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Dean WF, Nawara TJ, Albert RM, Mattheyses AL. OOPS: Object-Oriented Polarization Software for analysis of fluorescence polarization microscopy images. PLoS Comput Biol 2024; 20:e1011723. [PMID: 39133751 PMCID: PMC11341096 DOI: 10.1371/journal.pcbi.1011723] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Revised: 08/22/2024] [Accepted: 08/02/2024] [Indexed: 08/24/2024] Open
Abstract
Most essential cellular functions are performed by proteins assembled into larger complexes. Fluorescence Polarization Microscopy (FPM) is a powerful technique that goes beyond traditional imaging methods by allowing researchers to measure not only the localization of proteins within cells, but also their orientation or alignment within complexes or cellular structures. FPM can be easily integrated into standard widefield microscopes with the addition of a polarization modulator. However, the extensive image processing and analysis required to interpret the data have limited its widespread adoption. To overcome these challenges and enhance accessibility, we introduce OOPS (Object-Oriented Polarization Software), a MATLAB package for object-based analysis of FPM data. By combining flexible image segmentation and novel object-based analyses with a high-throughput FPM processing pipeline, OOPS empowers researchers to simultaneously study molecular order and orientation in individual biological structures; conduct population assessments based on morphological features, intensity statistics, and FPM measurements; and create publication-quality visualizations, all within a user-friendly graphical interface. Here, we demonstrate the power and versatility of our approach by applying OOPS to punctate and filamentous structures.
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Affiliation(s)
- William F. Dean
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Tomasz J. Nawara
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Rose M. Albert
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Alexa L. Mattheyses
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
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2
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Silva PL, Savchuk OA, Gallo J, García-Hevia L, Bañobre-López M, Nieder JB. Mapping intracellular thermal response of cancer cells to magnetic hyperthermia treatment. NANOSCALE 2020; 12:21647-21656. [PMID: 32766635 DOI: 10.1039/c9nr10370h] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Temperature is a key parameter for optimal cellular function and growth. Temperature perturbation may directly lead to cell death. This can be used in cancer therapies to kill cells in tumors, a therapeutic approach called hyperthermia. To avoid overheating of tumors that may damage healthy tissues, a knowledge of the intracellular temperature reached during the hyperthermia treatment of cancer cells is relevant. Recently, several luminescent intracellular nanothermometers have been proposed; however an application to sense temperature during a hyperthermia treatment is lacking. Here we present a technique to measure intracellular temperature changes in in vitro cancer cell models. For this purpose, we study for the first time the temperature dependence of the green fluorescent protein (GFP)'s fluorescence lifetime parameter. We find the fluorescence lifetime of GFP can be used for nanothermosensing. We use GFP in a bound form to actin filaments as an intracellular thermal reporter. Furthermore, we assess intracellular temperature during in vitro magnetothermal therapy on live HeLa cells incubated with polyacrylic acid-coated iron oxide nanoparticles. Compared to other thermosensitive materials and formulations reported so far, the GFP nanothermosensor is easily expressed via transfection and various GFP variants are commercially available. We foresee that the nanothermometer developed might find widespread applications in cancer therapy research and development.
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Affiliation(s)
- Pedro L Silva
- Ultrafast Bio- and Nanophotonics Group, INL - International Iberian Nanotechnology Laboratory, 4715-330 Braga, Portugal.
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3
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Fleissner F, Kumar S, Klein N, Wirth D, Dhiman R, Schneider D, Bonn M, Parekh SH. Tension Causes Unfolding of Intracellular Vimentin Intermediate Filaments. ACTA ACUST UNITED AC 2020; 4:e2000111. [DOI: 10.1002/adbi.202000111] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2019] [Revised: 09/18/2020] [Indexed: 12/27/2022]
Affiliation(s)
- Frederik Fleissner
- Department of Molecular Spectroscopy Max Planck Institute for Polymer Research Mainz 55128 Germany
| | - Sachin Kumar
- Department of Molecular Spectroscopy Max Planck Institute for Polymer Research Mainz 55128 Germany
- Department of Biomedical Engineering University of Texas at Austin Austin TX 78712 USA
| | - Noreen Klein
- Institute of Pharmacy and Biochemistry Johannes Gutenberg‐University Mainz 55128 Germany
| | - Daniel Wirth
- Institute of Pharmacy and Biochemistry Johannes Gutenberg‐University Mainz 55128 Germany
| | - Ravi Dhiman
- Department of Molecular Spectroscopy Max Planck Institute for Polymer Research Mainz 55128 Germany
| | - Dirk Schneider
- Institute of Pharmacy and Biochemistry Johannes Gutenberg‐University Mainz 55128 Germany
| | - Mischa Bonn
- Department of Molecular Spectroscopy Max Planck Institute for Polymer Research Mainz 55128 Germany
| | - Sapun H. Parekh
- Department of Molecular Spectroscopy Max Planck Institute for Polymer Research Mainz 55128 Germany
- Department of Biomedical Engineering University of Texas at Austin Austin TX 78712 USA
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4
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Imaging of fluorescence anisotropy during photoswitching provides a simple readout for protein self-association. Nat Commun 2020; 11:21. [PMID: 31911590 PMCID: PMC6946710 DOI: 10.1038/s41467-019-13843-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Accepted: 12/03/2019] [Indexed: 12/02/2022] Open
Abstract
Monitoring of protein oligomerization has benefited greatly from Förster Resonance Energy Transfer (FRET) measurements. Although donors and acceptors are typically fluorescent molecules with different spectra, homo-FRET can occur between fluorescent molecules of the same type if the emission spectrum overlaps with the absorption spectrum. Here, we describe homo-FRET measurements by monitoring anisotropy changes in photoswitchable fluorescent proteins while photoswitching to the off state. These offer the capability to estimate anisotropy in the same specimen during homo-FRET as well as non-FRET conditions. We demonstrate photoswitching anisotropy FRET (psAFRET) with a number of test chimeras and example oligomeric complexes inside living cells. We also present an equation derived from FRET and anisotropy equations which converts anisotropy changes into a factor we call delta r FRET (drFRET). This is analogous to an energy transfer efficiency and allows experiments performed on a given homo-FRET pair to be more easily compared across different optical configurations. Performing homo-FRET measurements in cells using a fluorescence microscope is challenging, especially when using high numerical aperture objective lenses. Here the authors present a method for improved homo-FRET measurements based on anisotropy changes in photoswitchable fluorescent proteins.
