Pericentric chromatin loops function as a nonlinear spring in mitotic force balance (original) (raw)
Related papers
Pericentric Chromatin Is an Elastic Component of the Mitotic Spindle
Current Biology, 2007
Background: Prior to chromosome segregation, the mitotic spindle bi-orients and aligns sister chromatids along the metaphase plate. During metaphase, spindle length remains constant, which suggests that spindle forces (inward and outward) are balanced. The contribution of microtubule motors, regulators of microtubule dynamics, and cohesin to spindle stability has been previously studied. In this study, we examine the contribution of chromatin structure on kinetochore positioning and spindle-length control. After nucleosome depletion, by either histone H3 or H4 repression, spindle organization was examined by live-cell fluorescence microscopy. Results: Histone repression led to a 2-fold increase in sister-centromere separation and an equal increase in metaphase spindle length. Histone H3 repression does not impair kinetochores, whereas H4 repression disrupts proper kinetochore function. Deletion of outward force generators, kinesins Cin8p and Kip1p, shortens the long spindles observed in histone-repressed cells. Oscillatory movements of individual sister chromatid pairs are not altered after histone repression. Conclusions: The increase in spindle length upon histone repression and restoration of wild-type spindle length by the loss of plus-end-directed motors suggests that during metaphase, centromere separation and spindle length are governed in part by the stretching of pericentric chromatin. Chromatin is an elastic molecule that is stretched in direct opposition to the outward force generators Cin8p and Kip1p. Thus, we assign a new role to chromatin packaging as an integral biophysical component of the mitotic apparatus.
Annual Review of Genetics, 2008
Accurate segregation of duplicated chromosomes ensures that daughter cells get one and only one copy of each chromosome. Errors in chromosome segregation result in aneuploidy and have severe consequences on human health. Incorrect chromosome number and chromosomal instability are hallmarks of tumor cells. Hence, segregation errors are thought to be a major cause of tumorigenesis. A study of the physical mechanical basis of chromosome segregation is essential to understand the processes that can lead to errors. Tremendous progress has been made in recent years in identifying the proteins necessary for chromosome movement and segregation, but the mechanism and structure of critical force generating components and the molecular basis of centromere stiffness remain poorly understood.
Biochimie, 2010
The mitotic spindle is a structure that forms during mitosis to help ensure that each daughter cell receives a full complement of genetic material. In metaphase, the spindle contains microtubules that nucleate inward from two opposing poles. Chromosomes are attached to plus-ends of these microtubules via protein structures called kinetochores. The centromere is the specific region of kinetochore attachment on the chromosome. Chromatin surrounding the centromere (pericentric chromatin) is subject to microtubule-based forces and is commonly modeled as a linear spring, where the force that it exerts is proportional to the distance that it is stretched. We have incorporated physically based models of chromatin to create more accurate and predictive models of the spindle. In addition, using fluorescence microscopy and motion analysis of fluorescently labeled chromatin spots we discovered that pericentric chromatin is restrained relative to free diffusive motion. The characterization of chromatin is crucial to understand mitotic spindle stability and to understand the cell cycle checkpoint regulating anaphase onset.
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.
Cell division through proper spindle formation is one of the key puzzles in cell biology. In most mammalian cells, chromosomes spontaneously arrange to achieve a stable bipolar spindle during metaphase which eventually ensures proper segregation of the DNA into the daughter cells. In this paper, we present a robust three-dimensional mechanistic model to investigate the formation and maintenance of a bipolar mitotic spindle in mammalian cells under different physiological constraints. Using realistic parameters, we test spindle viability by measuring the spindle length and studying the chromosomal configuration. The model strikingly predicts a feature of the spindle instability arising from the insufficient intercentrosomal angular separation and impaired sliding of the interpolar microtubules. In addition, our model successfully reproduces chromosomal patterns observed in mammalian cells, when activity of different motor proteins is perturbed.
Chromosome Movement in Mitosis Requires Microtubule Anchorage at Spindle Poles
Journal of Cell Biology, 2001
Anchorage of microtubule minus ends at spindle poles has been proposed to bear the load of poleward forces exerted by kinetochore-associated motors so that chromosomes move toward the poles rather than the poles toward the chromosomes. To test this hypothesis, we monitored chromosome movement during mitosis after perturbation of nuclear mitotic apparatus protein (NuMA) and the human homologue of the KIN C motor family (HSET), two noncentrosomal proteins involved in spindle pole organization in animal cells. Perturbation of NuMA alone disrupts spindle pole organization and delays anaphase onset, but does not alter the velocity of oscillatory chromosome movement in prometaphase. Perturbation of HSET alone increases the duration of prometaphase, but does not alter the velocity of chromosome movement in prometaphase or anaphase. In contrast, simultaneous perturbation of both HSET and NuMA severely suppresses directed chromosome movement in prometaphase. Chromosomes coalesce near the cen...
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
2019
Spindle microtubules, whose dynamics vary over time and at different locations, cooperatively drive chromosome segregation. Measurements of microtubule dynamics and spindle ultrastructure can provide insight into the behaviors of microtubules, helping elucidate the mechanism of chromosome segregation. Much work has focused on the dynamics and organization of kinetochore microtubules, i.e. on the region between chromosomes and poles. In comparison, microtubules in the central spindle region, between segregating chromosomes, have been less thoroughly characterized. Here, we report measurements of the movement of central spindle microtubules during chromosome segregation in human mitotic spindles, and Caenorhabditis elegans mitotic and female meiotic spindles. We found that these central spindle microtubules slide apart at the same speed as chromosomes, even as chromosomes move towards spindle poles. In these systems, damaging central spindle microtubules by laser ablation caused an im...