Most plasmalemmal proteins organize in submicrometer-sized clusters whose architecture and dynamics are still enigmatic. With syntaxin 1 as an example, we applied a combination of far-field optical ...nanoscopy, biochemistry, fluorescence recovery after photobleaching (FRAP) analysis, and simulations to show that clustering can be explained by self-organization based on simple physical principles. On average, the syntaxin clusters exhibit a diameter of 50 to 60 nanometers and contain 75 densely crowded syntaxins that dynamically exchange with freely diffusing molecules. Self-association depends on weak homophilic protein-protein interactions. Simulations suggest that clustering immobilizes and conformationally constrains the molecules. Moreover, a balance between self-association and crowding-induced steric repulsions is sufficient to explain both the size and dynamics of syntaxin clusters and likely of many oligomerizing membrane proteins that form supramolecular structures.
Chondrules in chondritic meteorites are unique witnesses of nebular and asteroidal processes that preceded large-scale planetary accretion. Together with refractory calcium-aluminium-rich inclusions ...(CAIs), they are the sources of our knowledge of the initial evolution of the early Solar System. We have investigated a single very large (>10 mm in longer dimension) chondrule, hereafter, the mega-chondrule A25-2, extracted from the Allende CV3 chondrite. We characterised texture, mineralogy and mineral chemistry of this chondrule, and studied its Al-Mg, U-Pb and U-isotope systematics. We also studied the distribution of U, Th and Pb, and measured Pb isotopic composition in individual minerals of A25-2 by secondary ion mass-spectrometry (SIMS). The main difficulty in absolute age determination was the presence of pervasive and resilient non-radiogenic Pb. In the search for the best way to separate radiogenic Pb from non-radiogenic Pb components of terrestrial and asteroidal origins, we used various protocols of multi-step leaching and assessed their efficiency in generating data suitable for the construction of an isochron. Testing the data filtering procedure led us to explore the behaviour of the stepwise leaching method in the presence of pervasive and resilient non-radiogenic Pb. The model age patterns observed in the final HF partial dissolution steps were probably induced by isotopic fractionation. Although step leaching did not yield fractions with highly radiogenic Pb, a Pb-Pb isochron age, corrected for measured 238U/235U was obtained by: (1) data filtering process based on strict analytical and geochemical criteria to include in the Pb-Pb isochron only leaching steps free from terrestrial contamination and (2) arithmetically recombined analyses to cancel the effects of leaching-induced isotopic fractionation.
This extensive data processing yielded the age of 4568.5 ± 3.0 Ma, which we consider reliable within its uncertainty limits, although it is not as precise as, and more model dependent than, the age that could have been obtained if Pb isotopic compositions were more radiogenic. The 238U/235U ratio of the mega-chondrule is 137.764 ± 0.016, which is similar to the ratios obtained from single chondrules yet slightly different from small pooled Allende chondrules. The initial 27Al/26Al ratio inferred from internal isochron obtained from SIMS Al-Mg isotope measurements is (5.4 ± 6.5) × 10–6, which corresponds to 4565.0 + 0.8/−∞ Ma, assuming homogeneous distribution of 26Al throughout the protoplanetary disk at the canonical level (∼5.2 × 10−5). This age is 3.5 ± 3.1 Ma younger than the Pb-isotopic age. Calculation of 26Al-26Mg age assuming initial (27Al/26Al)0 of (1.36 ± 0.72) × 10–5 in the CV chondrule-forming region yields the age of 4566.4 + 0.8/−∞, which is consistent with the Pb-isotopic age.
