DNA synthesis in radiation-induced micronuclei studied by bromodeoxyuridine (BrdUrd) labelling and anti-BrdUrd...

DNA synthesis in radiation-induced micronuclei of Chinese hamster cells was studied as a function of time after irradiation using pulse labelling of cells with bromodeoxyuridine (BrdUrd) and an immunofluorescence technique with anti-BrdUrd antibodies. It was shown with this technique that DNA synthesis in micronuclei corresponds with DNA synthesis in nuclei during S phase in approximately 98% of the micronuclei. The presence of radiation-induced micronuclei that are too large to be produced by acentric fragments alone was therefore attributed at least in part to DNA synthesis in micronuclei. A partially synchronized progression of micronuclei from G1 phase into S phase could be observed allowing the measurement of the duration of G1 phase in cells containing micronuclei. The duration of G1 phase in these cells agreed with the duration of G1 phase in unirradiated cells.