Abstract
We reports on a comparative study on the quantitative detection of γ-ray-induced DNA double-strand breaks (DSBs) and their repair in white blood cells of mice. The comparisons includes the effects of different radiation doses, two dose-rates (1 Gy/min versus 1 Gy/day) and two mouse strains namely, a wild type strain (C.B17+/+) which is DSB-repair proficient and a mutant strain (C.B17 scid /scid) which is deficient in this regard.
In wild-type mice, the signal intensity of γ-H2AX reached a maximum by 60 min and decreased subsequently to half the peak value at 240 min. In white blood cells of mutant mice, however, the signal intensity reached a peak value at around 100 min, but there was no subsequent falling-off up to 480 min.
In both unirradiated and irradiated cultured scid cells, cells with low and high fluorescence intensity were found (corresponding to two sub-populations of small and large cells, respectively). In both types of cells, the foci reached a maximum fluorescence intensity in 30 min. However, in small cells, the foci remained at the maximum intensity up to 480 min after irradiation. In large cells, the fluorescence intensity decreased to half the maximum value by 60 min. Additionally, after low dose rate irradiation, in white blood cells of wild type mice, signal intensity of γ-H2AX foci decreased, whereas in repair deficient scid cells, it remained essentially unaltered even after one day. Even in the wild type mice (repair-proficient), DSB repair was not completed soon after irradiation. Some of γ-H2AX foci remained for several hours. In conclusion, our studies provide further data validating the utility of the γ-H2AX immunofluorescence system for studies on radiation-induced DSBs and their repair.It seems to be good system to assess radiosensitivity for the patients undergoing radiotherapy by checking γ-H2AX foci activity or foci reduction rate before therapeutic irradiation.
(Supported by MEXT and JSPS)
