scholarly journals CLASP2 binding to curved microtubule tips promotes flux and stabilizes kinetochore attachments

2019 ◽  
pp. jcb.201905080 ◽  
Author(s):  
Hugo Girão ◽  
Naoyuki Okada ◽  
Tony A. Rodrigues ◽  
Alexandra O. Silva ◽  
Ana C. Figueiredo ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Protein Interaction ◽  
Half Life ◽  
Spindle Assembly Checkpoint ◽  
Underlying Mechanism ◽  
Microtubule Dynamics ◽  
Microtubule Depolymerization ◽  
Binding Properties ◽  
Chromosome Congression ◽  
Self Association

CLASPs are conserved microtubule plus-end–tracking proteins that suppress microtubule catastrophes and independently localize to kinetochores during mitosis. Thus, CLASPs are ideally positioned to regulate kinetochore–microtubule dynamics required for chromosome segregation fidelity, but the underlying mechanism remains unknown. Here, we found that human CLASP2 exists predominantly as a monomer in solution, but it can self-associate through its C-terminal kinetochore-binding domain. Kinetochore localization was independent of self-association, and driving monomeric CLASP2 to kinetochores fully rescued normal kinetochore–microtubule dynamics, while partially sustaining mitosis. CLASP2 kinetochore localization, recognition of growing microtubule plus-ends through EB–protein interaction, and the ability to associate with curved microtubule protofilaments through TOG2 and TOG3 domains independently sustained normal spindle length, timely spindle assembly checkpoint satisfaction, chromosome congression, and faithful segregation. Measurements of kinetochore–microtubule half-life and poleward flux revealed that CLASP2 regulates kinetochore–microtubule dynamics by integrating distinctive microtubule-binding properties at the kinetochore–microtubule interface. We propose that kinetochore CLASP2 suppresses microtubule depolymerization and detachment by binding to curved protofilaments at microtubule plus-ends.

scholarly journals CLASP2 lattice-binding near microtubule plus ends stabilizes kinetochore attachments

2019 ◽  
Author(s):  
Hugo Girão ◽  
Naoyuki Okada ◽  
Ana C. Figueiredo ◽  
Zaira Garcia ◽  
Tatiana Moutinho-Santos ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Chromosome Segregation ◽  
Spindle Assembly Checkpoint ◽  
Living Cells ◽  
Microtubule Dynamics ◽  
Binding Properties ◽  
Microtubule Stability ◽  
Chromosome Congression ◽  
Fine Regulation ◽  
Resistant Mutants

AbstractThe fine regulation of kinetochore microtubule dynamics during mitosis ensures proper chromosome segregation by promoting error correction and spindle assembly checkpoint (SAC) satisfaction. CLASPs are widely conserved microtubule plus-end-tracking proteins that regulate microtubule dynamics throughout the cell cycle and independently localize to kinetochores during mitosis. Thus, CLASPs are ideally positioned to regulate kinetochore microtubule dynamics, but the underlying molecular mechanism remains unknown. Here we found that human CLASP2 can dimerize through its C-terminal kinetochore-targeting domain, but kinetochore localization was independent of dimerization. CLASP2 kinetochore localization, microtubule plus-end-tracking and microtubule lattice binding through TOG2 and TOG3 (but not TOG1) domains, independently sustained normal spindle length, timely SAC satisfaction, chromosome congression and faithful segregation. Measurements of kinetochore microtubule half-life in living cells expressing RNAi-resistant mutants revealed that CLASP2 kinetochore localization, microtubule plus-end-tracking and lattice binding cooperatively modulate kinetochore microtubule stability during mitosis. Thus, CLASP2 regulates kinetochore microtubule dynamics by integrating distinctive microtubule-binding properties at the kinetochore-microtubule interface to ensure chromosome segregation fidelity.

scholarly journals csi2p modulates microtubule dynamics and organizes the bipolar spindle for chromosome segregation

