Dynein Antagonizes Eg5 by Crosslinking and Sliding Antiparallel Microtubules (original) (raw)
Related papers
The centromere geometry essential for keeping mitosis error free is controlled by spindle forces
Nature, 2007
Accurate segregation of chromosomes, essential for the stability of genome, depends on 'biorientation'-simultaneous attachment of each individual chromosome to both poles of the mitotic spindle 1. On bioriented chromosomes, kinetochores (macromolecular complexes that attach the chromosome to the spindle) reside on the opposite sides of chromosome's centromere 2. In contrast, sister kinetochores shift toward one side of the centromere on 'syntelic' chromosomes that erroneously attach to one spindle pole with both sister kinetochores. Syntelic attachments often arise during spindle assembly and must be corrected to prevent chromosome loss 3. It is assumed that restoration of proper centromere architecture occurs automatically due to elastic properties of the centromere 1, 2. Here we test this assumption by combining laser microsurgery and chemical biology assays. We find that kinetochores of syntelic chromosomes remain juxtaposed upon detachment from spindle microtubules. These findings reveal that correction of syntelic attachments involves an extra step that has previously been overlooked: external forces must be applied to move sister kinetochores to the opposite sides of the centromere. Further, we demonstrate that shape of the centromere is important for spindle assembly, as bipolar spindles do not form is cells lacking centrosomes when multiple chromosomes with juxtaposed kinetochores are present. Thus, proper architecture of the centromere makes an important contribution to achieving high fidelity of chromosome segregation. Kinetochores on bioriented chromosomes are positioned on the opposite sides of the centromere 2. However, during mitotic spindle formation both sister kinetochores sometimes attach to the same spindle pole becoming 'syntelic'. Under this condition, microtubuledependent forces shift sister kinetochores to the same side of the centromere. As syntelic attachment would lead to aneuploidy, this configuration is not stable 4,5. Kinetochore fibres (K-fibres) on syntelic chromosomes depolymerize so that the chromosome moves to the spindle pole where at least one of the two kinetochores detaches from microtubules 6-8. Detached kinetochores can then connect to microtubules from the opposite spindle pole to achieve proper bi-orientation. However, for this mechanism to work properly the shape of the centromere must be restored such that sister kinetochores return to opposite sides of the centromere. It is
Chromosome Tug of War: Dicentric Chromosomes and the Centromere Strength Hypothesis
Cells
It has been 70 years since the concept of varied centromere strengths was introduced based on the behavior of dicentric chromosomes. One of the key conclusions from those early experiments was that some centromeres could pull with sufficient force to break a dicentric chromosome bridge, while others could not. In the ensuing decades there have been numerous studies to characterize strengths of the various components involved, such as the spindle, the kinetochore, and the chromosome itself. We review these various measurements to determine if the conclusions about centromere strength are supported by current evidence, with special attention to characterization of Drosophila melanogaster kinetochores upon which the original conclusions were based.
The Journal of Cell Biology, 1996
We used video-light microscopy and laser microsurgery to test the hypothesis that as a bioriented prometaphase chromosome changes position in PtK1 cells, the kinetochore moving away from its associated pole (AP) exerts a pushing force on the centromere. When we rapidly severed congressing chromosomes near the spindle equator between the sister kinetochores, the kinetochore that was originally "leading" the motion towards a pole (P) always (17/17 cells) continued moving P whereas the "trailing" kinetochore moving AP always stopped moving as soon as the operation was completed. This trailing kinetochore then initiated motion towards the pole it was originally moving away from up to 50 s later. The same result was observed (15/15 cells) when we selectively destroyed the leading (P moving) kinetochore on a congressing chromosome positioned 1>3 ~m from the pole it was moving away from. When we conducted this experiment on congressing chromosomes positioned within 3 txm of the pole, the centromere region either stopped moving, before switching into motion towards the near pole (2/4 cells), or it continued to move AP for 30-44 s (2/4 cells) before switching into P motion. Finally, kinetochorefree chromosome fragments, generated in the polar regions of PtK1 spindles, were ejected AP and often towards the spindle equator at ~2 ~rn/min. From these data we conclude that the kinetochore moving AP on a moving chromosome does not exert a significant pushing force on the chromosome. Instead, our results reveal that, when not generating a P force, kinetochores are in a "neutral" state that allows them to remain stationary or to coast AP in response to external forces sufficient to allow their K-fiber to elongate.