Summary
Multicolour fluorescence imaging by STimulated Emission Depletion (STED) superresolution microscopy with doughnut‐shaped STED laser beams based on different wavelengths for each colour ...channel requires precise image registration. This is especially important when STED imaging is used for co‐localisation studies of two or more native proteins in biological specimens to analyse nanometric subcellular spatial arrangements. We developed a robust postprocessing image registration protocol, with the aim to verify and ultimately optimise multicolour STED image quality. Importantly, this protocol will support any subsequent quantitative localisation analysis at nanometric scales. Henceforth, using an approach that registers each colour channel present during STED imaging individually, this protocol reliably corrects for optical aberrations and inadvertent sample drift. To achieve the latter goal, the protocol combines the experimental sample information, from corresponding STED and confocal images using the same optical beam path and setup, with that of an independent calibration sample. As a result, image registration is based on a strategy that maximises the cross‐correlation between sequentially acquired images of the experimental sample, which are strategically combined by the protocol. We demonstrate the general applicability of the image registration protocol by co‐staining of the ryanodine receptor calcium release channel in primary mouse cardiomyocytes. To validate this new approach, we identify user‐friendly criteria, which – if fulfilled – support optimal image registration. In summary, we introduce a new method for image registration and rationally based postprocessing steps through a highly standardised protocol for multicolour STED imaging, which directly supports the reproducibility of protein co‐localisation analyses. Although the reference protocol is discussed exemplarily for two‐colour STED imaging, it can be readily expanded to three or more colours and STED channels.
Lay description
Multicolour imaging with fluorescent dyes was recently realized below the diffraction limit based on superresolution light microscopy. The first described method, STimulated Emission Depletion (STED), represents a targeted spatial approach for superresolution microscopy using doughnut‐shaped STED laser beams. For multicolour STED imaging, each colour channel requires precise image registration. This is particularly important when STED imaging is used for co‐localisation analysis of two or more proteins in biological specimens, ultimately to characterize subcellular spatial properties, for example between different fluorescently labelled proteins. Here, we present a robust postprocessing protocol for image registration aiming to verify and optimize multicolour STED image quality. Importantly, this protocol supports any subsequent quantitative analysis at nanometric scales. We demonstrate the general applicability and validity of the image registration protocol by costaining of the ryanodine receptor calcium release channel in mouse cardiomyocytes. In summary, a new method for image registration based on a highly standardized protocol for multicolour STED imaging was developed.
The most profound consequences of the presence of Ca–Mg carbonates
(CaCO3–MgCO3) in the Earth's upper mantle may be to lower the
melting temperatures of the mantle and control the melt composition.
...Low-degree partial melting of a carbonate-bearing mantle produces
CO2-rich, silica-poor melts compositionally imposed by the
melting relations of carbonates. Thus, understanding the melting relations
in the CaCO3–MgCO3 system facilitates the interpretation of
natural carbonate-bearing silicate systems. We report the melting relations of the CaCO3–MgCO3 system and
the partition coefficient of trace elements between carbonates and carbonate
melt from experiments at high pressure (6 and 9 GPa) and temperature
(1300–1800 ∘C) using a rocking multi-anvil press. In the
absence of water, Ca–Mg carbonates are stable along geothermal
gradients typical of subducting slabs. Ca–Mg carbonates
(∼ Mg0.1–0.9Ca0.9–0.1CO3) partially melt
beneath mid-ocean ridges and in plume settings. Ca–Mg carbonates
melt incongruently, forming periclase crystals and carbonate melt between 4
and 9 GPa. Furthermore, we show that the rare earth element (REE) signature
of Group-I kimberlites, namely strong REE fractionation and depletion of
heavy REE relative to the primitive mantle, is resembled by carbonate
melt in equilibrium with Ca-bearing magnesite and periclase at 6 and
9 GPa. This suggests that the dolomite–magnesite join of the
CaCO3–MgCO3 system might be useful to approximate the REE
signature of carbonate-rich melts parental to kimberlites.
Sublingual immunotherapy has been shown in some clinical studies to modulate allergen‐specific antibody responses with a decrease in the immunoglobulin E/immunoglobulin G4 (IgE/IgG4) ratio and to ...reduce the recruitment and activation of proinflammatory cells in target mucosa. Whereas a central paradigm for successful immunotherapy has been to reorient the pattern of allergen‐specific T‐cell responses in atopic patients from a T helper (Th)2 to Th1 profile, there is currently a growing interest in eliciting regulatory T cells, capable of downregulating both Th1 and Th2 responses through the production of interleukin (IL)‐10 and/or transforming growth factor (TGF)‐β. We discuss herein immune mechanisms involved during allergen‐specific sublingual immunotherapy (SLIT), in comparison with subcutaneous immunotherapy. During SLIT, the allergen is captured within the oral mucosa by Langerhans‐like dendritic cells expressing high‐affinity IgE receptors, producing IL‐10 and TGF‐β, and upregulating indoleamine dioxygenase (IDO), suggesting that such cells are prone to induce tolerance. The oral mucosa contains limited number of proinflammatory cells, such as mast cells, thereby explaining the well‐established safety profile of SLIT. In this context, second‐generation vaccines based on recombinant allergens in a native conformation formulated with adjuvants are designed to target Langerhans‐like cells in the sublingual mucosa, with the aim to induce allergen‐specific regulatory T cells. Importantly, such recombinant vaccines should facilitate the identification of biological markers of SLIT efficacy in humans.
