The Experts below are selected from a list of 204 Experts worldwide ranked by ideXlab platform
Kiichi Fukui - One of the best experts on this subject based on the ideXlab platform.
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3d observation of Chromosome Scaffold structure using a 360 electron tomography sample holder
Micron, 2019Co-Authors: Rinyaporn Phengchat, Misa Hayashida, Nobuko Ohmido, Darren Homeniuk, Kiichi FukuiAbstract:Abstract The Chromosome Scaffold is considered to be a key structure of the mitotic Chromosome. It plays a vital role in Chromosome condensation, shaping the X-shaped structure of the mitotic Chromosome, and also provides flexibility for Chromosome movement during cell division. However, it remains to be elucidated how the Chromosome Scaffold organizes the mitotic Chromosome and how it supports shaping the structure of the Chromosome during metaphase. Here we present a new technique that enables the observation of the Chromosome Scaffold structure in metaphase Chromosomes from any direction, by transferring an isolated Chromosome to a 360° rotational holder for electron tomography (ET). The Chromosome was stained with immunogold-labeled condensin complex, one of the major Chromosome Scaffold proteins and then observed in three dimensions using ET. Using the locations of gold nanoparticles to visualize the underlying structure, the tomograms we obtained reveal the patterns of Chromosome Scaffold organization, which appears to consist of a helical structure that serves to organize chromatin loops into the metaphase Chromosome.
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3D observation of Chromosome Scaffold structure using a 360° electron tomography sample holder
Micron, 2019Co-Authors: Rinyaporn Phengchat, Misa Hayashida, Nobuko Ohmido, Darren Homeniuk, Kiichi FukuiAbstract:Abstract The Chromosome Scaffold is considered to be a key structure of the mitotic Chromosome. It plays a vital role in Chromosome condensation, shaping the X-shaped structure of the mitotic Chromosome, and also provides flexibility for Chromosome movement during cell division. However, it remains to be elucidated how the Chromosome Scaffold organizes the mitotic Chromosome and how it supports shaping the structure of the Chromosome during metaphase. Here we present a new technique that enables the observation of the Chromosome Scaffold structure in metaphase Chromosomes from any direction, by transferring an isolated Chromosome to a 360° rotational holder for electron tomography (ET). The Chromosome was stained with immunogold-labeled condensin complex, one of the major Chromosome Scaffold proteins and then observed in three dimensions using ET. Using the locations of gold nanoparticles to visualize the underlying structure, the tomograms we obtained reveal the patterns of Chromosome Scaffold organization, which appears to consist of a helical structure that serves to organize chromatin loops into the metaphase Chromosome.
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Cdk1-dependent phosphorylation of KIF4A at S1186 triggers lateral Chromosome compaction during early mitosis.
PLOS ONE, 2018Co-Authors: Hideaki Takata, Marliza Madung, Kaoru Katoh, Kiichi FukuiAbstract:Chromosome organization during cell division is achieved through the timely association of proteins with chromatin and is regulated by protein phosphorylation. Kinesin family member 4A (KIF4A) plays an important role in the Chromosome organization through the formation of the Chromosome Scaffold structure. However, the relationship between the function of KIF4A and its phosphorylation remains unclear. Here, we demonstrate that Cdk1-dependent phosphorylation of KIF4A at S1186 is required for Chromosome binding and Chromosome Scaffold formation. The KIF4A mutant, which is not phosphorylated at S1186, was found to localize to the nucleus during interphase but did not accumulate in the Chromosome Scaffold after nuclear envelope breakdown. In addition, defects in KIF4A phosphorylation were found to disrupt the interaction of KIF4A with the condensin I complex. As a result, the morphology of the Chromosomes was observed to be laterally decondensed, without condensin I in the Chromosome Scaffold. Additionally, a defect in Chromosome segregation, Chromosome bridge formation, was often observed. Although both KIF4A and condensin I disappeared from the Chromosomes, the chromosomal localization of condensin II was not affected. Collectively, our novel results revealed that Cdk1-dependent KIF4A phosphorylation at S1186 is a trigger for chromosomal organization during early mitosis.
