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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.

Gisselsson D, Håkanson U, Stoller P, Marti D, Jin Y, Rosengren AH, Stewénius Y, Kahl F, Panagopoulos I - PLoS ONE (2008)

Bottom Line: 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.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.The capability of multipolar mitoses to circumvent the spindle assembly checkpoint system typically results in a near-random distribution of chromosomes to daughter cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Clinical Genetics, Lund University Hospital, Lund, Sweden. david.gisselsson@med.lu.se

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 isomies 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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Related in: MedlinePlus

Models of sister chromatid separation.Segregation according to the total disjunction (A), total nondisjunction (B), and binomial random segregation (C) models exemplified for a disomic chromosome in a tripolar mitosis with the homologues positioned in different metaphase axes. Straight arrows indicate the number of possible segregation patterns according to each model, curved arrows indicate additional segregation patterns not drawn, red/green distinguishes the different homologues, and open/filled centromeric circles distinguish sister chromatids.
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pone-0001871-g004: Models of sister chromatid separation.Segregation according to the total disjunction (A), total nondisjunction (B), and binomial random segregation (C) models exemplified for a disomic chromosome in a tripolar mitosis with the homologues positioned in different metaphase axes. Straight arrows indicate the number of possible segregation patterns according to each model, curved arrows indicate additional segregation patterns not drawn, red/green distinguishes the different homologues, and open/filled centromeric circles distinguish sister chromatids.

Mentions: In order to investigate the frequency of nondisjunction in MM, we then compared the segregation patterns found in multipolar ana-telophase cells (Table 1; Figure 4) to three models of chromosomes segregation. The first of these postulated separation of all sister chromatids (complete disjunction), the second postulated no sister chromatid separation at all (complete nondisjunction), while the third model postulated that sister chromatid disjunction would be just as likely as nondisjunction (binomial chromatid segregation). Even though a total number of >60 000 cell divisions were scored in these experiments, only the disomic/tripolar category in all cell lines and the tetrasomic/tripolar category in WiT49 contained a sufficient number of counts to allow statistical testing. However, in all these cases the segregation patterns were significantly different from those expected from the first two segregation models, whereas the third model could not be refuted. Furthermore, in all categories of polarity, segregation patterns were observed that were incompatible with either one or both of the first two models (Table 1), e.g. 7-1-0 segregation in tetrasomic/tripolar mitosis, which can occur only if three of the four homologous chromosomes fail to undergo sister chromatid separation while the fourth undergoes separation. Taken together with the observations of a disrupted separase cycle, retained chromosomal AURKB and MAD2L1 foci at ana-telophase, unsynchronized centromere separation, and the finding of diplochromosomes, this strongly indicated that some sister chromatids separate regularly in MM whereas others do not, ultimately resulting in a segregation pattern which is not distinct from a random allotment of sister chromatids to the daughter cells.


When the genome plays dice: circumvention of the spindle assembly checkpoint and near-random chromosome segregation in multipolar cancer cell mitoses.

Gisselsson D, Håkanson U, Stoller P, Marti D, Jin Y, Rosengren AH, Stewénius Y, Kahl F, Panagopoulos I - PLoS ONE (2008)

Models of sister chromatid separation.Segregation according to the total disjunction (A), total nondisjunction (B), and binomial random segregation (C) models exemplified for a disomic chromosome in a tripolar mitosis with the homologues positioned in different metaphase axes. Straight arrows indicate the number of possible segregation patterns according to each model, curved arrows indicate additional segregation patterns not drawn, red/green distinguishes the different homologues, and open/filled centromeric circles distinguish sister chromatids.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2289843&req=5

pone-0001871-g004: Models of sister chromatid separation.Segregation according to the total disjunction (A), total nondisjunction (B), and binomial random segregation (C) models exemplified for a disomic chromosome in a tripolar mitosis with the homologues positioned in different metaphase axes. Straight arrows indicate the number of possible segregation patterns according to each model, curved arrows indicate additional segregation patterns not drawn, red/green distinguishes the different homologues, and open/filled centromeric circles distinguish sister chromatids.
Mentions: In order to investigate the frequency of nondisjunction in MM, we then compared the segregation patterns found in multipolar ana-telophase cells (Table 1; Figure 4) to three models of chromosomes segregation. The first of these postulated separation of all sister chromatids (complete disjunction), the second postulated no sister chromatid separation at all (complete nondisjunction), while the third model postulated that sister chromatid disjunction would be just as likely as nondisjunction (binomial chromatid segregation). Even though a total number of >60 000 cell divisions were scored in these experiments, only the disomic/tripolar category in all cell lines and the tetrasomic/tripolar category in WiT49 contained a sufficient number of counts to allow statistical testing. However, in all these cases the segregation patterns were significantly different from those expected from the first two segregation models, whereas the third model could not be refuted. Furthermore, in all categories of polarity, segregation patterns were observed that were incompatible with either one or both of the first two models (Table 1), e.g. 7-1-0 segregation in tetrasomic/tripolar mitosis, which can occur only if three of the four homologous chromosomes fail to undergo sister chromatid separation while the fourth undergoes separation. Taken together with the observations of a disrupted separase cycle, retained chromosomal AURKB and MAD2L1 foci at ana-telophase, unsynchronized centromere separation, and the finding of diplochromosomes, this strongly indicated that some sister chromatids separate regularly in MM whereas others do not, ultimately resulting in a segregation pattern which is not distinct from a random allotment of sister chromatids to the daughter cells.

Bottom Line: 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.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.The capability of multipolar mitoses to circumvent the spindle assembly checkpoint system typically results in a near-random distribution of chromosomes to daughter cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Clinical Genetics, Lund University Hospital, Lund, Sweden. david.gisselsson@med.lu.se

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 isomies 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.

Show MeSH
Related in: MedlinePlus