IRBIT a Master Regulator of Cell Physiology

(excerpt) Hormones and neurotransmitters regulate cell functions by binding to their receptors, which activate intracellular signaling and produce the physiological response [1]. There are several intracellular pathways, including but not limited to, leading to the activation of protein kinases, phosphatases and increase in intracellular calcium (Ca2+) [1]

Environmental Constraints on the Distribution of the Non-native Grass, \u3ci\u3eMicrostegium vimineum\u3c/i\u3e

Microstegium vimineum (Trin.) A. Camus, commonly known as Japanese grass, is a non-native plant of particular ecological concern in the United States due to its potential impact on native ecosystems, yet surprisingly little is known of its ecological requirements. In spite of its rapid expansion throughout its North American range, M. vimineum tends to occur in discrete patches on the landscape and is frequently found in disturbed understory habitats along roadbanks, floodplains, and nearby mesic forest. It is not found in many apparently suitable locations, which suggests that certain environmental factors, or interactions of factors, limit the distribution of this invasive grass. I used a combination of field and greenhouse experiments and a biogeographical survey to examine environmental factors that might cause the complex pattern of presence/absence and performance exhibited by this species. The biogeographical survey was designed to (1) identify environmental factors that limit the distribution of this species to certain positions on the landscape (i.e., explain presence/absence), and (2) quantify the performance (i.e., height and biomass) of this species in response to environmental gradients. Within the study area, M. vimineum exhibited the broad environmental tolerance of many weedy species. Soil pH was the only environmental variable, among those measured, that was correlated with the presence of M. vimineum, whereas canopy openness and other species biomass are the most important variables that explain the performance of M. vimineum. This information can be used to predict habitats that are vulnerable to invasion by this species, prioritize the species as a land management concern, and guide the development of effective control strategies. Light and water are important resources for all plants, and it has been suggested that these resources are mutually substitutable, at least within a certain range of resource levels. I conducted a greenhouse experiment to test a hypothesized light/water trade-off in M. vimineum, whereby light and water would be mutually substitutable and would have an interactive effect on plant growth. The experiment consisted of a randomized, 4 x 5 factorial design that included light levels (75%, 25%, 10%, 5%, and 2% sunlight) and soil moisture levels (40%, 30%, 20%, and 10%) that encompassed the ranges likely to be experienced by this species in a natural setting. Results demonstrate a light/water trade-off in M. vimineum in terms of root, shoot, and total biomass accumulation (light x water interaction, ppp=0.005). Shifts in biomass accumulation between roots and shoots does not appear to be the mechanism responsible for the trade-off (p\u3e0.05), but stomatal conductance remains a plausible mechanism that should be tested in future research. Within its introduced range, M. vimineum often occurs as extensive, dense patches with sharp boundaries and distinct gaps in cover. One example of this distributional pattern was observed relative to the native shrub Asimina triloba (pawpaw), whereby dense M. vimineum cover ended abruptly at the drip line of the A. triloba patch and was absent beneath the A. triloba canopy. I conducted field and greenhouse experiments to test several hypotheses regarding the causes of this observed pattern of M. vimineum distribution, including allelopathy, lack of seed dispersal, soil moisture limitations, and light limitations. I concluded that light reduction by the A. triloba canopy prevented establishment of M. vimineum beneath this shrub. In a complementary field shade experiment, a 60% reduction in ambient understory light reduced seedling survival, and the threshold for seedling survival is between 60% and 16% ambient understory light. These findings suggest that habitats in deep shade are less vulnerable to invasion by this non-native grass. This research is the first explicit investigation of environmental constraints on the distribution of M. vimineum. I suggest that the complex pattern of this species\u27 distribution and abundance in its introduced range is the result of interactions between resources, especially light and water, and seed dispersal limitations. The importance of maintaining undisturbed native vegetation is one of the conservation implications of these findings. My survey results are consistent with other reports that roads and trails are the most common habitat in which M. vimineum is found in its introduced range, and these linear gaps forested systems appear to provide a corridor for the spread of this non-native species. Forest fragmentations by development, including agriculture, increases the amount of edge habitat that favors the establishment of M. vimineum and increases the opportunities for its invasion into nearby intact forest. Comparative studies of this species in its native and introduced ranges and research on its ecological impacts are needed