2014 ◽  
Vol 25 (24) ◽  
pp. 3900-3908 ◽  
Author(s):  
Judite Costa ◽  
Chuanhai Fu ◽  
V. Mohini Khare ◽  
Phong T. Tran
Keyword(s):  
Fission Yeast ◽  
Chromosome Segregation ◽  
Spindle Assembly Checkpoint ◽  
Microtubule Dynamics ◽  
High Rate ◽  
Spindle Formation ◽  
Bipolar Spindle ◽  
Eukaryotic Chromosome ◽  
Relative Contribution ◽  
Multiple Phenotypes

Proper chromosome segregation is of paramount importance for proper genetic inheritance. Defects in chromosome segregation can lead to aneuploidy, which is a hallmark of cancer cells. Eukaryotic chromosome segregation is accomplished by the bipolar spindle. Additional mechanisms, such as the spindle assembly checkpoint and centromere positioning, further help to ensure complete segregation fidelity. Here we present the fission yeast csi2+. csi2p localizes to the spindle poles, where it regulates mitotic microtubule dynamics, bipolar spindle formation, and subsequent chromosome segregation. csi2 deletion (csi2Δ) results in abnormally long mitotic microtubules, high rate of transient monopolar spindles, and subsequent high rate of chromosome segregation defects. Because csi2Δ has multiple phenotypes, it enables estimates of the relative contribution of the different mechanisms to the overall chromosome segregation process. Centromere positioning, microtubule dynamics, and bipolar spindle formation can all contribute to chromosome segregation. However, the major determinant of chromosome segregation defects in fission yeast may be microtubule dynamic defects.

scholarly journals BUB-1 promotes amphitelic chromosome biorientation via multiple activities at the kinetochore

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Frances Edwards ◽  
Gilliane Maton ◽  
Nelly Gareil ◽  
Julie C Canman ◽  
Julien Dumont
Keyword(s):  
Chromosome Segregation ◽  
Spindle Assembly Checkpoint ◽  
Underlying Mechanism ◽  
Microtubule Assembly ◽  
Spindle Poles ◽  
Microtubule Attachment ◽  
Anaphase Onset ◽  
Chromatid Segregation ◽  
Associated Proteins ◽  
Chromosome Attachment

Accurate chromosome segregation relies on bioriented amphitelic attachments of chromosomes to microtubules of the mitotic spindle, in which sister chromatids are connected to opposite spindle poles. BUB-1 is a protein of the Spindle Assembly Checkpoint (SAC) that coordinates chromosome attachment with anaphase onset. BUB-1 is also required for accurate sister chromatid segregation independently of its SAC function, but the underlying mechanism remains unclear. Here we show that, in Caenorhabditis elegans embryos, BUB-1 accelerates the establishment of non-merotelic end-on kinetochore-microtubule attachments by recruiting the RZZ complex and its downstream partner dynein-dynactin at the kinetochore. In parallel, BUB-1 limits attachment maturation by the SKA complex. This activity opposes kinetochore-microtubule attachment stabilisation promoted by CLS-2CLASP-dependent kinetochore-microtubule assembly. BUB-1 is therefore a SAC component that coordinates the function of multiple downstream kinetochore-associated proteins to ensure accurate chromosome segregation.

scholarly journals Spindle checkpoint–independent inhibition of mitotic chromosome segregation byDrosophilaMps1

2012 ◽  
Vol 23 (12) ◽  
pp. 2275-2291 ◽  
Author(s):  
Friederike Althoff ◽  
Roger E. Karess ◽  
Christian F. Lehner
Keyword(s):  
Chromosome Segregation ◽  
Sister Chromatid ◽  
Spindle Assembly Checkpoint ◽  
Mitotic Chromosome ◽  
Independent Manner ◽  
Spindle Poles ◽  
Anaphase Onset ◽  
Chromosome Congression ◽  
Monopolar Spindle ◽  
Chromatid Cohesion

