Induction Of Chromosome Malsegregation Research Articles

Induction of chromosome malsegregation by nanomaterials

NMs (nanomaterials), defined as materials with at least one dimension smaller than 100nm, are able to induce genotoxic effects. One of the hypotheses of the mode-of-action in which they exert their genotoxic potential is to mechanically interfere with subcellular structures, in particular the microtubules. In the present paper, we review studies exploring interactions between NMs and tubulin; therefore a PubMed literature search was performed. From this search 12 studies, applying both acellular and cellular assays, were retrieved and are summarized according to endpoint and particle type. These studies show that there are interactions between different types of NMs and tubulins in both acellular and cellular systems. For several types of NMs, the multi-walled carbon nanotubes, amorphous SiO(2), TiO(2) and CoCr, an induction of aneuploidy was observed in vitro. There is, therefore, a critical need to assess the capacity of NMs to interfere with the cytoskeleton, and in particular the tubulins. This might require definition of relevant dosimetry, adaptations of some testing protocols, possibly development of new methodologies and studies on a larger size-range of NMs.

The rodent carcinogens 1,4-dioxane and thiourea induce meiotic non-disjunction in Drosophila melanogaster females

The ability of the rodent carcinogens 1,4-dioxane (DX) and thiourea (TU) to induce meiotic non-disjunction (ND) was assessed in 3- and 6-day-old Drosophila melanogaster females. The chemicals were administered orally and three 24 h and one 48 h broods were obtained after mating, to sample oocytes treated in increasingly earlier stages of development. The broods represent mainly mature oocytes (brood I), nearly mature oocytes (brood II), early oocytes (brood III) and very early oocytes (brood IV). The toxicity of DX increased with dose (1% (not toxic), 1.5, 2, 3, 3.5%) as well as a reduction in fecundity which was moderate. Induction of ND in mature oocytes was positive with 2, 3 and 3.5% concentrations and was not related to dose. In immature oocytes it was also positive though already at the lowest concentration tested (1%), suggesting a sensitivity higher than that of mature oocytes. TU at 0.10–10%, did not affect viability, but since fecundity was seriously impaired at high doses, ND was not assessed beyond the 1.5% concentration. TU also induced ND in mature and in immature oocytes; neither a threshold nor a dose effect was detected. The response of mature oocytes was lower than that of immature oocytes. TU induced increases of ND in the earliest cells tested in a more consistent fashion than DX. The data clearly show that both chemicals induced ND in mature oocytes and in the three subsets in which immature oocytes were fractionated. Though toxicity may play a significant unspecific role in the induction of chromosome malsegregation by DX and TU, the induction of ND at low doses, moderately toxic to the oocytes, suggests that the interaction with specific targets contributed to the results obtained.

Inhibition of the Mr 70,000 S6 kinase pathway by rapamycin results in chromosome malsegregation in yeast and mammalian cells.

The antifungal and immunosuppressive drug rapamycin arrests the cell cycle in G1-phase in both yeast and mammalian cells. In mammalian cells, rapamycin selectively inhibits phosphorylation and activation of p70 S6 kinase (p70(S6K)), a protein involved in the translation of a subset of mRNAs, without affecting other known kinases. We now report that rapamycin causes chromosome malsegregation in mammalian and yeast cells. Chromosome malsegregation was determined by metaphase chromosome analysis of human lymphocytes and lymphoblasts, detection of CREST-positive micronuclei in human lymphoblasts and Chinese hamster embryonic fibroblast (CHEF) cells, and selection of doubly prototrophic cells in a specially constructed yeast strain. The number of ana-telophases with displaced chromosomes and interphase and mitotic cells with an irregular number of centrosomes was also determined in CHEF cells. In quiescent mammalian cells (human lymphocytes and CHEF cells) induced with growth factor to re-enter the cell cycle, rapamycin was effective when cells were exposed at the time of p70(S6K) activation. In yeast, rapamycin was more effective when treatment was started in G1- than in G2-synchronized cells. Cells from ataxia telangiectasia (A-T) patients are characterized by chromosome instability and have recently been found to be resistant to the growth-inhibiting effect of rapamycin. We found that an A-T lymphoblastoid cell line was also resistant to the induction of chromosome malsegregation by rapamycin, but the level of spontaneous aneuploidy was higher than in normal cells. In yeast, the induction of chromosome malsegregation was dependent on the presence of a wild-type TUB2 gene, encoding the beta-subunit of tubulin. The finding that rapamycin acts in different cell types and organisms suggests that the drug affects a conserved step important for proper segregation of chromosomes. One or more proteins required for chromosome segregation could be under the control of the rapamycin-sensitive pathway.

