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Centrosomes play a crucial role during immune cell interactions and initiation of the immune response. In proliferating cells, centrosome numbers are tightly controlled and generally limited to one in G1 and two prior to mitosis. Defects in regulating centrosome numbers have been associated with cell transformation and tumorigenesis. Here, we report the emergence of extra centrosomes in leukocytes during immune activation. Upon antigen encounter, dendritic cells pass through incomplete mitosis and arrest in the subsequent G1 phase leading to tetraploid cells with accumulated centrosomes. In addition, cell stimulation increases expression of polo-like kinase 2, resulting in diploid cells with two centrosomes in G1-arrested cells. During cell migration, centrosomes tightly cluster and act as functional microtubule-organizing centers allowing for increased persistent locomotion along gradients of chemotactic cues. Moreover, dendritic cells with extra centrosomes display enhanced secretion of inflammatory cytokines and optimized T cell responses. Together, these results demonstrate a previously unappreciated role of extra centrosomes for regular cell and tissue homeostasis.

The aim of this study was to analyze and compare the accuracy and quality of six 3D printing systems available on the market. Data acquisition was performed with 12 scans of human mandibles using an industrial 3D scanner and saved in STL format. These STL files were printed using six different printing systems. Previously defined distances were measured with a sliding caliper on the 72 printed mandibles. The printed models were then scanned once again. Measurements of volumes and surfaces for the STL files and the printed models were compared. Accuracy and quality were evaluated using industrial software. An analysis of the punctual aberration between the template and the printed model, based on a heat map, was also carried out. Secondary factors, such as costs, production times and expendable materials, were also examined. All printing systems performed well in terms of accuracy and quality for clinical usage. The Formiga P110 and the Form 2 showed the best results for volume, with average aberrations of 0.13 ± 0.23 cm3 and 0.12 ± 0.17 cm3, respectively. Similar results were achieved for the heat map aberration, with values of 0.008 ± 0.11 mm (Formiga P110) and 0.004 ± 0.16 mm (Form 2). Both printers showed no significant difference from the optimal neutral line (Formiga P110, p = 0.15; Form 2, p = 0.60). The cheapest models were produced by the Ultimaker 2+, with an average of 5€ per model, making such desktop printers affordable for rapid prototyping. Meanwhile, advanced printing systems with sterilizable and biocompatible printing materials, such as the Formiga P110 and the Form 2, fulfill the high expectations for maxillofacial surgery.

Spontaneous locomotion is a common feature of most metazoan cells, generally attributed to the fundamental properties of the actomyosin network. This force-producing machinery has been studied down to the most minute molecular details, especially in lamellipodium-driven migration. Nevertheless, how actomyosin networks work inside contraction-driven amoeboid cells still lacks unifying principles. Here, using stable motile blebs as a model amoeboid motile system, we image the dynamics of the actin cortex at the single filament level and reveal the co-existence of three phases of the actin network with distinct rheological properties. Physical modelling shows that these three phases organize spontaneously due to a rigidity percolation transition combined with an active advection of the percolated network. This spontaneous spatial organization of the mechanical properties of the actin network, which we propose to call advected percolation, constitutes a minimal and generic locomotion mechanism. It explains, down to the single actin filament level and up to the scale of the entire cell, how amoeboid cells can propel efficiently through complex 3D environments, a feature shared by immune and cancer cells.

A large body of work suggests that biomolecular condensates ensuing from liquid-liquid phase separation mature into various material states. How this aging process is controlled and if the naive and mature phases can have differential functions is currently unknown. Using Caenorhabditis elegans as a model, we show that MEC-2 Stomatin undergoes a rigidity phase transition during maturation from fluid to viscoelastic, glass-like condensates that facilitate either transport or mechanotransduction. This switch is promoted by the SH3 domain of UNC-89/Titin/Obscurin through a direct interaction with MEC-2 and suggests a physiological role for a percolation transition in force transmission during body wall touch. Together, our data demonstrate a novel function for rigidity maturation during mechanotransduction and a previously unidentified role for Titin homologs in neurons.

Errors in early embryogenesis are a cause of sporadic cell death and developmental failure1,2. Phagocytic activity has a central role in scavenging apoptotic cells in differentiated tissues3-6. However, how apoptotic cells are cleared in the blastula embryo in the absence of specialized immune cells remains unknown. Here we show that the surface epithelium of zebrafish and mouse embryos, which is the first tissue formed during vertebrate development, performs efficient phagocytic clearance of apoptotic cells through phosphatidylserine-mediated target recognition. Quantitative four-dimensional in vivo imaging analyses reveal a collective epithelial clearance mechanism that is based on mechanical cooperation by two types of Rac1-dependent basal epithelial protrusions. The first type of protrusion, phagocytic cups, mediates apoptotic target uptake. The second, a previously undescribed type of fast and extended actin-based protrusion that we call 'epithelial arms', promotes the rapid dispersal of apoptotic targets through Arp2/3-dependent mechanical pushing. On the basis of experimental data and modelling, we show that mechanical load-sharing enables the long-range cooperative uptake of apoptotic cells by multiple epithelial cells. This optimizes the efficiency of tissue clearance by extending the limited spatial exploration range and local uptake capacity of non-motile epithelial cells. Our findings show that epithelial tissue clearance facilitates error correction that is relevant to the developmental robustness and survival of the embryo, revealing the presence of an innate immune function in the earliest stages of embryonic development. Funding: Q.T.-R. acknowledges a grant funded by ‘The Ministerio de Ciencia, Innovación y Universidades and Fondo Social Europeo (FSE)’ (PRE2018-084393). M.I. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (ERC-StG-LS2-63759) and the Spanish Ministry of Economy and Competitiveness (BFU2014-55076-P). S.W. acknowledges support from the Government of Spain (MINECO’s Plan Nacional (PGC2018-098532-A-I00), Severo Ochoa (CEX2019- 000910-S) and Generalitat de Catalunya (CERCA, AGAUR). V.R. acknowledges support from the Spanish Ministry of Science and Innovation to the EMBL partnership, the Centro de Excelencia Severo Ochoa and MINECO’s Plan Nacional (BFU2017-86296-P)