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5
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Vinegoni C, Feruglio PF, Gryczynski I, Mazitschek R, Weissleder R. Fluorescence anisotropy imaging in drug discovery. Adv Drug Deliv Rev 2019; 151-152:262-288. [PMID: 29410158 PMCID: PMC6072632 DOI: 10.1016/j.addr.2018.01.019] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Revised: 01/29/2018] [Accepted: 01/30/2018] [Indexed: 12/15/2022]
Abstract
Non-invasive measurement of drug-target engagement can provide critical insights in the molecular pharmacology of small molecule drugs. Fluorescence polarization/fluorescence anisotropy measurements are commonly employed in protein/cell screening assays. However, the expansion of such measurements to the in vivo setting has proven difficult until recently. With the advent of high-resolution fluorescence anisotropy microscopy it is now possible to perform kinetic measurements of intracellular drug distribution and target engagement in commonly used mouse models. In this review we discuss the background, current advances and future perspectives in intravital fluorescence anisotropy measurements to derive pharmacokinetic and pharmacodynamic measurements in single cells and whole organs.
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Affiliation(s)
- Claudio Vinegoni
- Center for System Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
| | - Paolo Fumene Feruglio
- Center for System Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA; Department of Neurological, Biomedical and Movement Sciences, University of Verona, Verona, Italy
| | - Ignacy Gryczynski
- University of North Texas Health Science Center, Institute for Molecular Medicine, Fort Worth, TX, United States
| | - Ralph Mazitschek
- Center for System Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
| | - Ralph Weissleder
- Center for System Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
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6
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Abstract
Cellular behavior is continuously affected by microenvironmental forces through the process of mechanotransduction, in which mechanical stimuli are rapidly converted to biochemical responses. Mounting evidence suggests that the nucleus itself is a mechanoresponsive element, reacting to cytoskeletal forces and mediating downstream biochemical responses. The nucleus responds through a host of mechanisms, including partial unfolding, conformational changes, and phosphorylation of nuclear envelope proteins; modulation of nuclear import/export; and altered chromatin organization, resulting in transcriptional changes. It is unclear which of these events present direct mechanotransduction processes and which are downstream of other mechanotransduction pathways. We critically review and discuss the current evidence for nuclear mechanotransduction, particularly in the context of stem cell fate, a largely unexplored topic, and in disease, where an improved understanding of nuclear mechanotransduction is beginning to open new treatment avenues. Finally, we discuss innovative technological developments that will allow outstanding questions in the rapidly growing field of nuclear mechanotransduction to be answered.
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Affiliation(s)
- Melanie Maurer
- Meinig School of Biomedical Engineering and Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, New York 14853, USA; ,
| | - Jan Lammerding
- Meinig School of Biomedical Engineering and Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, New York 14853, USA; ,
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7
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Bhuckory S, Kays JC, Dennis AM. In Vivo Biosensing Using Resonance Energy Transfer. BIOSENSORS 2019; 9:E76. [PMID: 31163706 PMCID: PMC6628364 DOI: 10.3390/bios9020076] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/22/2019] [Revised: 05/20/2019] [Accepted: 05/27/2019] [Indexed: 01/05/2023]
Abstract
Solution-phase and intracellular biosensing has substantially enhanced our understanding of molecular processes foundational to biology and pathology. Optical methods are favored because of the low cost of probes and instrumentation. While chromatographic methods are helpful, fluorescent biosensing further increases sensitivity and can be more effective in complex media. Resonance energy transfer (RET)-based sensors have been developed to use fluorescence, bioluminescence, or chemiluminescence (FRET, BRET, or CRET, respectively) as an energy donor, yielding changes in emission spectra, lifetime, or intensity in response to a molecular or environmental change. These methods hold great promise for expanding our understanding of molecular processes not just in solution and in vitro studies, but also in vivo, generating information about complex activities in a natural, organismal setting. In this review, we focus on dyes, fluorescent proteins, and nanoparticles used as energy transfer-based optical transducers in vivo in mice; there are examples of optical sensing using FRET, BRET, and in this mammalian model system. After a description of the energy transfer mechanisms and their contribution to in vivo imaging, we give a short perspective of RET-based in vivo sensors and the importance of imaging in the infrared for reduced tissue autofluorescence and improved sensitivity.
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Affiliation(s)
- Shashi Bhuckory
- Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA.
| | - Joshua C Kays
- Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA.
| | - Allison M Dennis
- Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA.
