scholarly journals Direct kinetochore–spindle pole connections are not required for chromosome segregation

2014 ◽  
Vol 206 (2) ◽  
pp. 231-243 ◽  
Author(s):  
Vitali Sikirzhytski ◽  
Valentin Magidson ◽  
Jonathan B. Steinman ◽  
Jie He ◽  
Maël Le Berre ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Mammalian Cells ◽  
Genetic Material ◽  
Spindle Pole ◽  
Chromosome Movement ◽  
Parallel Mechanisms ◽  
Laser Microbeam ◽  
Kinetochore Assembly ◽  
Spindle Poles

Segregation of genetic material occurs when chromosomes move to opposite spindle poles during mitosis. This movement depends on K-fibers, specialized microtubule (MT) bundles attached to the chromosomes′ kinetochores. A long-standing assumption is that continuous K-fibers connect every kinetochore to a spindle pole and the force for chromosome movement is produced at the kinetochore and coupled with MT depolymerization. However, we found that chromosomes still maintained their position at the spindle equator during metaphase and segregated properly during anaphase when one of their K-fibers was severed near the kinetochore with a laser microbeam. We also found that, in normal fully assembled spindles, K-fibers of some chromosomes did not extend to the spindle pole. These K-fibers connected to adjacent K-fibers and/or nonkinetochore MTs. Poleward movement of chromosomes with short K-fibers was uncoupled from MT depolymerization at the kinetochore. Instead, these chromosomes moved by dynein-mediated transport of the entire K-fiber/kinetochore assembly. Thus, at least two distinct parallel mechanisms drive chromosome segregation in mammalian cells.

scholarly journals A Functional Relationship between NuMA and Kid Is Involved in Both Spindle Organization and Chromosome Alignment in Vertebrate Cells

2003 ◽  
Vol 14 (9) ◽  
pp. 3541-3552 ◽  
Author(s):  
Aime A. Levesque ◽  
Louisa Howard ◽  
Michael B. Gordon ◽  
Duane A. Compton
Keyword(s):  
Mammalian Cells ◽  
Functional Relationship ◽  
Spindle Pole ◽  
Chromosome Movement ◽  
Spindle Poles ◽  
Chromosome Alignment ◽  
Stark Contrast ◽  
Bipolar Spindles

We examined spindle morphology and chromosome alignment in vertebrate cells after simultaneous perturbation of the chromokinesin Kid and either NuMA, CENP-E, or HSET. Spindle morphology and chromosome alignment after simultaneous perturbation of Kid and either HSET or CENP-E were no different from when either HSET or CENP-E was perturbed alone. However, short bipolar spindles with organized poles formed after perturbation of both Kid and NuMA in stark contrast to splayed spindle poles observed after perturbation of NuMA alone. Spindles were disorganized if Kid, NuMA, and HSET were perturbed, indicating that HSET is sufficient for spindle organization in the absence of Kid and NuMA function. In addition, chromosomes failed to align efficiently at the spindle equator after simultaneous perturbation of Kid and NuMA despite appropriate kinetochore-microtubule interactions that generated chromosome movement at normal velocities. These data indicate that a functional relationship between the chromokinesin Kid and the spindle pole organizing protein NuMA influences spindle morphology, and we propose that this occurs because NuMA forms functional linkages between kinetochore and nonkinetochore microtubules at spindle poles. In addition, these data show that both Kid and NuMA contribute to chromosome alignment in mammalian cells.

scholarly journals A novel chromosome segregation mechanism during female meiosis

2016 ◽  
Vol 27 (16) ◽  
pp. 2576-2589 ◽  
Author(s):  
Karen Perry McNally ◽  
Michelle T. Panzica ◽  
Taekyung Kim ◽  
Daniel B. Cortes ◽  
Francis J. McNally
Keyword(s):  
Chromosome Segregation ◽  
Meiotic Chromosome ◽  
Spindle Pole ◽  
Chromosome Movement ◽  
Female Meiosis ◽  
Spindle Poles ◽  
Wide Range ◽  
Chromosome Separation ◽  
Meiotic Spindles ◽  
Anaphase B

