From standing to breaking antidunes, a Hopf bifurcation.

Antidunes are bed morphologies often observed in steep slope mountain flows but also in small streams flowing on a sand beach. Linear stability analysis of the shallow water equations (SWE), when coupled to a sediment transport equation, predicts the growth of selected wavelength when the Froude number exceeds unity. If the bedform amplitude grows sufficiently (without being stabilized by nonlinear effects (Colombini and Stocchino (2008)), hydraulic jump can form on the lee side while a transcritical point, situated roughly on the crest of the dune, connects the sub and supercritical states. This has been described in the literature as cyclic steps. Their stationary travelling wave solution has already been theoretically and experimentally investigated (Balmforth and Vakil (2012); Taki and Parker (2005); Sun and Parker (2005)). In this talk, we provide numerical and theoretical evidence that a time dependent quasi-periodic solution of cyclic steps also exists in the SWE+Exner equations for a certain choice of the parameters. We compare this quasi-periodic phenomenon to breaking antidunes often observed in natural rivers

Channel meta-stability: effects on bedload transport.

Large fluctuations in the sediment transport rate are observed in rivers, particularly in mountain streams at intermediate flow rates (Ancey, 2006). These fluctuations seem to be, to some degree, correlated with the evolution of morphologies in the stream. Today the central question remains how to understand and acco unt for the strong bedload variability. In this presentation, new experimental results give some ideas about the link between channel bed evolution and intermittency in bedload transport

Soil contamination following an industrial accident : towards efficient investigations and assessment

International audienceWhen an industrial accident occurs, e.g. the explosion or the fire of a chemical facility, soil investigations and subsequent risk mitigation generally need to be decided and performed rapidly. This requires specific organisation and tools: Procedures for an immediate and coordinated intervention of relevant actors: industrials, administrations for industrial facilities, emergency and health, local authorities, environmental consultants and laboratories, NGOs. Models and input data on emission, atmospheric transfer and deposition on soil, for an accidental source; investigation plans and adequate soil quality references, guidelines... But the European Seveso legislation, and its application in France and probably in Europe, is focused on the prevention of immediate impacts on health and constructions; and the Integrated Pollution Prevention and Control (IPPC) legislation deals with the chronic impacts of operating facilities. Thus, post-accidental impacts of industrial accidents are hardly dealt with, the specific organisation and tools are lacking, and when accidents occur, the industrials and administrations concerned are largely unprepared for managing their delayed impacts, first of them on soils

Secretory IgA mediates retrotranscytosis of intact gliadin peptides via the transferrin receptor in celiac disease

Celiac disease (CD) is an enteropathy resulting from an abnormal immune response to gluten-derived peptides in genetically susceptible individuals. This immune response is initiated by intestinal transport of intact peptide 31-49 (p31-49) and 33-mer gliadin peptides through an unknown mechanism. We show that the transferrin receptor CD71 is responsible for apical to basal retrotranscytosis of gliadin peptides, a process during which p31-49 and 33-mer peptides are protected from degradation. In patients with active CD, CD71 is overexpressed in the intestinal epithelium and colocalizes with immunoglobulin (Ig) A. Intestinal transport of intact p31-49 and 33-mer peptides was blocked by polymeric and secretory IgA (SIgA) and by soluble CD71 receptors, pointing to a role of SIgA–gliadin complexes in this abnormal intestinal transport. This retrotranscytosis of SIgA–gliadin complexes may promote the entry of harmful gliadin peptides into the intestinal mucosa, thereby triggering an immune response and perpetuating intestinal inflammation. Our findings strongly implicate CD71 in the pathogenesis of CD

T84-intestinal epithelial exosomes bear MHC class II/peptide complexes potentiating antigen presentation by dendritic cells: Function of intestinal epithelial exosomes

International audienceBackground and aims: Intestinal epithelial cells release antigen presenting vesicles (exosomes) bearing MHC class II/peptide complexes stimulating specific immune responses in vivo. To further characterize the role of human epithelial exosomes in antigen presentation, their capacity to load antigenic peptides, to bind immune target cells and to induce T cell activation was analyzed in vitro. Methods: The capacity of exosomes derived from the HLA-DR4 expressing, intestinal epithelial cell line T84, to load the HLA-DR4-specific peptide 3H-HSA 64-76 and to activate a HLA-DR4-restricted T cell hybridoma, was tested in the presence or absence of human monocyte-derived dendritic cells (DCs). Interaction of FITC-labeled exosomes with T cells and DCs was analyzed by flow cytometry and confocal microscopy. Results: T84-derived exosomes, enriched in CD9, CD81, CD82 and A33 antigen, were capable of binding specifically HSA 64-76 peptide on HLA-DR4 molecules and of interacting preferentially with DCs. HSA-loaded exosomes were unable to activate the T cell hybridoma directly, but induced a productive T cell activation through DCs. When HSA peptide was bound to exosomal HLA-DR4 molecules instead of in a soluble form, the threshold of peptide presentation by DCs was markedly decreased (x10-3). Conclusions: Exosomes released by intestinal epithelial cells bear exogenous peptides complexed to MHC class II molecules and interact preferentially with DCs, strongly potentiating peptide presentation to T cells. Epithelial exosomes constitute a powerful link between luminal antigens and local immune cells by mediating the transfer of tiny amounts of luminal antigenic information and facilitating immune surveillance at mucosal surfaces

