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8 Janelia Publications

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    Wu Lab
    10/01/17 | Molecular basis of CENP-C association with the CENP-A nucleosome at yeast centromeres.
    Xiao H, Wang F, Wisniewski J, Shaytan AK, Ghirlando R, Fitzgerald PC, Huang Y, Wei D, Li S, Landsman D, Panchenko AR, Wu C
    Genes & Development. 2017 Oct 01;31(19):1958-1972. doi: 10.1101/gad.304782.117

    Histone CENP-A-containing nucleosomes play an important role in nucleating kinetochores at centromeres for chromosome segregation. However, the molecular mechanisms by which CENP-A nucleosomes engage with kinetochore proteins are not well understood. Here, we report the finding of a new function for the budding yeast Cse4/CENP-A histone-fold domain interacting with inner kinetochore protein Mif2/CENP-C. Strikingly, we also discovered that AT-rich centromere DNA has an important role for Mif2 recruitment. Mif2 contacts one side of the nucleosome dyad, engaging with both Cse4 residues and AT-rich nucleosomal DNA. Both interactions are directed by a contiguous DNA- and histone-binding domain (DHBD) harboring the conserved CENP-C motif, an AT hook, and RK clusters (clusters enriched for arginine-lysine residues). Human CENP-C has two related DHBDs that bind preferentially to DNA sequences of higher AT content. Our findings suggest that a DNA composition-based mechanism together with residues characteristic for the CENP-A histone variant contribute to the specification of centromere identity.

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    02/16/16 | Multifocus microscopy with precise color multi-phase diffractive optics applied in functional neuronal imaging.
    Abrahamsson S, Ilic R, Wisniewski J, Mehl B, Yu L, Chen L, Davanco M, Oujedi L, Fiche J, Hajj B
    Biomedical Optics Express. 2016 Feb 16;7(3):855-69. doi: 10.1364/BOE.7.000855

    Multifocus microscopy (MFM) allows high-resolution instantaneous three-dimensional (3D) imaging and has been applied to study biological specimens ranging from single molecules inside cells nuclei to entire embryos. We here describe pattern designs and nanofabrication methods for diffractive optics that optimize the light-efficiency of the central optical component of MFM: the diffractive multifocus grating (MFG). We also implement a “precise color” MFM layout with MFGs tailored to individual fluorophores in separate optical arms. The reported advancements enable faster and brighter volumetric time-lapse imaging of biological samples. In live microscopy applications, photon budget is a critical parameter and light-efficiency must be optimized to obtain the fastest possible frame rate while minimizing photodamage. We provide comprehensive descriptions and code for designing diffractive optical devices, and a detailed methods description for nanofabrication of devices. Theoretical efficiencies of reported designs is ≈90% and we have obtained efficiencies of > 80% in MFGs of our own manufacture. We demonstrate the performance of a multi-phase MFG in 3D functional neuronal imaging in living C. elegans.


    Additional authors include:

    Xin Jin, Joan Pulupa, Christine Cho, Mustafa Mir, Mohamed El Beheiry, Xavier Darzacq, Marcelo Nollmann, Maxime Dahan, Carl Wu, Timothée Lionnet, J. Alexander Liddle, and Cornelia I. Bargmann


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    06/27/15 | H2A histone-fold and DNA elements in nucleosome activate SWR1-mediated H2A.Z replacement in budding yeast.
    Ranjan A, Wang F, Mizuguchi G, Wei D, Huang Y, Wu C
    eLife. 2015 Jun 27;4:. doi: 10.7554/eLife.06845

    The histone variant H2A.Z is a universal mark of gene promoters, enhancers, and regulatory elements in eukaryotic chromatin. The chromatin remodeler SWR1 mediates site-specific incorporation of H2A.Z by a multi-step histone replacement reaction, evicting histone H2A-H2B from the canonical nucleosome and depositing the H2A.Z-H2B dimer. Binding of both substrates, the canonical nucleosome and the H2A.Z-H2B dimer, is essential for activation of SWR1. We found that SWR1 primarily recognizes key residues within the α2 helix in the histone-fold of nucleosomal histone H2A, a region not previously known to influence remodeler activity. Moreover, SWR1 interacts preferentially with nucleosomal DNA at superhelix location 2 on the nucleosome face distal to its linker-binding site. Our findings provide new molecular insights on recognition of the canonical nucleosome by a chromatin remodeler and have implications for ATP-driven mechanisms of histone eviction and deposition.

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    Wu Lab
    05/20/14 | Imaging the fate of histone Cse4 reveals de novo replacement in S phase and subsequent stable residence at centromeres.
    Wisniewski J, Hajj B, Chen J, Mizuguchi G, Xiao H, Wei D, Dahan M, Wu C
    eLife. 2014 May 20;3:e02203. doi: 10.7554/eLife.02203

    The budding yeast centromere contains Cse4, a specialized histone H3 variant. Fluorescence pulse-chase analysis of an internally tagged Cse4 reveals that it is replaced with newly synthesized molecules in S phase, remaining stably associated with centromeres thereafter. In contrast, C-terminally-tagged Cse4 is functionally impaired, showing slow cell growth, cell lethality at elevated temperatures, and extra-centromeric nuclear accumulation. Recent studies using such strains gave conflicting findings regarding the centromeric abundance and cell cycle dynamics of Cse4. Our findings indicate that internally tagged Cse4 is a better reporter of the biology of this histone variant. Furthermore, the size of centromeric Cse4 clusters was precisely mapped with a new 3D-PALM method, revealing substantial compaction during anaphase. Cse4-specific chaperone Scm3 displays steady-state, stoichiometric co-localization with Cse4 at centromeres throughout the cell cycle, while undergoing exchange with a nuclear pool. These findings suggest that a stable Cse4 nucleosome is maintained by dynamic chaperone-in-residence Scm3.DOI:

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    Wu Lab
    02/06/14 | The catalytic subunit of the SWR1 remodeler is a histone chaperone for the H2A.Z-H2B dimer.
    Hong J, Feng H, Wang F, Ranjan A, Chen J, Jiang J, Ghirlando R, Xiao TS, Wu C, Bai Y
    Molecular Cell. 2014 Feb 6;53:498-505. doi: 10.1016/j.molcel.2014.01.010

    Histone variant H2A.Z-containing nucleosomes exist at most eukaryotic promoters and play important roles in gene transcription and genome stability. The multisubunit nucleosome-remodeling enzyme complex SWR1, conserved from yeast to mammals, catalyzes the ATP-dependent replacement of histone H2A in canonical nucleosomes with H2A.Z. How SWR1 catalyzes the replacement reaction is largely unknown. Here, we determined the crystal structure of the N-terminal region (599-627) of the catalytic subunit Swr1, termed Swr1-Z domain, in complex with the H2A.Z-H2B dimer at 1.78 Å resolution. The Swr1-Z domain forms a 310 helix and an irregular chain. A conserved LxxLF motif in the Swr1-Z 310 helix specifically recognizes the αC helix of H2A.Z. Our results show that the Swr1-Z domain can deliver the H2A.Z-H2B dimer to the DNA-(H3-H4)2 tetrasome to form the nucleosome by a histone chaperone mechanism.

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    Wu Lab
    09/12/13 | Molecular architecture of the ATP-dependent chromatin-remodeling complex SWR1.
    Nguyen VQ, Ranjan A, Stengel F, Wei D, Aebersold R, Wu C, Leschziner AE
    Cell. 2013 Sep 12;154(6):1220-31. doi: 10.1016/j.cell.2013.08.018

    The ATP-dependent chromatin-remodeling complex SWR1 exchanges a variant histone H2A.Z/H2B dimer for a canonical H2A/H2B dimer at nucleosomes flanking histone-depleted regions, such as promoters. This localization of H2A.Z is conserved throughout eukaryotes. SWR1 is a 1 megadalton complex containing 14 different polypeptides, including the AAA+ ATPases Rvb1 and Rvb2. Using electron microscopy, we obtained the three-dimensional structure of SWR1 and mapped its major functional components. Our data show that SWR1 contains a single heterohexameric Rvb1/Rvb2 ring that, together with the catalytic subunit Swr1, brackets two independently assembled multisubunit modules. We also show that SWR1 undergoes a large conformational change upon engaging a limited region of the nucleosome core particle. Our work suggests an important structural role for the Rvbs and a distinct substrate-handling mode by SWR1, thereby providing a structural framework for understanding the complex dimer-exchange reaction.

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    Wu Lab
    09/12/13 | Nucleosome-free region dominates histone acetylation in targeting SWR1 to promoters for H2A.Z replacement.
    Ranjan A, Mizuguchi G, Fitzgerald PC, Wei D, Wang F, Huang Y, Luk E, Woodcock CL, Wu C
    Cell. 2013 Sep 12;154(6):1232-45. doi: 10.1016/j.cell.2013.08.005

    The histone variant H2A.Z is a genome-wide signature of nucleosomes proximal to eukaryotic regulatory DNA. Whereas the multisubunit chromatin remodeler SWR1 is known to catalyze ATP-dependent deposition of H2A.Z, the mechanism of SWR1 recruitment to S. cerevisiae promoters has been unclear. A sensitive assay for competitive binding of dinucleosome substrates revealed that SWR1 preferentially binds long nucleosome-free DNA and the adjoining nucleosome core particle, allowing discrimination of gene promoters over gene bodies. Analysis of mutants indicates that the conserved Swc2/YL1 subunit and the adenosine triphosphatase domain of Swr1 are mainly responsible for binding to substrate. SWR1 binding is enhanced on nucleosomes acetylated by the NuA4 histone acetyltransferase, but recognition of nucleosome-free and nucleosomal DNA is dominant over interaction with acetylated histones. Such hierarchical cooperation between DNA and histone signals expands the dynamic range of genetic switches, unifying classical gene regulation by DNA-binding factors with ATP-dependent nucleosome remodeling and posttranslational histone modifications.

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    01/01/13 | Fast multicolor 3D imaging using aberration-corrected multifocus microscopy.
    Abrahamsson S, Chen J, Hajj B, Stallinga S, Katsov AY, Wisniewski J, Mizuguchi G, Soule P, Mueller F, Darzacq CD, Darzacq X, Wu C, Bargmann CI, Agard DA, Dahan M, Gustafsson MG
    Nature Methods. 2013;10(1):60-3. doi: 10.1038/nmeth.2277

    Conventional acquisition of three-dimensional (3D) microscopy data requires sequential z scanning and is often too slow to capture biological events. We report an aberration-corrected multifocus microscopy method capable of producing an instant focal stack of nine 2D images. Appended to an epifluorescence microscope, the multifocus system enables high-resolution 3D imaging in multiple colors with single-molecule sensitivity, at speeds limited by the camera readout time of a single image.

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