Association between G2-phase block and repair of radiation-induced chromosome fragments in human lymphocytes

We have studied the induction of chromosomal aberrations in human lymphocytes exposed in G(0) to X rays or carbon ions. Aberrations were analyzed in G(0), G(1), G(2) or M phase. Analysis during the interphase was performed by chemically induced premature chromosome condensation, which allows scoring of aberrations in G(1), G(2) and M phase; fusion-induced premature chromosome condensation was used to analyze the damage in G(0) cells after incubation for repair; M-phase cells were obtained by conventional Colcemid block. Aberrations were scored by Giemsa staining dr fluorescence in situ hybridization (chromosomes 2 and 4). Similar yields: of fragments were observed in G(1) and G(2) phase, but lower yields were scored in metaphase,The frequency of chromosomal exchanges was similar in G(0) (after repair), G(2) and M phase for cells exposed to X rays, while a lower frequency of exchanges was observed in M phase when lymphocytes were irradiated with high-LET carbon ions,The results suggest that radiation-induced G(2)-phase block is associated with unrejoined chromosome fragments induced by radiation exposure during G(0). (C) 1999 by Radiation Research Society.