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Trends in Biochemical Sciences Jun 2006Proteolysis mediated by the ubiquitin-proteasome system is a crucial regulatory mechanism in signal transduction cascades of temporal cellular processes such as cell... (Review)
Review
Proteolysis mediated by the ubiquitin-proteasome system is a crucial regulatory mechanism in signal transduction cascades of temporal cellular processes such as cell division. Two principal subtypes of modular ubiquitin ligase, the anaphase-promoting complex or cyclosome (APC/C) and the Skp1/Cullin-1/F-box protein complex, have emerged as essential regulators of key events in the cell cycle. The importance of these ligases is best illustrated by their roles in the checkpoint and repair pathways or in response to multiple stresses, where they affect activation of the M-phase-promoting factor or proper formation and/or maintenance of the mitotic spindle. Recent studies have considerably improved our understanding of the function of the concerted action of the phosphorylation and ubiquitin or SUMO systems in the regulation of the stability and activity of key components of the mitotic checkpoint.
Topics: Anaphase; Animals; Cell Division; Humans; Phosphorylation; Proteasome Endopeptidase Complex; Protein Processing, Post-Translational; SUMO-1 Protein; Signal Transduction; Ubiquitin
PubMed: 16647857
DOI: 10.1016/j.tibs.2006.04.001 -
Current Biology : CB Jul 2002The release of Cdc14 from the nucleolus occurs in two waves in early and late anaphase, controlled by the FEAR and MEN pathways, respectively. Two new papers report the... (Review)
Review
The release of Cdc14 from the nucleolus occurs in two waves in early and late anaphase, controlled by the FEAR and MEN pathways, respectively. Two new papers report the localisation at the spindle pole body of the Cdc14 released in early anaphase and, surprisingly, show that the two pulses of released Cdc14 have opposite effects on MEN activation.
Topics: Anaphase; Cell Cycle Proteins; Fungal Proteins; Mitosis; Phosphorylation; Protein Tyrosine Phosphatases; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins
PubMed: 12176346
DOI: 10.1016/s0960-9822(02)00963-6 -
ELife Aug 2019According to the prevailing 'clock' model, chromosome decondensation and nuclear envelope reformation when cells exit mitosis are byproducts of Cdk1 inactivation at the...
According to the prevailing 'clock' model, chromosome decondensation and nuclear envelope reformation when cells exit mitosis are byproducts of Cdk1 inactivation at the metaphase-anaphase transition, controlled by the spindle assembly checkpoint. However, mitotic exit was recently shown to be a function of chromosome separation during anaphase, assisted by a midzone Aurora B phosphorylation gradient - the 'ruler' model. Here we found that Cdk1 remains active during anaphase due to ongoing APC/C- and APC/C-mediated degradation of B-type Cyclins in and human cells. Failure to degrade B-type Cyclins during anaphase prevented mitotic exit in a Cdk1-dependent manner. Cyclin B1-Cdk1 localized at the spindle midzone in an Aurora B-dependent manner, with incompletely separated chromosomes showing the highest Cdk1 activity. Slowing down anaphase chromosome motion delayed Cyclin B1 degradation and mitotic exit in an Aurora B-dependent manner. Thus, a crosstalk between molecular 'rulers' and 'clocks' licenses mitotic exit only after proper chromosome separation.
Topics: Anaphase; Animals; Aurora Kinase B; CDC2 Protein Kinase; Cell Line; Cyclin B1; Drosophila; Drosophila Proteins; Humans; Proteolysis; Spatio-Temporal Analysis
PubMed: 31424385
DOI: 10.7554/eLife.47646 -
Molecular Cell Sep 2020A long-standing conundrum is how mitotic chromosomes can compact, as required for clean separation to daughter cells, while maintaining close parallel alignment of...
A long-standing conundrum is how mitotic chromosomes can compact, as required for clean separation to daughter cells, while maintaining close parallel alignment of sister chromatids. Pursuit of this question, by high resolution 3D fluorescence imaging of living and fixed mammalian cells, has led to three discoveries. First, we show that the structural axes of separated sister chromatids are linked by evenly spaced "mini-axis" bridges. Second, when chromosomes first emerge as discrete units, at prophase, they are organized as co-oriented sister linear loop arrays emanating from a conjoined axis. We show that this same basic organization persists throughout mitosis, without helical coiling. Third, from prophase onward, chromosomes are deformed into sequential arrays of half-helical segments of alternating handedness (perversions), accompanied by correlated kinks. These arrays fluctuate dynamically over <15 s timescales. Together these discoveries redefine the foundation for thinking about the evolution of mitotic chromosomes as they prepare for anaphase segregation.
