Inferring the flow properties of epithelial tissues from their geometry

Amorphous materials exhibit complex material properties with strongly nonlinear behaviors. Below a yield stress they behave as plastic solids, while they start to yield above a critical stress sigma(c). A key quantity controlling plasticity which is, however, hard to measure is the density P(x) of weak spots, where x is the additional stress required for local plastic failure. In the thermodynamic limit P(x) similar to x(theta) is singular at x = 0 in the solid phase below the yield stress sigma(c). This singularity is related to the presence of system spanning avalanches of plastic events. Here we address the question if the density of weak spots and the flow properties of a material can be determined from the geometry of an amorphous structure alone. We show that a vertex model for cell packings in tissues exhibits the phenomenology of plastic amorphous systems. As the yield stress is approached from above, the strain rate vanishes and the avalanches size S and their duration tau diverge. We then show that in general, in materials where the energy functional depends on topology, the value x is proportional to the length L of a bond that vanishes in a plastic event. For this class of models P(x) is therefore readily measurable from geometry alone. Applying this approach to a quantification of the cell packing geometry in the developing wing epithelium of the fruit fly, we find that in this tissue P(L) exhibits a power law with exponents similar to those found numerically for a vertex model in its solid phase. This suggests that this tissue exhibits plasticity and non-linear material properties that emerge from collective cell behaviors and that these material properties govern developmental processes. Our approach based on the relation between topology and energetics suggests a new route to outstanding questions associated with the yielding transition

Molecular, biochemical and behavioural evidence for a novel oxytocin receptor and serotonin 2C receptor heterocomplex

The complexity of oxytocin-mediated functions is strongly associated with its modulatory effects on other neurotransmission systems, including the serotonin (5-hydroxytryptamine, 5-HT) system. Signalling between oxytocin (OT) and 5-HT has been demonstrated during neurodevelopment and in the regulation of specific emotion-based behaviours. It is suggested that crosstalk between neurotransmitters is driven by interaction between their specific receptors, particularly the oxytocin receptor (OTR) and the 5-hydroxytryptamine 2C receptor (5-HTR2C), but evidence for this and the downstream signalling consequences that follow are lacking. Considering the overlapping central expression profiles and shared involvement of OTR and 5-HTR2C in certain endocrine functions and behaviours, including eating behaviour, social interaction and locomotor activity, we investigated the existence of functionally active OTR/5-HTR2C heterocomplexes. Here, we demonstrate evidence for a potential physical interaction between OTR and 5-HTR2C in vitro in a cellular expression system using flow cytometry-based FRET (fcFRET). We could recapitulate this finding under endogenous expression levels of both receptors via in silico analysis of single cell transcriptomic data and ex vivo proximity ligation assay (PLA). Next, we show that co-expression of the OTR/5-HTR2C pair resulted in a significant depletion of OTR-mediated G alpha q-signalling and significant changes in receptor trafficking. Of note, attenuation of OTR-mediated downstream signalling was restored following pharmacological blockade of the 5-HTR2C. Finally, we demonstrated a functional relevance of this novel heterocomplex, in vivo, as 5-HTR2C antagonism increased OT-mediated hypoactivity in mice. Overall, we provide compelling evidence for the formation of functionally active OTR/5-HTR2C heterocomplexes, adding another level of complexity to OTR and 5-HTR2C signalling functionality.This article is part of the special issue on Neuropeptides

Les hydrocarbures aromatiques polycycliques dans l'environnement : la réhabilitation des anciens sites industriels The Polycyclic Aromatic Hydrocarbons in the Environment : the Former Industrial Sites Remediation

