Premature Chromosome Condensation Following X Irradiation of Mammalian Cells: Expression Time and Dose-Response

Abstract

Premature chromosome condensation (PCC) in Chinese hamster ovary (CHO) cells following exposure to 300-kVp X rays was 1st detected in the mitosis that followed the 2nd postirradiation S phase. Cells irradiated in G1 1st expressed PCC at the 2nd postirradiation mitosis while cells irradiated in G2 did not express PCC until the 3rd postirradiation mitosis. Cells irradiated in the S phase expressed PCC at the 2nd postirradiation mitosis with a frequency that was related to the position of the cells in the S phase at the time of exposure, cells in the 1st half of the S phase (at the time of exposure) showing a higher frequency than cells positioned in the 2nd half. DNA replication during the 1st postirradiation S phase may be involved in the processing of lesions that eventually give rise to PCC. For cells in G1 at the time of exposure, the D0 [mean lethal dose value] for PCC expression at the 2nd postirradiation mitosis was around 825 rad, indicating that PCC may play only a minor role in X-ray-induced cell killing. Autoradiographic analysis indicated approximately 50% of the PCC patches scored were replicating DNA at the time condensation was attempted. Daughter cells derived from such cells would suffer loss of genetic material.