Publications by authors named "Duncan J Clarke"

58 Publications

MCPH1 Lack of Function Enhances Mitotic Cell Sensitivity Caused by Catalytic Inhibitors of Topo II.

Genes (Basel) 2020 04 8;11(4). Epub 2020 Apr 8.

Department of Experimental Biology, University of Jaén, 23071 Jaén, Spain.

The capacity of Topoisomerase II (Topo II) to remove DNA catenations that arise after replication is essential to ensure faithful chromosome segregation. Topo II activity is monitored during G2 by a specific checkpoint pathway that delays entry into mitosis until the chromosomes are properly decatenated. Recently, we demonstrated that the mitotic defects that are characteristic of cells depleted of MCPH1 function, a protein mutated in primary microcephaly, are not a consequence of a weakened G2 decatenation checkpoint response. However, the mitotic defects could be accounted for by a minor defect in the activity of Topo II during G2/M. To test this hypothesis, we have tracked at live single cell resolution the dynamics of mitosis in MCPH1 depleted HeLa cells upon catalytic inhibition of Topo II. Our analyses demonstrate that neither chromosome alignment nor segregation are more susceptible to minor perturbation in decatenation in MCPH1 deficient cells, as compared with control cells. Interestingly, MCPH1 depleted cells were more prone to mitotic cell death when decatenation was perturbed. Furthermore, when the G2 arrest that was induced by catalytic inhibition of Topo II was abrogated by Chk1 inhibition, the incidence of mitotic cell death was also increased. Taken together, our data suggest that the MCPH1 lack of function increases mitotic cell hypersensitivity to the catalytic inhibition of Topo II.
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http://dx.doi.org/10.3390/genes11040406DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7231051PMC
April 2020

Mitotic entry upon Topo II catalytic inhibition is controlled by Chk1 and Plk1.

FEBS J 2020 Nov 20;287(22):4933-4951. Epub 2020 Mar 20.

Departamento de Biología Experimental, Universidad de Jaén, Spain.

Catalytic inhibition of topoisomerase II during G2 phase delays onset of mitosis due to the activation of the so-called decatenation checkpoint. This checkpoint is less known compared with the extensively studied G2 DNA damage checkpoint and is partially compromised in many tumor cells. We recently identified MCPH1 as a key regulator that confers cells with the capacity to adapt to the decatenation checkpoint. In the present work, we have explored the contributions of checkpoint kinase 1 (Chk1) and polo-like kinase 1 (Plk1), in order to better understand the molecular basis of decatenation checkpoint. Our results demonstrate that Chk1 function is required to sustain the G2 arrest induced by catalytic inhibition of Topo II. Interestingly, Chk1 loss of function restores adaptation in cells lacking MCPH1. Furthermore, we demonstrate that Plk1 function is required to bypass the decatenation checkpoint arrest in cells following Chk1 inhibition. Taken together, our data suggest that MCPH1 is critical to allow checkpoint adaptation by counteracting Chk1-mediated inactivation of Plk1. Importantly, we also provide evidence that MCPH1 function is not required to allow recovery from this checkpoint, which lends support to the notion that checkpoint adaptation and recovery are different mechanisms distinguished in part by specific effectors.
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http://dx.doi.org/10.1111/febs.15280DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7483426PMC
November 2020

Topoisomerase II SUMOylation activates a metaphase checkpoint via Haspin and Aurora B kinases.

J Cell Biol 2020 01;219(1)

Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN.

Topoisomerase II (Topo II) is essential for mitosis since it resolves sister chromatid catenations. Topo II dysfunction promotes aneuploidy and drives cancer. To protect from aneuploidy, cells possess mechanisms to delay anaphase onset when Topo II is perturbed, providing additional time for decatenation. Molecular insight into this checkpoint is lacking. Here we present evidence that catalytic inhibition of Topo II, which activates the checkpoint, leads to SUMOylation of the Topo II C-terminal domain (CTD). This modification triggers mobilization of Aurora B kinase from inner centromeres to kinetochore proximal centromeres and the core of chromosome arms. Aurora B recruitment accompanies histone H3 threonine-3 phosphorylation and requires Haspin kinase. Strikingly, activation of the checkpoint depends both on Haspin and Aurora B. Moreover, mutation of the conserved CTD SUMOylation sites perturbs Aurora B recruitment and checkpoint activation. The data indicate that SUMOylated Topo II recruits Aurora B to ectopic sites, constituting the molecular trigger of the metaphase checkpoint when Topo II is catalytically inhibited.
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http://dx.doi.org/10.1083/jcb.201807189DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7039214PMC
January 2020

MCPH1 is essential for cellular adaptation to the G-phase decatenation checkpoint.

