scholarly journals Analysing plasma membrane asymmetry of lipid organisation by fluorescence lifetime and correlation spectroscopy

2019 ◽  
Author(s):  
Anjali Gupta ◽  
Thomas Korte ◽  
Andreas Herrmann ◽  
Thorsten Wohland
Keyword(s):  
Plasma Membrane ◽  
Fluorescence Lifetime ◽  
Mammalian Cells ◽  
Correlation Spectroscopy ◽  
Live Cells ◽  
Fluorescence Lifetime Imaging ◽  
Outer Leaflet ◽  
Liquid Ordered ◽  
Fluorescent Lipid Analogues ◽  
Fluorescent Lipid

ABSTRACTA fundamental feature of a eukaryotic cell membrane is the asymmetric arrangement of lipids in the two leaflets. A cell invests significant energy to maintain this asymmetry and utilizes it to regulate important biological processes such as apoptosis and vesiculation. Here, we employ fluorescence lifetime imaging microscopy (FLIM) and imaging total internal reflection fluorescence correlation spectroscopy (ITIR-FCS) to differentiate the dynamics and organization of the exofacial and cytoplasmic leaflet of live mammalian cells. We characterize the biophysical properties of fluorescent analogues of phosphatidylcholine (PC), sphingomyelin (SM) and phosphatidylserine (PS) in two mammalian cell membranes. Due to their specific transverse membrane distribution, these probes allow leaflet specific investigation of the plasma membrane. We compare the results with regard to the different temporal and spatial resolution of the methods. Fluorescence lifetimes of fluorescent lipid analogues were found to be in a characteristic range for the liquid ordered phase in the outer leaflet and liquid disordered phase in the inner leaflet. The observation of a more fluid inner leaflet is supported by free diffusion in the inner leaflet with high average diffusion coefficients. The liquid ordered phase in the outer leaflet is accompanied by slower diffusion and diffusion with intermittent transient trapping. Our results show that the combination of FLIM and ITIR-FCS with specific fluorescent lipid analogues provides a powerful tool to investigate lateral and trans-bilayer characteristics of plasma membrane in live cells.Abstract Figure

scholarly journals Plasma membrane asymmetry of lipid organization: fluorescence lifetime microscopy and correlation spectroscopy analysis

2019 ◽  
Vol 61 (2) ◽  
pp. 252-266 ◽  
Author(s):  
Anjali Gupta ◽  
Thomas Korte ◽  
Andreas Herrmann ◽  
Thorsten Wohland
Keyword(s):  
Plasma Membrane ◽  
Cell Lines ◽  
Fluorescence Lifetime ◽  
Mammalian Cells ◽  
Correlation Spectroscopy ◽  
Fluorescence Lifetime Imaging ◽  
Outer Leaflet ◽  
Mammalian Cell Lines ◽  
Liquid Ordered ◽  
Fluorescent Lipid

A fundamental feature of the eukaryotic cell membrane is the asymmetric arrangement of lipids in its two leaflets. A cell invests significant energy to maintain this asymmetry and uses it to regulate important biological processes, such as apoptosis and vesiculation. The dynamic coupling of the inner or cytoplasmic and outer or exofacial leaflets is a challenging open question in membrane biology. Here, we combined fluorescence lifetime imaging microscopy (FLIM) with imaging total internal reflection fluorescence correlation spectroscopy (ITIR-FCS) to differentiate the dynamics and organization of the two leaflets of live mammalian cells. We characterized the biophysical properties of fluorescent analogs of phosphatidylcholine, sphingomyelin, and phosphatidylserine in the plasma membrane of two mammalian cell lines (CHO-K1 and RBL-2H3). Because of their specific transverse membrane distribution, these probes allowed leaflet-specific investigation of the plasma membrane. We compared the results of the two methods having different temporal and spatial resolution. Fluorescence lifetimes of fluorescent lipid analogs were in ranges characteristic for the liquid ordered phase in the outer leaflet and for the liquid disordered phase in the inner leaflet. The observation of a more fluid inner leaflet was supported by free diffusion in the inner leaflet, with high average diffusion coefficients. The liquid ordered phase in the outer leaflet was accompanied by slower diffusion and diffusion with intermittent transient trapping. Our results show that the combination of FLIM and ITIR-FCS with specific fluorescent lipid analogs is a powerful tool for investigating lateral and transbilayer characteristics of plasma membrane in live cell lines.

scholarly journals C24 sphingolipids play a surprising and central role in governing cholesterol and lateral organization of the live cell plasma membrane

