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Kinetochore-independent chromosome poleward movement during anaphase of meiosis II in mouse eggs.

Deng M, Gao J, Suraneni P, Li R - PLoS ONE (2009)

Bottom Line: Disruption of dynein function abolished the poleward movements of DNA beads but not of the meiotic chromosomes, suggesting the existence of different dynein-dependent and dynein-independent force generation mechanisms for the chromosome poleward movement, and the latter may be dependent on the presence of kinetochores.Consistent with the observed DNA bead poleward movement, sperm haploid chromatin (which also induced bipolar spindle formation after injection to a metaphase egg without forming detectable kinetochore structures) also underwent similar poleward movement at anaphase as DNA beads.The results suggest that in the chromatin-induced meiotic spindles, kinetochore attachments to spindle microtubules are not absolutely required for chromatin poleward movements at anaphase.

View Article: PubMed Central - PubMed

Affiliation: Stowers Institute for Medical Research, Kansas City, Missouri, United States of America. MQD@stowers-institute.org

ABSTRACT
Kinetochores are considered to be the key structures that physically connect spindle microtubules to the chromosomes and play an important role in chromosome segregation during mitosis. Due to different mechanisms of spindle assembly between centrosome-containing mitotic cells and acentrosomal meiotic oocytes, it is unclear how a meiotic spindle generates the poleward forces to drive two rounds of meiotic chromosome segregation to achieve genome haploidization. We took advantage of the fact that DNA beads are able to induce bipolar spindle formation without kinetochores and studied the behavior of DNA beads in the induced spindle in mouse eggs during meiosis II. Interestingly, DNA beads underwent poleward movements that were similar in timing and speed to the meiotic chromosomes, although all the beads moved together to the same spindle pole. Disruption of dynein function abolished the poleward movements of DNA beads but not of the meiotic chromosomes, suggesting the existence of different dynein-dependent and dynein-independent force generation mechanisms for the chromosome poleward movement, and the latter may be dependent on the presence of kinetochores. Consistent with the observed DNA bead poleward movement, sperm haploid chromatin (which also induced bipolar spindle formation after injection to a metaphase egg without forming detectable kinetochore structures) also underwent similar poleward movement at anaphase as DNA beads. The results suggest that in the chromatin-induced meiotic spindles, kinetochore attachments to spindle microtubules are not absolutely required for chromatin poleward movements at anaphase.

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The effects of taxol on chromosome poleward movements during anaphase.(A) DNA beads (arrow) maintained at the equatorial position of the spindle after egg activation in the presence of 100 nM taxol. (B) The same egg shown in (A) showed anaphase onset and impaired poleward movement of maternal chromosomes. Note the cytokinetic furrow induced by the spindle midzone (arrow) and the lagging chromosomes. (C) Complete inhibition of chromosome poleward movement in a taxol-treated egg. Note that a cleavage furrow (arrow) is formed over the spindle midzone, suggesting that the egg did enter anaphase. (D) Quantification of chromosome poleward movements on both meiotic and DNA bead spindles in the presence of 100 nM taxol.
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pone-0005249-g005: The effects of taxol on chromosome poleward movements during anaphase.(A) DNA beads (arrow) maintained at the equatorial position of the spindle after egg activation in the presence of 100 nM taxol. (B) The same egg shown in (A) showed anaphase onset and impaired poleward movement of maternal chromosomes. Note the cytokinetic furrow induced by the spindle midzone (arrow) and the lagging chromosomes. (C) Complete inhibition of chromosome poleward movement in a taxol-treated egg. Note that a cleavage furrow (arrow) is formed over the spindle midzone, suggesting that the egg did enter anaphase. (D) Quantification of chromosome poleward movements on both meiotic and DNA bead spindles in the presence of 100 nM taxol.

Mentions: To test if microtubule depolymerization contributes to the observed DNA bead poleward movements, low concentrations of taxol (100 nM-10 µM) were used to block microtubule flux as previously reported [20], [37]. Poleward movements of both DNA beads and meiotic chromosomes were inhibited by taxol, resulting in DNA beads and most of the meiotic chromosomes staying at the equators of the spindles (Figure 5A–5C, arrows). A small percentage of eggs (18/53) showed partial inhibition of the maternal chromosome poleward movements with some lagging chromosomes at the equator regions (Figure 5B and 5D, arrows). The effects of taxol on DNA-bead and meiotic chromosome movements were unlikely due to cell cycle arrest as a result of possible checkpoint activation since typical telophase spindle morphology and anaphase spindle midzone-induced furrows were all observed in these eggs (Figure 5B and 5C, arrows), suggesting that cell cycle progression was unaffected by taxol treatment.


