Comet assay as a tool to screen for mouse models with inherited radiation sensitivity

Recent in vivo and in vitro data of patients analyzed for genetic susceptib ility to radiation during cancer therapy have shown structural changes in t he chromosomes to be prevalent both in the patients being treated and in th eir immediate family members. As structural changes in chromosomes frequent ly lead to activation of proto-oncogenes and elimination of tumor-suppresso r genes, they represent important mechanisms for the initiation of DNA repa ir processes and tumorigenesis. With the exception of rare genetic syndrome s such as AT (Ataxia telangiectasia) or NBS (Nijmegen Breakage Syndrome), t he background for the inheritance of genetic susceptibility to radiation is unknown. Recently, a large-scale genetic screen of mouse mutants has been establishe d within the German Human Genome Project (Hrabe de Angelis and Balling 1998 ). The goal of this ENU (ENU: ethylnitrosourea) mutagenesis screen is the g eneration of mutant mice that will serve as animal models for human disease s and genetic susceptibility. In order to fully utilize the potential of a genetic screen of this: magnit ude, in which exploration for genes responsible for genomic instability and radiation sensitivity is to occur, it is necessary to establish a simple a ssay system that is amenable to automation. Hence, we are using the single- cell gel electrophoresis (comet assay) to detect mouse mutants that display a genetic susceptibility to ionizing radiation. We have established the an alysis parameters in the comet assay which are currently used to detect rad iation-sensitive mouse mutants and to control the variance within the mouse population in the ENU screen. The assay can be used to isolate genes that are responsible for DNA repair and radiation sensitivity in mouse and human .