2017 ◽  
Author(s):  
K. C. Courtney ◽  
W Pezeshkian ◽  
R Raghupathy ◽  
C Zhang ◽  
A Darbyson ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Mammalian Cells ◽  
Acyl Chain ◽  
Live Cells ◽  
Membrane Microdomains ◽  
Giant Unilamellar Vesicles ◽  
Unilamellar Vesicles ◽  
Outer Leaflet ◽  
Acyl Chains ◽  
Lateral Organization

AbstractMammalian cell sphingolipids, primarily with C24 and C16 acyl chains, reside in the outer leaflet of the plasma membrane. Curiously, little is known how C24 sphingolipids impact cholesterol and membrane microdomains. Here, we generated giant unilamellar vesicles and live mammalian cells with C24 or C16 sphingomyelin exclusively in the outer leaflet and compared microdomain formation. In giant unilamellar vesicles, we observed that asymmetrically placed C24 sphingomyelin suppresses microdomains. Conversely, C16 sphingomyelin facilitates microdomains. Replacing endogenous sphingolipids with C24 or C16 sphingomyelin in live HeLa cells has a similar impact on microdomains, characterized by FRET between GPI-anchored proteins: C24, but not C16, sphingomyelin suppresses submicron domains in the plasma membrane. Molecular dynamics simulations indicated that, when in the outer leaflet, the acyl chain of C24 sphingomyelin interdigitates into the opposing leaflet, thereby favouring cholesterol in the inner leaflet. We indeed found that cholesterol prefers the inner over the outer leaflet of asymmetric unilamellar vesicles (80/20) when C24 sphingomyelin is in the outer leaflet. However, when C16 sphingomyelin is in the outer leaflet, cholesterol is evenly partitioned between leaflets (50/50). Interestingly, when a mixture of C24/C16 sphingomyelin is in the outer leaflet of unilamellar vesicles, cholesterol still prefers the inner leaflet (80/20). Indeed, in human erythrocyte plasma membrane, where a mixture of C24 and C16 sphingolipids are naturally in the outer leaflet, cholesterol prefers the cytoplasmic leaflet (80/20). Therefore, C24 sphingomyelin uniquely interacts with cholesterol and governs the lateral organization in asymmetric membranes, including the plasma membrane, potentially by generating cholesterol asymmetry.Statement of SignificanceThe plasma membrane bilayer of mammalian cells has distinct phospholipids between the outer and inner leaflet, with sphingolipids exclusively in the outer leaflet. A large portion of mammalian sphingolipids have very long acyl chains (C24). Little is known how C24 sphingolipids function in the outer leaflet. Mutations in the ceramide synthase 2 gene is found to decrease C24. This severely perturbs homeostasis in mice and humans. Here, we investigated unilamellar vesicles and mammalian cells with C24 sphingomyelin exclusively in the outer leaflet. We provide evidence that outer leaflet C24 sphingomyelin suppresses microdomains in model membranes and live cells by partitioning cholesterol into the inner leaflet. We propose that C24 sphingolipids are critical to the function of the plasma membrane.

scholarly journals Cholesterol-dependent phase separation in cell-derived giant plasma-membrane vesicles

2009 ◽  
Vol 424 (2) ◽  
pp. 163-167 ◽  
Author(s):  
Ilya Levental ◽  
Fitzroy J. Byfield ◽  
Pramit Chowdhury ◽  
Feng Gai ◽  
Tobias Baumgart ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Phase Separation ◽  
Membrane Vesicles ◽  
Correlation Spectroscopy ◽  
Model Systems ◽  
Live Cells ◽  
Lipid Phase ◽  
Plasma Membrane Vesicles ◽  
Liquid Ordered ◽  
Lipid Phase Separation

Cell-derived GPMVs (giant plasma-membrane vesicles) enable investigation of lipid phase separation in a system with appropriate biological complexity under physiological conditions, and in the present study were used to investigate the cholesterol-dependence of domain formation and stability. The cholesterol level is directly related to the abundance of the liquid-ordered phase fraction, which is the majority phase in vesicles from untreated cells. Miscibility transition temperature depends on cholesterol and correlates strongly with the presence of detergent-insoluble membrane in cell lysates. Fluorescence correlation spectroscopy reveals two distinct diffusing populations in phase-separated cell membrane-derived vesicles whose diffusivities correspond well to diffusivities in both model systems and live cells. The results of the present study extend previous observations in purified lipid systems to the complex environment of the plasma membrane and provide insight into the effect of cholesterol on lipid phase separation and abundance.

scholarly journals Visualising G-quadruplex DNA dynamics in live cells by fluorescence lifetime imaging microscopy

