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Exploring the environmental distribution of the oyster parasite Haplosporidium costale
No full textInternational audienceThe protozoan parasite Haplosporidium costale is known to occur in the USA where it has been associated with sharp seasonal mortality of the Eastern oyster Crassostrea virginica since the 1960’s. In 2019, the parasite was detected for the first time in the Pacific oyster Magallana gigas in France in the context of light mortality and was subsequently detected in archived material collected since 2008. This detection raised several questions regarding the ability of the parasite to maintain in the ecosystem and the potential involvement of other species in its life cycle. To answer these questions, an integrated sampling approach was deployed seasonally in three oyster farming areas where the parasite was already known to occur. Parasite presence was evaluated after checking the presence of PCR inhibitors and using a previously developed and validated Real Time PCR assay, optimized in this study to detect parasite DNA in various environmental compartments. Parasite DNA was almost only detected in cupped oysters. Considering the high number of oysters found positive with low infection intensity, a complementary experiment was undertaken to better characterize sub-clinical infections in oysters. The presence of the parasite was tested twice a week in water and sediment from aquaria hosting cupped oysters from a known infected site. After one month, oysters were sacrificed and tested regarding the presence of the parasite at the tissular level. Altogether, field and experimental results indicate that the parasite is stably established in oyster, particularly in gills, which may act as a reservoir all along the year. The detection of parasite DNA in nanoplankton and sediment suggests that H. costale is released from the oysters outside mortality event. Our results do not support the involvement of other species than cupped oyster in the parasite life cycle except periwinkles, whose role would deserve to be further investigate
SPHINGOLIPIDS AND Δ8-SPHINGOLIPID DESATURASE FROM THE PICOALGA OSTREOCOCCUS TAURI AND INVOLVEMENT IN TEMPERATURE ACCLIMATION
No full textAlternative title : SPHINGOLIPID‐8 DESATURASE CONTROLS THE UNSATURATION OF ACIDIC GLYCOSYLCERAMIDES AND IS INVOLVED IN TEMPERATURE ACCLIMATION IN THE MINIMAL GREEN ALGA OSTROCOCCUS TAURISphingolipids are crucial components of cell membranes. Sphingolipid Δ8-unsaturation is more specific to plants and is involved in the regulation of stress responses. The structure and functions of sphingolipids in microalgae are still poorly understood. Ostreococus tauri is a minimal microalga at the base of the green lineage, and is therefore a key organism for understanding lipid evolution. The present work reports the characterisation as well as the temperature regulation of sphingolipids and Δ8-sphingolipid desaturase from O. tauri . Complex sphingolipids are glycosylceramides with unique glycosyl moieties encompassing hexuronic acid residues, reminiscent of bacterial glucuronosylceramides, with up to three additional hexose residues. In contrast, the ceramide backbones show limited variety, with dihydroxylated C18/C18:1 EΔ8 sphingoid bases and C16:0 fatty-acyl chain being the main compounds. The sphingolipid Δ8-desaturase from O. tauri , although phylogenetically related to plant homologues has a substrate preference similar to the diatom homologue. Both sphingolipid Δ8-desaturase transcripts and sphingolipid Δ8-unsaturation are regulated in a temperature- dependent manner being higher at 14°C than 24°C. Overexpressing the sphingolipid Δ8- desaturase in O. tauri at 24°C results in higher sphingolipid unsaturation and impairs the increase in cell size, structure and chlorophyll. In particular, the cell-size defect is not detected in cells acclimated to 14°C and is furthermore suppressed upon transfer from 24°C to 14°C. Our work provides the first functional evidence for the involvement of sphingolipid Δ8-unsaturation for temperature acclimation in microalgae, suggesting that this function is an ancestral feature in the green lineage
Genuinely multi-dimensional stationarity preserving Finite Volume formulation for nonlinear hyperbolic PDEs
No full textInternational audienceClassical Finite Volume methods for multi-dimensional problems include stabilization (e.g. via a Riemann solver), that is derived by considering several one-dimensional problems in different directions. Such methods therefore ignore a possibly existing balance of contributions coming from different directions, such as the one characterizing multi-dimensional stationary states. Instead being preserved, they are usually diffused away by such methods. Stationarity preserving methods use a better suited stabilization term that vanishes at the stationary state, allowing the method to preserve it. This work presents a general approach to stationarity preserving Finite Volume methods for nonlinear conservation/balance laws. It is based on a multi-dimensional extension of the global flux approach. The new methods are shown to significantly outperform existing ones even if the latter are of higher order of accuracy and even on non-stationary solutions