In a wide range of eukaryotes, chromosome segregation occurs through anaphase A, in which chromosomes move toward stationary spindle poles, anaphase B, in which chromosomes move at the same velocity as outwardly moving spindle poles, or both. In contrast, Caenorhabditis elegans female meiotic spindles initially shorten in the pole-to-pole axis such that spindle poles contact the outer kinetochore before the start of anaphase chromosome separation. Once the spindle pole-to-kinetochore contact has been made, the homologues of a 4-μm-long bivalent begin to separate. The spindle shortens an additional 0.5 μm until the chromosomes are embedded in the spindle poles. Chromosomes then separate at the same velocity as the spindle poles in an anaphase B–like movement. We conclude that the majority of meiotic chromosome movement is caused by shortening of the spindle to bring poles in contact with the chromosomes, followed by separation of chromosome-bound poles by outward sliding.

scholarly journals TRIM37 prevents formation of condensate-organized ectopic spindle poles to ensure mitotic fidelity

2021 ◽  
Vol 220 (7) ◽  
Author(s):  
Franz Meitinger ◽  
Dong Kong ◽  
Midori Ohta ◽  
Arshad Desai ◽  
Karen Oegema ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Ubiquitin Ligase ◽  
Spindle Pole ◽  
Mitotic Entry ◽  
Centriole Duplication ◽  
Mulibrey Nanism ◽  
Spindle Poles ◽  
Pathological Mechanism ◽  
Pericentriolar Material ◽  
Centrosomal Proteins

Centrosomes are composed of a centriolar core surrounded by pericentriolar material that nucleates microtubules. The ubiquitin ligase TRIM37 localizes to centrosomes, but its centrosomal roles are not yet defined. We show that TRIM37 does not control centriole duplication, structure, or the ability of centrioles to form cilia but instead prevents assembly of an ectopic centrobin-scaffolded structured condensate that forms by budding off of centrosomes. In ∼25% of TRIM37-deficient cells, the condensate organizes an ectopic spindle pole, recruiting other centrosomal proteins and acquiring microtubule nucleation capacity during mitotic entry. Ectopic spindle pole–associated transient multipolarity and multipolar segregation in TRIM37-deficient cells are suppressed by removing centrobin, which interacts with and is ubiquitinated by TRIM37. Thus, TRIM37 ensures accurate chromosome segregation by preventing the formation of centrobin-scaffolded condensates that organize ectopic spindle poles. Mutations in TRIM37 cause the disorder mulibrey nanism, and patient-derived cells harbor centrobin condensate-organized ectopic poles, leading us to propose that chromosome missegregation is a pathological mechanism in this disorder.

scholarly journals Nsk1 ensures accurate chromosome segregation by promoting association of kinetochores to spindle poles during anaphase B

2011 ◽  
Vol 22 (23) ◽  
pp. 4486-4502 ◽  
Author(s):  
Graham J. Buttrick ◽  
John C. Meadows ◽  
Theresa C. Lancaster ◽  
Vincent Vanoosthuyse ◽  
Lindsey A. Shepperd ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Spindle Pole Body ◽  
Spindle Pole ◽  
Growth Defect ◽  
Catalytic Subunits ◽  
Spindle Poles ◽  
Sister Chromatids ◽  
Anaphase B ◽  
Novel Protein

Type 1 phosphatase (PP1) antagonizes Aurora B kinase to stabilize kinetochore–microtubule attachments and to silence the spindle checkpoint. We screened for factors that exacerbate the growth defect of Δdis2 cells, which lack one of two catalytic subunits of PP1 in fission yeast, and identified Nsk1, a novel protein required for accurate chromosome segregation. During interphase, Nsk1 resides in the nucleolus but spreads throughout the nucleoplasm as cells enter mitosis. Following dephosphorylation by Clp1 (Cdc14-like) phosphatase and at least one other phosphatase, Nsk1 localizes to the interface between kinetochores and the inner face of the spindle pole body during anaphase. In the absence of Nsk1, some kinetochores become detached from spindle poles during anaphase B. If this occurs late in anaphase B, then the sister chromatids of unclustered kinetochores segregate to the correct daughter cell. These unclustered kinetochores are efficiently captured, retrieved, bioriented, and segregated during the following mitosis, as long as Dis2 is present. However, if kinetochores are detached from a spindle pole early in anaphase B, then these sister chromatids become missegregated. These data suggest Nsk1 ensures accurate chromosome segregation by promoting the tethering of kinetochores to spindle poles during anaphase B.

