Changes in gene expression profiles in mouse liver induced by long-term low-dose-rate irradiation were examined by microarray analysis. Three groups of male C57BL/6J mice were exposed to whole-body radiation at dose rates of 1720 mGy/day, 0.861.0 mGy/day or 0.0420.050 mGy/day for 401485 days with cumulative doses of approximately 8 Gy, 0.4 Gy or 0.02 Gy, respectively. The gene expression levels in the livers of six animals from each exposure group were compared individually with that of pooled sham-irradiated animals. Some genes revealed a large variation in expression levels among individuals within each group, and the number of genes showing common changes in individuals from each group was limited: 20 and 11 genes showed more than 1.5-fold modulation with 1720 mGy/day and 0.861.0 mGy/day, respectively. Three genes showed more than 1.5-fold modulation even at the lowest dose-rate of 0.040.05 mGy/day. Most of these genes were down-regulated. RT-PCR analysis confirmed the expression profiles of the majority of these genes. The results indicate that a few genes are modulated in response to very low-dose-rate irradiation. The functional analysis suggests that these genes may influence many processes, including obesity and tumorigenesis.
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