Alginates along the filament of the brown alga Ectocarpus help cells cope with stress.

Ectocarpus is a filamentous brown alga, which cell wall is composed mainly of alginates and fucans (80%), two non-crystalline polysaccharide classes. Alginates are linear chains of epimers of 1,4-linked uronic acids, β-D-mannuronic acid (M) and α-L-guluronic acid (G). Previous physico-chemical studies showed that G-rich alginate gels are stiffer than M-rich alginate gels when prepared in vitro with calcium. In order to assess the possible role of alginates in Ectocarpus, we first immunolocalised M-rich or G-rich alginates using specific monoclonal antibodies along the filament. As a second step, we calculated the tensile stress experienced by the cell wall along the filament, and varied it with hypertonic or hypotonic solutions. As a third step, we measured the stiffness of the cell along the filament, using cell deformation measurements and atomic force microscopy. Overlapping of the three sets of data allowed to show that alginates co-localise with the stiffest and most stressed areas of the filament, namely the dome of the apical cell and the shanks of the central round cells. In addition, no major distinction between M-rich and G-rich alginate spatial patterns could be observed. Altogether, these results support that both M-rich and G-rich alginates play similar roles in stiffening the cell wall where the tensile stress is high and exposes cells to bursting, and that these roles are independent from cell growth and differentiation

New insights on the population genetic structure of the great scallop (Pecten maximus) in the English Channel coupling microsatellite data and demogenetic simulations.

International audienceThe great scallop (Pecten maximus) is a commercially important bivalve in Europe, particularly in the English Channel, where fisheries are managed at regional and local scales through the regulation of fishing effort. In the long term, knowledge about larval dispersal and gene flow between populations is essential to ensure proper stock management. Yet, previous population genetic studies have reported contradictory results. In this study, scallop samples collected across the main fishing grounds along the French and English coasts of the English Channel (20 samples with temporal replicates for three sites,n= 1059 individuals), and the population genetic structure was analysed using 13 microsatellite loci. Coupling empirical genetic data with demogenetic modelling based on a biophysical model simulating larval exchanges among scallop beds revealed a subtle genetic differentiation between south-west English populations and the rest of the English Channel, which was consistent with larval dispersal simulations. The present study provides a step forward in the understanding of great scallop population biology in the English Channel, underlining the fact that even in a context of potentially high gene flow and recent divergence times since the end of the last glacial maximum, weak but significant spatial genetic structure can be identified at a regional scale

Mother-offspring recognition via contact calls in cattle, Bos taurus.

Individual recognition in gregarious species is fundamental in order to avoid misdirected parental investment. In ungulates, two very different parental care strategies have been identified: ‘hider’ offspring usually lie concealed in vegetation whereas offspring of ‘follower’ species remain with their mothers while they forage. These two strategies have been suggested to impact on mother-offspring vocal recognition, with unidirectional recognition of the mother by offspring occurring in hiders and bidirectional recognition in followers. In domestic cattle, Bos taurus, a facultative hider species, vocal communication and recognition have not been studied in detail under free-ranging conditions, where cows and calves can graze freely and where hiding behaviour can occur. We hypothesized that, as a hider species, cattle under these circumstances would display unidirectional vocal recognition. To test this hypothesis, we conducted playback experiments using mother-offspring contact calls. We found that cows were more likely to respond, by moving their ears and/or looking, turning or walking towards the loudspeaker, to calls of their own calves than to calls from other calves. Similarly, calves responded more rapidly, and were more likely to move their ears and/or look, turn or walk towards the loudspeaker, and to call back and/or meet their mothers, in response to calls from their own mothers than to calls from other females. Contrary to our predictions, our results suggest that mother-offspring vocal individual recognition is bidirectional in cattle. Additionally, mothers of younger calves tended to respond more strongly to playbacks than mothers of older calves. Therefore, mother responses to calf vocalizations are at least partially influenced by calf age

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Evaluation du traitement par Tétrazépam versus manipulation vertébrale lors d'une exacerbation douloureuse dans le cadre de lombalgies chroniques en médecine générale