Les hydrocarbures aromatiques polycycliques ou HAP peuvent être d'origine naturelle mais ils proviennent principalement des processus de pyrolyse. On peut les retrouver dans les sols de certains anciens sites industriels. Cela peut être le cas des sites d'anciennes usines à gaz. Même si aucune conséquence sur la santé humaine n'a été signalée et même si les risques paraissent virtuels, le principe de précaution rend nécessaire de s'occuper des risques liés à ces anciens sites industriels. Gaz de France, propriétaire de 467 sites d'anciennes usines à gaz assume l'héritage industriel dans le cadre d'un protocole signé avec le ministère de l'Environnement. Après une étude des sols, une évaluation des risques est réalisée. En fonction des résultats de cette évaluation des risques et de l'usage du site (actuel et prévu), des solutions de traitement peuvent être mises en Suvre. Parmi les techniques applicables aux sols pollués par des HAP, un intérêt particulier s'est porté sur les traitements biologiques, en pleine évolution, qui offrent une solution économique bien adaptée au traitement de grands volumes de sols souillés par une pollution organique moyennement concentrée. <br> Polycyclic aromatic hydrocarbons (PAHs) can be found under natural conditions but they can be produced by pyrolysis processes. They can be found in former industrial sites subsoil, especially on Manufactured Gas Plant sites (MGP sites). Gaz de France has inherited the patrimony of former French gas companies on nationalisation in 1946; consequently, Gaz De France is still the owner of 467 of manufactured gas plants. Even if no impact on human health has been detected and even if the risks seem to be virtual, Gaz de France has to prevent any environmental consequence due to the possible presence of residues in the subsoil of the sites: a protocol has been signed with the French Ministry of Environment. Following the investigations on the site, a risk assessment, which takes into account the future use of the site, is achieved. The definition of remediation and monitoring of the site is based on risk assessment; the pollution is treated on the basis of specifications defined in accordance with public authorities. Biotreatments are potentially the most well adapted techniques to remediate big volumes of low or medium contaminated soils

Modélisation bidimensionnelle dynamique du transistor à effet de champ MESFET : application à la conception de profils optimisés pour fonctionnement en faible bruit

Un modèle de simulation numérique de transistor à effet de champ basé sur une résolution bidimensionnelle des équations des semiconducteurs est présenté. Il inclut les effets de dynamique non stationnaire et permet l'étude du comportement des composants tant en régime statique que dynamique (petit et grand signal, impulsionnel). Il est montré comment on peut accéder aux paramètres caractéristiques du régime petit signal, grâce à l'utilisation d'une transformation de Fourier rapide. Ce modèle est utilisé pour étudier l'influence du profil de dopage sur les éléments caractéristiques du comportement des composants et sur leurs performances potentielles. Il permet de mettre en évidence l'intérêt des composants à canal enterré tant pour l'amplification de puissance que pour l'amplification faible bruit, ce qui est clairement confirmé par les premiers résultats de l'étude expérimentale

Modélisation bidimensionnelle dynamique du transistor à effet de champ MESFET : application à la conception de profils optimisés pour fonctionnement en faible bruit

A GaAs MESFET model, based on the two dimensional resolution of the semiconductor hydrodynamic equations, is presented. It includes a carrier energy relaxation equation, allowing to account for non stationary electron dynamic effects. It is shown that it is possible to obtain an accurate determination of the main equivalent circuit elements by using transient response and fast Fourier transform. This model is systematically used to study the influence of doping profile on device characteristics and the expected performances. The potential interest of burried channel devices is clearly shown under large signal and low noise conditions respectively. These conclusions are confirmed by experiment.Un modèle de simulation numérique de transistor à effet de champ basé sur une résolution bidimensionnelle des équations des semiconducteurs est présenté. Il inclut les effets de dynamique non stationnaire et permet l'étude du comportement des composants tant en régime statique que dynamique (petit et grand signal, impulsionnel). Il est montré comment on peut accéder aux paramètres caractéristiques du régime petit signal, grâce à l'utilisation d'une transformation de Fourier rapide. Ce modèle est utilisé pour étudier l'influence du profil de dopage sur les éléments caractéristiques du comportement des composants et sur leurs performances potentielles. Il permet de mettre en évidence l'intérêt des composants à canal enterré tant pour l'amplification de puissance que pour l'amplification faible bruit, ce qui est clairement confirmé par les premiers résultats de l'étude expérimentale

Comparative functional anatomy using rigid multibody simulation and anatomical transfer: Homo sapiens, Pan paniscus and Papio anubis

International audienc

Ectopic expression of Pax4 in pancreatic δ cells results in β-like cell neogenesis

The recent demonstration that pancreatic a cells can be continuously regenerated and converted into beta-like cells upon ectopic expression of Pax4 opened new avenues of research in the endocrine cell differentiation and diabetes fields. To determine whether such plasticity was also shared by delta cells, we generated and characterized transgenic animals that express Pax4 specifically in somatostatin-expressing cells. We demonstrate that the ectopic expression of Pax4 in d cells is sufficient to induce their conversion into functional beta-like cells. Importantly, this conversion induces compensatory mechanisms involving the reactivation of endocrine developmental processes that result in dramatic beta-like cell hyperplasia. Importantly, these beta-like cells are functional and can partly reverse the consequences of chemically induced diabetes