scholarly journals CENP-32 is required to maintain centrosomal dominance in bipolar spindle assembly

2015 ◽  
Vol 26 (7) ◽  
pp. 1225-1237 ◽  
Author(s):  
Shinya Ohta ◽  
Laura Wood ◽  
Iyo Toramoto ◽  
Ken-Ichi Yagyu ◽  
Tatsuo Fukagawa ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Additional Data ◽  
Weak Interactions ◽  
Metaphase Plate ◽  
Spindle Pole ◽  
Animal Cells ◽  
Central Spindle ◽  
Spindle Poles ◽  
Spindle Microtubules ◽  
Bipolar Spindles

Centrosomes nucleate spindle formation, direct spindle pole positioning, and are important for proper chromosome segregation during mitosis in most animal cells. We previously reported that centromere protein 32 (CENP-32) is required for centrosome association with spindle poles during metaphase. In this study, we show that CENP-32 depletion seems to release centrosomes from bipolar spindles whose assembly they had previously initiated. Remarkably, the resulting anastral spindles function normally, aligning the chromosomes to a metaphase plate and entering anaphase without detectable interference from the free centrosomes, which appear to behave as free asters in these cells. The free asters, which contain reduced but significant levels of CDK5RAP2, show weak interactions with spindle microtubules but do not seem to make productive attachments to kinetochores. Thus CENP-32 appears to be required for centrosomes to integrate into a fully functional spindle that not only nucleates astral microtubules, but also is able to nucleate and bind to kinetochore and central spindle microtubules. Additional data suggest that NuMA tethers microtubules at the anastral spindle poles and that augmin is required for centrosome detachment after CENP-32 depletion, possibly due to an imbalance of forces within the spindle.

scholarly journals Central-spindle microtubules are strongly coupled to chromosomes during both anaphase A and anaphase B

2019 ◽  
Vol 30 (19) ◽  
pp. 2503-2514 ◽  
Author(s):  
Che-Hang Yu ◽  
Stefanie Redemann ◽  
Hai-Yin Wu ◽  
Robert Kiewisz ◽  
Tae Yeon Yoo ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Tomographic Reconstruction ◽  
Mitotic Spindles ◽  
Strongly Coupled ◽  
Central Spindle ◽  
Spindle Poles ◽  
Meiotic Spindles ◽  
Spindle Microtubules ◽  
Anaphase B ◽  
Chromosome Motion

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, that is, 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 toward spindle poles. In these systems, damaging central-spindle microtubules by laser ablation caused an immediate and complete cessation of chromosome motion, suggesting a strong coupling between central-spindle microtubules and chromosomes. Electron tomographic reconstruction revealed that the analyzed anaphase spindles all contain microtubules with both ends between segregating chromosomes. Our results provide new dynamical, functional, and ultrastructural characterizations of central-spindle microtubules during chromosome segregation in diverse spindles and suggest that central-spindle microtubules and chromosomes are strongly coupled in anaphase.

scholarly journals Central spindle microtubules are strongly coupled to chromosomes during both anaphase A and anaphase B

2019 ◽  
Author(s):  
Che-Hang Yu ◽  
Stefanie Redemann ◽  
Hai-Yin Wu ◽  
Robert Kiewisz ◽  
Tae Yeon Yoo ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Tomographic Reconstruction ◽  
Mitotic Spindles ◽  
Strongly Coupled ◽  
Central Spindle ◽  
Spindle Poles ◽  
Meiotic Spindles ◽  
Spindle Microtubules ◽  
Anaphase B ◽  
Chromosome Motion

AbstractSpindle 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 immediate and complete cessation of chromosome motion, suggesting a strong coupling between central spindle microtubules and chromosomes. Electron tomographic reconstruction revealed that the analyzed anaphase spindles all contain microtubules with both ends between segregating chromosomes. Our results provide new dynamical, functional, and ultrastructural characterizations of central spindle microtubules during chromosome segregation in diverse spindles, and suggest that central spindle microtubules and chromosomes are strongly coupled in anaphase.

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.

