報告書番号

L06014

タイトル（和文）

低線量放射線による自然突然変異の抑制

タイトル（英文）

Reduction of background mutation by low dose irradiation at a low dose rate.

概要 （図表や脚注は「報告書全文」に掲載しております）

ショウジョウバエ伴性劣性致死突然変異試験をおこなって、X線照射による未熟な精子における突然変異の誘発頻度にしきい線量の存在することを見出した。またしきい値の大きさはDNA修復機能の有無により変化した。同じ試験系で線量・効果関係は直線的でしきい値がないとしたMuller等の結果はDNA修復機能のない成熟精子という特殊な細胞系を用いたために得られたのであって、発がん性の評価には適さないものであると考えられる。

概要 （英文）

The dose-response relationship of ionizing radiation and its stochastic effects has been thought to be linear without any thresholds for a long time. The linear dose response relationship was reported as early as 1930 using a sex-linked recessive lethal assay in mature sperm of the fruit fly Drosophila melanogaster. However, mature sperm has no DNA repair function. We have previously reported that somatic mutation frequency was not proportional to the X-ray dose and that there was a threshold at around 1Gy. Furthermore, the threshold value was dependent on the DNA repair function. In this paper, we examined the dose-response relationship of X-ray irradiation and mutation in repair proficient immature sperm of Drosophila, and found that a low dose irradiation at a low dose rate caused a decrease, rather than increase, of mutation frequency compared to the non-irradiated control. The threshold was again dependent on the DNA repair function. It was indicated that the DNA repair function contributes to establishing of the threshold and that the so-called linear non-threshold (LNT) model is valid only in repair deficient cells.

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