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Liang Z, Solano A, Lou J, Hinde E. Histone FRET reports the spatial heterogeneity in nanoscale chromatin architecture that is imparted by the epigenetic landscape at the level of single foci in an intact cell nucleus. Chromosoma 2024; 133:5-14. [PMID: 38265456 PMCID: PMC10904561 DOI: 10.1007/s00412-024-00815-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Revised: 12/28/2023] [Accepted: 01/03/2024] [Indexed: 01/25/2024]
Abstract
Genome sequencing has identified hundreds of histone post-translational modifications (PTMs) that define an open or compact chromatin nanostructure at the level of nucleosome proximity, and therefore serve as activators or repressors of gene expression. Direct observation of this epigenetic mode of transcriptional regulation in an intact single nucleus, is however, a complex task. This is because despite the development of fluorescent probes that enable observation of specific histone PTMs and chromatin density, the changes in nucleosome proximity regulating gene expression occur on a spatial scale well below the diffraction limit of optical microscopy. In recent work, to address this research gap, we demonstrated that the phasor approach to fluorescence lifetime imaging microscopy (FLIM) of Förster resonance energy transfer (FRET) between fluorescently labelled histones core to the nucleosome, is a readout of chromatin nanostructure that can be multiplexed with immunofluorescence (IF) against specific histone PTMs. Here from application of this methodology to gold standard gene activators (H3K4Me3 and H3K9Ac) versus repressors (e.g., H3K9Me3 and H3K27Me), we find that while on average these histone marks do impart an open versus compact chromatin nanostructure, at the level of single chromatin foci, there is significant spatial heterogeneity. Collectively this study illustrates the importance of studying the epigenetic landscape as a function of space within intact nuclear architecture and opens the door for the study of chromatin foci sub-populations defined by combinations of histone marks, as is seen in the context of bivalent chromatin.
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Affiliation(s)
- Zhen Liang
- Department of Biochemistry and Pharmacology, University of Melbourne, Melbourne, VIC, Australia
- Cancer and RNA Laboratory, St. Vincent's Institute of Medical Research, Melbourne, VIC, Australia
- Department of Medicine, Melbourne Medical School, St Vincent's Hospital, University of Melbourne, Melbourne, VIC, Australia
| | - Ashleigh Solano
- School of Physics, University of Melbourne, Melbourne, VIC, Australia
| | - Jieqiong Lou
- School of Physics, University of Melbourne, Melbourne, VIC, Australia
| | - Elizabeth Hinde
- Department of Biochemistry and Pharmacology, University of Melbourne, Melbourne, VIC, Australia.
- School of Physics, University of Melbourne, Melbourne, VIC, Australia.
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Coucke Q, Parveen N, Fernández GS, Qian C, Hofkens J, Debyser Z, Hendrix J. Particle-based phasor-FLIM-FRET resolves protein-protein interactions inside single viral particles. BIOPHYSICAL REPORTS 2023; 3:100122. [PMID: 37649577 PMCID: PMC10463199 DOI: 10.1016/j.bpr.2023.100122] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Accepted: 08/07/2023] [Indexed: 09/01/2023]
Abstract
Fluorescence lifetime imaging microscopy (FLIM) is a popular modality to create additional contrast in fluorescence images. By carefully analyzing pixel-based nanosecond lifetime patterns, FLIM allows studying complex molecular populations. At the single-molecule or single-particle level, however, image series often suffer from low signal intensities per pixel, rendering it difficult to quantitatively disentangle different lifetime species, such as during Förster resonance energy transfer (FRET) analysis in the presence of a significant donor-only fraction. In this article we investigate whether an object localization strategy and the phasor approach to FLIM have beneficial effects when carrying out FRET analyses of single particles. Using simulations, we first showed that an average of ∼300 photons, spread over the different pixels encompassing single fluorescing particles and without background, is enough to determine a correct phasor signature (SD < 5% for a 4-ns lifetime). For immobilized single- or double-labeled dsDNA molecules, we next validated that particle-based phasor-FLIM-FRET readily allows estimating fluorescence lifetimes and FRET from single molecules. Thirdly, we applied particle-based phasor-FLIM-FRET to investigate protein-protein interactions in subdiffraction HIV-1 viral particles. To do this, we first quantitatively compared the fluorescence brightness, lifetime, and photostability of different popular fluorescent protein-based FRET probes when genetically fused to the HIV-1 integrase enzyme in viral particles, and conclude that eGFP, mTurquoise2, and mScarlet perform best. Finally, for viral particles coexpressing FRET-donor/acceptor-labeled IN, we determined the absolute FRET efficiency of IN oligomers. Available in a convenient open-source graphical user interface, we believe that particle-based phasor-FLIM-FRET is a promising tool to provide detailed insights in samples suffering from low overall signal intensities.
