Findings obtained from mechanism studies

The purpose of Radiation Effect Mechanisms Research Group is to establish a scientific basis for the risk assessment of low-dose radiation that can be used to refine the regulatory framework. Several subthemes have been investigated, including ''untargeted radiation carcinogenesis'' and ''radioadaptive responses''. For untargeted radiation carcinogenesis, we have established a mouse experiment system where carcinogenesis due to changes in the microenvironment could be analyzed. It was found that, when thymuses of unirradiated new-born mice were transplanted in thymectomized, irradiated mice, T-cell lymphomas of transplanted thymus origin were induced depending on the radiation dose. This untargeted radiation carcinogenesis was observed with the doses as low as 0.1 Gy when scid mice were used as the host. For radioadaptive responses, we identified the genes associated with the radioadaptive response of mouse fetuses. When pregnant ICR mice are irradiated with high dose of X-rays (4 Gy) on day 12 after fertilization, only about three living fetuses will be born per dam, and most of them will be malformed. But if the mice are pre-exposed to low doses of X-rays on day 11, the number of living fetuses will be increased, and the fraction of malformed fetuses will be decreased. By performing microarray analyses and RNA interference analyses, we could identify several genes, such as Tead3 and Cacna1a, which were functionally involved in radioadaptive response of mouse fetuses. (author)