1
|
Houston JP, Valentino S, Bitton A. Fluorescence Lifetime Measurements and Analyses: Protocols Using Flow Cytometry and High-Throughput Microscopy. Methods Mol Biol 2024; 2779:323-351. [PMID: 38526793 DOI: 10.1007/978-1-0716-3738-8_15] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/27/2024]
Abstract
This chapter focuses on applications and protocols that involve the measurement of the fluorescence lifetime as an informative cytometric parameter. The timing of fluorescence decay has been well-studied for cell counting, sorting, and imaging. Therefore, provided herein is an overview of the techniques used, how they enhance cytometry protocols, and the modern techniques used for lifetime analysis. The background and theory behind fluorescence decay kinetic measurements in cells is first discussed followed by the history of the development of time-resolved flow cytometry. These sections are followed by a review of applications that benefit from the quantitative nature of fluorescence lifetimes as a photophysical trait. Lastly, perspectives on the modern ways in which the fluorescence lifetime is scanned at high throughputs which include high-speed microscopy and machine learning are provided.
Collapse
Affiliation(s)
- Jessica P Houston
- Department of Chemical & Materials Engineering, New Mexico State University, Las Cruces, NM, USA.
| | - Samantha Valentino
- Department of Chemical & Materials Engineering, New Mexico State University, Las Cruces, NM, USA
| | | |
Collapse
|
2
|
Abstract
Recent advances have revolutionized the oldest high-throughput single-cell analytical tool, flow cytometry. Fluorescent analyzers and sorters with up to seven lasers and the potential to detect up to 50 parameters are changing the way flow cytometry is used, but old school practices which are inadequate for new technologies remain alive. This chapter summarizes recent advances, explains the most salient new features and offers a step-by-step guide to develop and successfully execute high-dimensional fluorescent flow cytometry experiments.
Collapse
Affiliation(s)
- Shafiuddin Siddiqui
- Center for Cancer Research, Laboratory of Genome Integrity, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
| | - Ferenc Livák
- Center for Cancer Research, Laboratory of Genome Integrity, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA.
| |
Collapse
|
3
|
Bitton A, Sambrano J, Valentino S, Houston JP. A Review of New High-Throughput Methods Designed for Fluorescence Lifetime Sensing From Cells and Tissues. FRONTIERS IN PHYSICS 2021; 9:648553. [PMID: 34007839 PMCID: PMC8127321 DOI: 10.3389/fphy.2021.648553] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Though much of the interest in fluorescence in the past has been on measuring spectral qualities such as wavelength and intensity, there are two other highly useful intrinsic properties of fluorescence: lifetime (or decay) and anisotropy (or polarization). Each has its own set of unique advantages, limitations, and challenges in detection when it comes to use in biological studies. This review will focus on the property of fluorescence lifetime, providing a brief background on instrumentation and theory, and examine the recent advancements and applications of measuring lifetime in the fields of high-throughput fluorescence lifetime imaging microscopy (HT-FLIM) and time-resolved flow cytometry (TRFC). In addition, the crossover of these two methods and their outlooks will be discussed.
Collapse
|
4
|
Lifetime encoding in flow cytometry for bead-based sensing of biomolecular interaction. Sci Rep 2020; 10:19477. [PMID: 33173064 PMCID: PMC7655863 DOI: 10.1038/s41598-020-76150-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Accepted: 10/07/2020] [Indexed: 12/19/2022] Open
Abstract
To demonstrate the potential of time-resolved flow cytometry (FCM) for bioanalysis, clinical diagnostics, and optically encoded bead-based assays, we performed a proof-of-principle study to detect biomolecular interactions utilizing fluorescence lifetime (LT)-encoded micron-sized polymer beads bearing target-specific bioligands and a recently developed prototype lifetime flow cytometer (LT-FCM setup). This instrument is equipped with a single excitation light source and different fluorescence detectors, one operated in the photon-counting mode for time-resolved measurements of fluorescence decays and three detectors for conventional intensity measurements in different spectral windows. First, discrimination of bead-bound biomolecules was demonstrated in the time domain exemplarily for two targets, Streptavidin (SAv) and the tumor marker human chorionic gonadotropin (HCG). In a second step, the determination of biomolecule concentration levels was addressed representatively for the inflammation-related biomarker tumor necrosis factor (TNF-α) utilizing fluorescence intensity measurements in a second channel of the LT-FCM instrument. Our results underline the applicability of LT-FCM in the time domain for measurements of biomolecular interactions in suspension assays. In the future, the combination of spectral and LT encoding and multiplexing and the expansion of the time scale from the lower nanosecond range to the longer nanosecond and the microsecond region is expected to provide many distinguishable codes. This enables an increasing degree of multiplexing which could be attractive for high throughput screening applications.