- Division of Materials Science and Engineering, Boston University, Boston, MA 02215, USA.
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8
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Ströhl F, Kaminski CF. A concept for single-shot volumetric fluorescence imaging via orthogonally polarized excitation lattices. Sci Rep 2019; 9:6425. [PMID: 31015487 PMCID: PMC6478832 DOI: 10.1038/s41598-019-42743-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Accepted: 04/08/2019] [Indexed: 11/08/2022] Open
Abstract
The deconvolution of widefield fluorescence images provides only guesses of spatial frequency information along the optical axis due to the so called missing cone in the optical transfer function. Retaining the single-shot imaging speed of deconvolution microscopy while gaining access to missing cone information is thus highly desirable for microscopy of volumetric samples. Here, we present a concept that superimposes two orthogonally polarized excitation lattices with a phase-shift of p between them. In conjunction with a non-iterative image reconstruction algorithm this permits the restoration of missing cone information. We show how fluorescence anisotropy could be used as a method to encode and decode the patterns simultaneously and develop a rigorous theoretical framework for the method. Through in-silico experiments and imaging of fixed biological cells on a structured illumination microscope that emulates the proposed setup we validate the feasibility of the method.
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Affiliation(s)
- Florian Ströhl
- Department of Chemical Engineering and Biotechnology, University of Cambridge, CB3 0AS, Cambridge, UK.
- Department of Physics and Technology, UiT-The Arctic University of Norway, 9037, Tromsø, Norway.
| | - Clemens F Kaminski
- Department of Chemical Engineering and Biotechnology, University of Cambridge, CB3 0AS, Cambridge, UK.
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9
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Obashi K, Matsuda A, Inoue Y, Okabe S. Precise Temporal Regulation of Molecular Diffusion within Dendritic Spines by Actin Polymers during Structural Plasticity. Cell Rep 2019; 27:1503-1515.e8. [DOI: 10.1016/j.celrep.2019.04.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Revised: 02/22/2019] [Accepted: 03/29/2019] [Indexed: 10/26/2022] Open
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10
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Cutrale F, Rodriguez D, Hortigüela V, Chiu CL, Otterstrom J, Mieruszynski S, Seriola A, Larrañaga E, Raya A, Lakadamyali M, Fraser SE, Martinez E, Ojosnegros S. Using enhanced number and brightness to measure protein oligomerization dynamics in live cells. Nat Protoc 2019; 14:616-638. [DOI: 10.1038/s41596-018-0111-9] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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11
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Snell NE, Rao VP, Seckinger KM, Liang J, Leser J, Mancini AE, Rizzo MA. Homotransfer of FRET Reporters for Live Cell Imaging. BIOSENSORS-BASEL 2018; 8:bios8040089. [PMID: 30314323 PMCID: PMC6316388 DOI: 10.3390/bios8040089] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Revised: 09/27/2018] [Accepted: 10/10/2018] [Indexed: 01/01/2023]
Abstract
Förster resonance energy transfer (FRET) between fluorophores of the same species was recognized in the early to mid-1900s, well before modern heterotransfer applications. Recently, homotransfer FRET principles have re-emerged in biosensors that incorporate genetically encoded fluorescent proteins. Homotransfer offers distinct advantages over the standard heterotransfer FRET method, some of which are related to the use of fluorescence polarization microscopy to quantify FRET between two fluorophores of identical color. These include enhanced signal-to-noise, greater compatibility with other optical sensors and modulators, and new design strategies based upon the clustering or dimerization of singly-labeled sensors. Here, we discuss the theoretical basis for measuring homotransfer using polarization microscopy, procedures for data collection and processing, and we review the existing genetically-encoded homotransfer biosensors.
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Affiliation(s)
- Nicole E Snell
- Department of Physiology, University of Maryland School of Medicine, 660 W Redwood St/HH525B, Baltimore, MD 21201, USA.
| | - Vishnu P Rao
- Department of Physiology, University of Maryland School of Medicine, 660 W Redwood St/HH525B, Baltimore, MD 21201, USA.
| | - Kendra M Seckinger
- Department of Physiology, University of Maryland School of Medicine, 660 W Redwood St/HH525B, Baltimore, MD 21201, USA.
| | - Junyi Liang
- Department of Physiology, University of Maryland School of Medicine, 660 W Redwood St/HH525B, Baltimore, MD 21201, USA.
| | - Jenna Leser
- Department of Physiology, University of Maryland School of Medicine, 660 W Redwood St/HH525B, Baltimore, MD 21201, USA.
| | - Allison E Mancini
- Department of Physiology, University of Maryland School of Medicine, 660 W Redwood St/HH525B, Baltimore, MD 21201, USA.
| | - M A Rizzo
- Department of Physiology, University of Maryland School of Medicine, 660 W Redwood St/HH525B, Baltimore, MD 21201, USA.
