Analysis by FISH of the spectrum of chromosome aberrations induced by x-rays in G(o) human lymphocytes and their fate through mitotic divisions in culture

The induction, distribution, and persistence of chromosome aberrations in h uman lymphocytes exposed to X-rays in G(0) were analyzed in 48-, 70-, and 9 4-hr cultures by conventional metaphase analysis and painting of chromosome s 1, 2, and 4 by FISH. All cells that had been scored by FISH were relocate d to determine by differential staining of chromatids whether they had pass ed through 1, 2, or greater than or equal to 3 divisions. FISH revealed a d ose-dependent induction of stable and unstable aberrations, while chromatid labeling showed mitotic lag caused by irradiation in G(0). Relative to the ir DNA contents, there was a small but significant overrepresentation of ch romosome 4 and underrepresentation of chromosome 2 among the aberrations in volving chromosomes 1,2, and 4. FISH slightly underestimated the genomic fr equency of unstable aberrations measured by conventional metaphase analysis . There was a slight excess of translocations relative to dicentrics, but t he data are compatible with the 1:1 ratio expected From cytogenetic theory. Many of the translocations were apparently incomplete (i.e., nonreciprocal ). Incomplete translocations were more frequent at higher X-ray dose and in first division, suggesting that they may be associated with complex damage and are more apt to be lost in mitosis than complete translocations. Among the incomplete translocations, t(Ab) outnumbered t(Ba) - a difference ascr ibable to the FISH technique. Aberration frequencies de dined as the cells divided in culture. The overall decline in the frequency of aberrant cells (approximate to 29% per cell generation) reflects a rapid decline in dicent rics and fragments (approximate to 60% per cell generation) and the relativ e stability of translocations. The frequency of translocation-bearing cells underwent a modest decline in culture (approximate to 13% per cell generat ion). (C) 1999 Wiley-Liss, Inc.