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  • 1
    Language: English
    In: Seminars in Cell and Developmental Biology, Dec, 2010, Vol.21(9), p.909(8)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.semcdb.2010.08.001 Byline: Julien Guizetti, Daniel W. Gerlich Keywords: Cell division; Cytokinesis; Abscission; Midbody Abbreviations: PE, phosphatidylethanolamine; SNARE, soluble N-ethylmaleimide-sensitive-factor attachment receptor; PIP.sub.2, phosphatidylinisitol 4,5 bisphosphate; PIP5K, phosphatidylinisitol 4,5 bisphosphate 5 kinase; ESCRT-III, Endosomal Sorting Complex Required for Transport III; CHM, Charged Multivesicular body Proteins Abstract: Cytokinesis leads to the separation of dividing cells, which in animal cells involves the contraction of an actin-myosin ring and subsequent fission during abscission. Abscission requires a series of dynamic events, including midbody-targeted vesicle secretion, specialization of plasma membrane domains, disassembly of midbody-associated microtubule bundles and plasma membrane fission. A large number of molecular factors required for abscission have been identified through localization, loss-of-function and proteomics studies, but their coordinate function in abscission is still poorly understood. Here, we review the structural elements and molecular factors known to contribute to abscission, and discuss their potential role in the context of proposed models for the abscission mechanism. Author Affiliation: Institute of Biochemistry, Swiss Federal Institute of Technology Zurich (ETHZ), Schafmattstr. 18, CH-8093 Zurich, Switzerland
    ISSN: 1084-9521
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Science, March 25, 2011, Vol.331(6024), p.1616(5)
    Description: After partitioning of cytoplasrnic contents by cleavage furrow ingression, animal cells remain connected by an intercellular bridge, which subsequently splits by abscission. Here, we examined intermediate stages of abscission in human cells by using five imaging, three- dimensional structured illumination microscopy, and electron tomography. We identified helices of 17-nanometer-diameter filaments, which narrowed the cortex of the intercellular bridge to a single stalk. The endosomal sorting complex required for transport (ESCRT)-III co-locatized with constriction zones and was required for assembly of 17-nanometer-diameter filaments. Simuttaneous spastin-mediated removal of underlying microtubules enabled full constriction at the abscission site. The identification of contractile filament helices at the intercellular bridge has broad implications for the understanding of cell division and of ESCRT-III- mediated fission of large membrane structures. 10.1126/science.1201847
    Keywords: Cell Division -- Genetic Aspects ; Protein Structure -- Research
    ISSN: 0036-8075
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  • 3
    Language: English
    In: Science (New York, N.Y.), 25 March 2011, Vol.331(6024), pp.1616-20
    Description: After partitioning of cytoplasmic contents by cleavage furrow ingression, animal cells remain connected by an intercellular bridge, which subsequently splits by abscission. Here, we examined intermediate stages of abscission in human cells by using live imaging, three-dimensional structured illumination microscopy, and electron tomography. We identified helices of 17-nanometer-diameter filaments, which narrowed the cortex of the intercellular bridge to a single stalk. The endosomal sorting complex required for transport (ESCRT)-III co-localized with constriction zones and was required for assembly of 17-nanometer-diameter filaments. Simultaneous spastin-mediated removal of underlying microtubules enabled full constriction at the abscission site. The identification of contractile filament helices at the intercellular bridge has broad implications for the understanding of cell division and of ESCRT-III-mediated fission of large membrane structures.
