A novel chemoenzymatic glycosylation strategy: application to lysozyme modification

AbstractHen egg lysozyme has been non-specifically glycosylated using a novel two-step strategy. First, a number of sucrose molecules have been chemically bound to the protein surface lysines, then the glycosidic chains have been enzymically lengthened, using a glycosyltransferase. For this task, a fructosyltransferase and a levansucrase have been tested, the latter appearing as the most effective one. In all cases, reactions have been optimised and several degrees of modification have been obtained. Finally, the effects of the modifications on lysozyme hydrophobicity, hydrolytic activity, hydrolysis substrate affinity and thermostability have been assessed

Metamorphosis-Induced Changes in the Coupling of Spinal Thoraco-Lumbar Motor Outputs During Swimming in Xenopus laevis

International audienceBeyeler A, Métais C, Combes D, Simmers J, Le Ray D. Metamorphosis induced changes in the coupling of spinal thoraco-lumbar motor outputs during swimming in Xenopus laevis. Anuran metamorphosis includes a complete remodeling of the animal's biomechanical apparatus, requiring a corresponding functional reorganization of underlying central neural circuitry. This involves changes that must occur in the coordination between the motor outputs of different spinal segments to harmonize locomotor and postural functions as the limbs grow and the tail regresses. In premetamorphic Xenopus laevis tadpoles, axial motor output drives rostrocaudally propagating segmental myotomal contractions that generate propulsive body undulations. During metamorphosis, the anterior axial musculature of the tadpole progressively evolves into dorsal muscles in the postmetamorphic froglet in which some of these back muscles lose their implicit locomotor function to serve exclusively in postural control in the adult. To understand how locomotor and postural systems interact during locomotion in juvenile Xenopus, we have investigated the coordination between postural back and hindlimb muscle activity during free forward swimming. Axial/ dorsal muscles, which contract in bilateral alternation during undulatory swimming in premetamorphic tadpoles, change their left-right coordination to become activated in phase with bilaterally synchronous hindlimb extensions in locomoting juveniles. Based on in vitro electrophysiologi-cal experiments as well as specific spinal lesions in vivo, a spinal cord region was delimited in which propriospinal interactions are directly responsible for the coordination between leg and back muscle contractions. Our findings therefore indicate that dynamic postural adjustments during adult Xenopus locomotion are mediated by local intraspinal pathways through which the lumbar generator for hindlimb propulsive kicking provides caudorostral commands to thoracic spinal circuitry controlling the dorsal trunk musculature

Building modular FSPM under OpenAlea: concepts and applications

International audienceThe OpenAlea platform (Pradal et al., 2008) was designed to facilitate the integration and inter-operability of heterogeneous models to get comprehensive FSPMs. It relies on Python gluing capabilities, that allow non intrusive integration of programs written in various languages (Fortran, C, C++, R, L-system); and on the dataflow computing paradigm, that promotes decomposition of applications into independent components that can be recombined dynamically into customized workflows. Still, a plugable collection of components is not by itself a solution to the modularity problem in FSPM modeling. First, heterogeneities between components inputs and outputs can lead to exponential needs for specific adaptors and converters to get functional assemblies. Second, several ways exist to decompose models into independent components. This can lead to incompatibilities or difficulties for re-assembly into comprehensive models. Last, users of the platform may find difficult to build applications, without some knowledge on how a simulation has to be reasoned within the data-flow computing paradigm. Here, we propose a modeling strategy to help for building coherent, yet modular FSPM under OpenAlea. We first define the key concepts of this strategy, illustrate how they can be used under Visualea and how it lead to a first set of reusable components resulting from various ecophysiological studies

What determines the complex kinetics of stomatal conductance under blueless PAR in Festuca arundinacea? Subsequent effects on leaf transpiration

