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PubMed1997

Industrial Genotoxicology Group collaborative trial to investigate cell cycle parameters in human lymphocyte cytogenetics studies.

Human lymphocyte cultures have been used for many years for assessing the in vitro clastogenic potential of test substances. In these assays the harvest time should be based on the cell cycle time in order to ensure that cells are sampled at an appropriate time for the detection of clastogenic effects. The sources of variation in the cell cycle time in routine cytogenetic assays have not been well studied. Consequently 13 laboratories, all members of the Industrial Genotoxicology Group, participated in a collaborative study to measure the variation in cell cycle time in cultured human peripheral blood lymphocytes under various conditions. The study was performed in two phases, spaced 6 months apart. The average generation time (AGT) was measured by the incorporation of bromodeoxyuridine. Very similar AGTs were found in the presence and absence of S9 mix. The mean AGT (mean of four donors) in each laboratory varied from 11.2 to 17.1 h, indicating there is significant variability in cell cycle times of human peripheral blood lymphocytes between laboratories. There was greater variation between laboratories than within laboratories. A comparison of AGT values at 72 h performed in experiments at least 6 months apart indicated good reproducibility in most laboratories. The study indicates that a 24 h post-treatment harvest may result in the analysis of very few first division cells unless very significant cell cycle delay is induced by the test substance. It was also found that a post-harvest time equivalent to 1.5 cell cycles will result in an approximately equal mixture of first and second division cells and therefore should by suitable for assessing both the induction of chromosome aberrations and polyploidy.

Animals↗
PubMed1999

Validation study of the in vitro micronucleus test in a Chinese hamster lung cell line (CHL/IU).

We conducted a collaborative validation study, under the auspices of the Japanese Ministry of Labour, on the in vitro micronucleus test to see if it could be used as an alternative to the in vitro chromosome aberration test for evaluation of chemical safety. We used the Chinese hamster lung cell line (CHL/IU), which is the most widely used system for the latter test in Japan, and evaluated 66 chemicals, including clastogens and polyploidy inducers. The cytochalasin B cytokinesis blocking method, which is commonly used in human lymphocyte culture, was applied to the established cell line, but did not improve the detection of chemically-induced micronuclei in continuously growing cells. The highest micronucleus frequencies were obtained at 48 or 72 h continuous treatments. In short treatments (6 h), a 42 h recovery time yielded the best responses. Concordance between the results of the micronucleus test and the chromosomal aberration test was satisfactorily high (88.7%), and we concluded that the in vitro micronucleus test could be used in place of the chromosomal aberration test as a simple and rapid method for detecting clastogens and aneugens in vitro. We also propose a protocol for the test.

Animals↗
PubMed1993

Noscapine does not show aneugenic activity in mouse oocytes.

To clarify if noscapine has the ability to induce polyploidy in rodent germ cells in vivo, a cytogenetic study of mouse metaphase II oocytes was conducted after oral treatment with noscapine at the doses of 20, 120 and 400 mg/kg. Plasma concentrations of noscapine were measured by reversed-phase liquid chromatography and UV detection in three satellite groups of mice up to 8 h after administration of these doses. Thus, the relationship of the maximum plasma concentration and the area under the curve (AUC) with that of meiotic progression could be established. Although noscapine was tested at the maximum tolerated dose, no delay of meiotic progression or induction of chromosome malsegregation could be shown as no increase in the frequency of metaphase I-arrested, polyploid or hyperploid oocytes were found. At the highest dose only, noscapine affected the physiology of superovulation as shown by a significant decrease in the mean number of oocytes harvested per female. In view of the large span covered by the doses tested, corresponding to concentrations far above those detected in humans, and the similarity between the pharmacokinetics of noscapine in mouse and humans, it is unlikely that noscapine represents a genetic risk for humans at therapeutic dosages.

Aneuploidy↗
PubMed2006

Topoisomerase II inhibition and high yield of endoreduplication induced by the flavonoids luteolin and quercetin.

