Quantitative detection of γ-radiation-induced DNA double-strand breaks using γ-H2AX foci in mouse organs, lymphocytes and scid lymphoma cell line

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Several biological markers, mutation, chromosome aberration, microneuclei, colony formation, etc. have been used to measure radiation doses. However, enormous numbers of animals or cells are required to measure such low frequent events induced by radiations. To measure the radiation damage more precisely and sensitively, it is better to detect the first or earliest events in cells after irradiation (DNA double-strand breaks), especially in repair deficient cells or animals. Mice (C.B17 strain) and scid lymphoma cells (from C.B17-scid mice) were exposed to ^<137>Csγ-rays (0.1, 0.2, 0.5, 1, 2 and 4 Gy). Quantitation of DNA double-strand breaks in scid lymphoma cells, C.B17 peripheral lymphocytes, and organs was carried out by measuring signal intensity or counting fluorescence signal number of γ-H2AX foci in cells. The γ-H2AX foci appeared within 3 min after irradiation and reached a maximum fluorescence in 60 min. In lymphocytes, lymphoma cells, and cells from the mouse organs (brain, liver, kidney, testis), the relationships between the numbers of γ-H2AX foci and radiation dose was found to be linear over the entire dose range studied. These results suggest that quantitation of DNA double-strand breaks by the γ-H2AX foci is an useful biodosimeter for detecting high and low dose radiation damage in mice. Intriguingly, in the villi cells from the small intestine, no increase of γ-H2AX foci was found after irradiation. Genes related to the γ-H2AX phosphorylation are supposed to express in all cells of organs to repair spontaneous DNA double-strand breaks caused environmental effects, e.g. radiation and chemicals, however, it seems that theses essential systems are not working in all organs.