scholarly journals Spindly switch controls anaphase: Spindly and RZZ functions in chromosome attachment and mitotic checkpoint control

Cell Cycle ◽  
2011 ◽  
Vol 10 (3) ◽  
pp. 449-456 ◽  
Author(s):  
Marin Barisic ◽  
Stephan Geley
Keyword(s):  
Mitotic Checkpoint ◽  
Checkpoint Control ◽  
Chromosome Attachment

The ‘anaphase problem’: how to disable the mitotic checkpoint when sisters split

2010 ◽  
Vol 38 (6) ◽  
pp. 1660-1666 ◽  
Author(s):  
María Dolores Vázquez-Novelle ◽  
Lesia Mirchenko ◽  
Frank Uhlmann ◽  
Mark Petronczki
Keyword(s):  
Error Correction ◽  
Mitotic Checkpoint ◽  
Eukaryotic Cells ◽  
Checkpoint Control ◽  
Anaphase Onset ◽  
Sister Chromatids ◽  
Error Correction Mechanism ◽  
Chromosomal Passenger ◽  
Chromosome Attachment ◽  
Spindle Midzone

Two closely connected mechanisms safeguard the fidelity of chromosome segregation in eukaryotic cells. The mitotic checkpoint monitors the attachment of kinetochores to microtubules and delays anaphase onset until all sister kinetochores have become attached to opposite poles. In addition, an error correction mechanism destabilizes erroneous attachments that do not lead to tension at sister kinetochores. Aurora B kinase, the catalytic subunit of the CPC (chromosomal passenger complex), acts as a sensor and effector in both pathways. In this review we focus on a poorly understood but important aspect of mitotic control: what prevents the mitotic checkpoint from springing into action when sister centromeres are split and tension is suddenly lost at anaphase onset? Recent work has shown that disjunction of sister chromatids, in principle, engages the mitotic checkpoint, and probably also the error correction mechanism, with potentially catastrophic consequences for cell division. Eukaryotic cells have solved this ‘anaphase problem’ by disabling the mitotic checkpoint at the metaphase-to-anaphase transition. Checkpoint inactivation is in part due to the reversal of Cdk1 (cyclin-dependent kinase 1) phosphorylation of the CPC component INCENP (inner centromere protein; Sli15 in budding yeast), which causes the relocation of the CPC from centromeres to the spindle midzone. These findings highlight principles of mitotic checkpoint control: when bipolar chromosome attachment is reached in mitosis, the checkpoint is satisfied, but still active and responsive to loss of tension. Mitotic checkpoint inactivation at anaphase onset is required to prevent checkpoint re-engagement when sister chromatids split.

scholarly journals Spc98p Directs the Yeast γ-Tubulin Complex into the Nucleus and Is Subject to Cell Cycle-dependent Phosphorylation on the Nuclear Side of the Spindle Pole Body

1998 ◽  
Vol 9 (4) ◽  
pp. 775-793 ◽  
Author(s):  
Gislene Pereira ◽  
Michael Knop ◽  
Elmar Schiebel
Keyword(s):  
Cell Cycle ◽  
Spindle Pole Body ◽  
Mitotic Checkpoint ◽  
Spindle Pole ◽  
Nuclear Localization Sequence ◽  
Checkpoint Control ◽  
Yeast Saccharomyces Cerevisiae ◽  
Pole Body ◽  
Cycle Dependent ◽  
Cytoplasmic Side

In the yeast Saccharomyces cerevisiae, microtubules are organized by the spindle pole body (SPB), which is embedded in the nuclear envelope. Microtubule organization requires the γ-tubulin complex containing the γ-tubulin Tub4p, Spc98p, and Spc97p. The Tub4p complex is associated with cytoplasmic and nuclear substructures of the SPB, which organize the cytoplasmic and nuclear microtubules. Here we present evidence that the Tub4p complex assembles in the cytoplasm and then either binds to the cytoplasmic side of the SPB or is imported into the nucleus followed by binding to the nuclear side of the SPB. Nuclear import of the Tub4p complex is mediated by the essential nuclear localization sequence of Spc98p. Our studies also indicate that Spc98p in the Tub4p complex is phosphorylated at the nuclear, but not at the cytoplasmic, side of the SPB. This phosphorylation is cell cycle dependent and occurs after SPB duplication and nucleation of microtubules by the new SPB and therefore may have a role in mitotic spindle function. In addition, activation of the mitotic checkpoint stimulates Spc98p phosphorylation. The kinase Mps1p, which functions in SPB duplication and mitotic checkpoint control, seems to be involved in Spc98p phosphorylation. Our results also suggest that the nuclear and cytoplasmic Tub4p complexes are regulated differently.

