Mécanismes de précipitation de carbonate de calcium dans les biofilms photosynthétiques

La précipitation de carbonate de calcium dans les systèmes benthiques est souvent associée aux biofilms photosynthétiques, et notamment observée au sein de structures d'une grande complexité morphologique comme les tapis microbiens, les stromatolithes et les microbialithes. Cette biocalcification modifie les flux de CO2, de calcium et d'alcalinité dans les hydrosystèmes (séquestration du carbone inorganique et d'alcalinité). Ce processus paraît donc très sensible aux impacts anthropiques, e.g. la perturbation globale du cycle du carbone et les contaminations atmosphériques. Son étude revêt une importance capitale pour la compréhension des paléoenvironnements. Différentes hypothèses ont été avancées pour expliquer la biocalcification dans ces biofilms. L'activité photosynthétique des cyanobactéries est souvent mise en cause, mais ce mécanisme est parfois contesté, privilégiant l'activité métabolique des bactéries organohétérotrophes, e.g. les bactéries sulfato-réductrices, qui sont associées aux micro-organismes phototrophes dans les biofilms La calcification peut aussi être contrôlée directement par l'interaction du calcium avec la matière organique, notamment les polymères extracellulaires sécrétés par les microorganismes (EPS) ou les fractions macromoléculaires riches en acides aspartique et glutamique de la matière organique dissoute (MOD)

New periodic variable stars coincident with ROSAT sources discovered using SuperWASP

We present optical lightcurves of 428 periodic variable stars coincident with ROSAT X-ray sources, detected using the first run of the SuperWASP photometric survey. Only 68 of these were previously recognised as periodic variables. A further 30 of these objects are previously known pre-main sequence stars, for which we detect a modulation period for the first time. Amongst the newly identified periodic variables, many appear to be close eclipsing binaries, their X-ray emission is presumably the result of RS CVn type behaviour. Others are probably BY Dra stars, pre-main sequence stars and other rapid rotators displaying enhanced coronal activity. A number of previously catalogued pulsating variables (RR Lyr stars and Cepheids) coincident with X-ray sources are also seen, but we show hat these are likely to be misclassifications. We identify four objects which are probable low mass eclipsing binary stars, based on their very red colour and light curve morphology

Variable Outer Disk Shadowing Around the Dipper Star RX J1604.3-2130

Low brightness dips have recently been observed in images of protoplanetary disks, and they are believed to be shadows by the inner disk. We present VLT/SPHERE polarimetric differential imaging of the transition disk around the dipper star RX J1604.3-2130. We gathered 11 epochs that cover a large temporal baseline, to search for variability over timescales of years, months, weeks, and days. Our observations unambiguously reveal two dips along an almost face-on narrow ring (with a width of ∼20 au), and the location of the peak of this ring is at ∼65 au. The ring lies inside the ring-like structure observed with ALMA, which peaks at ∼83 au. This segregation can result from particle trapping in pressure bumps, potentially due to planet(s). We find that the dips are variable, both in morphology and in position. The eastern dip, at a position angle (PA) of ∼83.°7 ±13.°7, has an amplitude that varies between 40% to 90%, and its angular width varies from 10° to 34°. The western dip, at a PA of ∼265.°90 ±13.°0, is more variable, with amplitude and width variations of 31% to 95% and 12° to 53°, respectively. The separation between the dips is 178.°3 ±14.°5, corresponding to a large misalignment between the inner and outer disks, supporting the classification of J1604 as an aperiodic dipper. The variability indicates that the innermost regions are highly dynamic, possibly due to a massive companion or to a complex magnetic field topology.</p

MAP6-F is a temperature sensor that directly binds to and protects microtubules from cold-induced depolymerization.: Microtubule stabilization by MAP6

International audienceMicrotubules are dynamic structures that present the peculiar characteristic to be ice-cold labile in vitro. In vivo, microtubules are protected from ice-cold induced depolymerization by the widely expressed MAP6/STOP family of proteins. However, the mechanism by which MAP6 stabilizes microtubules at 4 °C has not been identified. Moreover, the microtubule cold sensitivity and therefore the needs for microtubule stabilization in the wide range of temperatures between 4 and 37 °C are unknown. This is of importance as body temperatures of animals can drop during hibernation or torpor covering a large range of temperatures. Here, we show that in the absence of MAP6, microtubules in cells below 20 °C rapidly depolymerize in a temperature-dependent manner whereas they are stabilized in the presence of MAP6. We further show that in cells, MAP6-F binding to and stabilization of microtubules is temperature- dependent and very dynamic, suggesting a direct effect of the temperature on the formation of microtubule/MAP6 complex. We also demonstrate using purified proteins that MAP6-F binds directly to microtubules through its Mc domain. This binding is temperature-dependent and coincides with progressive conformational changes of the Mc domain as revealed by circular dichroism. Thus, MAP6 might serve as a temperature sensor adapting its conformation according to the temperature to maintain the cellular microtubule network in organisms exposed to temperature decrease