The sensation of mechanical force underlies many of our daily activities. As the sense of touch determines the quality of life, the subconscious sense of proprioception and visceral mechanosensation is indispensible for survival. Many internal organs change shape, either as an active part of their physiology or passively due to body movements. Importantly, these shape changes need to be sensed and balanced properly to prevent organ failure and dysfunction. Consequently, a failure to properly sense volume changes of internal organs has a huge clinical relevance, manifested by a plethora of congenital and age-related diseases. Here we review novel data on mammalian stretch reception as well as classical studies from insect and nematode proprioceptors with the aim to highlight the missing link between organ-level deformation and mechanosensing on the molecular level.

Fever is an evolutionary conserved response able to stimulate and boost both innate and adaptive immunity. Temperature variations in general modify the homeostatic setpoint such as blood flow in warm blooded animals and can change gene-expression patterns on the single cell level [1] . Neutrophils and dendritic cells (DCs) patrol tissues under various temperature levels and their effective encounter and response to ‘danger signals’ is key for optimal immune defence [2] . Still, the thermo-regulation of immune cell dynamics remains largely elusive. Here we show that the local temperature controls immune cell dynamics, such as shape changes, cell migration speed and persistence in 2D/2.5D/3D biomimetic micro-environments.

SUMMARY Nucleosomes form heterogeneous groups in vivo, named clutches. Clutches are smaller and less dense in mouse embryonic stem cells (ESCs) compared to neural progenitor cells (NPCs). Using coarse-grained modeling of the pluripotency Pou5f1 gene, we show that the genome-wide clutch differences between ESCs and NPCs can be reproduced at a single gene locus. Larger clutch formation in NPCs is associated with changes in the compaction and internucleosome contact probability of the Pou5f1 fiber. Using single-molecule tracking (SMT), we further show that the core histone protein H2B is dynamic, and its local mobility relates to the structural features of the chromatin fiber. H2B is less stable and explores larger areas in ESCs compared to NPCs. The amount of linker histone H1 critically affects local H2B dynamics. Our results have important implications for how nucleosome organization and H2B dynamics contribute to regulate gene activity and cell identity., Graphical Abstract, In Brief Gómez-García et al. show that the Pou5f1 gene folds into nucleosome clutches, with larger clutches in differentiated cells than in stem cells. These clutch changes are accompanied by enhanced hierarchical looping in differentiated cells. H2B dynamics is cell-type specific, correlates with clutch patterns, and is regulated by linker histone H1.

Due to the global rise of type 2 diabetes mellitus (T2DM) in combination with insulin resistance, novel compounds to efficiently treat this pandemic disease are needed. Screening for compounds that induce the translocation of glucose transporter 4 (GLUT4) from the intracellular compartments to the plasma membrane in insulin-sensitive tissues is an innovative strategy. Here, we compared the applicability of three fluorescence microscopy-based assays optimized for the quantitation of GLUT4 translocation in simple cell systems. An objective-type scanning total internal reflection fluorescence (TIRF) microscopy approach was shown to have high sensitivity but only moderate throughput. Therefore, we implemented a prism-type TIR reader for the simultaneous analysis of large cell populations grown in adapted microtiter plates. This approach was found to be high throughput and have sufficient sensitivity for the characterization of insulin mimetic compounds in live cells. Finally, we applied confocal microscopy to giant plasma membrane vesicles (GPMVs) formed from GLUT4-expressing cells. While this assay has only limited throughput, it offers the advantage of being less sensitive to insulin mimetic compounds with high autofluorescence. In summary, the combined implementation of different fluorescence microscopy-based approaches enables the quantitation of GLUT4 translocation with high throughput and high content.

