ATLAS inner detector alignment Göttfert, T
Journal of physics. Conference series,
05/2008, Letnik:
110, Številka:
9
Journal Article
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ATLAS is one of the four experiments under preparation for the LHC accelerator at CERN in Geneva. The reconstruction of charged particle tracks will be performed by the Inner Detector, consisting of ...silicon-based and drift-tube-based detectors. To achieve the physics goals of ATLAS, the system with its almost 36000 degrees of freedom must be aligned to a precision of a few micrometers. The algorithms which are used for aligning the Inner Detector with tracks have been exercised on several challenges with simulated as well as testbeam and real data. Results from these challenges are presented, showing that track-based alignment is feasible using the implemented techniques. In order to fulfill the requirements from the computing model, it is foreseen that a dedicated alignment and calibration data stream enables the software to produce updated alignment constants 24 hours after recording the corresponding data.
This paper recalls the essential system requirements and elements for the joint TerraSAR-X / TanDEM-X mission planning system. Its commissioning approach, tests and results are described in detail.
Here we present a far-red, silicon-rhodamine-based fluorophore (SiR700) for live-cell multicolor imaging. SiR700 has excitation and emission maxima at 690 and 715 nm, respectively. SiR700-based ...probes for F-actin, microtubules, lysosomes, and SNAP-tag are fluorogenic, cell-permeable, and compatible with superresolution microscopy. In conjunction with probes based on the previously introduced carboxy-SiR650, SiR700-based probes permit multicolor live-cell superresolution microscopy in the far-red, thus significantly expanding our capacity for imaging living cells.
Neuronal communication across synapses relies on neurotransmitter release from presynaptic active zones (AZs) followed by postsynaptic transmitter detection. Synaptic plasticity homeostatically ...maintains functionality during perturbations and enables memory formation. Postsynaptic plasticity targets neurotransmitter receptors, but presynaptic mechanisms regulating the neurotransmitter release apparatus remain largely enigmatic. By studying Drosophila neuromuscular junctions (NMJs) we show that AZs consist of nano-modular release sites and identify a molecular sequence that adds modules within minutes of inducing homeostatic plasticity. This requires cognate transport machinery and specific AZ-scaffolding proteins. Structural remodeling is not required for immediate potentiation of neurotransmitter release, but necessary to sustain potentiation over longer timescales. Finally, mutations in Unc13 disrupting homeostatic plasticity at the NMJ also impair short-term memory when central neurons are targeted, suggesting that both plasticity mechanisms utilize Unc13. Together, while immediate synaptic potentiation capitalizes on available material, it triggers the coincident incorporation of modular release sites to consolidate synaptic potentiation.
In the axons of cultured hippocampal neurons, actin forms various structures, including bundles, patches (involved in the preservation of neuronal polarity), and a recently reported periodic ...ring-like structure. Nevertheless, the overlaying organization of actin in neurons and in the axon initial segment (AIS) is still unclear, due mainly to a lack of adequate imaging methods. By harnessing live-cell stimulated emission depletion (STED) nanoscopy and the fluorescent probe SiR-Actin, we show that the periodic subcortical actin structure is in fact present in both axons and dendrites. The periodic cytoskeleton organization is also found in the peripheral nervous system, specifically at the nodes of Ranvier. The actin patches in the AIS co-localize with pre-synaptic markers. Cytosolic actin organization strongly depends on the developmental stage and subcellular localization. Altogether, the results of this study reveal unique neuronal cytoskeletal features.
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•Dendrites exhibit periodic actin organization•Cytoskeletal proteins show the same periodicity at nodes of Ranvier•Cytosolic actin organization is developmentally and spatially regulated•Actin patches in the axon initial segment co-localize with synaptic markers
Harnessing STED nanoscopy, D’Este et al. reveal novel patterns of actin organization at the nanoscale in living hippocampal neurons.
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.