Topics: Adenosine Triphosphatases; Anaphase; Animals; Cell Cycle Proteins; Chromatids; Chromosomal Proteins, Non-Histone; Chromosomes; DNA Topoisomerases, Type II; DNA-Binding Proteins; Imaging, Three-Dimensional; Mammals; Metaphase; Mitosis; Prophase
PubMed: 32768407
DOI: 10.1016/j.molcel.2020.07.002 -
Genes & Development Jun 2008Mitotic cyclin-dependent kinases (CDKs) control entry into mitosis, but their role during mitotic progression is less well understood. Here we characterize the functions...
Mitotic cyclin-dependent kinases (CDKs) control entry into mitosis, but their role during mitotic progression is less well understood. Here we characterize the functions of CDK activity associated with the mitotic cyclins Clb1, Clb2, and Clb3. We show that Clb-CDKs are important for the activation of the ubiquitin ligase Anaphase-Promoting Complex/Cyclosome (APC/C)-Cdc20 that triggers the metaphase-anaphase transition. Furthermore, we define an essential role for Clb-CDK activity in anaphase spindle elongation. Thus, mitotic CDKs serve not only to initiate M phase, but are also needed continuously throughout mitosis to trigger key mitotic events such as APC/C activation and anaphase spindle elongation.
Topics: Anaphase; Cell Cycle; Cyclin-Dependent Kinases; Metaphase; Mitosis; Saccharomyces cerevisiae; Spindle Apparatus
PubMed: 18519644
DOI: 10.1101/gad.1638308 -
Communications Biology Dec 2021Mitotic divisions achieve equal re-partition of chromosomes into daughter cells. In their recent work in , Sen, Harrison et al. propose that the risk of mis-segregation...
Mitotic divisions achieve equal re-partition of chromosomes into daughter cells. In their recent work in , Sen, Harrison et al. propose that the risk of mis-segregation in human mitotic cells is higher than previously thought and identify the existence of an early-anaphase correction mechanism. The study documents kinetochore dynamics in unprecedented detail, providing a detailed look at the events preceding loss of correct chromosomal numericity and genomic stability.
Topics: Anaphase; Chromosome Segregation; Humans; Kinetochores; Mitosis
PubMed: 34903809
DOI: 10.1038/s42003-021-02933-1 -
The Journal of Biological Chemistry Aug 2016The error-free segregation of chromosomes, which requires the precisely timed search and capture of chromosomes by spindles during early mitotic and meiotic cell...
The error-free segregation of chromosomes, which requires the precisely timed search and capture of chromosomes by spindles during early mitotic and meiotic cell division, is responsible for genomic stability and is achieved by the spindle assembly checkpoint in the metaphase-anaphase transition. Mitotic kinases orchestrate M phase events, such as the reorganization of cell architecture and kinetochore (KT) composition with the exquisite phosphorylation of mitotic regulators, to ensure timely and temporal progression. However, the molecular mechanisms underlying the changes of KT composition for stable spindle attachment during mitosis are poorly understood. Here, we show that the sequential action of the kinase Cdk1 and the phosphatase Cdc14A control spindle attachment to KTs. During prophase, the mitotic spindle protein Spag5/Astrin is transported into centrosomes by Kinastrin and phosphorylated at Ser-135 and Ser-249 by Cdk1, which, in prometaphase, is loaded onto the spindle and targeted to KTs. We also demonstrate that Cdc14A dephosphorylates Astrin, and therefore the overexpression of Cdc14A sequesters Astrin in the centrosome and results in aberrant chromosome alignment. Mechanistically, Plk1 acts as an upstream kinase for Astrin phosphorylation by Cdk1 and targeting phospho-Astrin to KTs, leading to the recruitment of outer KT components, such as Cenp-E, and the stable attachment of spindles to KTs. These comprehensive findings reveal a regulatory circuit for protein targeting to KTs that controls the KT composition change of stable spindle attachment and chromosome integrity.
Topics: Anaphase; CDC2 Protein Kinase; Cell Cycle Proteins; Chromosomal Proteins, Non-Histone; Cyclin-Dependent Kinases; HeLa Cells; Humans; Kinetochores; Metaphase; Phosphoric Monoester Hydrolases; Phosphorylation; Protein Serine-Threonine Kinases; Protein Tyrosine Phosphatases; Proto-Oncogene Proteins; Polo-Like Kinase 1
PubMed: 27325694
DOI: 10.1074/jbc.M115.712745 -
ELife Jun 2022The chromokinesin KIF22 generates forces that contribute to mitotic chromosome congression and alignment. Mutations in the α2 helix of the motor domain of KIF22 have...
