1415K)
Regular Papers
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Li ZHANG, Zhe XIONG, Zhengjia LI, Bei YAO, Donghua ZHANG2009 Volume 50 Issue 2 Pages 109-117
Published: 2009
Released on J-STAGE: April 02, 2009
Advance online publication: January 22, 2009JOURNAL FREE ACCESSLow intensity irradiation of cells by laser was an effective method of biostimulation. Here, we have extended these actions to evaluate the apoptosis effects in red light emitting diode (RLED) exposure. Through morphological observation, flow cytometric analysis, intracellular calcium measurement and RT-PCR, we found that HeLa cells in 24 h RLED irradiation in in-vitro experiments would significantly affects the induction of cellular apoptosis, and morphological changes such as the loose arrangement of cells, the noticeable development of apoptotic bodies,and the accompaniment of arrested S phase and activated caspases-3,-6,-8. Moreover, intracellular calcium concentrations markedly increased 40.3 ± 1.3% and 43.1 ± 0.8% respectively, relative to an extracellular solution containing the Ca2+ and Ca2+ free unexposed group. In in-vivo tests, RLED irradiation decreased the growth of tumors on day 50 and attenuated the elevation of vascular endothelial growth factor (VEGF) expression in HeLa cell implanted BALB/c mice. Taken together, our results suggest that RLED could induce HeLa cell apoptosis and convey potential antitumor properties.View full abstractDownload PDF (532K) -
Michiyo SUZUKI, Tetsuya SAKASHITA, Sumino YANASE, Masahiro KIKUCHI, Hi ...2009 Volume 50 Issue 2 Pages 119-125
Published: 2009
Released on J-STAGE: April 02, 2009
Advance online publication: February 04, 2009JOURNAL FREE ACCESSLocomotory behavior (motility) and mechanosensation are of vital importance in animals. We examined the effects of ionizing radiation (IR) on locomotory behavior and mechanosensation using a model organism, the nematode Caenorhabditis elegans. Bacterial mechanosensation in C. elegans induces the dopamine-mediated slowing of locomotion in the presence of bacteria (food), known as the basal slowing response. We previously reported an IR-induced reduction of locomotory rate in the absence of food. In the present study, we observed a similar IR-induced reduction of locomotory rate in the cat-2 mutant, which is defective in bacterial mechanosensation. The dose response pattern of the locomotory rate in the presence of food was relatively flat in wild-type animals, but not in cat-2 mutants. This suggests that the dopamine system, which is related to bacterial mechanosensation in C. elegans, might have a dominant effect on locomotory rate in the presence of food, which masks the effects of other stimuli. Moreover, we found that the behavioral responses of hydrogen peroxide-exposed wild-type animals are similar to those of IR-exposed animals. Our findings suggest that the IR-induced reduction of locomotory rate in the absence of food is mediated by a different pathway from that for bacterial mechanosensation, at least partially through IR-produced hydrogen peroxide.View full abstractDownload PDF (747K) -
Hanako YOSHII, Masami WATANABE2009 Volume 50 Issue 2 Pages 127-137
Published: 2009
Released on J-STAGE: April 02, 2009
Advance online publication: February 04, 2009JOURNAL FREE ACCESSOxygen is essential for life, and cells have therefore developed numerous adaptive responses to oxygen change. Here, we examined the difference in oxygen-control functions of human (HE), mouse (ME), and Syrian hamster embryo (SHE) cells cultured under different oxygen conditions (0.5%, 2% and 20%), and also examined whether oxygen tensions contributed to cellular lifespan and transformation. HE cells had their replicative lifespan slightly extended under hypoxic (0.5% and 2% oxygen) conditions, but were not immortalized under any of the oxygen concentrations. On the other hand, although ME cells cultured under 20% oxygen tension decreased their proliferation potency temporarily at early stage, all rodent cells were immortalized and acquired anchorage-independency, regardless of oxygen tension. These results suggest that cellular oxygen control function is related to sensitivities cellular immortalization and transformation. To understand intervention of oxygen control ability on cellular immortalization and transformation, we examined the intracellular oxidative level, mitochondria functions and radiation sensitivity. Intracellular oxidative levels of hypoxically cultured rodent cells were significantly enhanced. Mitochondrial membrane potential was altered depend on oxygen tensions, but the change was not parallel to mitochondria number in rodent cells. ME cells were particularly sensitive to oxygen change, and showed a clear oxygen effect on the X-ray survival. However, there was no difference in frequency of radiation-induced micronuclei between HE and ME cells. These results suggest that the response to oxygen change differs markedly in HE and rodent cells.View full abstractDownload PDF (932K) -
Daila S. GRIDLEY, Asma RIZVI, Xian LUO-OWEN, Adeola Y. MAKINDE, Michae ...2009 Volume 50 Issue 2 Pages 139-150
Published: 2009
Released on J-STAGE: April 02, 2009
