Morphology and Origin of Micronuclei Induced by Mitotic Inhibitors

In order to elucidate the morphological variation and the origin of erythrocytic micronuclei induced by mitotic inhibitors, each of clastogens (mitomycin C and cyclophosphamide) and spindle poisons (vincristine and colchicine) was administered intraperitoneally into a rat. After 24 h, the bone marrow smear was prepared and subjected to the microscopic analysis. In consequence, the sizes of micronuclei (MNSs) induced by spindle poisons were generally larger than those (MNCs) induced by clastogens. On the other hand, the bone marrow cells containing micronucleated erythrocytes were fractionated by cellulose column chromatography and then Percoll-gradient centrifugation. The micronuclear DNA was extracted from the resulting erythrocyte fraction and subjected to the dot blot hybridization with a centromeric or telomeric DNA probe. This experiment showed that centromeric and/or telomeric DNAs are enriched more in MNSs than in MNCs. Thus, such hybridization techniques and the morphological analysis would be available for classifying micronucleus-inducing drugs.