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Affiliation(s)
- Quinten Coucke
- Molecular Imaging and Photonics Division, Department of Chemistry, KU Leuven, Leuven, Belgium
| | - Nagma Parveen
- Molecular Imaging and Photonics Division, Department of Chemistry, KU Leuven, Leuven, Belgium
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, India
| | - Guillermo Solís Fernández
- Molecular Imaging and Photonics Division, Department of Chemistry, KU Leuven, Leuven, Belgium
- UFIEC, National Institute of Health Carlos III, Madrid, Spain
| | - Chen Qian
- Department of Chemistry, Center for Nano Science (CENS), Center for Integrated Protein Science Munich (CIPSM), and Nanosystems Initiative Munich (NIM), Ludwig Maximilians-Universität München, Munich, Germany
| | - Johan Hofkens
- Molecular Imaging and Photonics Division, Department of Chemistry, KU Leuven, Leuven, Belgium
- Max Planck Institute for Polymer Research, Mainz, Germany
| | - Zeger Debyser
- Laboratory for Molecular Virology and Gene Therapy, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Leuven, Belgium
| | - Jelle Hendrix
- Molecular Imaging and Photonics Division, Department of Chemistry, KU Leuven, Leuven, Belgium
- Dynamic Bioimaging Lab, Advanced Optical Microscopy Centre and Biomedical Research Institute, Hasselt University, Hasselt, Belgium
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Locatelli M, Lawrimore J, Lin H, Sanaullah S, Seitz C, Segall D, Kefer P, Salvador Moreno N, Lietz B, Anderson R, Holmes J, Yuan C, Holzwarth G, Bloom KS, Liu J, Bonin K, Vidi PA. DNA damage reduces heterogeneity and coherence of chromatin motions. Proc Natl Acad Sci U S A 2022; 119:e2205166119. [PMID: 35858349 PMCID: PMC9304018 DOI: 10.1073/pnas.2205166119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Accepted: 06/07/2022] [Indexed: 01/14/2023] Open
Abstract
Chromatin motions depend on and may regulate genome functions, in particular the DNA damage response. In yeast, DNA double-strand breaks (DSBs) globally increase chromatin diffusion, whereas in higher eukaryotes the impact of DSBs on chromatin dynamics is more nuanced. We mapped the motions of chromatin microdomains in mammalian cells using diffractive optics and photoactivatable chromatin probes and found a high level of spatial heterogeneity. DNA damage reduces heterogeneity and imposes spatially defined shifts in motions: Distal to DNA breaks, chromatin motions are globally reduced, whereas chromatin retains higher mobility at break sites. These effects are driven by context-dependent changes in chromatin compaction. Photoactivated lattices of chromatin microdomains are ideal to quantify microscale coupling of chromatin motion. We measured correlation distances up to 2 µm in the cell nucleus, spanning chromosome territories, and speculate that this correlation distance between chromatin microdomains corresponds to the physical separation of A and B compartments identified in chromosome conformation capture experiments. After DNA damage, chromatin motions become less correlated, a phenomenon driven by phase separation at DSBs. Our data indicate tight spatial control of chromatin motions after genomic insults, which may facilitate repair at the break sites and prevent deleterious contacts of DSBs, thereby reducing the risk of genomic rearrangements.
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Affiliation(s)
- Maëlle Locatelli
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Josh Lawrimore
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Hua Lin
- Department of Physics, Indiana University–Purdue University Indianapolis, Indianapolis, IN 46202
| | - Sarvath Sanaullah
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Clayton Seitz
- Department of Physics, Indiana University–Purdue University Indianapolis, Indianapolis, IN 46202
| | - Dave Segall
- Department of Physics, Wake Forest University, Winston-Salem, NC 27109
| | - Paul Kefer
- Department of Physics, Wake Forest University, Winston-Salem, NC 27109
| | - Naike Salvador Moreno
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Benton Lietz
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Rebecca Anderson
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Julia Holmes
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC 27157
| | - Chongli Yuan
- Davidson School of Chemical Engineering, Purdue University, West Lafayette, IN 47907
| | - George Holzwarth
- Department of Physics, Wake Forest University, Winston-Salem, NC 27109
| | - Kerry S. Bloom
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Jing Liu
- Department of Physics, Indiana University–Purdue University Indianapolis, Indianapolis, IN 46202
- Melvin and Bren Simon Comprehensive Cancer Center, Indiana University, Indianapolis, IN 46202
- Center for Computational Biology and Bioinformatics, Indiana University, Indianapolis, IN 46202
| | - Keith Bonin
- Department of Physics, Wake Forest University, Winston-Salem, NC 27109
- Atrium Health Wake Forest Baptist Comprehensive Cancer Center, Winston-Salem, NC 27157
| | - Pierre-Alexandre Vidi
- Department of Cancer Biology, Wake Forest School of Medicine, Winston-Salem, NC 27157
- Atrium Health Wake Forest Baptist Comprehensive Cancer Center, Winston-Salem, NC 27157
- Laboratoire InGenO, Institut de Cancérologie de l’Ouest, 49055 Angers, France
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