FASEB J 2019 07 9;33(7):8363-8374. Epub 2019 Apr 9.

Departamento de Biología Experimental, Universidad de Jaén, Jaén, Spain.

Cellular checkpoints controlling entry into mitosis monitor the integrity of the DNA and delay mitosis onset until the alteration is fully repaired. However, this canonical response can weaken, leading to a spontaneous bypass of the checkpoint, a process referred to as checkpoint adaptation. Here, we have investigated the contribution of microcephalin 1 (MCPH1), mutated in primary microcephaly, to the decatenation checkpoint, a less-understood G pathway that delays entry into mitosis until chromosomes are properly disentangled. Our results demonstrate that, although MCPH1 function is dispensable for activation and maintenance of the decatenation checkpoint, it is required for the adaptive response that bypasses the topoisomerase II inhibition----mediated G arrest. MCPH1, however, does not confer adaptation to the G arrest triggered by the ataxia telangiectasia mutated- and ataxia telangiectasia and rad3 related-based DNA damage checkpoint. In addition to revealing a new role for MCPH1 in cell cycle control, our study provides new insights into the genetic requirements that allow cellular adaptation to G checkpoints, a process that remains poorly understood.-Arroyo, M., Kuriyama, R., Guerrero, I., Keifenheim, D., Cañuelo, A., Calahorra, J., Sánchez, A., Clarke, D. J., Marchal, J. A. MCPH1 is essential for cellular adaptation to the G-phase decatenation checkpoint.
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http://dx.doi.org/10.1096/fj.201802009RRDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6593890PMC
July 2019

Cell cycle regulation of condensin Smc4.

Oncotarget 2019 Jan 8;10(3):263-276. Epub 2019 Jan 8.

Department of Genetics, Cell Biology and Development, University of Minnesota Medical School, Minneapolis, MN, USA.

The condensin complex is a conserved ATPase which promotes the compaction of chromatin during mitosis in eukaryotic cells. Condensin complexes have in addition been reported to contribute to interphase processes including sister chromatid cohesion. It is not understood how condensins specifically become competent to facilitate chromosome condensation in preparation for chromosome segregation in anaphase. Here we describe evidence that core condensin subunits are regulated at the level of protein stability in budding yeast. In particular, Smc2 and Smc4 abundance is cell cycle regulated, peaking at mitosis and falling to low levels in interphase. Smc4 degradation at the end of mitosis is dependent on the Anaphase Promoting Complex/Cyclosome and is mediated by the proteasome. Overproduction of Smc4 results in delayed decondensation, but has a limited ability to promote premature condensation in interphase. Unexpectedly, the Mad2 spindle checkpoint protein is required for mitotic Smc4 degradation. These studies have revealed the novel finding that condensin protein levels are cell cycle regulated and have identified the factors necessary for Smc4 proteolysis.
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http://dx.doi.org/10.18632/oncotarget.26467DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6349450PMC
January 2019

Monitoring the DNA Topoisomerase II Checkpoint in Saccharomyces cerevisiae.

Methods Mol Biol 2018 ;1703:217-240

Department of Genetics, Cell Biology & Development, University of Minnesota, 420 Washington Ave SE, Minneapolis, MN, 55455, USA.