Luteolin and quercetin are widely distributed plant flavonoids that possess a variety of chemical and biological activities, including free-radical scavenging and antioxidant activity. Recently, both flavonoids have been reported to inhibit DNA topoisomerases I and II (topo I and topo II), a property that, together with their ability to induce DNA and chromosome damage, has made them candidate anticancer compounds. In the present study, we confirmed that both compounds are topo II inhibitors by conducting a comparative study of their effect on topo II activity from Chinese hamster ovary AA8 cells. Because interference with the function of topo II to resolve DNA entanglement at the end of replication results in chromosome malsegregation at mitosis, we investigated whether luteolin and quercetin are effective in inducing endoreduplication in AA8 cells. Concentrations of luteolin and quercetin that inhibited topo II catalytic activity resulted in extraordinarily high yields of metaphases showing diplochromosomes. Given the established relationship of polyploidy with tumor development via aneuploidy and genetic instability, these results question the usefulness of luteolin and quercetin in cancer therapy.

Animals↗
PubMed1987

Prevalence and distribution of chromosome abnormalities in a sample of first trimester internal abortions.

Cytogenetic analysis was performed directly on villus material from 202 samples obtained at the evacuation of the uterine cavity in cases of retained abortion in the first trimester, identified as such by ultrasound examination. A precise delineation of the karyotype was obtained in 94% of the cases, while the efficiency of karyotype analysis in samples of spontaneous abortion was not higher than 50%. An abnormal chromosome constitution was found in 145 fetuses (76.7%) of which 117, including mosaics, were aneuploid (70%), 16 polyploid (8.5%) and 12 had structural abnormalities (6.3%). The relative proportion of chromosome abnormalities in this material is higher than that found in spontaneous abortion for trisomies and double trisomies, but lower for 45,X and polyploidy. The method was found to be efficient in obtaining fetal karyotypes also in those cases in which the villous material was scarce (1 mg), and thus it seems appropriate for routine cytogenetic studies in the first trimester abortions.

Abortion, Spontaneous↗
PubMed1997

Persistent nuclear ribosomal DNA sequence polymorphism in the Amelanchier agamic complex (Rosaceae).

Individual plants of several Amelanchier taxa contain many polymorphic nucleotide sites in the internal transcribed spacers (ITS) of nuclear ribosomal DNA (nrDNA). This polymorphism is unusual because it is not recent in origin and thus has resisted homogenization by concerted evolution. Amelanchier ITS sequence polymorphism is hypothesized to be the result of gene flow between two major North American clades resolved by phylogenetic analysis of ITS sequences. Western North American species plus A. humilis and A. sanguinea of eastern North America form one clade (A), and the remaining eastern North American Amelanchier make up clade B. Five eastern North American taxa are polymorphic at many of the nucleotide sites where clades A and B have diverged and are thought to be of hybrid origin, with A. humilis or A. sanguinea as one parent and various members of clade B as the other parent. Morphological evidence suggests that A. humilis is one of the parents of one of the polymorphic taxa, a microspecies that we refer to informally as A. "erecta." Sequences of 21 cloned copies of the ITS1-5.8S gene-ITS2 region from one A. "erecta" individual are identical to A. humilis sequence or to the clade B consensus sequence, or they are apparent recombinants of A. humilis and clade B ITS repeats. Amelanchier "erecta" and another polymorphic taxon are suspected to be relatively old because both grow several hundred kilometers beyond the range of one of their parents. ITS sequence polymorphisms have apparently persisted in these two taxa perhaps because of polyploidy and/or agamospermy (asexual seed production), which are prevalent in the genus.

Base Sequence↗
PubMed1999

Interspecific hybrid ancestry of a plant adaptive radiation: allopolyploidy of the Hawaiian silversword alliance (Asteraceae) inferred from floral homeotic gene duplications.

