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"Sommer, Christoph"
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Vehicular networking
\"With this essential guide to vehicular networking, you will learn about everything from conceptual approaches and state-of-the-art protocols, to system designs and their evaluation. Covering both in- and inter-vehicle communication, this comprehensive work outlines the foundations of vehicular networking as well as demonstrating its commercial applications, from improved vehicle performance, to entertainment, and traffic information systems. All of this is supported by in-depth case studies and detailed information on proposed protocols and solutions for access technologies and information dissemination, as well as topics on rulemaking, regulations, and standardization. Importantly, for a field which is attracting increasing commercial interest, you will learn about the future trends of this technology, its problems, and solutions to overcome them. Whether you are a student, a communications professional or a researcher, this is an invaluable resource\"-- Provided by publisher.
Book
Fluorogenic probes for live-cell imaging of the cytoskeleton
Far-red fluorogenic probes for live-cell imaging of either actin or tubulin are described and used for super-resolution microscopy of various structures in a variety of cell types.
We introduce far-red, fluorogenic probes that combine minimal cytotoxicity with excellent brightness and photostability for fluorescence imaging of actin and tubulin in living cells. Applied in stimulated emission depletion (STED) microscopy, they reveal the ninefold symmetry of the centrosome and the spatial organization of actin in the axon of cultured rat neurons with a resolution unprecedented for imaging cytoskeletal structures in living cells.
Journal Article
Cul3 regulates cytoskeleton protein homeostasis and cell migration during a critical window of brain development
De novo loss of function mutations in the ubiquitin ligase-encoding gene
Cullin3
(
CUL3)
lead to autism spectrum disorder (ASD). In mouse, constitutive
Cul3
haploinsufficiency leads to motor coordination deficits as well as ASD-relevant social and cognitive impairments. However, induction of
Cul3
haploinsufficiency later in life does not lead to ASD-relevant behaviors, pointing to an important role of
Cul3
during a critical developmental window. Here we show that
Cul3
is essential to regulate neuronal migration and, therefore, constitutive
Cul3
heterozygous mutant mice display cortical lamination abnormalities. At the molecular level, we found that Cul3 controls neuronal migration by tightly regulating the amount of Plastin3 (Pls3), a previously unrecognized player of neural migration. Furthermore, we found that Pls3 cell-autonomously regulates cell migration by regulating actin cytoskeleton organization, and its levels are inversely proportional to neural migration speed. Finally, we provide evidence that cellular phenotypes associated with autism-linked gene haploinsufficiency can be rescued by transcriptional activation of the intact allele in vitro, offering a proof of concept for a potential therapeutic approach for ASDs.
De novo loss of function mutations in the ubiquitin ligase-encoding gene
Cullin3
(
CUL3
) lead to autism spectrum disorder (ASD). Here, the authors show that Cul3 is essential to regulate neuronal migration by tightly regulating Plastin3 (Pls3). Pls3 cell-autonomously regulates cell migration by regulating the actin cytoskeleton organization.
Journal Article
In vitro reconstitution of Escherichia coli divisome activation
The actin-homologue FtsA is essential for
E. coli
cell division, as it links FtsZ filaments in the Z-ring to transmembrane proteins. FtsA is thought to initiate cell constriction by switching from an inactive polymeric to an active monomeric conformation, which recruits downstream proteins and stabilizes the Z-ring. However, direct biochemical evidence for this mechanism is missing. Here, we use reconstitution experiments and quantitative fluorescence microscopy to study divisome activation in vitro. By comparing wild-type FtsA with FtsA R286W, we find that this hyperactive mutant outperforms FtsA WT in replicating FtsZ treadmilling dynamics, FtsZ filament stabilization and recruitment of FtsN. We could attribute these differences to a faster exchange and denser packing of FtsA R286W below FtsZ filaments. Using FRET microscopy, we also find that FtsN binding promotes FtsA self-interaction. We propose that in the active divisome FtsA and FtsN exist as a dynamic copolymer that follows treadmilling filaments of FtsZ.
In E. coli, FtsA and FtsZ control the place and time of cell division. Here, the authors use in vitro experiments to show how FtsA can follow FtsZ treadmilling and that downstream proteins form dynamic copolymers with FtsA to initiate division.
Journal Article
Automated Detection and Segmentation of Synaptic Contacts in Nearly Isotropic Serial Electron Microscopy Images
We describe a protocol for fully automated detection and segmentation of asymmetric, presumed excitatory, synapses in serial electron microscopy images of the adult mammalian cerebral cortex, taken with the focused ion beam, scanning electron microscope (FIB/SEM). The procedure is based on interactive machine learning and only requires a few labeled synapses for training. The statistical learning is performed on geometrical features of 3D neighborhoods of each voxel and can fully exploit the high z-resolution of the data. On a quantitative validation dataset of 111 synapses in 409 images of 1948×1342 pixels with manual annotations by three independent experts the error rate of the algorithm was found to be comparable to that of the experts (0.92 recall at 0.89 precision). Our software offers a convenient interface for labeling the training data and the possibility to visualize and proofread the results in 3D. The source code, the test dataset and the ground truth annotation are freely available on the website http://www.ilastik.org/synapse-detection.
Journal Article
Anterior variable-angle locked plating versus tension band wiring of simple and complex patella fractures – a biomechanical investigation
Background
The aim of this study was to investigate the biomechanical performance of novel anterior variable-angle locking plates versus tension band wiring used for fixation of simple and complex patella fractures.
