| Project/Area Number |
15510047
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Risk sciences of radiation/Chemicals
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| Research Institution | Kyoto University |
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Principal Investigator |
TACHIBANA Akira Kyoto University, Radiation Biology Center, Associate Professor, 放射線生物研究センター, 助教授 (20188262)
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| Co-Investigator(Kenkyū-buntansha) |
TODO Takeshi Kyoto University, Radiation Biology Center, Professor, 放射線生物研究センター, 教授 (90163948)
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| Project Period (FY) |
2003 – 2005
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| Project Status |
Completed (Fiscal Year 2005)
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| Budget Amount *help |
¥3,800,000 (Direct Cost: ¥3,800,000)
Fiscal Year 2005: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2004: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2003: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Keywords | radioadaptive response / low-dose radiation / DNA double-strand break / p53 / end-joining / mutagenesis / 突然変異 / Hprt遺伝子 / multilex PCR |
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| Research Abstract |
Radioadaptive response is a biological defense mechanism that is induced by low-dose ionizing irradiation for cellular resistance to the genotoxic effects of subsequent irradiation. Nuclear extracts were prepared from unirradiated cells (unirradiated extract), cells exposed to either 2 cGy (2 cGy extract) or 3 Gy (3 Gy extract) of X-rays, and cells pre-exposed with 2 cGy and then challenged with 3 Gy (2 cGy+3 Gy extract). The efficiency of end joining by the 3 Gy extract was somewhat reduced, but the rejoining efficiency of the 2 cGy+3 Gy extract was similar to the efficiency of the unirradiated extract. The fidelity of end-joining was estimated from the frequency of mutant plasmids. The mutant frequency by the 3 Gy extract was higher than the unirradiated level. But, the mutant frequency by the 2 cGy+3 Gy extract was about half of the unirradiated level, indicatinging high fidelity of rejoining. Moreover, we have demonstrated that the radioadaptive response is absent in p53-deficient mouse cells. We examined the end-joining reaction using the extracts isolated from p53-deficient mouse cells irradiated with X-rays with or without pre-irradiation. No change was observed either in the efficiency or in the fidelity of end-joining irrespective of pre-irradiation. Therefore, p53 could be an important regulatory factor of end-joining in radioadaptive response. We further examined mutations induced by ionizing radiation with or without radioadaptive response at the Hprt locus in mouse m5S cells. We analyzed the Hprt gene in 6-thioguanine-resistant mutants by amplification of all the nine exons of the mouse Hprt gene. Our results showed that the proportion of partial deletions was much higher in mutants isolated from the pre-exposed radioadaptive culture than in non-primed irradiated culture.
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