Non-disjunction and chromosome loss in gamma-irradiated human lymphocytes:A fluorescence in situ hybridization analysis using centromere-specific probes

Centromere-specific DNA probes for chromosomes 4, 7 and 18 were used to sim ultaneously analyze chromosome loss, nondisjunction, breaks within the labe led region, and nucleoplasmic bridges induced by gamma rays in binucleated human lymphocytes, The doses used were 0, 1, 2 and 4 Gy, and approximately 1000 cells were scored per dose. Micronucleus frequency increased in a line ar-quadratic fashion. For chromosome loss, significant increases were obser ved at 2 and 4 Gy, whereas for non-disjunction significant increases were o bserved at 1 Gy; thus non-disjunction allowed us to detect the effects of r adiation at a lower dose than chromosome loss. The use of centromere-specif ic probes allowed discrimination between the clastogenic and aneugenic effe cts of ionizing radiation. The analysis of chromosome loss, not taking frag mented signals into account, ensures the detection of an aneugenic effect, which was not possible using pancentromeric probes. The frequency of chromo some breakage within the labeled regions was higher in nuclei than in micro nuclei, suggesting an increase in the engulfment of chromosomal material by nuclei as a consequence of the presence of cytochalasin B in the cultures. Chromatin filaments connecting main nuclei, the so-called nucleoplasmic br idges, were observed in irradiated samples, and are a manifestation of rear ranged chromosomes producing anaphase bridges. (C) 2001 by Radiation Resear ch Society.