HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
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CTCF-dependent insulation of Hoxb13 and the heterochronic control of tail length
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Angiogenesis and full thickness wound repair in a cell sheet-based vascularized skin substitute
No full textInternational audienceSkin tissue engineering is undergoing tremendous expansion as a result from clinical needs, mandatory replacement of animal models and development of new technologies. Many approaches have been used to produce vascularized skin substitutes for grafting purposes showing the presence of capillary-like structures but with limited analysis of their in vitro maturation and plasticity. Such knowledge is however important for the development of tissue substitutes with improved implantation success as well as for validation of vascularization in vitro models, including as a readout in pharmacological analyses. For optimal interactions of cells with microenvironment and vasculature, we here used a cell sheet approach consisting in the sole production of matrix by the cells. In this context, we limited the density of endothelial cells seeded for self-assembly and rather relied on the stimulation of angiogenesis for the development of an extensive connected microvascular-like network. After detailed characterization of this network, we challenged its plasticity both during and after establishment of the skin substitute. We show that fine tuning of VEGF concentration and time of application differentially affects formation of capillary-like structures and their perivascular coverage. Furthermore, we performed a deep wound assay that displayed tissue repair and angiogenesis with unique characteristics of the physiological process. These studies demonstrate the importance of cell-derived microenvironment for the establishment of mature yet dynamic vascularized skin models allowing a wide range of pharmacological and basic investigations
Synthesis of biobased and versatile monomers from itaconic acid and homocysteine thiolactone and their applications in step-growth and radical polymerization approaches
No full textInternational audienceIn the context of the development of fully bio-based materials, access to multi-functional bio-based monomers represents one of the primary industrial challenges in the upcoming years. Itaconic acid and N-acetyl homocysteine thiolactone are two promising sustainable building blocks displaying complementary reactivities. In this paper, we design new sustainable monomers, β-N-homocysteine thiolactyl itaconamic acid and α,β-N,N'-homocysteine thiolactyl itaconamide, by functionalizing itaconic acid with one or two thiolactone moieties by amidification reaction in water. These synthesized monomers are very versatile bearing both an activated vinyl group that can react through either radical or Michael addition mechanisms, and a thiolactone ring, which is prone to undergo nucleophilic ring-opening reaction primary amines liberating a highly reactive thiol. The polymerizability of these two monomers was then examined according to two polymerization pathways. In a first stage, the step-growth polyaddition of both monomers according to an aminolysis-thiol-Michael addition mechanism was studied in the presence of various functional primary amines, leading to the preparation of original multi-functional oligopoly(amide-thioether)s. In a second stage, the chain-growth free radical (co)polymerization of both monomers was investigated and enabled the synthesis of COOH-containing and functionalizable polymethacrylates. All the monomer and (co)polymer structures were carefully characterized by 1H, 13C, COSY, HSQC
Molecular and genetic regulation of petal number variation
No full textInternational audienceAbstract Floral forms with an increased number of petals, also known as double-flower phenotypes, have been selected and conserved in many domesticated plants, particularly in ornamentals, because of their great economic value. The molecular and genetic mechanisms that control this trait are therefore of great interest, not only for scientists, but also for breeders. In this review, we summarize current knowledge of the gene regulatory networks of flower initiation and development and known mutations that lead to variation of petal number in many species. In addition to the well-accepted miR172/AP2-like module, for which many questions remain unanswered, we also discuss other pathways in which mutations also lead to the formation of extra petals, such as those involved in meristem maintenance, hormone signalling, epigenetic regulation, and responses to environmental signals. We discuss how the concept of ‘natural mutants’ and recent advances in genomics and genome editing make it possible to explore the molecular mechanisms underlying double-flower formation, and how such knowledge could contribute to the future breeding and selection of this trait in more crops
