Chromosomal inversions, such as those occurring following exposure to ionizing radiation, are especially difficult to detect by current techniques. Therefore, their true frequency and importance have been underappreciated. Even the impressive technology of whole genome sequencing, which is becoming more readily and rapidly available, is useless for the detection of many chromosomal rearrangements within a chromosome. Likewise, stateof- the-art cytogenetic mBAND analysis of irradiated normal human tissue can only occasionally reveal radiationinduced inversions. A novel and innovative approach called differential Genomic Hybridization (dGH) or chromatid painting has been developed to further explore, expand, and capitalize on this new frontier of molecular cytogenetics.

Chromatid paint detecting inversions. Multiple single-stranded probes are prepared to unique sequence chromosomal targets, all of which are on the same chromatid and span its length (left). An example of a very small inversion is shown on the right (arrow).
Presently, the dicentric chromosome is the gold-standard cytogenetic biodosimeter. Dicentric chromosomes are unstable and disappear with time. Small inversions are likely to be stable aberrations and are therefore expected to remain in a cell lineage. The detection of small inversions will serve as a reliable and stable retrospective biodosimeter. The purpose of the innovation is to develop a new and greatly improved technology to detect chromosomal inversions.

A chromosome paint is a complex probe cocktail that hybridizes in many places along the length of a specific chromosome. The improvement to chromosomal painting created here is to prepare multiple single-stranded probes to unique sequence chromosomal targets i.e. directional probes, all of which are hybridized to the same chromatid and span its length (see figure). The visual effect is to paint just one sister chromatid or only one longitudinal half of a chromosome.

Chromatid painting detects inversions in a new way, through a shift in signal from one sister chromatid to the other. The pattern produced by the signal shift is readily identifiable, even to comparatively unskilled observers. Detection of inversions is independent of band size; instead, the resolution depends on the spacing of probes along the length of the chromatid. With a densely spaced probe set, inversions smaller than the theoretical limit of light microscopy could be detected. Thus, with chromatid paints, inversions go from the most difficult-to-observe chromosome aberrations to the aberration that can be detected with the highest resolution.

This work was done by Edwin Goodwin of KromaTiD; Andrew Ray, Susan Bailey, and Joel Bedford of Colorado State University; and Michael Cornforth of UTMB for Johnson Space Center. For further information, contact the JSC Technology Transfer Office at (281) 483-3809. MSC-24647-1

NASA Tech Briefs Magazine

This article first appeared in the July, 2015 issue of NASA Tech Briefs Magazine.

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