The polyploid Hawaiian silversword alliance (Asteraceae), a spectacular example of adaptive radiation in plants, was shown previously to have descended from North American tarweeds of the Madia/Raillardiopsis group, a primarily diploid assemblage. The origin of the polyploid condition in the silversword alliance was not resolved in earlier biosystematic, cytogenetic, and molecular studies, apart from the determination that polyploidy in modern species of Madia/Raillardiopsis arose independent of that of the Hawaiian group. We determined that two floral homeotic genes, ASAP3/TM6 and ASAP1, are found in duplicate copies within members of the Hawaiian silversword alliance and appear to have arisen as a result of interspecific hybridization between two North American tarweed species. Our molecular phylogenetic analyses of the ASAP3/TM6 loci suggest that the interspecific hybridization event in the ancestry of the Hawaiian silversword alliance involved members of lineages that include Raillardiopsis muirii (and perhaps Madia nutans) and Raillardiopsis scabrida. The ASAP1 analysis also indicates that the two species of Raillardiopsis are among the closest North American relatives of the Hawaiian silversword alliance. Previous biosystematic evidence demonstrates the potential for allopolyploid formation between members of the two North American tarweed lineages; a vigorous hybrid between R. muirii and R. scabrida has been produced that formed viable, mostly tetraporate (diploid) pollen, in keeping with observed meiotic failure. Various genetic consequences of allopolyploidy may help to explain the phenomenal evolutionary diversification of the silversword alliance.

Adaptation, Physiological↗
PubMed2004

2,2',4,6,6'-Pentachlorobiphenyl induces mitotic arrest and p53 activation.

Polychlorinated biphenyls (PCBs), a class of persistent organic pollutants (POPs), have been considered to be involved in cancers, but the underlying mechanisms are not known well. Various cancers are closely related to genetic alteration; therefore, we investigated the effect of PCBs on genetic stability, through p53, a guardian of genome, in NIH 3T3 fibroblasts. Among several congeners examined, 2,2',4,6,6'-pentachlorobiphenyl (PeCB) specifically activated p53-dependent transcription. It also induced p53 nuclear accumulation, but did not cause DNA strand breakage. On the other hand, cell cycle progression that is closely connected to p53 was affected by 2,2',4,6,6'-PeCB, resulting in mitotic arrest. In the arrested cells, mitotic spindle damage was detected. Moreover, in the absence of functional p53, polyploidy was caused by 2,2',4,6,6'-PeCB. These results imply that 2,2',4,6,6'-PeCB induces mitotic arrest by interfering with mitotic spindle assembly, followed by genetic instability which triggers p53-activating signals to prevent further polyploidization. Taking these findings together, we suggest that 2,2',4,6,6'-PeCB could be involved in cancer development by causing genetic instability through mitotic spindle damage, which brings about aneuploidy in p53-deficient tumor cells.

Animals↗
PubMed1993

Cryopreservation of mouse oocytes: mutagenic effects in the embryo?

We have shown in previous studies that the complete cycle of cryopreservation and prefreezing manipulations increases the degeneration and decreases the fecundability of mouse oocytes. The present study confirms these results. Moreover, we show that the increase of polyploidy previously observed in one-cell zygotes derived from frozen-thawed oocytes persists during the early stages of embryonic development. Furthermore, embryos obtained from frozen oocytes or oocytes exposed to prefreezing manipulations show an increase in the frequency of sister chromatid exchanges. Since the estimation of sister chromatid exchange is a sensitive test of mutagenicity, this suggests that the complete cycle of cryopreservation might alter the oocyte and, more particularly, induce DNA damage.

Animals↗
PubMed2000

Chromosome aberrations in in vitro-produced bovine embryos at days 2-5 post-insemination.

Availability of embryos of high quality is required to obtain satisfactory embryonic developmental rates and normal calves following transfer of in vitro-produced (IVP) bovine embryos. One relevant quality parameter is the frequency of chromosome aberrations, which can be evaluated using multicolor fluorescent in situ hybridization (FISH) with chromosome 6- and chromosome 7-specific probes in cattle. In this study, interphase nuclei (n = 3805) were analyzed from 426 bovine IVP embryos. We found that 73%, 72%, 81%, and 58% of the embryos from Days 2, 3, 4, and 5 post-insemination (pi), respectively, displayed a normal diploid chromosome number in all cells. When looking at the types of chromosome aberrations, the percentages of mixoploidy at Days 2, 3, 4, and 5 pi were 22%, 15%, 16%, and 42%, respectively, whereas the percentages of polyploidy (i.e., all nuclei in an embryo were analyzed and were polyploid) were 5%, 13%, 3%, and 0%, respectively. In conclusion, numerical chromosome aberrations were detected as early as Day 2 pi. The development of polyploid embryos is slow and is apparently arrested during the third cell cycle, whereas the mixoploid embryos seem to continue development.