Super-resolution fluorescence microscopy has become a powerful tool in cell biology to observe sub-cellular organization and molecular details below the diffraction limit of light. Super-resolution methods are generally classified into three main concepts: stimulated emission depletion (STED), single molecule localization microscopy (SMLM) and structured illumination microscopy (SIM). Here, we highlight the novel concept of modulation-enhanced localization microscopy (meLM) which we designate as the 4th super-resolution method. Recently, a series of modulation-enhanced localization microscopy methods have emerged, namely MINFLUX, SIMPLE, SIMFLUX, ModLoc and ROSE. Although meLM combines key ideas from STED, SIM and SMLM, the main concept of meLM relies on a different idea: isolated emitters are localized by measuring their modulated fluorescence intensities in a precisely shifted structured illumination pattern. To position meLM alongside state-of-the-art super-resolution methods we first highlight the basic principles of existing techniques and show which parts of these principles are utilized by the meLM method. We then present the overall novel super-resolution principle of meLM that can theoretically reach unlimited localization precision whenever illumination patterns are translated by an arbitrarily small distance. L R acknowledges support of a fellowship from 'la Caixa' Foundation (ID 100010434, LCF/BQ/IN18/11660032) and funding from the European Union´s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 713673. V R acknowledges support from the Spanish Ministry of Economy and Competitiveness through the Program 'Centro de Excelencia Severo Ochoa 2013-2017', the CERCA Programme/Generalitat de Catalunya, MINECO's Plan Nacional (BFU2017-86296-P) and support from the CRG Advanced Light Microscopy Facility. S W acknowledges support from the Spanish Ministry of Economy and Competitiveness through the 'Severo Ochoa' program for Centres of Excellence in R&D (SEV-2015-0522), from Fundació Privada Cellex, and from Generalitat de Catalunya through the CERCA program.

The physical microenvironment regulates cell behavior during tissue development and homeostasis. How single cells decode information about their geometrical shape under mechanical stress and physical space constraints within tissues remains largely unknown. Here, using a zebrafish model, we show that the nucleus, the biggest cellular organelle, functions as an elastic deformation gauge that enables cells to measure cell shape deformations. Inner nuclear membrane unfolding upon nucleus stretching provides physical information on cellular shape changes and adaptively activates a calcium-dependent mechanotransduction pathway, controlling actomyosin contractility and migration plasticity. Our data support that the nucleus establishes a functional module for cellular proprioception that enables cells to sense shape variations for adapting cellular behavior to their microenvironment. Funding: V.V. acknowledges support from the ICFOstepstone PhD Programme funded by the European Union’s Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant agreement 665884. F.P. and Q.T.-R. acknowledge grants funded by Ministerio de Ciencia, Innovación y Universidades and Fondo Social Europeo (FSE) (BES2017-080523-SO, PRE2018-084393). M.A.V. acknowledges support from the Spanish Ministry of Science, Education and Universities through grant RTI2018-099718-B-100 and an institutional “Maria de Maeztu Programme” for Units of Excellence in R&D (CEX2018-000792-M) and FEDER funds.S.W. and M.K. acknowledge support from the Spanish Ministry of Economy and Competitiveness through the Severo Ochoa program for Centres of Excellence in R&D (CEX2019-000910-S), from Fundació Privada Cellex, Fundación Mig-Puig, and from Generalitat de Catalunya through the CERCA program and LaserLab (654148). M.K. acknowledges support through Spanish Ministry of Economy and Competitiveness (RYC-2015-17935, EQC2018-005048-P, AEI-010500-2018-228, and PGC2018-097882-A-I00),Generalitat de Catalunya (2017 SGR 1012), the ERC (715243), and the HFSPO (CDA00023/2018). S.W. acknowledges support through the Spanish Ministry of Economy and Competitiveness via MINECO’s Plan Nacional (PGC2018-098532-A-I00). V.R. acknowledges support from the Spanish Ministry of Science and Innovation to the EMBL partnership, the Centro de Excelencia Severo Ochoa, the CERCA Programme/Generalitat de Catalunya, and the MINECO’s Plan Nacional (BFU2017-86296-P)

The physical microenvironment regulates cell behavior during tissue development and homeostasis. How single cells decode information about their geometrical shape under mechanical stress and physical space constraints within their local environment remains largely unknown. Here we show that the nucleus, the biggest cellular organelle, functions as a non-dissipative cellular shape deformation gauge that enables cells to continuously measure shape variations on the time scale of seconds. Inner nuclear membrane unfolding together with the relative spatial intracellular positioning of the nucleus provides physical information on the amplitude and type of cellular shape deformation. This adaptively activates a calcium-dependent mechano-transduction pathway, controlling the level of actomyosin contractility and migration plasticity. Our data support that the nucleus establishes a functional module for cellular proprioception that enables cells to sense shape variations for adapting cellular behaviour to their microenvironment.One Sentence SummaryThe nucleus functions as an active deformation sensor that enables cells to adapt their behavior to the tissue microenvironment.

SUMMARYNeurons are among the most highly polarized cell types. They possess structurally and functionally different processes, axon and dendrites, to mediate information flow through the nervous system. Although it is well known that the microtubule cytoskeleton has a central role in establishing neuronal polarity, how its specific organization is established and maintained is little understood.Using the in vivo model system Caenorhabditis elegans, we found that the highly conserved UNC-119 protein provides a link between the membrane-associated Ankyrin (UNC-44) and the microtubule-associated CRMP (UNC-33). Together they form a periodic membrane-associated complex that anchors axonal and dendritic microtubule bundles to the cell cortex. This anchoring is critical to maintain microtubule organization by opposing kinesin-1 powered microtubule sliding. Disturbing this molecular complex alters neuronal polarity and causes strong developmental defects of the nervous system leading to severely paralyzed animals.

