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Budding yeast chromosome structure and dynamics during mitosis.

Pearson CG, Maddox PS, Salmon ED, Bloom K - J. Cell Biol. (2001)

Bottom Line: Centromeres are in a metaphase-like conformation, whereas chromosome arms are neither aligned nor separated before anaphase.The stretched chromatin was observed to segregate to the spindle pole bodies at rates greater than centromere to pole movement, indicative of rapid elastic recoil between the chromosome arm and the centromere.These results indicate that the elastic properties of DNA play an as of yet undiscovered role in the poleward movement of chromosome arms.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA. cgpearso@email.unc.edu

ABSTRACT
Using green fluorescent protein probes and rapid acquisition of high-resolution fluorescence images, sister centromeres in budding yeast are found to be separated and oscillate between spindle poles before anaphase B spindle elongation. The rates of movement during these oscillations are similar to those of microtubule plus end dynamics. The degree of preanaphase separation varies widely, with infrequent centromere reassociations observed before anaphase. Centromeres are in a metaphase-like conformation, whereas chromosome arms are neither aligned nor separated before anaphase. Upon spindle elongation, centromere to pole movement (anaphase A) was synchronous for all centromeres and occurred coincident with or immediately after spindle pole separation (anaphase B). Chromatin proximal to the centromere is stretched poleward before and during anaphase onset. The stretched chromatin was observed to segregate to the spindle pole bodies at rates greater than centromere to pole movement, indicative of rapid elastic recoil between the chromosome arm and the centromere. These results indicate that the elastic properties of DNA play an as of yet undiscovered role in the poleward movement of chromosome arms.

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Model of chromosome oscillations, alignment, and segregation.
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Figure 7: Model of chromosome oscillations, alignment, and segregation.

Mentions: The greatest physical evidence for tension-dependent chromatin stretching and elastic recoil during mitosis is apparent upon anaphase onset, when chromatin snaps toward the separating spindle pole body at rates much greater than exhibited by centromeres during anaphase A and B movements. A previous report indicated that a marker ∼23 kb from CEN3 separated by 1.8 μm in the 26-s interval observed, predicting a rapid separation rate of 3.6 μm/min (Straight et al. 1997). Using rapid image acquisition, we were able to obtain velocity measurements of these fast chromosome separation rates. Upon anaphase onset, spindle elongation and centromere movement to the spindle pole body began coincidentally and was followed by further stretching of the chromatin linking sister centromeres (Fig. 5 B and 7). This increase in distance from the spindle pole body is not evident in the GFP–Tub1 or Cse4–GFP analyses, indicating that the stretching occurs between the centromere and the chromosome markers. This stretching is presumably before the release of cohesion, since chromosome arms have not segregated (Fig. 7). Loss of cohesion creates a release of tension in the chromatin stretched between sister centromeres and causes chromosome arms to undergo a rapid elastic recoil toward the spindle pole body (Fig. 7). Because markers closer to the centromere segregate earlier than telomere proximal markers (Straight et al. 1997), the simplest model for the elastic recoil is a “zippering” effect that results in a progressive separation and recoil of the DNA toward the spindle pole bodies (Fig. 7). Interestingly, the rate of spindle elongation (labeled with Spc29–GFP, GFP–Tub1, Spc72–GFP, or Nuf2–GFP) did not exhibit rapid transient movements distinguishable from the normal rates of spindle elongation. This indicates that the polar forces involved in maintaining the proper spindle length during anaphase B spindle pole body separation are much greater than the forces provided by stretched chromosomes. The ability for stretched DNA to recoil in vivo is analogous to a histone-dependent folding mechanism where stretched nucleosomal DNA is placed under tension and then undergoes a reversible repacking (Cui and Bustamante 2000; Poirier et al. 2000).


Budding yeast chromosome structure and dynamics during mitosis.

Pearson CG, Maddox PS, Salmon ED, Bloom K - J. Cell Biol. (2001)

Model of chromosome oscillations, alignment, and segregation.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2199205&req=5

Figure 7: Model of chromosome oscillations, alignment, and segregation.
Mentions: The greatest physical evidence for tension-dependent chromatin stretching and elastic recoil during mitosis is apparent upon anaphase onset, when chromatin snaps toward the separating spindle pole body at rates much greater than exhibited by centromeres during anaphase A and B movements. A previous report indicated that a marker ∼23 kb from CEN3 separated by 1.8 μm in the 26-s interval observed, predicting a rapid separation rate of 3.6 μm/min (Straight et al. 1997). Using rapid image acquisition, we were able to obtain velocity measurements of these fast chromosome separation rates. Upon anaphase onset, spindle elongation and centromere movement to the spindle pole body began coincidentally and was followed by further stretching of the chromatin linking sister centromeres (Fig. 5 B and 7). This increase in distance from the spindle pole body is not evident in the GFP–Tub1 or Cse4–GFP analyses, indicating that the stretching occurs between the centromere and the chromosome markers. This stretching is presumably before the release of cohesion, since chromosome arms have not segregated (Fig. 7). Loss of cohesion creates a release of tension in the chromatin stretched between sister centromeres and causes chromosome arms to undergo a rapid elastic recoil toward the spindle pole body (Fig. 7). Because markers closer to the centromere segregate earlier than telomere proximal markers (Straight et al. 1997), the simplest model for the elastic recoil is a “zippering” effect that results in a progressive separation and recoil of the DNA toward the spindle pole bodies (Fig. 7). Interestingly, the rate of spindle elongation (labeled with Spc29–GFP, GFP–Tub1, Spc72–GFP, or Nuf2–GFP) did not exhibit rapid transient movements distinguishable from the normal rates of spindle elongation. This indicates that the polar forces involved in maintaining the proper spindle length during anaphase B spindle pole body separation are much greater than the forces provided by stretched chromosomes. The ability for stretched DNA to recoil in vivo is analogous to a histone-dependent folding mechanism where stretched nucleosomal DNA is placed under tension and then undergoes a reversible repacking (Cui and Bustamante 2000; Poirier et al. 2000).

Bottom Line: Centromeres are in a metaphase-like conformation, whereas chromosome arms are neither aligned nor separated before anaphase.The stretched chromatin was observed to segregate to the spindle pole bodies at rates greater than centromere to pole movement, indicative of rapid elastic recoil between the chromosome arm and the centromere.These results indicate that the elastic properties of DNA play an as of yet undiscovered role in the poleward movement of chromosome arms.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA. cgpearso@email.unc.edu

ABSTRACT
Using green fluorescent protein probes and rapid acquisition of high-resolution fluorescence images, sister centromeres in budding yeast are found to be separated and oscillate between spindle poles before anaphase B spindle elongation. The rates of movement during these oscillations are similar to those of microtubule plus end dynamics. The degree of preanaphase separation varies widely, with infrequent centromere reassociations observed before anaphase. Centromeres are in a metaphase-like conformation, whereas chromosome arms are neither aligned nor separated before anaphase. Upon spindle elongation, centromere to pole movement (anaphase A) was synchronous for all centromeres and occurred coincident with or immediately after spindle pole separation (anaphase B). Chromatin proximal to the centromere is stretched poleward before and during anaphase onset. The stretched chromatin was observed to segregate to the spindle pole bodies at rates greater than centromere to pole movement, indicative of rapid elastic recoil between the chromosome arm and the centromere. These results indicate that the elastic properties of DNA play an as of yet undiscovered role in the poleward movement of chromosome arms.

Show MeSH
Related in: MedlinePlus