Collapse
|
5
|
Nichani K, Li J, Suzuki M, Houston JP. Evaluation of Caspase-3 Activity During Apoptosis with Fluorescence Lifetime-Based Cytometry Measurements and Phasor Analyses. Cytometry A 2020; 97:1265-1275. [PMID: 32790129 PMCID: PMC7738394 DOI: 10.1002/cyto.a.24207] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2019] [Revised: 07/30/2020] [Accepted: 08/07/2020] [Indexed: 12/12/2022]
Abstract
Caspase-3 is a well-described protease with many roles that impact the fate of a cell. During apoptosis, caspase-3 acts as an executioner caspase with important proteolytic functions that lead to the final stages of programmed cell death. Owing to this key role, caspase-3 is exploited intracellularly as a target of control of apoptosis for therapeutic outcomes. Yet the activation of caspase-3 during apoptosis is challenged by other roles and functions (e.g., paracrine signaling). This brief report presents a way to track caspase-3 levels using a flow cytometer that measures excited state fluorescence lifetimes and a signal processing approach that leads to a graphical phasor-based interpretation. An established Förster resonance energy transfer (FRET) bioprobe was used for this test; the connected donor and acceptor fluorophore is cleavable by caspase-3 during apoptosis induction. With the cell-by-cell decay kinetic data and phasor analyses we generate a caspase activation trajectory, which is used to interpret activation throughout apoptosis. When lifetime-based cytometry is combined with a FRET bioprobe and phasor analyses, enzyme activation can be simplified and quantified with phase and modulation data. We envision extrapolating this approach to high content screening, and reinforce the power of phasor approaches with cytometric data. Analyses such as these can be used to cluster cells by their phase and modulation "lifetime fingerprint" when the intracellular fluorescent probe is utilized as a sensor of enzyme activity. © 2020 The Authors. Cytometry Part A published by Wiley Periodicals LLC on behalf of International Society for Advancement of Cytometry.
Collapse
Affiliation(s)
- Kapil Nichani
- Department of Chemical & Materials EngineeringNew Mexico State UniversityLas CrucesNew MexicoUSA
| | - Jianzhi Li
- Department of Chemical & Materials EngineeringNew Mexico State UniversityLas CrucesNew MexicoUSA
| | - Miho Suzuki
- Department of Functional Materials and ScienceGraduate School of Science and Engineering, Saitama UniversitySaitama338‐8570Japan
| | - Jessica P. Houston
- Department of Chemical & Materials EngineeringNew Mexico State UniversityLas CrucesNew MexicoUSA
- Department of Functional Materials and ScienceGraduate School of Science and Engineering, Saitama UniversitySaitama338‐8570Japan
| |
Collapse
|
6
|
Kage D, Hoffmann K, Nifontova G, Krivenkov V, Sukhanova A, Nabiev I, Resch-Genger U. Tempo-spectral multiplexing in flow cytometry with lifetime detection using QD-encoded polymer beads. Sci Rep 2020; 10:653. [PMID: 31959852 PMCID: PMC6971033 DOI: 10.1038/s41598-019-56938-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2019] [Accepted: 12/18/2019] [Indexed: 01/09/2023] Open
Abstract
Semiconductor quantum dots (QDs) embedded into polymer microbeads are known to be very attractive emitters for spectral multiplexing and colour encoding. Their luminescence lifetimes or decay kinetics have been, however, rarely exploited as encoding parameter, although they cover time ranges which are not easily accessible with other luminophores. We demonstrate here the potential of QDs made from II/VI semiconductors with luminescence lifetimes of several 10 ns to expand the lifetime range of organic encoding luminophores in multiplexing applications using time-resolved flow cytometry (LT-FCM). For this purpose, two different types of QD-loaded beads were prepared and characterized by photoluminescence measurements on the ensemble level and by single-particle confocal laser scanning microscopy. Subsequently, these lifetime-encoded microbeads were combined with dye-encoded microparticles in systematic studies to demonstrate the potential of these QDs to increase the number of lifetime codes for lifetime multiplexing and combined multiplexing in the time and colour domain (tempo-spectral multiplexing). These studies were done with a recently developed novel luminescence lifetime flow cytometer (LT-FCM setup) operating in the time-domain, that presents an alternative to reports on phase-sensitive lifetime detection in flow cytometry.