In vitro reconstitutions reveal the essential components of a mammalian, cytoplasmic mRNA transport system and their functions., Through the asymmetric distribution of messenger RNAs (mRNAs), cells spatially regulate gene expression to create cytoplasmic domains with specialized functions. In neurons, mRNA localization is required for essential processes such as cell polarization, migration, and synaptic plasticity underlying long-term memory formation. The essential components driving cytoplasmic mRNA transport in neurons and mammalian cells are not known. We report the first reconstitution of a mammalian mRNA transport system revealing that the tumor suppressor adenomatous polyposis coli (APC) forms stable complexes with the axonally localized β-actin and β2B-tubulin mRNAs, which are linked to a kinesin-2 via the cargo adaptor KAP3. APC activates kinesin-2, and both proteins are sufficient to drive specific transport of defined mRNA packages. Guanine-rich sequences located in 3′UTRs of axonal mRNAs increase transport efficiency and balance the access of different mRNAs to the transport system. Our findings reveal a minimal set of proteins sufficient to transport mammalian mRNAs.

Through the asymmetric distribution of mRNAs cells spatially regulate gene expression to create cyto-plasmic domains with specialized functions. In mammalian neurons, mRNA localization is required for essential processes as cell polarization, migration and synaptic plasticity underlying long-term memory formation. The essential components driving cytoplasmic mRNA transport in neurons and mammalian cells are not known. Here, we report the first reconstitution of a mammalian mRNA transport system revealing that the tumour suppressor adenomatous polyposis coli (APC) forms stable complexes with the axonally localised β-actin and β2B-tubulin mRNAs which are linked to a heterotrimeric kinesin-2 via the cargo adaptor KAP3. APC activates kinesin-2 and both proteins are sufficient to drive specific transport of defined mRNA packages. Guanine-rich sequences located in 3’UTRs of axonal mRNAs increase transport efficiency and balance the access of different mRNAs to the transport system. Our findings reveal for the first time a minimal set of proteins capable of driving kinesin-based, mammalian mRNA transport.

We present a structured illumination microscopy based point localization estimator (SIMPLE) that achieves a 2-fold increase in single molecule localization precision compared to conventional centroid estimation methods. SIMPLE advances the recently introduced MINFLUX concept by using precisely phase-shifted sinusoidal wave patterns as nanometric rulers for simultaneous particle localization based on photon count variation over a 20 μm field of view. We validate SIMPLE in silico and experimentally on a TIRF-SIM setup using a digital micro-mirror device (DMD) as a spatial light modulator. Funding: “la Caixa” Foundation (ID 100010434, LCF/BQ/IN18/11660032); Marie Skłodowska-Curie Horizon 2020 (713673, 754558, 642157); Spanish Ministry Centro de Excelencia Severo Ochoa (SEV-2015-0522); MINECO’s Plan Nacional (BFU2017-86296-P); Generalitat de Catalunya (CERCA); Fundació Privada Cellex

Most migrating cells extrude their front by the force of actin polymerization. Polymerization requires an initial nucleation step, which is mediated by factors establishing either parallel filaments in the case of filopodia or branched filaments that form the branched lamellipodial network. Branches are considered essential for regular cell motility and are initiated by the Arp2/3 complex, which in turn is activated by nucleation-promoting factors of the WASP and WAVE families(1). Here we employed rapid amoeboid crawling leukocytes and found that deletion of the WAVE complex eliminated actin branching and thus lamellipodia formation. The cells were left with parallel filaments at the leading edge, which translated, depending on the differentiation status of the cell, into a unipolar pointed cell shape or cells with multiple filopodia. Remarkably, unipolar cells migrated with increased speed and enormous directional persistence, while they were unable to turn towards chemotactic gradients. Cells with multiple filopodia retained chemotactic activity but their migration was progressively impaired with increasing geometrical complexity of the extracellular environment. These findings establish that diversified leading edge protrusions serve as explorative structures while they slow down actual locomotion.

Cell migration has important functions in immune response, development and cancer proliferation. Cell movement essentially requires the establishment of an axis of polarity. To maintain migration in one direction - called persistent cell migration - the polarity axis needs to be stabilized in the direction of movement.Biochemical feedback loops between signaling molecules have been recognized to play an important role for stabilizing cell polarity by reinforcing actin polymerization at the leading edge. Here we describe a reverse feedback mechanism coupling the retrograde flowing actin cytoskeleton in migrating cells back to cell polarity and persistent migration supporting an essential mechano-chemical coupling of signaling cascades and the flowing cytoskeletal meshwork in migrating cells (Maiuri et al., 2015). We used genetic, physical and chemical tools to modulate cytoskeletal flows in migrating dendritic cells and found a strong increase in the stability of cellular polarization and migration persistence upon increasing retrograde flow speed. We provide experimental evidence that the spatial distribution of different actin binding proteins (Myosin-GFP, Lifeact-GFP and Utrophin-GFP) with varying actin-binding strength gets significantly shifted towards the cell rear for increasing retrograde flow speeds upon sufficient coupling to the flowing actin network. Finally we show that a minimal theoretical model build on the mechano-chemical coupling between polarity markers and cytoskeletal flows can predict the stability of cell polarity in dependence on retrograde flow speeds and can capture the broad range of cell migration phenotypes from Brownian, to persistent and intermittent random walks.Maiuri, P.∗, Rupprecht, J.-F.∗, Wieser, S.∗, Ruprecht, V., Benichou, O., Carpi, N., Coppey, M., De Beco, S., Gov, N., Heisenberg, C.-P., et al. (2015). Actin Flows Mediate a Universal Coupling between Cell Speed and Cell Persistence. Cell 161, 374-386. ∗contributed equally.

