BD12

Analysis Of Micronuclei By Flow Sorting And FISH.

M. Nüsse¹*, A. Slavotinek², B.M. Miller³, ¹GSF-AG Durchflußzytometric, D-85758 Oberschleißheim, ²Dept. Clinical Genetics, Churchill Hospital, Oxford, England, ³PRPT, Preclinical Division, Hoffmann La-Roche AG, Basel, Switzerland

The chromosomal composition of radiation-induced MN sorted according to their DNA content was studied in mouse 3T3 cells and in various human cell lines with different radiation sensitivity using FISH with centromeric DNA probes and with chromosome-specific painting probes. Most MN in 3T3 cells were found to contain acentric fragments, with increasing DNA content, however, the frequencies of MN containing 1, 2 or 3 hybridization signals increased demonstrating the presence of one or several chromosomes in larger MN. These data agreed with results obtained on fixed cells using a combination of telomeric and centromeric DNA probes. The DNA distribution of radiation-induced MN measured by flow cytometry could be simulated by a random breakage model of chromosomes using these results.

In situ hybridization with whole chromosome painting probes to paint radiation-induced MN was used to further investigate the nature of radiation-induced cytogenetic damage. The results obtained for four chromosomes (1, 7, 11, 14) in three human cell lines with differing radiosensitivity showed that there was a significant deviation of the numbers of signal positive MN from that expected on the basis of DNA proportionality. The results were dependent mainly on chromosome 7 which was underrepresented in the numbers of signal positive MN in the group of chromosomes studied. If it is assumed that the chromosomal content of the MN is an accurate reflection of the radiation-induced damage, then these results support a non-random model of radiation-induced cytogenetic damage.