Mechanisms for the induction of C-metaphases and anaphase bridges by chemical substances
Asiachi, Mulindi Eric
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Anaphase bridges and C-metaphases are common end points in the induction of clastogenicity often used in genotoxicity screening. Together with other chromosome aberrations, their induction by chemical substances has implicit biomedical effects such as cancer, aging and genetic diseases. This study investigates their possible mechanisms of induction by chemical substances and is part of an IPCS project. The plant cytogenetic test systems of Vicia faba var minor and Allium Cepa L. root tip cells were used to assay salts of elements selected from the periodic table for induction of anaphase bridges and C-metaphase. Treatment was done for 2 hours with recovery durations of 26 hours. The pH of treatment solutions was 6.8 and temperature at 20 ±2oC. The concentrations of the test agents used were 10-2ppm, 102ppm. Scoring was done by counting the number of cells with the aberrations per 100 anaphase and metaphase cells respectively. Results indicate that the induction of anaphase bridges and C-metaphase was not confined to any particular cations and anions or oxidation states of the elements. Some agents were positive in either A. cepa or V. faba but not in both. A few agents could induce either anaphase bridges or C-metaphases. Further investigations revealed that the agents positive in the V. faba root tip mitotic system were also positive in the V. faba pollen mother cell meiotic system. The number of bridges was seen to range from one to four per cell. However, the single per cell was the most common feature in both A. cepa and V. faba. Bridge formation was not limited to any specific chromosome. The effects of the agents were dose-dependent. Fewer aberrations were recorded at the lowest treatment doses. In view of the current knowledge of cellular macromolecular structure, the reunion and exchange theories are applied to explain how anaphase bridges are induced by chemical substances. Also considered is the phenomenon of chromosome stickiness in bridge formation. The interaction of chemical agents with the spindle apparatus to induce C-metaphase is discussed. Further investigations need to be carried out at the molecular level and with mammalian cytogenetic test systems for better understanding of these mechanisms.