Nonadherent polarized cells have been observed to have a pearlike, elongated shape. Using a minimal model that describes the cell cortex as a thin layer of contractile active gel, we show that the anisotropy of active stresses, controlled by cortical viscosity and filament ordering, can account for this morphology. The predicted shapes can be determined from the flow pattern only; they prove to be independent of the mechanism at the origin of the cortical flow, and are only weakly sensitive to the cytoplasmic rheology. In the case of actin flows resulting from a contractile instability, we propose a phase diagram of three-dimensional cell shapes that encompasses nonpolarized spherical, elongated, as well as oblate shapes, all of which have been observed in experiment.

Cationic antimicrobial peptides (CAMPs) selectively target bacterial membranes by electrostatic interactions with negatively charged lipids. It turned out that for inhibition of microbial growth a high CAMP membrane concentration is required, which can be realized by the incorporation of hydrophobic groups within the peptide. Increasing hydrophobicity, however, reduces the CAMP selectivity for bacterial over eukaryotic host membranes, thereby causing the risk of detrimental side-effects. In this study we addressed how cationic amphipathic peptides—in particular a CAMP with Lysine–Leucine–Lysine repeats (termed KLK)—affect the localization and dynamics of molecules in eukaryotic membranes. We found KLK to selectively inhibit the endocytosis of a subgroup of membrane proteins and lipids by electrostatically interacting with negatively charged sialic acid moieties. Ultrastructural characterization revealed the formation of membrane invaginations representing fission or fusion intermediates, in which the sialylated proteins and lipids were immobilized. Experiments on structurally different cationic amphipathic peptides (KLK, 6-MO-LF11-322 and NK14-2) indicated a cooperation of electrostatic and hydrophobic forces that selectively arrest sialylated membrane constituents., Research highlights ► Cationic antimicrobial peptide KLK affects eukaryotic host cells ► KLK induces accumulation of plasma mebrane proteins/lipids ► Dependent on sialic acid residues ► Application of KLK leads to a recycling inhibition of sialyted molecules

Saccharomyces cerevisiae Lpe10p is a homologue of the Mg2+-channel-forming protein Mrs2p in the inner mitochondrial membrane. Deletion of MRS2, LPE10 or both results in a petite phenotype, which exhibits a respiratory growth defect on nonfermentable carbon sources. Only coexpression of MRS2 and LPE10 leads to full complementation of the mrs2Δ/lpe10Δ double disruption, indicating that these two proteins cannot substitute for each other. Here, we show that deletion of LPE10 results in a loss of rapid Mg2+ influx into mitochondria, as has been reported for MRS2 deletion. Additionally, we found a considerable loss of the mitochondrial membrane potential (ΔΨ) in the absence of Lpe10p, which was not detected in mrs2Δ cells. Addition of the K+/H+-exchanger nigericin, which artificially increases ΔΨ, led to restoration of Mg2+ influx into mitochondria in lpe10Δ cells, but not in mrs2Δ/lpe10Δ cells. Mutational analysis of Lpe10p and domain swaps between Mrs2p and Lpe10p suggested that the maintenance of ΔΨ and that of Mg2+ influx are functionally separated. Cross-linking and Blue native PAGE experiments indicated interaction of Lpe10p with the Mrs2p-containing channel complex. Using the patch clamp technique, we showed that Lpe10p was not able to mediate high-capacity Mg2+ influx into mitochondrial inner membrane vesicles without the presence of Mrs2p. Instead, coexpression of Lpe10p and Mrs2p yielded a unique, reduced conductance in comparison to that of Mrs2p channels. In summary, the data presented show that the interplay of Lpe10p and Mrs2p is of central significance for the transport of Mg2+ into mitochondria of S. cerevisiae. Structured digital abstract • MINT-7905005: LPE10 (uniprotkb:Q02783) physically interacts (MI:0915) with MRS2 (uniprotkb:Q01926) by anti tag coimmunoprecipitation (MI:0007) • MINT-7905028: LPE10 (uniprotkb:Q02783) and LPE10 (uniprotkb:Q02783) covalently bind (MI:0195) by cross-linking study (MI:0030) • MINT-7905072: LPE10 (uniprotkb:Q02783) and MRS2 (uniprotkb:Q01926) covalently bind (MI:0195) by cross-linking study (MI:0030)

Communication between cells is crucial for proper functioning of multicellular organisms. The recently discovered membranous tubes, named tunneling nanotubes, that directly bridge neighboring cells may offer a very specific and effective way of intercellular communication. Our experiments on RT4 and T24 urothelial cell lines show that nanotubes that bridge neighboring cells can be divided into two types. The nanotubes of type I are shorter and more dynamic than those of type II, and they contain actin filaments. They are formed when cells explore their surroundings to make contact with another cell. The nanotubes of type II are longer and more stable than type I, and they have cytokeratin filaments. They are formed when two already connected cells start to move apart. On the nanotubes of both types, small vesicles were found as an integral part of the nanotubes (that is, dilatations of the nanotubes). The dilatations of type II nanotubes do not move along the nanotubes, whereas the nanotubes of type I frequently have dilatations (gondolas) that move along the nanotubes in both directions. A possible model of formation and mechanical stability of nanotubes that bridge two neighboring cells is discussed.