Animals↗
PubMed2000

Constraints on polyploid evolution: a test of the minority cytotype exclusion principle.

Polyploid evolution is often considered a mechanism of instant speciation; yet the establishment of rare tetraploids within diploid populations may be constrained by a frequency-dependent mating disadvantage (minority cytotype exclusion principle). I tested this hypothesis using experimental populations of Chamerion angustifolium (Onagraceae) that contained different proportions of tetraploids and diploids. Fitness, measured as total seed production over the entire flowering season, was calculated from a census of flower number and estimates of ovule number per flower and proportion of seed set per fruit. The fitness of tetraploids relative to diploids was frequency dependent, increasing from 0.4, when tetraploids were rare, to 0.7 when at 50% and 1.15 when they were in the majority (67%). This pattern exists because of a negative relationship between tetraploid frequency and seed set per fruit in diploids. Seed set in tetraploids was independent of cytotype frequency. The frequency-independent effect in tetraploids reflects higher assortative mating, partly because of non-random patterns of bee visitation. Bees visited a disproportionately high number of diploid inflorescences; however, the proportion of successive flights between tetraploids increased above random expectations as the frequency of tetraploids decreased. These results provide the first experimental test of frequency-dependent fitness in diploid-polyploid mixtures and suggest an important role for more gradual, population processes governing the evolution of polyploidy in natural populations.

Biological Evolution↗
PubMed2006

Following tetraploidy in an Arabidopsis ancestor, genes were removed preferentially from one homeolog leaving clusters enriched in dose-sensitive genes.

Approximately 90% of Arabidopsis' unique gene content is found in syntenic blocks that were formed during the most recent whole-genome duplication. Within these blocks, 28.6% of the genes have a retained pair; the remaining genes have been lost from one of the homeologs. We create a minimized genome by condensing local duplications to one gene, removing transposons, and including only genes within blocks defined by retained pairs. We use a moving average of retained and non-retained genes to find clusters of retention and then identify the types of genes that appear in clusters at frequencies above expectations. Significant clusters of retention exist for almost all chromosomal segments. Detailed alignments show that, for 85% of the genome, one homeolog was preferentially (1.6x) targeted for fractionation. This homeolog fractionation bias suggests an epigenetic mechanism. We find that islands of retention contain "connected genes," those genes predicted-by the gene balance hypothesis-to be resistant to removal because the products they encode interact with other products in a dose-sensitive manner, creating a web of dependency. Gene families that are overrepresented in clusters include those encoding components of the proteasome/protein modification complexes, signal transduction machinery, ribosomes, and transcription factor complexes. Gene pair fractionation following polyploidy or segmental duplication leaves a genome enriched for "connected" genes. These clusters of duplicate genes may help explain the evolutionary origin of coregulated chromosomal regions and new functional modules.

Arabidopsis↗
PubMed2005

Cell expansion and endoreduplication show a large genetic variability in pericarp and contribute strongly to tomato fruit growth.

Postanthesis growth of tomato (Solanum lycopersicon) as of many types of fruit relies on cell division and cell expansion, so that some of the largest cells to be found in plants occur in fleshy fruit. Endoreduplication is known to occur in such materials, which suggests its involvement in cell expansion, although no data have demonstrated this hypothesis as yet. We have analyzed pattern formation, cell size, and ploidy in tomato fruit pericarp. A first set of data was collected in one cherry tomato line throughout fruit development. A second set of data was obtained from 20 tomato lines displaying a large weight range in fruit, which were compared as ovaries at anthesis and as fully grown fruit at breaker stage. A remarkable conservation of pericarp pattern, including cell layer number and cell size, is observed in all of the 20 tomato lines at anthesis, whereas large variations of growth occur afterward. A strong, positive correlation, combining development and genetic diversity, is demonstrated between mean cell size and ploidy, which holds for mean cell diameters from 10 to 350 microm (i.e. a 32,000-times volume variation) and for mean ploidy levels from 3 to 80 C. Fruit weight appears also significantly correlated with cell size and ploidy. These data provide a framework of pericarp patterning and growth. They strongly suggest the quantitative importance of polyploidy-associated cell expansion as a determinant of fruit weight in tomato.

