Past exposure to densely ionizing radiation leaves a unique permanent signature in the genome

Abstract

Speculation has long surrounded the question of whether past exposure to ionizing radiation leaves a unique permanent signature in the genome. Intrachromosomal rearrangements or deletions are produced much more efficiently by densely ionizing radiation than by chemical mutagens, x-rays, or endogenous aging processes. Until recently, such stable intrachromosomal aberrations have been very hard to detect, but a new chromosome band painting technique has made their detection practical. We report the detection and quantification of stable intrachromosomal aberrations in lymphocytes of healthy former nuclear-weapons workers who were exposed to plutonium many years ago. Even many years after occupational exposure, more than half the blood cells of the healthy plutonium workers contain large (>6 Mb) intrachromosomal rearrangements. The yield of these aberrations was highly correlated with plutonium dose to the bone marrow. The control groups contained very few such intrachromosomal aberrations. Quantification of this large-scale chromosomal damage in human populations exposed many years earlier will lead to new insights into the mechanisms and risks of cytogenetic damage.

Figure 1

Schematics of production of stable interchromosomal and intrachromosomal aberrations. a, Interchromosomal aberration produced by misrejoining of chromosome, showing breaks on two different chromosomes. b–d, Intrachromosomal aberrations produced by misrejoining of breaks. Effects of misrejoining of breaks on two different arms of a single chromosome (b) or within a single chromosome arm (c and d) are shown. Intrachromosomal aberrations generally originate from pairs of chromosome breaks that are closer together than those producing interchromosomal aberrations; densely ionizing radiations are more likely than other mutagens to produce such multiple chromosome breaks close together.

Figure 2

Intrachromosomal aberrations in chromosome 5 detected by use of the mBAND technique. Localization of the RSCP is shown in images captured using six different filters, specifically DAPI (A), FITC (B), Gold (C), Texas Red (D), Cy5 (E), and Aqua (F). Quantitative color ratio analysis of these different chromosome paints yields a “merged color” fluorescence intensity pattern (G) along the chromosome axis, indicating continuously changing color ratios. Finally, “pseudocolors” are assigned to sections of the chromosome with similar color ratios (H). Top, Intrachromosomal interarm aberration (pericentric inversion), as shown in figure 3b. Middle, Intrachromosomal intra-arm aberration (paracentric inversion), as shown in figure 3c. Bottom, Intrachromosomal intra-arm aberration (intra-arm deletion), as shown in figure 3d.

Figure 3

Stable inter- and intrachromosomal aberrations in Mayak plutonium workers (pseudocolor images). The panels correspond to the schematics in figure 1. a, Interchromosomal aberration (simple translocation) (white arrows), detected using mFISH. b–d, Intrachromosomal aberrations (gray arrows) in chromosome 5 detected using mBAND, showing centromere. Left chromosome in each pair is normal; right chromosome shows aberration. b, Interarm aberration (pericentric inversion), showing the region of the chromosome that was inverted (yellow arrows). c, Intrachromosomal intra-arm aberration (paracentric inversion), showing the region of the chromosome that was inverted (yellow arrows). d, Intrachromosomal intra-arm aberration (intra-arm deletion), showing the region of the arm that was deleted (red arrows).

Figure 4

Measured yields of stable chromosomal aberrations in peripheral blood lymphocytes of highly-exposed plutonium workers, moderately-exposed plutonium workers, reactor workers, and unexposed control individuals. Shown on the histograms are the number of aberrations found/number of metaphase cells examined. a, Intrachromosomal aberration (pericentric inversions, paracentric inversions, and intra-arm inversions) measured in chromosome 5. b, Interchromosomal aberrations (apparently simple translocations between any heterologous pair of chromosomes). Note the rarity of intrachromosomal aberrations in the highly exposed reactor workers (who received no plutonium exposure) and in the control group.