SummaryCell movement has essential functions in development, immunity, and cancer. Various cell migration patterns have been reported, but no general rule has emerged so far. Here, we show on the basis of experimental data in vitro and in vivo that cell persistence, which quantifies the straightness of trajectories, is robustly coupled to cell migration speed. We suggest that this universal coupling constitutes a generic law of cell migration, which originates in the advection of polarity cues by an actin cytoskeleton undergoing flows at the cellular scale. Our analysis relies on a theoretical model that we validate by measuring the persistence of cells upon modulation of actin flow speeds and upon optogenetic manipulation of the binding of an actin regulator to actin filaments. Beyond the quantitative prediction of the coupling, the model yields a generic phase diagram of cellular trajectories, which recapitulates the full range of observed migration patterns.

This thesis investigates flexible self-organizing overlay networks for multimedia delivery - networks that are dynamically built on existing infrastructure to support the preferences of applications using them. These devices connect to each other to exchange videos. However, as the interests of their owners change, the overlay must adapt as well: existing connections must be replaced with connections to other relevant devices, such as devices of other visitors with similar interests. Deciding which devices should connect to each other, while also optimizing network performance is not trivial. This thesis attempts to solve that issue by using a flexible and scalable self-organizing overlay located between an application and its underlying network, which optimizes itself based the application's interest in content and network quality. A special focus is placed on including metrics relevant to multimedia delivery, such as jitter and bottleneck bandwidth, in the optimization. As these metrics cannot be predicted by a third node, established approaches such as matchmaking cannot be used. Therefore, a new approach based on a novel interest-property concept is introduced, which provides the flexibility of traditional matchmaking approaches, but also supports optimization based on parameters that can only be determined once two potential neighbours connect. In addition, a distributed way for nodes to estimate the level of service they are likely to receive to another node is introduced. A ``Flocks'' prototype overlay that implements the concepts and techniques described in this thesis is developed and evaluated. Results show that Flocks optimize even large overlays based on content and network metrics quickly and with modest overhead., Keine Zusammenfassung vorhanden, Stefan Wieser, Abweichender Titel laut Übersetzung der Verfasserin/des Verfassers, Klagenfurt, Alpen-Adria-Univ., Diss., 2012

Cell migration is key for various biological processes and potentially leads to cancer dissemination if reactivated by tumour cells. Here we used zebrafish embryos from blastula to gastrula stages as a model system to monitor cell transformations under defined culture conditions and within the physiological tissue environment. This experimental framework allowed us to uncover a simple polarization mechanism that drives the transformation of embryonic cells into a highly efficient amoeboid migration mode irrespective of the specific progenitor cell type [1]. The observed amoeboid motility switch strongly depends on mechanical and contractile properties of the cellular cytoskeleton and was triggered by stochastic changes in cortex architecture when cells were exposed to biochemical stimuli or compressive forces from the 3D environment. Supported by theoretical modeling we show that cell transformation is induced by cortical instabilities above a critical threshold level of Myosin II mediated contractility, resulting in polarized cells with exceptionally high retrograde cortical flows and a pronounced increase in cortical actomyosin density towards the cell rear. We further show through a combination of experiments and theory that these cortical flows are essential for stabilization of cell polarity and cell shape and, in addition, provide the intracellular force required for cell locomotion in confined environments. Finally, we provide evidence for the existence of a similar amoeboid migration phenotype within the gastrulating embryo in vivo and show that amoeboid cell transformations can be induced in response to embryo wounding.[1] V. Ruprecht, S. Wieser, A. Callan-Jones, M. Smutny, H. Morita, K. Sako, V. Barone, M. Ritsch-Marte, M. Sixt, R. Voituriez, and C.-P. Heisenberg, “Cortical contractility triggers a stochastic switch to fast amoeboid cell motility”, Cell, vol. 160, no. 4, pp. 673-685, Feb. 2015.

A systematic study or sequence of preparation steps is presented for a successful quantification of the condition caused by creeping on high-temperature resistant materials. The sequence allows to expose the creep pores already in the stage of formation. To establish the preparation times required, the respective erosion rates are determined by intensive preparation tests on a series of 9-12 % Cr steels. An effort is made to examine the interaction of the microstructure with the kinetics of damage such as pore formation and growth. Therefore, a novel grain boundary etching technique (after Schalk) is presented which makes it possible to excellently image the lath structure of the former austenite grain boundaries and the carbide. This is an absolute prerequisite for the further examinations planned on the interaction between microstructure and the kinetics of damage.

International audience; In the past decade carbon nanotubes (CNTs) have been widely studied as a potential drug-delivery system, especially with functionality for cellular targeting. Yet, little is known about the actual process of docking to cell receptors and transport dynamics after internalization. Here we performed single-particle studies of folic acid (FA) mediated CNT binding to human carcinoma cells and their transport inside the cytosol. In particular, we employed molecular recognition force spectroscopy, an atomic force microscopy based method, to visualize and quantify docking of FA functionalized CNTs to FA binding receptors in terms of binding probability and binding force. We then traced individual fluorescently labeled, FA functionalized CNTs after specific uptake, and created a dynamic 'roadmap' that clearly showed trajectories of directed diffusion and areas of nanotube confinement in the cytosol. Our results demonstrate the potential of a single-molecule approach for investigation of drug-delivery vehicles and their targeting capacity.

