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Iain M Cheeseman

Publications and source records attributed to Iain M Cheeseman.

14 recordsLinked to original sources
PubMed2025

KIF18A promotes chromosome congression in cooperation with CENP-E downstream of CENP-C.

Chromosome congression is a key process that acts to align chromosomes at the spindle equator via kinetochore-microtubule interactions, with defects in chromosome alignment leading to chromosomal instability. However, defining the mechanisms that underlie chromosome congression is limited due to the multiple factors that act in parallel to regulate chromosome movement. Here, we conducted a genome-wide Cas9-based functional genetics screen using a hypomorphic CENP-C mutant that affects its kinetochore interactions. Our analysis identified KIF18A, whose knockout resulted in synthetic lethality with the CENP-C mutant. Further analysis revealed that the synthetic defect was due to a reduction in CENP-E function in the CENP-C mutant. Our work suggests that KIF18A promotes chromosome alignment in cooperation with CENP-E downstream of CENP-C during early prometaphase. Thus, our analysis enables us to dissect parallel molecular mechanisms for chromosome congression and identify sensitivities and biomarkers that might guide anti-KIF18A chemotherapeutics.

Kinesins↗
PubMed2006

The conserved KMN network constitutes the core microtubule-binding site of the kinetochore.

The microtubule-binding interface of the kinetochore is of central importance in chromosome segregation. Although kinetochore components that stabilize, translocate on, and affect the polymerization state of microtubules have been identified, none have proven essential for kinetochore-microtubule interactions. Here, we examined the conserved KNL-1/Mis12 complex/Ndc80 complex (KMN) network, which is essential for kinetochore-microtubule interactions in vivo. We identified two distinct microtubule-binding activities within the KMN network: one associated with the Ndc80/Nuf2 subunits of the Ndc80 complex, and a second in KNL-1. Formation of the complete KMN network, which additionally requires the Mis12 complex and the Spc24/Spc25 subunits of the Ndc80 complex, synergistically enhances microtubule-binding activity. Phosphorylation by Aurora B, which corrects improper kinetochore-microtubule connections in vivo, reduces the affinity of the Ndc80 complex for microtubules in vitro. Based on these findings, we propose that the conserved KMN network constitutes the core microtubule-binding site of the kinetochore.

Amino Acid Sequence↗
PubMed2006

The CENP-H-I complex is required for the efficient incorporation of newly synthesized CENP-A into centromeres.

In vertebrates, centromeres lack defined sequences and are thought to be propagated by epigenetic mechanisms involving the incorporation of specialized nucleosomes containing the histone H3 variant centromere protein (CENP)-A. However, the precise mechanisms that target CENP-A to centromeres remain poorly understood. Here, we isolated a multi-subunit complex, which includes the established inner kinetochore components CENP-H and CENP-I, and nine other proteins, from both human and chicken cells. Our analysis of these proteins demonstrates that the CENP-H-I complex can be divided into three functional sub-complexes, each of which is required for faithful chromosome segregation. Interestingly, newly expressed CENP-A is not efficiently incorporated into centromeres in knockout mutants of a subclass of CENP-H-I complex proteins, indicating that the CENP-H-I complex may function, in part, as a marker directing CENP-A deposition to centromeres.

Animals↗
PubMed2006

The human Mis12 complex is required for kinetochore assembly and proper chromosome segregation.

During cell division, kinetochores form the primary chromosomal attachment sites for spindle microtubules. We previously identified a network of 10 interacting kinetochore proteins conserved between Caenorhabditis elegans and humans. In this study, we investigate three proteins in the human network (hDsn1Q9H410, hNnf1PMF1, and hNsl1DC31). Using coexpression in bacteria and fractionation of mitotic extracts, we demonstrate that these proteins form a stable complex with the conserved kinetochore component hMis12. Human or chicken cells depleted of Mis12 complex subunits are delayed in mitosis with misaligned chromosomes and defects in chromosome biorientation. Aligned chromosomes exhibited reduced centromere stretch and diminished kinetochore microtubule bundles. Consistent with this, localization of the outer plate constituent Ndc80HEC1 was severely reduced. The checkpoint protein BubR1, the fibrous corona component centromere protein (CENP) E, and the inner kinetochore proteins CENP-A and CENP-H also failed to accumulate to wild-type levels in depleted cells. These results indicate that a four-subunit Mis12 complex plays an essential role in chromosome segregation in vertebrates and contributes to mitotic kinetochore assembly.

