RADIATION CYTOGENETICS: THE COLOR REVOLUTION

Analysis of radiation-induced chromosomal aberrations has long been a powerful tool to understand the mechanisms of radiation action in living cells. Early cytogenetics was based on observations of solid-stained chromosomes, although banding techniques were soon developed for karyotyping human cells. Banding is a complex, error-prone, and timeconsuming methodology, especially when applied to radiation-induced aberrations that, unlike genetic syndromes, are randomly induced in the genome and in the cellular population. The “color revolution” occurred in the 80’s with the introduction of fluorescence in situ hybridization (FISH) The first great improvement provided by FISH-painting was the opportunity to analyze symmetrical, transmissible aberrations (such as translocations and inversions) simply and rapidly, whereas dicentrics had long been the main endpoint analyzed by solid staining. Multi-color painting demonstrated that radiation-induced rearrangements are much more complex than previously thought, and even low doses of densely ionizing radiation produce mostly complex-type exchanges. The impact of multi-color painting on the understanding of radiation-induced genetic effects will be discussed here.