量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum and Radiological Science and Technology.
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An X-ray microbeam irradiation system using synchrotron radiation has been developed at the Photon Factory, KEK, Japan, and is now being fully operated for various biological experiments. The energy of microbeam X-rays is 5.35 keV which is suitable for experiments using mammalian cells, because the X-rays can penetrate the thickness of cells and the range of secondary electrons is within few micrometers. The synchrotron radiation has extremely low divergence, so it is easy to get X-ray beam with micrometer-dimension. The high-precision slit installed in the system is the simplest way to get a microbeam without focusing. The minimum beamsize by the slit is 5-micrometer-square, and the size of the microbeam can be changed quickly and arbitrarily. This specification might be ideal to investigate localization of the damage induction and subsequent cellular responses in cells irradiated with subcellular-sized beam.
To visualize the DNA damage induction, the microbeam-irradiated cells were immuno-stained by phosphorylated histone H2AX (gamma-H2AX) antibody. Most DNA double strand breaks were observed in localized area in cell nuclei, the size of which was almost the same as the beam size. Dose dependence of gamma-H2AX induction was also clearly observed.
GFP-tagged protein enables us to visualize cellular responses in living cells. We constructed Chinese hamster ovary (CHO) cells having GFP-tagged RAD51, one of the protein related homologous recombination. Within 1 hour after irradiation, significant number of foci of GFP-RAD51 could be observed at the microbeam-irradiated site in the majority of the irradiated cell nuclei, and remained at least 5 hours after irradiation. The foci were appeared in the restricted area in the cell nuclei, which was corresponded to the damage induced area visualized with gamma-H2AX. In some of the cells the foci could not appeared at all even after 12 hours, and the percentage of the population was almost same as the estimated population of G1-phase cells at the irradiated time.
会議概要（会議名, 開催地, 会期, 主催者等）
The 13th International Congress of Radiation Research
Visualization of the damage induction and the accumulation of Rad51 in the cells