Collapse
Affiliation(s)
- Daniel Kage
- Federal Institute for Materials Research and Testing (BAM), Biophotonics Division 1.2, Richard-Willstätter-Str. 11, D-12489, Berlin, Germany.,Department of Physics, Humboldt-Universität zu Berlin, Newtonstr. 15, D-12489, Berlin, Germany
| | - Katrin Hoffmann
- Federal Institute for Materials Research and Testing (BAM), Biophotonics Division 1.2, Richard-Willstätter-Str. 11, D-12489, Berlin, Germany
| | - Galina Nifontova
- Laboratory of Nano-bioengineering, National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 115409, Moscow, Russian Federation
| | - Victor Krivenkov
- Laboratory of Nano-bioengineering, National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 115409, Moscow, Russian Federation
| | - Alyona Sukhanova
- Laboratoire de Recherche en Nanosciences, LRN-EA4682, Université de Reims Champagne-Ardenne, 51100, Reims, France
| | - Igor Nabiev
- Laboratory of Nano-bioengineering, National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 115409, Moscow, Russian Federation.,Laboratoire de Recherche en Nanosciences, LRN-EA4682, Université de Reims Champagne-Ardenne, 51100, Reims, France.,Sechenov First Moscow State Medical University, 119991, Moscow, Russian Federation
| | - Ute Resch-Genger
- Federal Institute for Materials Research and Testing (BAM), Biophotonics Division 1.2, Richard-Willstätter-Str. 11, D-12489, Berlin, Germany.
| |
Collapse
|
7
|
Kage D, Hoffmann K, Wittkamp M, Ameskamp J, Göhde W, Resch-Genger U. Luminescence lifetime encoding in time-domain flow cytometry. Sci Rep 2018; 8:16715. [PMID: 30425307 PMCID: PMC6233182 DOI: 10.1038/s41598-018-35137-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Accepted: 10/30/2018] [Indexed: 01/04/2023] Open
Abstract
Time-resolved flow cytometry represents an alternative to commonly applied spectral or intensity multiplexing in bioanalytics. At present, the vast majority of the reports on this topic focuses on phase-domain techniques and specific applications. In this report, we present a flow cytometry platform with time-resolved detection based on a compact setup and straightforward time-domain measurements utilizing lifetime-encoded beads with lifetimes in the nanosecond range. We provide general assessment of time-domain flow cytometry and discuss the concept of this platform to address achievable resolution limits, data analysis, and requirements on suitable encoding dyes. Experimental data are complemented by numerical calculations on photon count numbers and impact of noise and measurement time on the obtained lifetime values.
Collapse
Affiliation(s)
- Daniel Kage
- Federal Institute for Materials Research and Testing (BAM), Biophotonics Division 1.2, Richard-Willstätter-Str. 11, D-12489, Berlin, Germany
- Department of Physics, Humboldt-Universität zu Berlin, Newtonstr. 15, D-12489, Berlin, Germany
| | - Katrin Hoffmann
- Federal Institute for Materials Research and Testing (BAM), Biophotonics Division 1.2, Richard-Willstätter-Str. 11, D-12489, Berlin, Germany
| | - Marc Wittkamp
- Quantum Analysis GmbH, Mendelstraße 17, D-48149, Münster, Germany
| | - Jens Ameskamp
- Quantum Analysis GmbH, Mendelstraße 17, D-48149, Münster, Germany
| | - Wolfgang Göhde
- Quantum Analysis GmbH, Mendelstraße 17, D-48149, Münster, Germany
| | - Ute Resch-Genger
- Federal Institute for Materials Research and Testing (BAM), Biophotonics Division 1.2, Richard-Willstätter-Str. 11, D-12489, Berlin, Germany.
| |
Collapse
|
8
|
Houston JP, Yang Z, Sambrano J, Li W, Nichani K, Vacca G. Overview of Fluorescence Lifetime Measurements in Flow Cytometry. Methods Mol Biol 2018; 1678:421-446. [PMID: 29071689 DOI: 10.1007/978-1-4939-7346-0_18] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The focus of this chapter is time-resolved flow cytometry, which is broadly defined as the ability to measure the timing of fluorescence decay from excited fluorophores that pass through cytometers or high-throughput cell counting and cell sorting instruments. We focus on this subject for two main reasons: first, to discuss the nuances of hardware and software modifications needed for these measurements because currently, there are no widespread time-resolved cytometers nor a one-size-fits-all approach; and second, to summarize the application space for fluorescence lifetime-based cell counting/sorting owing to the recent increase in the number of investigators interested in this approach. Overall, this chapter is structured into three sections: (1) theory of fluorescence decay kinetics, (2) modern time-resolved flow cytometry systems, and (3) cell counting and sorting applications. These commentaries are followed by conclusions and discussion about new directions and opportunities for fluorescence lifetime measurements in flow cytometry.
