1
|
Agbleke AA, Amitai A, Buenrostro JD, Chakrabarti A, Chu L, Hansen AS, Koenig KM, Labade AS, Liu S, Nozaki T, Ovchinnikov S, Seeber A, Shaban HA, Spille JH, Stephens AD, Su JH, Wadduwage D. Advances in Chromatin and Chromosome Research: Perspectives from Multiple Fields. Mol Cell 2020; 79:881-901. [PMID: 32768408 PMCID: PMC7888594 DOI: 10.1016/j.molcel.2020.07.003] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Revised: 06/12/2020] [Accepted: 07/06/2020] [Indexed: 12/12/2022]
Abstract
Nucleosomes package genomic DNA into chromatin. By regulating DNA access for transcription, replication, DNA repair, and epigenetic modification, chromatin forms the nexus of most nuclear processes. In addition, dynamic organization of chromatin underlies both regulation of gene expression and evolution of chromosomes into individualized sister objects, which can segregate cleanly to different daughter cells at anaphase. This collaborative review shines a spotlight on technologies that will be crucial to interrogate key questions in chromatin and chromosome biology including state-of-the-art microscopy techniques, tools to physically manipulate chromatin, single-cell methods to measure chromatin accessibility, computational imaging with neural networks and analytical tools to interpret chromatin structure and dynamics. In addition, this review provides perspectives on how these tools can be applied to specific research fields such as genome stability and developmental biology and to test concepts such as phase separation of chromatin.
Collapse
Affiliation(s)
| | - Assaf Amitai
- Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Jason D Buenrostro
- Department of Stem Cell and Regenerative Biology, Harvard University, Cambridge, MA, USA
| | - Aditi Chakrabarti
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
| | - Lingluo Chu
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA
| | - Anders S Hansen
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Kristen M Koenig
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA; JHDSF Program, Harvard University, Cambridge, MA 02138, USA
| | - Ajay S Labade
- Department of Stem Cell and Regenerative Biology, Harvard University, Cambridge, MA, USA
| | - Sirui Liu
- FAS Division of Science, Harvard University, Cambridge, MA 02138, USA
| | - Tadasu Nozaki
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA
| | - Sergey Ovchinnikov
- JHDSF Program, Harvard University, Cambridge, MA 02138, USA; FAS Division of Science, Harvard University, Cambridge, MA 02138, USA
| | - Andrew Seeber
- JHDSF Program, Harvard University, Cambridge, MA 02138, USA; Center for Advanced Imaging, Harvard University, Cambridge, MA 02138, USA.
| | - Haitham A Shaban
- Center for Advanced Imaging, Harvard University, Cambridge, MA 02138, USA; Spectroscopy Department, Physics Division, National Research Centre, Dokki, 12622 Cairo, Egypt
| | - Jan-Hendrik Spille
- Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Andrew D Stephens
- Biology Department, University of Massachusetts, Amherst, Amherst, MA 01003, USA
| | - Jun-Han Su
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA
| | - Dushan Wadduwage
- JHDSF Program, Harvard University, Cambridge, MA 02138, USA; Center for Advanced Imaging, Harvard University, Cambridge, MA 02138, USA
| |
Collapse
|
2
|
Iyer KV, Pulford S, Mogilner A, Shivashankar GV. Mechanical activation of cells induces chromatin remodeling preceding MKL nuclear transport. Biophys J 2012; 103:1416-28. [PMID: 23062334 DOI: 10.1016/j.bpj.2012.08.041] [Citation(s) in RCA: 125] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2012] [Revised: 07/30/2012] [Accepted: 08/16/2012] [Indexed: 10/27/2022] Open
Abstract
For cells to adapt to different tissues and changes in tissue mechanics, they must be able to respond to mechanical cues by changing their gene expression patterns. Biochemical signaling pathways for these responses have been elucidated, and recent evidence points to the involvement of force-induced deformation of the nucleus. However, it is still unclear how physical cues received at the plasma membrane (PM) spatiotemporally integrate to the functional chromatin organization of the cell nucleus. To investigate this issue, we applied mechanical forces through magnetic particles adhered to the PM of single cells and mapped the accompanying changes in actin polymerization, nuclear morphology, chromatin remodeling, and nuclear transport of soluble signaling intermediates using high-resolution fluorescence anisotropy imaging. Using this approach, we show the timescales associated with force-induced polymerization of actin and changes in the F/G actin ratio resulting in nuclear translocation of the G-actin-associated transcriptional cofactor, megakaryoblastic acute leukemia factor-1 (MKL). Further, this method of measuring nuclear organization at high spatiotemporal resolution with simultaneous force application revealed the physical propagation of forces to the nucleus, resulting in changes to chromatin organization, followed by nuclear deformation. We also describe a quantitative model that incorporates active stresses and chemical kinetics to evaluate the observed timescales. Our work suggests that mechanical activation of cells is accompanied by distinct timescales involved in the reorganization of actin and chromatin assembly, followed by translocation of transcription cofactors from the cytoplasm to the nucleus.