Light quality and, in particular, its content of blue light is involved in plant functioning and morphogenesis. Blue light variation frequently occurs within a stand as shaded zones are characterized by a simultaneous decrease of PAR and blue light levels which both affect plant functioning, for example, gas exchange. However, little is known about the effects of low blue light itself on gas exchange. The aims of the present study were (i) to characterize stomatal behaviour in Festuca arundinacea leaves through leaf gas exchange measurements in response to a sudden reduction in blue light, and (ii) to test the putative role of Ci on blue light gas exchange responses. An infrared gas analyser (IRGA) was used with light transmission filters to study stomatal conductance (gs), transpiration (Tr), assimilation (A), and intercellular concentration of CO2 (Ci) responses to blueless PAR (1.80 μmol m−2 s−1). The results were compared with those obtained under a neutral filter supplying a similar photosynthetic efficiency to the blueless PAR filter. It was shown that the reduction of blue light triggered a drastic and instantaneous decrease of gs by 43.2% and of Tr by 40.0%, but a gradual stomatal reopening began 20 min after the start of the low blue light treatment, thus leading to new steady-states. This new stomatal equilibrium was supposed to be related to Ci. The results were confirmed in more developed plants although they exhibited delayed and less marked responses. It is concluded that stomatal responses to blue light could play a key role in photomorphogenetic mechanisms through their effect on transpiration

Quantum dynamics of simultaneously measured non-commuting observables.

In quantum mechanics, measurements cause wavefunction collapse that yields precise outcomes, whereas for non-commuting observables such as position and momentum Heisenberg's uncertainty principle limits the intrinsic precision of a state. Although theoretical work has demonstrated that it should be possible to perform simultaneous non-commuting measurements and has revealed the limits on measurement outcomes, only recently has the dynamics of the quantum state been discussed. To realize this unexplored regime, we simultaneously apply two continuous quantum non-demolition probes of non-commuting observables to a superconducting qubit. We implement multiple readout channels by coupling the qubit to multiple modes of a cavity. To control the measurement observables, we implement a 'single quadrature' measurement by driving the qubit and applying cavity sidebands with a relative phase that sets the observable. Here, we use this approach to show that the uncertainty principle governs the dynamics of the wavefunction by enforcing a lower bound on the measurement-induced disturbance. Consequently, as we transition from measuring identical to measuring non-commuting observables, the dynamics make a smooth transition from standard wavefunction collapse to localized persistent diffusion and then to isotropic persistent diffusion. Although the evolution of the state differs markedly from that of a conventional measurement, information about both non-commuting observables is extracted by keeping track of the time ordering of the measurement record, enabling quantum state tomography without alternating measurements. Our work creates novel capabilities for quantum control, including rapid state purification, adaptive measurement, measurement-based state steering and continuous quantum error correction. As physical systems often interact continuously with their environment via non-commuting degrees of freedom, our work offers a way to study how notions of contemporary quantum foundations arise in such settings

Sharing efforts for modelling plant systems: from publications to reusable software components

http://www-sop.inria.fr/virtualplants/Publications/2009/FPCBLRCCBMSVEAG09/[email protected] audiencePlant models become increasingly complex and their implementation often implies the use of advanced techniques in computer science. This evolution has been accompanied by the production of dedicated plant modelling tools, such as simulation platforms, that facilitate research in this field. However, much less sharing is observed for plant models themselves, that is for computer programs produced by scientists to address their specific questions. Yet, these programs could be highly valuable for other researchers, to avoid redundant development of similar code or to help non-specialists to simulate parts of a complex system. Model descriptions found in academic publications, even combined with code sources, are generally not sufficient for model reuse. Most difficulties come from the heterogeneity of language used, the structure of the programs, the download and installation procedures, the accessibility to the source code of the model, and the availability of documentation. The OpenAlea initiative (http://openalea.gforge.inria.fr) has been launched to address these problems by providing plant modellers with collaborative tools and guidelines to increase software quality, hence re-usability of their models. The Alinea pilot project further tested these concepts in a sample community of ecophysiologists and biophysicists. Based on this experience, we illustrate pros and cons of the approach and discuss future direction of progress. We foresee three steps towards a better re-usability of models: a better interoperability of existing tools and simulation platforms, the emergence of design patterns for plant modelling, and the definition of standardised data structures

Platelets Alter Gene Expression Profile in Human Brain Endothelial Cells in an In Vitro Model of Cerebral Malaria

