Selective nanomanipulation using optical forces

We present a detailed theoretical study of the recent proposal for selective nanomanipulation of nanometric particles above a substrate using near-field optical forces [Chaumet {\it et al.} Phys. Rev. Lett. {\bf 88}, 123601 (2002)]. Evanescent light scattering at the apex of an apertureless near-field probe is used to create an optical trap. The position of the trap is controlled on a nanometric scale via the probe and small objects can be selectively trapped and manipulated. We discuss the influence of the geometry of the particles and the probe on the efficiency of the trap. We also consider the influence of multiple scattering among the particles on the substrate and its effect on the robustness of the trap.Comment: 12 pages, 17 figure

Discrete dipole approximation in time domain through the Laplace transform

We present a form of the discrete dipole approximation for electromagnetic scattering computations in time domain. We show that the introduction of complex frequencies, through the Laplace transform, significantly improves the computation time. We also show that the Laplace transform and its inverse can be combined to extract the field inside a scatterer at a real resonance frequenc

First-principles method for high-QQ photonic crystal cavity mode calculations

We present a first-principles method to compute radiation properties of ultra-high quality factor photonic crystal cavities. Our Frequency-domain Approach for Radiation (FAR) can compute the far-field radiation pattern and quality factor of cavity modes $\sim 100$ times more rapidly than conventional finite-difference time domain calculations. It also provides a simple rule for engineering the cavity's far-field radiation pattern

Retrograde trafficking of β-dystroglycan from the plasma membrane to the nucleus

β-Dystroglycan (β-DG) is a transmembrane protein with critical roles in cell adhesion, cytoskeleton remodeling and nuclear architecture. This functional diversity is attributed to the ability of β-DG to target to, and conform specific protein assemblies at the plasma membrane (PM) and nuclear envelope (NE). Although a classical NLS and importin α/β mediated nuclear import pathway has already been described for β-DG, the intracellular trafficking route by which β-DG reaches the nucleus is unknown. In this study, we demonstrated that β-DG undergoes retrograde intracellular trafficking from the PM to the nucleus via the endosome-ER network. Furthermore, we provided evidence indicating that the translocon complex Sec61 mediates the release of β-DG from the ER membrane, making it accessible for importins and nuclear import. Finally, we show that phosphorylation of β-DG at Tyr890 is a key stimulus for β-DG nuclear translocation. Collectively our data describe the retrograde intracellular trafficking route that β-DG follows from PM to the nucleus. This dual role for a cell adhesion receptor permits the cell to functionally connect the PM with the nucleus and represents to our knowledge the first example of a cell adhesion receptor exhibiting retrograde nuclear trafficking and having dual roles in PM and NE

L-Ilf3 and L-NF90 Traffic to the Nucleolus Granular Component: Alternatively-Spliced Exon 3 Encodes a Nucleolar Localization Motif

Ilf3 and NF90, two proteins containing double-stranded RNA-binding domains, are generated by alternative splicing and involved in several functions. Their heterogeneity results from posttranscriptional and posttranslational modifications. Alternative splicing of exon 3, coding for a 13 aa N-terminal motif, generates for each protein a long and short isoforms. Subcellular fractionation and localization of recombinant proteins showed that this motif acts as a nucleolar localization signal. Deletion and substitution mutants identified four arginines, essential for nucleolar targeting, and three histidines to stabilize the proteins within the nucleolus. The short isoforms are never found in the nucleoli, whereas the long isoforms are present in the nucleoplasm and the nucleoli. For Ilf3, only the posttranslationally-unmodified long isoform is nucleolar, suggesting that this nucleolar targeting is abrogated by posttranslational modifications. Confocal microscopy and FRAP experiments have shown that the long Ilf3 isoform localizes to the granular component of the nucleolus, and that L-Ilf3 and L-NF90 exchange rapidly between nucleoli. The presence of this 13 aminoacid motif, combined with posttranslational modifications, is responsible for the differences in Ilf3 and NF90 isoforms subcellular localizations. The protein polymorphism of Ilf3/NF90 and the various subcellular localizations of their isoforms may partially explain the various functions previously reported for these proteins

Gender Differences in Sleep Deprivation Effects on Risk and Inequality Aversion: Evidence from an Economic Experiment

