A histone-H3-like protein in C. elegans

Buchwitz, Brian J.; Ahmad, Kami; Moore, Landon L.; Roth, Mark B.; Henikoff, Steven

doi:10.1038/44062

Cited by 240 publications

(211 citation statements)

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“…Other conserved kinetochore components have also been identified in C. elegans. Two inner kinetochore proteins CENP-A and CENP-C act upstream of KNL-1, a novel kinetochore protein, and are all required for kinetochore assembly and chromosome segregation (Buchwitz et al, 1999;Oegema et al, 2001;Desai et al, 2003). CeBUB-1 and two CENP-F-related proteins called HCP-1 and HCP-2 also localize to kinetochores in one-cell embryos.…”

Section: Introductionmentioning

confidence: 99%

A Spindle Checkpoint Functions during Mitosis in the EarlyCaenorhabditis elegansEmbryo

Encalada

Willis

Lyczak

et al. 2005

MBoC

118

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During mitosis, chromosome segregation is regulated by a spindle checkpoint mechanism. This checkpoint delays anaphase until all kinetochores are captured by microtubules from both spindle poles, chromosomes congress to the metaphase plate, and the tension between kinetochores and their attached microtubules is properly sensed. Although the spindle checkpoint can be activated in many different cell types, the role of this regulatory mechanism in rapidly dividing embryonic animal cells has remained controversial. Here, using time-lapse imaging of live embryonic cells, we show that chemical or mutational disruption of the mitotic spindle in early Caenorhabditis elegans embryos delays progression through mitosis. By reducing the function of conserved checkpoint genes in mutant embryos with defective mitotic spindles, we show that these delays require the spindle checkpoint. In the absence of a functional checkpoint, more severe defects in chromosome segregation are observed in mutants with abnormal mitotic spindles. We also show that the conserved kinesin CeMCAK, the CENP-F-related proteins HCP-1 and HCP-2, and the core kinetochore protein CeCENP-C all are required for this checkpoint. Our analysis indicates that spindle checkpoint mechanisms are functional in the rapidly dividing cells of an early animal embryo and that this checkpoint can prevent chromosome segregation defects during mitosis. INTRODUCTIONDuring mitosis, some microtubules emanating from bipolar microtubule organizing centers grow toward chromosomes and attach to specialized chromosomal regions called kinetochores (Skibbens and Hieter, 1998;Cleveland et al., 2003). Once captured, sister chromatids are segregated, one to each of two daughter cells. Eukaryotic cells have evolved a mechanism called the spindle checkpoint, to monitor chromosomal segregation and increase the fidelity of mitosis (reviewed in Gardner and Burke, 2000;McIntosh et al., 2002). Until spindle microtubules from both poles capture and align all sister chromatid pairs at a metaphase plate, the spindle checkpoint produces a delay in the onset of anaphase. If this delay is bypassed by reducing checkpoint function, anaphase starts prematurely, and daughter cells may receive unequal complements of chromosomes. Such genomic instability can result in lethality and in tumorigenesis (Hartwell and Kastan, 1994;Basu et al., 1999).Originally identified and characterized in Saccharomyces cerevisiae, seven spindle assembly checkpoint genes (MAD1, MAD2, MAD3, BUB1, BUB2, BUB3, and MPS1) are known to function at kinetochores to inhibit anaphase onset, or to mediate mitotic exit in the presence of spindle abnormalities (Hoyt et al., 1991;Li and Murray, 1991). Mutations in these genes reduce or eliminate the cell cycle delays that normally occur after treatment with microtubule depolymerizing drugs (Wang and Burke, 1995;Pangilinan and Spencer, 1996). Bub1 and Bub3 form a protein kinase complex that, in concert with Mps1, functions at kinetochores upstream of Mad1 and Mad2 (Roberts et al., 1994;H...

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Section: Introductionmentioning

confidence: 99%

A Spindle Checkpoint Functions during Mitosis in the EarlyCaenorhabditis elegansEmbryo

Encalada

Willis

Lyczak

et al. 2005

MBoC

118

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“…One hallmark of all kinetochores is the essential CenH3 (Palmer et al, 1987;Stoler et al, 1995;Buchwitz et al, 1999;Henikoff et al, 2000;Takahashi et al, 2000;Sanyal and Carbon, 2002;Talbert et al, 2002;Zhong et al, 2002;Edwards and Murray, 2005). CenH3s contain a unique N terminus and a well-conserved C terminus that is highly homologous to histone H3 (Malik and Henikoff, 2003).…”

Section: Introductionmentioning

confidence: 99%

“…Outer kinetochore complexes include the conserved NDC80 (Ndc80, Spc24, Spc25, and Nuf2) and DAM1 (Dam1, Ask1, Duo1, Dad1, Dad2, Dad3, Dad4, Spc19, Spc34, and Hsk3) complexes. DAM1 is considered to be the outermost complex because it requires microtubules and all other complexes for kinetochore localization (Enquist-Newman et al, 2001;Janke et al, 2002;Li et al, 2002).One hallmark of all kinetochores is the essential CenH3 (Palmer et al, 1987;Stoler et al, 1995;Buchwitz et al, 1999;Henikoff et al, 2000;Takahashi et al, 2000;Sanyal and Carbon, 2002;Talbert et al, 2002;Zhong et al, 2002;Edwards and Murray, 2005). CenH3s contain a unique N terminus and a well-conserved C terminus that is highly homologous to histone H3 (Malik and Henikoff, 2003).…”

