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Search Results: 1 - 10 of 1788 matches for " Gilbert Engler "
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Using the pea aphid Acrythociphon pisum as a tool for screening biological responses to chemicals and drugs
Aviv Dombrovsky, Terence Ledger, Gilbert Engler, Alain Robichon
BMC Research Notes , 2009, DOI: 10.1186/1756-0500-2-185
Abstract: We designed a simple test for screening drugs by investigating simultaneously zygote mitotic division, the progression of embryo development, cell differentiation at early developmental stages and finally organogenesis and population growth rate. We aimed to analyze the toxicology effects of compounds and/or their interference on cellular signalling by examining at which step of the cascade, from zygote to mature embryo, the developmental process is perturbed. We reasoned that a parthenogenetic founder insect, in which the ovarioles shelter numerous embryos at different developmental stages, would allow us to precisely pinpoint the step of embryogenesis in which chemicals act through specific molecular targets as the known ordered homeobox genes.Using this method we report the results of a genotoxicological and demographic analysis of three compound models bearing in common a bromo group: one is integrated as a base analog in DNA synthesis, two others activate permanently kinases. We report that one compound (Br-du) altered drastically embryogenesis, which argues in favor of this simple technique as a cheap first screening of chemicals or drugs to be used in a number of genotoxicology applications.Sex is evolutionary beneficial due to genetic variation in the offspring. Meiotic recombination and allele complementation are two mechanisms inherent to sexual reproduction through which individuals adapt to the environment. Recombination will bring together advantageous alleles on the same chromosome that would be inherited as an assembled entity and new gene combinations might be selected for their fitness in a given environmental toxicology context. Moreover, genetic recombination at the meiosis stage is inherently linked to DNA repair mechanisms of damage in double-stranded DNA, which is usually lethal if not corrected [1,2]. Some workers have proposed that the genome in asexual reproduction accumulates deleterious mutations on single or double stranded DNA. In evolut
Continued Neurogenesis in Adult Drosophila as a Mechanism for Recruiting Environmental Cue-Dependent Variants
Selim Ben Rokia-Mille, Sylvette Tinette, Gilbert Engler, Laury Arthaud, Sophie Tares, Alain Robichon
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0002395
Abstract: Background The skills used by winged insects to explore their environment are strongly dependent upon the integration of neurosensory information comprising visual, acoustic and olfactory signals. The neuronal architecture of the wing contains a vast array of different sensors which might convey information to the brain in order to guide the trajectories during flight. In Drosophila, the wing sensory cells are either chemoreceptors or mechanoreceptors and some of these sensors have as yet unknown functions. The axons of these two functionally distinct types of neurons are entangled, generating a single nerve. This simple and accessible coincidental signaling circuitry in Drosophila constitutes an excellent model system to investigate the developmental variability in relation to natural behavioral polymorphisms. Methodology/Principal Findings A fluorescent marker was generated in neurons at all stages of the Drosophila life cycle using a highly efficient and controlled genetic recombination system that can be induced in dividing precursor cells (MARCM system, flybase web site). It allows fluorescent signals in axons only when the neuroblasts and/or neuronal cell precursors like SOP (sensory organ precursors) undergo division during the precedent steps. We first show that a robust neurogenesis continues in the wing after the adults emerge from the pupae followed by an extensive axonal growth. Arguments are presented to suggest that this wing neurogenesis in the newborn adult flies was influenced by genetic determinants such as the frequency dependent for gene and by environmental cues such as population density. Conclusions We demonstrate that the neuronal architecture in the adult Drosophila wing is unfinished when the flies emerge from their pupae. This unexpected developmental step might be crucial for generating non-heritable variants and phenotypic plasticity. This might therefore constitute an advantage in an unstable ecological system and explain much regarding the ability of Drosophila to robustly adapt to their environment.
