Chromosome nondisjunction and loss induced by protons and X rays in primary human fibroblasts: Role of centromeres in aneuploidy

To study the origin of micronuclei induced in human primary fibroblasts by low-energy protons (7.7 and 28.5 keV/mum) and X rays, we have developed a c ombined antikinetochore-antibody (CREST) and FISH staining with pancentrome ric probes. This technique allowed us to analyze the integrity of the kinet ochore and centromeric DNA structures and to assess their role in induced a neuploidy. The effect of LET on radiation-induced chromosome nondisjunction was studied in binucleated cells with centromeric-specific DNA probes for chromosomes 7 and 11. Our results indicate that, though more than 90% of ra diation-induced micronuclei were CREST-/FISH-, 28.5 keV/mum protons and X r ays were also able to induce statistically significant increases in the num ber of micronuclei that were CREST-/FISH+ and CREST+/FISH+, respectively. O ne interpretation of these results could be that the protons induced chromo some loss by kinetochore detachment or by breakage in the centromeric DNA r egion, whereas X rays induced aneuploidy through a non-DNA damage mechanism . Nondisjunction appears to be a far more important mechanism leading to ra diation-induced aneuploidy. Irrespective of the higher frequency of micronu clei induced by 28.5 keV/mum protons, the frequency of chromosome loss was markedly higher for X rays than for 28.5 keV/mum protons, strengthening the hypothesis that non-DNA targets, such as components of the mitotic spindle apparatus, may be involved in aberrations in chromosome segregation after X irradiation. (C) 2001 by Radiation Research Society.