Quantitative and qualitative studies of micronucleus induction in mouse erythrocytes using flow cytometry. II. Analysis of micronuclei of aneugenic and clastogenic origin by dual-colour FISH on populations of bone marrow PCEs flow sorted on the basis of their relative DNA content

Simultaneous dual-colour fluorescent in situ hybridization (FISH) with the major and minor mouse satellite probes was performed on flow-sorted fractions of micronuclei with defined Hoeschst 33342 fluorescence intensities, reflecting their relative DNA content. The purpose of the study was to investigate the relationship between probe binding and the size of micronuclei induced by a set of chemicals with different mechanisms of micronucleus induction. The agents studied were vinblastine, cyclophosphamide, hydroquinone and 5-bromo-2-deoxyuridine. The Hoechst 33342 fluorescence distributions of induced micronuclei differ markedly between cyclophosphamide, vinblastine and hydroquinone. While the distributions for cyclophosphamide and vinblastine agree well with those obtained for other model aneugens and clastogens, hydroquinone shows a distribution with characteristics similar to both clastogens and aneugens. A comparison between the Hoechst 33342 fluorescence distributions of hydroquinone-induced micronuclei positive for both major and minor probes and those positive for the major probe only indicates that the former consist of whole chromosomes, while the latter originate from chromosome fragments. The absolute frequency and Hoechst 33342 fluorescence distribution of major-only-positive micronuclei induced by vinblastine indicates that this model aneugen also shows a certain in vivo clastogenic potential. Micronuclei induced by 5-bromo-2-deoxyuridine indicate that this agent is a clastogen, preferentially inducing pericentric breaks, but may also to some extent be aneugenic.