scholarly journals Bub1 kinase activity drives error correction and mitotic checkpoint control but not tumor suppression

2012 ◽  
Vol 199 (6) ◽  
pp. 931-949 ◽  
Author(s):  
Robin M. Ricke ◽  
Karthik B. Jeganathan ◽  
Liviu Malureanu ◽  
Andrew M. Harrison ◽  
Jan M. van Deursen
Keyword(s):  
Error Correction ◽  
Tumor Suppression ◽  
Kinase Activity ◽  
Chromosome Instability ◽  
Mitotic Checkpoint ◽  
Histone H2a ◽  
Checkpoint Control ◽  
Proliferating Cells ◽  
Checkpoint Signaling ◽  
Mitotic Checkpoint Protein

The mitotic checkpoint protein Bub1 is essential for embryogenesis and survival of proliferating cells, and bidirectional deviations from its normal level of expression cause chromosome missegregation, aneuploidy, and cancer predisposition in mice. To provide insight into the physiological significance of this critical mitotic regulator at a modular level, we generated Bub1 mutant mice that lack kinase activity using a knockin gene-targeting approach that preserves normal protein abundance. In this paper, we uncover that Bub1 kinase activity integrates attachment error correction and mitotic checkpoint signaling by controlling the localization and activity of Aurora B kinase through phosphorylation of histone H2A at threonine 121. Strikingly, despite substantial chromosome segregation errors and aneuploidization, mice deficient for Bub1 kinase activity do not exhibit increased susceptibility to spontaneous or carcinogen-induced tumorigenesis. These findings provide a unique example of a modular mitotic activity orchestrating two distinct networks that safeguard against whole chromosome instability and reveal the differential importance of distinct aneuploidy-causing Bub1 defects in tumor suppression.

scholarly journals Mutations in the Essential Spindle Checkpoint Gene bub1 Cause Chromosome Missegregation and Fail to Block Apoptosis in Drosophila

1999 ◽  
Vol 146 (1) ◽  
pp. 13-28 ◽  
Author(s):  
Joydeep Basu ◽  
Hassan Bousbaa ◽  
Elsa Logarinho ◽  
ZeXiao Li ◽  
Byron C. Williams ◽  
...  
Keyword(s):  
Metaphase Plate ◽  
Mitotic Checkpoint ◽  
P Element ◽  
Checkpoint Control ◽  
Chromosome Fragmentation ◽  
Chromosome Missegregation ◽  
Meiotic Chromosomes ◽  
Mitotic Abnormalities ◽  
The Relationship ◽  
Control Protein

We have characterized the Drosophila mitotic checkpoint control protein Bub1 and obtained mutations in the bub1 gene. Drosophila Bub1 localizes strongly to the centromere/kinetochore of mitotic and meiotic chromosomes that have not yet reached the metaphase plate. Animals homozygous for P-element–induced, near-null mutations of bub1 die during late larval/pupal stages due to severe mitotic abnormalities indicative of a bypass of checkpoint function. These abnormalities include accelerated exit from metaphase and chromosome missegregation and fragmentation. Chromosome fragmentation possibly leads to the significantly elevated levels of apoptosis seen in mutants. We have also investigated the relationship between Bub1 and other kinetochore components. We show that Bub1 kinase activity is not required for phosphorylation of 3F3/2 epitopes at prophase/prometaphase, but is needed for 3F3/2 dephosphorylation at metaphase. Neither 3F3/2 dephosphorylation nor loss of Bub1 from the kinetochore is a prerequisite for anaphase entry. Bub1's localization to the kinetochore does not depend on the products of the genes zw10, rod, polo, or fizzy, indicating that the kinetochore is constructed from several independent subassemblies.

scholarly journals Kinetochore recruitment of CENP-F illustrates how paralog divergence shapes kinetochore composition and function

2018 ◽  
Author(s):  
Giuseppe Ciossani ◽  
Katharina Overlack ◽  
Arsen Petrovic ◽  
Pim Huis in ‘t Veld ◽  
Carolin Körner ◽  
...  
Keyword(s):  
Coiled Coil ◽  
Kinase Domain ◽  
Mitotic Checkpoint ◽  
Checkpoint Control ◽  
Directed Motion ◽  
Coil Structure ◽  
Evolutionary Relatedness ◽  
Chromosome Alignment ◽  
And Function ◽  
Paralogous Proteins

