MICRONUCLEI WITH KINETOCHORES IN HUMAN-MELANOMA CELLS AND RECTAL CARCINOMAS

Micronucleus frequencies were analysed in an X-irradiated human melanoma cell line and in untreated rectal carcinoma cells. As a special aspect of the micronucleus formation, micronuclei-containing kinetochores were analysed by the method of indirect immunofluorescence. The incidence of kinetochorepositive micronuclei was taken as a measure of chromosome loss. In order to show kinetochores, an anti-kinetochore serum of a CREST syndrome patient was used. In irradiated melanoma cells the mean number of micronuclei increased linearly with increasing dose whereas the proportion of kinetochorepositive micronuclei decreased. The analysis of the time-dependent formation of micronuclei revealed an increase of the micronucleus frequency from 24 to 48 h after irradiation (p.r.) and a slight decrease from 48 to 72 h p.r. The highest number of kinetochore-containing micronuclei was scored 72 h p.r. In rectal carcinoma cells a high rate of spontaneously formed micronuclei was observed. At least 30% of these micronuclei contained complete chromosomes, as indicated by the kinetochore-positive staining. We have attempted to summarize the data by means of a numerical expression which takes into account the relation between lost chromosomes, visible as kinetochore-positive micronuclei, and the total sum of micronuclei.