Methods
Sixteen pairs of human cadaveric knees were used to simulate two-part simple transverse AO/OTA 34-C1 and five-part complex AO/OTA 34-C3 patella fractures. The complex fracture pattern was characterized with a medial and a lateral proximal fragment, together with an inferomedial, an inferolateral and an inferior fragment mimicking comminution around the distal patella pole. Eight pairs with simple fractures were split for fixation via either tension band wiring (TBW) through two parallel cannulated screws or anterior variable-angle locked plating, whereas other eight pairs with complex fractures were split for either TBW through two parallel cannulated screws plus circumferential cerclage wiring, or anterior variable-angle locked plating using a cortical caudo-cranial polar screw. Each specimen was tested over 5000 cycles with a range of motion from 90° flexion to full extension by pulling on the quadriceps tendon. Interfragmentary movements were captured by motion tracking.
Results
For both fracture types, the longitudinal and shear articular displacements, measured between the proximal and distal fragments at the central patella aspect between 1000 and 5000 cycles, together with the relative rotations of these fragments around the mediolateral axis were all significantly smaller following anterior variable-angle locked plating versus TBW, p ≤ 0.01.
Conclusions
From a biomechanical perspective, anterior locked plating of both simple and complex patella fractures resulted in less interfragmentary displacement under extended cyclic loading.
Journal Article
Dense 4D nanoscale reconstruction of living brain tissue
Three-dimensional (3D) reconstruction of living brain tissue down to an individual synapse level would create opportunities for decoding the dynamics and structure–function relationships of the brain’s complex and dense information processing network; however, this has been hindered by insufficient 3D resolution, inadequate signal-to-noise ratio and prohibitive light burden in optical imaging, whereas electron microscopy is inherently static. Here we solved these challenges by developing an integrated optical/machine-learning technology, LIONESS (live information-optimized nanoscopy enabling saturated segmentation). This leverages optical modifications to stimulated emission depletion microscopy in comprehensively, extracellularly labeled tissue and previous information on sample structure via machine learning to simultaneously achieve isotropic super-resolution, high signal-to-noise ratio and compatibility with living tissue. This allows dense deep-learning-based instance segmentation and 3D reconstruction at a synapse level, incorporating molecular, activity and morphodynamic information. LIONESS opens up avenues for studying the dynamic functional (nano-)architecture of living brain tissue.
A combination of gentle stimulated emission depletion microscopy imaging and deep-learning-based improvements in signal-to-noise ratio enables high-resolution reconstruction of neuronal architecture in living tissue.
Journal Article
Bioselectivity of silk protein-based materials and their bio-inspired applications
Adhesion to material surfaces is crucial for almost all organisms regarding subsequent biological responses. Mammalian cell attachment to a surrounding biological matrix is essential for maintaining their survival and function concerning tissue formation. Conversely, the adhesion and presence of microbes interferes with important multicellular processes of tissue development. Therefore, tailoring bioselective, biologically active, and multifunctional materials for biomedical applications is a modern focus of biomaterial research. Engineering biomaterials that stimulate and interact with cell receptors to support binding and subsequent physiological responses of multicellular systems attracted much interest in the last years. Further to this, the increasing threat of multidrug resistance of pathogens against antibiotics to human health urgently requires new material concepts for preventing microbial infestation and biofilm formation. Thus, materials exhibiting microbial repellence or antimicrobial behaviour to reduce inflammation, while selectively enhancing regeneration in host tissues are of utmost interest. In this context, protein-based materials are interesting candidates due to their natural origin, biological activity, and structural properties. Silk materials, in particular those made of spider silk proteins and their recombinant counterparts, are characterized by extraordinary properties including excellent biocompatibility, slow biodegradation, low immunogenicity, and non-toxicity, making them ideally suited for tissue engineering and biomedical applications. Furthermore, recombinant production technologies allow for application-specific modification to develop adjustable, bioactive materials. The present review focusses on biological processes and surface interactions involved in the bioselective adhesion of mammalian cells and repellence of microbes on protein-based material surfaces. In addition, it highlights the importance of materials made of recombinant spider silk proteins, focussing on the progress regarding bioselectivity.
Journal Article
Seeing like a tourist city: how administrative constructions of conflictive urban tourism shape its future
PurposeThe purpose of this paper is to clarify the administrative problematisations of conflict-prone urban tourism (e.g. noise) as political processes predetermining the future of city tourism. It is shaped by today’s administrative ways of knowing increasing visitor pressure as an issue for urban (tourism) development.Design/methodology/approachThe problematisation of conflictive urban tourism in Berlin is used as case study and lens to analyse how administrative bodies see conflictive tourism like a tourist city. Drawing on Mariana Valverde’s idea of Seeing Like a City (2011), the paper demonstrates how disparate governmental bodies see and reduce the complexity of conflicts resulting from tourism in order to handle it. The authors use policy documents as the basis for the analysis.FindingsThe paper provides empirical insights about how political knowledge on urban tourism conflicts is produced in Berlin. The marginalisation of these conflicts on the federal state level seemingly aces out the calls for action on the borough level (Friedrichshain-Kreuzberg). According to these disparate modes of problematisation, older and younger governmental gazes on conflictive tourism and its future relevance interrelate in contingent combination.Originality/valueThis paper fills a gap in the existing urban tourism literature, by focussing on the definition of policy problems by governmental bodies as powerfully linked to the availability of solutions.
Journal Article