| 1. |
- Lundberg, Gisela, et al.
(författare)
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Binomial mitotic segregation of MYCN-carrying double minutes in neuroblastoma illustrates the role of randomness in oncogene amplification.
- 2008
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 3:8
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Amplification of the oncogene MYCN in double minutes (DMs) is a common finding in neuroblastoma (NB). Because DMs lack centromeric sequences it has been unclear how NB cells retain and amplify extrachromosomal MYCN copies during tumour development. PRINCIPAL FINDINGS: We show that MYCN-carrying DMs in NB cells translocate from the nuclear interior to the periphery of the condensing chromatin at transition from interphase to prophase and are preferentially located adjacent to the telomere repeat sequences of the chromosomes throughout cell division. However, DM segregation was not affected by disruption of the telosome nucleoprotein complex and DMs readily migrated from human to murine chromatin in human/mouse cell hybrids, indicating that they do not bind to specific positional elements in human chromosomes. Scoring DM copy-numbers in ana/telophase cells revealed that DM segregation could be closely approximated by a binomial random distribution. Colony-forming assay demonstrated a strong growth-advantage for NB cells with high DM (MYCN) copy-numbers, compared to NB cells with lower copy-numbers. In fact, the overall distribution of DMs in growing NB cell populations could be readily reproduced by a mathematical model assuming binomial segregation at cell division combined with a proliferative advantage for cells with high DM copy-numbers. CONCLUSION: Binomial segregation at cell division explains the high degree of MYCN copy-number variability in NB. Our findings also provide a proof-of-principle for oncogene amplification through creation of genetic diversity by random events followed by Darwinian selection.
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| 2. |
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| 3. |
- Gisselsson Nord, David, et al.
(författare)
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When the genome plays dice: circumvention of the spindle assembly checkpoint and near-random chromosome segregation in multipolar cancer cell mitoses.
- 2008
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 3:4
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Normal cell division is coordinated by a bipolar mitotic spindle, ensuring symmetrical segregation of chromosomes. Cancer cells, however, occasionally divide into three or more directions. Such multipolar mitoses have been proposed to generate genetic diversity and thereby contribute to clonal evolution. However, this notion has been little validated experimentally. PRINCIPAL FINDINGS: Chromosome segregation and DNA content in daughter cells from multipolar mitoses were assessed by multiphoton cross sectioning and fluorescence in situ hybridization in cancer cells and non-neoplastic transformed cells. The DNA distribution resulting from multipolar cell division was found to be highly variable, with frequent nullisomies in the daughter cells. Time-lapse imaging of H2B/GFP-labelled multipolar mitoses revealed that the time from the initiation of metaphase to the beginning of anaphase was prolonged and that the metaphase plates often switched polarity several times before metaphase-anaphase transition. The multipolar metaphase-anaphase transition was accompanied by a normal reduction of cellular cyclin B levels, but typically occurred before completion of the normal separase activity cycle. Centromeric AURKB and MAD2 foci were observed frequently to remain on the centromeres of multipolar ana-telophase chromosomes, indicating that multipolar mitoses were able to circumvent the spindle assembly checkpoint with some sister chromatids remaining unseparated after anaphase. Accordingly, scoring the distribution of individual chromosomes in multipolar daughter nuclei revealed a high frequency of nondisjunction events, resulting in a near-binomial allotment of sister chromatids to the daughter cells. CONCLUSION: The capability of multipolar mitoses to circumvent the spindle assembly checkpoint system typically results in a near-random distribution of chromosomes to daughter cells. Spindle multipolarity could thus be a highly efficient generator of genetically diverse minority clones in transformed cell populations.
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| 4. |
- Jin, Yuesheng, et al.
(författare)
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Distinct mitotic segregation errors mediate chromosomal instability in aggressive urothelial cancers.
- 2007
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Ingår i: Clinical Cancer Research. - 1078-0432. ; 13:6, s. 1703-1712
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Chromosomal instability (CIN) is believed to have an important role in the pathogenesis of urothelial cancer (UC). The aim of this study was to evaluate whether disturbances of mitotic segregation contribute to CIN in UC, if these processes have any effect on the course of disease, and how deregulation of these mechanisms affects tumor cell growth. Experimental Design: We developed molecular cytogenetic methods to classify mitotic segregation abnormalities in a panel of UC cell lines. Mitotic instabilities were then scored in biopsies from 52 UC patients and compared with the outcome of tumor disease. Finally, UC cells were exposed in vitro to a telomerase inhibitor to assess how this affects mitotic stability and cell proliferation. Results: Three distinct chromosome segregation abnormalities were identified: (a) telomere dysfunction, which triggers structural rearrangements and loss of chromosomes through anaphase bridging; (b) sister chromatid nondisjunction, which generates discrete chromosomal copy number variations; and (c) supernumerary centrosomes, which cause dramatic shifts in chromosome copy number through multipolar cell division. Chromosome segregation errors were already present in preinvasive tumors and a high rate mitotic instability was an independent predictor of poor survival. However, induction of even higher levels of the same segregation abnormalities in UC cells by telomerase inhibition in vitro led to reduced tumor cell proliferation and clonogenic survival. Conclusion: Several distinct chromosome segregation errors contribute to CIN in UC, and the rate of such mitotic errors has a significant effect on the clinical course. Efficient tumor cell proliferation may depend on the tight endogenous control of these processes.