Topoisomerase II activity is crucial to maintain genome stability through the removal of catenanes in the DNA formed during DNA replication and scaffolding the mitotic chromosome. Perturbed Topo II activity causes defects in chromosome segregation due to persistent catenations and aberrant DNA condensation during mitosis. Recently, novel top2 alleles in the yeast Saccharomyces cerevisiae revealed a checkpoint control which responds to perturbed Topo II activity. Described in this chapter are protocols for assaying the phenotypes seen in top2 mutants on a cell biological basis in live cells: activation of the Topo II checkpoint using spindle morphology, chromosome condensation using fluorescently labeled chromosomal loci and cell cycle progression by flow cytometry. Further characterization of this novel checkpoint is warranted so that we can further our understanding of the cell cycle, genomic stability, and the possibility of identifying novel drug targets.
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http://dx.doi.org/10.1007/978-1-4939-7459-7_16DOI Listing
July 2018

Analyzing Mitotic Chromosome Structural Defects After Topoisomerase II Inhibition or Mutation.

Methods Mol Biol 2018 ;1703:191-215

Department of Genetics, Cell Biology & Development, University of Minnesota, 420 Washington Ave SE, Minneapolis, MN, 55455, USA.

For analyzing chromosome structural defects that result from topoisomerase II (topo II) dysfunction we have adapted classical cell cycle experiments, classical cytological techniques and the use of a potent topo II inhibitor (ICRF-193). In this chapter, we describe in detail the protocols used and we discuss the rational for our choice and for the adaptations applied. We clarify in which cell cycle stages each of the different chromosomal aberrations induced by inhibiting topo II takes place: lack of chromosome segregation, undercondensation, lack of sister chromatid resolution, and lack of chromosome individualization. We also put these observations into the context of the two topo II-dependent cell cycle checkpoints. In addition, we have devised a system to analyze phenotypes that result when topo II is mutated in human cells. This serves as an alternative strategy to the use of topo II inhibitors to perturb topo II function.
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http://dx.doi.org/10.1007/978-1-4939-7459-7_15DOI Listing
July 2018

Non-Catalytic Roles of the Topoisomerase IIα C-Terminal Domain.

Int J Mol Sci 2017 Nov 17;18(11). Epub 2017 Nov 17.

Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045, USA.

DNA Topoisomerase IIα (Topo IIα) is a ubiquitous enzyme in eukaryotes that performs the strand passage reaction where a double helix of DNA is passed through a second double helix. This unique reaction is critical for numerous cellular processes. However, the enzyme also possesses a C-terminal domain (CTD) that is largely dispensable for the strand passage reaction but is nevertheless important for the fidelity of cell division. Recent studies have expanded our understanding of the roles of the Topo IIα CTD, in particular in mitotic mechanisms where the CTD is modified by Small Ubiquitin-like Modifier (SUMO), which in turn provides binding sites for key regulators of mitosis.
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http://dx.doi.org/10.3390/ijms18112438DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5713405PMC
November 2017

Cell surface damage activates a cell cycle checkpoint (comment on DOI: 10.1002/bies.201600210).

Authors:
Duncan J Clarke

Bioessays 2017 04 7;39(4). Epub 2017 Mar 7.

Department of Genetics Cell Biology & Development, University of Minnesota, Minneapolis, MN, USA.

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http://dx.doi.org/10.1002/bies.201700022DOI Listing
April 2017

A noncatalytic function of the topoisomerase II CTD in Aurora B recruitment to inner centromeres during mitosis.

J Cell Biol 2016 06;213(6):651-64

Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455

Faithful chromosome segregation depends on the precise timing of chromatid separation, which is enforced by checkpoint signals generated at kinetochores. Here, we provide evidence that the C-terminal domain (CTD) of DNA topoisomerase IIα (Topo II) provides a novel function at inner centromeres of kinetochores in mitosis. We find that the yeast CTD is required for recruitment of the tension checkpoint kinase Ipl1/Aurora B to inner centromeres in metaphase but is not required in interphase. Conserved CTD SUMOylation sites are required for Ipl1 recruitment. This inner-centromere CTD function is distinct from the catalytic activity of Topo II. Genetic and biochemical evidence suggests that Topo II recruits Ipl1 via the Haspin-histone H3 threonine 3 phosphorylation pathway. Finally, Topo II and Sgo1 are equally important for Ipl1 recruitment to inner centromeres. This indicates H3 T3-Phos/H2A T120-Phos is a universal epigenetic signature that defines the eukaryotic inner centromere and provides the binding site for Ipl1/Aurora B.
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http://dx.doi.org/10.1083/jcb.201511080DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4915189PMC
June 2016

Visualizing chromosome segregation in live cells.