Control-based continuation (CBC) is a general and systematic method to probe the dynamics of nonlinear experiments. In this paper, CBC is combined with a novel continuation algorithm that is robust ...to experimental noise and enables the tracking of geometric features of the response surface such as folds. The method uses Gaussian process regression to create a local model of the response surface on which standard numerical continuation algorithms can be applied. The local model evolves as continuation explores the experimental parameter space, exploiting previously captured data to actively select the next data points to collect such that they maximise the potential information gain about the feature of interest. The method is demonstrated experimentally on a nonlinear structure featuring harmonically coupled modes. Fold points present in the response surface of the system are followed and reveal the presence of an isola, i.e. a branch of periodic responses detached from the main resonance peak.
A ground-based synthetic aperture radar (GB-SAR) interferometer is used to retrieve the velocity field of a landslide. High-resolution images are obtained by means of a time domain SAR processor. An ...in-depth analysis of the sequence of SAR interferograms enables the recognition of a slowly deforming upper scarp in the scene, and a debris flow that feeds the accumulation zone of the landslide, where a fast change in terrain morphology is observed. The estimated deformation map is in agreement with the available measurements obtained by means of Global Positioning System receivers. Results show that GB-SAR interferometry is a cost-effective solution for the monitoring of landslides. The proposed method is shown to be a valid complement to space- and airborne SAR and to the traditional geodetic instruments.
•Quantitative C–O–H analyses of fluids after piston cylinder experiments.•Carbonation of serpentinites in the forearc region of the mantle wedge.•Carbonation is rapid and occurs within the first hour ...of the experiments.•Magnesite is a good monitor for Ca, Ba, Sr and Pb in subduction zone fluids.
The carbonation of serpentinites in the forearc region of the mantle wedge in subduction zones and of serpentinites within the subducting slab by fluids derived from prograde dehydration and decarbonation has important implications for the deep Earth carbon cycle. This study shows that the carbonation of serpentinites under the forearc can establish, over time, a significant reservoir for carbon within a partially hydrated mantle wedge and that carbonation of (ultra-) mafic rocks within the subducting slab contributes to C-transfer to greater depths and might supply carbon for arc volcanism or the deep mantle.
We report a new high pressure experimental investigation of the interactions between oxidised C–O–H fluids and serpentinite and model the reaction progress with time series experiments. The CO2, H2O and alkane (CnH2n+2, n=1–6; e.g. methane, ethane) contents in the fluid phase from quenched experimental run products have been analysed by gas chromatography and the results are compared with thermodynamic calculations. With progressive carbonation, the formation of magnesite + chlorite together with quartz, quartz + talc or talc at 1–2 GPa and 500–650 °C was observed. At temperatures above antigorite stability (T≳700 °C and 2 GPa) magnesite + chlorite is stable together with talc, talc + enstatite, enstatite or enstatite + forsterite for decreasing CO2-content in the fluid. Carbonation of serpentinite is a rapid process where magnesite forms within the first hour of the experiments, filtering CO2 from the fluid effectively and equilibrium is approached within 48 h. The CO2-sequestration and magnesite production are less pronounced at higher temperatures. Therefore, C–O–H fluids released under subarc conditions might migrate through the mantle with only minor changes in their carbon budget whereas significant carbonation likely occurs under the forearc. Furthermore, partition coefficients for Ca, Ba, Sr and Pb between magnesite and a C-poor aqueous fluid have been established to demonstrate the potential of newly formed magnesite to sequester fluid mobile elements.
We present a continuation method that enables one to track or continue branches of periodic orbits directly in an experiment when a parameter is changed. A control-based setup in combination with ...Newton iterations ensures that the periodic orbit can be continued even when it is unstable. This is demonstrated with the continuation of initially stable rotations of a vertically forced pendulum experiment through a fold bifurcation to find the unstable part of the branch.
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