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Results for “polyploidy”

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PubMed1977

Effect of polyploidy on phosphoglucose isomerase diversity in Festuca microstachys.

Studies of the inheritance of electrophoretic banding patterns in Festuca microstachys support the hypothesis that three closely related loci, one located in each of the three ancestral genomes, code the multiple phosphoglucose isomerase (glucosephosphate isomerase; D-glucose-6-phosphate ketol-isomerase, EC 5.3.1.9) variants found in this hexaploid species. The close relationship among the three loci is indicated by the observation that hybrid enzymes of intercistronic origin form when the loci in different genomes carry alleles coding homodimers with unlike migration rates. Homozygous individuals fixed for different alleles in different genomes produce hybrid enzymes and, when self-fertilized, they breed true for isozyme patterns normally found only in the heterozygotes of diploid species. Biochemical diversity due to this "fixed heterozygosity" is high in F. microstachys; although this species is more than 99% self-fertilized the proportion of individuals with at least one heterodimer exceeded 61% in all of the 16 natural populations studied and it exceeded 92% in 11 of the populations. This great biochemical diversity may contribute to the ability of F. microstachys to survive in the wide range of habitats in which it is found over western North America.

Alleles↗
PubMed1999

Altered dosage of the Saccharomyces cerevisiae spindle pole body duplication gene, NDC1, leads to aneuploidy and polyploidy.

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.

Aneuploidy↗
PubMed2002

Natural and induced polyploidy in Acacia dealbata Link. and Acacia mangium Willd.

Seeds were obtained from seven natural populations of Acacia dealbata, three natural populations of A. mangium and a seed orchard of A. mangium, representing the natural range of the two species. Polyploids were discovered in two of the seven populations of A. dealbata. The 2C DNA amount for diploid A. dealbata (2n = 2x = 26) was 1.74 pg, and for diploid A. mangium (2n = 2x = 26) was 1.30 pg. A naturally occurring tetraploid of A. dealbata (2n = 4x = 52) had a 2C DNA amount of 3.41 pg and a naturally occurring triploid genotype had a 2C DNA amount of 2.53 pg. The use of colchicine and oryzalin was investigated as a means of producing higher frequencies of tetraploids of both A. mangium and A. dealbata for incorporation into breeding programmes. Colchicine treatment gave tetraploid frequencies up to 29% for A. dealbata seedlings, and up to 18% for A. mangium seedlings. In contrast, no tetraploid A. mangium was detected following oryzalin treatment, and the low frequencies of tetraploids observed in A. dealbata could be attributed to their natural occurrence.

Acacia↗
PubMed2006

Oxalis debilis in China: distribution of flower morphs, sterile pollen and polyploidy.

BACKGROUND AND AIMS: Oxalis debilis is a South American tristylous species that is currently naturalizing in China. Based on field observations and herbarium data a report is made on its pollination, morph frequencies, pollen viability, seed set and chromosome number. In addition, a new chromosome count for the species in Africa is provided. METHODS: Field observations were conducted in six provinces in south-east China. Flower visitors were recorded and nectar sugar was measured with a refractometer. The species' compatibility system was determined by carrying out experimental self- and cross-pollinations on bagged inflorescences. Stigma receptivity and pollen viability was determined using the MTT test. KEY RESULTS AND CONCLUSIONS: Populations of O. debilis in China contain either the mid-style-length morph or the short morph, but not both. Pollination is by nectar- and pollen-foraging bees; pollen viability is low; and seed set in natural and experimentally self- or cross-pollinated flowers is extremely low. Chromosome counts indicate that O. debilis contains diploid and tetraploid forms in its native as well as introduced range, which does not support a previous hypothesis that the predominant vegetative reproduction in this species is an escape from pentaploidy.

China↗
PubMed1996

Long crocidolite asbestos fibers cause polyploidy by sterically blocking cytokinesis.