scholarly journals CENP-E Is Essential for Reliable Bioriented Spindle Attachment, but Chromosome Alignment Can Be Achieved via Redundant Mechanisms in Mammalian Cells

2001 ◽  
Vol 12 (9) ◽  
pp. 2776-2789 ◽  
Author(s):  
Bruce F. McEwen ◽  
Gordon K.T. Chan ◽  
Beata Zubrowski ◽  
Matthew S. Savoian ◽  
Matthew T. Sauer ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Protein Localization ◽  
Mitotic Arrest ◽  
Spindle Pole ◽  
Critical Determinant ◽  
Microtubule Binding ◽  
Checkpoint Protein ◽  
Spindle Poles ◽  
Chromosome Position ◽  
Chromosome Alignment

CENP-E is a kinesin-like protein that when depleted from mammalian kinetochores leads to mitotic arrest with a mixture of aligned and unaligned chromosomes. In the present study, we used immunofluorescence, video, and electron microscopy to demonstrate that depletion of CENP-E from kinetochores via antibody microinjection reduces kinetochore microtubule binding by 23% at aligned chromosomes, and severely reduces microtubule binding at unaligned chromosomes. Disruption of CENP-E function also reduces tension across the centromere, increases the incidence of spindle pole fragmentation, and results in monooriented chromosomes approaching abnormally close to the spindle pole. Nevertheless, chromosomes show typical patterns of congression, fast poleward motion, and oscillatory motions. Furthermore, kinetochores of aligned and unaligned chromosomes exhibit normal patterns of checkpoint protein localization. These data are explained by a model in which redundant mechanisms enable kinetochore microtubule binding and checkpoint monitoring in the absence of CENP-E at kinetochores, but where reduced microtubule-binding efficiency, exacerbated by poor positioning at the spindle poles, results in chronically monooriented chromosomes and mitotic arrest. Chromosome position within the spindle appears to be a critical determinant of CENP-E function at kinetochores.

scholarly journals Role of astral microtubules and actin in spindle orientation and migration in the budding yeast, Saccharomyces cerevisiae.

1992 ◽  
Vol 119 (3) ◽  
pp. 583-593 ◽  
Author(s):  
R E Palmer ◽  
D S Sullivan ◽  
T Huffaker ◽  
D Koshland
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Chromosome Segregation ◽  
Mother Cell ◽  
Fold Increase ◽  
Spindle Pole ◽  
Spindle Orientation ◽  
Temperature Sensitive ◽  
Chromosome Movement ◽  
Yeast Saccharomyces Cerevisiae ◽  
Cytoskeletal Elements

In the yeast Saccharomyces cerevisiae, before the onset of anaphase, the spindle apparatus is always positioned with one spindle pole at, or through, the neck between the mother cell and the growing bud. This spindle orientation enables proper chromosome segregation to occur during anaphase, allowing one replicated genome to be segregated into the bud and the other to remain in the mother cell. In this study, we synchronized a population of cells before the onset of anaphase such that > 90% of the cells in the population had spindles with the correct orientation, and then disrupted specific cytoskeletal elements using temperature-sensitive mutations. Disruption of either the astral microtubules or actin function resulted in improper spindle orientation in approximately 40-50% of the cells. When cells with disrupted astral microtubules or actin function entered into anaphase, there was a 100-200-fold increase in the frequency of binucleated cell bodies. Thus, the maintenance of proper spindle orientation by these cytoskeletal elements was essential for proper chromosome segregation. These data are consistent with the model that proper spindle orientation is maintained by directly or indirectly tethering the astral microtubules to the actin cytoskeleton. After nuclear migration, but before anaphase, bulk chromosome movement occurs within the nucleus apparently because the chromosomes are attached to a mobile spindle. The frequency and magnitude of bulk chromosome movement is greatly diminished by disruption of the astral microtubules but not by disruption of the nonkinetochore spindle microtubules. These results suggest that astral microtubules are not only important for spindle orientation before anaphase, but they also mediate force on the spindle, generating spindle displacement and in turn chromosome movement. Potential roles for this force in spindle assembly and orientation are discussed.