The Peer-to-Peer Epi-Transport Protocol (PPETP) [1] is a peer-to-peer protocol designed for multimedia data distribution between end users. While its robustness and flexibility are attractive properties for multimedia cloud services, its lack of routing poses an issue if distant or specific nodes must be reached to, for example, provide service, or cloud interoperability. This paper describes an extension to the PPETP that provides fast routing based on Dynamic Linked Data Structures (DLDS) and hierarchical topology aggregation. We provide a hierarchical routing algorithm with low runtime complexity that offers PPETP several suitable paths needed to draw full benefit from its ability to send multiple reduced streams. DLDS are used to speed-up the routing of packets belonging to long-lasting streams, in periods where their paths do not change. We describe the challenges encountered implementing this solution, and evaluate its performance through simulation.

When dealing with multimedia delivery, scalability, efficiency and Quality of Service (QoS) are challenging features for today's networks. Overlay networks can compensate for the lack of control over the network routers, but for real-world applications overlay network performance is an issue. This paper presents an efficient solution for software implementation of overlay network nodes. A new, advanced Distributed Linked Data Structures (DLDS) schema has been developed to provide scalable per-flow resource reservation and fast, searchless routing/forwarding table lookup. This schema has been integrated in a new overlay network framework that features hierarchical dynamic routing and QoS estimation based on performance measures of the underlying network. The proposed technique has been implemented and tested in a large, realistic network simulation environment, and experimental results are presented.

International audience; Resolving the dynamical interplay of proteins and lipids in the live-cell plasma membrane represents a central goal in current cell biology. Superresolution concepts have introduced a means of capturing spatial heterogeneity at a nanoscopic length scale. Similar concepts for detecting dynamical transitions (superresolution chronoscopy) are still lacking. Here, we show that recently introduced spot-variation fluorescence correlation spectroscopy allows for sensing transient confinement times of membrane constituents at dramatically improved resolution. Using standard diffraction-limited optics, spot-variation fluorescence correlation spectroscopy captures signatures of single retardation events far below the transit time of the tracer through the focal spot. We provide an analytical description of special cases of transient binding of a tracer to pointlike traps, or association of a tracer with nanodomains. The influence of trap mobility and the underlying binding kinetics are quantified. Experimental approaches are suggested that allow for gaining quantitative mechanistic insights into the interaction processes of membrane constituents.

Self-organizing overlay networks have received a lot of attention in the recent years. However, despite the popularity of content-aware and topology-aware overlay networks, surprisingly little research has been done to combine both approaches. In this paper, we create robust and flexible overlay networks that we call “Flocks”, which can be content-aware, topology-aware, or a combination of both. We model affinity with interests and properties and show the resulting overlay networks work in a decentralized, self-organizing way, and stabilize quickly.

We have developed an assay for quantitative analysis of the interaction between a fluorescently marked protein (prey) and a membrane protein (bait) using microstructured surfaces covered with biotinylated ligands (antibodies) targeted against the bait. The proof-of-concept was demonstrated for the interaction between CD4, a major co-receptor in T-cell signalling, and Lck, a protein tyrosine kinase essential for early T cell signalling. Here we present improvements and a more precise characterization of the method as well as the applicability of the assay for the analysis of protein interactions within lipid rafts in the inner and outer leaflet of the plasma membrane. We stably expressed fluorescently labelled raft and non-raft proteins in the human T24 cell line as prey proteins and determined the degree of interaction with the antibody-targeted bait proteins CD59 (GPI-anchored protein, raft marker) and CD71 (Transferrin-receptor, non-raft marker), respectively. We found strong interaction of CD59 with putative raft markers including various GPI-GFP constructs, the inner-leaflet associated proteins Lck and Flottilin1 and a Pleckstrin-Homology domain fused to GFP. Importantly, we did not find interaction of CD59 with CD71-GFP and other potential non-raft proteins. When CD71 was used as the bait protein we did not find interaction with the putative raft markers. While the detected absence of CD71 from and the presence of CD59 in lipid rafts confirm current knowledge, it is still very unclear if a lipid-raft dependent coupling of proteins and certain especially negatively charged lipids across the plasma-membrane bilayer exists. Thus, our micropatterning assay will be of great interest to address this question.

Dual color single molecule tracking is a state-of-the-art fluorescence microscopy technique to study molecular associations. Featuring high spatial and temporal resolution, the method allows for catching associations with extremely high reliability. In this review, we describe robust data analysis approaches to identify and characterize molecular associations from dual color fluorescence images and show how colocalization can be statistically discriminated from accidental colocalizations. We discriminate the case of static analysis where colocalizations are revealed from individual dual color fluorescence images, and the case of dynamic analysis where colocalizations are tracked in time.