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interdependency and phosphorylation of kif4 and condensin i are essential for organization of Chromosome Scaffold
PLOS ONE, 2017Co-Authors: Rawin Poonperm, Kiichi Fukui, Hideaki Takata, Susumu UchiyamaAbstract:Kinesin family member 4 (KIF4) and condensins I and II are essential chromosomal proteins for Chromosome organization by locating primarily to the Chromosome Scaffold. However, the mechanism of how KIF4 and condensins localize to the Chromosome Scaffold is poorly understood. Here, we demonstrate a close relationship between the Chromosome localization of KIF4 and condensin I, but not condensin II, and show that KIF4 and condensin I assist each other for stable Scaffold formation by forming a stable complex. Moreover, phosphorylation of KIF4 and condensin I by Aurora B and polo-like kinase 1 (Plk1) is important for KIF4 and condensin I localization to the Chromosome. Aurora B activity facilitates the targeting of KIF4 and condensin I to the Chromosome, whereas Plk1 activity promotes the dissociation of these proteins from the Chromosome. Thus, the interdependency between KIF4 and condensin I, and their phosphorylation states play important roles in Chromosome Scaffold organization during mitosis.
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Calcium ions function as a booster of Chromosome condensation.
Scientific Reports, 2016Co-Authors: Rinyaporn Phengchat, Hideaki Takata, Susumu Uchiyama, Kenichi Morii, Noriko Inada, Hideji Murakoshi, Kiichi FukuiAbstract:Chromosome condensation is essential for the faithful transmission of genetic information to daughter cells during cell division. The depletion of Chromosome Scaffold proteins does not prevent Chromosome condensation despite structural defects. This suggests that other factors contribute to condensation. Here we investigated the contribution of divalent cations, particularly Ca2+, to Chromosome condensation in vitro and in vivo. Ca2+ depletion caused defects in proper mitotic progression, particularly in Chromosome condensation after the breakdown of the nuclear envelope. Fluorescence lifetime imaging microscopy-Forster resonance energy transfer and electron microscopy demonstrated that Chromosome condensation is influenced by Ca2+. Chromosomes had compact globular structures when exposed to Ca2+ and expanded fibrous structures without Ca2+. Therefore, we have clearly demonstrated a role for Ca2+ in the compaction of chromatin fibres.
William C Earnshaw - One of the best experts on this subject based on the ideXlab platform.
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Proteins of the inner and outer centromere of mitotic Chromosomes
Genome, 2011Co-Authors: William C Earnshaw, Carol A CookeAbstract:We have used immunocytochemistry and molecular cloning methods to identify and characterize structural polypeptides of the centromere. These studies permit us to resolve two distinct regions: the inner and outer centromere. (i) Components of the outer centromere: autoantibodies from certain patients with rheumatic disease identify a family of three immunologically related polypeptides that we have designated CENP-A (17 kDa), CENP-B (80 kDa), and CENP-C (140 kDa). CENP-B has been cloned and sequenced. DNA sequence analysis indicates that this polypeptide possesses two large regions with extraordinary concentrations of acidic residues (region I: 61 residues with 79% glu + asp; region II: 31 residues with 87% glu + asp). Despite this concentration of negative charge, immunocytochemical experiments suggest that CENP-B may be a DNA binding protein. In these experiments, the levels of CENP-B are seen to vary reproducibly from Chromosome to Chromosome. The role of CENP-B in vivo is unknown. However, it is unlikely to bind directly to the spindle microtubules since it is found at an inactive centromere that apparently does not attach to the spindle. (ii) Components of the inner centromere: we have injected mice with the whole Chromosome Scaffold fraction to elicit production of monoclonal antibodies. One such antibody identifies two structurally related polypeptides (the INCENP antigens, 135 and 155 kDa) that are preferentially located between the sister chromatids at the centromere. The INCENP antigens undergo dramatic movements from the Chromosomes to the central spindle during mitosis. They are ultimately sequestered in the midbody and discarded. Several lines of evidence suggest that the INCENP polypeptides may be involved in the regulation of sister chromatid separation at the metaphase-anaphase transition.
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Novel components of human mitotic Chromosomes identified by proteomic analysis of the Chromosome Scaffold fraction
Chromosoma, 2005Co-Authors: Reto Gassmann, Alexander J. Henzing, William C EarnshawAbstract:Chromosomal nonhistone proteins have important roles in mitotic Chromosome formation and dynamics. In order to identify novel abundant proteins with a potential involvement in these processes, we initiated a proteomic screen of the Chromosome Scaffold fraction. This screen identified 79 proteins, 30 of which had not previously been described as components of mitotic Chromosomes. Furthermore, half of these proteins had no documented function. We analyzed the cell-cycle dependent distribution of three uncharacterized proteins by expressing them as green fluorescent protein (GFP) fusions and showed that they associate with mitotic Chromosomes in vivo. One of the proteins, nuclear protein p30, is a novel component of the inner centromere. Over-expression experiments indicated that p30 may have an active role in the formation of centromeric heterochromatin.
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Condensin is required for nonhistone protein assembly and structural integrity of vertebrate mitotic Chromosomes.
