On a Model for Phase Separation on Biological Membranes and its Relation to the Ohta-Kawasaki Equation

We provide a detailed mathematical analysis of a model for phase separation on biological membranes which was recently proposed by Garcke, R\"atz, R\"oger and the second author. The model is an extended Cahn-Hilliard equation which contains additional terms to account for the active transport processes. We prove results on the existence and regularity of solutions, their long-time behaviour, and on the existence of stationary solutions. Moreover, we investigate two different asymptotic regimes. We study the case of large cytosolic diffusion and investigate the effect of an infinitely large affinity between membrane components. The first case leads to the reduction of coupled bulk-surface equations in the model to a system of surface equations with non-local contributions. Subsequently, we recover a variant of the well-known Ohta-Kawasaki equation as the limit for infinitely large affinity between membrane components.Comment: 41 page

Phase separation on biological membranes

We provide a detailed mathematical analysis of a model for lipid raft formation in cell membranes which was recently proposed by Garcke, Rätz, Röger and the author. Lipid rafts are domains of a specific molecule composition (mostly saturated lipids and cholesterols) in biological membranes. In principle, the proposed model is a phase-field model describing phase separation between saturated and unsaturated lipids. Additionally, the model is based the assumption that active transport processes of cholesterols into and out of the membrane influence the phase separation within the membrane, due to a high affinity between cholesterols and saturated lipids. As such, the model takes the form of an extended Cahn-Hilliard equation which contains additional terms to account for the cholesterol transport. We prove results on the existence and regularity of solutions, their long-time behaviour, and on the existence of stationary solutions. Moreover, we investigate three different asymptotic regimes. The first two are connected to model parameters: We study the case of large cytosolic diffusion and investigate the effect of a infinitely large affinity between cholesterols and saturated lipids. The third is a detailed analysis of the sharp-interface limit of the phase-field model. The first case leads to the reduction of coupled bulk-surface equations in the lipid raft model to a system of surface equations with non-local contributions. Subsequently, we recover the well-known Ohta-Kawasaki equations as the limit for infinitely large affinity between cholesterols and saturated lipids. We prove the convergence of solutions of the lipid raft model to weak solutions of the sharp-interface limit in the sense of varifolds. Finally, we directly prove the existence of weak solutions to the sharp-interface limit

Advanced control strategies for the continuous production of monoclonal antibodies

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Effects of different leukocyte subpopulations and flow conditions on leukocyte accumulation during reperfusion

Background/Aims: The study examined the interdependent effects of shear stress and different leukocyte subpopulations on endothelial cell activation and cell interactions during low flow and reperfusion. Methods: Human umbilical venous endothelial cells were perfused with either neutrophils or monocytes at different shear stress (2-0.25 dyn/cm 2) and adhesion was quantified by microscopy. Effects of adherent neutrophils and monocytes on endothelial cell adhesion molecule expression were analyzed by flow cytometry after 4-hour static coincubation. After coincubation, the cocultures were reperfused with labeled neutrophils at 2 dyn/cm 2 and their adhesion was quantified selectively. For the control, endothelium monocultures with and without lipopolysaccharide activation were used. Results: At 2 dyn/cm 2, adhesion did not exceed baseline levels on nonactivated endothelium. Decreasing shear stress to 0.25 dyn/cm 2 largely increased the adhesion of both leukocyte subpopulations, similar to the effect of lipopolysaccharide at 2 dyn/cm 2. However, only adherent monocytes increased adhesion molecule expression, whereas neutrophils had no effect. As a functional consequence, adherent monocytes largely increased neutrophil adhesion during reperfusion, whereas adherent neutrophils did not. Conclusion: Compromised shear stress is an autonomous trigger of leukocyte adhesion even in the absence of additional activators. Exceeding this immediate effect, adherent monocytes induce further endothelial activation and enhance further neutrophil adhesion during reperfusion. Copyrigh

Formal asymptotic limit of a diffuse-interface tumor-growth model

We consider a diffuse-interface tumor-growth model which has the form of a phase-field system. We characterize the singular limit of this problem. More precisely, we formally prove that as the coefficient of the reaction term tends to infinity, the solution converges to the solution of a novel free boundary problem. We present numerical simulations which illustrate the convergence of the diffuse-interface model to the identified sharp-interface limit