Découpe de matériaux souples
No full textCutting is a ubiquitous process with wide ranging implications, culturally and technologically. Experimenting on the kitchen table, we quickly learn that the easiest way to cut soft solids with a knife is by a slicing action, i.e., dragging the sharp blade over the soft surface without pushing too strongly into it; indeed, pushing the edge of a knife too strongly into a soft solid only squashes it. Moreover, applying a compression in a plane orthogonal to the direction of cutting can be of great help for guiding the cut. However, more generally the forces applied for both cutting and holding the object are responsible for uncomfortable large strains, which induce strong perturbations in the final shape of the parts. Beyond these everyday examples, the cutting of soft materials is of great interest in industrial food processing, in tissue analysis in the context of histology, etc. [1]. The initial developments of cutting science and technology were mostly devoted to metal machining and focused on plastic deformations induced by the motion of the blades though the material. The importance of fracture toughness in cutting was only acknowledged in the 60’s after the development of linear elastic fracture mechanics, leading to important advances in the understanding of cutting mechanics of more brittle materials [2]. However, a unifying physical view of cutting that may be suitable for a larger class of materials is still lacking, especially for soft materials. The standard tools of linear elastic fracture mechanics are not suited to treat a problem where the driving arises directly at the crack lips instead of remotely. The local crack fields are strongly coupled with the shape and motion of the blade, involving subtle adhesion and friction problems. In this context the fracture energy and direction of propagation are not independent of shape of the blade and new tools have to be developed to describe them. Although the case of soft materials is of particular importance for many industrial applications, very few tools are available to deal with the very strong nonlinear deformations at different scales, which make it difficult to cut parts of the desired shape and with good surface finish. This project aims at performing cutting experiments on model soft materials in controlled situations, in order to bridge this gap, while profiting of the significant advances that have recently been made on fracture and adhesion of soft dissipative materials [3]. On the one hand, we aim at clarifying the relevant notions of cutting energy and directionality of the cut as a function the shape and motion of the blade. On the other hand, was intended the development tools for predicting the final shape of the cut parts in order to allow forward design.[1] E. Reyssat, T. Tallinen,1, M. Le Merrer, and L. Mahadevan. Slicing Softly with Shear. PRL 109, 244301 (2012).[2] T. Atkins. The Science and Engineering of Cutting (2009).[3] C. Creton and M. Ciccotti. Fracture and adhesion of soft materials : a review, Reports on Progress in Physics, 79, Art N. 046601 (2016).La découpe est un processus omniprésent avec des implications étendues, tant culturellement que technologiquement. En expérimentant à la table de cuisine, nous apprenons rapidement que la manière la plus facile de couper des solides mous avec un couteau est par une action de tranchage, c'est-à-dire en faisant glisser la lame tranchante sur la surface molle sans trop pousser dessus ; en effet, pousser trop fort avec le bord d'un couteau dans un solide mou ne fait que l'écraser. De plus, l'application d'une compression dans un plan orthogonal à la direction de la coupe peut être d'une grande aide pour guider la découpe. Cependant, de manière plus générale, les forces appliquées à la fois pour la coupe et pour maintenir l'objet sont responsables de grandes contraintes inconfortables, qui induisent de fortes perturbations dans la forme finale des pièces. Au-delà de ces exemples quotidiens, la découpe des matériaux mous présente un grand intérêt dans le traitement industriel des aliments, dans l'analyse des tissus dans le contexte de l'histologie, etc. [1]. Les premiers développements de la science et de la technologie de la découpe étaient principalement consacrés à l'usinage des métaux et se concentraient sur les déformations plastiques induites par le mouvement des lames à travers le matériau. L'importance de la ténacité à la rupture dans la découpe n'a été reconnue qu'à partir des années 60, après le développement