G1 arrest and relative protein expressions in mouse thymocytes induced by whole body X-ray irradiation

To investigate the molecular regulation of G1 arrest of mouse thymocytes induced by ionizing radiation.

Cell cycle was analyzed by flow cytometry (FCM) following staining of cells with propidium iodide. Fluorescent staining and flow cytometry analysis were employed for measurement of protein expression.

It was demonstrated that G1 phase of mouse thymocytes increased significantly at 12 h after whole body irradiation (WBI) with the doses of 0.5, 1.0 and 2.0 Gy, and at 24 h following 2.0 Gy exposure, measured by FCM. In the time course experiment, it was found that G1 phase of thymocytes increased significantly at 4 h, reached a peak level at 24 h and came down toward 48 h after WBI with 2.0 Gy X-rays. The results also showed that after 2.0 Gy exposure, the expression of proteins in mouse thymocytes increased significantly from 1 h to 8 h for p53, for p21 from 4 h to 48 h, and for MDM2 at 4 h and 8 h, measured by FCM. But no change was found for GADD45 protein expression.

These results suggest that G1 arrest could be induced by a single dose of 0.5 Gy, 1.0 Gy or 2.0 Gy, and its molecular control might be established through the p53-p21 pathway.