Exploratory behaviour in NO-dependent cyclase mutants of Drosophila shows defects in coincident neuronal signalling
Sylvette Tinette, Lixing Zhang, Amélie Garnier, Gilbert Engler, Sophie Tares, Alain Robichon
BMC Neuroscience , 2007, DOI: 10.1186/1471-2202-8-65
Abstract: Flies perform cycles of exploration/aggregation depending on the resources of the environment. This behavioural ecology constitutes an excellent model for analyzing simultaneous processing of neurosensory information. We reasoned that the decision of flies to land somewhere in order to achieve aggregation is based on simultaneous integration of signals (visual, olfactory, acoustic) during their flight. On the basis of what flies do in nature, we designed laboratory tests to analyze the phenomenon of neuronal coincidence. We screened many mutants of genes involved in neuronal metabolism and the synaptic machinery.Mutants of NO-dependent cyclase show a specifically-marked behaviour phenotype, but on the other hand they are associated with moderate biochemical defects. We show that these mutants present errors in integrative and/or coincident processing of signals, which are not reducible to the functions of the peripheral sensory cells.We have shown that exploration in Drosophila is a powerful behavioural tool for analyzing the genetic basis of the machinery involved in the integration of multiple environmental signs [1]. We therefore designed protocols to test the exploratory skills of the flies [1]. We reasoned that the efficiency of exploration depends on the simultaneous integration of neurosensory signals during flight to guide the aggregation of individuals on a specific spot. When a food spot becomes disadvantageous, the flies reset a new cycle of exploration/aggregation [1]. We previously showed that the first flies to find the appropriate food spot (explorers) signal to the others (followers) [1]. Such collective exploration leads to remarkably efficient aggregation. They aggregate to screen sex partners and to lay eggs on the food spot most favourable for sustaining the development of larvae. This cooperative task suggests that costly individual foraging behaviour has not been selected by evolution because encounters would have been random, unpredictable and
Feeding Cells Induced by Phytoparasitic Nematodes Require γ-Tubulin Ring Complex for Microtubule Reorganization
Mohamed Youssef Banora,Natalia Rodiuc,Fabien Baldacci-Cresp,Andrei Smertenko,Teresa Bleve-Zacheo,Maria Teresa Mellilo,Mansour Karimi,Pierre Hilson,Jean-Luc Evrard,Bruno Favery,Gilbert Engler,Pierre Abad,Janice de Almeida Engler
PLOS Pathogens , 2011, DOI: 10.1371/journal.ppat.1002343
Abstract: Reorganization of the microtubule network is important for the fast isodiametric expansion of giant-feeding cells induced by root-knot nematodes. The efficiency of microtubule reorganization depends on the nucleation of new microtubules, their elongation rate and activity of microtubule severing factors. New microtubules in plants are nucleated by cytoplasmic or microtubule-bound γ-tubulin ring complexes. Here we investigate the requirement of γ-tubulin complexes for giant feeding cells development using the interaction between Arabidopsis and Meloidogyne spp. as a model system. Immunocytochemical analyses demonstrate that γ-tubulin localizes to both cortical cytoplasm and mitotic microtubule arrays of the giant cells where it can associate with microtubules. The transcripts of two Arabidopsis γ-tubulin (TUBG1 and TUBG2) and two γ-tubulin complex proteins genes (GCP3 and GCP4) are upregulated in galls. Electron microscopy demonstrates association of GCP3 and γ-tubulin as part of a complex in the cytoplasm of giant cells. Knockout of either or both γ-tubulin genes results in the gene dose-dependent alteration of the morphology of feeding site and failure of nematode life cycle completion. We conclude that the γ-tubulin complex is essential for the control of microtubular network remodelling in the course of initiation and development of giant-feeding cells, and for the successful reproduction of nematodes in their plant hosts.