Bradyrhizobium diazoefficiens, a bacterial symbiont of soybean and other leguminous plants, enters a nodulation‐promoting genetic programme in the presence of host‐produced flavonoids and related ...signalling compounds. Here, we describe the crystal structure of an isoflavonoid‐responsive regulator (FrrA) from Bradyrhizobium, as well as cocrystal structures with inducing and noninducing ligands (genistein and naringenin, respectively). The structures reveal a TetR‐like fold whose DNA‐binding domain is capable of adopting a range of orientations. A single molecule of either genistein or naringenin is asymmetrically bound in a central cavity of the FrrA homodimer, mainly via C–H contacts to the π‐system of the ligands. Strikingly, however, the interaction does not provoke any conformational changes in the repressor. Both the flexible positioning of the DNA‐binding domain and the absence of structural change upon ligand binding are corroborated by small‐angle X‐ray scattering (SAXS) experiments in solution. Together with a model of the promoter‐bound state of FrrA our results suggest that inducers act as a wedge, preventing the DNA‐binding domains from moving close enough together to interact with successive positions of the major groove of the palindromic operator.
Rhizobia are bacterial symbionts of legumes attracted by substances that are released by the plant, especially (iso)flavonoids and related compounds. The toxicity of flavonoids requires active efflux systems of the bacteria. The isoflavonoid‐responsive regulator FrrA from Bradyrhizobium diazoefficiens is characterized by crystal structure analyses and SAXS in solution. The mobility of the DNA‐binding domains of the TetR‐like repressor is regulated by isoflavonoids acting as a wedge to prevent DNA binding.
Photobleaching remains a limiting factor in superresolution fluorescence microscopy. This is particularly true for stimulated emission depletion (STED) and reversible saturable/switchable optical ...fluorescence transitions (RESOLFT) microscopy, where adjacent fluorescent molecules are distinguished by sequentially turning them off (or on) using a pattern of light formed as a doughnut or a standing wave. In sample regions where the pattern intensity reaches or exceeds a certain threshold, the molecules are essentially off (or on), whereas in areas where the intensity is lower, that is, around the intensity minima, the molecules remain in the initial state. Unfortunately, the creation of on/off state differences on subdiffraction scales requires the maxima of the intensity pattern to exceed the threshold intensity by a large factor that scales with the resolution. Hence, when recording an image by scanning the pattern across the sample, each molecule in the sample is repeatedly exposed to the maxima, which exacerbates bleaching. Here, we introduce MINFIELD, a strategy for fundamentally reducing bleaching in STED/RESOLFT nanoscopy through restricting the scanning to subdiffraction-sized regions. By safeguarding the molecules from the intensity of the maxima and exposing them only to the lower intensities (around the minima) needed for the off-switching (on-switching), MINFIELD largely avoids detrimental transitions to higher molecular states. A bleaching reduction by up to 100-fold is demonstrated. Recording nanobody-labeled nuclear pore complexes in Xenopus laevis cells showed that MINFIELD-STED microscopy resolved details separated by <25 nm where conventional scanning failed to acquire sufficient signal.
The spatial organization of membrane proteins in the plasma membrane is critical for signal transduction, cell communication and membrane trafficking. Tetraspanins organize functional higher-order ...protein complexes called 'tetraspanin-enriched microdomains (TEMs)' via interactions with partner molecules and other tetraspanins. Still, the nanoscale organization of TEMs in native plasma membranes has not been resolved. Here, we elucidated the size, density and distribution of TEMs in the plasma membrane of human B cells and dendritic cells using dual color stimulated emission depletion (STED) microscopy. We demonstrate that tetraspanins form individual nanoclusters smaller than 120 nm and quantified that a single tetraspanin CD53 cluster contains less than ten CD53 molecules. CD53 and CD37 domains were adjacent to and displayed only minor overlap with clusters containing tetraspanins CD81 or CD82. Moreover, CD53 and CD81 were found in closer proximity to their partners MHC class II and CD19 than to other tetraspanins. Although these results indicate that tetraspanin domains are adjacently positioned in the plasma membrane, they challenge the current view of the tetraspanin web of multiple tetraspanin species organized into a single domain. This study increases the molecular understanding of TEMs at the nanoscale level which is essential for comprehending tetraspanin function in cell biology.
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