Chromatid break rejoining and exchange aberration formation following gamma-ray exposure: analysis in G(2) human fibroblasts by chemically induced premature chromosome condensation

Purpose: To analyse the kinetics of chromatid break induction, rejoining, a nd misrejoining after gamma-irradiation in G(2) phase human cells using pre mature chromosome condensation induced by calyculin A. Materials and methods: Human fibroblast AG1522 cells were irradiated with g amma-rays and chromosomes were then prematurely condensed by calyculin A. T he number of chromatid breaks and chromatid exchanges in G(2) chromosomes w ere scored, and fitted curves were calculated. Results: Calyculin A induced premature chromosome condensation in cells imm ediately after irradiation. Kinetics of rejoining of chromatid breaks demon strated two exponential components with rapid and slow time constants. With in 5 min after irradiation, the number of chromatid breaks fell rapidly to about one-half, then gradually decreased. Chromatid exchanges were formed v ery quickly, reaching a plateau within 20 min from exposure. Conclusions: Chemically induced premature chromosome condensation technique allows a simple, rapid and precise analysis of chromatid breakage and rejo ining. The rapid kinetic component was particularly well characterized.