Flow cytometric analysis of micronuclei found in cells after irradiation

Exposure of mammalian cells to either ionizing radiation or mutagenic and carcinogenic substances can induce chromosome aberrations. These aberrations in turn may give rise to micronuclei which can be found in cells during the interphase after division. A two-step method is presented that allows separation of micronuclei from cell nuclei. They can then be measured and analysed according to their DNA content in a flow cytometer. The method involves an initial detergent treatment of cells followed by a second treatment with sucrose and citric acid. Micronuclei with DNA content larger than 2% of the G1-nuclei can be measured. The method is tested and compared with microscopic observations of micronucleated cells in irradiated, asynchronous, and synchronized Ehrlich ascites tumour cells growing in vitro. The agreement between the flow cytometric technique and microscopic observations is excellent when the dose-dependent number of micronuclei per cell is taken into consideration.