Abstract
The time courses of the development and disappearance of gamma-H2AX foci after irradiation was measured in the nuclei of non cycling G0 human fibroblasts, and in the same cells after induction of premature chromosome condensation. The purpose was to investigate possible connections between the rejoining and mis-rejoining of DNA DSBs and the early formation of chromosome aberrations.
For gamma-H2AX foci assayed in G0 nuclei after irradiation of G0 human fibroblasts, a maximum of about 30 foci per cell was observed after 1 Gy in agreement with estimation of the number of DNA DSBs expected for this dose. About three times the number of foci were seen in dose of 3 Gy after induction of premature chromosome condensation. For both assays the number of foci then decrease at about the same rate when foci were measured at various times after irradiation.
gamma-H2AX foci in the prematurely condensed chromosomes were after seen at the broken ends of PCC fragments, and instances were also seen of gamma-H2AX foci at the junction point of translocation. Lesions allowing expression gamma-H2AX foci persist even after irradiated G0 cells are subcultured and allowed to progress to mitosis, but incubation of G0 cells up to for 12 hours after irradiation before subculture resulted in the disappearance of these foci on mitotic chromosomes.
Numerous gamma-H2AX foci are seen in the nuclear of unirradiated S phase cells, and an enormous phosphorylation of H2AX was seen in unirradiated S cells but not G0 cells after fusion with mitotic HeLa cells.
