Abstract
In order to assess the biological effects associated with transcriptional changes on long-term low-dose-rate gamma irradiation, DNA microarray analysis was performed using Affymetrix Mouse Genome 430 2.0 GeneChips. Three groups of 8 weeks old male C57BL/6 mice were exposed to whole body irradiation for 485 days at dose-rates of 32 nGy/min, 650 nGy/min or 12.5 μGy/min (cumulative doses; 20.6 mGy, 416 mGy or 8030 mGy). Another group was sham irradiated for use as a control group. Liver RNA was isolated immediately after the irradiation from 3 animals of each exposure group and the control group. At first, RNA probes were generated with pooled total RNA from irradiated and control animals. Of the 45000 oligos, approximately 19900, 20700, 20400 and 20300 had a positive signal in the control, 32 nGy/min, 650 nGy/min and 12.5 μGy/min groups. Using the change algorithm based on the Wilcoxon's Signed Rank test, approximately 400, 320 and 500 genes were judged to show > 2-fold changes in the expression levels compared with the control for 32 nGy/min, 650 nGy/min and 12.5 μGy/min. Secondly, the expression levels of 3 irradiated animals were individually compared with that of pooled control animals. The data showed the relatively large variation in expression levels among 3 individuals and the number of genes showing common changes was decreased. However, 25 genes showed > 2-fold changes even at the lowest dose rate of 32 nGy/min. Our results suggest that there are a few genes that are responding to the very low-dose-rate irradiation.