We propose here an approach for the analysis of single-molecule trajectories which is based on a comprehensive comparison of an experimental data set with multiple Monte Carlo simulations of the diffusion process. It allows quantitative data analysis, particularly whenever analytical treatment of a model is infeasible. Simulations are performed on a discrete parameter space and compared with the experimental results by a nonparametric statistical test. The method provides a matrix of p-values that assess the probability for having observed the experimental data at each setting of the model parameters. We show the testing approach for three typical situations observed in the cellular plasma membrane: i), free Brownian motion of the tracer, ii), hop diffusion of the tracer in a periodic meshwork of squares, and iii), transient binding of the tracer to slowly diffusing structures. By plotting the p-value as a function of the model parameters, one can easily identify the most consistent parameter settings but also recover mutual dependencies and ambiguities which are difficult to determine by standard fitting routines. Finally, we used the test to reanalyze previous data obtained on the diffusion of the glycosylphosphatidylinositol-protein CD59 in the plasma membrane of the human T24 cell line.

In recent years, the development of fast and highly sensitive microscopy has changed the way of thinking of cell biologists: it became more and more important to study the structural origin for cellular function, and industry turned its attention to the improvement of the required instruments. Optical microscopy has now reached a milestone in sensitivity by resolving the signal of a single, fluorescence-labeled biomolecule within a living cell. First steps towards these pioneering studies were set by methods developed in the late eighties for tracking single biomolecules labeled with fluorescent latex spheres or gold-particles. Meanwhile, a time-resolution of milliseconds for imaging weakly fluorescent cellular structures like small organelles, vesicles, or even single molecules is state-of-the-art. The advances in the fields of microscopy brought new cell biological questions into reach. The investigation of a single fluorescent molecule-or simultaneously of an ensemble of individual molecules-provides principally new information, which is generally hidden in ensemble-averaged signals of molecules. In this paper we describe strategies how to make use of single molecule trajectories for deducing information about nanoscopic structures in a live cell context. In particular, we focus our discussion on elucidating the plasma membrane organization by single molecule tracking. A diffusing membrane constituent--e.g. a protein or a lipid--experiences a manifold of interactions on its path: the most rapid interactions represent the driving force for free diffusion; stronger or correlated interactions can be frequently observed as subdiffusive behavior. Correct interpretation of the data has the potential to shine light on this enigmatic organelle, where membrane rafts, protein microdomains, fences and pickets still frolic through the text-book sketches. We summarize available analytical models and point out potential pitfalls, which may result in quantitative or three even qualitative misinterpretations.

Selective uptake of high density lipoprotein (HDL)-associated cholesteryl-esters (CE) by hepatocytes is a crucial process for the removal of cholesterol from the circulation. Together with triglycerides, CE is transported in the hydrophobic core of HDL particles; free cholesterol, phospholipids, and apolipoproteins build up the particles' amphiphilic surface monolayer. The lipid transfer process itself is highly speculative: it is still unclear how lipids are removed from the circulation and transferred from HDL - a main carrier of cholesterol in the blood stream - to cells.In this study we provide a mechanistic understanding of the cargo exchange process between HDL and biomembranes. The interaction between HDL and synthetic lipid membranes was investigated with force spectroscopy and high speed atomic force microscopy; the transfer of single cargo molecules was directly visualized using a combined and simultaneously operating fluorescence and force microscope. Experimental evidence points to the fact that i) cargo transfer requires contact; ii) only amphiphilic cargo is transferred; iii) upon contact the particle incorporates into the hydrophobic core of the bilayer where it can diffuse. In particular, we compared the transfer of the fluorescently labelled lipids DiI, and Bodipy-labelled cholesterol and cholesteryl-ester. Live cell experiments confirmed the data obtained on the synthetic systems and on GPMV's (giant plasma membrane vesicles). Particle incorporation and cargo transfer was abolished at increased membrane cholesterol levels, as a consequence of the reduced membrane elasticity. These observations reveal a mechanism for regulation of lipid uptake based on sensing plasma membrane cholesterol levels. The function of the corresponding receptor SR-B1 is primarily an anchor to hold the particle close to the plasma membrane; once in proximity, elastic properties of the membrane regulate the fusion of the particle.

There is increasing interest in a detailed understanding of the structure and dynamics of the cellular plasma membrane, primarily based on recognizing its essential role for controlling cellular signaling processes. Various pictures emerged, which ascribe the plasma membrane a high degree of organization at very short length scales of tens of nanometers. We employed single molecule fluorescence microscopy to study diffusion of CD59, a GPI-anchored protein, in the plasma membrane of living T24 cells at sub-wavelength resolution, both on the cell body and on tunneling nanotubules connecting cells. By separating longitudinal and transversal mobility, we found isotropic diffusion behavior on the surface of tunneling nanotubules, rendering direct influences of the membrane skeleton unlikely.In both studies we analyzed the mean square displacement as a function of the time-lag and the distribution of displacement steps. However, a closed analytical theory for these analysis is only available for the simplest models. To address a suspected diffusion process we reasoned that a full analytical description may not be required; it may well be sufficient to compare the experimental data with Monte Carlo simulations of the process. We demonstrated the working principle for the analysis of free diffusion, hop diffusion and transient binding of the tracer molecule to slowly moving receptors.In the recent years increasing evidence was reported for an inherent heterogeneity of cell populations. Our reasoning was that mobility probes nanometer-sized properties of the moving protein and its local environment. Automated and tailored data analysis routines allowed for the analysis of the required large data sets: ∼200.000 trajectories obtained on ∼350 cells were analyzed in total. We found up to five-fold higher variability of the diffusion constant between cells compared to the uncertainty for the determination of the diffusion constant on a single cell.