The chromokinesin KIF22 generates forces that contribute to mitotic chromosome congression and alignment. Mutations in the α2 helix of the motor domain of KIF22 have been identified in patients with abnormal skeletal development, and we report the identification of a patient with a novel mutation in the KIF22 tail. We demonstrate that pathogenic mutations do not result in a loss of KIF22's functions in early mitosis. Instead, mutations disrupt chromosome segregation in anaphase, resulting in reduced proliferation, abnormal daughter cell nuclear morphology, and, in a subset of cells, cytokinesis failure. This phenotype could be explained by a failure of KIF22 to inactivate in anaphase. Consistent with this model, constitutive activation of the motor via a known site of phosphoregulation in the tail phenocopied the effects of pathogenic mutations. These results suggest that the motor domain α2 helix may be an important site for regulation of KIF22 activity at the metaphase to anaphase transition. In support of this conclusion, mimicking phosphorylation of α2 helix residue T158 also prevents inactivation of KIF22 in anaphase. These findings demonstrate the importance of both the head and tail of the motor in regulating the activity of KIF22 and offer insight into the cellular consequences of preventing KIF22 inactivation and disrupting force balance in anaphase.
Topics: Anaphase; Chromosome Segregation; DNA-Binding Proteins; Kinesins; Metaphase; Mitosis; Mutation; Nuclear Proteins; Spindle Apparatus
PubMed: 35730929
DOI: 10.7554/eLife.78653 -
Biophysical Journal Apr 2015Elongation of the mitotic spindle during anaphase B contributes to chromosome segregation in many cells. Here, we quantitatively test the ability of two models for...
Elongation of the mitotic spindle during anaphase B contributes to chromosome segregation in many cells. Here, we quantitatively test the ability of two models for spindle length control to describe the dynamics of anaphase B spindle elongation using experimental data from Drosophila embryos. In the slide-and-flux-or-elongate (SAFE) model, kinesin-5 motors persistently slide apart antiparallel interpolar microtubules (ipMTs). During pre-anaphase B, this outward sliding of ipMTs is balanced by depolymerization of their minus ends at the poles, producing poleward flux, while the spindle maintains a constant length. Following cyclin B degradation, ipMT depolymerization ceases so the sliding ipMTs can push the poles apart. The competing slide-and-cluster (SAC) model proposes that MTs nucleated at the equator are slid outward by the cooperative actions of the bipolar kinesin-5 and a minus-end-directed motor, which then pulls the sliding MTs inward and clusters them at the poles. In assessing both models, we assume that kinesin-5 preferentially cross-links and slides apart antiparallel MTs while the MT plus ends exhibit dynamic instability. However, in the SAC model, minus-end-directed motors bind the minus ends of MTs as cargo and transport them poleward along adjacent, parallel MT tracks, whereas in the SAFE model, all MT minus ends that reach the pole are depolymerized by kinesin-13. Remarkably, the results show that within a narrow range of MT dynamic instability parameters, both models can reproduce the steady-state length and dynamics of pre-anaphase B spindles and the rate of anaphase B spindle elongation. However, only the SAFE model reproduces the change in MT dynamics observed experimentally at anaphase B onset. Thus, although both models explain many features of anaphase B in this system, our quantitative evaluation of experimental data regarding several different aspects of spindle dynamics suggests that the SAFE model provides a better fit.
Topics: Anaphase; Animals; Drosophila; Kinesins; Microtubules; Models, Biological; Spindle Apparatus
PubMed: 25902440
DOI: 10.1016/j.bpj.2015.03.018 -
Nature Communications Sep 2021The RAD51 recombinase plays critical roles in safeguarding genome integrity, which is fundamentally important for all living cells. While interphase functions of RAD51...
The RAD51 recombinase plays critical roles in safeguarding genome integrity, which is fundamentally important for all living cells. While interphase functions of RAD51 in maintaining genome stability are well-characterised, its role in mitosis remains contentious. In this study, we show that RAD51 protects under-replicated DNA in mitotic human cells and, in this way, promotes mitotic DNA synthesis (MiDAS) and successful chromosome segregation. In cells experiencing mild replication stress, MiDAS was detected irrespective of mitotically generated DNA damage. MiDAS broadly required de novo RAD51 recruitment to single-stranded DNA, which was supported by the phosphorylation of RAD51 by the key mitotic regulator Polo-like kinase 1. Importantly, acute inhibition of MiDAS delayed anaphase onset and induced centromere fragility, suggesting a mechanism that prevents the satisfaction of the spindle assembly checkpoint while chromosomal replication remains incomplete. This study hence identifies an unexpected function of RAD51 in promoting genomic stability in mitosis.
Topics: Anaphase; Cell Cycle Proteins; Cell Line; Chromatin; Chromosome Segregation; DNA; DNA Damage; DNA Repair; DNA Replication; Genomic Instability; Humans; Intravital Microscopy; M Phase Cell Cycle Checkpoints; Phosphorylation; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Rad51 Recombinase; Polo-Like Kinase 1
PubMed: 34508092
DOI: 10.1038/s41467-021-25643-y