de la mécanique de la rupture élastique linéaire, ce qui a conduit à des avancées importantes dans la compréhension de la mécanique de la découpe des matériaux plus cassants [2]. Cependant, une vue physique unifiée de la découpe, adaptée à une plus large classe de matériaux, fait toujours défaut, notamment pour les matériaux mous. Les outils standards de la mécanique de la rupture élastique linéaire ne sont pas adaptés pour traiter un problème où la fissuration se produit directement au niveau des lèvres de la fissure plutôt que de manière éloignée. Les champs locaux de fissuration sont fortement couplés avec la forme et le mouvement de la lame, impliquant des problèmes subtils d'adhésion et de friction. Dans ce contexte, l'énergie de rupture et la direction de propagation ne sont pas indépendantes de la forme de la lame et de nouveaux outils doivent être développés pour les décrire. Bien que le cas des matériaux mous soit d'une importance particulière pour de nombreuses applications industrielles, très peu d'outils sont disponibles pour traiter les déformations très fortement non linéaires à différentes échelles, ce qui rend difficile la découpe de pièces de la forme désirée avec une bonne finition de surface. Ce projet vise à réaliser des expériences de découpe sur des matériaux mous modèles dans des situations contrôlées, afin de combler cette lacune, tout en profitant des avancées significatives récemment réalisées dans le domaine de la rupture et de l'adhésion des matériaux dissipatifs mous [3]. D'une part, nous visons à clarifier les notions pertinentes d'énergie de découpe et de directionnalité de la coupe en fonction de la forme et du mouvement de la lame.[1] E. Reyssat, T. Tallinen,1, M. Le Merrer, and L. Mahadevan. Slicing Softly with Shear. PRL 109, 244301 (2012).[2] T. Atkins. The Science and Engineering of Cutting (2009).[3] C. Creton and M. Ciccotti. Fracture and adhesion of soft materials: a review, Reports on Progress in Physics, 79, Art N. 046601 (2016)
Régulation du sommeil paradoxal en condition de stress : implication des projections corticales au noyau préoptique ventrolatéral
No full textAlthough much attention has been dedicated to dissect the complex circuits underlying basic sleep architecture, how sleep centers dynamically adapt to environmental challenges remains to be fully understood. The objective of this thesis was to determine, in mice, how and by which mechanisms sleep is influenced by stress.The first part of my thesis demonstrates that the social defeat stress (SDS) induces an initial state of insomnia before sleep quantities return to normal. Beside this apparent recovery, mice showed a REM sleep fragmentation that persisted many hours after SDS. Using chemogenetic inhibition, we demonstrated that prefrontal cortex (PFC) projections to the VLPO are selectively recruited under stressful situations and necessary for the SDS-induced REM sleep fragmentation. We further demonstrate that the optogenetic activation of the PFC- VLPO pathway is sufficient to mimic the REM sleep fragmentation in the absence of an actual stressor. Finally, using ex vivo optogenetics, we precise the cellular mechanism underlying this pathway by showing that the PFC directly modulates VLPO sleep-promoting neurons. Consistent with that, we show that in vivo activation of the PFC-VLPO pathway interrupts REM sleep in favor of NREM sleep, which is in line with the well established role of the VLPO. Altogether these results provide a mechanism to shorten the time spent in REM sleep, a state of great vulnerability, allowing the individual to be more responsive and ready to face a danger, without suppressing the total amount of sleep, essential for survival.In the second part of my work, we showed that the CRH-expressing neurons (VLPOCRH) were a predilection target from the PFC excitatory projections. We then investigated the role of the VLPOCRH neurons in basal sleep regulation. Our results highlight that activation of the VLPOCRH neurons strongly suppress REM sleep, favoring a more consolidated NREM sleep. However, chemogenetic inhibition of the VLPOCRH neurons had no effect on the sleep architecture.The third, and last part, of my work sought to establish a novel method to accurately and automatically classify REM sleep. Indeed, previous parts of my thesis highlighted that stress can cause REM sleep bouts to be particularly short. These brief periods can be overlooked by classical scoring methods. We developed an approach capable of capturing these fine sleep modifications and tracking parameters that can be usually subjective with manual scoring, thus ensuring maximal reproducibility.Bien que beaucoup d'attention ait été consacrée à la dissection des circuits neuronaux qui sous-tendent l’architecture