Shimada, A., Eguchi, H., Yoshinaga, S. and Shima, A. Dose-Rate Effect on Transgenerational Mutation Frequencies in Spermatogonial Stem Cells of the Medaka Fish. Radiat. Res. 163, 112–114 (2005).

The estimation of transgenerational genetic risk of radiation exposure to non-human species is crucial for the protection of ecosystems. Here we determined the frequency of specific-locus mutations at the five pigmentation loci in medaka spermatogonial stem cells after γ irradiation at 0.03 cGy/min and 95 cGy/min. At each total dose, the mutation frequency was significantly lower in the 0.03-cGy/min group than in the 95-cGy/min group, suggesting a dose-rate effect. The ratio of the induced mutation frequency at 0.03 cGy/min to that at 95 cGy/min was ∼0.42 from 0 to 1.9 Gy and ∼0.33 from 1.9 to 4.75 cGy. In the mouse, this ratio is estimated to be 0.33 (Russell and Kelly, Proc. Natl. Acad. Sci. USA 79, 542–544, 1982). It is thus possible that the magnitude of the dose-rate effect on transgenerational mutation frequencies is comparable between mouse and medaka spermatogonia, suggesting similar dose-rate effects among vertebrates.