The Effect of Mitomycin C on Human Chromosomes with G-banding Patterns

ABSTRACT

Mitomycin C was introduced to human leukocyte cultures to investigate the analysis of chromosome aberration by G-banding patterns. The relationship between mitomycin C and secondary constriction; length of treatment and exposure time of the compound; and G-banding pattern were discussed. The results are summarized as follows 1. The mitotic rate of cultures exposed to mitomycin C at a concentration of 0. 1 microgram/ml for 24 hours did not inhibit significantly compared with that of the control, and chromosome aberrations were relatively very low. However, the mitotic index of cells exposed to 1.0 microgram/ml for 1 hour or 24 hours was significantly below the control index and a relatively high number of aberrations were found. With the concentration of 0.5 microgram/ml for the last 24 hours of cultural incubation, there was little inhibition of mitotic activity and the highest frequency of observable aberrations were found. Thus, in this study, treatment of the concentration of 0.5 microgram/ml for the last 24 hours of cultures proved to be the most efficient combination for examining the effect of this compound on human leukocyte chromosomes. 2. Mitomycin C did not appear to break the chromosome randomly. More than half of the aberrations were of the interchange type which were in most cases involved with chromosomes 1, 9 and 16. They are joined in, at least, the secondary constrictrion regions of one of these chromosomes. The secondary constriction regions contain 60 to 70 percent of the total breaks of each of these chromosomes. The other types of chromosome aberrations were simple chromatid and chromosome breaks at the interband of G-bands and translocations. The frequent association of satellites with 2 to 5 acrocentric chromosomes was also observed. In conclusion, it can be stated that mitomycin C is very specific in causing lesions to appear at the secondary constriction of human chromosomes 1, 9 and 16. The dosage of mitomycin C, length of treatment and exposure time during the culture period are very important factors for induction of chromosome abnormalities, which vary with the individual's leukocytes that have different genetic constitutions.