Monopolar spindle 1 (Mps1) is essential for the spindle assembly checkpoint (SAC), which prevents anaphase onset in the presence of misaligned chromosomes. Moreover, Mps1 kinase contributes in a SAC-independent manner to the correction of erroneous initial attachments of chromosomes to the spindle. Our characterization of the Drosophila homologue reveals yet another SAC-independent role. As in yeast, modest overexpression of Drosophila Mps1 is sufficient to delay progression through mitosis during metaphase, even though chromosome congression and metaphase alignment do not appear to be affected. This delay in metaphase depends on the SAC component Mad2. Although Mps1 overexpression in mad2 mutants no longer causes a metaphase delay, it perturbs anaphase. Sister kinetochores barely move apart toward spindle poles. However, kinetochore movements can be restored experimentally by separase-independent resolution of sister chromatid cohesion. We propose therefore that Mps1 inhibits sister chromatid separation in a SAC-independent manner. Moreover, we report unexpected results concerning the requirement of Mps1 dimerization and kinase activity for its kinetochore localization in Drosophila. These findings further expand Mps1's significance for faithful mitotic chromosome segregation and emphasize the importance of its careful regulation.

scholarly journals Molecular mechanism underlying the non-essentiality of Bub1 for the fidelity of chromosome segregation in human cells

2021 ◽  
Author(s):  
Qinfu Chen ◽  
Miao Zhang ◽  
Xuan Pan ◽  
Linli Zhou ◽  
Haiyan Yan ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Spindle Assembly Checkpoint ◽  
Mitotic Chromosome ◽  
Threshold Level ◽  
Underlying Mechanism ◽  
Human Cells ◽  
Strong Reduction ◽  
Checkpoint Signaling ◽  
Chromosome Alignment ◽  
Redundant Role

SUMMARYThe multi-task protein kinase Bub1 has long been considered important for chromosome alignment and spindle assembly checkpoint signaling during mitosis. However, recent studies provide surprising evidence that Bub1 may not be essential in human cells, with the underlying mechanism unknown. Here we show that Bub1 plays a redundant role with the non-essential CENP-U complex in recruiting Polo-like kinase 1 (Plk1) to the kinetochore. While disrupting either pathway of Plk1 recruitment does not affect the accuracy of whole chromosome segregation, loss of both pathways leads to a strong reduction in the kinetochore accumulation of Plk1 under a threshold level required for proper chromosome alignment and segregation. Thus, parallel recruitment of Plk1 to kinetochores by Bub1 and the CENP-U complex ensures high fidelity of mitotic chromosome segregation. This study may have implications for targeted treatment of cancer cells harboring mutations in either Bub1 or the CENP-U complex.

scholarly journals The Interplay of the N- and C-Terminal Domains of MCAK Control Microtubule Depolymerization Activity and Spindle Assembly

2007 ◽  
Vol 18 (1) ◽  
pp. 282-294 ◽  
Author(s):  
Stephanie C. Ems-McClung ◽  
Kathleen M. Hertzer ◽  
Xin Zhang ◽  
Mill W. Miller ◽  
Claire E. Walczak
Keyword(s):  
High Activity ◽  
Chromosome Segregation ◽  
Spindle Assembly ◽  
Microtubule Dynamics ◽  
Microtubule Depolymerization ◽  
Terminal Domain ◽  
Egg Extracts ◽  
Assembly Activity ◽  
Terminal Domains

Spindle assembly and accurate chromosome segregation require the proper regulation of microtubule dynamics. MCAK, a Kinesin-13, catalytically depolymerizes microtubules, regulates physiological microtubule dynamics, and is the major catastrophe factor in egg extracts. Purified GFP-tagged MCAK domain mutants were assayed to address how the different MCAK domains contribute to in vitro microtubule depolymerization activity and physiological spindle assembly activity in egg extracts. Our biochemical results demonstrate that both the neck and the C-terminal domain are necessary for robust in vitro microtubule depolymerization activity. In particular, the neck is essential for microtubule end binding, and the C-terminal domain is essential for tight microtubule binding in the presence of excess tubulin heterodimer. Our physiological results illustrate that the N-terminal domain is essential for regulating microtubule dynamics, stimulating spindle bipolarity, and kinetochore targeting; whereas the C-terminal domain is necessary for robust microtubule depolymerization activity, limiting spindle bipolarity, and enhancing kinetochore targeting. Unexpectedly, robust MCAK microtubule (MT) depolymerization activity is not needed for sperm-induced spindle assembly. However, high activity is necessary for proper physiological MT dynamics as assayed by Ran-induced aster assembly. We propose that MCAK activity is spatially controlled by an interplay between the N- and C-terminal domains during spindle assembly.