Introduction : La prise en charge des lombalgies est un enjeu de santé publique. Le but de cette étude est de tester le Tétrazépam, thérapeutique médicamenteuse et la manipulation vertébrale, thérapeutique non médicamenteuse, lors d'une exacerbation douloureuse dans le cadre de lombalgies chroniques communes (grade B dans les recommandations de l HAS de 2000). Présentation de l'étude et de la méthode : Il s agit d'une étude prospective descriptive réalisée auprès de patients lombalgiques chroniques consultants des médecins généralistes du Poitou-Charentes durant les mois de mai et juin 2012. L'étude est réalisée à l'aide de questionnaires anonymes pré et post thérapeutiques (Echelle numérique, Echelle EIFEL et Echelle de DALLAS). L'efficacité est évaluée huit jours après la fin de la thérapeutique choisie. Résultats : Quarante cinq patients ont été inclus, vingt pour le Tétrazépam et vingt cinq pour la manipulation vertébrale. Le Tétrazépam peut apporter un soulagement en termes de douleur et d'incapacité fonctionnelle mais pas sur la qualité de vie des patients contrairement à la manipulation vertébrale qui permet une amélioration de tous ces paramètres (p<0,05). Les médecins et les patients sont satisfaits de l'efficacité de la manipulation (7,5/10) à huit jours contrairement à celle du Tétrazépam (4,5/10). Conclusion : La manipulation vertébrale se présente comme étant une alternative non médicamenteuse intéressante dans le soulagement de la douleur, du retentissement fonctionnel et de la qualité de vie à court terme. Cette thérapeutique peut donc être une méthode intéressante à proposer aux patients ayant une recrudescence de leur douleur dans le cadre de lombalgies chroniques, par leur médecin généraliste. La prescription du Tétrazépam dans cette indication est plus contestable.POITIERS-BU Médecine pharmacie (861942103) / SudocSudocFranceF

Production of genetically and developmentally modified seaweeds: exploiting the potential of artificial selection techniques

International audiencePlant feedstock with specific, modified developmental features has been a quest for centuries. Since the development and spread of agriculture, there has been a desire for plants producing disproportionate—or more abundant and more nutritional—biomass that meet human needs better than their native counterparts. Seaweed aquaculture, targeted for human consumption and the production of various raw materials, is a rapidly expanding field and its stakeholders have increasing vested interest for cost-effective and lucrative seaweed cultivation processes. Thus, scientific research on seaweed development is particularly timely: the potential for expansion of seaweed cultivation depends on the sector's capacity to produce seaweeds with modified morphological features (e.g., thicker blades), higher growth rates or delayed (or even no) fertility. Here, we review the various technical approaches used to modify development in macroalgae, which have attracted little attention from developmental biologists to date. Because seaweed (or marine macroalgae) anatomy is much less complex than that of land plants and because seaweeds belong to three different eukaryotic phyla, the mechanisms controlling their morphogenesis are key to understanding their development. Here, we present efficient sources of developmentally and genetically modified seaweeds—somatic variants, artificial hybrids and mutants—as well as the future potential of these techniques

The brown algal mode of tip growth: Keeping stress under control

International audienceTip growth has been studied in pollen tubes, root hairs, and fungal and oomycete hyphae and is the most widely distributed unidirectional growth process on the planet. It ensures spatial colonization, nutrient predation, fertilization, and symbiosis with growth speeds of up to 800 μm h −1. Although turgor-driven growth is intuitively conceivable, a closer examination of the physical processes at work in tip growth raises a paradox: growth occurs where bio-physical forces are low, because of the increase in curvature in the tip. All tip-growing cells studied so far rely on the modulation of cell wall extensibility via the polarized excretion of cell wall-loosening compounds at the tip. Here, we used a series of quantitative measurements at the cellular level and a biophysical simulation approach to show that the brown alga Ectocarpus has an original tip-growth mechanism. In this alga, the establishment of a steep gradient in cell wall thickness can compensate for the variation in tip curvature, thereby modulating wall stress within the tip cell. Bootstrap analyses support the robustness of the process, and experiments with fluorescence recovery after photobleaching (FRAP) confirmed the active vesicle trafficking in the shanks of the apical cell, as inferred from the model. In response to auxin, biophysical measurements change in agreement with the model. Although we cannot strictly exclude the involvement of a gradient in mechanical properties in Ectocarpus morphogenesis, the viscoplastic model of cell wall mechanics strongly suggests that brown algae have evolved an alternative strategy of tip growth. This strategy is largely based on the control of cell wall thickness rather than fluctuations in cell wall mechanical properties