Asbestos has been described as a physical carcinogen in that its carcinogenic effects appear to be related primarily to fiber dimensions. It has been hypothesized that long asbestos fibers may interfere with chromosome distribution during cell division, causing genomic changes that lead to cell transformation and neoplastic progression. Using high-resolution time-lapse light microscopy and serial-section electron microscopy, we have followed individual crocidolite asbestos fibers through the later stages of cell division in LLC-MK2 epithelial cells, and have detailed for the first time their effect on cytokinesis. We found that long fibers (15-55 microgram), trapped by the cleavage furrow, sterically blocked cytokinesis, sometimes resulting in the formation of a binucleated cell. The ends of blocking fibers were usually found within invaginations of the newly formed nuclei. Nuclear envelope-fiber attachment was evident when a chromatin strand ran with the fiber into the intercellular bridge. Such strands may break, causing chromosome structural rearrangements. Our data are the first to show that individual crocidolite fibers can cause genomic changes by sterically blocking cytokinesis and that fiber length and affinity for the nuclear envelope are important factors. Such genomic changes may be among the initial events leading to asbestos-induced cancers.

Animals↗
PubMed2000

Spontaneous blastomere fusion after freezing and thawing of early human embryos leads to polyploidy and chromosomal mosaicism.

The incidence of blastomere fusion after cryopreservation of early human embryos (day 2 and day 3) was investigated using the standard propanediol technique. The process of fusion was observed in all developmental stages (from 2 to 10 cells) and the frequency of this event was 4.6% in day 2 (41/889) and 1.5% in day 3 (10/646) embryos that survived the thawing (embryos with 50-100% intact cells). Fusion of two, and occasionally of several, blastomeres resulted in the formation of multinucleated hybrid cells, which clearly indicated that the ploidy of these newly created cells had been altered. This event, depending on the number of fused cells per embryo, transformed the embryos into either entirely polyploid embryos (complete fusion at 2- or 3-cell stage) or into mosaics being a mixture of polyploid and normal cells. Chromosomal preparations of embryos affected by blastomere fusion indicated the presence of tetraploid mitotic plates. Also, fluorescence in-situ hybridization (FISH) analysis using DNA probes targeting unique sequences on chromosomes 9, 15, 17 and 22 indicated the existence of tetraploid and diploid fluorescence signals in the interphase nuclei within mosaics. Therefore, observations on live and fixed embryos suggested that tetraploid (4n) or hexaploid (6n) and tetraploid-diploid or more complex aberrations of ploidy might be formed as a consequence of blastomere fusion. Furthermore, this demonstrates that freezing and thawing may induce numerical chromosomal changes in human embryos.

Blastomeres↗
PubMed2001

Familial sperm polyploidy induced by genetic spermatogenesis failure: case report.

We report a case of oligoasthenoteratozoospermia in a 40 year-old patient with a familial history that revealed multiple cases of infertility and perinatal deaths. The patient's semen sample contained 2x10(6) spermatozoa/ml, with an overall progressively motile population of <5%. Cytological analysis revealed a teratozoospermia with 100% of abnormal macrocephalic sperm heads and an irregular acrosomal cap in 38% of cells. Moreover, 72% of spermatozoa carried multiple flagella (2-5). The midpiece was elongated and/or enlarged with cytoplasmic droplets in 15% of cells. The multiple anomalies index (MAI) was 3.3 (normal value = 1.6), reflecting the high incidence of spermatozoal morphological abnormalities in this patient. Ultrastructural analysis revealed the presence of 2 or 3 vacuolated nuclei per sperm head. The acrosome was abnormal and the chromatin, partially packaged, appeared rough. In some cases, a large amount of cytoplasm containing vacuoles was observed around the nucleus and the acrosome. The mitochondrial helix was disorganized. Chromosome analysis performed on blood cells revealed a normal karyotype. Three-colour fluorescence in-situ hybridization (FISH) analysis of 1148 spermatozoa showed 21.6% to be diploid, 62.4% triploid, 13.3% quadriploid and 2.7% hyperploid (<4n). In conclusion, we suggest that this case could result from a genetically induced spermiation failure, the origin of which is discussed.

Acrosome↗
PubMed1998

Spindle poisons can induce polyploidy by mitotic slippage and micronucleate mononucleates in the cytokinesis-block assay.