Effect of Media and Estrogen on Morphological Change in Candida albicans

Introduction: Candida albicans (C. albicans), an opportunistic pathogen, lives symbiotically within the intestine of its human host. Temperature and chemical factors have been shown to induce a morphological change in C. albicans from yeast to filamentous form turning C. albicans pathogenic. In this study, we investigated the intestinal cues that might be responsible for the change. We found that different solid media impact the morphological phenotype so we focused on characterizing these before further testing. We tested Estradiol (E2) because of its known linkage to sepsis and higher levels during infections. Experiments were conducted to compare solid agar plates of YEPD, Minimal Media (MM), and Spider Media (SP) for C. albicans growth to choose the best one for further testing with E2 and other factors that could be prone to causing morphological changes. Methods: C. albicans was inoculated through streak method on different solid media (YEPD, MM, SP) and incubated at 30℃. The effect of 0.1nM E2 on C. albicans morphology was also tested. Morphological changes were assayed through bright-field microscopy. Results: Using the three different medias, we found three distinctive phenotypes: A, B, and C. Out of 6 experiments of 14 MM plates, the expressed phenotype was 86% A and 14% inconclusive of the time. 8 experiments of 17 SP plates showed 100% of phenotype B. 6 experiments of 14 YEPD plates presented phenotype C 92% of the time and 8% inconclusive. For E2 trials, 2 experiments, 6 MM plates showed 50% phenotype A and 50% inconclusive. 4 experiments, 10 SP plates had phenotype B 100%. YEPD 2 experiments, 2 plates had phenotype C at 100%. Conclusion: We have established experimental conditions of media controls for further testing whether E2 and other cues, such as inflammatory cytokines, have inhibitory or positive effects on the growth of C. albicans

Leptoquarks decaying to a top quark and a charged lepton at hadron colliders

We study the sensitivity of the Tevatron and the 7 TeV LHC to a leptoquark S coupling to a top quark and a charged lepton L (= e, mu, or tau). For the Tevatron, we focus on the case m_S < m_t, where the leptoquark pair production cross section is large, and the decay is three-body: S --> W b L^{\pm}. We argue that existing Tevatron observations could exclude m_S \lsim 160 GeV. For m_S > m_t, we show that the LHC experiments with low integrated luminosity could be sensitive to such leptoquarks decaying to tl^{\pm} with l= mu or tau.Comment: 13 pages, 6 figures, minor changes (typos

Anomalous Increase in Carbon Capacitance at Pore Sizes Less Than 1 Nanometer

Carbon supercapacitors, which are energy storage devices that use ion adsorption on the surface of highly porous materials to store charge, have numerous advantages over other power-source technologies, but could realize further gains if their electrodes were properly optimized. Studying the effect of the pore size on capacitance could potentially improve performance by maximizing the electrode surface area accessible to electrolyte ions, but until recently, no studies had addressed the lower size limit of accessible pores. Using carbide-derived carbon, we generated pores with average sizes from 0.6 to 2.25 nanometer and studied double-layer capacitance in an organic electrolyte. The results challenge the long-held axiom that pores smaller than the size of solvated electrolyte ions are incapable of contributing to charge storage

L’organisation des circuits d’approvisionnement en lait de la ville de N’Djamena (Tchad)

Objectif : L’objectif de l’étude est de comprendre l’organisation et le fonctionnement des circuits d’approvisionnement de la ville de N’Djamena en produits laitiers locaux. Elle a été réalisée à partir d’une enquête semi-structurée. Methodologie et résultats : Les informations ont été collectées auprès des acteurs impliqués dans les différents circuits : consommateurs, collecteurs, revendeuses, transformateurs et producteurs. Les résultats ont montré que la consommation par les ménages des produits laitiers locaux et importés dépend des habitudes alimentaires et du niveau de revenu du foyer. Celle des produits laitiers hors domicile est en plein essor grâce au succès du rayeb, un lait fermenté entier distribué principalement par les bars laitiers de la ville. L’analyse du marché ressortir le dynamisme et la complémentarité des filières qui approvisionnent la ville en produits laitiers locaux : lait frais, lait caillé, lait de chamelle. Parmi elles, la filière « lait frais » de vache, composée de microentreprises de collecte et de transformation laitières, est la plus dynamique. L’essor de la filière lait de chamelle est lié à la spécificité du produit qui n’entre pas en concurrence avec le lait de vache ; ce lait est consommé par les populations originaires des zones pastorales du nord du pays. Conclusion et Application : L’étude a permis de mettre en évidence le rôle des systèmes d’élevage pastoraux et agropastoraux dans l’approvisionnement de la ville de N’Djamena en lait local ainsi que ses mutations profondes sous l’effet de l’intégration au marché. Une politique ambitieuse visant à lever les contraintes techniques et économiques d’une production laitière très saisonnière doit être mise en place pour pérenniser la filière. Mots-clés : Tchad, N’Djaména, lait, produits laitiers, circuits, organisation

