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

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 ∼ 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 micro-nuclei. The duration of G1 phase in these cells agreed with the duration of G1 phase in unirradiated cells. (author)