    Keywords: Cell Division ; Endosomal Sorting Complexes Required for Transport -- Chemistry ; Microtubules -- Metabolism
    ISSN: 00368075
    E-ISSN: 1095-9203
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  • 4
    Language: English
    In: Nature, November 2018, Vol.563(7729), pp.121-125
    Description: Many evolutionarily distant pathogenic organisms have evolved similar survival strategies to evade the immune responses of their hosts. These include antigenic variation, through which an infecting organism prevents clearance by periodically altering the identity of proteins that are visible to the immune system of the host. Antigenic variation requires large reservoirs of immunologically diverse antigen genes, which are often generated through homologous recombination, as well as mechanisms to ensure the expression of one or very few antigens at any given time. Both homologous recombination and gene expression are affected by three-dimensional genome architecture and local DNA accessibility. Factors that link three-dimensional genome architecture, local chromatin conformation and antigenic variation have, to our knowledge, not yet been identified in any organism. One of the major obstacles to studying the role of genome architecture in antigenic variation has been the highly repetitive nature and heterozygosity of antigen-gene arrays, which has precluded complete genome assembly in many pathogens. Here we report the de novo haplotype-specific assembly and scaffolding of the long antigen-gene arrays of the model protozoan parasite Trypanosoma brucei, using long-read sequencing technology and conserved features of chromosome folding. Genome-wide chromosome conformation capture (Hi-C) reveals a distinct partitioning of the genome, with antigen-encoding subtelomeric regions that are folded into distinct, highly compact compartments. In addition, we performed a range of analyses-Hi-C, fluorescence in situ hybridization, assays for transposase-accessible chromatin using sequencing and single-cell RNA sequencing-that showed that deletion of the histone variants H3.V and H4.V increases antigen-gene clustering, DNA accessibility across sites of antigen expression and switching of the expressed antigen isoform, via homologous recombination. Our analyses identify histone variants as a molecular link between global genome architecture, local chromatin conformation and antigenic variation.
    Keywords: Antigenic Variation -- Genetics ; Chromatin -- Genetics ; DNA, Protozoan -- Metabolism ; Genome -- Genetics ; Trypanosoma Brucei Brucei -- Genetics
    ISSN: 00280836
    E-ISSN: 1476-4687
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  • 5
    In: Nucleic Acids Research, 2016, Vol. 44(20), pp.9710-9718
    Description: Monoallelic expression of the var multigene family enables immune evasion of the malaria parasite Plasmodium falciparum in its human host. At a given time only a single member of the 60-member var gene family is expressed at a discrete perinuclear region called the ‘ var expression site’. However, the mechanism of var gene counting remains ill-defined. We hypothesize that activation factors associating specifically with the expression site play a key role in this process. Here, we investigate the role of a GC-rich non-coding RNA (ncRNA) gene family composed of 15 highly homologous members. GC-rich genes are positioned adjacent to var genes in chromosome-central gene clusters but are absent near subtelomeric var genes. Fluorescence in situ hybridization demonstrates that GC-rich ncRNA localizes to the perinuclear expression site of central and subtelomeric var genes in trans. Importantly, overexpression of distinct GC-rich ncRNA members disrupts the gene counting process at the single cell level and results in activation of a specific subset of var genes in distinct clones. We identify the first trans-acting factor targeted to the elusive perinuclear var expression site and open up new avenues to investigate ncRNA function in antigenic variation of malaria and other protozoan pathogens.