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12
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Köker T, Fernandez A, Pinaud F. Characterization of Split Fluorescent Protein Variants and Quantitative Analyses of Their Self-Assembly Process. Sci Rep 2018; 8:5344. [PMID: 29593344 PMCID: PMC5871787 DOI: 10.1038/s41598-018-23625-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2018] [Accepted: 03/16/2018] [Indexed: 02/01/2023] Open
Abstract
Many biotechniques use complementary split-fluorescent protein (sFPs) fragments to visualize protein-protein interactions, image cells by ensemble or single molecule fluorescence microscopy, or assemble nanomaterials and protein superstructures. Yet, the reassembly mechanisms of sFPs, including fragment binding rates, folding, chromophore maturation and overall photophysics remain poorly characterized. Here, we evolved asymmetric and self-complementing green, yellow and cyan sFPs together with their full-length equivalents (flFPs) and described their biochemical and photophysical properties in vitro and in cells. While re-assembled sFPs have spectral properties similar to flFPs, they display slightly reduced quantum yields and fluorescence lifetimes due to a less sturdy β-barrel structure. The complementation of recombinant sFPs expressed in vitro follows a conformational selection mechanism whereby the larger sFP fragments exist in a monomer-dimer equilibrium and only monomers are competent for fluorescence complementation. This bimolecular fragment interaction involves a slow and irreversible binding step, followed by chromophore maturation at a rate similar to that of flFPs. When expressed as fusion tags in cells, sFPs behave as monomers directly activated with synthetic complementary fragments. This study resulted in the development of sFP color variants having improved maturation kinetics, brightness, and photophysics for fluorescence microscopy imaging of cellular processes, including single molecule detection.
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Affiliation(s)
- Tuğba Köker
- Department of Biological Sciences, University of Southern California, 1050 Child Way, Los Angeles, 90089, California, USA
| | - Anthony Fernandez
- Department of Biological Sciences, University of Southern California, 1050 Child Way, Los Angeles, 90089, California, USA
| | - Fabien Pinaud
- Department of Biological Sciences, University of Southern California, 1050 Child Way, Los Angeles, 90089, California, USA. .,Department of Chemistry, University of Southern California, 1050 Child Way, Los Angeles, 90089, California, USA. .,Department of Physics and Astronomy, University of Southern California, 1050 Child Way, Los Angeles, 90089, California, USA.
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13
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Ströhl F, Wong HHW, Holt CE, Kaminski CF. Total internal reflection fluorescence anisotropy imaging microscopy: setup, calibration, and data processing for protein polymerization measurements in living cells. Methods Appl Fluoresc 2017; 6:014004. [PMID: 28824013 PMCID: PMC5735343 DOI: 10.1088/2050-6120/aa872e] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Fluorescence anisotropy imaging microscopy (FAIM) measures the depolarization properties of fluorophores to deduce molecular changes in their environment. For successful FAIM, several design principles have to be considered and a thorough system-specific calibration protocol is paramount. One important calibration parameter is the G factor, which describes the system-induced errors for different polarization states of light. The determination and calibration of the G factor is discussed in detail in this article. We present a novel measurement strategy, which is particularly suitable for FAIM with high numerical aperture objectives operating in TIRF illumination mode. The method makes use of evanescent fields that excite the sample with a polarization direction perpendicular to the image plane. Furthermore, we have developed an ImageJ/Fiji plugin, AniCalc, for FAIM data processing. We demonstrate the capabilities of our TIRF-FAIM system by measuring [Formula: see text]-actin polymerization in human embryonic kidney cells and in retinal neurons.
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Affiliation(s)
- Florian Ströhl
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge, CB3 0AS, United Kingdom
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14
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Shroder DY, Lippert LG, Goldman YE. Single molecule optical measurements of orientation and rotations of biological macromolecules. Methods Appl Fluoresc 2016; 4:042004. [PMID: 28192292 PMCID: PMC5308470 DOI: 10.1088/2050-6120/4/4/042004] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Subdomains of macromolecules often undergo large orientation changes during their catalytic cycles that are essential for their activity. Tracking these rearrangements in real time opens a powerful window into the link between protein structure and functional output. Site-specific labeling of individual molecules with polarized optical probes and measurement of their spatial orientation can give insight into the crucial conformational changes, dynamics, and fluctuations of macromolecules. Here we describe the range of single molecule optical technologies that can extract orientation information from these probes, review the relevant types of probes and labeling techniques, and highlight the advantages and disadvantages of these technologies for addressing specific inquiries.
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15
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Ghosh S, Ozcelikkale A, Dutton JC, Han B. Role of intracellular poroelasticity on freezing-induced deformation of cells in engineered tissues. J R Soc Interface 2016; 13:rsif.2016.0480. [PMID: 27707905 DOI: 10.1098/rsif.2016.0480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Accepted: 09/06/2016] [Indexed: 11/12/2022] Open
Abstract
Freezing of biomaterials is important in a wide variety of biomedical applications, including cryopreservation and cryosurgeries. For the success of these applications to various biomaterials, biophysical mechanisms, which determine freezing-induced changes in cells and tissues, need to be well understood. Specifically, the significance of the intracellular mechanics during freezing is not well understood. Thus, we hypothesize that cells interact during freezing with the surroundings such as suspension media and the extracellular matrix (ECM) via two distinct but related mechanisms-water transport and cytoskeletal mechanics. The underlying rationale is that the cytoplasm of the cells has poroelastic nature, which can regulate both cellular water transport and cytoskeletal mechanics. A poroelasticity-based cell dehydration model is developed and confirmed to provide insight into the effects of the hydraulic conductivity and stiffness of the cytoplasm on the dehydration of cells in suspension during freezing. We further investigated the effect of the cytoskeletal structures on the cryoresponse of cells embedded in the ECM by measuring the spatio-temporal intracellular deformation with dermal equivalent as a model tissue. The freezing-induced change in cell, nucleus and cytoplasm volume was quantified, and the possible mechanism of the volumetric change was proposed. The results are discussed considering the hierarchical poroelasticity of biological tissues.
