Induction, processing and persistence of radiation-induced chromosomal aberrations involving hamster euchromatin and heterochromatin

Euchromatic and heterochromatic regions are easily distinguished in Chinese hamster sex chromosomes, hence offering the possibility of studying the ro le of chromatin structure in the induction, processing and persistence of r adiation-induced chromosome damage. X-ray (4 Gy)-induced breaks in the euch romatic Xp and in the heterochromatic Xq were analysed immediately and 4h a fter irradiation by premature chromosome condensation (PCC) in combination with either FISH using chromosome arm-specific probes or Giemsa staining. T he study, performed with female Chinese hamster splenocytes, was extended t o a 34 h recovery followed by arm-specific FISH in metaphase. A significant over-involvement of the heterochromatic Xq in radiation-induced breakage w as observed at all sampling times (p<0.001). However, the heterochromatic s tate had little effect on the processing of the induced lesions. In a secon d experiment, the persistence of radiation-induced chromosome aberrations ( CAs) involving Xp, Xq and Y chromosome was studied with cultured Chinese ha mster male splenocytes sampled 30, 56 and 96 h after irradiation (4 Gy). A higher involvement of the heterochromatic regions (Xq and Y) in radiation-i nduced CAs was again observed in the first sampling time (p<0.001), suggest ing that Chinese hamster heterochromatin could be more radiosensitive than euchromatin. Cells with CAs involving heterochromatin were apparently less persistent than those with lesions involving euchromatin. This observation could be attributable to either the distribution of CA per cell or to the f raction of potentially stable exchanges. (C) 2000 Elsevier Science B.V. All rights reserved.