du sommeil de base, les mécanismes par lesquels les centres du sommeil s’adaptent de manière dynamique aux défis environnementaux demeurent mal connus. L'objectif de cette thèse était de déterminer comment et par quels mécanismes le sommeil est influencé par le stress chez la souris.La première partie de ma thèse a mis en évidence que le stress de défaite sociale (SDS) induit un état initial et transitoire d'insomnie, suivi d’un retour à des quantités de sommeil normales. Malgré cette récupération apparente, les souris ont montré une fragmentation du sommeil paradoxal qui a persisté plusieurs heures après le SDS. Grâce à l'inhibition chémogénétique, nous avons démontré que les projections du cortex préfrontal (PFC) vers le noyau préoptique ventrolatéral (VLPO) sont recrutées sélectivement dans des situations stressantes et sont nécessaires à la fragmentation du sommeil paradoxal induite par le SDS. De plus, nous avons montré que l’activation de la voie PFC-VLPO est suffisante pour imiter la fragmentation du sommeil paradoxal en l'absence d’un stress. Grâce à une approche optogénétique ex vivo, nous avons précisé le mécanisme cellulaire sous-jacent à cette voie en montrant que le PFC module directement les neurones promoteurs de sommeil du VLPO. En outre, l'activation in vivo de la voie PFC-VLPO interrompt le sommeil paradoxal au profit du sommeil lent, ce qui est en accord avec le rôle bien établi du VLPO. L'ensemble de ces résultats suggère un mécanisme limitant le temps passé en sommeil paradoxal, un état de forte vulnérabilité, qui permettrait à l'individu d'être plus réactif et prêt à affronter un danger ; sans toutefois supprimer la quantité totale de sommeil, indispensable à la survie.Dans la deuxième partie de mon travail, nous avons montré que les neurones du VLPO exprimant le CRH (VLPOCRH) étaient une cible privilégiée des projections excitatrices du PFC. Nos résultats mettent en évidence que l'activation chémogénétique des neurones VLPOCRH diminue fortement le sommeil paradoxal au profit d’un sommeil lent plus consolidé. Cependant, leur inhibition chémogénétique n'a eu aucun effet sur l'architecture du sommeil, suggérant que ces neurones ne seraient pas actifs de manière tonique en condition normale/ non stressante.La troisième et dernière partie de mon travail a consisté à développer une nouvelle méthode de classification précise et automatique du sommeil paradoxal. En effet, les parties précédentes de ma thèse ont mis en évidence que le stress peut entraîner des périodes de sommeil paradoxal particulièrement brèves qui peuvent être négligées par les méthodes de classification classiques. J’ai donc mis au point une approche permettant de capturer les fines modifications du sommeil et de quantifier les paramètres qui peuvent être subjectifs avec une classification manuelle. Ces résultats s’inscrivent donc dans une démarche de reproductibilité maximale
Complementary Speckle STED Microscopy
No full textInternational audienceStimulated Emission Depletion (STED) microscopy has emerged as a powerful technique providing visualization of biological structures at the molecular level in living samples. In this technique, the diffraction limit is broken by selectively depleting the fluorophore's excited state by stimulated emission, typically using a donut-shaped optical vortex beam. STED microscopy performs unrivalably well in degraded optical conditions such as living tissues. Nevertheless, photo-bleaching and acquisition time are among the main challenges for imaging large volumetric field of views. In this regard, random light beams like speckle patterns have proved to be especially promising for three-dimensional imaging in compressed sensing schemes. Taking advantage of the high spatial density of intrisic optical vortices in speckles -- the most commonly used beam spatial structure used in STED microscopy -- we propose here a novel scheme consisting in performing STED microscopy using speckles. Two speckle patterns are generated at the excitation and the depletion wavelengths, respectively, exhibiting inverted intensity contrasts. We illustrate spatial resolution enhancement using complementary speckles as excitation and depletion beam on both fluorescent beads and biological samples. Our results establish a robust method for super-resolved three-dimensional imaging with promising perspectives in terms of temporal resolution and photobleaching
Influence of interface voltage on charge build-up under high voltage