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Affiliation(s)
- Soham Ghosh
- School of Mechanical Engineering, Purdue University, West Lafayette, IN, USA
| | - Altug Ozcelikkale
- School of Mechanical Engineering, Purdue University, West Lafayette, IN, USA
| | - J Craig Dutton
- Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Bumsoo Han
- School of Mechanical Engineering, Purdue University, West Lafayette, IN, USA Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, USA Birck Nanotechnology Center, Purdue University, West Lafayette, IN, USA
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16
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Zhanghao K, Chen L, Yang XS, Wang MY, Jing ZL, Han HB, Zhang MQ, Jin D, Gao JT, Xi P. Super-resolution dipole orientation mapping via polarization demodulation. LIGHT, SCIENCE & APPLICATIONS 2016; 5:e16166. [PMID: 30167126 PMCID: PMC6059828 DOI: 10.1038/lsa.2016.166] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2015] [Revised: 05/09/2016] [Accepted: 05/17/2016] [Indexed: 05/07/2023]
Abstract
Fluorescence polarization microscopy (FPM) aims to detect the dipole orientation of fluorophores and to resolve structural information for labeled organelles via wide-field or confocal microscopy. Conventional FPM often suffers from the presence of a large number of molecules within the diffraction-limited volume, with averaged fluorescence polarization collected from a group of dipoles with different orientations. Here, we apply sparse deconvolution and least-squares estimation to fluorescence polarization modulation data and demonstrate a super-resolution dipole orientation mapping (SDOM) method that resolves the effective dipole orientation from a much smaller number of fluorescent molecules within a sub-diffraction focal area. We further apply this method to resolve structural details in both fixed and live cells. For the first time, we show that different borders of a dendritic spine neck exhibit a heterogeneous distribution of dipole orientation. Furthermore, we illustrate that the dipole is always perpendicular to the direction of actin filaments in mammalian kidney cells and radially distributed in the hourglass structure of the septin protein under specific labelling. The accuracy of the dipole orientation can be further mapped using the orientation uniform factor, which shows the superiority of SDOM compared with its wide-field counterpart as the number of molecules is decreased within the smaller focal area. Using the inherent feature of the orientation dipole, the SDOM technique, with its fast imaging speed (at sub-second scale), can be applied to a broad range of fluorescently labeled biological systems to simultaneously resolve the valuable dipole orientation information with super-resolution imaging.
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Affiliation(s)
- Karl Zhanghao
- Department of Biomedical Engineering, College of Engineering, Peking University, Beijing 100871, China
| | - Long Chen
- Department of Automation, Tsinghua University, Beijing 100084, China
- Bioinformatics Division, TNLIST, MOE Key Laboratory of Bioinformatics and Center for Synthetic & Systems Biology, Tsinghua University, Beijing 100084, China
| | - Xu-San Yang
- Department of Biomedical Engineering, College of Engineering, Peking University, Beijing 100871, China
| | - Miao-Yan Wang
- Department of Biomedical Engineering, College of Engineering, Peking University, Beijing 100871, China
| | - Zhen-Li Jing
- Department of Automation, Tsinghua University, Beijing 100084, China
- Bioinformatics Division, TNLIST, MOE Key Laboratory of Bioinformatics and Center for Synthetic & Systems Biology, Tsinghua University, Beijing 100084, China
| | - Hong-Bin Han
- Department of Radiology, Peking University Third Hospital, Beijing 100191, China
| | - Michael Q Zhang
- Bioinformatics Division, TNLIST, MOE Key Laboratory of Bioinformatics and Center for Synthetic & Systems Biology, Tsinghua University, Beijing 100084, China
- Department of Biological Sciences, Center for Systems Biology, The University of Texas, Dallas 800 West Campbell Road, RL11, Richardson, TX 75080-3021, USA
- Department of Basic Medical Sciences, School of Medicine, Tsinghua University, Beijing 100084, China
| | - Dayong Jin
- Institute for Biomedical Materials and Devices (IBMD), Faculty of Science, University of Technology Sydney, NSW 2007, Australia
| | - Jun-Tao Gao
- Department of Automation, Tsinghua University, Beijing 100084, China
- Bioinformatics Division, TNLIST, MOE Key Laboratory of Bioinformatics and Center for Synthetic & Systems Biology, Tsinghua University, Beijing 100084, China
- ;, ;,
| | - Peng Xi
- Department of Biomedical Engineering, College of Engineering, Peking University, Beijing 100871, China
- Institute for Biomedical Materials and Devices (IBMD), Faculty of Science, University of Technology Sydney, NSW 2007, Australia
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17
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Vinegoni C, Dubach JM, Feruglio PF, Weissleder R. Two-photon Fluorescence Anisotropy Microscopy for Imaging and Direct Measurement of Intracellular Drug Target Engagement. IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS : A PUBLICATION OF THE IEEE LASERS AND ELECTRO-OPTICS SOCIETY 2016; 22:6801607. [PMID: 27440991 PMCID: PMC4946648 DOI: 10.1109/jstqe.2015.2501384] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Small molecule therapeutic drugs must reach their intended cellular targets (pharmacokinetics) and engage them to modulate therapeutic effects (pharmacodynamics). These processes are often difficult to measure in vivo due to their complexities and occurrence within single cells. It has been particularly difficult to directly measure cellular drug target binding. Fluorescence polarization is commonly used in pharmacological screening assays to measure drug-protein or protein-protein interactions. We hypothesized that fluorescence polarization imaging could be adapted and used with fluorescently labeled drugs to measure drug target engagement in vivo. Here we summarize recent results using two photon fluorescence anisotropy microscopy. Our imaging technique offers quantitative pharmacological binding information of diverse molecular interactions at the microscopic level, differentiating between bound and unbound states. Used in combination with other recent advances in the development of novel fluorescently labeled drugs, we expect that the described imaging modality will provide a window into the distribution and efficacy of drugs in real time and in vivo at the cellular and subcellular level.