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confidence: 99%

De Novo Kinetochore Assembly Requires the Centromeric Histone H3 Variant

Collins

Castillo

Tatsutani

et al. 2005

MBoC

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Kinetochores mediate chromosome attachment to the mitotic spindle to ensure accurate chromosome segregation. Budding yeast is an excellent organism for kinetochore assembly studies because it has a simple defined centromere sequence responsible for the localization of >65 proteins. In addition, yeast is the only organism where a conditional centromere is available to allow studies of de novo kinetochore assembly. Using a conditional centromere, we found that yeast kinetochore assembly is not temporally restricted and can occur in both G 1 phase and prometaphase. We performed the first investigation of kinetochore assembly in the absence of the centromeric histone H3 variant Cse4 and found that all proteins tested depend on Cse4 to localize. Consistent with this observation, Cse4-depleted cells had severe chromosome segregation defects. We therefore propose that yeast kinetochore assembly requires both centromeric DNA specificity and centromeric chromatin. INTRODUCTIONAccurate chromosome segregation in mitosis and meiosis is essential for the maintenance of genomic stability. Chromosomes attach to the mitotic spindle at the kinetochore, the protein complex that assembles onto centromeric DNA. Although kinetochore function is conserved, the underlying centromeric DNA is highly variable. Budding yeast contain a 125-base pair sequence-specific centromere that is sufficient for kinetochore formation (Fitzgerald-Hayes et al., 1982). In contrast, centromeres in multicellular eukaryotes are composed of megabases of highly repetitive DNA that lack sequence specificity (for review, see Sullivan et al., 2001). In these organisms, kinetochore assembly seems to be propagated by unidentified epigenetic component(s) (Karpen and Allshire, 1997;Sullivan et al., 2001).The best-characterized kinetochore is in budding yeast where Ͼ65 components have been identified that constitutively localize to the kinetochore (for reviews, see Biggins and Walczak, 2003;McAinsh et al., 2003). Most of the yeast kinetochore proteins are found in biochemically distinct complexes known as the CBF3, CTF19/COMA, MTW1, NDC80, and DAM1 complexes that seem to assemble on a single centromeric nucleosome (Meluh et al., 1998). Although the exact architecture of the kinetochore is not known, dependency relationships subdivide the kinetochore into inner, central, and outer domains. The inner kinetochore contains the CBF3 complex (Ndc10, Cep3, Skp1, and Ctf13) as well as the DNA binding proteins Mif2, Cbf1, and the yeast centromeric histone H3 variant (CenH3) Cse4. CBF3 binds directly to the centromeric DNA and is thought to nucleate kinetochore assembly because all kinetochore proteins require it for localization (Russell et al., 1999;Goshima and Yanagida, 2000;He et al., 2001;Janke et al., 2001Janke et al., , 2002. The central kinetochore contains the MTW1 (Mtw1, Dsn1, Nnf1, and Nsl1) and CTF19/COMA (Ctf19, Mcm16, Mcm19, Mcm21, Mcm22, Ctf3, Chl4, Okp1, Ame1, Iml3, Nkp1, and Nkp2) complexes. CTF19/COMA can be further divided into two subcomplexes, with Ame1...

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“…Two distinct chromosome architectures are prevalent among metazoans: monocentric, in which kinetochore assembly is restricted to a localized region of each chromatid, and holocentric, in which diffuse kinetochores assemble along the entire chromatid length (14). Both monocentric and holocentric chromosomes assemble kinetochores on chromatin containing the histone H3 variant CENP-A (15)(16)(17)(18). After condensation in vertebrates (monocentric), CENP-Acontaining chromatin is positioned on the poleward surface of each sister chromatid in a localized chromosomal region called the primary constriction.…”

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confidence: 99%

Molecular analysis of mitotic chromosome condensation using a quantitative time-resolved fluorescence microscopy assay

Maddox

Portier

Desai

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

111

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Chromosomes condense during mitotic entry to facilitate their segregation. Condensation is typically assayed in fixed preparations, limiting analysis of contributing factors. Here, we describe a quantitative method to monitor condensation kinetics in living cells expressing GFP fused to a core histone. We demonstrate the utility of this method by using it to analyze the molecular requirements for the condensation of holocentric chromosomes during the first division of the Caenorhabditis elegans embryo. In control embryos, the fluorescence intensity distribution for nuclear GFP:histone changes during two distinct time intervals separated by a plateau phase. During the first interval, primary condensation converts diffuse chromatin into discrete linear chromosomes. After the plateau, secondary condensation compacts the curvilinear chromosomes to form shorter bar-shaped structures. We quantitatively compared the consequences on this characteristic profile of depleting the condensin complex, the mitosis-specific histone H3 kinase Aurora B, the centromeric histone CENP-A, and CENP-C, a conserved protein required for kinetochore assembly. Both condensin and CENP-A play critical but distinct roles in primary condensation. In contrast, depletion of CENP-C slows but does not prevent primary condensation. Finally, Aurora B inhibition has no effect on primary condensation, but slightly delays secondary condensation. These results provide insights into the process of condensation, help resolve apparent contradictions from prior studies, and indicate that CENP-A chromatin has an intrinsic role in the condensation of holocentric chromosomes that is independent of its requirement for kinetochore assembly. Aurora B ͉ CENP-A ͉ condensin ͉ kinetochore ͉ C. elegans

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A histone-H3-like protein in C. elegans

Cited by 240 publications

References 10 publications

A Spindle Checkpoint Functions during Mitosis in the EarlyCaenorhabditis elegansEmbryo

A Spindle Checkpoint Functions during Mitosis in the EarlyCaenorhabditis elegansEmbryo

De Novo Kinetochore Assembly Requires the Centromeric Histone H3 Variant

Molecular analysis of mitotic chromosome condensation using a quantitative time-resolved fluorescence microscopy assay

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