scholarly journals Aneuploid abortion correlates positively with MAD1 overexpression and miR-125b down-regulation

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Juan Zhao ◽  
Hui Li ◽  
Guangxin Chen ◽  
Lijun Du ◽  
Peiyan Xu ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Spindle Assembly Checkpoint ◽  
Mitotic Checkpoint ◽  
Early Embryo ◽  
Vital Role ◽  
Control Group ◽  
Embryo Abortion ◽  
Protein Levels ◽  
Mitotic Checkpoint Complex

Abstract Background Aneuploidy is the most frequent cause of early-embryo abortion. Any defect in chromosome segregation would fail to satisfy the spindle assembly checkpoint (SAC) during mitosis, halting metaphase and causing aneuploidy. The mitotic checkpoint complex (MCC), comprising MAD1, MAD2, Cdc20, BUBR1 and BUB3, plays a vital role in SAC activation. Studies have confirmed that overexpression of MAD2 and BUBR1 can facilitate correct chromosome segregation and embryo stability. Research also proves that miR-125b negatively regulates MAD1 expression by binding to its 3′UTR. However, miR-125b, Mad1 and Bub3 gene expression in aneuploid embryos of spontaneous abortion has not been reported to date. Methods In this study, embryonic villi from miscarried pregnancies were collected and divided into two groups (aneuploidy and euploidy) based on High-throughput ligation-dependent probe amplification (HLPA) and Fluorescence in situ hybridization (FISH) analyses. RNA levels of miR-125b, MAD1 and BUB3 were detected by Quantitative real-time PCR (qRT-PCR); protein levels of MAD1 and BUB3 were analysed by Western blotting. Results statistical analysis (p < 0.05) showed that miR-125b and BUB3 were significantly down-regulated in the aneuploidy group compared to the control group and that MAD1 was significantly up-regulated. Additionally, the MAD1 protein level was significantly higher in aneuploidy abortion villus, but BUB3 protein was only mildly increased. Correlation analysis revealed that expression of MAD1 correlated negatively with miR-125b. Conclusion These results suggest that aneuploid abortion correlates positively with MAD1 overexpression, which might be caused by insufficient levels of miR-125b. Taken together, our findings first confirmed the negative regulatory mode between MAD1 and miR-125b, providing a basis for further mechanism researches in aneuploid abortion.

scholarly journals The Role of Cdh1p in Maintaining Genomic Stability in Budding Yeast

Genetics ◽  
2003 ◽  
Vol 165 (2) ◽  
pp. 489-503 ◽  
Author(s):  
Karen E Ross ◽  
Orna Cohen-Fix
Keyword(s):  
Cell Cycle ◽  
Chromosome Segregation ◽  
Spindle Assembly Checkpoint ◽  
Chromosome Loss ◽  
Cyclin Dependent Kinase ◽  
Anaphase Promoting Complex ◽  
Growth Defects ◽  
Genes Encoding ◽  
Specificity Factor

