Taxol, vincristine or nocodazole induces lethality in G1-checkpoint-defective human astrocytoma U373MG cells by triggering hyperploid progression.
(9/1578)
In this report, we describe a novel lytic mechanism exploited by antimicrotubule drugs (AMDs) such as Taxol which are frequently used to treat multiple human cancers including breast and ovarian cancers. In cells lacking the G1-arresting capacity due to the defect in retinoblastoma or p53 gene function, AMDs trigger hyperploid progression and death. The hyperploid progression occurs via continued cell-cycle progression without cell division. Blocking hyperploid progression through hydroxyurea or ectopically expressed p27(Kip1), a G1-specific Cdk inhibitor, abrogates AMD cytotoxicity. Thus, AMDs induce lethality in G1-checkpoint-defective cells by triggering hyperploid progression. The phenomenon is reminiscent of that observed previously with bub-1 yeast mutant. The potential significance of this finding lies in that hyperploid progression-mediated death may be exploited to develop a therapy with tumor-specificity at the genetic level. As a large fraction of human cancers are mutated in p53 gene, it may have a wide therapeutic applicability. (+info)
Anaphase aberrations in the embryos of the marine tubeworm Pomatoceros lamarckii (Polychaeta: Serpulidae): a new in vivo test assay for detecting aneugens and clastogens in the marine environment.
(10/1578)
The marine environment receives a wide variety of chemical inputs, many of which have the potential to damage DNA or interfere with the process of cell division. Here we describe a new assay based on the early embryo and larval stages of a planktonic spawning, tube dwelling marine worm, Pomatoceros lamarckii, which for experimental purposes has the advantage of producing large numbers of ripe gametes throughout the majority of the year. One of the most promising end-points is the use of dividing cells to detect anaphase aberrations such as lagging chromosomes, tripolar anaphases, acentric fragments and chromosome bridges. Apart from the reference mutagens mitomycin C and cyclophosphamide and the well-documented spindle poison colchicine, we tested the fungicide carbendazim, a primary metabolite of the fungicide benomyl, and thiabendazole, a pesticide and antihelminthic drug; both of which are known to act as aneugens in other test systems. In addition we tested sodium hypochlorite, a widely used oxidizing agent and disinfectant, di-butylphthalate, a commercial plasticizer and suspected aneugen, and sodium chloride, a recognized non-genotoxin. Significant increases in the frequency of anaphase abnormalities occurred with most test compounds at relatively low concentrations, confirming the sensitivity of the new assay. Sodium chloride yielded a negative response except at the highest non-relevant concentrations, where some chromatid stickiness was observed. In addition, the developmental consequences of exposure to these compounds were assessed in 4-8 cell embryos and at 48 h once the embryos had metamorphosed into free swimming larvae. Mitotic inhibition and anaphase aberrations were found to be a more sensitive indicator of genotoxic exposure than larval development, although there was a suggestion of a possible mechanistic link between aneugenicity/clastogenicity and larval fitness. The new test assay provides a rapid and inexpensive method for screening chemicals and effluents destined for release into the marine environment for potential gamete effects. (+info)
Ploidy regulation of gene expression.
(11/1578)
Microarray-based gene expression analysis identified genes showing ploidy-dependent expression in isogenic Saccharomyces cerevisiae strains that varied in ploidy from haploid to tetraploid. These genes were induced or repressed in proportion to the number of chromosome sets, regardless of the mating type. Ploidy-dependent repression of some G1 cyclins can explain the greater cell size associated with higher ploidies, and suggests ploidy-dependent modifications of cell cycle progression. Moreover, ploidy regulation of the FLO11 gene had direct consequences for yeast development. (+info)
Comparative investigation on spindle behavior and MPF activity changes during oocyte maturation between gynogenetic and amphimictic crucian carp.
(12/1578)
The spindle behavior and MPF activity changes in the progression of oocyte maturation were investigated and compared with cytological observation and kinase assay between gynogenetic silver crucian carp and amphimictic colored crucian carp. MPF activity was measured by using histone H1 as phosphorylation substrate. There were two similar oscillatory MPF kinase activity changes during oocyte maturation in two kinds of fishes with different reproductive modes, but there existed some subtle difference between them. The subtle difference was that the first peak of MPF kinase activity was kept to a longer-lasting time in the gynogenetic silver crucian carp than in the amphimictic colored crucian carp. It was suggested that the difference may be related to the spindle behavior changes, such as tripolar spindle formation and spindle rearrangement in the gynogenetic crucian carp. (+info)
Mutagenicity tests on epristeride in vitro and in vivo.
