Induction of micronuclei by mitomycin C and colchicine in the marine mussel Mytilus galloprovincialis.

The frequencies of micronuclei (MNi) in the gill cells of the mussel Mytilus galloprovincialis were determined over a long period (up to 28 days) following a 48-h treatment with colchicine. The frequency of MNi at the end of treatment was significantly higher than in controls and 24 h later it had increased even more. After this period, the frequency of MNi rapidly declined until a plateau level was reached on day 2-3, which was significantly higher than the control baseline level, and persisted until the end of the experiment (28th day). In the same cell system we previously reported a persistence of an increased frequency of MNi after treatment with mitomycin C (MMC) (Majone et al., 1987). In order to establish the origin of MNi, the difference between their size distribution in MMC- and colchicine-treated animals was determined at the end of treatment as well as during the plateau phase. The difference was statistically significant (P less than 0.001) at the end of treatment, the MNi induced by MMC being smaller than those induced by colchicine. However, the difference during the plateau phase was not statistically significant. Human CREST antikinetochore fluorescent antibodies reacted with chromosome centromeres of Mytilus and were applied to gill cells at the end of a 48-h treatment with MMC or colchicine. About 60% of the MNi induced by colchicine but only 30% of those produced by MMC reacted positively with the fluorescent antibodies. This result indicates that the majority of MNi observed at the end of a 48-h treatment with MMC or colchicine originate, respectively, from acentric chromosome fragments and from whole lagging chromosomes.