Chromosomes attain a metaphase position on half-spindles in the absence of an opposing spindle pole

1992 ◽  
Vol 103 (1) ◽  
pp. 125-130
Author(s):  
R.J. Leslie
Keyword(s):  
Metaphase Plate ◽  
Spindle Pole ◽  
Normal Density ◽  
Bipolar Spindle ◽  
In Vivo Experiments ◽  
Culture Cells ◽  
Spindle Poles ◽  
Metastable Condition ◽  
Spindle Microtubules

To examine the relative roles of chromosomes, spindle poles and microtubules in the formation of the metaphase spindle and metakinesis, I have experimentally placed an extra centrosome-free pronucleus close to a forming bipolar spindle in a living cell. The chromosomes from the extra nucleus induce the formation of an extra half-spindle from one pole of the otherwise normal bipolar spindle with chromosomes positioned at the putative metaphase plate. I conclude that chromosomes determine the location of half-spindles by sustaining a higher than normal density of microtubules. These results are surprising for two reasons: first, because previous in vivo experiments in tissue culture cells show that mono-oriented chromosomes with functional attachments to spindle microtubules do not support half-spindle formation but oscillate unstably or move to one spindle pole. Additionally, the generally accepted view is that chromosomes attain a metastable condition at the metaphase plate as a result of a balance between forces directed to opposite spindle poles. However, our observation that chromosomes on extra half-spindles attain a metastable position in the absence of an opposing spindle pole, suggests that Ostergren's model does not account for metakinesis in sea urchin embryos.

scholarly journals KLP-7 acts through the Ndc80 complex to limit pole number in C. elegans oocyte meiotic spindle assembly

2015 ◽  
Vol 210 (6) ◽  
pp. 917-932 ◽  
Author(s):  
Amy A. Connolly ◽  
Kenji Sugioka ◽  
Chien-Hui Chuang ◽  
Joshua B. Lowry ◽  
Bruce Bowerman
Keyword(s):  
Chromosome Segregation ◽  
Spindle Assembly ◽  
Spindle Pole ◽  
Meiotic Spindle ◽  
Meiotic Cell ◽  
Bipolar Structure ◽  
C Elegans ◽  
Spindle Poles ◽  
Ndc80 Complex ◽  
Bipolar Spindles

During oocyte meiotic cell division in many animals, bipolar spindles assemble in the absence of centrosomes, but the mechanisms that restrict pole assembly to a bipolar state are unknown. We show that KLP-7, the single mitotic centromere–associated kinesin (MCAK)/kinesin-13 in Caenorhabditis elegans, is required for bipolar oocyte meiotic spindle assembly. In klp-7(−) mutants, extra microtubules accumulated, extra functional spindle poles assembled, and chromosomes frequently segregated as three distinct masses during meiosis I anaphase. Moreover, reducing KLP-7 function in monopolar klp-18(−) mutants often restored spindle bipolarity and chromosome segregation. MCAKs act at kinetochores to correct improper kinetochore–microtubule (k–MT) attachments, and depletion of the Ndc-80 kinetochore complex, which binds microtubules to mediate kinetochore attachment, restored bipolarity in klp-7(−) mutant oocytes. We propose a model in which KLP-7/MCAK regulates k–MT attachment and spindle tension to promote the coalescence of early spindle pole foci that produces a bipolar structure during the acentrosomal process of oocyte meiotic spindle assembly.

Meiosis in Coprinus Lagopus: A Comparative Study with Light and Electron Microscopy

1967 ◽  
Vol 2 (4) ◽  
pp. 529-536
Author(s):  
B. C. LU
Keyword(s):  
Nuclear Fusion ◽  
Light And Electron Microscopy ◽  
Central Component ◽  
Fruiting Bodies ◽  
Homologous Pairing ◽  
Animal Cells ◽  
Characteristic Structure ◽  
Homologous Chromosomes ◽  
Central Spindle ◽  
Spindle Microtubules