Literatur-Rundschau

Literatur-RundschauPeter-Claus Burens, Der Spenderknigge Sabine Hatscher, Kollekten, Spenden, Sponsoring (Claudia Müller)Michael Haller (Hg.), Message. Internationale Fachzeitschrift für Journalismus (Michael Schmolke)Stefan Hartwig, Trojanische Pferde der Kommunikation? (Susanne Haverkamp)Joan Hemels, Journalistlek en religie in de actuele culturbeleving (Johannes Fischer)Walter Hömberg (Hg.), Rundfunk-Kultur und Kultur-Rundfunk (Susanne Kampmann) Clemens Knobloch, Moralisierung und Sachzwang (Lars Rademacher) Anton Kolb /Reinhold Esterbauer /Hans-Walter Rucken bauer (Hg.), Cyberethik (Lars Rademacher) Markus Nolte/Ludger Verst, Vonnix kommt nix (SusanneKampmann)Mattbias Pöhlmann, Kampf der Geister (Susanne Haverkamp)Elizabeth Frommer, Kinobesuch im Lebenslauf (Susanne Kampmann)Michael Schmolke, Aufklärung und Aberwissen (Susanne Kampmann)Wolfgang Wunden (Hg.), Freiheit und Medien (Lars Rademacher

New factors for protein transport identified by a genome-wide CRISPRi screen in mammalian cells

Protein and membrane trafficking pathways are critical for cell and tissue homeostasis. Traditional genetic and biochemical approaches have shed light on basic principles underlying these processes. However, the list of factors required for secretory pathway function remains incomplete, and mechanisms involved in their adaptation poorly understood. Here, we present a powerful strategy based on a pooled genome-wide CRISPRi screen that allowed the identification of new factors involved in protein transport. Two newly identified factors, TTC17 and CCDC157, localized along the secretory pathway and were found to interact with resident proteins of ER-Golgi membranes. In addition, we uncovered that upon TTC17 knockdown, the polarized organization of Golgi cisternae was altered, creating glycosylation defects, and that CCDC157 is an important factor for the fusion of transport carriers to Golgi membranes. In conclusion, our work identified and characterized new actors in the mechanisms of protein transport and secretion, and opens stimulating perspectives for the use of our platform in physiological and pathological contexts.Includes Wellcome Trust, MRC and H202

Epitaxial Metal Halide Perovskites by Inkjet‐Printing on Various Substrates

Metal‐halide‐perovskites revolutionized the field of thin‐film semiconductor technology, due to their favorable optoelectronic properties and facile solution processing. Further improvements of perovskite thin‐film devices require structural coherence on the atomic scale. Such perfection is achieved by epitaxial growth, a method that is based on the use of high‐end deposition chambers. Here epitaxial growth is enabled via a ≈1000 times cheaper device, a single nozzle inkjet printer. By printing, single‐crystal micro‐ and nanostructure arrays and crystalline coherent thin films are obtained on selected substrates. The hetero‐epitaxial structures of methylammonium PbBr3 grown on lattice matching substrates exhibit similar luminescence as bulk single crystals, but the crystals phase transitions are shifted to lower temperatures, indicating a structural stabilization due to interfacial lattice anchoring by the substrates. Thus, the inkjet‐printing of metal‐halide perovskites provides improved material characteristics in a highly economical way, as a future cheap competitor to the high‐end semiconductor growth technologies.DFG, 404984854, Bleifreie Perovksite für die RöntgendetektionDFG, 399073171, GRK 2495: Energiekonvertierungssysteme: von Materialien zu Bauteile

Potential of Core-Collapse Supernova Neutrino Detection at JUNO

JUNO is an underground neutrino observatory under construction in Jiangmen, China. It uses 20kton liquid scintillator as target, which enables it to detect supernova burst neutrinos of a large statistics for the next galactic core-collapse supernova (CCSN) and also pre-supernova neutrinos from the nearby CCSN progenitors. All flavors of supernova burst neutrinos can be detected by JUNO via several interaction channels, including inverse beta decay, elastic scattering on electron and proton, interactions on C12 nuclei, etc. This retains the possibility for JUNO to reconstruct the energy spectra of supernova burst neutrinos of all flavors. The real time monitoring systems based on FPGA and DAQ are under development in JUNO, which allow prompt alert and trigger-less data acquisition of CCSN events. The alert performances of both monitoring systems have been thoroughly studied using simulations. Moreover, once a CCSN is tagged, the system can give fast characterizations, such as directionality and light curve