No full textInternational audienceThe interface voltage appearing when two materials are brought into contact was measured with a high sensitive pressure-wave-propagation measurement setup in various low density and high density polyethylene samples coated either with aluminum or gold electrodes. The samples were then tested under high voltage (40 kV/mm) for 24 h to assess the correlation between interface voltage and charge injection at 22 °C. Aluminum electrodes induce a positive interface voltage toward the insulator favoring electron injection at the cathode while gold electrodes induce a negative interface voltage toward the insulator favoring hole injection at the anode. After the injections due to interface voltage, charges diffuse more easily in low density polyethylene that triggers a subsequent injection due to heterocharges buildup
Dépendance de la vitesse de déformation et de la composition des verres silicatés sur leurs mécanismes de plasticité
No full textUnderstanding the mechanisms of glass fracture is crucial due to the extensive industrial applications of these materials, where the control of their mechanical properties is key to ensuring performance and durability. In-depth examination of plasticity mechanisms under indentation in aluminoborosilicate glasses has highlighted the critical role of chemical composition in mechanical behavior and crack resistance. It has been observed that the presence and relative concentration of network modifiers, such as alkaline earth oxides, or a higher concentration of boron as a network former, significantly influence localized plastic flow in the form of shear bands, as well as the resistance to crack initiation and propagation. This suggests that precise adjustments in composition can enhance the material's resilience under mechanical stress. Additionally, a series of mechanical and thermal characterizations of these glasses have established correlations between their structure and mechanical behavior under indentation. Furthermore, the study of the effects of electron irradiation on the plasticity of silicate glasses revealed that exposure to electrons can increase these materials' susceptibility to plastic deformation, altering their microscopic structure and mechanical properties. It was found that electron irradiation catalyzes structural rearrangements under stress, leading to a marked decrease in the yield stress of silicate glasses. These changes were analyzed through advanced relaxation and deformation models, allowing for the quantification and prediction of irradiation's impact on glass behavior. This work advances the understanding of plasticity processes in glasses and paves the way for strategies to optimize their mechanical properties, particularly by designing specific compositions to enhance their resistance in demanding industrial environments or under severe conditions.Comprendre les mécanismes de rupture des verres est d'une importance cruciale en raison des vastes applications industrielles de ces matériaux, où la maîtrise de leurs propriétés mécaniques détermine leur performance et leur durabilité. L'examen approfondi des mécanismes de plasticité sous indentation dans les verres aluminoborosilicatés a mis en évidence le rôle déterminant de la composition chimique sur le comportement mécanique et à la rupture. Il est apparu que la présence et la concentration relative de modificateurs de réseau tels que les oxydes alcalino-terreux, ou bien une plus grande concentration de bore en tant que formateur de réseau, influencent significativement l'écoulement plastique localisé sous forme de bandes de cisaillement ainsi que la résistance à l'initiation et à la propagation des fissures, suggérant que des ajustements précis de la composition peuvent améliorer la résistance de ces matériaux face aux sollicitations mécaniques. D'autre part, un ensemble de caractérisations mécaniques et thermiques de ces verres a permis d'établir des premières corrélations entre leur structure et leur comportement mécanique sous indentation. Par ailleurs, l'étude de l'effet de l'irradiation électronique sur la plasticité des verres silicatés a révélé que l'exposition aux électrons peut accroître la sensibilité de ces matériaux à la déformation plastique, modifiant leur structure microscopique et leurs propriétés mécaniques. Il s'est avéré que l'irradiation électronique catalyse les réarrangements structuraux, sous contrainte, liés à la plasticité, entraînant une nette diminution de la limite d'élasticité du verre silicaté. Ces modifications ont été analysées à travers des modèles avancés de relaxation et de déformation, permettant de quantifier et de prévoir l'impact de l'irradiation sur le comportement des verres. Ces travaux contribuent à la compréhension des processus de plasticité dans les verres et ouvrent la voie à des stratégies d'optimisation de leurs propriétés mécaniques, notamment en concevant des compositions spécifiques pour renforcer leur résistance dans des environnements industriels exigeants ou soumis à des conditions sévères