Collapse
Affiliation(s)
- K Venkatesan Iyer
- Mechanobiology Institute, National University of Singapore, Singapore
| | | | | | | |
Collapse
|
3
|
Collepardo-Guevara R, Schlick T. Crucial role of dynamic linker histone binding and divalent ions for DNA accessibility and gene regulation revealed by mesoscale modeling of oligonucleosomes. Nucleic Acids Res 2012; 40:8803-17. [PMID: 22790986 PMCID: PMC3467040 DOI: 10.1093/nar/gks600] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Monte Carlo simulations of a mesoscale model of oligonucleosomes are analyzed to examine the role of dynamic-linker histone (LH) binding/unbinding in high monovalent salt with divalent ions, and to further interpret noted chromatin fiber softening by dynamic LH in monovalent salt conditions. We find that divalent ions produce a fiber stiffening effect that competes with, but does not overshadow, the dramatic softening triggered by dynamic-LH behavior. Indeed, we find that in typical in vivo conditions, dynamic-LH binding/unbinding reduces fiber stiffening dramatically (by a factor of almost 5, as measured by the elasticity modulus) compared with rigidly fixed LH, and also the force needed to initiate chromatin unfolding, making it consistent with those of molecular motors. Our data also show that, during unfolding, divalent ions together with LHs induce linker-DNA bending and DNA–DNA repulsion screening, which guarantee formation of heteromorphic superbeads-on-a-string structures that combine regions of loose and compact fiber independently of the characteristics of the LH–core bond. These structures might be important for gene regulation as they expose regions of the DNA selectively. Dynamic control of LH binding/unbinding, either globally or locally, in the presence of divalent ions, might constitute a mechanism for regulation of gene expression.
Collapse
|
4
|
Collepardo-Guevara R, Schlick T. The effect of linker histone's nucleosome binding affinity on chromatin unfolding mechanisms. Biophys J 2012; 101:1670-80. [PMID: 21961593 DOI: 10.1016/j.bpj.2011.07.044] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2011] [Revised: 07/14/2011] [Accepted: 07/25/2011] [Indexed: 10/17/2022] Open
Abstract
Eukaryotic gene activation requires selective unfolding of the chromatin fiber to access the DNA for processes such as DNA transcription, replication, and repair. Mutation/modification experiments of linker histone (LH) H1 suggest the importance of dynamic mechanisms for LH binding/dissociation, but the effects on chromatin's unfolding pathway remain unclear. Here we investigate the stretching response of chromatin fibers by mesoscale modeling to complement single-molecule experiments, and present various unfolding mechanisms for fibers with different nucleosome repeat lengths (NRLs) with/without LH that are fixed to their cores or bind/unbind dynamically with different affinities. Fiber softening occurs for long compared to short NRL (due to facile stacking rearrangements), dynamic compared to static LH/core binding as well as slow rather than fast dynamic LH rebinding (due to DNA stem destabilization), and low compared to high LH concentration (due to DNA stem inhibition). Heterogeneous superbead constructs--nucleosome clusters interspersed with extended fiber regions--emerge during unfolding of medium-NRL fibers and may be related to those observed experimentally. Our work suggests that fast and slow LH binding pools, present simultaneously in vivo, might act cooperatively to yield controlled fiber unfolding at low forces. Medium-NRL fibers with multiple dynamic LH pools offer both flexibility and selective DNA exposure, and may be evolutionarily suitable to regulate chromatin architecture and gene expression.