Excessive working hours—even at night—are becoming increasingly common in our modern 24/7 society. The prefrontal cortex (PFC) is particularly vulnerable to the effects of sleep loss and, consequently, the specific behaviors subserved by the functional integrity of the PFC, such as risk-taking and pro-social behavior, may be affected significantly. This paper seeks to assess the effects of one night of sleep deprivation on subjects’ risk and social preferences, which are probably the most explored behavioral domains in the tradition of Experimental Economics. This novel cross-over study employs thirty-two university students (gender-balanced) participating to 2 counterbalanced laboratory sessions in which they perform standard risk and social preference elicitation protocols. One session was after one night of undisturbed sleep at home, and the other was after one night of sleep deprivation in the laboratory. Sleep deprivation causes increased sleepiness and decreased alertness in all subjects. After sleep loss males make riskier decisions compared to the rested condition, while females do the opposite. Females likewise show decreased inequity aversion after sleep deprivation. As for the relationship between cognitive ability and economic decisions, sleep deprived individuals with higher cognitive reflection show lower risk aversion and more altruistic behavior. These results show that one night of sleep deprivation alters economic behavior in a gender-sensitive way. Females’ reaction to sleep deprivation, characterized by reduced risky choices and increased egoism compared to males, may be related to intrinsic psychological gender differences, such as in the way men and women weigh up probabilities in their decision-making, and/or to the different neurofunctional substrate of their decision-making.The authors acknowledge financial support from the Spanish Ministry of Economic Competititveness (ECO2012-34928), Italian Ministry of University and Research MIUR (PRIN 20103S5RN3_002), Generalitat Valenciana (Research Projects Gruposo3/086), the Instituto Valenciano de Investigaciones Económicas (IVIE), and the Ministero della Salute (RF-2009-1528677)

Transfert et distribution des pesticides dans les biofilms en lien avec les effets toxiques associés

Fiche techniqueEn 2000, la Directive Cadre sur l'Eau a exigé le retour au bon état chimique et écologique des cours d'eau. Elle a notamment classé 45 substances comme étant prioritaires pour cette évaluation (directive 2013/39/UE), dont en grande partie des pesticides. En effet, en raison de leur utilisation massive, on retrouve aujourd'hui ces contaminants dans tous les compartiments de l'environnement. Par ailleurs, au vu de sa capacité à intégrer les contaminations, le biofilm est considéré comme un excellent bioindicateur pour l'évaluation de la qualité de l'eau (Edwards & Kjellerup, 2013). Celui-ci est à la base de la chaîne trophique dans les milieux aquatiques (Mora-Gómez et al., 2016) et se compose de microorganismes (microalgues, bactéries, champignons, etc...) enchâssés dans une matrice de substances polymériques extracellulaires (EPS) (Bonnineau et al., accepté). Mes recherches de doctorat ont porté sur l'étude des mécanismes de transfert et de distribution des pesticides dans les biofilms en lien avec les effets toxiques associés. Ces travaux ont été réalisés avec une approche toxicocinétique par laquelle la bioaccumulation du diuron (un herbicide inhibiteur de la photosynthèse) a été suivie dans les différents compartiments du biofilm mature (Figure 1). Ce suivi a été réalisé sous plusieurs conditions abiotiques (vitesses de courant, températures et photopériodes) pour différentes durées d'exposition. En parallèle, des descripteurs fonctionnels et structuraux ont été mesurés comme des activités photosynthétique (pour les communautés autotrophes) et enzymatiques (pour les communautés hétérotrophes), ainsi que la biomasse totale, la production de protéines et de polysaccharides

Transfert du diuron dans les biofilms fluviaux : constantes d’accumulation et de distribution dans la matrice, puis impacts toxiques associés

