Abstract
The system in PF BL27 to irradiate culture cells with microbeam soft X rays is useful to observe the phenomena which are occurring in situ in the cells with irradiation and to clarify the important fundamental problems in radiation biology. The problem why the cells in M phase has high radiosensitivity has been interested in radiation biology, however, the exact mechanism of the radiosensitivity remains unclear. In this study, abnormal cell-cycle progression in the M phase was investigated using the microbeam irradiation system in PF BL-27B, when a single M phase cell in each mitotic stage was irradiated with a 5.35 keV X-ray microbeam focused on the cell nucleus. HeLa cells, genetically modified and expressing EGFP-tagged aurora kinase B, were used as irradiated samples, in order to recognize the stage of each cell in the M phase, such as prophase, prometaphase, metaphase anaphase and telophase. Each single cell at each stage was irradiated with 10 micro-m x 10 micro-m monochromatic microbeam focusing on the nucleus, and each irradiated cell was pursuited on line to watch mitotic cell division to the end. Each cell at each stage was irradiated with 10 Gy at the dose rate of 20 Gy/min and the average times to take in each stage were measured. From the results, it is clearly observed that cell-cycle progression in the M phase has mitotic arrest due to a delay of the metaphase/anaphase transition. The dose dependence of the elongation of the M phase was also examined and one of checkpoint proteins was observed by immunostaining assay.