Cell Enlargement↗
PubMed2004

Widespread paleopolyploidy in model plant species inferred from age distributions of duplicate genes.

It is often anticipated that many of today's diploid plant species are in fact paleopolyploids. Given that an ancient large-scale duplication will result in an excess of relatively old duplicated genes with similar ages, we analyzed the timing of duplication of pairs of paralogous genes in 14 model plant species. Using EST contigs (unigenes), we identified pairs of paralogous genes in each species and used the level of synonymous nucleotide substitution to estimate the relative ages of gene duplication. For nine of the investigated species (wheat [Triticum aestivum], maize [Zea mays], tetraploid cotton [Gossypium hirsutum], diploid cotton [G. arboretum], tomato [Lycopersicon esculentum], potato [Solanum tuberosum], soybean [Glycine max], barrel medic [Medicago truncatula], and Arabidopsis thaliana), the age distributions of duplicated genes contain peaks corresponding to short evolutionary periods during which large numbers of duplicated genes were accumulated. Large-scale duplications (polyploidy or aneuploidy) are strongly suspected to be the cause of these temporal peaks of gene duplication. However, the unusual age profile of tandem gene duplications in Arabidopsis indicates that other scenarios, such as variation in the rate at which duplicated genes are deleted, must also be considered.

Computational Biology↗
PubMed1976

Myofibrillar ATPase, DNA and hydroxyproline content of human hypertrophied heart.

70 human hearts were studied less than 36 hours after death. The apex, and in some cases other parts of the myocardium were homogenized, DNA, hydroxyproline content, myofibrillar Ca2+ and Mg2+ ATPase were measured. In normal hearts the DNA and collagen content were 372 +/- 9 mg and 36 +/- 7 mg. Ca2+ and Mg2+ ATPase of the myofibrils prepared from these hearts have shown the same specific activity (35 +/- 5 and 34 +/- 6 nmol/min./mg) as those from fresh biopsies taken during open-chest surgery. The heart weight correlates with the DNA content (r= + 0.58 -p less than 0.01) and with the myofibrillar ATPase (r= - 0.33 - p less than 0.02) but not with the DNA concentration nor with the collagen content or concentration. The main result of this study was the presence of a negative correlation between the DNA content of the heart and the Mg2+ or Ca2+ myofibrillar ATPase (r= - 0.31, p less than 0.05 - r= - 0.45, p less than 0.01). This correlation was analysed with reference to the histological and biochemical studies published by several authors in human or experimental heart hypertrophy and it was suggested that in human heart hypertrophy the decrease of the myofibrillar or myosin ATPase is a direct consequence of the high degree of polyploidy of the muscular cells observed in this condition.

Adenosine Triphosphatases↗
PubMed2006

Patterns of recurrent evolution and geographic parthenogenesis within apomictic polyploid Easter daises (Townsendia hookeri).

Geographic patterns of parthenogenesis and the number of transitions from sexual diploidy to asexual (apomictic) autopolyploidy were examined for 40 populations of the Easter daisy, Townsendia hookeri. Analyses of pollen diameter and stainability characterized 15 sexual diploid and 25 apomictic polyploid populations from throughout the plant's western North American range. Sexual diploids were restricted to two Wisconsin refugia: Colorado/Wyoming, south of the ice sheets, and northern Yukon/Beringia. Chloroplast DNA sequencing uncovered 17 polymorphisms within the ndhF gene and trnK intron, yielding 10 haplotypes. Phylogenetic analyses indicated that five exclusively polyploid haplotypes were derived from four haplotypes that are shared among ploidies, conservatively inferring a minimum of four origins of apomictic polyploidy. Three of these apomictic polyploid origins were derived from southern sexual diploids, while the fourth origin was derived from northern sexual diploids. Analyses of regional diversity were suggestive of a formerly broad distribution for sexual diploids that has become subsequently fragmented, possibly due to the last round of glaciation. As sexual diploids were exclusively found north and south of the glacial maximum, while formerly glaciated areas were exclusively inhabited by asexual polyploids derived from both northern and southern sexual lineages, it is more likely that patterns of glaciation, as opposed to a particular latitudinal trend, played a causal role in the establishment of the observed pattern of geographic parthenogenesis in Easter daisies.