Animals↗
PubMed2005

The CENP-F-like proteins HCP-1 and HCP-2 target CLASP to kinetochores to mediate chromosome segregation.

During chromosome segregation, kinetochores form dynamic connections with spindle microtubules. In vertebrates, these attachments require the activities of a number of outer kinetochore proteins, including CENP-F [1, 2] and the widely conserved microtubule-associated protein CLASP [3]. Here, we investigate the functional relationship between HCP-1/2, two redundant CENP-F-like proteins, and CLASP(CLS-2) in Caenorhabditis elegans. HCP-1/2 and CLASP(CLS-2) localize transiently to mitotic C. elegans kinetochores with nearly identical kinetic profiles, and biochemical purifications demonstrate that they also associate physically. In embryos depleted of HCP-1/2, CLASP(CLS-2) no longer localizes to chromosomes, whereas CLASP(CLS-2) depletion does not prevent HCP-1/2 targeting. Consistent with the localization dependency and biochemical association, depletion of HCP-1/2 or CLASP(CLS-2) resulted in virtually identical defects in mitotic chromosome segregation characterized by a failure of sister-chromatid biorientation. This phenotype could be partially suppressed by disrupting the astral forces that pull spindle poles apart in the 1 cell embryo, indicating that CLASP(CLS-2) is required for biorientation when chromosome-spindle attachments are subjected to poleward force. Our results establish that the key role of HCP-1/2 is to target CLASP(CLS-2) to kinetochores, and they support the recently proposed model that CLASP functions to promote the polymerization of kinetochore bound microtubules [4].

Animals↗
PubMed2005

A combined approach for the localization and tandem affinity purification of protein complexes from metazoans.

An understanding of a protein's function is greatly aided by the knowledge of its localization in vivo and identification of any interacting partners. Here, we describe a method, based on expression of a genetically encoded fusion protein, that allows for protein localization and affinity purification (LAP) in metazoans. This method makes it possible to rapidly identify transformants and to conduct live imaging of protein localization and dynamics. In addition, the same tag can be used in a modified tandem affinity purification (TAP) procedure to isolate native protein complexes of high purity. The efficacy of this purification procedure allows for the characterization of rare protein complexes that are largely inaccessible to classical biochemical purifications. The LAP strategy should be widely applicable to the characterization of protein function in cellular and developmental contexts in various metazoans.

Amino Acid Sequence↗
PubMed2004

A conserved protein network controls assembly of the outer kinetochore and its ability to sustain tension.

Kinetochores play an essential role in chromosome segregation by forming dynamic connections with spindle microtubules. Here, we identify a set of 10 copurifying kinetochore proteins from Caenorhabditis elegans, seven of which were previously uncharacterized. Using in vivo assays to monitor chromosome segregation, kinetochore assembly, and the mechanical stability of chromosome-microtubule attachments, we show that this copurifying protein network plays a central role at the kinetochore-microtubule interface. In addition, our analysis suggests that the network is comprised of three groups of proteins that contribute in distinct ways to this interface: KNL proteins act after the assembly of centromeric chromatin to generate the core of the microtubule-binding interface, MIS proteins control the rate and extent of formation of this interface, and NDC proteins are necessary to sustain tension during interactions with spindle microtubules. We also purify a similar set of associated proteins from human cells that includes four novel proteins and has recognizable homologs from each functional class. Thus, this protein network is a conserved constituent of the outer kinetochore, and the functions defined by our analysis in C. elegans are likely to be widely relevant.

Amino Acid Sequence↗
PubMed2004

Cell division: AAAtacking the mitotic spindle.

Cell division requires the assembly of a microtubule-based spindle which captures and segregates sister chromatids. But how is this spindle broken down once chromosome segregation is complete? New evidence implicates a highly conserved AAA-ATPase in spindle disassembly at the end of mitosis.

Adenosine Triphosphatases↗
PubMed2004

"Holo"er than thou: chromosome segregation and kinetochore function in C. elegans.