Effects of bioactive extracellular compounds and paralytic shellfish toxins produced by Alexandrium minutum on growth and behaviour of juvenile great scallops Pecten maximus

Dinoflagellates of the genus Alexandrium are a major cause of harmful algal blooms (HABs) that have increasingly disrupted coastal ecosystems for the last several decades. Microalgae from the genus Alexandrium are known to produce paralytic shellfish toxins (PST) but also bioactive extracellular compounds (BEC) that can display cytotoxic, allelopathic, ichtyotoxic or haemolytic effects upon marine organisms. The objective of this experimental study was to assess the effects of PST and BEC produced by A. minutum upon juvenile great scallops Pecten maximus. Scallops were exposed for one week to two different strains of A. minutum, the first producing both PST and BEC and the second producing only BEC. Escape response to starfish, daily shell growth, histological effects, and accumulation of PST were recorded after one week of exposure, and after two subsequent weeks of recovery. Daily shell growth was delayed three days in scallops exposed to the BEC-producing A. minutum strain, probably during the three first days of exposure. An increase of reaction time to predators was observed in scallops exposed to the BEC condition, suggesting that BEC may have altered sensing processes. Scallops exposed to PST displayed a less-efficient escape response and muscular damage which could reflect the effects of paralytic toxins upon the nervous system of scallops. This study demonstrates contrasting effects of the distinct toxic compounds produced by A. minutum upon marine bivalves, thus highlighting the importance to better characterize these extracellular, bioactive compounds to better understand responses of other marine organisms

Genetic and phenotypic intra-species diversity of alga Tisochrysis lutea reveals original genetic structure and domestication potential

Oceanic phytoplankton species are generally composed of many strains, with intra-species diversity consisting of genetic and phenotypic variability. Despite its importance in ecological and biotechnological contexts, this intra-species diversity and variation among strains has been little studied. We investigated the intra-species diversity of the microalga Tisochrysis lutea, a haptophyte of the Isochrysidales order. Inter-strain diversity of T. lutea was studied because of the economic importance of the species as a feed in aquaculture and for antioxidant metabolite production, particularly fucoxanthin and other carotenoids, which have health benefits. We analysed Tara Ocean datasets which revealed that T. lutea was present in the Pacific, Atlantic and Indian Oceans but not in the Arctic or Austral Oceans. We next made phenotypic and genotypic comparisons of 11 strains of T. lutea from worldwide algal collections. All strains were cultivated in the same controlled conditions for one week, and several phenotypic traits were measured, notably antioxidant content. In parallel, the genomes of each strain were sequenced, and genetic variants identified. At the genetic and phenotypic levels, the strains were distinct from each other and our analysis revealed natural trait variations of interest in relation to further exploitation in domestication programmes. A large number of genetic variations were identified among the strains, but no major differences in genome size were observed. Moreover, limited genetic structure was observed among these strains, which could be a consequence of the complex life history of species within the Isochrysidales. Our study provides new knowledge on the intra-species diversity that should be considered in future environmental studies and breeding programmes. Highlights Tisochrysis lutea is found in many parts of the world’s oceans. T. lutea has high inter-strain phenotypic and genomic variation. Genetic structure of strains from culture collections is limited

Projet SA6 HQFISH: Impact de la qualité des habitats estuariens de la Seine sur le fonctionnement d'une population de poisson (du recrutement des juvéniles, au processus de maturation)

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