scholarly journals Chiasmata and the kinetochore component Dam1 are crucial for elimination of erroneous chromosome attachments and centromere oscillation at meiosis I

Open Biology ◽  
2021 ◽  
Vol 11 (2) ◽  
Author(s):  
Misuzu Wakiya ◽  
Eriko Nishi ◽  
Shinnosuke Kawai ◽  
Kohei Yamada ◽  
Kazuhiro Katsumata ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Spindle Pole ◽  
Oriented Attachment ◽  
Aurora B ◽  
Correction Factors ◽  
Homologous Chromosomes ◽  
Spindle Poles ◽  
Sister Chromatids ◽  
Potential Link ◽  
Meiosis I

Establishment of proper chromosome attachments to the spindle requires elimination of erroneous attachments, but the mechanism of this process is not fully understood. During meiosis I, sister chromatids attach to the same spindle pole (mono-oriented attachment), whereas homologous chromosomes attach to opposite poles (bi-oriented attachment), resulting in homologous chromosome segregation. Here, we show that chiasmata that link homologous chromosomes and kinetochore component Dam1 are crucial for elimination of erroneous attachments and oscillation of centromeres between the spindle poles at meiosis I in fission yeast. In chiasma-forming cells, Mad2 and Aurora B kinase, which provides time for attachment correction and destabilizes erroneous attachments, respectively, caused elimination of bi-oriented attachments of sister chromatids, whereas in chiasma-lacking cells, they caused elimination of mono-oriented attachments. In chiasma-forming cells, in addition, homologous centromere oscillation was coordinated. Furthermore, Dam1 contributed to attachment elimination in both chiasma-forming and chiasma-lacking cells, and drove centromere oscillation. These results demonstrate that chiasmata alter attachment correction patterns by enabling error correction factors to eliminate bi-oriented attachment of sister chromatids, and suggest that Dam1 induces elimination of erroneous attachments. The coincidental contribution of chiasmata and Dam1 to centromere oscillation also suggests a potential link between centromere oscillation and attachment elimination.

scholarly journals K-fiber bundles in the mitotic spindle are mechanically reinforced by Kif15

2021 ◽  
Author(s):  
Marcus A Begley ◽  
April L Solon ◽  
Elizabeth Mae Davis ◽  
Michael Grant Sherrill ◽  
Ryoma Ohi ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Mitotic Spindle ◽  
Mammalian Cells ◽  
Binding Ability ◽  
Microtubule Binding ◽  
Mechanical Integrity ◽  
Spindle Poles ◽  
Rigor State ◽  
Physical Response

The mitotic spindle, a self-constructed microtubule-based machine, segregates chromosomes during cell division. In mammalian cells, microtubule bundles called kinetochore-fibers (k-fibers) connect chromosomes to the spindle poles. Chromosome segregation thus depends on the mechanical integrity of k-fibers. Here, we investigate the physical and molecular basis of k-fiber bundle cohesion. We detach k-fibers from poles by laser ablation-based cutting, thus revealing the contribution of pole-localized forces to k-fiber cohesion. We then measure the physical response of the remaining kinetochore-bound segments of the k-fibers. We observe that microtubules within ablated k-fibers often splay apart from their minus-ends. Furthermore, we find that minus-end clustering forces induced by ablation seem at least partially responsible for k-fiber splaying. We also investigate the role of the k-fiber-binding kinesin-12 Kif15. We find that pharmacological inhibition of Kif15-microtubule binding reduces the mechanical integrity of k-fibers. In contrast, inhibition of its motor activity but not its microtubule binding ability, i.e., locking Kif15 into a rigor state, does not greatly affect splaying. Altogether, the data suggest that forces holding k-fibers together are of similar magnitude to other spindle forces, and that Kif15, acting as a microtubule crosslinker, helps fortify and repair k-fibers. This feature of Kif15 may help support robust k-fiber function and prevent chromosome segregation errors. [Media: see text] [Media: see text] [Media: see text]