The metazoan proteins CENP-E and CENP-F are components of a fibrous layer of mitotic kinetochores named the corona. Several features suggest that CENP-E and CENP-F are paralogs: they are very large (approximately 2700 and 3200 residues, respectively), rich in predicted coiled-coil structure, C-terminally prenylated, and endowed with microtubule-binding sites at their termini. In addition, CENP-E contains an ATP-hydrolyzing motor domain that promotes microtubule plus-end directed motion. Here, we show that CENP-E and CENP- F are recruited to mitotic kinetochores independently of the Rod-Zwilch-ZW10 (RZZ) complex, the main corona constituent. We identify selective interactions of CENP-E and CENP-F respectively with BubR1 and Bub1, paralogous proteins involved in mitotic checkpoint control and chromosome alignment. While BubR1 is dispensable for kinetochore localization of CENP-E, Bub1 is stringently required for CENP-F localization. Through biochemical reconstitution, we demonstrate that the CENP-E:BubR1 and CENP-F:Bub1 interactions are direct and require similar determinants, a dimeric coiled-coil in CENP-E or CENP-F and a kinase domain in BubR1 or Bub1. Our findings are consistent with the existence of ‘pseudo-symmetric’, paralogous Bub1:CENP-F and BubR1:CENP-E axes, supporting evolutionary relatedness of CENP-E and CENP-F.

scholarly journals Human Papillomavirus Oncoproteins E6 and E7 Independently Abrogate the Mitotic Spindle Checkpoint

1998 ◽  
Vol 72 (2) ◽  
pp. 1131-1137 ◽  
Author(s):  
Jennifer T. Thomas ◽  
Laimonis A. Laimins
Keyword(s):  
Human Papillomavirus ◽  
High Risk ◽  
Mitotic Spindle ◽  
Spindle Checkpoint ◽  
Human Keratinocytes ◽  
Mitotic Checkpoint ◽  
Cell Cycle Checkpoint ◽  
Checkpoint Control ◽  
Mitotic Spindle Checkpoint ◽  
E6 And E7

ABSTRACT The E6 and E7 genes of the high-risk human papillomavirus (HPV) types encode oncoproteins, and both act by interfering with the activity of cellular tumor suppressor proteins. E7 proteins act by associating with members of the retinoblastoma family, while E6 increases the turnover of p53. p53 has been implicated as a regulator of both the G1/S cell cycle checkpoint and the mitotic spindle checkpoint. When fibroblasts from p53 knockout mice are treated with the spindle inhibitor nocodazole, a rereplication of DNA occurs without transit through mitosis. We investigated whether E6 or E7 could induce a similar loss of mitotic checkpoint activity in human keratinocytes. Recombinant retroviruses expressing high-risk E6 alone, E7 alone, and E6 in combination with E7 were used to infect normal human foreskin keratinocytes (HFKs). Established cell lines were treated with nocodazole, stained with propidium iodide, and analyzed for DNA content by flow cytometry. Cells infected with high-risk E6 were found to continue to replicate DNA and accumulated an octaploid (8N) population. Surprisingly, expression of E7 alone was also able to bypass this checkpoint. Cells expressing E7 alone exhibited increased levels of p53, while those expressing E6 had significantly reduced levels. The p53 present in the E7 cells was active, as increased levels of p21 were observed. This suggested that E7 bypassed the mitotic checkpoint by a p53-independent mechanism. The levels of MDM2, a cellular oncoprotein also implicated in control of the mitotic checkpoint, were significantly elevated in the E7 cells compared to the normal HFKs. In E6-expressing cells, the levels of MDM2 were undetectable. It is possible that abrogation of Rb function by E7 or increased expression of MDM2 contributes to the loss of mitotic spindle checkpoint control in the E7 cells. These findings suggest mechanisms by which both HPV oncoproteins contribute to genomic instability at the mitotic checkpoint.