Abstract Cdh1p, a substrate specificity factor for the cell cycle-regulated ubiquitin ligase, the anaphase-promoting complex/cyclosome (APC/C), promotes exit from mitosis by directing the degradation of a number of proteins, including the mitotic cyclins. Here we present evidence that Cdh1p activity at the M/G1 transition is important not only for mitotic exit but also for high-fidelity chromosome segregation in the subsequent cell cycle. CDH1 showed genetic interactions with MAD2 and PDS1, genes encoding components of the mitotic spindle assembly checkpoint that acts at metaphase to prevent premature chromosome segregation. Unlike cdh1Δ and mad2Δ single mutants, the mad2Δ cdh1Δ double mutant grew slowly and exhibited high rates of chromosome and plasmid loss. Simultaneous deletion of PDS1 and CDH1 caused extensive chromosome missegregation and cell death. Our data suggest that at least part of the chromosome loss can be attributed to kinetochore/spindle problems. Our data further suggest that Cdh1p and Sic1p, a Cdc28p/Clb inhibitor, have overlapping as well as nonoverlapping roles in ensuring proper chromosome segregation. The severe growth defects of both mad2Δ cdh1Δ and pds1Δ cdh1Δ strains were rescued by overexpressing Swe1p, a G2/M inhibitor of the cyclin-dependent kinase, Cdc28p/Clb. We propose that the failure to degrade cyclins at the end of mitosis leaves cdh1Δ mutant strains with abnormal Cdc28p/Clb activity that interferes with proper chromosome segregation.

scholarly journals Pericentric chromatin loops function as a nonlinear spring in mitotic force balance

2013 ◽  
Vol 200 (6) ◽  
pp. 757-772 ◽  
Author(s):  
Andrew D. Stephens ◽  
Rachel A. Haggerty ◽  
Paula A. Vasquez ◽  
Leandra Vicci ◽  
Chloe E. Snider ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Spindle Assembly Checkpoint ◽  
Force Balance ◽  
Nonlinear Spring ◽  
Sister Chromatids ◽  
Spindle Dynamics ◽  
Restoring Forces ◽  
Cross Links ◽  
Mean And Variance

The mechanisms by which sister chromatids maintain biorientation on the metaphase spindle are critical to the fidelity of chromosome segregation. Active force interplay exists between predominantly extensional microtubule-based spindle forces and restoring forces from chromatin. These forces regulate tension at the kinetochore that silences the spindle assembly checkpoint to ensure faithful chromosome segregation. Depletion of pericentric cohesin or condensin has been shown to increase the mean and variance of spindle length, which have been attributed to a softening of the linear chromatin spring. Models of the spindle apparatus with linear chromatin springs that match spindle dynamics fail to predict the behavior of pericentromeric chromatin in wild-type and mutant spindles. We demonstrate that a nonlinear spring with a threshold extension to switch between spring states predicts asymmetric chromatin stretching observed in vivo. The addition of cross-links between adjacent springs recapitulates coordination between pericentromeres of neighboring chromosomes.

scholarly journals RanBP2 and SENP3 Function in a Mitotic SUMO2/3 Conjugation-Deconjugation Cycle on Borealin

2009 ◽  
Vol 20 (1) ◽  
pp. 410-418 ◽  
Author(s):  
Ulf R. Klein ◽  
Markus Haindl ◽  
Erich A. Nigg ◽  
Stefan Muller
Keyword(s):  
Mammalian Cells ◽  
Spindle Assembly Checkpoint ◽  
Critical Role ◽  
Specific Interaction ◽  
Regulatory Function ◽  
Mitotic Progression ◽  
Chromosome Congression ◽  
Chromosomal Passenger

The ubiquitin-like SUMO system controls cellular key functions, and several lines of evidence point to a critical role of SUMO for mitotic progression. However, in mammalian cells mitotic substrates of sumoylation and the regulatory components involved are not well defined. Here, we identify Borealin, a component of the chromosomal passenger complex (CPC), as a mitotic target of SUMO. The CPC, which additionally comprises INCENP, Survivin, and Aurora B, regulates key mitotic events, including chromosome congression, the spindle assembly checkpoint, and cytokinesis. We show that Borealin is preferentially modified by SUMO2/3 and demonstrate that the modification is dynamically regulated during mitotic progression, peaking in early mitosis. Intriguingly, the SUMO ligase RanBP2 interacts with the CPC, stimulates SUMO modification of Borealin in vitro, and is required for its modification in vivo. Moreover, the SUMO isopeptidase SENP3 is a specific interaction partner of Borealin and catalyzes the removal of SUMO2/3 from Borealin. These data thus delineate a mitotic SUMO2/3 conjugation–deconjugation cycle of Borealin and further assign a regulatory function of RanBP2 and SENP3 in the mitotic SUMO pathway.

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