    Keywords: Base Composition ; Gene Expression Regulation ; Transcriptional Activation ; Malaria, Falciparum -- Parasitology ; Plasmodium Falciparum -- Genetics ; Protozoan Proteins -- Genetics ; RNA, Untranslated -- Genetics;
    ISSN: 0305-1048
    E-ISSN: 1362-4962
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  • 6
    Language: English
    In: Nucleic Acids Research, 07/27/2016, p.gkw664
    ISSN: 0305-1048
    E-ISSN: 1362-4962
    Source: Oxford University Press (via CrossRef)
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  • 7
    Language: English
    In: Nature, 18 September 2014, Vol.513(7518), pp.431-5
    Description: Antigenic variation of the Plasmodium falciparum multicopy var gene family enables parasite evasion of immune destruction by host antibodies. Expression of a particular var subgroup, termed upsA, is linked to the obstruction of blood vessels in the brain and to the pathogenesis of human cerebral malaria. The mechanism determining upsA activation remains unknown. Here we show that an entirely new type of gene silencing mechanism involving an exonuclease-mediated degradation of nascent RNA controls the silencing of genes linked to severe malaria. We identify a novel chromatin-associated exoribonuclease, termed PfRNase II, that controls the silencing of upsA var genes by marking their transcription start site and intron-promoter regions leading to short-lived cryptic RNA. Parasites carrying a deficient PfRNase II gene produce full-length upsA var transcripts and intron-derived antisense long non-coding RNA. The presence of stable upsA var transcripts overcomes monoallelic expression, resulting in the simultaneous expression of both upsA and upsC type PfEMP1 proteins on the surface of individual infected red blood cells. In addition, we observe an inverse relationship between transcript levels of PfRNase II and upsA-type var genes in parasites from severe malaria patients, implying a crucial role of PfRNase II in severe malaria. Our results uncover a previously unknown type of post-transcriptional gene silencing mechanism in malaria parasites with repercussions for other organisms. Additionally, the identification of RNase II as a parasite protein controlling the expression of virulence genes involved in pathogenesis in patients with severe malaria may provide new strategies for reducing malaria mortality.
    Keywords: Gene Silencing ; Exoribonucleases -- Metabolism ; Genes, Protozoan -- Genetics ; Malaria, Cerebral -- Parasitology ; Plasmodium Falciparum -- Enzymology ; RNA, Protozoan -- Metabolism
    ISSN: 00280836
    E-ISSN: 1476-4687
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  • 8
    Language: English
    In: The Journal of Cell Biology, 14 June 2010, Vol.189(6), pp.945-54
    Description: Posttranslational glutamylation of tubulin is present on selected subsets of microtubules in cells. Although the modification is expected to contribute to the spatial and temporal organization of the cytoskeleton, hardly anything is known...
    Keywords: Adenosine Triphosphatases ; Animals ; Protein Processing, Post-Translational ; Protein Subunits ; Recombinant Fusion Proteins ; Tubulin ; Cytoskeleton ; Glutamic Acid ; Hela Cells ; Humans ; Isoenzymes ; Mice ; Microtubules ; Peptide Synthases ; Life Sciences ; Biochemistry, Molecular Biology
    ISSN: 00219525
    E-ISSN: 15408140
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  • 9
    Language: English
    In: Trends in Cell Biology, March 2012, Vol.22(3), pp.133-140
    Description: The endosomal sorting complex required for transport (ESCRT)-III machinery contributes to membrane deformation and scission in cytokinesis, intraluminal vesicle formation, autophagy and virus budding. Recombinant ESCRT-III subunits polymerize into filaments, tubes, sheets or rings, and ESCRT-III-dependent filaments have been observed in cells at virus bud necks and at the cytokinetic abscission site. These observations have inspired speculation about how ESCRT-III could mediate constriction and fission of membrane necks. Based on the polymer structures observed and , we discuss models for ESCRT-III function and outline how emerging technologies could be used to test these models.
    Keywords: Biology
    ISSN: 0962-8924
    E-ISSN: 1879-3088
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  • 10
    Language: English
    In: Seminars in Cell and Developmental Biology, 2010, Vol.21(9), pp.909-916
    Description: Cytokinesis leads to the separation of dividing cells, which in animal cells involves the contraction of an actin–myosin ring and subsequent fission during abscission. Abscission requires a series of dynamic events, including midbody-targeted vesicle secretion, specialization of plasma membrane domains, disassembly of midbody-associated microtubule bundles and plasma membrane fission. A large number of molecular factors required for abscission have been identified through localization, loss-of-function and proteomics studies, but their coordinate function in abscission is still poorly understood. Here, we review the structural elements and molecular factors known to contribute to abscission, and discuss their potential role in the context of proposed models for the abscission mechanism.
    Keywords: Cell Division ; Cytokinesis ; Abscission ; Midbody ; Biology
    ISSN: 1084-9521
    E-ISSN: 1096-3634
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