Platelet adhesion to the brain microvasculature has been associated with cerebral malaria (CM) in humans, suggesting that platelets play a role in the pathogenesis of this syndrome. In vitro co-cultures have shown that platelets can act as a bridge between Plasmodium falciparum-infected red blood cells (pRBC) and human brain microvascular endothelial cells (HBEC) and potentiate HBEC apoptosis. Using cDNA microarray technology, we analyzed transcriptional changes of HBEC in response to platelets in the presence or the absence of tumor necrosis factor (TNF) and pRBC, which have been reported to alter gene expression in endothelial cells. Using a rigorous statistical approach with multiple test corrections, we showed a significant effect of platelets on gene expression in HBEC. We also detected a strong effect of TNF, whereas there was no transcriptional change induced specifically by pRBC. Nevertheless, a global ANOVA and a two-way ANOVA suggested that pRBC acted in interaction with platelets and TNF to alter gene expression in HBEC. The expression of selected genes was validated by RT-qPCR. The analysis of gene functional annotation indicated that platelets induce the expression of genes involved in inflammation and apoptosis, such as genes involved in chemokine-, TREM1-, cytokine-, IL10-, TGFβ-, death-receptor-, and apoptosis-signaling. Overall, our results support the hypothesis that platelets play a pathogenic role in CM

Comparaison de modèles de transferts radiatifs pour simuler la distribution du rayonnement actif sur la morphogenèse (MAR) au sein d'un peuplement végétal à une échelle locale

*INRA Unité d'Ecophysiologie des plantes fourragères Lusignan (FRA) Diffusion du document : INRA Unité d'Ecophysiologie des plantes fourragères Lusignan (FRA) Diplôme : Dr. d'UniversitéThe capacity of 3D volumic models of radiative transfer (DART and RIRI) based on the turbid medium analogy to simulate the spatial distribution of photomorphogenetically active radiations at 660 and 730 nm was evaluated. The simulations of light interception and scattering were both compared to the outputs of surfacic models (CANESTRA and PARCINOPY), taken as references. These comparisons were conducted on virtual plants of sorghum and wallnut trees obtained by 3D digitizing. The directional optical properties of leaves were obtained using a specially designed goniophotometer. A complementary study of on the whole visible-near infrared spectrum was also conducted by comparing the simulation of a volumic model to punctual spectrophotometric measurements within the crown of an adult walnut tree. The hypotheses of the Beer-Lambert law proved to be more or less adequate depending on the structure of the plants. The accuracy of the simulation is not very sensitive to the choice of the numerical parameters in the volumic model, but very sensitive to the size of the cells of the mesh used for the numerical simulations. However, in most cases the discrepancies between the estimate of light interception at the local scale by volumic models and the reference were significant. Light scattering, as estimated by volumic, models differed significantly from the reference whatever the phase function, even when a specular component was included. In the case of the simplest phase function (R=T), the difference was larger for the DOM method implemented in DART than for the radiosity method that was developed in RIRI. In all the cases, the accuracy of the estimates of light scattering strongly depends on the accuracy of the estimate of light interception.Ce travail a porté sur l'évaluation de la capacité de modèles volumiques 3D de transferts radiatifs (RIRI et DART) à simuler la distribution spatiale des flux radiatifs à 660 et 730 nm importants pour la photomorphogenèse. Les simulations de l'interception et des rediffusions, étudiées séparément, ont été comparées avec les résultats de modèles surfaciques considérés comme références (CANESTRA et PARCINOPY). Ces comparaisons ont porté sur des structures de sorgho et de noyer obtenues par digitalisation 3D. Un goniophotomètre a été développé pour caractériser les propriétés optiques directionnelles des feuilles. Cette étude a été complétée par une comparaison sur l’ensemble du spectre visible-proche infrarouge avec des mesures spectroradiométriques locales au sein d’un noyer âgé. Les résultats concernant l'interception montrent que les hypothèses de la loi de Beer-Lambert sont plus ou moins respectées selon la structure. La qualité des estimations dépend peu des paramètres numériques du modèle volumique mais beaucoup des dimensions de la maille de discrétisation. Dans la plupart des cas, l’estimation des flux interceptés à l’échelle locale reste peu précise. Les rediffusions estimées par les modèles volumiques divergent de la référence quelle que soit la fonction de phase. L’introduction d'une composante spéculaire ne réduit pas ces écarts. Pour la fonction de phase la plus simple (R=T), cette divergence est plus importante pour l'approche DOM utilisée dans DART que pour la méthode des radiosités développée dans RIRI. Dans tous les cas, la qualité des estimations du rayonnement rediffusé avec un modèle volumique dépend fortement du traitement de l'interception