Effect of the stellar spin history on the tidal evolution of close-in planets

We investigate how the evolution of the stellar spin rate affects, and is affected by, planets in close orbits, via star-planet tidal interactions. To do this, we used a standard equilibrium tidal model to compute the orbital evolution of single planets orbiting both Sun-like stars and 0.1 M\odot M-dwarfs. We tested two stellar spin evolution profiles, one with fast initial rotation (P=1.2 day) and one with slow initial rotation (P=8 day). We tested the effect of varying the stellar and planetary dissipation and the planet's mass and initial orbital radius. Conclusions: Tidal evolution allows to differentiate the early behaviors of extremely close-in planets orbiting either a rapidly rotating star or a slowly rotating star. The early spin-up of the star allows the close-in planets around fast rotators to survive the early evolution. For planets around M-dwarfs, surviving the early evolution means surviving on Gyr timescales whereas for Sun-like stars the spin-down brings about late mergers of Jupiter planets. In light of this study, we can say that differentiating between one spin evolution from another given the present position of planets can be very tricky. Unless we can observe some markers of former evolution it is nearly impossible to distinguish the two very different spin profiles, let alone intermediate spin profiles. Though some conclusions can still be drawn from statistical distributions of planets around fully convective M-dwarfs. However, if the tidal evolution brings about a merger late in its history it can also entail a noticeable acceleration of the star in late ages, so that it is possible to have old stars that spin rapidly. This raises the question of better constraining the age of stars

Chemogenetics defines receptor-mediated functions of short chain free fatty acids

Differentiating actions of short chain fatty acids (SCFAs) at free fatty acid receptor 2 (FFA2) from other free fatty acid-responsive receptors and from non-receptor-mediated effects has been challenging. Using a novel chemogenetic and knock-in strategy, whereby an engineered variant of FFA2 (FFA2-DREADD) that is unresponsive to natural SCFAs but is instead activated by sorbic acid replaced the wild-type receptor, we determined that activation of FFA2 in differentiated adipocytes and colonic crypt enteroendocrine cells of mouse accounts fully for SCFA-regulated lipolysis and release of the incretin glucagon-like peptide-1 (GLP-1), respectively. In vivo studies confirmed the specific role of FFA2 in GLP-1 release and also demonstrated a direct role for FFA2 in accelerating gut transit. Thereby, we establish the general principle that such a chemogenetic knock-in strategy can successfully define novel G-protein-coupled receptor (GPCR) biology and provide both target validation and establish therapeutic potential of a ‘hard to target’ GPCR

Comprehensive Signaling Profiles Reveal Unsuspected Functional Selectivity of δ-Opioid Receptor Agonists and Allow the Identification of Ligands with the Greatest Potential for Inducing Cyclase Superactivation

Prolonged exposure to opioid receptor agonists triggers adaptations in the adenylyl cyclase (AC) pathway that lead to enhanced production of cyclic adenosine monophosphate (cAMP) upon withdrawal. This cellular phenomenon contributes to withdrawal symptoms, hyperalgesia and analgesic tolerance that interfere with clinical management of chronic pain syndromes. Since δ-opioid receptors (DOPrs) are a promising target for chronic pain management, we were interested in finding out if cell-based signaling profiles as generated for drug discovery purposes could inform us of the ligand potential to induce sensitization of the cyclase path. For this purpose, signaling of DOPr agonists was monitored at multiple effectors. The resulting signaling profiles revealed marked functional selectivity, particularly for Met-enkephalin (Met-ENK) whose signaling bias profile differed from those of synthetic ligands like SNC-80 and ARM390. Signaling diversity among ligands was systematized by clustering agonists according to similarities in Emax and Log(τ) values for the different responses. The classification process revealed that the similarity in Gα/Gβγ, but not in β-arrestin (βarr), responses was correlated with the potential of Met-ENK, deltorphin II, (d-penicillamine2,5)-enkephalin (DPDPE), ARM390, and SNC-80 to enhance cAMP production, all of which required Ca2+ mobilization to produce this response. Moreover, superactivation by Met-ENK, which was the most-effective Ca2+ mobilizing agonist, required Gαi/o activation, availability of Gβγsubunits at the membrane, and activation of Ca2+ effectors such as calmodulin and protein kinase C (PKC). In contrast, superactivation by (N-(l-tyrosyl)-(3S)-1,2,3,4-tetrahydroisoquinoline-3-carbonyl)-l-phenylalanyl-l-phenylalanine (TIPP), which was set in a distinct category through clustering, required activation of Gαi/o subunits but was independent of the Gβγdimer and Ca2+ mobilization, relying instead on Src and Raf-1 to induce this cellular adaptation