Conservative models and numerical methods for pyrolysis-thermal coupling of heat shield degradation and deformations
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Sur les traces du temps
No full textInternational audienceWhat is time? Does it constitute an autonomous reality or merely a relation between beings? An irreducible element of the world, or a form of consciousness—perhaps even a subjective illusion? Does it flow toward the past or toward the future? Is it reversible or irreversible? Can it even be defined? This book sets out to reconsider these questions anew, drawing on several recent contributions from philosophy and the natural sciences. Its point of departure is the conviction that thought about time must be freed from the ontological primacy of the present, which consists either in asserting that only the present exists, relegating the past and the future to nothingness, or in conceiving them on the model of the present, of which they would be merely derivative or degraded forms. The future, the present, and the past all exist to an equal degree, but according to different modalities that this inquiry undertakes to analyze through three principal categories, united like the panels of a triptych: power, presence, and trace. While these three concepts apply first and foremost to the world of things and events, it remains, in the final stage of this work, to examine the specific form this triptych takes for human beings. In other words, how is human temporality to be characterized?Qu’est-ce que le temps ? Constitue-t-il une réalité autonome ou une simple relation entre les êtres ? Un élément irréductible du monde ou une forme de la conscience, voire une illusion subjective ? S’écoule-t-il vers le passé ou vers l’avenir ? Est-il réversible ou irréversible ? Peut-il même être défini ? Ce livre se propose d’instruire ces questions à nouveaux frais, en s’appuyant sur plusieurs apports récents de la philosophie et des sciences de la nature. Son point de départ est la conviction qu’il faut libérer la pensée du temps du primat ontologique du présent, qui consiste soit à affirmer que seul le présent existe, en reléguant le passé et l’avenir dans le néant, soit à concevoir ceux-ci sur le modèle du présent, dont ils ne seraient que des formes dérivées ou dégradées. L’avenir, le présent et le passé existent tout autant, mais selon des modalités différentes que cette enquête se donne pour tâche d’analyser selon trois catégories principales, unies comme les volets d’un triptyque : la puissance, la présence et la trace. Si ces trois concepts s’appliquent en premier lieu au monde des choses et des événements, il reste à examiner, dans la dernière étape de cet ouvrage, quelle est la forme spécifique que revêt ce triptyque pour les êtres humains. Comment, en d’autres termes, la temporalité humaine se laisse-t-elle caractériser
Rett_analysis
No full textMachine-Learning-Driven Prediction of Neurochemical Signatures in the Rett Syndrome Mouse Brai
Modulation of succinyl‐ CoA :3‐ketoacid CoA transferase activity by a single amino acid residue in acetate:succinate CoA transferase from <i>Trypanosoma brucei</i> , the causative agent of African sleeping sickness
No full textInternational audienceTrypanosomatids are protozoan parasites that remain a global health challenge due to the limited efficacy, safety, and durability of current treatments. Acetate: succinate CoA transferase (ASCT), together with succinyl-CoA synthase (SCS), forms the ASCT/SCS cycle that fuels ATP production and generates acetate, a central metabolic intermediate essential for mitochondrial pathways in these parasites. Although Trypanosoma brucei ASCT (TbASCT) shares 52% amino acid identity with mammalian succinyl-CoA:3-ketoacid CoA transferase (mSCOT), the latter catalyzes a ratelimiting step of ketone body catabolism. Because ASCT and SCOT perform distinct reactions, understanding their mechanistic divergence is crucial for identifying parasite-specific vulnerabilities and advancing selective drug discovery. Here, we report crystal structures of TbASCT bound to all substrates and products, revealing the molecular basis of substrate recognition Kota Mochizuki and Daniel Ken Inaoka have contributed equally to this study.</div
Dog therapy for dental care among autistic children: A randomized trial
