Induction and persistence of cytogenetic damage in mouse splenocytes following whole-body X-irradiation analysed by fluorescence in situ hybridization. III. Chromosome malsegregation/aneuploidy.

Transgenic mice with foreign DNA inserted into three pairs of chromosomes were exposed to 2 Gy X-rays in order to study the induction and persistence of chromosome malsegregation and aneuploidy up to 28 days after exposure. By tracing the marker chromosomes in cytokinesis-blocked binucleated splenocytes using fluorescence in situ hybridization (FISH), reciprocal products of chromosome malsegregation in the daughter nuclei were analysed. FISH with murine minor satellite DNA was employed to detect chromosome loss (MN with a centromere) in binucleated splenocytes. In addition to its clastogenic effects, X-irradiation also showed aneugenic activity, which was observed as centromere positive micronuclei (C + MN) and malsegregated marker chromosomes detected by FISH. The initial frequency of micronuclei (MN) analysed by Acridine Orange staining immediately after X-ray exposure was found to be 42.3 per 100 binucleated cells. The MN frequency declined in an exponential manner and at day 14, reached about half the value observed immediately after irradiation and 14% MN were detected at day 28. Of these MN, 25% were centromere positive at day 0 as detected by minor satellite signal after FISH. The percentage C + MN increased further at day 3 and declined at day 14 to the level observed at day 0. There were 7.6% malsegregated cells immediately after X-irradiation as analysed by two colour FISH. This value increased further during later intervals and remained stable until day 28. A combination of the Acridine Orange staining and FISH with minor satellite DNA and marker DNA to detect aneuploidy and chromosome malsegregation, was utilized in the present study to demonstrate the induction and persistence of aneugenic and clastogenic damage in transgenic mice irradiated in vivo.