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Affiliation(s)
- Claudio Vinegoni
- Center for System Biology, Massachusetts General Hospital and Harvard Medical School, Richard B. Simches Research Center, 185 Cambridge Street, Boston 02114, USA
| | - John M. Dubach
- Center for System Biology, Massachusetts General Hospital and Harvard Medical School, Richard B. Simches Research Center, 185 Cambridge Street, Boston 02114, USA
| | - Paolo Fumene Feruglio
- Center for System Biology, Massachusetts General Hospital and Harvard Medical School, Richard B. Simches Research Center, 185 Cambridge Street, Boston 02114, USA and with the Department of Neurological and Movement Sciences, University of Verona, Strada Le Grazie 8, 37134 Verona, Italy
| | - Ralph Weissleder
- Center for System Biology, Massachusetts General Hospital and Harvard Medical School, Richard B. Simches Research Center, 185 Cambridge Street, Boston 02114, USA
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Quantitative nanoscale imaging of orientational order in biological filaments by polarized superresolution microscopy. Proc Natl Acad Sci U S A 2016; 113:E820-8. [PMID: 26831082 DOI: 10.1073/pnas.1516811113] [Citation(s) in RCA: 69] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Essential cellular functions as diverse as genome maintenance and tissue morphogenesis rely on the dynamic organization of filamentous assemblies. For example, the precise structural organization of DNA filaments has profound consequences on all DNA-mediated processes including gene expression, whereas control over the precise spatial arrangement of cytoskeletal protein filaments is key for mechanical force generation driving animal tissue morphogenesis. Polarized fluorescence is currently used to extract structural organization of fluorescently labeled biological filaments by determining the orientation of fluorescent labels, however with a strong drawback: polarized fluorescence imaging is indeed spatially limited by optical diffraction, and is thus unable to discriminate between the intrinsic orientational mobility of the fluorophore labels and the real structural disorder of the labeled biomolecules. Here, we demonstrate that quantitative single-molecule polarized detection in biological filament assemblies allows not only to correct for the rotational flexibility of the label but also to image orientational order of filaments at the nanoscale using superresolution capabilities. The method is based on polarized direct stochastic optical reconstruction microscopy, using dedicated optical scheme and image analysis to determine both molecular localization and orientation with high precision. We apply this method to double-stranded DNA in vitro and microtubules and actin stress fibers in whole cells.
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Hedde PN, Ranjit S, Gratton E. 3D fluorescence anisotropy imaging using selective plane illumination microscopy. OPTICS EXPRESS 2015; 23:22308-17. [PMID: 26368202 PMCID: PMC4646523 DOI: 10.1364/oe.23.022308] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Fluorescence anisotropy imaging is a popular method to visualize changes in organization and conformation of biomolecules within cells and tissues. In such an experiment, depolarization effects resulting from differences in orientation, proximity and rotational mobility of fluorescently labeled molecules are probed with high spatial resolution. Fluorescence anisotropy is typically imaged using laser scanning and epifluorescence-based approaches. Unfortunately, those techniques are limited in either axial resolution, image acquisition speed, or by photobleaching. In the last decade, however, selective plane illumination microscopy has emerged as the preferred choice for three-dimensional time lapse imaging combining axial sectioning capability with fast, camera-based image acquisition, and minimal light exposure. We demonstrate how selective plane illumination microscopy can be utilized for three-dimensional fluorescence anisotropy imaging of live cells. We further examined the formation of focal adhesions by three-dimensional time lapse anisotropy imaging of CHO-K1 cells expressing an EGFP-paxillin fusion protein.
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Zhang H, Wu Q, Berezin MY. Fluorescence anisotropy (polarization): from drug screening to precision medicine. Expert Opin Drug Discov 2015; 10:1145-61. [PMID: 26289575 DOI: 10.1517/17460441.2015.1075001] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
INTRODUCTION Fluorescence anisotropy (FA) is one of the major established methods accepted by industry and regulatory agencies for understanding the mechanisms of drug action and selecting drug candidates utilizing a high-throughput format. AREAS COVERED This review covers the basics of FA and complementary methods, such as fluorescence lifetime anisotropy and their roles in the drug discovery process. The authors highlight the factors affecting FA readouts, fluorophore selection and instrumentation. Furthermore, the authors describe the recent development of a successful, commercially valuable FA assay for long QT syndrome drug toxicity to illustrate the role that FA can play in the early stages of drug discovery. EXPERT OPINION Despite the success in drug discovery, the FA-based technique experiences competitive pressure from other homogeneous assays. That being said, FA is an established yet rapidly developing technique, recognized by academic institutions, the pharmaceutical industry and regulatory agencies across the globe. The technical problems encountered in working with small molecules in homogeneous assays are largely solved, and new challenges come from more complex biological molecules and nanoparticles. With that, FA will remain one of the major work-horse techniques leading to precision (personalized) medicine.