Kinetochores are proteinaceous organelles that assemble on centromeric DNA to direct chromosome segregation in all eukaryotes. While many aspects of kinetochore function are conserved, the nature of the chromosomal domain upon which kinetochores assemble varies dramatically between different species. In monocentric eukaryotes, kinetochores assemble on a localized region of each chromosome. In contrast, holocentric species such as the nematode Caenorhabditis elegans have diffuse kinetochores that form along the entire length of their chromosomes. Here, we discuss the nature of chromosome segregation in C. elegans. In addition to reviewing what is known about kinetochore function, chromosome structure, and chromosome movement, we consider the consequences of the specialized holocentric architecture on chromosome segregation.

Animals↗
PubMed2003

Architecture of the budding yeast kinetochore reveals a conserved molecular core.

How kinetochore proteins are organized to connect chromosomes to spindle microtubules, and whether any structural and organizational themes are common to kinetochores from distantly related organisms, are key unanswered questions. Here, we used affinity chromatography and mass spectrometry to generate a map of kinetochore protein interactions. The budding yeast CENP-C homologue Mif2p specifically copurified with histones H2A, H2B, and H4, and with the histone H3-like CENP-A homologue Cse4p, strongly suggesting that Cse4p replaces histone H3 in a specialized centromeric nucleosome. A novel four-protein Mtw1 complex, the Nnf1p subunit of which has homology to the vertebrate kinetochore protein CENP-H, also copurified with Mif2p and a variety of central kinetochore proteins. We show that Mif2 is a critical in vivo target of the Aurora kinase Ipl1p. Chromatin immunoprecipitation studies demonstrated the biological relevance of these associations. We propose that a molecular core consisting of CENP-A, -C, -H, and Ndc80/HEC has been conserved from yeast to humans to link centromeres to spindle microtubules.

Amino Acid Sequence↗
PubMed2003

Kinetochore protein interactions and their regulation by the Aurora kinase Ipl1p.

Although there has been a recent explosion in the identification of budding yeast kinetochore components, the physical interactions that underlie kinetochore function remain obscure. To better understand how kinetochores attach to microtubules and how this attachment is regulated, we sought to characterize the interactions among kinetochore proteins, especially with respect to the microtubule-binding Dam1 complex. The Dam1 complex plays a crucial role in the chromosome-spindle attachment and is a key target for phospho-regulation of this attachment by the Aurora kinase Ipl1p. To identify protein-protein interactions involving the Dam1 complex, and the effects of Dam1p phosphorylation state on these physical interactions, we conducted both a genome-wide two-hybrid screen and a series of biochemical binding assays for Dam1p. A two-hybrid screen of a library of 6000 yeast open reading frames identified nine kinetochore proteins as Dam1p-interacting partners. From 113 in vitro binding reactions involving all nine subunits of the Dam1 complex and 32 kinetochore proteins, we found at least nine interactions within the Dam1 complex and 19 potential partners for the Dam1 complex. Strikingly, we found that the Dam1p-Ndc80p and Dam1p-Spc34p interactions were weakened by mutations mimicking phosphorylation at Ipl1p sites, allowing us to formulate a model for the effects of phosphoregulation on kinetochore function.

Aurora Kinases↗
PubMed2002

Phospho-regulation of kinetochore-microtubule attachments by the Aurora kinase Ipl1p.

The Aurora kinase Ipl1p plays a crucial role in regulating kinetochore-microtubule attachments in budding yeast, but the underlying basis for this regulation is not known. To identify Ipl1p targets, we first purified 28 kinetochore proteins from yeast protein extracts. These studies identified five previously uncharacterized kinetochore proteins and defined two additional kinetochore subcomplexes. We then used mass spectrometry to identify 18 phosphorylation sites in 7 of these 28 proteins. Ten of these phosphorylation sites are targeted directly by Ipl1p, allowing us to identify a consensus phosphorylation site for an Aurora kinase. Our systematic mutational analysis of the Ipl1p phosphorylation sites demonstrated that the essential microtubule binding protein Dam1p is a key Ipl1p target for regulating kinetochore-microtubule attachments in vivo.

Amino Acid Sequence↗
PubMed2002

Simple centromere, complex kinetochore: linking spindle microtubules and centromeric DNA in budding yeast.

Although the budding yeast centromere is extremely short (125 bp) compared to those of other eukaryotes, the kinetochore that assembles on this DNA displays a rich molecular complexity. Here, we describe recent advances in our understanding of kinetochore function in budding yeast and present a model describing the attachment that is formed between spindle microtubules and centromeric DNA. This analysis may provide general principles for kinetochore function and regulation.

DNA, Fungal↗