| 1. |
- Ashrafzadeh, Parham, et al.
(författare)
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Methods applicable to membrane nanodomain studies?
- 2015
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Ingår i: Essays in Biochemistry. - London : Portland Press. - 0071-1365 .- 1744-1358. ; 57, s. 57-68
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Forskningsöversikt (refereegranskat)abstract
- Membrane nanodomains are dynamic liquid entities surrounded by another type of dynamic liquid. Diffusion can take place inside, around and in and out of the domains, and membrane components therefore continuously shift between domains and their surroundings. In the plasma membrane, there is the further complexity of links between membrane lipids and proteins both to the extracellular matrix and to intracellular proteins such as actin filaments. In addition, new membrane components are continuously delivered and old ones removed. On top of this, cells move. Taking all of this into account imposes great methodological challenges, and in the present chapter we discuss some methods that are currently used for membrane nanodomain studies, what information they can provide and their weaknesses.
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| 2. |
- Adler, Jeremy, et al.
(författare)
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Conventional analysis of movement on non-flat surfaces like the plasma membrane makes Brownian motion appear anomalous.
- 2019
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Ingår i: Communications biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 2
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Tidskriftsartikel (refereegranskat)abstract
- Cells are neither flat nor smooth, which has serious implications for prevailing plasma membrane models and cellular processes like cell signalling, adhesion and molecular clustering. Using probability distributions from diffusion simulations, we demonstrate that 2D and 3D Euclidean distance measurements substantially underestimate diffusion on non-flat surfaces. Intuitively, the shortest within surface distance (SWSD), the geodesic distance, should reduce this problem. The SWSD is accurate for foldable surfaces but, although it outperforms 2D and 3D Euclidean measurements, it still underestimates movement on deformed surfaces. We demonstrate that the reason behind the underestimation is that topographical features themselves can produce both super- and subdiffusion, i.e. the appearance of anomalous diffusion. Differentiating between topography-induced and genuine anomalous diffusion requires characterising the surface by simulating Brownian motion on high-resolution cell surface images and a comparison with the experimental data.
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| 3. |
- Adler, Jeremy, et al.
(författare)
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Quantifying Colocalization: the Case for Discarding the Manders Overlap Coefficient.
- 2021
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Ingår i: Cytometry. Part A : the journal of the International Society for Analytical Cytology. - : Wiley. - 1552-4930. ; 99:9, s. 910-920
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Tidskriftsartikel (refereegranskat)abstract
- Colocalization measurements aim to characterize the relative distribution of two molecules within a biologically relevant area. It is efficient to measure two distinct features, co-occurrence, the extent to which the molecules appear together, and correlation, how well variations in concentration of the two molecules match. The Manders overlap coefficient (MOC) appears in most colocalization software but the literature contains three interpretations of its measurements: a) co-occurrence, b) correlation or c) a combination of both. This is surprising given the simplicity of the underlying equation. Testing shows that the MOC responds both to changes in co-occurrence and to changes in correlation. Further testing reveals that different distributions of intensity (Gaussian, gamma, uniform, exponential) dramatically alter the balance between the contribution from co-occurrence and correlation. It follows that the MOC's ability to differentiate between different patterns of colocalization is very limited, since any value is compatible with widely differing combinations of co-occurrence, correlation and intensity distribution. To characterize colocalization we recommend reporting both co-occurrence and correlation, using coefficients specific for each attribute. Since the MOC has no clear role in the measurement of colocalization and causes considerable confusion, we conclude that it should be discarded. This article is protected by copyright. All rights reserved.
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| 4. |
- Lisowska, Halina, et al.