Collapse
|
5
|
Abstract
Cells integrate physicochemical signals on the nanoscale from the local microenvironment, resulting in altered functional nuclear landscape and gene expression. These alterations regulate diverse biological processes including stem cell differentiation, establishing robust developmental genetic programs and cellular homeostatic control systems. The mechanisms by which these signals are integrated into the 3D spatiotemporal organization of the cell nucleus to elicit differential gene expression programs are poorly understood. In this review I analyze our current understanding of mechanosignal transduction mechanisms to the cell nucleus to induce differential gene regulation. A description of both physical and chemical coupling, resulting in a prestressed nuclear organization, is emphasized. I also highlight the importance of spatial dimension in chromosome assembly, as well as the temporal filtering and stochastic processes at gene promoters that may be important in understanding the biophysical design principles underlying mechanoregulation of gene transcription.
Collapse
Affiliation(s)
- G V Shivashankar
- Mechanobiology Institute & Department of Biological Sciences, National University of Singapore, Singapore.
| |
Collapse
|
7
|
Chromatin fiber dynamics under tension and torsion. Int J Mol Sci 2010; 11:1557-79. [PMID: 20480035 PMCID: PMC2871131 DOI: 10.3390/ijms11041557] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2009] [Revised: 02/20/2010] [Accepted: 03/19/2010] [Indexed: 01/22/2023] Open
Abstract
Genetic and epigenetic information in eukaryotic cells is carried on chromosomes, basically consisting of large compact supercoiled chromatin fibers. Micromanipulations have recently led to great advances in the knowledge of the complex mechanisms underlying the regulation of DNA transaction events by nucleosome and chromatin structural changes. Indeed, magnetic and optical tweezers have allowed opportunities to handle single nucleosomal particles or nucleosomal arrays and measure their response to forces and torques, mimicking the molecular constraints imposed in vivo by various molecular motors acting on the DNA. These challenging technical approaches provide us with deeper understanding of the way chromatin dynamically packages our genome and participates in the regulation of cellular metabolism.
Collapse
|
8
|
Mazumder A, Roopa T, Kumar A, Iyer KV, Ramdas NM, Shivashankar GV. Prestressed nuclear organization in living cells. Methods Cell Biol 2010; 98:221-39. [PMID: 20816237 DOI: 10.1016/s0091-679x(10)98010-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The nucleus is maintained in a prestressed state within eukaryotic cells, stabilized mechanically by chromatin structure and other nuclear components on its inside, and cytoskeletal components on its outside. Nuclear architecture is emerging to be critical to the governance of chromatin assembly, regulation of genome function and cellular homeostasis. Elucidating the prestressed organization of the nucleus is thus important to understand how the nuclear architecture impinges on its function. In this chapter, various chemical and mechanical methods have been described to probe the prestressed organization of the nucleus.
Collapse
Affiliation(s)
- Aprotim Mazumder
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bellary Road, Bangalore 560065, India
| | | | | | | | | | | |
Collapse
|
10
|
Dynamics of chromatin decondensation reveals the structural integrity of a mechanically prestressed nucleus. Biophys J 2008; 95:3028-35. [PMID: 18556763 DOI: 10.1529/biophysj.108.132274] [Citation(s) in RCA: 100] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Genome organization within the cell nucleus is a result of chromatin condensation achieved by histone tail-tail interactions and other nuclear proteins that counter the outward entropic pressure of the polymeric DNA. We probed the entropic swelling of chromatin driven by enzymatic disruption of these interactions in isolated mammalian cell nuclei. The large-scale decondensation of chromatin and the eventual rupture of the nuclear membrane and lamin network due to this entropic pressure were observed by fluorescence imaging. This swelling was accompanied by nuclear softening, an effect that we quantified by measuring the fluctuations of an optically trapped bead adhered onto the nucleus. We also measured the pressure at which the nuclear scaffold ruptured using an atomic force microscope cantilever. A simple theory based on a balance of forces in a swelling porous gel quantitatively explains the diffusive dynamics of swelling. Our experiments on decondensation of chromatin in nuclei suggest that its compaction is a critical parameter in controlling nuclear stability.
Collapse
|