JOURNAL FREE ACCESSA better understanding of low dose radiation effects is needed to accurately estimate health risks. In this study, C57BL/6 mice were γ-irradiated to total doses of 0, 0.01, 0.05, and 0.1 Gy (57Co; ~0.02 cGy/h). Subsets per group were euthanized at the end of irradiation (day 0) and on days 4 and 21 thereafter. Relative spleen mass and splenic white blood cell (WBC) counts, major leukocyte populations, and spontaneous DNA synthesis were consistently higher in the irradiated groups on day 0 compared to 0 Gy controls, although significance was not always obtained. In the spleen, all three major leukocyte types were significantly elevated on day 0 (P < 0.05). By day 21 post-irradiation the T, B, and natural killer (NK) cell counts, as well as CD4+ T cells and CD4:CD8 T cell ratio, were low especially in the 0.01 Gy group. Although blood analyses showed no significant differences in leukocyte counts or red blood cell and platelet characteristics, the total T cells, CD4+ T cells, and NK cells were increased by day 21 after 0.01 Gy (P < 0.05). Gene analysis of CD4+ T cells negatively isolated from spleens on day 0 after 0.1 Gy showed significantly enhanced expression of Il27 and Tcfcp2, whereas Inha and Socs5 were down-regulated by 0.01 Gy and 0.1 Gy, respectively (P < 0.05). A trend for enhancement was noted in two additional genes (Il1r1 and Tbx21) in the 0.1 Gy group (P < 0.1). The data show that protracted low dose photons had dose- and time-dependent effects on CD4+ T cells after whole-body exposure.View full abstractDownload PDF (919K) -
Tomohiro YOSHIKAWA, Genro KASHINO, Koji ONO, Masami WATANABE2009 Volume 50 Issue 2 Pages 151-160
Published: 2009
Released on J-STAGE: April 02, 2009
Advance online publication: February 07, 2009JOURNAL FREE ACCESSIonizing radiation causes DNA double strand breaks (DSBs), which produce a chromosomal change with the modification of chromatin protein. The histone H2AX is phosphorylated, and phosphorylated H2AX makes a focus. The phosphorylated H2AX focus is regarded as recruiting mediators of repair factors of DNA DSBs. Although most of the initial phosphorylated H2AX foci disappear with the repair of DNA DSBs, a few foci remain, and whether these residual DSBs are correlated with radiosensitivity is not clear. Therefore, we examined the correlation between residual DSBs and cellular radiosensitivity after ionizing radiation. We found that half of the non-irradiated normal cells had a few phosphorylated H2AX foci constantly, and most of the cells irradiated with less than 1% of the colony-forming dose had phosphorylated H2AX foci even 5 days after irradiation. Some tumor cell lines had phosphorylated H2AX foci even under non-irradiated conditions. These results indicate that residual phosphorylated H2AX foci may show loss of colony-forming potential after irradiation in normal cell lines. However, results suggested that there was not a close correlation between residual foci and radiosensitivity in some tumor cell lines, which showed high expression of endogenous phosphorylated H2AX foci. Moreover, micronuclei induced by X-ray irradiation had phosphorylated H2AX foci, but phosphorylated ATM, phosphorylated DNA-PKcs, and 53BP1 foci were not co-localized. These results suggest that DNA DSBs may be not a direct cause of micronuclei generation or H2AX phosphorylation. (227 words)View full abstractDownload PDF (885K) -
Hidemasa KAWAMURA, Kazuaki TATEI, Tetsuo NONAKA, Hideru OBINATA, Tomoy ...2009 Volume 50 Issue 2 Pages 161-169
Published: 2009
Released on J-STAGE: April 02, 2009
JOURNAL FREE ACCESSCells exposed to genotoxic stress, such as ionizing radiation and DNA damaging reagents, either arrest the cell cycle to repair the genome, or undergo apoptosis, depending on the extent of the DNA damage. DNA damage also has been implicated in various differentiation processes. It has been reported that gamma-ray exposure or treatment with DNA-damaging agents could induce myogenic differentiation in Drosophila Schneider cells. However, the mechanism underlying this process has been poorly understood. In this study, exposure of Schneider cells to X-rays or energetic carbon ion beams caused increase of TUNEL-positive cells and conversion of round-shaped cells to elongated cells. Both upregulation of genes related to myogenesis and increase of myosin indicate that the radiation-induced morphological changes of Schneider cells were accompanied with myogenic differentiation. Because the intracellular ceramide was increased in Schneider cells after exposure to X-ray, we examined whether exogenous ceramide could mimic radiation-induced myogenic differentiation. Addition of membrane-permeable C2-ceramide to Schneider cells increased apoptosis and expression of myogenic genes. These results suggest that ceramide plays important roles in both apoptosis and the radiation-induced myogenic differentiation process.View full abstractDownload PDF (1215K)
Short Communication
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Yuichiro YOKOTA, Seiichi WADA, Yoshihiro HASE, Tomoo FUNAYAMA, Yasuhik ...2009 Volume 50 Issue 2 Pages 171-175
Published: 2009
Released on J-STAGE: April 02, 2009
Advance online publication: October 29, 2008JOURNAL FREE ACCESSThe rejoining efficiency of double-strand breaks (DSBs) was quantified by a DNA fragment-size analysis in tobacco protoplasts and CHO-K1 cells following γ-ray irradiation in order to compare DNA reparability of higher plants with mammals. Results showed that the DSB rejoining efficiency of tobacco protoplasts is dependent on the temperature of post-irradiation cultivation and that it reaches a maximum at 27°C, which represents the most suitable temperature for protoplast cultivation. The DSB rejoining kinetics of tobacco protoplasts were well represented by a biphasic-exponential equation: half of initial-induced DSBs were rejoined for 1 h and the others were almost rejoined within 4 h. We found that the DSB rejoining kinetics of tobacco protoplasts at 27°C are the same as those of CHO-K1 cells at 37°C. These findings indicate that the DSB rejoining efficiency of tobacco protoplasts and CHO-K1 cells are comparable at their respective cell cultivation temperatures, suggesting that DSB rejoining efficiency is little responsible for the higher radiation-tolerance of tobacco protoplasts.View full abstractDownload PDF (316K)
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