Centromere Tethering Confines Chromosome Domains
Molecular Cell, 2013
The organization of chromosomes into territories plays an important role in a wide range of cellular processes, including gene expression, transcription, and DNA repair. Current understanding has largely excluded the spatiotemporal dynamic fluctuations of the chromatin polymer. We combine in vivo chromatin motion analysis with mathematical modeling to elucidate the physical properties that underlie the formation and fluctuations of territories. Chromosome motion varies in predicted ways along the length of the chromosome, dependent on tethering at the centromere. Detachment of a tether upon inactivation of the centromere results in increased spatial mobility. A confined bead-spring chain tethered at both ends provides a mechanism to generate observed variations in local mobility as a function of distance from the tether. These predictions are realized in experimentally determined higher effective spring constants closer to the centromere. The dynamic fluctuations and territorial organization of chromosomes are, in part, dictated by tethering at the centromere.
Nature Cell Biology, 2012
Loss of spindle-pole integrity during mitosis leads to multipolarity independent of centrosome amplification 1-4 . Multipolar-spindle conformation favours incorrect kinetochore-microtubule attachments, compromising faithful chromosome segregation and daughter-cell viability 5,6 . Spindle-pole organization influences and is influenced by kinetochore activity 7,8 , but the molecular nature behind this critical force balance is unknown. CLASPs are microtubule-, kinetochore-and centrosome-associated proteins whose functional perturbation leads to three main spindle abnormalities: monopolarity, short spindles and multipolarity 9-13 . The first two reflect a role at the kinetochore-microtubule interface through interaction with specific kinetochore partners 10,11,14 , but how CLASPs prevent spindle multipolarity remains unclear. Here we found that human CLASPs ensure spindle-pole integrity after bipolarization in response to CENP-E-and Kid-mediated forces from misaligned chromosomes. This function is independent of end-on kinetochore-microtubule attachments and involves the recruitment of ninein to residual pericentriolar satellites. Distinctively, multipolarity arising through this mechanism often persists through anaphase. We propose that CLASPs and ninein confer spindle-pole resistance to traction forces exerted during chromosome congression, thereby preventing irreversible spindle multipolarity and aneuploidy.
Non-specific (entropic) forces as major determinants of the structure of mammalian chromosomes
Chromosome Research, 2011
Four specific forces (H-bonds, van der Waals forces, hydrophobic and charge interactions) shape the structure of proteins, and many biologists assume they will determine the shape of all structures in the cell. However, as the mass and contour length of a human chromosome are~7 orders of magnitude larger than those of a typical protein, additional forces can become significant. We review evidence that additional non-specific (entropic) forces are major determinants of chromosomal shape and position. They are sufficient to drive the segregation (de-mixing) of newly replicated DNA to the poles of bacterial cells, while an entropic centrifuge can both form human chromosomes into territories and position them appropriately in nuclei; more locally, a depletion attraction can loop bacterial and human genomes.
Centromere mechanical maturation during mammalian cell mitosis
Nature Communications
During mitosis, tension develops across the centromere as a result of spindle-based forces. Metaphase tension may be critical in preventing mitotic chromosome segregation errors, however, the nature of force transmission at the centromere and the role of centromere mechanics in controlling metaphase tension remains unknown. We combined quantitative, biophysical microscopy with computational analysis to elucidate the mechanics of the centromere in unperturbed, mitotic human cells. We discovered that the mechanical stiffness of the human centromere matures during mitotic progression, which leads to amplified centromere tension specifically at metaphase. Centromere mechanical maturation is disrupted across multiple aneuploid cell lines, leading to a weak metaphase tension signal. Further, increasing deficiencies in centromere mechanical maturation are correlated with rising frequencies of lagging, merotelic chromosomes in anaphase, leading to segregation defects at telophase. Thus, we reveal a centromere maturation process that may be critical to the fidelity of chromosome segregation during mitosis.
2016
The spindle checkpoint ensures that newly born cells receive one copy of each chromosome by preventing chromosomes from segregating until they are all correctly attached to the spindle. The checkpoint monitors tension to distinguish between correctly aligned chromosomes and those with both sisters attached to the same spindle pole. Tension arises when sister kinetochores attach to and are pulled toward opposite poles, stretching the chromatin around centromeres and elongating kinetochores. We distinguished between two hypotheses for where the checkpoint monitors tension: between the kinetochores, by detecting alterations in the distance between them, or by responding to changes in the structure of the kinetochore itself. To distinguish these models, we inhibited chromatin stretch by tethering sister chromatids together by binding a tetrameric form of the Lac repressor to arrays of the Lac operator located on either side of a centromere. Inhibiting chromatin stretch did not activate ...