SCARLET – A European Effort to Develop HTS and MgB2 Based MVDC Cables

Superconducting cables have been proven in a variety of pilot projects and utility installations, demonstrating several of their advantages, including compact size and low energy losses, which can make the technology economically attractive for certain applications. It is clear though that different applications impose different requirements and challenges, but also opportunities for the cables. An interesting application is high-power DC transfer at medium voltage (MVDC). The high-current capability of the superconductor allows for a reduction in voltage while maintaining or increasing the power transfer level. In this way, one MVDC superconducting cable can replace one or more conventional high-voltage DC cables. In the European project SCARLET (Superconducting cables for sustainable energy transition), two types of MVDC cables will be developed, one based on HTS and one on MgB2 materials. Additionally, protection requirements will be considered, including the development of a modular DC fault current limiter for 10 kA. A main motivation for the development is the elimination of costly high-voltage converter stations when going from high to medium voltage, e.g., for offshore wind power plants. Another feature is the combined hydrogen and electricity transmission from generation sites to industry or mobility end users. This paper describes the superconducting MVDC cable concept as well as the main challenges and research needed to develop and type test the cables.SCARLET – A European Effort to Develop HTS and MgB2 Based MVDC CablesacceptedVersio

Exploring use of unsupervised clustering to associate signaling profiles of GPCR ligands to clinical response.

Signaling diversity of G protein-coupled (GPCR) ligands provides novel opportunities to develop more effective, better-tolerated therapeutics. Taking advantage of these opportunities requires identifying which effectors should be specifically activated or avoided so as to promote desired clinical responses and avoid side effects. However, identifying signaling profiles that support desired clinical outcomes remains challenging. This study describes signaling diversity of mu opioid receptor (MOR) ligands in terms of logistic and operational parameters for ten different in vitro readouts. It then uses unsupervised clustering of curve parameters to: classify MOR ligands according to similarities in type and magnitude of response, associate resulting ligand categories with frequency of undesired events reported to the pharmacovigilance program of the Food and Drug Administration and associate signals to side effects. The ability of the classification method to associate specific in vitro signaling profiles to clinically relevant responses was corroborated using β2-adrenergic receptor ligands.This research was supported by a research contract from Pfizer Inc. and grants from the Natural Sciences and Engineering Research Council of Canada (Grant 311997 to G.P.) and the Canadian Institutes of Health Research MOP 324876 (to G.P.), MOP 102630 (to M.B. and O.L.) and Foundation grant (FDN-148431) to MB. MB holds a Canada Research Chair in Signal Transduction and Molecular Pharmacology. Dr Lichtarge’s research was supported by National Institutes of Health (NIH 2R01 GM066099; NIH 5R01 GM079656). B.B. was supported by a studentship from Fonds de Recherche en Santé du Québec. P.D. was supported by a MITACS fellowship

Mapping physiological G protein-coupled receptor signaling pathways reveals a role for receptor phosphorylation in airway contraction.

G protein-coupled receptors (GPCRs) are known to initiate a plethora of signaling pathways in vitro. However, it is unclear which of these pathways are engaged to mediate physiological responses. Here, we examine the distinct roles of Gq/11-dependent signaling and receptor phosphorylation-dependent signaling in bronchial airway contraction and lung function regulated through the M3-muscarinic acetylcholine receptor (M3-mAChR). By using a genetically engineered mouse expressing a G protein-biased M3-mAChR mutant, we reveal the first evidence, to our knowledge, of a role for M3-mAChR phosphorylation in bronchial smooth muscle contraction in health and in a disease state with relevance to human asthma. Furthermore, this mouse model can be used to distinguish the physiological responses that are regulated by M3-mAChR phosphorylation (which include control of lung function) from those responses that are downstream of G protein signaling. In this way, we present an approach by which to predict the physiological/therapeutic outcome of M3-mAChR-biased ligands with important implications for drug discovery.This study is funded by the Medical Research Council (MRC) through funding of program leaders provided by the MRC Toxicology Unit (to A.B.T.)