Kinetochore-independent chromosome poleward movement during anaphase of meiosis II in mouse eggs.

Deng M, Gao J, Suraneni P, Li R - PLoS ONE (2009)

The effects of taxol on chromosome poleward movements during anaphase.(A) DNA beads (arrow) maintained at the equatorial position of the spindle after egg activation in the presence of 100 nM taxol. (B) The same egg shown in (A) showed anaphase onset and impaired poleward movement of maternal chromosomes. Note the cytokinetic furrow induced by the spindle midzone (arrow) and the lagging chromosomes. (C) Complete inhibition of chromosome poleward movement in a taxol-treated egg. Note that a cleavage furrow (arrow) is formed over the spindle midzone, suggesting that the egg did enter anaphase. (D) Quantification of chromosome poleward movements on both meiotic and DNA bead spindles in the presence of 100 nM taxol.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2664963&req=5

pone-0005249-g005: The effects of taxol on chromosome poleward movements during anaphase.(A) DNA beads (arrow) maintained at the equatorial position of the spindle after egg activation in the presence of 100 nM taxol. (B) The same egg shown in (A) showed anaphase onset and impaired poleward movement of maternal chromosomes. Note the cytokinetic furrow induced by the spindle midzone (arrow) and the lagging chromosomes. (C) Complete inhibition of chromosome poleward movement in a taxol-treated egg. Note that a cleavage furrow (arrow) is formed over the spindle midzone, suggesting that the egg did enter anaphase. (D) Quantification of chromosome poleward movements on both meiotic and DNA bead spindles in the presence of 100 nM taxol.
Mentions: To test if microtubule depolymerization contributes to the observed DNA bead poleward movements, low concentrations of taxol (100 nM-10 µM) were used to block microtubule flux as previously reported [20], [37]. Poleward movements of both DNA beads and meiotic chromosomes were inhibited by taxol, resulting in DNA beads and most of the meiotic chromosomes staying at the equators of the spindles (Figure 5A–5C, arrows). A small percentage of eggs (18/53) showed partial inhibition of the maternal chromosome poleward movements with some lagging chromosomes at the equator regions (Figure 5B and 5D, arrows). The effects of taxol on DNA-bead and meiotic chromosome movements were unlikely due to cell cycle arrest as a result of possible checkpoint activation since typical telophase spindle morphology and anaphase spindle midzone-induced furrows were all observed in these eggs (Figure 5B and 5C, arrows), suggesting that cell cycle progression was unaffected by taxol treatment.

Bottom Line: Disruption of dynein function abolished the poleward movements of DNA beads but not of the meiotic chromosomes, suggesting the existence of different dynein-dependent and dynein-independent force generation mechanisms for the chromosome poleward movement, and the latter may be dependent on the presence of kinetochores.Consistent with the observed DNA bead poleward movement, sperm haploid chromatin (which also induced bipolar spindle formation after injection to a metaphase egg without forming detectable kinetochore structures) also underwent similar poleward movement at anaphase as DNA beads.The results suggest that in the chromatin-induced meiotic spindles, kinetochore attachments to spindle microtubules are not absolutely required for chromatin poleward movements at anaphase.

View Article: PubMed Central - PubMed

Affiliation: Stowers Institute for Medical Research, Kansas City, Missouri, United States of America. MQD@stowers-institute.org

ABSTRACT
Kinetochores are considered to be the key structures that physically connect spindle microtubules to the chromosomes and play an important role in chromosome segregation during mitosis. Due to different mechanisms of spindle assembly between centrosome-containing mitotic cells and acentrosomal meiotic oocytes, it is unclear how a meiotic spindle generates the poleward forces to drive two rounds of meiotic chromosome segregation to achieve genome haploidization. We took advantage of the fact that DNA beads are able to induce bipolar spindle formation without kinetochores and studied the behavior of DNA beads in the induced spindle in mouse eggs during meiosis II. Interestingly, DNA beads underwent poleward movements that were similar in timing and speed to the meiotic chromosomes, although all the beads moved together to the same spindle pole. Disruption of dynein function abolished the poleward movements of DNA beads but not of the meiotic chromosomes, suggesting the existence of different dynein-dependent and dynein-independent force generation mechanisms for the chromosome poleward movement, and the latter may be dependent on the presence of kinetochores. Consistent with the observed DNA bead poleward movement, sperm haploid chromatin (which also induced bipolar spindle formation after injection to a metaphase egg without forming detectable kinetochore structures) also underwent similar poleward movement at anaphase as DNA beads. The results suggest that in the chromatin-induced meiotic spindles, kinetochore attachments to spindle microtubules are not absolutely required for chromatin poleward movements at anaphase.

Show MeSH