Asteraceae↗
PubMed2004

Conservation of the microstructure of genome segments in Brassica napus and its diploid relatives.

The cultivated Brassica species are the group of crops most closely related to Arabidopsis thaliana (Arabidopsis). They represent models for the application in crops of genomic information gained in Arabidopsis and provide an opportunity for the investigation of polyploid genome formation and evolution. The scientific literature contains contradictory evidence for the dynamics of the evolution of polyploid genomes. We aimed at overcoming the inherent complexity of Brassica genomes and clarify the effects of polyploidy on the evolution of genome microstructure in specific segments of the genome. To do this, we have constructed bacterial artificial chromosome (BAC) libraries from genomic DNA of B. rapa subspecies trilocularis (JBr) and B. napus var Tapidor (JBnB) to supplement an existing BAC library from B. oleracea. These allowed us to analyse both recent polyploidization (under 10,000 years in B. napus) and more ancient polyploidization events (ca. 20 Myr for B. rapa and B. oleracea relative to Arabidopsis), with an analysis of the events occurring on an intermediate time scale (over the ca. 4 Myr since the divergence of the B. rapa and B. oleracea lineages). Using the Arabidopsis genome sequence and clones from the JBr library, we have analysed aspects of gene conservation and microsynteny between six regions of the genome of B. rapa with the homoeologous regions of the genomes of B. oleracea and Arabidopsis. Extensive divergence of gene content was observed between the B. rapa paralogous segments and their homoeologous segments within the genome of Arabidopsis. A pattern of interspersed gene loss was identified that is similar, but not identical, to that observed in B. oleracea. The conserved genes show highly conserved collinearity with their orthologues across genomes, but a small number of species-specific rearrangements were identified. Thus the evolution of genome microstructure is an ongoing process. Brassica napus is a recently formed polyploid resulting from the hybridization of B. rapa (containing the Brassica A genome) and B. oleracea (containing the Brassica C genome). Using clones from the JBnB library, we have analysed the microstructure of the corresponding segments of the B. napus genome. The results show that there has been little or no change to the microstructure of the analysed segments of the Brassica A and C genomes as a consequence of the hybridization event forming natural B. napus. The observations indicate that, upon polyploid formation, these segments of the genome did not undergo a burst of evolution discernible at the scale of microstructure.

Brassica↗
PubMed2006

Elimination of deleterious mutations in plastid genomes by gene conversion.

Asexual reproduction is believed to be detrimental, mainly because of the accumulation of deleterious mutations over time, a hypothesis known as Muller's ratchet. In seed plants, most asexually reproducing genetic systems are polyploid, with apomictic species (plants forming seeds without fertilization) as well as plastids and mitochondria providing prominent examples. Whether or not polyploidy helps asexual genetic systems to escape Muller's ratchet is unknown. Gene conversion, particularly when slightly biased, represents a potential mechanism that could allow asexual genetic systems to reduce their mutation load in a genome copy number-dependent manner. However, direct experimental evidence for the operation of gene conversion between genome molecules to correct mutations is largely lacking. Here we describe an experimental system based on transgenic tobacco chloroplasts that allows us to analyze gene conversion events in higher plant plastid genomes. We provide evidence for gene conversion acting as a highly efficient mechanism by which the polyploid plastid genetic system can correct deleterious mutations and make one good genome out of two bad ones. Our finding that gene conversion can be biased may provide a molecular link between asexual reproduction, high genome copy numbers and low mutation rates.

Base Sequence↗