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Affiliation(s)
- Hairong Zhang
- a 1 Washington University School of Medicine, Department of Radiology , St. Louis 63110, USA
| | - Qian Wu
- a 1 Washington University School of Medicine, Department of Radiology , St. Louis 63110, USA
| | - Mikhail Y Berezin
- a 1 Washington University School of Medicine, Department of Radiology , St. Louis 63110, USA.,b 2 Washington University School of Medicine, Institute of Materials Science and Engineering, Department of Radiology , 510 S. Kingshighway, Barnard Bldg, 6th floor, 6604A, St. Louis, MO, USA +1 314 747 0701 ; +1 314 747 5191 ;
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Melo AM, Fedorov A, Prieto M, Coutinho A. Exploring homo-FRET to quantify the oligomer stoichiometry of membrane-bound proteins involved in a cooperative partition equilibrium. Phys Chem Chem Phys 2015; 16:18105-17. [PMID: 24722583 DOI: 10.1039/c4cp00060a] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The establishment of protein-protein interactions between membrane-bound proteins is associated with several biological functions and dysfunctions. Here, an analytical framework that uses energy homo transfer to directly probe quantitatively the oligomerization state of membrane-bound proteins engaged in a three-state cooperative partition is presented. Briefly, this model assumes that monomeric protein molecules partition into the bilayer surface and reversibly assemble into oligomers with k subunits. A general equation relating the overall steady-state fluorescence anisotropy of the sample to its fractional labeling was derived by considering explicitly that the anisotropy of mixed oligomers containing i-labeled monomers is inversely proportional to the number of labeled subunits per oligomer (Runnels and Scarlata limit). This method was very robust in describing the electrostatic interaction of Alexa Fluor 488 fluorescently labeled lysozyme (Lz-A488) with phosphatidylserine-containing membranes. The pronounced decrease detected in the fluorescence anisotropy of Lz-A488 always correlated with the system reaching a high membrane surface density of the protein (at a low lipid-to-protein (L/P) molar ratio). The occurrence of energy homo transfer-induced fluorescence depolarization was further confirmed by measuring the anisotropy decays of Lz-A488 under these conditions. A global analysis of the steady-state anisotropy data obtained under a wide range of experimental conditions (variable anionic lipid content of the liposomes, L/P molar ratios and protein fractional labeling) confirmed that membrane-bound Lz-A488 assembled into oligomeric complexes, possibly with a stoichiometry of k = 6 ± 1. This study illustrates that even in the presence of a coupled partition-oligomerization equilibrium, steady-state anisotropy measurements provide a simple and reliable tool to monitor the self-assembly of membrane-bound proteins.
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Affiliation(s)
- Ana M Melo
- Centro de Química-Física Molecular and Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
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23
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Koskinen M, Hotulainen P. Measuring F-actin properties in dendritic spines. Front Neuroanat 2014; 8:74. [PMID: 25140131 PMCID: PMC4122166 DOI: 10.3389/fnana.2014.00074] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2014] [Accepted: 07/16/2014] [Indexed: 12/28/2022] Open
Abstract
During the last decade, numerous studies have demonstrated that the actin cytoskeleton plays a pivotal role in the control of dendritic spine shape. Synaptic stimulation rapidly changes the actin dynamics and many actin regulators have been shown to play roles in neuron functionality. Accordingly, defects in the regulation of the actin cytoskeleton in neurons have been implicated in memory disorders. Due to the small size of spines, it is difficult to detect changes in the actin structures in dendritic spines by conventional light microscopy imaging. Instead, to know how tightly actin filaments are bundled together, and how fast the filaments turnover, we need to use advanced microscopy techniques, such as fluorescence recovery after photobleaching (FRAP), photoactivatable green fluorescent protein (PAGFP) fluorescence decay and fluorescence anisotropy. Fluorescence anisotropy, which measures the Förster resonance energy transfer (FRET) between two GFP fluorophores, has been proposed as a method to measure the level of actin polymerization. Here, we propose a novel idea that fluorescence anisotropy could be more suitable to study the level of actin filament bundling instead of actin polymerization. We validate the method in U2OS cell line where the actin structures can be clearly distinguished and apply to analyze how actin filament organization in dendritic spines changes during neuronal maturation. In addition to fluorescence anisotropy validation, we take a critical look at the properties and limitations of FRAP and PAGFP fluorescence decay methods and offer our proposals for the analysis methods for these approaches. These three methods complement each other, each providing additional information about actin dynamics and organization in dendritic spines.
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Affiliation(s)
- Mikko Koskinen
- Neuroscience Center, University of Helsinki Helsinki, Finland
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Dubach J, Vinegoni C, Mazitschek R, Fumene Feruglio P, Cameron L, Weissleder R. In vivo imaging of specific drug-target binding at subcellular resolution. Nat Commun 2014; 5:3946. [PMID: 24867710 PMCID: PMC4362617 DOI: 10.1038/ncomms4946] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2013] [Accepted: 04/23/2014] [Indexed: 01/11/2023] Open
Abstract
The possibility of measuring binding of small-molecule drugs to desired targets in live cells could provide a better understanding of drug action. However, current approaches mostly yield static data, require lysis or rely on indirect assays and thus often provide an incomplete understanding of drug action. Here, we present a multiphoton fluorescence anisotropy microscopy live cell imaging technique to measure and map drug-target interaction in real time at subcellular resolution. This approach is generally applicable using any fluorescently labelled drug and enables high-resolution spatial and temporal mapping of bound and unbound drug distribution. To illustrate our approach we measure intracellular target engagement of the chemotherapeutic Olaparib, a poly(ADP-ribose) polymerase inhibitor, in live cells and within a tumour in vivo. These results are the first generalizable approach to directly measure drug-target binding in vivo and present a promising tool to enhance understanding of drug activity.