No full textInternational audienceWe aimed to assess whether the presence of a therapy dog during 2 dental care sessions could facilitate subsequent dog-free dental care for anxious autistic children who had difficulty cooperating. METHODS We conducted a parallel-arm randomized trial: control group using usual behavioral strategies only and experimental group using animal-assisted therapy (AAT) strategies combined with usual behavioral strategies. All patients had 3 dental care sessions. In the experimental group, the therapy dog was present during the first 2 dental sessions, and the third dental session was dog-free. The primary outcome was the mean overall anxiety during the dog-free third treatment session. Generalized estimating equations (GEEs) were also used to account for the correlation of repeated measures. RESULTS A total of 49 patients were enrolled. The most frequently usual behavioral strategies were positive reinforcement (n = 31; 64%), hypnosis (n = 28; 58%), demystification (n = 26; 52%), and in vivo modeling (n = 25; 51%). AAT-specific strategies included imitating dog (n = 18; 69%), positive supportive reinforcement with dog incentives (n = 14; 54%), and distraction or therapeutic touch (n = 11; 42%). Mean anxiety scores were significantly lower in the experimental group during the third session (mean difference, −1.4; 95% CI, −2.43 to −0.37). GEE analysis showed a significant reduction in anxiety over time in the experimental group compared with controls (P = .0001; β = −1.03). CONCLUSION Dog served mainly as an in vivo model and positive reinforcer. Our findings suggest that AAT could play a key role in helping children acclimate to dental procedures, and, consequently, ease the transition back to conventional, animal-free dental treatments.</p
De l’image au concept, la valeur des « expériences de pensée » comme processus graduel de fictionnalité
No full textInternational audienceL’histoire des sciences, l’examen génétique des découvertes et des inventions dans l’avènement de l’esprit scientifique, nous rappellent combien l’imagination et les processus de fictionnalité, loin d’être des obstacles, constituent le nexus de la création scientifique. Maintes découvertes scientifiques relèvent le fait selon lequel l’imagination se révèle plus importante que le savoir, en raison de l’importance des expériences de pensée comme processus fictionnel lesquelles ont conduit à la résolution de problèmes fondamentaux. Mais qu’est-ce qu’une « expérience de pensée » ? Pour quelles raisons les expériences de pensée sont-elles de précieuses auxiliaires fictionnelles à la connaissance scientifique ? Comment ces fictions surviennent-elles à l’esprit scientifique en vue d’établir la vérité, relativement à des degrés possibles de fictionnalité ? Est-il possible de caractériser les « expériences de pensée » scientifiques par leurs, peu ou prou, degrés de fictionnalité ? Pour quelles raisons ? Et comment ?En effet, toute recherche ne peut déterminer absolument ce qu’elle cherche et ce qu’elle va trouver. C’est le paradoxe de toute connaissance. Les découvertes sont toujours en quelque sorte inattendues. Lorsque les scientifiques savent précisément ce qu’ils ou ce qu’elles cherchent, c’est qu’ils ou elles ont découvert intellectuellement, par hypothèse ou par un raisonnement imaginatif. Ce raisonnement imaginatif est « l’expérience de pensée » entendu comme processus fictionnel et graduel en son rapport à la connaissance et à la vérité. Est-il possible de produire une typification de ces « expériences de pensées scientifiques » comme artefacts culturels hybrides? Quelles conséquences pouvons-nous en déduire ? A l’inverse, de toute velléité à prétendre se défaire de la puissance évocatrice de l’imagination afin d’atteindre supposément une rationalité abstraite, les expériences de pensée, consacrent leurs fonctions d’opérateurs fictionnels primordiaux à l’esprit scientifiques et à ses productions. A l’égal du concept de sérendipité, les expériences de pensée, comme fictions, comme processus graduels et hétérogènes de fictionnalité soulignent la liberté créatrice de la subjectivité dans les découvertes de l’ensemble des sciences et réfèrent indéfectiblement à la fois, à une conception humaniste et graduelle de la connaissance et à une interfécondité des registres des degrés de fictionnalité et des registres critériels à l’établissement de l’idée de vérité, en termes scientifiques. C’est pourquoi, notre propos s’attachera dans un cadre comparatif et possiblement typologique, avec les expériences de pensée en philosophie, à rendre compte de la richesse et de la complexité des expériences de pensée, comme laboratoire de l’esprit scientifique, dans leurs possibles fonctions imaginatives et processuelles d’inventions, de créations, de degrés de fictionnalité en science et ce, relativement à l’avènement de l’idée de mondes possibles