Cell Cycle 2016 07 10;15(14):1811. Epub 2016 May 10.

b Department of Genetics , Cell Biology and Development, University of Minnesota , Minneapolis , MN , USA.

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http://dx.doi.org/10.1080/15384101.2016.1185852DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4968893PMC
July 2016

Novel kinetochore function of Topoisomerase IIα.

Authors:
Duncan J Clarke

Cell Cycle 2015 7;14(18):2875-6. Epub 2015 Aug 7.

a Department of Genetics ; Cell Biology & Development; University of Minnesota ; Minneapolis , MN USA.

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http://dx.doi.org/10.1080/15384101.2015.1076303DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4825621PMC
June 2016

Sororin is tethered to Cohesin SA2.

Cell Cycle 2015 ;14(8):1133

a Department of Genetics, Cell Biology and Development ; University of Minnesota ; Minneapolis , MN USA.

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http://dx.doi.org/10.1080/15384101.2015.1018055DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4614277PMC
December 2015

Pericentromere tension is self-regulated by spindle structure in metaphase.

J Cell Biol 2014 May;205(3):313-24

Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455.

During cell division, a mitotic spindle is built by the cell and acts to align and stretch duplicated sister chromosomes before their ultimate segregation into daughter cells. Stretching of the pericentromeric chromatin during metaphase is thought to generate a tension-based signal that promotes proper chromosome segregation. However, it is not known whether the mitotic spindle actively maintains a set point tension magnitude for properly attached sister chromosomes to facilitate robust mechanochemical checkpoint signaling. By imaging and tracking the thermal movements of pericentromeric fluorescent markers in Saccharomyces cerevisiae, we measured pericentromere stiffness and then used the stiffness measurements to quantitatively evaluate the tension generated by pericentromere stretch during metaphase in wild-type cells and in mutants with disrupted chromosome structure. We found that pericentromere tension in yeast is substantial (4-6 pN) and is tightly self-regulated by the mitotic spindle: through adjustments in spindle structure, the cell maintains wild-type tension magnitudes even when pericentromere stiffness is disrupted.
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http://dx.doi.org/10.1083/jcb.201312024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4018788PMC
May 2014

A novel chromatin tether domain controls topoisomerase IIα dynamics and mitotic chromosome formation.

J Cell Biol 2013 Nov;203(3):471-86

Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN 55455.

DNA topoisomerase IIα (Topo IIα) is the target of an important class of anticancer drugs, but tumor cells can become resistant by reducing the association of the enzyme with chromosomes. Here we describe a critical mechanism of chromatin recruitment and exchange that relies on a novel chromatin tether (ChT) domain and mediates interaction with histone H3 and DNA. We show that the ChT domain controls the residence time of Topo IIα on chromatin in mitosis and is necessary for the formation of mitotic chromosomes. Our data suggest that the dynamics of Topo IIα on chromosomes are important for successful mitosis and implicate histone tail posttranslational modifications in regulating Topo IIα.
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http://dx.doi.org/10.1083/jcb.201303045DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3824022PMC
November 2013

Direct monitoring of the strand passage reaction of DNA topoisomerase II triggers checkpoint activation.

PLoS Genet 2013 3;9(10):e1003832. Epub 2013 Oct 3.

Department of Genetics, Cell Biology & Development, University of Minnesota, Minneapolis, Minnesota, United States of America.