Structural and mechanistic bases for the induction of mitotic chromosomal loss and duplication (`malsegregation') in the yeast Saccharomyces cerevisiae: Relevance to human carcinogenesis and developmental toxicology

MultiCASE has the ability to automatically determine the structural features responsible for the biological activity of chemicals. In the present study, 93 chemicals tested for their ability to induce chromosomal `malsegregation' in the yeast Saccharomyces cerevisiae were analyzed. This `malsegregation' mimics molecular events that occur during human development and carcinogenesis resulting in an effective loss of one chromosome of an autosomal pair and duplication of the homologue. Structural features associated with the ability to induce such chromosome loss and duplication were identified and compared with those obtained from examination of other toxicological data bases. The most significant structural similarities were identified between the induction of chromosomal malsegregation and several toxicological phenomena such as cellular toxicity, induction of sister chromatid exchanges in vitro and rodent developmental toxicity. Very significant structural similarities were also found with systemic toxicity, induction of micronuclei in vivo and human developmental toxicity. Less significant structural overlaps were found between yeast malsegregation and rodent carcinogenicity, DNA reactivity and mutagenicity, and the induction of chromosome aberrations in vitro and sister chromatid exchanges in vivo. These overlaps may indicate mechanistic similarities between the induction of chromosomal malsegregation and other toxicological phenomena. The predictivity of the SAR model derived from the present data base is relatively low, however. This may be merely a reflection of the small size and composition of the data base, however, further analyses suggest that it reflects primarily the multiple mechanisms responsible for the induction of chromosomal malsegregation in yeast and the complexity of the phenomenon.

Analysis of nine known or suspected spindle poisons for mitotic chromosome malsegregation using Saccharomyces cerevisiae D61.M

We tested nine (cadmium chloride, chloral hydrate, colchicine, diazepam, econazole nitrate, hydroquinone, pyrimethamine, thiabendazole, thimerosal) of the 10 known or suspected spindle poisons of the coordinated programme to study aneuploidy induction sponsored by the Commission of the European Communities using Saccharomyces cerevisiae D61.M (mitotic chromosomal malsegregation system). Mitotic malsegregation of chromosome VII was induced by chloral hydrate, thiabendazole and thimerosal. Diazepam, colchicine, cadmium chloride, econazole nitrate, hydroquinone and pyrimethamine revealed no induction of chromosomal malsegregation.

Influence of different factors on the induction of chromosome malsegregation in Saccharomyces cerevisiae D61.M by bavistan and assessment of its genotoxic property in the Ames test and in Saccharomyces cerevisiae D7

Bavistan is known to be a potent inducer of chromosome malsegregation in Saccharomyces cerevisiae. The influence of different factors on the induction of chromosome malsegregation in S. cerevisiae D61.M was investigated. With both standard protocols used (16 h overnight incubation and cold treatment protocol) bavistan, in a concentration range of 2.5–20 μg/ml, induced malsegregants to the same extent. The frequencies of malsegregants obtained were not influenced by the plating volume used on selective medium. Induction of malsegregants and toxicity became stronger with increasing supplementation of the incubation medium with yeast extract and peptone. The effects of bavistan on chromosome malsegregation were more pronounced at 28°C — the normal temperature for yeast growth — as compared to 33 and 37°C. A study of the time dependence of the induction of chromosome loss showed that malsegregants can already be detected after 8 h and 1.5 h (second incubation period) using the incubation protocols without and with cold treatment, respectively. To clarify whether a selection towards malsegregants occurs, the growth of mixed cultures of red, cycloheximide-sensitive cells and white, cycloheximide-resistant, leucine-auxotrophic cells prepared at different ratios was compared. A strong selection towards red cells and against the malsegregants was observed. In addition, bavistan was tested for genotoxic activity in Salmonella (Ames test) and in yeast S. cerevisiae D7. No mutagenic activity was detected using S. cerevisiae D7 (gene conversion, reverse mutation, mitotic crossing-over) with and without rat-liver S9. In contrast bavistan induced histidine revertants in the frameshift strains TA1537, TA1538, TA97 of Salmonella typhimurium after addition of an exogenous metabolic activation system.