Gall-forming insects concentrate on hybrid phenotypes of Eucalyptus hosts

We examined distributions of 33 gall forming insect species on parent species and three hybrid phenotypes in two Eucalyptus hybrid zones in Australia. Variation in insect abundance among hybrid classes was greater than variation between species suggesting that hybrid zones are sites of dynamic interactions between plants and herbivores. For instance, of 25 galling species in Victoria, 52% showed significant differences in abundance among hybrid classes, whereas only 24% differed between pure host species. While some components of hybrid use were very predictable, others were not. Based on galler use of pure species, we could accurately predict which hybrid phenotype would be most used. Our data show that most gall species concentrate on the hybrid class that is most similar to the parent species on which it is most abundant. However, species related taxonomically or by feeding guild did not exhibit consistent responses to hybrid and parent hosts. Thus pooling either hybrid classes or insect species for statistical analysis may mask underlying patterns. Overall, galler responses to three hybrid phenotypes are consistent with the hypothesis that plant hybrid zones and especially backcross hybrids are centers of insect species richness and abundance. Furthermore, galler response to hybrids plants suggests that the narrow host specificity characteristic of gallers may be less strongly influenced by plant developmental processes than generally thought. Our observations support the hypothesis that genetic differences among host plants in hybrid zones underlies patterns of insect host use. They also suggest that other mechanisms might be involved. Hybrid zone studies may have much to tell us about the ecology and evolution of plant-herbivore interactions

Mapping the energy and diffusion landscapes of membrane proteins at the cell surface using high-density single-molecule imaging and Bayesian inference: application to the multi-scale dynamics of glycine receptors in the neuronal membrane

Protein mobility is conventionally analyzed in terms of an effective diffusion. Yet, this description often fails to properly distinguish and evaluate the physical parameters (such as the membrane friction) and the biochemical interactions governing the motion. Here, we present a method combining high-density single-molecule imaging and statistical inference to separately map the diffusion and energy landscapes of membrane proteins across the cell surface at ~100 nm resolution (with acquisition of a few minutes). When applying these analytical tools to glycine neurotransmitter receptors (GlyRs) at inhibitory synapses, we find that gephyrin scaffolds act as shallow energy traps (~3 kBT) for GlyRs, with a depth modulated by the biochemical properties of the receptor-gephyrin interaction loop. In turn, the inferred maps can be used to simulate the dynamics of proteins in the membrane, from the level of individual receptors to that of the population, and thereby, to model the stochastic fluctuations of physiological parameters (such as the number of receptors at synapses). Overall, our approach provides a powerful and comprehensive framework with which to analyze biochemical interactions in living cells and to decipher the multi-scale dynamics of biomolecules in complex cellular environments.Comment: 23 pages, 4 figure

Bootstrap for log Wavelet Leaders Cumulant based Multifractal Analysis.

Multifractal analysis, which mostly consists of estimating scaling exponents related to the power law behaviors of the moments of wavelet coefficients, is becoming a popular tool for empirical data analysis. However, little is known about the statistical performance of such procedures. Notably, despite their being of major practical importance, no confidence intervals are available. Here, we choose to replace wavelet coefficients with wavelet Leaders and to use a log-cumulant based multifractal analysis. We investigate the potential use of bootstrap to derive confidence intervals for wavelet Leaders log-cumulant multifractal estimation procedures. From numerical simulations involving well-known and well-controlled synthetic multifractal processes, we obtain two results of major importance for practical multifractal analysis : we demonstrate that the use of Leaders instead of wavelet coefficients brings significant improvements in log-cumulant based multifractal estimation, we show that accurate bootstrap designed confidence intervals can be obtained for a single finite length time series