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| 5. |
- Karlsson, Christine, et al.
(författare)
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Genetic intratumour heterogeneity in high-grade brain tumours is associated with telomere-dependent mitotic instability.
- 2007
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Ingår i: Neuropathology & Applied Neurobiology. - : Wiley. - 1365-2990 .- 0305-1846. ; 33:4, s. 440-454
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Tidskriftsartikel (refereegranskat)abstract
- Glioblastoma multiforme (GBM) and other high-grade brain tumours are typically characterized by complex chromosome abnormalities and extensive intratumour cytogenetic heterogeneity. The mechanisms behind this diversity have been little explored. In this study, we analysed the pattern of chromosome segregation at mitosis in 20 brain tumours. We found an abnormal segregation of chromatids at mitosis through anaphase bridging (10-25% of anaphase cells) in all 10 GBMs. Anaphase bridging was also found in two medulloblastomas (7-15%), one anaplastic astrocytoma (17%) and one oligodendroglioma (6%). These tumours showed a relatively high degree of cytogenetic complexity and heterogeneity. In contrast, cell division abnormalities were not found in low-grade brain tumours with less complex karyotypes, including two pilocytic astrocytomas and two ependymomas. Further analysis of two GBMs by fluorescence in situ hybridization with telomeric repeat probes revealed excessive shortening of TTAGGG repeats, indicating dysfunctional protection of chromosome ends. In xenografts established from these GBMs, there was a gradual reduction in cytogenetic heterogeneity through successive passages as the proportion of abnormally short telomeres was reduced and the frequency of anaphase bridges decreased from >25% to 0. However, bridging could be reintroduced in late-passage xenograft cells by pharmacological induction of telomere shortening, using a small-molecule telomerase inhibitor. Telomere-dependent abnormal segregation of chromosomes at mitosis is thus a common phenomenon in high-grade brain tumours and may be one important factor behind cytogenetic intratumour diversity in GBM.
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| 6. |
- Petersén, Åsa, et al.
(författare)
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Euploidy in somatic cells from R6/2 transgenic Huntington's disease mice
- 2005
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Ingår i: BMC Cell Biology. - : Springer Science and Business Media LLC. - 1471-2121. ; 6:34
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Tidskriftsartikel (refereegranskat)abstract
- Background: Huntington's disease (HD) is a hereditary neurodegenerative disorder caused by a CAG repeat expansion in the HD gene. The huntingtin protein expressed from HD has an unknown function but is suggested to interact with proteins involved in the cell division machinery. The R6/2 transgenic mouse is the most widely used model to study HD. In R6/2 fibroblast cultures, a reduced mitotic index and high frequencies of multiple centrosomes and aneuploid cells have recently been reported. Aneuploidy is normally a feature closely connected to neoplastic disease. To further explore this unexpected aspect of HD, we studied cultures derived from 6- and 12-week- old R6/2 fibroblasts, skeletal muscle cells, and liver cells. Results: Cytogenetic analyses revealed a high frequency of polyploid cells in cultures from both R6/2 and wild-type mice with the greatest proportions of polyploid cells in cultures derived from skeletal muscle cells of both genotypes. The presence of polyploid cells in skeletal muscle in vivo was confirmed by fluorescence in situ hybridisation with centromeric probes. Enlarged and supernumerary centrosomes were found in cultures from both R6/ 2 and wild-type mice. However, no aneuploid cells could be found in any of the tissues. Conclusion: We conclude that polyploid cells are found in fibroblast and skeletal muscle cultures derived from R6/2 and wild-type littermate mice and that aneuploidy is unlikely to be a hallmark of HD.
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| 7. |
- Stewénius, Ylva, et al.
(författare)
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Cryptic terminal chromosome rearrangements in colorectal carcinoma cell lines detected by subtelomeric FISH analysis.
- 2006
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Ingår i: Cytogenetic and Genome Research. - : S. Karger AG. - 1424-859X .- 1424-8581. ; 114:3-4, s. 257-262
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Tidskriftsartikel (refereegranskat)abstract
- Epithelial tumour karyotypes are often difficult to study by standard cytogenetic methods because of poor chromosome preparation quality and the high complexity of their genomic rearrangements. Subtelomeric fluorescence in situ hybridisation (FISH) has proved to be a useful method for detecting cryptic constitutional chromosomal rearrangements but little is known about its usefulness for tumour cytogenetic analysis. Using a combination of chromosome banding, multicolour karyotyping and subtelomeric FISH, five colorectal cancer cell lines were characterised. The resulting data were compared to results from previous studies by comparative genomic hybridisation and spectral karyotyping or multicolour FISH. Subtelomeric FISH made it possible to resolve several highly complex chromosome rearrangements, many of which had not been detected or were incompletely characterised by the other methods. In particular, previously undetected terminal imbalances were found in the two cell lines not showing microsatellite instability. Copyright (c) 2006 S. Karger AG, Basel
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| 8. |
- Stewénius, Ylva, et al.