Induction of chromosome malsegregation by halogenated organic solvents in Aspergillus nidulans: unspecific or specific mechanism?

Three chloromethanes (dichloromethane, chloroform and carbon tetrachloride) and 8 chlorinated ethanes (1,1- and 1,2-dichloroethane, 1,1,1- and 1,1,2-trichloroethane, 1,1,1,2- and 1,1,2,2-tetrachloroethane, pentachloroethane and hexachloroethane) were assayed in tests for the induction of mitotic segregation in Aspergillus nidulans diploid strain P1. Eight of the 11 compounds assayed (dichloromethane, chloroform, carbon tetrachloride, 1,1- and 1,2-dichloroethhane, 1,1,2-trichloroethane, 1,1,1,2- and 1,1,2,2-tetrachloroethane) significantly increased the frequency of morphologically abnormal colonies which produced euploid whole-chromosome segregants (haploids and non-disjunctional diploids). Only in one case (1,1,1,2-tetrachloroethane) was a borderline increase in crossing-over frequency observed, thus suggesting the involvement of non-DNA targets in aneuploidy induction by these chlorinated hydrocarbons. Conclusive evidence for the induction of aneuploidy as the primary genetic event was provided by experiments in haploid strain 35 with 1,2-dichloroethane and 1,1,1,2-tetrachloroethane. Mutagenic, lethal and growth-arresting activities were quantitatively estimated and compared to a series of descriptors of physical and chemical properties of the molecules by means of multivariate statistical analysis. Lipophilicity, known to be related to c-mitotic activity, did not show any significant relationship with aneuploidizing activity, whereas a possible correlation among physico-chemical descriptors and toxic properties of test chemicals was highlighted.

Aprotic polar solvents inducing chromosomal malsegregation in yeast interfere with the assembly of porcine brain tubulin in vitro

A number of aprotic solvents which had previously been found to induce mitotic aneuploidy in yeast were tested for their effects on re-assembly of twice recycled tubulin from pig brain. Some of the solvents which were strong aneuploidy-inducing mutagens in yeast slowed down tubulin assembly in vitro at concentrations lower than those required for aneuploidy induction. Ethyl acetate, methyl acetate, diethyl ketone and acetonitrile fell into this category. Other strong aneuploidy-inducing agents like acetone and 2-methoxyethyl acetate accelerated tubulin assembly. Non-genetically active methyl isopropyl ketone and isopropyl acetate both accelerated assembly, whereas methyl n-propyl ketone and n-propyl acetate were weak inducers of aneuploidy and slowed down the rate and extent of assembly. Those chemicals which slowed down the assembly rate also reduced the extent of assembly. Most chemicals which accelerated assembly also led to an increased extent of assembly, with the exception of isopropyl acetate. At the higher concentrations, however, a maximum assembly rate was reached which was followed by a slow decline. Although a perfect correlation between effects on the induction of chromosomal malsegregation and the interference with tubulin assembly in vitro was not seen, the experiments with tubulin were carried out using this class of chemicals because some of them strongly induced mitotic aneuploidy under conditions which suggested tubulin to be the prime target. The lack of a perfect coincidence might be due to species differences between the porcine brain and the yeast spindle tubulin, or the test for aneuploidy induction may have been negative because the concentrations required for an effect on yeast tubulin may be greater than the general lethal toxicity limit. Bearing this reservation in mind, the results suggest that the yeast aneuploidy test has a considerable predictive value for mammalian mutagenicity.