Uncoupled Embryonic and Extra-Embryonic Tissues Compromise Blastocyst Development after Somatic Cell Nuclear Transfer

Somatic cell nuclear transfer (SCNT) is the most efficient cell reprogramming technique available, especially when working with bovine species. Although SCNT blastocysts performed equally well or better than controls in the weeks following embryo transfer at Day 7, elongation and gastrulation defects were observed prior to implantation. To understand the developmental implications of embryonic/extra-embryonic interactions, the morphological and molecular features of elongating and gastrulating tissues were analysed. At Day 18, 30 SCNT conceptuses were compared to 20 controls (AI and IVP: 10 conceptuses each); one-half of the SCNT conceptuses appeared normal while the other half showed signs of atypical elongation and gastrulation. SCNT was also associated with a high incidence of discordance in embryonic and extra-embryonic patterns, as evidenced by morphological and molecular “uncoupling”. Elongation appeared to be secondarily affected; only 3 of 30 conceptuses had abnormally elongated shapes and there were very few differences in gene expression when they were compared to the controls. However, some of these differences could be linked to defects in microvilli formation or extracellular matrix composition and could thus impact extra-embryonic functions. In contrast to elongation, gastrulation stages included embryonic defects that likely affected the hypoblast, the epiblast, or the early stages of their differentiation. When taking into account SCNT conceptus somatic origin, i.e. the reprogramming efficiency of each bovine ear fibroblast (Low: 0029, Med: 7711, High: 5538), we found that embryonic abnormalities or severe embryonic/extra-embryonic uncoupling were more tightly correlated to embryo loss at implantation than were elongation defects. Alternatively, extra-embryonic differences between SCNT and control conceptuses at Day 18 were related to molecular plasticity (high efficiency/high plasticity) and subsequent pregnancy loss. Finally, because it alters re-differentiation processes in vivo, SCNT reprogramming highlights temporally and spatially restricted interactions among cells and tissues in a unique way

Retinoid X receptor gamma signaling accelerates CNS remyelination

The molecular basis of CNS myelin regeneration (remyelination) is poorly understood. We generated a comprehensive transcriptional profile of the separate stages of spontaneous remyelination that follow focal demyelination in the rat CNS and found that transcripts that encode the retinoid acid receptor RXR-γ were differentially expressed during remyelination. Cells of the oligodendrocyte lineage expressed RXR-γ in rat tissues that were undergoing remyelination and in active and remyelinated multiple sclerosis lesions. Knockdown of RXR-γ by RNA interference or RXR-specific antagonists severely inhibited oligodendrocyte differentiation in culture. In mice that lacked RXR-γ, adult oligodendrocyte precursor cells efficiently repopulated lesions after demyelination, but showed delayed differentiation into mature oligodendrocytes. Administration of the RXR agonist 9-cis-retinoic acid to demyelinated cerebellar slice cultures and to aged rats after demyelination caused an increase in remyelinated axons. Our results indicate that RXR-γ is a positive regulator of endogenous oligodendrocyte precursor cell differentiation and remyelination and might be a pharmacological target for regenerative therapy in the CNS

Bedload transport in steep mountain stream : a consistent stochastic framework.

We demonstrate in this poster the role played by stochasticity in bedload transport on steep slope. Multiscale and multifractal behavior is observed, while long range correlation takes place

Characterization of bedload transport in steep-slope streams.

Large fluctuations in the sediment transport rate are observed in rivers, particularly in mountain streams at intermediate flow rates. These fluctuations seem to be, to some degree, correlated to the formation and migration of bedforms. Today the central question is still how to understand and account for the strong bedload variability. Recent experimental studies shed new light on the processes. The objective of this presentation is to show some of our results. To understand the behavior and the origins of sediment transport rate fluctuations in the case of steep-slope streams, we conducted laboratory experiments in a 3-m long, 8-cm wide, transparent flume. The experimental parameters are the flume inclination, flow rate and sediment input rate. Well-sorted natural gravel (8.5 mm mean diameter) were used. We focused on two-dimensional flows and incipient bedforms (i.e. for flow rates just above the threshold of incipient motion). A technique based on accelerometers was developed to record every particle passing through the flume outlet (more specifically, we measured the vibrations of a metallic slab, which was impacted by the falling particles). Analysis of bedload transport rates was then possible on all time scales. Moreover, the bed and flow were monitored using 2 cameras.We computed bed elevation, water depth and erosion/deposition at high temporal and spatial rates from camera shots (one image per second during several hours or days). In our laboratory experiments, the fluctuations of the sediment rate were large even for steady flow conditions involving well-sorted particles. Time series exhibited fluctuations at all scales and displayed long range correlations with a Hurst exponent close to 0.8. The results were compared for different input solid discharges. The main bedforms observed in our flume were anti-dunes migrating upstream. Bedform formation and propagation showed intermittency with pulses (high activity) followed by long sequences of low activity. We tried to interpret our results (bedform behavior, bed scouring) in terms of sediment outflow rate