Dbl3 drives Cdc42 signaling at the apical margin to regulate junction position and apical differentiation

Epithelial cells develop morphologically characteristic apical domains that are bordered by tight junctions, the apical-lateral border. Cdc42 and its effector complex Par6-atypical protein kinase c (aPKC) regulate multiple steps during epithelial differentiation, but the mechanisms that mediate process-specific activation of Cdc42 to drive apical morphogenesis and activate the transition from junction formation to apical differentiation are poorly understood. Using a small interfering RNA screen, we identify Dbl3 as a guanine nucleotide exchange factor that is recruited by ezrin to the apical membrane, that is enriched at a marginal zone apical to tight junctions, and that drives spatially restricted Cdc42 activation, promoting apical differentiation. Dbl3 depletion did not affect junction formation but did affect epithelial morphogenesis and brush border formation. Conversely, expression of active Dbl3 drove process-specific activation of the Par6-aPKC pathway, stimulating the transition from junction formation to apical differentiation and domain expansion, as well as the positioning of tight junctions. Thus, Dbl3 drives Cdc42 signaling at the apical margin to regulate morphogenesis, apical-lateral border positioning, and apical differentiation

Persistence of blood paste proteins in a dry white wine after clarification

Until the end of 1997, plasmatic proteins and blood cells could be used to clarify wines. The aim of our work was to study the persistence of these animal proteins in a dry white wine during clarification. The effects of some clarification parameters were also estimated. We used two protocols to discriminate between blood paste proteins and native proteins of unclarified wine (e.g. from grapes, yeasts, bacteria). The first protocol was a radiolabel of blood paste proteins with chloroglycouril and Na125I. The 125I-labelled animal proteins were revealed with autoradiography of sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and quantified with a gamma scintillator. The second protocol was purification with affinity chromatography. The antibodies of this affinity chromatography were specific of whole beef serum. After this purification, harvested proteins were loaded onto two-dimensional gel electrophoresis (2D). After migration, proteins were silver-stained. With the radiolabel protocol, we show that the concentration of animal proteins found in dry white wine after clarification and filtration increased with the concentration of blood paste proteins used during clarification. This relation is almost linear. The duration of the blend blood paste / wine incubation step is also a significant parameter. After incubation for one minute, about 40 p. cent of animal proteins were found in clarified and filtered wine. After four days of incubation, a maximum of 88 p. cent blood paste proteins were found in both clarified and filtered wine. The use of bentonite decreased 4-to 6-fold the concentration of blood paste proteins. The filtration step also strongly decreased the concentration of these proteins : quantitation with a phosphoimager showed that wine clarified (with 250 μg of blood paste proteins in 4 heures of incubation time, without bentonite) and filtered retained 6 p. cent, i.e. 12 mg of blood paste proteins. The membrane porosity (0,2 or 0,45 μ) for the filtration had no effect. Affinity chromatography and 2D procedures also showed that proteins of animal origin could subsist in wine after clarification, while others in the original composition of wine disappeared

Utilisation de quelques éléments minéraux dans la différenciation des vins de Galice

La composition métallique de 44 vins de 6 cépages différents a été étudiée. Tous les cépages ont été cultivés sur le même type de terrain avec des conditions identiques. Les vins ont été élaborés en suivant les mêmes procédés de vinification. Les techniques de pattern recognition (analyse en composantes principales, analyse discriminante et KNN) ont été appliquées aux données métalliques obtenues. La teneur métallique des vins est en rapport avec le cépage correspondant pour Mencía, Godello et Jerez. Des teneurs métalliques similaires ont été trouvées dans les vins des cépages Treixadura, Torrontés et Dona Branca

Test particle dynamics in low-frequency tokamak turbulence

International audienceWe study the evolution of one million test particles in a turbulent plasma simulation, using the gyrokinetic code Trapped Element REduction in Semi-Lagrangian Approach (TERESA), as a method to get insights into the type of transport governing the plasma. TERESA (Trapped Element REduction in Semi-Lagrangian Approach) is a collisionless global 4D code which treats the trapped particles kinetically, while the passing particles are considered adiabatic. The Vlasov-Poisson system of equations is averaged over the cyclotron and the trapped particle's bounce motion, and thus, the model focuses on slow phenomena of the order of the toroidal precession motion of the banana orbits. We initialize the test particles, which are de facto “test banana-centers,” at a time of the simulation when the plasma is turbulent. We impose an initial temperature and density gradients, and only the Trapped Ion Mode (TIM) instability can develop in this system. We then calculate the Mean Squared Displacement of the test particles as a function of time in order to obtain a random walk diffusion coefficient. We observe that the radial diffusion of the test particles depends on their toroidal precession kinetic energy (E), in such a way that the transport of particles is dominated by a strong, relatively narrow peak at the resonant energies. A radial particle diffusion flux is then calculated and compared to the total radial particle flux accounting for all the transport processes such as diffusion and advection which is obtained directly from the TERESA code. We can thus compare the diffusive contribution to the particle flux against the nondiffusive contributions. The results show that the total flux is essentially diffusive which is consistent with our simulation setup aiming for “global turbulence.” Both fluxes present a peak around a resonance energy ER≈1.74Ti between the TIM and the particles. Both thermal and high-energy particles do not contribute significantly to radial transpor

Diffusive impurity transport driven by trapped particle turbulence in tokamak plasmas

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Impurity density gradient influence on trapped particle modes

International audienceThe effect of the presence of an impurity species on the trapped particle turbulence is studied using the gyro-bounce kinetic code TERESA, which allows the study of Trapped Electron Modes and Trapped Ion Modes. The impurity species is treated self-consistently and its influence on the nature of the turbulence, ion driven or electron driven, is investigated. It is found that the presence of heavy impurities with a flat density profile tends to stabilize the both electron and ion modes, whereas a peaked or hollow impurity density profile can change the turbulence from an electron driven turbulence to an ion driven turbulence. The effect of the turbulence regime on impurity transport is studied