Meiosis within fruiting bodies of Coprinus lagopus Fr. is closely synchronized. This conveniently facilitates joint light- and electron-microscope observations. Before nuclear fusion the chromatin appears diffuse in the light microscope; after nuclear fusion individual chromosomes can be recognized. In the electron micrographs the chromatin of pre-fusion and early fusion nuclei cannot be recognized as defined structures with the fixation and staining procedures employed. At the time of synapsis the lateral components of the synaptinemal complexes can be seen in the micrographs. The pairing process of the two chromosomes of the homologous pairs is believed to involve two steps: (1) two homologous chromosomes become aligned in parallel, and (2) pairing occurs by formation of the synaptinemal complex including the central synaptic component. The term synaptic centre is coined for the central component, which is believed to be the zone where crossing-over occurs. The formation of this structure in relation to homologous pairing, and the structural organization of the synaptinemal complexes are discussed. At meiotic metaphase, the chromosomes congregate around the central spindle microtubules. They are contracted and contain densely packed chromatin fibrils. Two types of spindle microtubules are demonstrated: (1) the chromosomal microtubules directly connecting the chromosomes to the centrosomes, and (2) the central spindle microtubules connecting the two centrosomes. The centrosomes are round, fibril-containing bodies approximately 0.3 µ in diameter. They have been observed outside the nuclear envelope at pachytene, but do not show the characteristic structure normally found in animal cells.

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 Kinetochore-mediated outward force promotes spindle pole separation in fission yeast

2019 ◽  
Vol 30 (22) ◽  
pp. 2802-2813 ◽  
Author(s):  
Yutaka Shirasugi ◽  
Masamitsu Sato
Keyword(s):  
Fission Yeast ◽  
Motor Proteins ◽  
Spindle Assembly ◽  
Spindle Pole ◽  
Double Knockout ◽  
Bipolar Spindle ◽  
Spindle Poles ◽  
Bipolar Spindles ◽  
Meiosis I

Bipolar spindles are organized by motor proteins that generate microtubule-­dependent forces to separate the two spindle poles. The fission yeast Cut7 (kinesin-5) is a plus-end-directed motor that generates the outward force to separate the two spindle poles, whereas the minus-end-directed motor Pkl1 (kinesin-14) generates the inward force. Balanced forces by these antagonizing kinesins are essential for bipolar spindle organization in mitosis. Here, we demonstrate that chromosomes generate another outward force that contributes to the bipolar spindle assembly. First, it was noted that the cut7 pkl1 double knockout failed to separate spindle poles in meiosis I, although the mutant is known to succeed it in mitosis. It was assumed that this might be because meiotic kinetochores of bivalent chromosomes joined by cross-overs generate weaker tensions in meiosis I than the strong tensions in mitosis generated by tightly tethered sister kinetochores. In line with this idea, when meiotic mono-oriented kinetochores were artificially converted to a mitotic bioriented layout, the cut7 pkl1 mutant successfully separated spindle poles in meiosis I. Therefore, we propose that spindle pole separation is promoted by outward forces transmitted from kinetochores to spindle poles through microtubules.

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 Aster-free spindle poles in insect spermatocytes: evidence for chromosome-induced spindle formation?

1986 ◽  
Vol 102 (5) ◽  
pp. 1679-1687 ◽  
Author(s):  
W Steffen ◽  
H Fuge ◽  
R Dietz ◽  
M Bastmeyer ◽  
G Müller
Keyword(s):  
Spindle Pole ◽  
Serial Sections ◽  
Spindle Formation ◽  
Microtubule Polymerization ◽  
Spindle Poles ◽  
Pericentriolar Material ◽  
Lysis Buffer ◽  
Bipolar Spindles

Tipulid spermatocytes form normally functioning bipolar spindles after one of the centrosomes is experimentally dislocated from the nucleus in late diakinesis (Dietz, R., 1959, Z. Naturforsch., 14b:749-752; Dietz, R., 1963, Zool. Anz. Suppl., 23:131-138; Dietz, R., 1966, Heredity, 19:161-166). The possibility that dissociated pericentriolar material (PCM) is nevertheless responsible for the formation of the spindle in these cells cannot be ruled out based on live observation. In studying serial sections of complete cells and of lysed cells, it was found that centrosome-free spindle poles in the crane fly show neither pericentriolar-like material nor aster microtubules, whereas the displaced centrosomes appear complete, i.e., consist of a centriole pair, aster microtubules, and PCM. Exposure to a lysis buffer containing tubulin resulted in an increase of centrosomal asters due to aster microtubule polymerization. Aster-free spindle poles did not show any reaction, also indicating the absence of PCM at these poles. The results favor the hypothesis of chromosome-induced spindle pole formation at the onset of prometaphase and the dispensability of PCM in Pales.

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