Developmental Cell, 2003Co-Authors: Damien F. Hudson, Reto Gassmann, Paola Vagnarelli, William C EarnshawAbstract:Abstract The dramatic condensation of Chromosomes that occurs during mitosis is widely thought to be largely controlled by a protein complex termed condensin. Here, we describe a conditional knockout of the condensin subunit ScII/SMC2 in chicken DT40 cells. In cells lacking this condensin subunit, Chromosome condensation is delayed, but ultimately reaches near-normal levels. However, these Chromosomes are structurally compromised. Kinetochores appear normal, but the localization of nonhistone proteins such as topoisomerase II and INCENP is aberrant. Both proteins also fail to partition into the Chromosome Scaffold fraction, which appears to be largely missing in the absence of condensin. Furthermore, the Chromosomes lack structural integrity, as defined by an assay that tests the stability of the chromosomal higher-order structure. Thus, a major function of condensin is to promote the correct association of nonhistone proteins with mitotic Chromosomes, and this is essential for establishment of a robust Chromosome structure.
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the smc proteins and the coming of age of the Chromosome Scaffold hypothesis
BioEssays, 1995Co-Authors: Noriko Saitoh, Iiya Goldberg, William C EarnshawAbstract:: The mechanism of Chromosome condensation is one of the classic mysteries of mitosis. A number of years ago, it was suggested that nonhistone proteins of the Chromosome Scaffold fraction might help Chromosomes to condense, possibly by constructing a framework for the condensed structure. Recent results have shown that topoisomerase II and the SMC proteins, two abundant members of the Scaffold fraction, are required for Chromosome condensation and segregation during mitosis. Topoisomerase II is a well-characterized enzyme. In contrast, nothing is yet known about the function of the SMC proteins. We summarize evidence suggesting that these proteins may be enzymes whose activity is somehow involved in the establishment and maintenance of mitotic Chromosome morphology.
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scii an abundant Chromosome Scaffold protein is a member of a family of putative atpases with an unusual predicted tertiary structure
Journal of Cell Biology, 1994Co-Authors: Noriko Saitoh, Ilya G Goldberg, Edgar R Wood, William C EarnshawAbstract:Here, we describe the cloning and characterization of ScII, the second most abundant protein after topoisomerase II, of the Chromosome Scaffold fraction to be identified. ScII is structurally related to a protein, Smc1p, previously found to be required for accurate Chromosome segregation in Saccharomyces cerevisiae. ScII and the other members of the emerging family of SMC1-like proteins are likely to be novel ATPases, with NTP-binding A and B sites separated by two lengthy regions predicted to form an alpha-helical coiled-coil. Analysis of the ScII B site predicted that ScII might use ATP by a mechanism similar to the bacterial recN DNA repair and recombination enzyme. ScII is a mitosis-specific Scaffold protein that colocalizes with topoisomerase II in mitotic Chromosomes. However, ScII appears not to be associated with the interphase nuclear matrix. ScII might thus play a role in mitotic processes such as Chromosome condensation or sister chromatid disjunction, both of which have been previously shown to involve topoisomerase II.
Noriko Saitoh - One of the best experts on this subject based on the ideXlab platform.
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the smc proteins and the coming of age of the Chromosome Scaffold hypothesis
BioEssays, 1995Co-Authors: Noriko Saitoh, Iiya Goldberg, William C EarnshawAbstract:: The mechanism of Chromosome condensation is one of the classic mysteries of mitosis. A number of years ago, it was suggested that nonhistone proteins of the Chromosome Scaffold fraction might help Chromosomes to condense, possibly by constructing a framework for the condensed structure. Recent results have shown that topoisomerase II and the SMC proteins, two abundant members of the Scaffold fraction, are required for Chromosome condensation and segregation during mitosis. Topoisomerase II is a well-characterized enzyme. In contrast, nothing is yet known about the function of the SMC proteins. We summarize evidence suggesting that these proteins may be enzymes whose activity is somehow involved in the establishment and maintenance of mitotic Chromosome morphology.
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scii an abundant Chromosome Scaffold protein is a member of a family of putative atpases with an unusual predicted tertiary structure
Journal of Cell Biology, 1994Co-Authors: Noriko Saitoh, Ilya G Goldberg, Edgar R Wood, William C EarnshawAbstract:Here, we describe the cloning and characterization of ScII, the second most abundant protein after topoisomerase II, of the Chromosome Scaffold fraction to be identified. ScII is structurally related to a protein, Smc1p, previously found to be required for accurate Chromosome segregation in Saccharomyces cerevisiae. ScII and the other members of the emerging family of SMC1-like proteins are likely to be novel ATPases, with NTP-binding A and B sites separated by two lengthy regions predicted to form an alpha-helical coiled-coil. Analysis of the ScII B site predicted that ScII might use ATP by a mechanism similar to the bacterial recN DNA repair and recombination enzyme. ScII is a mitosis-specific Scaffold protein that colocalizes with topoisomerase II in mitotic Chromosomes. However, ScII appears not to be associated with the interphase nuclear matrix. ScII might thus play a role in mitotic processes such as Chromosome condensation or sister chromatid disjunction, both of which have been previously shown to involve topoisomerase II.
