Localization of radiation-induced chromosomal breakpoints along human chromosome 1 using a combination of G-banding and FISH

Purpose: To determine the exact location of radiation-induced chromosomal b reakpoints along the euchromatic or heterochromatic regions: G-light and G- dark bands, respectively. Materials and methods: The distribution of radiation-induced chromosomal br eakpoints was scored in human lymphocytes irradiated in vitro with 3 Gy of gamma-radiation. Image analysis was applied to combine G-banded and FISH-pa inted images of the human chromosome 1. Results: A total of 195 chromosomal breakpoints in 176 cells with structura l chromosomal aberrations was used for the present analysis. Radiation-indu ced breakpoints were found to be distributed randomly with respect to the p or q arms of chromosome 1 and specific band or band length, but more break points were mapped to G-light than to G-dark bands, the difference being st atistically significant. Conclusions: The results can well be interpreted in terms of concepts of ex isting models of nuclear architecture, chromatin structure and transcriptio nal activities of the chromatin, which can influence the induction of prima ry chromosomal aberrations by gamma-rays. Differential repair of randomly p roduced primary aberrations may also explain the non-random distribution of radiation-induced breakpoints.