Mutation Induction by Ionizing Radiation

Fluorescence in situ hybridization (FISH) has opened new perspectives for the identification and classification of radiation induced chromosome aberrations. Selective staining of individual human chromosomes by chromosome painting allows a rapid microscopic observation of dicentric and translocation chromosomes. Methods of automated digital image analysis accelerate the evaluation of FISH labeled metaphase spreads. In the case of aberration screening as for instance after a radiation accident, next to cell culture, the hybridization procedure itself may be the most time consuming part of the analysis. Therefore, a new fast-FISH technique has been developed. For different repetitive, centromere-specific DNA-probes (useful for dicentric screening) the whole labeling procedure can be performed in about half on hour. Under appropriate conditions a simultaneous labeling of all centromeres can be obtained. Further new perspectives in accelerating biological dosimetry are offered by a laser-technological approach called slit-scan flow fluorometry. Isolated chromosomes very rapidly pass one after another a ribbon shaped laser beam. The chromosomes are orientated perpendicularly to the laserfocus so that time resolved fluorescence profiles different for normal and aberrant chromosomes can be obtained. In the case of homogenous staining, a normal chromosome is represented by a bimodal profile while a dicentric chromosome shows a trimodal profile. According to profile parameters the Heidelberg slit-scan flow fluorometer will sort particles so that chromosomes classified as aberrant may be enriched for further microscopic analysis.