@article{1239, abstract = {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.}, author = {Callan Jones, Andrew and Ruprecht, Verena and Wieser, Stefan and Heisenberg, Carl-Philipp J and Voituriez, Raphaël}, journal = {Physical Review Letters}, number = {2}, publisher = {American Physical Society}, title = {{Cortical flow-driven shapes of nonadherent cells}}, doi = {10.1103/PhysRevLett.116.028102}, volume = {116}, year = {2016}, } @article{1275, author = {Callan Jones, Andrew and Ruprecht, Verena and Wieser, Stefan and Heisenberg, Carl-Philipp J and Voituriez, Raphaël}, journal = {Physical Review Letters}, number = {13}, publisher = {American Physical Society}, title = {{Callan-Jones et al. Reply}}, doi = {10.1103/PhysRevLett.117.139802}, volume = {117}, year = {2016}, } @article{1321, abstract = {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. 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.}, author = {Leithner, Alexander F and Eichner, Alexander and Müller, Jan and Reversat, Anne and Brown, Markus and Schwarz, Jan and Merrin, Jack and De Gorter, David and Schur, Florian and Bayerl, Jonathan and De Vries, Ingrid and Wieser, Stefan and Hauschild, Robert and Lai, Frank and Moser, Markus and Kerjaschki, Dontscho and Rottner, Klemens and Small, Victor and Stradal, Theresia and Sixt, Michael K}, journal = {Nature Cell Biology}, pages = {1253 -- 1259}, publisher = {Nature Publishing Group}, title = {{Diversified actin protrusions promote environmental exploration but are dispensable for locomotion of leukocytes}}, doi = {10.1038/ncb3426}, volume = {18}, year = {2016}, } @article{1553, abstract = {Cell 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.}, author = {Maiuri, Paolo and Rupprecht, Jean and Wieser, Stefan and Ruprecht, Verena and Bénichou, Olivier and Carpi, Nicolas and Coppey, Mathieu and De Beco, Simon and Gov, Nir and Heisenberg, Carl-Philipp J and Lage Crespo, Carolina and Lautenschlaeger, Franziska and Le Berre, Maël and Lennon Duménil, Ana and Raab, Matthew and Thiam, Hawa and Piel, Matthieu and Sixt, Michael K and Voituriez, Raphaël}, journal = {Cell}, number = {2}, pages = {374 -- 386}, publisher = {Cell Press}, title = {{Actin flows mediate a universal coupling between cell speed and cell persistence}}, doi = {10.1016/j.cell.2015.01.056}, volume = {161}, year = {2015}, } @article{1537, abstract = {3D amoeboid cell migration is central to many developmental and disease-related processes such as cancer metastasis. Here, we identify a unique prototypic amoeboid cell migration mode in early zebrafish embryos, termed stable-bleb migration. Stable-bleb cells display an invariant polarized balloon-like shape with exceptional migration speed and persistence. Progenitor cells can be reversibly transformed into stable-bleb cells irrespective of their primary fate and motile characteristics by increasing myosin II activity through biochemical or mechanical stimuli. Using a combination of theory and experiments, we show that, in stable-bleb cells, cortical contractility fluctuations trigger a stochastic switch into amoeboid motility, and a positive feedback between cortical flows and gradients in contractility maintains stable-bleb cell polarization. We further show that rearward cortical flows drive stable-bleb cell migration in various adhesive and non-adhesive environments, unraveling a highly versatile amoeboid migration phenotype.}, author = {Ruprecht, Verena and Wieser, Stefan and Callan Jones, Andrew and Smutny, Michael and Morita, Hitoshi and Sako, Keisuke and Barone, Vanessa and Ritsch Marte, Monika and Sixt, Michael K and Voituriez, Raphaël and Heisenberg, Carl-Philipp J}, journal = {Cell}, number = {4}, pages = {673 -- 685}, publisher = {Cell Press}, title = {{Cortical contractility triggers a stochastic switch to fast amoeboid cell motility}}, doi = {10.1016/j.cell.2015.01.008}, volume = {160}, year = {2015}, } @article{1925, abstract = {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.}, author = {Lamprecht, Constanze and Plochberger, Birgit and Ruprecht, Verena and Wieser, Stefan and Rankl, Christian and Heister, Elena and Unterauer, Barbara and Brameshuber, Mario and Danzberger, Jürgen and Lukanov, Petar and Flahaut, Emmanuel and Schütz, Gerhard and Hinterdorfer, Peter and Ebner, Andreas}, journal = {Nanotechnology}, number = {12}, publisher = {IOP Publishing}, title = {{A single-molecule approach to explore binding uptake and transport of cancer cell targeting nanotubes}}, doi = {10.1088/0957-4484/25/12/125704}, volume = {25}, year = {2014}, } @article{3286, abstract = {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.}, author = {Weghuber, Julian and Aichinger, Michael C. and Brameshuber, Mario and Stefan Wieser and Verena Ruprecht and Plochberger, Birgit and Madl, Josef and Horner, Andreas and Reipert, Siegfried and Lohner, Karl and Henics, Tamas and Schuetz, Gerhard J}, journal = {Biochimica et Biophysica Acta (BBA) - Biomembranes}, number = {10}, pages = {2581 -- 2590}, publisher = {Elsevier}, title = {{Cationic amphipathic peptides accumulate sialylated proteins and lipids in the plasma membrane of eukaryotic host cells}}, doi = {10.1016/j.bbamem.2011.06.007}, volume = {1808}, year = {2011}, } @article{3287, abstract = {Diffusing membrane constituents are constantly exposed to a variety of forces that influence their stochastic path. Single molecule experiments allow for resolving trajectories at extremely high spatial and temporal accuracy, thereby offering insights into en route interactions of the tracer. In this review we discuss approaches to derive information about the underlying processes, based on single molecule tracking experiments. In particular, we focus on a new versatile way to analyze single molecule diffusion in the absence of a full analytical treatment. The method is based on comprehensive comparison of an experimental data set against the hypothetical outcome of multiple experiments performed on the computer. Since Monte Carlo simulations can be easily and rapidly performed even on state-of-the-art PCs, our method provides a simple way for testing various - even complicated - diffusion models. We describe the new method in detail, and show the applicability on two specific examples: firstly, kinetic rate constants can be derived for the transient interaction of mobile membrane proteins; secondly, residence time and corral size can be extracted for confined diffusion.}, author = {Ruprecht, Verena and Axmann, Markus and Wieser, Stefan and Schuetz, Gerhard}, journal = {Current Protein & Peptide Science}, number = {8}, pages = {714 -- 724}, publisher = {Bentham Science Publishers}, title = {{What can we learn from single molecule trajectories?}}, doi = {10.2174/138920311798841753}, volume = {12}, year = {2011}, } @article{3285, abstract = {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.}, author = {Ruprecht, Verena and Wieser, Stefan and Marguet, Didier and Schuetz, Gerhard}, journal = {Biophysical Journal}, number = {11}, pages = {2839 -- 2845}, publisher = {Biophysical Society}, title = {{Spot variation fluorescence correlation spectroscopy allows for superresolution chronoscopy of confinement times in membranes}}, doi = {10.1016/j.bpj.2011.04.035}, volume = {100}, year = {2011}, }