National audienceDans cette étude on s’intéresse à la distribution et au transfert des pesticides dans le biofilm en lien avec les effets toxiques associés. Le biofilm est à la base de la chaine trophique, il représente un bon bioindicateur de la contamination aquatique en raison de sa capacité à réagir aux contaminants et à intégrer les pollutions. Il est de plus en plus utilisé en écotoxicologie pour évaluer la qualité de l’eau et les risques associés aux contaminants (métaux, composés pharmaceutiques, pesticides..). Les pesticides étudiés ici sont le diuron, l’une des substances classées prioritaires par la DCE, et ses deux principaux métabolites. Il s’agit d’un herbicide inhibiteur de la photosynthèse utilisé jusqu’en 2008 dans les cultures d’arbres fruitiers, de légumes, de lentilles, de cannes à sucre, ou encore comme désherbant dans les viticultures et les voies ferrées. Cette étude porte sur la détermination des constantes cinétiques et d’équilibre du diuron dans le biofilm, sur une durée expérimentale de 7 jours. Une expérimentation a été menée en bioréacteur annulaire avec une exposition du biofilm à ces composés à la concentration nominale de 5 µg/L. En conditions abiotiques, la sorption du diuron après équilibrage du système sur les parois du bioréacteur et les coupons utilisés comme substrat pour le biofilm n’est pas significative. En présence de biofilm, l’équilibre est atteint rapidement pour les trois molécules testées, et les constantes cinétiques d’accumulation et d’élimination ont pu être déterminées. En parallèle, l’impact biologique a été évalué par la mesure de l’inhibition de la photosynthèse. Trois phases ont été mises en évidence: (1) inhibition précoce (en quelques heures), laissant supposer une internalisation rapide des contaminants dans les cellules, (2) une stabilisation de l’inhibition autour de 20% d’effet, (3) une récupération (au bout de quelques jours) qui pourrait être liée à l’adaptation des microorganismes. Par ailleurs, le biofilm étant composé de microorganismes (microalgues, bactéries, champignons) et d’une matrice EPS (substances polymériques extracellulaires), contenant des espaces interstitiels (canaux de pores) pouvant retenir de l’eau, il est primordial de caractériser la distribution du diuron dans les différentes fractions : dans l’eau interstitielle, les EPS (capsulaires et colloïdales), et à l’intérieur des cellules. L’abattement du diuron dans l’eau en fonction du temps est à déterminer, ainsi que sa bioaccumulation dans le biofilm. Ceci permet d’obtenir une vision générale quant à la répartition et l’accumulation des pesticides dans le biofilm

Utilisation des courbes temps-réponse pour l'évaluation des effets à court-terme du diuron sur les biofilms

International audienceDiuron-induced photosynthesis inhibition of freshwater biofilms and subsequent EC50s (half maximal effective concentrations) are determined using a 3-hour exposure in average. However, given the known rapid action of diuron, earlier responses can be expected. In this study, we performed different time-response experiments to confirm the short time lag for diuron to reach its cellular target, and to assesss whether time-response curves (i.e. photosynthesis inhibition as a function of time, when diuron exposure is kept constant) can improve the assessment of short-time (pulse) pre-exposure to diuron. Our results demonstrated that: i) diuron reaches its cellular target in a very short time-span (100µg.L-1) to 7:20 minutes (exposure to EC25). We were also able to demonstrate previous pulsed (3 hours) exposure to increasing concentrations of diuron (0, 5 and 50µg.L-1) using time-responses curves, providing a new, easy-to-implement, method to assess short-term exposure to PSII inhibitors based on community photosynthesis

Isothermes de sorption du diuron dans les biofilms d'eau douce

International audienceIn 2000, the EU Water Framework Directive (directive 2000/06/EC) was implemented with the objective of reaching the good ecological status of rivers. 45 chemicals were indexed as priority including 19 pesticides. The biofilm is at the basis of the trophic chain in aquatic environments and considered as an excellent bioindicator for water quality assessment (Edwards and Kjellerup 2013) because of its ability to integrate contamination (Vercraene-Eairmal et al. 2010). In this study, we used a photosynthesis inhibitor herbicide: diuron, one of the priority substances to the EU Water Framework Directive. Previous experiments carried out in order to characterize diuron bioaccumulation in biofilms, with two different exposure concentrations, suggest that pesticide uptake by microorganisms was not proportional to contaminant concentration in the water. For this experiment, we supposed that diuron absorption isotherms are not linear, and in order to confirm this hypothesis, bioaccumulation and toxic impact were simultaneously assessed at the equilibrium. To that aim, mature biofilm previously grown on glass slides during one month was exposed in channels at 8 increasing concentrations of diuron: 0, 1, 5, 10, 25, 50, 75 and 500 µg.L-1 for two hours, with a flow velocity of 2 cm.s-1. Then, Langmuir isotherm equation (Praus et al. 2007) was fitted to the bioaccumulation data. Diuron bioaccumulation in biofilm at equilibrium was not linear. A plateau was reached over 5 µg.L-1 of diuron in the water. This suggested that all absorption sites were saturated, and then diuron concentration in the biofilm became independent of diuron concentration in the water. The fitting of a Langmuir isotherm allowed to estimate a maximal diuron concentration in biofilm at 2073 µg.g-1, and the equilibrium constant at 0.378. Photosynthesis inhibition was correlated (R²=0.75) to diuron concentration in the water. The data didn't clearly highlighted a relationship between bioaccumulation and photosynthesis inhibition. This study establishes that diuron bioaccumulation in biofilm is nonlinear, and allows to calculate the equilibrium constant and maximal amount of diuron potentially accumulated in biofilm. These two constants can be used to further predict diuron concentrations in biofilm from diuron concentration in the water. The coupling of toxicokinetic and toxicodynamic approach provides original information about pesticide behaviour and impact in periphytic microorganisms