By necessity, the ancient activity of type II topoisomerases co-evolved with the double-helical structure of DNA, at least in organisms with circular genomes. In humans, the strand passage reaction of DNA topoisomerase II (Topo II) is the target of several major classes of cancer drugs which both poison Topo II and activate cell cycle checkpoint controls. It is important to know the cellular effects of molecules that target Topo II, but the mechanisms of checkpoint activation that respond to Topo II dysfunction are not well understood. Here, we provide evidence that a checkpoint mechanism monitors the strand passage reaction of Topo II. In contrast, cells do not become checkpoint arrested in the presence of the aberrant DNA topologies, such as hyper-catenation, that arise in the absence of Topo II activity. An overall reduction in Topo II activity (i.e. slow strand passage cycles) does not activate the checkpoint, but specific defects in the T-segment transit step of the strand passage reaction do induce a cell cycle delay. Furthermore, the cell cycle delay depends on the divergent and catalytically inert C-terminal region of Topo II, indicating that transmission of a checkpoint signal may occur via the C-terminus. Other, well characterized, mitotic checkpoints detect DNA lesions or monitor unattached kinetochores; these defects arise via failures in a variety of cell processes. In contrast, we have described the first example of a distinct category of checkpoint mechanism that monitors the catalytic cycle of a single specific enzyme in order to determine when chromosome segregation can proceed faithfully.
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http://dx.doi.org/10.1371/journal.pgen.1003832DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3789831PMC
March 2014

Genome instability: does genetic diversity amplification drive tumorigenesis?

Bioessays 2012 Nov 5;34(11):963-72. Epub 2012 Sep 5.

Department of Genetics, Cell Biology & Development, University of Minnesota, Minneapolis, MN, USA.

Recent data show that catastrophic events during one cell cycle can cause massive genome damage producing viable clones with unstable genomes. This is in contrast with the traditional view that tumorigenesis requires a long-term process in which mutations gradually accumulate over decades. These sudden events are likely to result in a large increase in genomic diversity within a relatively short time, providing the opportunity for selective advantages to be gained by a subset of cells within a population. This genetic diversity amplification, arising from a single aberrant cell cycle, may drive a population conversion from benign to malignant. However, there is likely a period of relative genome stability during the clonal expansion of tumors - this may provide an opportunity for therapeutic intervention, especially if mechanisms that limit tolerance of aneuploidy are exploited.
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http://dx.doi.org/10.1002/bies.201200082DOI Listing
November 2012

Are tumor cells protected from some anti-cancer drugs by elevated APC/C activity? (comment on DOI: 10.1002/bies.201100094).

Authors:
Duncan J Clarke

Bioessays 2011 Dec 2;33(12):898. Epub 2011 Nov 2.

Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN, USA.

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http://dx.doi.org/10.1002/bies.201100158DOI Listing
December 2011

Timeless makes some time for itself.

Cell Cycle 2011 Jul 15;10(14):2254. Epub 2011 Jul 15.

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http://dx.doi.org/10.4161/cc.10.14.15853DOI Listing
July 2011

Cohesin is needed for bipolar mitosis in human cells.

Cell Cycle 2010 May 15;9(9):1764-73. Epub 2010 May 15.

Department of Genetics, Cell Biology & Development, University of Minnesota Medical School, Minneapolis, MN, USA.

Multi-polar mitosis is strongly linked with aggressive cancers and it is a histological diagnostic of tumor-grade. However, factors that cause chromosomes to segregate to more than two spindle poles are not well understood. Here we show that cohesins Rad21, Smc1 and Smc3 are required for bipolar mitosis in human cells. After Rad21 depletion, chromosomes align at the metaphase plate and bipolar spindles assemble in most cases, but in anaphase the separated chromatids segregate to multiple poles. Time-lapse microscopy revealed that the spindle poles often become split in Rad21-depleted metaphase cells. Interestingly, exogenous expression of non-cleavable Rad21 results in multi-polar anaphase. Since cohesins are present at the spindle poles in mitosis, these data are consistent with a non-chromosomal function of cohesin.
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http://dx.doi.org/10.4161/cc.9.9.11525DOI Listing
May 2010

Determinants of Rad21 localization at the centrosome in human cells.

Cell Cycle 2010 May 15;9(9):1759-63. Epub 2010 May 15.

Department of Genetics, Cell Biology & Development, University of Minnesota Medical School, Minneapolis, MN, USA.