(författare)
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Radiation-induced DNA damage and repair in human gammadelta and alphabeta T-lymphocytes analysed by the alkaline comet assay
- 2010
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Ingår i: Genome integrity. - : Springer Science and Business Media LLC. - 2041-9414. ; 1:1, s. 8-
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Tidskriftsartikel (refereegranskat)abstract
- It has been shown by a number of authors that the radiosensitivity of peripheral blood mononuclear cells (PBMC) is higher in cancer patients compared to healthy donors, which is interpreted as a sign of genomic instability. PBMC are composed of different cell subpopulations which are differently radiosensitive and the difference between cancer patients and healthy donors could also be due to different composition of their PBMC pools. Gamma-delta T-lymphocytes play an important role in immunosurveillance and are promising cells for immunotherapy. Their abundance is frequently reduced in cancer patients so should their sensitivity to radiation be lower than that of other T-lymphocytes, this could, at least partly explain the low radiosensitivity of PBMC from healthy individuals compared to cancer patients. The present investigation was carried out to test this. Using the alkaline comet assay we analysed the level of DNA damage and repair in isolated gammadelta T-lymphocytes, pan T-lymphocytes and in total PBMC exposed in vitro to gamma radiation. We found no difference in the level of DNA damage and the capacity of DNA repair between the T cell populations. This is the first study that addresses the question of sensitivity to radiation of gamma-delta T-cells.
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| 5. |
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| 6. |
- Gesper, A., et al.
(författare)
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Variations in Plasma Membrane Topography Can Explain Heterogenous Diffusion Coefficients Obtained by Fluorescence Correlation Spectroscopy
- 2020
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Ingår i: Frontiers in Cell and Developmental Biology. - : Frontiers Media SA. - 2296-634X. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescence correlation spectroscopy (FCS) is frequently used to study diffusion in cell membranes, primarily the plasma membrane. The diffusion coefficients reported in the plasma membrane of the same cell type and even within single cells typically display a large spread. We have investigated whether this spread can be explained by variations in membrane topography throughout the cell surface, that changes the amount of membrane in the FCS focal volume at different locations. Using FCS, we found that diffusion of the membrane dye DiI in the apical plasma membrane was consistently faster above the nucleus than above the cytoplasm. Using live cell scanning ion conductance microscopy (SICM) to obtain a topography map of the cell surface, we demonstrate that cell surface roughness is unevenly distributed with the plasma membrane above the nucleus being the smoothest, suggesting that the difference in diffusion observed in FCS is related to membrane topography. FCS modeled on simulated diffusion in cell surfaces obtained by SICM was consistent with the FCS data from live cells and demonstrated that topography variations can cause the appearance of anomalous diffusion in FCS measurements. Furthermore, we found that variations in the amount of the membrane marker DiD, a proxy for the membrane, but not the transmembrane protein TCRζ or the lipid-anchored protein Lck, in the FCS focal volume were related to variations in diffusion times at different positions in the plasma membrane. This relationship was seen at different positions both at the apical cell and basal cell sides. We conclude that it is crucial to consider variations in topography in the interpretation of FCS results from membranes. © Copyright © 2020 Gesper, Wennmalm, Hagemann, Eriksson, Happel and Parmryd.
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| 7. |
- Mahammad, Saleemulla, et al.
(författare)
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Cholesterol homeostasis in T cells. Methyl-beta-cyclodextrin treatment results in equal loss of cholesterol from Triton X-100 soluble and insoluble fractions.
- 2008
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Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434 .- 0005-2736. ; 1778:5, s. 1251-8
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Tidskriftsartikel (refereegranskat)abstract
- Methyl-beta-cycloclextrin (MBCD) is frequently used to acutely deplete cells of cholesterol. A widespread assumption is that MBCD preferentially targets cholesterol in lipid rafts and that sensitivity to MBCD is proof of lipid raft involvement in a cellular process. To analyse any MBCD preference systematically, progressive cholesterol depletion of Jurkat T cells was performed using MBCD and [H-3]-cholesterol. It was found that at 37 degrees C, MBCD extracts similar proportions of cholesterol from the Triton X-100 resistant (lipid raft enriched) as it does from other cellular fractions and that the cells rapidly reestablish the relative differences in cholesterol concentration between different compartments. Moreover, cells restore the cholesterol level in the plasma membrane by mobilising cholesterol from intracellular cholesterol stores. Interestingly, mere incubation at 0 degrees C caused a loss of plasma membrane cholesterol with a concomitant increase in cholesteryl esters and adiposomes. Moreover, only 35% of total cholesterol could be extracted by MBCD at 0 degrees C and was accompanied by a complete loss of plasma membrane and endocytotic recycling centre filipin staining. This study clearly shows that MBCD does not specifically extract cholesterol from any cellular fraction, that cholesterol redistributes upon temperature changes and that intracellular cholesterol stores can be used to replenish plasma membrane cholesterol.
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