On the Speed of Spread for Fractional Reaction-Diffusion Equations
Hans Engler
International Journal of Differential Equations , 2010, DOI: 10.1155/2010/315421
Abstract: The fractional reaction diffusion equation is discussed, where is a fractional differential operator on of order , the function vanishes at and , and either on or near . In the case of nonnegative g, it is shown that solutions with initial support on the positive half axis spread into the left half axis with unbounded speed if satisfies some weak growth condition near in the case , or if is merely positive on a sufficiently large interval near in the case . On the other hand, it shown that solutions spread with finite speed if . The proofs use comparison arguments and a suitable family of travelling wave solutions. 1. Introduction The scalar reaction-diffusion equation has been the subject of much study, beginning with the celebrated paper [1]. The authors of [1] proposed this equation, with being positive and concave on such that , as a model for a population that undergoes logistic growth and Brownian diffusion. If , the Heaviside function, and , the equation in fact has an exact probabilistic interpretation, given in [2]. Consider a population of particles that undergo independent Brownian motion and branching processes, with each child particle again following the same behavior. Then is the probability that there is a particle to the left of position at time , assuming that there was exactly one particle at position at time . Equation (1.1) also can be derived heuristically for the mean behavior of an interacting particle process in which two types of particles (call them - and -particles) simultaneously undergo Brownian diffusion and conversion reactions with suitable reaction rates. Then the volume density fraction of -particles in the hydrodynamic limit of large particle numbers per unit volume formally satisfies (1.1) with where depends on the reaction rates in (1.2); see [3] for a discussion of the underlying limit procedure and an exact connection to a stochastic version of (1.1). If instead the conversion reactions are then the equation for becomes (1.1) with . Other polynomial reaction terms occur in similar ways. For (1.1) with , it is known that solutions approach a wave profile in the sense that where is the median, . It turns out that for a suitable asymptotic finite wave speed . Larger asymptotic speeds are only possible if the initial data are supported on . A more general result, given in [4], implies that there is a critical speed such that for fairly general initial data that are nonnegative and supported on , whenever and whenever . If is interpreted as the density of a quantity whose spread is governed by (1.1), a runner may
Teoria da Religi o Norte-americana: Alguns Debates Recentes
Steven Engler
REVER : Revista de Estudos da Religi?o , 2004,
Abstract: This paper looks a recent theme in theory of religion, the status of the generic concept of "religion". The idea that all cultural phenomena labeled "religions" share something in common that justifies the use of the generic terms is most commonly rooted in a concept of the "sacred", drawn from interpretive phenomenology, However, this concept is arguably susceptible to three sorts of critiques: semantic, epistemological, and ideological. After describing these critiques, the article briefly discusses two approaches to "religion" that seem to avoid these critiques: Benson Saler′s prototype theory and material/relational theories. In conclusion, the article looks at historical and current relations between these theoretical issues and the institutional context of the study of religion in North America.
Two Problems with Constructionism in the Study of Religion
Steven Engler
REVER : Revista de Estudos da Religi?o , 2005,
Abstract: This essay examines the role of "constructionism" in the academic study of religion. It argues that the use of this theoretical perspective have had little value for three reasons. (1) Misinterpreted as necessarily relativistic, it has served as a superficial foil for theological and phenomenological realisms. (2) Instead of specifying what is constructed from what and how, the theory has been taken for granted rather than clarified. As a result, the language of "construction" adds little, given that most work in the field already places religious phenomena in their contingent social context.
Tipos de Criacionismos Crist os
Steven Engler
REVER : Revista de Estudos da Religi?o , 2007,
Abstract: This paper examines two attempts to characterize the differences among the variety of Christian creationisms. Based on an evaluation of the strengths and weaknesses of these two typologies, it proposes a broader one. This typology can help orient studies of Christian creationisms and facilitate the comparison of Christian and non-Christian creationisms.
Strong solutions of quasilinear integro-differential equations with singular kernels in several space dimensions
Hans Engler
Electronic Journal of Differential Equations , 1995,
Abstract: $$ u_t - a*A(u) = f,,$$ where $a$ is a scalar singular integral kernel that behaves like $t^{-alpha}$, $1/2 leq alpha < 1$ and $A$ is a second order quasilinear elliptic operator in divergence form, solutions are found for which $A(u)$ is integrable over space and time.
Asymptotic stability of traveling wave solutions for perturbations with algebraic decay
Hans Engler
Physics , 2001,
Abstract: For a class of scalar partial differential equations that incorporate convection, diffusion, and possibly dispersion in one space and one time dimension, the stability of traveling wave solutions is investigated. If the initial perturbation of the traveling wave profile decays at an algebraic rate, then the solution is shown to converge to a shifted wave profile at a corresponding temporal algebraic rate, and optimal intermediate results that combine temporal and spatial decay are obtained. The proofs are based on a general interpolation principle which says that algebraic decay results of this form always follow if exponential temporal decay holds for perturbation with exponential spatial decay and the wave profile is stable for general perturbations.
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