(13/1578)
AIM: To evaluate the genetic effects of epristeride (Epr), a new prospective drug for treating benign prostatic hyperplasia. METHODS: 1) Assaying reverse mutation in histidine nutritional deficiency strain of Salmonella typhimurium 2) detecting chromosome aberrations in Chinese hamster lung cells (CHL); 3) micronucleus assays of mouse bone marrow; 4) counting sperm shape abnormalities 35 d after first ig Epr. RESULTS: 1) The reverse mutation happened at almost the same rate of the negative control. Epr did not induce bacterial mutation. 2) In vitro, the rates of aberration were all below 3%, thus Epr did not induce chromosome damage in CHL. 3) Micronucleated polychromatic erythroblasts (PCE) were not apparently more than those of sovent control, Epr did not induce the formation of micronuclei in PCE. 4) With Epr 818, 682, and 341 mg.kg-1, the head abnormalities of sperms were 5.3% +/- 2.7%, 5.3% +/- 1.9%, and 5.2% +/- 1.2%, respectively. CONCLUSION: No genetic toxicity of Epr was detected. (+info)
Altered dosage of the Saccharomyces cerevisiae spindle pole body duplication gene, NDC1, leads to aneuploidy and polyploidy.
(14/1578)
Saccharomyces cerevisiae cells are exquisitely sensitive to altered dosage of the spindle pole body duplication gene, NDC1. We show that the NDC1 locus is haploinsufficient because diploid yeast cells cannot survive with a single chromosomal copy of the NDC1 gene. Diploid cells with a single copy of NDC1 can survive by gaining an extra copy of the NDC1-containing chromosome. NDC1 haploinsufficiency is a dominant loss-of-function phenotype that leads to aneuploidy. Furthermore, we report that overexpression of NDC1 leads to spindle pole body duplication defects indistinguishable from those observed in ndc1-1 mutant cells. Cells overexpressing NDC1 arrest with monopolar spindles and exhibit increase-in-ploidy phenotypes. Thus, both increased and decreased NDC1 dosage can lead to aneuploidy. The striking sensitivity of yeast cells to changes in NDC1 gene dosage suggests a model for the behavior of some tumor suppressor genes and oncogenes in which loss-of-function mutations and overexpression, respectively, lead to increased genetic instability. (+info)
Inferences on the genome structure of progenitor maize through comparative analysis of rice, maize and the domesticated panicoids.
(15/1578)
Corn and rice genetic linkage map alignments were extended and refined by the addition of 262 new, reciprocally mapped maize cDNA loci. Twenty chromosomal rearrangements were identified in maize relative to rice and these included telomeric fusions between rice linkage groups, nested insertion of rice linkage groups, intrachromosomal inversions, and a nonreciprocal translocation. Maize genome evolution was inferred relative to other species within the Panicoideae and a progenitor maize genome with eight linkage groups was proposed. Conservation of composite linkage groups indicates that the tetrasomic state arose during maize evolution either from duplication of one progenitor corn genome (autoploidy) or from a cross between species that shared the composite linkages observed in modern maize (alloploidy). New evidence of a quadruplicated homeologous segment on maize chromosomes 2 and 10, and 3 and 4, corresponded to the internally duplicated region on rice chromosomes 11 and 12 and suggested that this duplication in the rice genome predated the divergence of the Panicoideae and Oryzoideae subfamilies. Charting of the macroevolutionary steps leading to the modern maize genome clarifies the interpretation of intercladal comparative maps and facilitates alignments and genomic cross-referencing of genes and phenotypes among grass family members. (+info)
Induction of polyploidy and apoptosis after exposure to high concentrations of the spindle poison nocodazole.
(16/1578)
The proportions of aneuploid/polyploid versus euploid cells formed after treatment with spindle poisons like nocodazole are of course dependent on the relative survival of cells with numerical chromosome aberrations. This work aimed at studying the survival of polyploid cells formed after treatment with a nocodazole concentration sufficient to significantly decrease tubulin polymerization (0.1 microg/ml). First, normal primary lymphocytes were analysed and the following complementary chromosomal parameters were quantified: mitotic index, frequency of abnormal mitoses, polyploid metaphases and apoptotic cells. The results clearly indicate a positive correlation between abnormal mitotic figures, apoptosis and the induction of polyploidy. They therefore led to a single cell approach in which both apoptosis and polyploidy induction could be scored in the same cell. For this purpose, actively proliferating cells are required and two human leukaemic cell lines were used, KS (p53-positive) and K562 (p53-negative), which have a near-triploid karyotype. Cells were separated into an apoptotic and a viable fraction by means of annexin-V staining and flow cytometry. In KS, treatment with nocodazole induced a similar fraction of hexaploid cells in both the viable and apoptotic fraction, but no dodecaploid cells were ever observed. In contrast, a population of dodecaploid cells (essentially viable) was clearly observed in the K562 cell line. The results in KS, as compared with K562, confirm that wild-type p53 can prevent further cycling of polyploid cells by blocking rereplication. The most probable explanation for these data is that not only the mitotic spindle but also interphase microtubules are sensitive to nocodazole treatment. Our data thus strongly suggest that besides the G(1)/S checkpoint under the control of p53, the G(2)/M transition may be sensitive to depolymerization of microtubules, possibly under the control of Cdc2, Bcl-2, Raf-1 and/or Rho. (+info)