Collapse
Affiliation(s)
- Jessica P Houston
- Department of Chemical & Materials Engineering, New Mexico State University, MSC, PO Box 30001, Las Cruces, NM, 88003, USA.
| | - Zhihua Yang
- Department of Chemical & Materials Engineering, New Mexico State University, MSC, PO Box 30001, Las Cruces, NM, 88003, USA
| | - Jesse Sambrano
- Department of Chemical & Materials Engineering, New Mexico State University, MSC, PO Box 30001, Las Cruces, NM, 88003, USA
| | - Wenyan Li
- Department of Chemical & Materials Engineering, New Mexico State University, MSC, PO Box 30001, Las Cruces, NM, 88003, USA
| | - Kapil Nichani
- Department of Chemical & Materials Engineering, New Mexico State University, MSC, PO Box 30001, Las Cruces, NM, 88003, USA
| | - Giacomo Vacca
- Kinetic River Corp., 897, Independence Avenue, Suite 4A, Mountain View, CA, 94043-2357, USA
| |
Collapse
|
9
|
Skilitsi AI, Turko T, Cianfarani D, Barre S, Uhring W, Hassiepen U, Léonard J. Towards sensitive, high-throughput, biomolecular assays based on fluorescence lifetime. Methods Appl Fluoresc 2017; 5:034002. [PMID: 28699919 DOI: 10.1088/2050-6120/aa7f66] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Time-resolved fluorescence detection for robust sensing of biomolecular interactions is developed by implementing time-correlated single photon counting in high-throughput conditions. Droplet microfluidics is used as a promising platform for the very fast handling of low-volume samples. We illustrate the potential of this very sensitive and cost-effective technology in the context of an enzymatic activity assay based on fluorescently-labeled biomolecules. Fluorescence lifetime detection by time-correlated single photon counting is shown to enable reliable discrimination between positive and negative control samples at a throughput as high as several hundred samples per second.
Collapse
Affiliation(s)
- Anastasia Ioanna Skilitsi
- Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, F-67000 Strasbourg, France
| | | | | | | | | | | | | |
Collapse
|
10
|
Cao R, Jenkins P, Peria W, Sands B, Naivar M, Brent R, Houston JP. Phasor plotting with frequency-domain flow cytometry. OPTICS EXPRESS 2016; 24:14596-607. [PMID: 27410612 PMCID: PMC5025209 DOI: 10.1364/oe.24.014596] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2016] [Revised: 05/14/2016] [Accepted: 06/04/2016] [Indexed: 05/23/2023]
Abstract
Interest in time resolved flow cytometry is growing. In this paper, we collect time-resolved flow cytometry data and use it to create polar plots showing distributions that are a function of measured fluorescence decay rates from individual fluorescently-labeled cells and fluorescent microspheres. Phasor, or polar, graphics are commonly used in fluorescence lifetime imaging microscopy (FLIM). In FLIM measurements, the plotted points on a phasor graph represent the phase-shift and demodulation of the frequency-domain fluorescence signal collected by the imaging system for each image pixel. Here, we take a flow cytometry cell counting system, introduce into it frequency-domain optoelectronics, and process the data so that each point on a phasor plot represents the phase shift and demodulation of an individual cell or particle. In order to demonstrate the value of this technique, we show that phasor graphs can be used to discriminate among populations of (i) fluorescent microspheres, which are labeled with one fluorophore type; (ii) Chinese hamster ovary (CHO) cells labeled with one and two different fluorophore types; and (iii) Saccharomyces cerevisiae cells that express combinations of fluorescent proteins with different fluorescence lifetimes. The resulting phasor plots reveal differences in the fluorescence lifetimes within each sample and provide a distribution from which we can infer the number of cells expressing unique single or dual fluorescence lifetimes. These methods should facilitate analysis time resolved flow cytometry data to reveal complex fluorescence decay kinetics.
