46. A Large-scale Gene Expression Analysis of Radiosensitive and Radioresistant Rats Exposed to Ionizing Radiation

Atsushi Tsuji, Aya Sugyo, Sagara Masashi, Toshiaki Ogiu, Hiroshi Aburatani, Takashi Imai and Yoshinobu Harada

Keywords: rat, X-ray,s microarray

The LEC rat is an X-ray hypersensitive animal characterized by radiation-induced bone marrow death, intestinal death, and an impaired ability to repair DNA double-strand breaks. This radiosensitivity is controlled by the responsible gene, mapped on rat chromosome 4 by Agui et al. in 2000. LEC rat is useful for investigating a molecular mechanism of radiation-induced responses in vivo. To identify the radiation-induced LEC-specific gene expression, we performed a large-scale gene expression analysis using microarrays between LEC and F344 rats.

We extracted mRNAs of LEC and F344 tails before exposure and 6 hours after whole-body irradiation at 4.5Gy. These mRNAs were labeled and hybridized three types of rat GeneChip microarrays (RGU34A·B·C, Affymetrix, Santa Clara, CA) according to the recommendations of Affymetrix. We normalized fluorescence intensities and performed comparative analysis of gene expressions of 26,379 probe-sets (24,681 genes or ESTs) using GeneChip 3.1 software, and excluded 11,855 probe-sets, which were undetected expression in all samples. An increase or decrease of 2-fold was chosen as a criterion for changes in gene expression.

We found 223 genes/ESTs increased or decreased in LEC rat, but not in F344 rat. By contrast, we identified 303 genes/ESTs increased or decreased in F344 rat, but not in LEC rat. In addition, 85 genes/ESTs had 2-fold different expression levels between LEC and F344 rats after irradiation. This result suggests these genes/ESTs could be associated with radiosensitivity in LEC rat. Gadd45, known for cell cycle regulation and DNA repair, was induced 5-fold in LEC rat, but was unchanged in F344 rat. Gadd45 expression is known to be increased by irradiation in normal susceptible tissues and cells. We, however, mapped Gadd45 near the responsible locus on rat chromosome 4. Then, we compared the Gadd45 cording sequence of LEC rat with that of F344 rat, and we found no difference, resulting that another gene was associated with radiosensitivity in LEC rat.

In the present study we detected approximately 600 genes/ESTs, which were shown to have different expression manners between radiosensitive and radioresistant rats exposed to ionizing radiation. This finding shouls be useful for investigating a molecular mechanism of radiation-induced response.