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purification and characterization of a nuclear dna binding factor complex containing topoisomerase ii and Chromosome Scaffold protein 2
Journal of Biological Chemistry, 1993Co-Authors: Noriko Saitoh, Peter J CurtisAbstract:Abstract In a search for factors that influence the process of erythroid differentiation at the molecular level, we have identified UB2, a nuclear protein factor that was originally observed for its ability to bind to a very specific and highly conserved sequence motif present in human, mouse, rabbit, and chicken beta-globin genes, as well as carbonic anhydrase I, c-myb, and the immunoglobulin heavy chain enhancer region. It was also observed for its appearance in undifferentiated but not differentiated mouse erythroleukemia cells. Purification of UB2 by DEAE-cellulose chromatography and repeated passages through a DNA affinity column, revealed a complex pattern with three major components of 170, 116, and 48 kDa, respectively. The 170-kDa protein was identified as topoisomerase (topo) II by Western blot analysis, catalytic assays, and antibody interference with UB2 binding. The complex topo II in UB2, however, has a more stringent sequence requirement for DNA binding than does topo II. The 116-kDa protein has been determined to be a proteolytic product of topo II. The Chromosome Scaffold protein 2 (135 kDa) copurified with UB2, and anti-Scaffold protein 2 serum inhibited UB2 binding to DNA.
Xiao Guang Wang - One of the best experts on this subject based on the ideXlab platform.
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tropomyosin is localized in the nuclear matrix and Chromosome Scaffold of physarum polycephalum
Cell Research, 1999Co-Authors: Xian Lu Zeng, Ming Da Jiao, Miao Xing, Xiao Guang WangAbstract:Tropomyosin is localized in the nuclear matrix and Chromosome Scaffold of physarum polycephalum
Zhonghe Zhai - One of the best experts on this subject based on the ideXlab platform.
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Composition and structure of nucleolar skeleton (nucleolar matrix) : Actin and fibrillarin are two main protein components of nucleolar skeleton.
Science China-life Sciences, 1999Co-Authors: Jianming Chen, Yan Shen, Renjie Jiao, Zhonghe ZhaiAbstract:Purified nucleoli of HeLa cells were treated sequentially with nonionic detergent, nucleic acid enzyme, low salt and high salt. The residual nucleolar structure termed nucleolar skeleton (nucleolar matrix) was shown as a fine network under electron microscope with DGD embedding-unembedding technique. Such structures of BHK-21 cell and mouse liver cell are similar to that of HeLa cell. The protein composition of the nucleolar skeleton of HeLa cells was analyzed. The protein composition of such nucleolar residual shows obvious difference from the compositions of nuclear matrix and Chromosome Scaffold. The major protein composition of the nucleolar skeleton of HeLa cells contains 6–7 polypeptides. Their molecular weights are about 48, 43, 36 and 33 ku. Further studies show that actin and fibrillarin are two major protein components of nucleolar skeleton of HeLa cells.
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identification of the nuclear matrix and Chromosome Scaffold in dinoflagellate crypthecodinium cohnii
Cell Research, 1992Co-Authors: Congmei Zeng, Jingyan Li, Zhonghe ZhaiAbstract:Dinoflagellate is one of the primitive eukaryotes, whose nucleus may represent one of the transition stages from prokaryotic nucleoid to typical eukaryotic nucleus. Using selective extraction together with embeddment−free section and whole mount electron microscopy, a delicate nuclear matrix filament network was shown, for the first time, in dinoflagellate Crypthecodinium cohnii nucleus. Chromosome residues are connected with nuclear matrix filaments to form a complete network spreading over the nucleus. Moreover, we demonstrated that the dinoflagellate Chromosome retains a protein Scaffold after the depletion of DNA and soluble proteins. This Scaffold preserves the characteristic morphology of the Chromosome. Two dimensional electrophoreses indicated that the nuclear matrix and Chromosome Scaffold are mainly composed of acidic proteins. Our results demonstrated that a framework similar to the nuclear matrix and Chromosome Scaffold in mammalian cells appears in this primitive eukaryote,suggesting that these structures may have been originated from the early stages of eukaryote evolution.