2020 ◽  
Author(s):  
Peter Andrew Summers ◽  
Ben Lewis ◽  
Jorge Gonzalez-Garcia ◽  
Rosa Maria Porreca ◽  
Aaron H M Lim ◽  
...  
Keyword(s):  
Fluorescence Lifetime ◽  
Mammalian Cells ◽  
Live Cells ◽  
Fluorescence Lifetime Imaging Microscopy ◽  
Fluorescence Lifetime Imaging ◽  
Dna Dynamics ◽  
Drug Candidates ◽  
Lifetime Imaging ◽  
Wide Range

Guanine rich regions of oligonucleotides fold into quadruple-stranded structures called G-quadruplexes (G4). Increasing evidence suggests that these G4 structures form in vivo and play a crucial role in cellular processes. However, their direct observation in live cells remains a challenge. Here we demonstrate that a fluorescent probe (DAOTA-M2) in conjunction with Fluorescence Lifetime Imaging Microscopy (FLIM) can identify G4 within nuclei of live and fixed cells. We present a new FLIM-based cellular assay to study the interaction of non-fluorescent small molecules with G4 and apply it to a wide range of drug candidates. We also demonstrate that DAOTA-M2 can be used to study G4 stability in live cells. Reduction of FancJ and RTEL1 expression in mammalian cells increases the DAOTA-M2 lifetime and therefore suggests an increased number of G4 in these cells, implying that FancJ and RTEL1 play a role in resolving G4 structures in cellulo.

scholarly journals Visualising G-quadruplex DNA dynamics in live cells by fluorescence lifetime imaging microscopy

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Peter A. Summers ◽  
Benjamin W. Lewis ◽  
Jorge Gonzalez-Garcia ◽  
Rosa M. Porreca ◽  
Aaron H. M. Lim ◽  
...  
Keyword(s):  
Fluorescence Lifetime ◽  
Mammalian Cells ◽  
Live Cells ◽  
Fluorescence Lifetime Imaging Microscopy ◽  
Fluorescence Lifetime Imaging ◽  
Dna Dynamics ◽  
Drug Candidates ◽  
Lifetime Imaging ◽  
Wide Range

AbstractGuanine rich regions of oligonucleotides fold into quadruple-stranded structures called G-quadruplexes (G4s). Increasing evidence suggests that these G4 structures form in vivo and play a crucial role in cellular processes. However, their direct observation in live cells remains a challenge. Here we demonstrate that a fluorescent probe (DAOTA-M2) in conjunction with fluorescence lifetime imaging microscopy (FLIM) can identify G4s within nuclei of live and fixed cells. We present a FLIM-based cellular assay to study the interaction of non-fluorescent small molecules with G4s and apply it to a wide range of drug candidates. We also demonstrate that DAOTA-M2 can be used to study G4 stability in live cells. Reduction of FancJ and RTEL1 expression in mammalian cells increases the DAOTA-M2 lifetime and therefore suggests an increased number of G4s in these cells, implying that FancJ and RTEL1 play a role in resolving G4 structures in cellulo.

scholarly journals Streamlined histone-based fluorescence lifetime imaging microscopy reveals ATM regulation of chromatin compaction

2017 ◽  
Author(s):  
Alice Sherrard ◽  
Paul Bishop ◽  
Melanie Panagi ◽  
Maria Beatriz Villagomez ◽  
Dominic Alibhai ◽  
...  
Keyword(s):  
Dna Damage ◽  
Fluorescence Lifetime ◽  
Genotoxic Stress ◽  
Live Cells ◽  
Fluorescence Lifetime Imaging Microscopy ◽  
Fluorescence Lifetime Imaging ◽  
Chromatin Compaction ◽  
Lifetime Imaging ◽  
Detailed Method ◽  
Chromatin Organisation

AbstractChanges in chromatin compaction are crucial during genomic responses. Thus, methods that enable such measurements are instrumental for investigating genome function. Here, we address this challenge by developing, validating, and streamlining histone-based fluorescence lifetime imaging microscopy (FLIM) that robustly detects chromatin compaction states in fixed and live cells; in 2D and 3D. We present quality-controlled and detailed method that is simpler and faster than previous approches, and uses FLIMfit open-source software. We demonstrate the versatility of our method through its combination with immunofluorescence and its implementation in immortalised cells and primary neurons. Owing to these developments, we applied this method to elucidate the function of the DNA damage response kinase, ATM, in regulating chromatin organisation after genotoxic-stress. We unravelled a role for ATM in regulating chromatin compaction independently of DNA damage. Collectively, we present an adaptable chromatin FLIM method for examining chromatin structure in cells, and establish its broader utility.

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