scholarly journals Timing of centrosome separation is important for accurate chromosome segregation

2012 ◽  
Vol 23 (3) ◽  
pp. 401-411 ◽  
Author(s):  
William T. Silkworth ◽  
Isaac K. Nardi ◽  
Raja Paul ◽  
Alex Mogilner ◽  
Daniela Cimini
Keyword(s):  
Nuclear Envelope ◽  
Chromosome Segregation ◽  
Intermediate Stage ◽  
Spindle Pole ◽  
Cellular Space ◽  
Nuclear Envelope Breakdown ◽  
Spindle Poles ◽  
Centrosome Separation ◽  
Large Numbers ◽  
Close Proximity

Spindle assembly, establishment of kinetochore attachment, and sister chromatid separation must occur during mitosis in a highly coordinated fashion to ensure accurate chromosome segregation. In most vertebrate cells, the nuclear envelope must break down to allow interaction between microtubules of the mitotic spindle and the kinetochores. It was previously shown that nuclear envelope breakdown (NEB) is not coordinated with centrosome separation and that centrosome separation can be either complete at the time of NEB or can be completed after NEB. In this study, we investigated whether the timing of centrosome separation affects subsequent mitotic events such as establishment of kinetochore attachment or chromosome segregation. We used a combination of experimental and computational approaches to investigate kinetochore attachment and chromosome segregation in cells with complete versus incomplete spindle pole separation at NEB. We found that cells with incomplete spindle pole separation exhibit higher rates of kinetochore misattachments and chromosome missegregation than cells that complete centrosome separation before NEB. Moreover, our mathematical model showed that two spindle poles in close proximity do not “search” the entire cellular space, leading to formation of large numbers of syntelic attachments, which can be an intermediate stage in the formation of merotelic kinetochores.

scholarly journals Mitotic Chromosome Biorientation in Fission Yeast Is Enhanced by Dynein and a Minus-end–directed, Kinesin-like Protein

2007 ◽  
Vol 18 (6) ◽  
pp. 2216-2225 ◽  
Author(s):  
Ekaterina L. Grishchuk ◽  
Ilia S. Spiridonov ◽  
J. Richard McIntosh
Keyword(s):  
Fission Yeast ◽  
Chromosome Segregation ◽  
Mitotic Chromosome ◽  
Spindle Pole ◽  
Ultrastructural Analysis ◽  
Yeast Cells ◽  
Mitotic Spindles ◽  
Wild Type ◽  
Spindle Poles ◽  
Spindle Microtubules

Chromosome biorientation, the attachment of sister kinetochores to sister spindle poles, is vitally important for accurate chromosome segregation. We have studied this process by following the congression of pole-proximal kinetochores and their subsequent anaphase segregation in fission yeast cells that carry deletions in any or all of this organism's minus end–directed, microtubule-dependent motors: two related kinesin 14s (Pkl1p and Klp2p) and dynein. None of these deletions abolished biorientation, but fewer chromosomes segregated normally without Pkl1p, and to a lesser degree without dynein, than in wild-type cells. In the absence of Pkl1p, which normally localizes to the spindle and its poles, the checkpoint that monitors chromosome biorientation was defective, leading to frequent precocious anaphase. Ultrastructural analysis of mutant mitotic spindles suggests that Pkl1p contributes to error-free biorientation by promoting normal spindle pole organization, whereas dynein helps to anchor a focused bundle of spindle microtubules at the pole.

Sign in / Sign up

Export Citation Format

Share Document