Paclitaxel-dependent cell lines reveal a novel drug activity.

We previously described the isolation of Tax 18 and Tax 11-6, two paclitaxel-dependent cell lines that assemble low amounts of microtubule polymer and require the drug for cell division. In the present studies, fluorescence time-lapse microscopy was used to measure microtubule dynamic instability behavior in these cells. The mutations were found to cause small decreases in microtubule growth and shortening, but the changes seemed unable to explain the defects in microtubule polymer levels or cell division. Moreover, paclitaxel further suppressed microtubule dynamics at low drug concentrations that were insufficient to rescue the mutant phenotype. Wild-type (WT) cells treated with similar low drug concentrations also had highly suppressed microtubules, yet experienced no problems with cell division. Thus, the effects of paclitaxel on microtubule dynamics seemed to be unrelated to cell division in both WT and mutant cell lines. The higher drug concentrations needed to rescue the mutant phenotype instead inhibited the formation of unstable microtubule fragments that appeared at high frequency in the drug-dependent, but not WT, cell lines. Live cell imaging revealed that the fragments were generated by microtubule detachment from centrosomes, a process that was reversed by paclitaxel. We conclude that paclitaxel rescues mutant cell division by inhibiting the detachment of microtubule minus ends from centrosomes rather than by altering plus-end microtubule dynamics.

DNA damage in male gonad cells of Green mussel (Perna viridis) upon exposure to tobacco products.

DNA damage (determined by the Comet Assay) and the occurrence of deformed nuclei were measured as endpoints of genotoxicity in male gonad cells of the marine mussel (Perna viridis). Upon exposure of the organism to varying concentrations of extracts of smoked and non-smoked cigar tobacco over a period of 16 days, DNA damage was found to be highest in marine mussels exposed to extracts of smoked cigar tobacco. Conversely, more deformed nuclei were detected in marine mussels exposed to extracts of non-smoked cigar tobacco. The level of DNA damage and the number of deformed nuclei reach a maximum at day 12 of exposure to both extracts but decrease thereafter. This phenomenon is attributed to the organism's capacity to maintain the integrity of its genetic material upon exposure to potential genotoxicants present in the tobacco extracts. A dose response in DNA damage and deformed nuclei was also detected in isolated gonad cells upon in vitro exposure to hydrogen peroxide a known DNA strand breaking agent. The results of this study indicate that the DNA in male gonad cells of the marine mussel is damaged upon exposure to genotoxicants, and suggests the suitability of the organism for future investigations into the effect of such agents on its reproductive capacities.