Article

The Kinetochore-Bound Ska1 Complex Tracks Depolymerizing Microtubules and Binds to Curved Protofilaments

Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142, USA.
Developmental Cell (Impact Factor: 9.71). 10/2012; 23(5). DOI: 10.1016/j.devcel.2012.09.012
Source: PubMed

ABSTRACT

To ensure equal chromosome segregation during mitosis, the macromolecular kinetochore must remain attached to depolymerizing microtubules, which drive chromosome movements. How kinetochores associate with depolymerizing microtubules, which undergo dramatic structural changes forming curved protofilaments, has yet to be defined in vertebrates. Here, we demonstrate that the conserved kinetochore-localized Ska1 complex tracks with depolymerizing microtubule ends and associates with both the microtubule lattice and curved protofilaments. In contrast, the Ndc80 complex, a central player in the kinetochore-microtubule interface, binds only to the straight microtubule lattice and lacks tracking activity. We demonstrate that the Ska1 complex imparts its tracking capability to the Ndc80 complex. Finally, we present a structure of the Ska1 microtubule-binding domain that reveals its interaction with microtubules and its regulation by Aurora B. This work defines an integrated kinetochore-microtubule interface formed by the Ska1 and Ndc80 complexes that associates with depolymerizing microtubules, potentially by interacting with curved microtubule protofilaments.

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Available from: Ekaterina L Grishchuk, Jan 04, 2014
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    • "Recent studies on human kinetochore proteins have identified the Ska1 complex (Hanisch et al., 2006; Gaitanos et al., 2009; Welburn et al., 2009) and shown that it binds to curling tubulin; the interaction is on a part of tubulin that faces the MT exterior, but Ska1 prefers that surface when tubulin is bent (Schmidt et al., 2012). This complex also associates with a ubiquitous kinetochore protein, the Ndc80 complex, which binds weakly to the MT wall at one of its ends and to proteins of the inner kinetochore with the other (Sundin et al., 2011). "
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    ABSTRACT: Firm attachments between kinetochores and dynamic spindle microtubules (MTs) are important for accurate chromosome segregation. Centromere protein F (CENP-F) has been shown to include two MT-binding domains, so it may participate in this key mitotic process. Here, we show that the N-terminal MT-binding domain of CENP-F prefers curled oligomers of tubulin relative to MT walls by approximately fivefold, suggesting that it may contribute to the firm bonds between kinetochores and the flared plus ends of dynamic MTs. A polypeptide from CENP-F's C terminus also bound MTs, and either protein fragment diffused on a stable MT wall. They also followed the ends of dynamic MTs as they shortened. When either fragment was coupled to a microbead, the force it could transduce from a shortening MT averaged 3-5 pN but could exceed 10 pN, identifying CENP-F as a highly effective coupler to shortening MTs. © 2015 Volkov et al.
    Full-text · Article · Jun 2015 · The Journal of Cell Biology
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    • "Such a mechanism must involve proteins that (1) mediate end-on microtubule–kinetochore attachments, (2) maintain attachment to depolymerising microtubules and (3) ensure the K-fibre remains in a net depolymerising state through control of kinetochore–microtuble dynamics. The Ndc80 and Ska complexes can directly bind to microtubules in vitro, with the Ska complex (but not the Ndc80 complex) able to autonomously track depolymerising microtubule plus-ends (Schmidt et al., 2012). Extensive depletion of either complex results in a severe failure in chromosome congression and the inability to form a metaphase plate (Daum et al., 2009; Gaitanos et al., 2009; Welburn et al., 2010). "
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    ABSTRACT: A key step of mitosis is the congression of chromosomes to the spindle equator. Congression is driven by at least two distinct mechanisms: (1) kinetochores slide along the microtubule lattice using the plus-end directed CENP-E motor, and (2) kinetochores biorientating near the pole move to the equator through microtubule depolymerisation-coupled pulling. Here, we show that CENP-Q - a subunit of the CENP-O/P/Q/U complex that targets polo-like kinase (Plk1) to kinetochores - is also required for the recruitment of CENP-E to kinetochores. We further reveal a CENP-E recruitment-independent role for CENP-Q in depolymerisation-coupled pulling. Both these functions are abolished by a single point mutation in CENP-Q (S50A) - a residue that is phosphorylated in vivo. Importantly, the S50A mutant does not affect Plk1 loading onto kinetochores and leaves the CENP-O complex intact. Thus, the function of CENP-Q in CENP-E loading and depolymerisation-coupled pulling are independent from its role in Plk1 recruitment and CENP-O/P/Q/U complex stabilization. Together, our data provide evidence that phospho-regulation of CENP-Q plays a central function in coordinating chromosome congression mechanisms.
    Full-text · Article · Nov 2014 · Journal of Cell Science
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    • "Overexpression of AURK-A has been shown to be associated with aneuploidy, chromosome instablity, tumorigenic transformation and progression in mammalian cells (Bischoff et al. 1998; revised in Gómez-López et al. 2014). AURK-B has been shown to regulate SKA1 (Schmidt et al. 2012). KIF11 is a protein required from prophase until metaphase which participates in spindle assembly, centrosome separation, post-mitotic centrosome movement and bipolar spindle formation. "
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    ABSTRACT: Approximately 15% of eukaryotes contain supernumerary B chromosomes. When present, B chromosomes frequently represent as much as 5% of the genome. Despite thousands of reports describing the distribution of supernumeraries in various taxa, a comprehensive theory for the origin, maintenance and evolution of B chromosomes has not emerged. Here we sequence the complete genomes of individual cichlid fish (Astatotilapia latifasciata) with and without B chromosomes, as well as microdissected B chromosomes, to identify DNA sequences on the B. B sequences were further analyzed through qPCR and in situ hybridization. We find that the B chromosome contains thousands of sequences duplicated from essentially every chromosome in the ancestral karyotype. Although most genes on the B chromosome are fragmented, a few are largely intact and we detect evidence that at least three of them are transcriptionally active. We propose a model in which the B chromosome originated early in the evolutionary history of Lake Victoria cichlids from a small fragment of one autosome. DNA sequences originating from several autosomes, including protein-coding genes and transposable elements, subsequently inserted into this proto-B. We propose that intact B chromosome genes involved with spindle fusion and kinetochore attachment may play a role in driving the transmission of the B chromosome. Furthermore, our work suggests that karyotyping is an essential step prior to genome sequencing to avoid problems in genome assembly as well as analytical biases created by the presence of high copy number sequences on the B chromosome.
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