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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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Time-lapse 3D confocal observation of chromosome poleward movements during anaphase of meiosis II.(A) Movement of DNA beads (top) and meiotic chromosomes (lower) at different time points shown in minute in a timelapse 3D movie. M chromosomes represent maternal chromosomes. DNA beads and meiotic chromosomes are shown in green and spindle in red. Note that the apparent round morphology of DNA-bead spindle shown at 48 min was due to a slight spindle rotation in the Z dimension. (B) Entire oocyte showing synchronous anaphase events (including anaphase onset, chromosome poleward movement, spindle rotation, and polar body extrusion) in both the DNA bead-spindle (arrows) and the meiotic spindle (arrowheads).
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pone-0005249-g002: Time-lapse 3D confocal observation of chromosome poleward movements during anaphase of meiosis II.(A) Movement of DNA beads (top) and meiotic chromosomes (lower) at different time points shown in minute in a timelapse 3D movie. M chromosomes represent maternal chromosomes. DNA beads and meiotic chromosomes are shown in green and spindle in red. Note that the apparent round morphology of DNA-bead spindle shown at 48 min was due to a slight spindle rotation in the Z dimension. (B) Entire oocyte showing synchronous anaphase events (including anaphase onset, chromosome poleward movement, spindle rotation, and polar body extrusion) in both the DNA bead-spindle (arrows) and the meiotic spindle (arrowheads).

Mentions: To compare the rates of poleward movement of the DNA beads with that of the maternal chromosomes, time-lapse 3D confocal movies were made to follow the anaphase events (Figure 2, Supplementary Figure S1). First, we observed that the poleward movements of DNA beads and maternal chromosomes occurred almost synchronously after egg activation, suggesting that the forces that drove DNA bead movement were under the same cell cycle control as those moving the maternal chromosomes. Second, transition from metaphase to anaphase was coupled with re-orientation of the spindle such that the spindle was positioned ∼90° to the polar cortex where the polar body is extruded. Using Imaris 4D tracking software, the rate of poleward movement was calculated to be 0.24±0.06 µm/min (n = 3) and 0.28±0.06 µm/min (n = 3). Thus, DNA beads underwent poleward movement at a speed similar to that of the meiotic chromosomes.


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

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

Time-lapse 3D confocal observation of chromosome poleward movements during anaphase of meiosis II.(A) Movement of DNA beads (top) and meiotic chromosomes (lower) at different time points shown in minute in a timelapse 3D movie. M chromosomes represent maternal chromosomes. DNA beads and meiotic chromosomes are shown in green and spindle in red. Note that the apparent round morphology of DNA-bead spindle shown at 48 min was due to a slight spindle rotation in the Z dimension. (B) Entire oocyte showing synchronous anaphase events (including anaphase onset, chromosome poleward movement, spindle rotation, and polar body extrusion) in both the DNA bead-spindle (arrows) and the meiotic spindle (arrowheads).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0005249-g002: Time-lapse 3D confocal observation of chromosome poleward movements during anaphase of meiosis II.(A) Movement of DNA beads (top) and meiotic chromosomes (lower) at different time points shown in minute in a timelapse 3D movie. M chromosomes represent maternal chromosomes. DNA beads and meiotic chromosomes are shown in green and spindle in red. Note that the apparent round morphology of DNA-bead spindle shown at 48 min was due to a slight spindle rotation in the Z dimension. (B) Entire oocyte showing synchronous anaphase events (including anaphase onset, chromosome poleward movement, spindle rotation, and polar body extrusion) in both the DNA bead-spindle (arrows) and the meiotic spindle (arrowheads).
Mentions: To compare the rates of poleward movement of the DNA beads with that of the maternal chromosomes, time-lapse 3D confocal movies were made to follow the anaphase events (Figure 2, Supplementary Figure S1). First, we observed that the poleward movements of DNA beads and maternal chromosomes occurred almost synchronously after egg activation, suggesting that the forces that drove DNA bead movement were under the same cell cycle control as those moving the maternal chromosomes. Second, transition from metaphase to anaphase was coupled with re-orientation of the spindle such that the spindle was positioned ∼90° to the polar cortex where the polar body is extruded. Using Imaris 4D tracking software, the rate of poleward movement was calculated to be 0.24±0.06 µm/min (n = 3) and 0.28±0.06 µm/min (n = 3). Thus, DNA beads underwent poleward movement at a speed similar to that of the meiotic chromosomes.

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