The human in vitro cytokinesis-blocked micronucleus (MN) assay has been extensively used for detection of clastogenic and aneugenic agents. In this test binucleate cells are generally considered to be the main target cell population for assessing genotoxic effect and almost no attention is paid to the biological information contained in mono-nucleate cells. In this study we analysed the frequencies of micronucleate mononucleates in a control population and after in vitro exposure to clastogens or aneugens. A clear increase in MN in mononucleates was found only after exposure to aneugenic compounds. By means of fluorescence in situ hybridization using a chromosome 1-specific probe we further analysed the proportion of mononucleate cells with and without MN which were tetrasomic (tetraploid) and would have been induced during aneugen treatment by mitotic slippage. The data indicate that treatment with nocodazole induces tetrasomy for chromosome 1 (tetraploidy) and an increase in MN frequency in mononucleate diploid and tetraploid lymphocytes. The results thus confirm that some mononucleates pass mitosis without chromatid segregation to daughter nuclei. These data suggest that MN in mononucleates may be useful to distinguish clastogens from aneugens and increase the sensitivity of the test.

Benzimidazoles↗
PubMed1993

Assessment of polyploidy in human morulae and blastocysts using co-culture and fluorescent in-situ hybridization.

Fluorescence in-situ hybridization with DNA probes for X, Y and no. 18 chromosomes was used to analyse human morulae (n = 13) and blastocysts (n = 41), obtained after co-culture on Vero cells. On the basis of the number of hybridization signals, the proportion of embryos with more than five polyploid cells was 30.8% for morulae and 29.3% for blastocysts. These values are similar to those for mixoploidy (mosaicism of diploid and polyploid cells) observed in blastocysts of animal species. The results were confirmed by scanning electron microscopy, which showed a wide variation in the size of blastocyst nuclei, and by classical cytogenetic analysis. Mixoploidy seems to be a normal feature in preimplantation embryos and to occur very early in human embryo development. This lays open to doubt the preimplantation diagnosis of genetic errors at these stages, since results obtained from single cell analysis may not be representative of the whole embryo.

Animals↗
PubMed1994

Monospermic polyploidy and atypical embryo morphology.

Monospermic cleavage-arrested human embryos were analysed by fluorescence in-situ hybridization using specific DNA probes for chromosomes X, Y and 18 simultaneously. Two groups of monospermic polyploid embryos could be distinguished: (i) embryos (n = 13) with only one large cell surrounded by smaller blastomere-sized extracellular fragments. These embryos were polyploid and frequently polyploid mosaic. (ii) Embryos developing from larger than normal oocytes were triploid or triploid mosaics (n = 4). Atypical morphology was not seen in eight other polyploid monospermic embryos. The atypical morphologies described here are quite rare, but are genetically uniform. Polyspermic embryos are the only other known example of a dual genetic-morphological abnormality.

Blastomeres↗
PubMed2006

Comparative genomics of Brassica oleracea and Arabidopsis thaliana reveal gene loss, fragmentation, and dispersal after polyploidy.

We sequenced 2.2 Mb representing triplicated genome segments of Brassica oleracea, which are each paralogous with one another and homologous with a segmentally duplicated region of the Arabidopsis thaliana genome. Sequence annotation identified 177 conserved collinear genes in the B. oleracea genome segments. Analysis of synonymous base substitution rates indicated that the triplicated Brassica genome segments diverged from a common ancestor soon after divergence of the Arabidopsis and Brassica lineages. This conclusion was corroborated by phylogenetic analysis of protein families. Using A. thaliana as an outgroup, 35% of the genes inferred to be present when genome triplication occurred in the Brassica lineage have been lost, most likely via a deletion mechanism, in an interspersed pattern. Genes encoding proteins involved in signal transduction or transcription were not found to be significantly more extensively retained than those encoding proteins classified with other functions, but putative proteins predicted in the A. thaliana genome were underrepresented in B. oleracea. We identified one example of gene loss from the Arabidopsis lineage. We found evidence for the frequent insertion of gene fragments of nuclear genomic origin and identified four apparently intact genes in noncollinear positions in the B. oleracea and A. thaliana genomes.

Arabidopsis↗
PubMed1981

Polyploidy in the murine colonic pericryptal fibroblast sheath.

The cause of the apparently paradoxical occurrence of relatively high levels of labelling and low levels of mitotic activity in the pericryptal fibroblast sheath (PCFS) was investigated. Analysis of the distribution of grain densities over epithelial cells and the PCFS in the colon demonstrated that, although the former had a unimodal peak, the PCFS had a multi-peak distribution. The PCFS nuclei with the higher grain densities gradually disappeared with time, due not to proliferation but to lateral migration into the lamina propria. Photodensitometric analysis confirmed the existence of polyploid cells in the colonic PCFS, but not in the epithelium.

Animals↗