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  • Coupling of vinculin to F-actin requires Syndecan-4 proteoglycan

    Heparan Sulfate Proteoglycans act as a cell surface co-receptors for many proteins in which a signal is sent downstream via its cytosolic domain. The role of syndecan-4 proteoglycans in FA assembly was studied in endothelial cells, and single molecule localization super-resolution microscopy showed that Syn4 loss altered the cytoskeleton protein network assembly. Using molecular and cell biology approaches we were able to demonstrate that syndecan-4 plays a pivotal role in endothelial cell behavior. Super-resolution microscopy revealed that syndecan-4 knockdown alters the level and arrangement of essential proteins for focal adhesion, including actin network and a selective decoupling of vinculin from actin, leading to lamellipodia assembly and filopodia protrusions (Figure 1). Furthermore, using Coherent Anti-stokes Raman Scattering (CARS) microscopy, the structure of the tumors formed by such cells in mice was revealed showing its network of vascularization (Figure 2). We propose a model in which syndecan-4 acts as a central mediator: serving as a cell-signaling center in which ECM (fibronectin), cell surface (integrins) and intracellular components (actin and vinculin) come together.
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  • Actin-Dependent Vacuolar Occupancy of the Cell Determines Auxin-Induced Growth Repression

    The cytoskeleton is an early attribute of cellular life, and its main components are composed of conserved proteins. The actin cytoskeleton has a direct impact on the control of cell size in animal cells, but its mechanistic contribution to cellular growth in plants remains largely elusive. Here, we reveal a role of actin in regulating cell size in plants. The actin cytoskeleton shows proximity to vacuoles, and the phytohormone auxin not only controls the organization of actin filaments but also impacts vacuolar morphogenesis in an actin-dependent manner.
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  • Initiation of Lamellipodia and Ruffles Involves Cooperation Between mDia1 and the Arp2/3 Complex

    Protrusion of lamellipodia and ruffles requires polymerization of branched actin filaments by the Arp2/3 complex. Although regulation of Arp2/3 complex activity has been extensively investigated, the mechanism of initiation of lamellipodia and ruffles remains poorly understood. Here, we show that mDia1 acts in concert with the Arp2/3 complex to promote initiation of lamellipodia and ruffles.
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  • The Actin Cytoskeleton Modulates the Activation of iNKT Cells by Segregating CD1d Nanoclusters on Antigen-Presenting Cells

    The ability of invariant natural killer T (iNKT) cells to recognize endogenous antigens represents a distinct immune recognition strategy, which underscores the constitutive memory phenotype of iNKT cells and their activation during inflammatory conditions. By using superresolution microscopy, we show that CD1d molecules form nanoclusters at the cell surface of APCs, and their size and density are constrained by the actin cytoskeleton.
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  • Lytic Immune Synapse Function Requires Filamentous Actin Deconstruction by Coronin 1A

    Natural killer (NK) cells are cytolytic effector cells of the innate immune system. Here, we show that deconstruction of synaptic cortical filamentous (F)-actin by Coronin 1A (Coro1A) is required for NK cell cytotoxicity through the remodeling of F-actin to enable lytic granule secretion. We define this requirement for remodeling using superresolution nanoscopy and Coro1A-deficient NK cells. In addition, we use NK cells from a patient with a rare Coro1A mutation, thus illustrating a critical link between Coro1A function and human health.
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  • Cortical Actin Networks Induce Spatio-temporal Confinement of Phospholipids in the Plasma Membrane – A Minimally Invasive Investigation by STED-FCS

    Important discoveries in the last decades have changed our view of the plasma membrane organisation. Specifically, the cortical cytoskeleton has emerged as a key modulator of the lateral diffusion of membrane proteins. Cytoskeleton-dependent compartmentalised lipid diffusion has been proposed, but this concept remains controversial because this phenomenon has thus far only been observed with artefact-prone probes in combination with a single technique: single particle tracking.
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  • A Lipid Bound Actin Meshwork Organizes Liquid Phase Separation in Model Membranes

    The eukaryotic cell membrane is connected to a dense actin rich cortex. We present FCS and STED experiments showing that dense membrane bound actin networks have severe influence on lipid phase separation. Our results reveal a mechanism how cells may prevent macroscopic demixing of their membrane components, while at the same time regulate the local membrane composition.
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  • ICln: A New Regulator of Non-Erythroid 4.1R Localisation and Function

    To optimise the efficiency of cell machinery, cells can use the same protein (often called a hub protein) to participate in different cell functions by simply changing its target molecules. There are large data sets describing protein-protein interactions ("interactome") but they frequently fail to consider the functional significance of the interactions themselves.
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  • Abstracts of the 4th European Super-Resolution User-Club Meeting

    The 4th Super-Resolution User Club Meeting was held in collaboration with Christian Eggeling and the Weatherall Institute of Molecular Medicine in Oxford, UK. Here we present the abstracts of the talks and interviews with participants.
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  • Visualization of the Natural Killer Cell Immune Synapse by Super-Resolution Nanoscopy

    Natural killer (NK) cells are innate immune effectors that recognize and kill virally infected and tumorigenic cells. Central to their effector function is the formation of an immunological synapse with a target cell followed by directed secretion of cytolytic granules.
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  • Dual Channel STED Nanoscopy of Lytic Granules on Actin Filaments in Natural Killer Cells

    Natural killer (NK) cells are innate immune effectors that eliminate diseased and tumorigenic targets through the directed secretion of specialized secretory lysosomes, termed lytic granules. This directed secretion is triggered following the formation of an immunological synapse (IS), which is characterized by actin re-modeling and receptor organization at the interface between the NK cell and its susceptible target.
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  • Natural Killer Cell Lytic Granule Secretion Occurs through a Pervasive Actin Network at the Immune Synapse

    Accumulation of filamentous actin (F-actin) at the immunological synapse (IS) is a prerequisite for the cytotoxic function of natural killer (NK) cells. Subsequent to reorganization of the actin network, lytic granules polarize to the IS where their contents are secreted directly toward a target cell, providing critical access to host defense.
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  • STED Nanoscopy of Actin Dynamics in Synapses deep inside Living Brain Slices

    It is difficult to investigate the mechanisms that mediate long-term changes in synapse function because synapses are small and deeply embedded inside brain tissue. Although recent fluorescence nanoscopy techniques afford improved resolution, they have so far been restricted to dissociated cells or tissue surfaces. However, to study synapses under realistic conditions, one must image several cell layers deep inside more-intact, three-dimensional preparations that exhibit strong light scattering, such as brain slices or brains in vivo.
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