Collapse
Affiliation(s)
- Ruofan Cao
- Department of Chemical and Materials Engineering, New Mexico State University, MSC 3805, PO BOX 30001, 1040 South Horseshoe Drive, Las Cruces, NM 88003,
USA
- The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an, Shanxi,
China
- Bioinspired Engineering and Biomechanics Center, Xi'an Jiaotong University, Xi'an, Shanxi,
China
| | - Patrick Jenkins
- Department of Chemical and Materials Engineering, New Mexico State University, MSC 3805, PO BOX 30001, 1040 South Horseshoe Drive, Las Cruces, NM 88003,
USA
| | - William Peria
- Fred Hutchinson Cancer Research Center, Seattle, WA,
USA
| | - Bryan Sands
- Fred Hutchinson Cancer Research Center, Seattle, WA,
USA
| | | | - Roger Brent
- Fred Hutchinson Cancer Research Center, Seattle, WA,
USA
| | - Jessica P. Houston
- Department of Chemical and Materials Engineering, New Mexico State University, MSC 3805, PO BOX 30001, 1040 South Horseshoe Drive, Las Cruces, NM 88003,
USA
| |
Collapse
|
11
|
Jenkins P, Naivar MA, Houston JP. Toward the measurement of multiple fluorescence lifetimes in flow cytometry: maximizing multi-harmonic content from cells and microspheres. JOURNAL OF BIOPHOTONICS 2015; 8:908-17. [PMID: 25727072 PMCID: PMC4869968 DOI: 10.1002/jbio.201400115] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Revised: 12/21/2014] [Accepted: 01/23/2015] [Indexed: 05/20/2023]
Abstract
Flow cytometry is a powerful means for in vitro cellular analyses where multi-fluorescence and multi-angle light scattering can indicate unique biochemical or morphological features of single cells. Yet, to date, flow cytometry systems have lacked the ability to capture complex fluorescence dynamics due to the transient nature of flowing cells. In this contribution we introduce a simple approach for measuring multiple fluorescence lifetimes from a single cytometric event. We leverage square wave modulation, Fourier analysis, and high frequency digitization and show the ability to resolve more than one fluorescence lifetime from fluorescently-labelled cells and microspheres. Illustration of a flow cytometer capable of capturing multiple fluorescence lifetime measurements; creating potential for multi-parametric, time-resolved signals to be captured for every color channel.
Collapse
Affiliation(s)
- Patrick Jenkins
- Department of Chemical Engineering, New Mexico State University, MSC 3805 P.O. Box 30001 Las Cruces, NM 88003-8001
| | | | - Jessica P. Houston
- Department of Chemical Engineering, New Mexico State University, MSC 3805 P.O. Box 30001 Las Cruces, NM 88003-8001
- Corresponding author: , Phone: 575-646-5563, Fax: 575-646-7706
| |
Collapse
|
12
|
Petersen KJ, Peterson KC, Muretta JM, Higgins SE, Gillispie GD, Thomas DD. Fluorescence lifetime plate reader: resolution and precision meet high-throughput. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2014; 85:113101. [PMID: 25430092 PMCID: PMC4242087 DOI: 10.1063/1.4900727] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
We describe a nanosecond time-resolved fluorescence spectrometer that acquires fluorescence decay waveforms from each well of a 384-well microplate in 3 min with signal-to-noise exceeding 400 using direct waveform recording. The instrument combines high-energy pulsed laser sources (5-10 kHz repetition rate) with a photomultiplier and high-speed digitizer (1 GHz) to record a fluorescence decay waveform after each pulse. Waveforms acquired from rhodamine or 5-((2-aminoethyl)amino) naphthalene-1-sulfonic acid dyes in a 384-well plate gave lifetime measurements 5- to 25-fold more precise than the simultaneous intensity measurements. Lifetimes as short as 0.04 ns were acquired by interleaving with an effective sample rate of 5 GHz. Lifetime measurements resolved mixtures of single-exponential dyes with better than 1% accuracy. The fluorescence lifetime plate reader enables multiple-well fluorescence lifetime measurements with an acquisition time of 0.5 s per well, suitable for high-throughput fluorescence lifetime screening applications.
Collapse
Affiliation(s)
- Karl J Petersen
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Kurt C Peterson
- Fluorescence Innovations, Inc., Minneapolis, Minnesota 55455, USA
| | - Joseph M Muretta
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Sutton E Higgins
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - Gregory D Gillispie
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - David D Thomas
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
| |
Collapse
|