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Affiliation(s)
- J.M. Dubach
- Center for System Biology, Massachusetts General Hospital and Harvard Medical School, Richard B. Simches Research Center, 185 Cambridge Street, Boston 02114, USA
| | - C. Vinegoni
- Center for System Biology, Massachusetts General Hospital and Harvard Medical School, Richard B. Simches Research Center, 185 Cambridge Street, Boston 02114, USA
| | - R. Mazitschek
- Center for System Biology, Massachusetts General Hospital and Harvard Medical School, Richard B. Simches Research Center, 185 Cambridge Street, Boston 02114, USA
| | - P. Fumene Feruglio
- Center for System Biology, Massachusetts General Hospital and Harvard Medical School, Richard B. Simches Research Center, 185 Cambridge Street, Boston 02114, USA
| | | | - R. Weissleder
- Center for System Biology, Massachusetts General Hospital and Harvard Medical School, Richard B. Simches Research Center, 185 Cambridge Street, Boston 02114, USA
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Rebollo E, Karkali K, Mangione F, Martín-Blanco E. Live imaging in Drosophila: The optical and genetic toolkits. Methods 2014; 68:48-59. [PMID: 24814031 DOI: 10.1016/j.ymeth.2014.04.021] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2014] [Revised: 04/27/2014] [Accepted: 04/28/2014] [Indexed: 11/19/2022] Open
Abstract
Biological imaging based on light microscopy comes at the core of the methods that let us understanding morphology and its dynamics in synergy to the spatiotemporal distribution of cellular and molecular activities as the organism develops and becomes functional. Non-linear optical tools and superesolution methodologies are under constant development and their applications to live imaging of whole organisms keep improving as we speak. Genetically coded biosensors, multicolor clonal methods and optogenetics in different organisms and, in particular, in Drosophila follow equivalent paths. We anticipate a brilliant future for live imaging providing the roots for the holistic understanding, rather than for individual parts, of development and function at the whole-organism level.
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Affiliation(s)
- Elena Rebollo
- Instituto de Biología Molecular de Barcelona, Consejo Superior de Investigaciones Científicas, Parc Cientific de Barcelona, Baldiri Reixac 10, 08028 Barcelona, Spain
| | - Katerina Karkali
- Instituto de Biología Molecular de Barcelona, Consejo Superior de Investigaciones Científicas, Parc Cientific de Barcelona, Baldiri Reixac 10, 08028 Barcelona, Spain
| | - Federica Mangione
- Instituto de Biología Molecular de Barcelona, Consejo Superior de Investigaciones Científicas, Parc Cientific de Barcelona, Baldiri Reixac 10, 08028 Barcelona, Spain
| | - Enrique Martín-Blanco
- Instituto de Biología Molecular de Barcelona, Consejo Superior de Investigaciones Científicas, Parc Cientific de Barcelona, Baldiri Reixac 10, 08028 Barcelona, Spain.
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Mapping the local organization of cell membranes using excitation-polarization-resolved confocal fluorescence microscopy. Biophys J 2014; 105:127-36. [PMID: 23823231 DOI: 10.1016/j.bpj.2013.05.043] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Revised: 04/12/2013] [Accepted: 05/21/2013] [Indexed: 12/28/2022] Open
Abstract
Fluorescence anisotropy and linear dichroism imaging have been widely used for imaging biomolecular orientational distributions in protein aggregates, fibrillar structures of cells, and cell membranes. However, these techniques do not give access to complete orientational order information in a whole image, because their use is limited to parts of the sample where the average orientation of molecules is known a priori. Fluorescence anisotropy is also highly sensitive to depolarization mechanisms such as those induced by fluorescence energy transfer. A fully excitation-polarization-resolved fluorescence microscopy imaging that relies on the use of a tunable incident polarization and a nonpolarized detection is able to circumvent these limitations. We have developed such a technique in confocal epifluorescence microscopy, giving access to new regions of study in the complex and heterogeneous molecular organization of cell membranes. Using this technique, we demonstrate morphological changes at the subdiffraction scale in labeled COS-7 cell membranes whose cytoskeleton is perturbed. Molecular orientational order is also seen to be affected by cholesterol depletion, reflecting the strong interplay between lipid-packing regions and their nearby cytoskeleton. This noninvasive optical technique can reveal local organization in cell membranes when used as a complement to existing methods such as generalized polarization.
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Abstract
Fluorescence can be characterized by its intensity, position, wavelength, lifetime, and polarization. The more of these features are acquired in a single measurement, the more can be learned about the sample, i.e., the microenvironment of the fluorescence probe. Polarization-resolved fluorescence lifetime imaging-time-resolved fluorescence anisotropy imaging, TR-FAIM-allows mapping of viscosity or binding or of homo-FRET which can indicate dimerization or generally oligomerization.
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Affiliation(s)
- Klaus Suhling
- Department of Physics, King's College London, London, UK
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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.
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Affiliation(s)
- K Venkatesan Iyer
- Mechanobiology Institute, National University of Singapore, Singapore
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