Abstract
A stem cell contributes to the maintenance of tissue homeostasis by retaining an ability to divide asymmetrically into a stem cell and a transit daughter cell. Several reports suggest that stem cells segregate their chromosomes selectively. On the other hand, the cells that lose the ability of the selective chromosome segregation may be involved in carcinogenesis. In the present study, we investigated the effect of ionizing radiation on the selective chromosome segregation in neural stem cells. Neurosphere (NS) cells that contain a fraction of neural stem cells and fibroblast cells (MEF) were obtained from embryos of ICR mice at day 14.5 of gestation. The cells were irradiated with 1 Gy, 2 Gy and 3 Gy of X-rays, and then their chromosomes were labeled with 5-ethynyl-2'-deoxyuridine (EdU) for 48 h. We determined the frequency of the selective chromosome segregation by scoring the unequal fluorescent intensity of the EdU-labeled nuclei in binuclear cells induced by inhibiting cytokinesis. In unirradiated NS cells, 1.2% of cells showed the selective chromosome segregation, while no cell segregated their chromosomes selectively in MEF cells, suggesting the selective chromosome segregation in neural stem cells. Irradiations with 1 Gy, 2 Gy and 3 Gy of X-rays reduced the frequency of the selective chromosome segregation in irradiated NS cells to 60%, 45%, and 15% levels, respectively, compared to that in the unirradiated NS cells. The present result indicates that exposure to ionizing radiation decreases the number of stem cells retaining the selective chromosome segregation, suggesting the implication for the radiation effect on tissue homeostasis.