Cohesin proteins help maintain the physical associations between sister chromatids that arise in S-phase and are removed in anaphase. Recent studies found that cohesins also localize to the centrosomes, the organelles that organize the mitotic bipolar spindle. We find that the cohesin protein Rad21 localizes to centrosomes in a manner that is dependent upon known regulators of sister chromatid cohesion as well as regulators of centrosome function. These data suggest that Rad21 functions at the centrosome and that the regulators of Rad21 coordinate the centrosome and chromosomal functions of cohesin.
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http://dx.doi.org/10.4161/cc.9.9.11523DOI Listing
May 2010

Rad21 is required for centrosome integrity in human cells independently of its role in chromosome cohesion.

Cell Cycle 2010 May 15;9(9):1774-80. Epub 2010 May 15.

Department of Genetics, Cell Biology & Development, University of Minnesota Medical School, Minneapolis, MN, USA.

Classically, chromosomal functions in DNA repair and sister chromatid association have been assigned to the cohesin proteins. More recent studies have provided evidence that cohesins also localize to the centrosomes, which organize the bipolar spindle during mitosis. Depletion of cohesin proteins is associated with multi-polar mitosis in which spindle pole integrity is compromised. However, the spindle pole defects after cohesin depletion could be an indirect consequence of a chromosomal cohesion defect which might impact centrosome integrity via alterations to the spindle microtubule network. Here we show that the cohesin Rad21 is required for centrosome integrity independently of its role as a chromosomal cohesin. Thus, Rad21 may promote accurate chromosome transmission not only by virtue of its function as a chromosomal cohesin, but also because it is required for centrosome function.
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http://dx.doi.org/10.4161/cc.9.9.11524DOI Listing
May 2010

Cytological analysis of chromosome structural defects that result from topoisomerase II dysfunction.

Methods Mol Biol 2009 ;582:189-207

Reproducción Celular y Animal, CIB, CSIC, Madrid, Spain.

For analyzing chromosome structural defects that result from topoisomerase II (topo II) dysfunction, we have adapted classical cell cycle experiments, classical cytological techniques, and the use of a potent topo II inhibitor (ICRF-193). In this chapter, we describe in detail the protocols used and we discuss the rationale for our choice and for the adaptations applied. We clarify in which cell cycle stages each of the different chromosomal aberrations induced by inhibiting topo II take place: lack of chromosome segregation, undercondensation, lack of sister chromatid resolution, and lack of chromosome individualization. We also put these observations into the context of the two topo II-dependent cell cycle checkpoints.
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http://dx.doi.org/10.1007/978-1-60761-340-4_15DOI Listing
January 2010

Assaying topoisomerase II checkpoints in yeast.

Methods Mol Biol 2009 ;582:167-87

Department of Genetics, University of Minnesota, Minneapolis, MN, USA.

Topoisomerase II activity is crucial to maintain genome stability through the removal of catenanes in the DNA formed during DNA replication and scaffolding the mitotic chromosome. Perturbed Topo II activity causes defects in chromosome segregation due to persistent catenations and aberrant DNA condensation during mitosis. Recently, novel top2 alleles in the yeast Saccharomyces cerevisiae revealed a checkpoint control that responds to perturbed Topo II activity. Described in this chapter are protocols for assaying the phenotypes seen in top2 mutants on a cell biological basis in live cells: activation of the Topo II checkpoint using spindle morphology, chromosome condensation using fluorescently labeled chromosomal loci, and cell cycle progression by flow cytometry. Further characterization of this novel checkpoint is warranted so that we can further our understanding of the cell cycle, genomic stability, and the possibility of identifying novel drug targets.
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http://dx.doi.org/10.1007/978-1-60761-340-4_14DOI Listing
January 2010

Introduction: emerging themes in DNA topoisomerase research.

Methods Mol Biol 2009 ;582:1-9

Department of Genetics, University of Minnesota, Medical School, Minneapolis, MN, USA.

