Abstract

The spectral karyotyping (SKY) method is a novel molecular cytogenetic technique which simultaneously discerns entire chromosomes. In order to elucidate the origins of micronuclei induced under hyperthermic conditions in human lymphocyte culture, peripheral blood cells were cultured at 40°C or 42°C for 3-24 h, using the cytokinesis-block method with cytochalasin B. The induced micronuclei were identified by the fluorescence in situ hybridization (FISH) and SKY methods. At 42°C for more than 6 h, the frequency of occurrence of micronuclei in binucleated cells rose with increasing incubation time. By the FISH method, 83.3% of micronuclei induced in 24 h culture at 42°C were shown to be positive for the human centromeric probes. By the SKY method, each micronucleus induced under the hyperthermic conditions was identified unequivocally and shown to contain a specific chromosome. These results suggest that the micronuclei induced under the hyperthermic conditions in human lymphocyte culture contain chromosomes which do not migrate to the poles at the anaphase of the cell cycle because of the breakdown of the spindle apparatus.