Spindle Checkpoint Insufficiency in Acute Myeloid Leukemia.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 873-873
Author(s):  
Dominik Schnerch ◽  
Julia Felthaus ◽  
Monika Engelhardt ◽  
Ralph M. Waesch
Keyword(s):  
Acute Myeloid Leukemia ◽  
Cell Lines ◽  
Mitotic Spindle ◽  
Myeloid Leukemia ◽  
Mitotic Checkpoint ◽  
Mitotic Arrest ◽  
Cyclin B ◽  
Resting Cells ◽  
Chromosome Attachment ◽  
Acute Myeloid

Abstract Chromosomal instability and aneuploidy are hallmarks of most human malignancies. Various mechanisms have been shown to give rise to numerical chromosome aberrations. Compromised function of the spindle assembly checkpoint (SAC) is generally regarded as one of the most powerful ways to drive genome instability. The SAC is a mitotic checkpoint mechanism ensuring the equal segregation of the mitotic chromosomes onto the developing daughter cells. Unfaithful mitotic surveillance by the SAC favors chromosomal misdistribution as error-prone chromosome attachment to the mitotic spindle does not induce a strong mitotic arrest by interference with anaphase promoting complex (APC)-dependent proteolysis. The APC is an important ubiquitin ligase that triggers the transition from mitosis into G1-phase by targeted proteolysis of mitotic regulators such as cyclin B and securin. The SAC prevents the proteolysis of those regulator proteins in the presence of mitotic aberrancies by inhibition of the APC. This leads to a delayed progression through mitosis and provides time to recover from defective chromosomal spindle attachment. SAC malfunction weakens the tight control on chromosome attachment and tension across the kinetochore favoring chromosomal misdistribution. We performed expression analyses of key proteins in SAC signaling in acute myeloid leukemia (AML). We found the SAC-components Bub1 and BubR1 to be down-regulated in most of the investigated AML cell lines. Functional assays revealed a defective mitotic arrest mechanism in comparison to SAC-competent cell lines after exposure to the microtubule disrupting agent nocodazole. This finding was accompanied by the observation of a decline in cyclin B and securin levels despite severe damage to the mitotic spindle induced by nocodazole. Expression of cyclin B and securin in the presence of spindle damage could be stabilized by proteasome inhibition. We established a shRNA-based model to evaluate the effects of BubR1- and/or Bub1-repression to levels found among AML cell lines to directly compare the Bub1/BubR1 knockdown phenotype with the investigated AML cell lines. Interestingly, BubR1 knockdown was sufficient to generate a phenotype resembling the behavior of our AML cell lines. Further experiments revealed a strong relation between premature degradation of cyclin B and the degree of BubR1 downregulation. Given the potent role of BubR1 in the generation of a mitotic arrest deficient phenotype, we addressed the BubR1 expression levels in a number of patients exhibiting karyotype abnormalities. Primary myeloid blast cells were stimulated with cytokines to force the largely resting cells into an actively dividing state. The maximum expression level of BubR1 in G2/M was used to define SAC-compentent and SAC-deficient populations. Strikingly, six out of eight (6/8) primary AML samples exhibited BubR1 expression patterns resembling the BubR1-knockdown model suggesting deficient mitotic surveillance in most of the primary AML samples. Since SAC deficiency is an important mechanism in creating numerical chromosomal aberrations and genetic instability, our findings underline a role for impaired SAC function in rise and progression of AML.

scholarly journals Release of Mps1 from kinetochores is crucial for timely anaphase onset

2010 ◽  
Vol 191 (2) ◽  
pp. 281-290 ◽  
Author(s):  
Nannette Jelluma ◽  
Tobias B. Dansen ◽  
Tale Sliedrecht ◽  
Nicholas P. Kwiatkowski ◽  
Geert J.P.L. Kops
Keyword(s):  
Error Correction ◽  
Chromosome Segregation ◽  
Kinase Activity ◽  
Mitotic Checkpoint ◽  
Normal Chromosome ◽  
Half Time ◽  
Anaphase Onset ◽  
Chromosome Attachment

Mps1 kinase activity is required for proper chromosome segregation during mitosis through its involvements in microtubule–chromosome attachment error correction and the mitotic checkpoint. Mps1 dynamically exchanges on unattached kinetochores but is largely removed from kinetochores in metaphase. Here we show that Mps1 promotes its own turnover at kinetochores and that removal of Mps1 upon chromosome biorientation is a prerequisite for mitotic checkpoint silencing. Inhibition of Mps1 activity increases its half-time of recovery at unattached kinetochores and causes accumulation of Mps1 protein at these sites. Strikingly, preventing dissociation of active Mps1 from kinetochores delays anaphase onset despite normal chromosome attachment and alignment, and high interkinetochore tension. This delay is marked by continued recruitment of Mad1 and Mad2 to bioriented chromosomes and is attenuated by Mad2 depletion, indicating chronic engagement of the mitotic checkpoint in metaphase. We propose that release of Mps1 from kinetochores is essential for mitotic checkpoint silencing and a fast metaphase-to-anaphase transition.

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