DNA topoisomerases are enzymes that alter the topology of DNA. They have important functions in DNA replication, transcription, Holliday junction dissolution, chromosome condensation, and sister chromatid separation. Deficiencies in these enzymes are associated with diseases that result from genome instability. The last 10-15 years has seen a great deal of exciting research in the field of topoisomerase. Here we discuss a selection of the new themes that have been recently introduced into the already large body of topoisomerase research.
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http://dx.doi.org/10.1007/978-1-60761-340-4_1DOI Listing
January 2010

Decatenation: fixing your knots.

Authors:
Duncan J Clarke

Blood 2009 Aug;114(9):1721-2

University of Minnesota.

How tumor cells gain resistance to drugs is critically important to elucidate for developing better cancer therapy. In this issue of Blood, Wray and colleagues have identified a mechanism whereby acute leukemia cells use a stimulator of topoisomerase II activity to allow proliferation despite drug inhibition of this essential enzyme.
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http://dx.doi.org/10.1182/blood-2009-06-224279DOI Listing
August 2009

Chromosome cohesion and the spindle checkpoint.

Cell Cycle 2009 Sep 30;8(17):2733-40. Epub 2009 Sep 30.

UT-Southwestern Medical Center, Department of Pharmacology, Dallas, TX 75390, USA.

Accurate chromosome segregation constitutes the basis of inheritance. Mistakes in chromosome segregation during mitosis lead to aneuploidy, a common feature of tumors. The accuracy of chromosome segregation is governed by a complex network of processes which ensure that each daughter cell receives the correct number of chromosomes. Herein we review recent developments in the understanding of chromosome segregation, focusing on the cohesion that holds the sister chromatids together and the spindle checkpoint which regulates anaphase onset.
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http://dx.doi.org/10.4161/cc.8.17.9403DOI Listing
September 2009

Strong inducible knockdown of Cdc20 does not cause mitotic arrest in human somatic cells: implications for cancer therapy?

Authors:
Duncan J Clarke

Cell Cycle 2009 Feb 15;8(4):515-6. Epub 2009 Feb 15.

Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota, USA.

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http://dx.doi.org/10.4161/cc.8.4.8057DOI Listing
February 2009

Chromosome cohesion - rings, knots, orcs and fellowship.

J Cell Sci 2008 Jul;121(Pt 13):2107-14

Department of Pharmacology, UT-Southwestern Medical Center, 6001 Forest Park Rd, Dallas, TX75390, USA.

Sister-chromatid cohesion is essential for accurate chromosome segregation. A key discovery towards our understanding of sister-chromatid cohesion was made 10 years ago with the identification of cohesins. Since then, cohesins have been shown to be involved in cohesion in numerous organisms, from yeast to mammals. Studies of the composition, regulation and structure of the cohesin complex led to a model in which cohesin loading during S-phase establishes cohesion, and cohesin cleavage at the onset of anaphase allows sister-chromatid separation. However, recent studies have revealed activities that provide cohesion in the absence of cohesin. Here we review these advances and propose an integrative model in which chromatid cohesion is a result of the combined activities of multiple cohesion mechanisms.
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http://dx.doi.org/10.1242/jcs.029132DOI Listing
July 2008

Kinetochore structure and spindle assembly checkpoint signaling in the budding yeast, Saccharomyces cerevisiae.

Front Biosci 2008 May 1;13:6787-819. Epub 2008 May 1.

Department of Genetics, Cell Biology and Development, University of Minnesota Medical School, Minneapolis, MN 55455, USA.

The Spindle Assembly Checkpoint (SAC) delays the onset of anaphase until every chromosome is properly bioriented at the spindle equator. Mutations in SAC genes have been found in tumors and compromised SAC function can increase the incidence of some carcinomas in mice, providing further links between cancer etiology, chromosome segregation defects and aneuploidy. Here we review recent developments in our understanding of SAC control with particular emphasis on the role of the kinetochore, the nature of the tension sensing mechanism and the possibility that the SAC encompasses more than just stabilization of securin and/or cyclin-B via inhibition of the APC/C to delay anaphase initiation. Our primary emphasis is on the SAC in the budding yeast Saccharomyces cerevisiae. However, relevant findings in other cells are also discussed to highlight the generally conserved nature of SAC signaling mechanisms.
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http://dx.doi.org/10.2741/3189DOI Listing
May 2008