(författare)
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Defective chromosome segregation and telomere dysfunction in aggressive Wilms' tumors
- 2007
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Ingår i: Clinical Cancer Research. - 1078-0432. ; 13:22, s. 6593-6602
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: In many childhood neoplasms, prognostic subgroups have been defined based on specific chromosome changes. In Wilms' tumor (WT), such subclassification has been hampered by the diverse and relatively unspecific pattern of chromosomal imbalances present in these tumors. Unspecific patterns of cytogenetic imbalances in tumors are often caused by mitotic segregation errors due to short dysfunctional telomeres. As an alternative to cytogenetic classification, we therefore have evaluated whether the rate of telomere-dependent chromosomal instability could influence the clinical course inWT patients. Experimental Design: Telomere function and mitotic segregation errors were assessed in 12 cultured tumors and in tumor tissue sections from 41 WT patients. Results: Abnormal telomere shortening was found in cultured cells and in tissue sections from highly aggressive tumors. In vitro, dysfunctional telomeres were associated to specific cell division abnormalities, including anaphase bridges and multipolar mitoses. Assessment of mitotic figures in tissue sections revealed that anaphase bridges and multipolar mitoses were predominantly, but not exclusively, present in high-risk tumors and were predictors of poor event-free and overall survival. Conclusions: Telomere-dependent mitotic instability is present in a subgroup of WT predominately consisting of high-risk tumors.
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| 9. |
- Stewénius, Ylva, et al.
(författare)
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High-resolution molecular cytogenetic analysis of Wilms tumors highlights diagnostic difficulties among small round cell kidney tumors.
- 2008
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Ingår i: Genes, Chromosomes and Cancer. - : Wiley. - 1045-2257 .- 1098-2264. ; 47:10, s. 845-852
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Tidskriftsartikel (refereegranskat)abstract
- Many solid tumors exhibit characteristic gene fusions, which are reflected by balanced translocations at the cytogenetic level. These changes might be useful diagnostic and prognostic tools. In Wilms tumor (WT, nephroblastoma) no fusions genes or recurrent balanced translocations have been described thus far. To screen for cryptic balanced translocations, we have analyzed 17 renal neoplasms, histopathologically classified as WT, by a combination of G-banding, multicolor FISH, and subtelomeric FISH. This approach revealed several submicroscopic chromosomal aberrations and three different seemingly balanced translocations, resulting in a heterozygous deletion of HACE1, an EWSR1/ERG fusion, and an EWSR1/FLI1 fusion, respectively. As EWSR1 rearrangements are known to be a characteristic of Ewing tumors (ET), our findings illustrate the diagnostic problems regarding small cell kidney tumors and strongly argue for the need of adjuvant diagnostic techniques in this group of neoplasms. In summary, our genomic screening approach proved efficient in finding structural chromosomal aberrations. The fact that no recurrent translocations were found in the WTs of this study argues against the presence of a frequent pathognomonic translocation in this disease entity. (c) 2008 Wiley-Liss, Inc.
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| 10. |
- Stewénius, Ylva
(författare)
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Mechanisms and Consequences of Chromosomal Instability in Malignant tumours
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, telomere deficiency with subsequent anaphase bridging was found to be associated with chromosomal instability in established colorectal cancer cell lines and in Wilms tumour. In colorectal cancer cell lines, anaphase bridging was observed to generate both numerical and structural chromosomal aberrations and was also associated with the presence of multipolar mitoses. In contrast to cells having undergone anaphase bridging, daughter cells from these multipolar mitotic figures were observed not to form clones in culture, possibly because of the severe aneuploidy which is the result of multipolar mitosis. Chromosomal instability was observed also in colorectal cancer cell lines with mutations in the mismatch repair genes. In Wilms tumour, chromosomal instability was found to be associated with an aggressive tumour phenotype and poor survival. Telomere shortening was more pronounced in the immature tumour components, which could explain the fact that anaphase bridges and multipolar mitoses were only observed in these tumour elements. Because of breakage-fusion-bridge cycles, chromosomal instability is associated with karyotypes with extensive structural chromosomal rearrangements. By applying a combination of subtelomeric FISH, G-banding and multicolour FISH, a high resolution for cytogenetic analysis of tumours with chromosomal instability could be obtained. This combined approached was used also to search for reciprocal translocations leading to fusion genes in Wilms tumour. Although the technique proved efficient, no recurrent reciprocal translocation was found in Wilms tumour. Our results indicate that telomere dependent chromosomal instability is present in both colorectal cancer and Wilms tumour and could be an important prognostic factor in Wilms tumours.
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