The kinetics of postirradiation chromatin restitution as revealed by chromosome aberrations detected by premature chromosome condensation and fluorescence in situ hybridization

In a study of X-ray-induced chromosome aberrations in human G(0) lymphocyte s irradiated with 4 Gy using premature chromosome condensation (PCC) and fl uorescence in situ hybridization (FISH), the time-dependent pattern of chro mosome fragments and interchromosomal exchanges involving chromosome 4 was recorded after postirradiation incubation times varying from 0.5 to 46.5 h, Unattached acentric fragments and incomplete interchromosomal exchanges ha ve high initial yields, followed by an exponential decrease, while complete interchromosomal exchanges have almost zero initial yield with a subsequen t increase in their number. Plateau values of all yields are reached after about 25 h, This temporal variation of aberration yields can consistently b e explained by the competition of disruptive PCC stress with the progress o f postirradiation structural restitution at the sites of radiation-induced chromatin instabilities, Details of the temporal pattern of incomplete exch anges reflect the different kinetics of the alpha and beta components of th e yield of aberrations. The observed large difference between late-PCC and metaphase yields of unattached acentric fragments and the almost perfect co nversion from incomplete prematurely condensed chromosomes into complete me taphase exchanges are explained by a difference in the magnitude of chromos ome condensation stress between PCC and mitotic conditions. Chromatin sites prone to fragmentation and incompleteness under conditions of PCC can ther efore persist as genetic instabilities hidden during mitosis. (C) 2000 by R adiation Research Society.