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Search Results: 1 - 10 of 15073 matches for " Louis Du Pasquier "
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Characterization of a Nonclassical Class I MHC Gene in a Reptile, the Galápagos Marine Iguana (Amblyrhynchus cristatus)
Scott Glaberman, Louis Du Pasquier, Adalgisa Caccone
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0002859
Abstract: Squamates are a diverse order of vertebrates, representing more than 7,000 species. Yet, descriptions of full-length major histocompatibility complex (MHC) genes in this group are nearly absent from the literature, while the number of MHC studies continues to rise in other vertebrate taxa. The lack of basic information about MHC organization in squamates inhibits investigation into the relationship between MHC polymorphism and disease, and leaves a large taxonomic gap in our understanding of amniote MHC evolution. Here, we use both cDNA and genomic sequence data to characterize a class I MHC gene (Amcr-UA) from the Galápagos marine iguana, a member of the squamate subfamily Iguaninae. Amcr-UA appears to be functional since it is expressed in the blood and contains many of the conserved peptide-binding residues that are found in classical class I genes of other vertebrates. In addition, comparison of Amcr-UA to homologous sequences from other iguanine species shows that the antigen-binding portion of this gene is under purifying selection, rather than balancing selection, and therefore may have a conserved function. A striking feature of Amcr-UA is that both the cDNA and genomic sequences lack the transmembrane and cytoplasmic domains that are necessary to anchor the class I receptor molecule into the cell membrane, suggesting that the product of this gene is secreted and consequently not involved in classical class I antigen-presentation. The truncated and conserved character of Amcr-UA lead us to define it as a nonclassical gene that is related to the few available squamate class I sequences. However, phylogenetic analysis placed Amcr-UA in a basal position relative to other published classical MHC genes from squamates, suggesting that this gene diverged near the beginning of squamate diversification.
Intragenic tandem repeats in Daphnia magna: structure, function and distribution
Isabelle Colson, Louis Du Pasquier, Dieter Ebert
BMC Research Notes , 2009, DOI: 10.1186/1756-0500-2-206
Abstract: Seventy-four polymorphic markers were isolated and characterised. Analyses of repeat structure, putative gene function and polymorphism indicated that intragenic tandem repeats are not distributed randomly in the mRNA sequences; instead, dinucleotides are more frequent in non-coding regions, whereas trinucleotides (and longer motifs involving multiple-of-three nucleotide repeats) are preferentially situated in coding regions. We also observed differential distribution of repeat motifs across putative genetic functions. This indicates differential selective constraints and possible functional significance of VNTR polymorphism in at least some genes.Databases of VNTR markers situated in genes whose putative function can be inferred from homology searches will be a valuable resource for the genetic study of functional variation and selection.Waterfleas of the genus Daphnia (Crustacea:Cladocera) are small planktonic crustaceans found in standing freshwater bodies around the world. They have a long history as model organisms for evolutionary, ecological and ecotoxicological research. Recently, the genus has been the focus of a major sequencing effort, and the full genome sequence of Daphnia pulex is now available [1]. Genomic resources are steadily being developed for another species of the genus, D. magna. In particular, a database of around 12,000 expressed sequence tags (EST) is currently available [1,2], providing a useful resource to isolate polymorphic genetic markers in this species. Developing genetic markers from transcribed sequences offers specific advantages compared to traditional methods of screening enriched genomic libraries. Apart from the lower cost and higher speed of development, EST-derived genetic markers have a higher probability of being functionally significant and of being located in gene-rich regions [3-5]. This makes them highly useful markers for QTL mapping of ecologically-relevant phenotypes and for the study of selection in natural populat
Somatic Mutations During an Immune Response inXenopus Tadpoles
Melanie Wilson,Anne Marcuz,Louis Du Pasquier
Clinical and Developmental Immunology , 1995, DOI: 10.1155/1995/38639
Abstract:
Lymphoid Tumors of Xenopus laevis with Different Capacities for Growth in Larvae and Adults
Jacques Robert,Chantal Guiet,Louis Du Pasquier
Clinical and Developmental Immunology , 1994, DOI: 10.1155/1994/37392
Abstract:
A Large Repertoire of Parasite Epitopes Matched by a Large Repertoire of Host Immune Receptors in an Invertebrate Host/Parasite Model
Yves Moné,Benjamin Gourbal,David Duval,Louis Du Pasquier,Sylvie Kieffer-Jaquinod,Guillaume Mitta
PLOS Neglected Tropical Diseases , 2010, DOI: 10.1371/journal.pntd.0000813
Abstract: For many decades, invertebrate immunity was believed to be non-adaptive, poorly specific, relying exclusively on sometimes multiple but germ-line encoded innate receptors and effectors. But recent studies performed in different invertebrate species have shaken this paradigm by providing evidence for various types of somatic adaptations at the level of putative immune receptors leading to an enlarged repertoire of recognition molecules. Fibrinogen Related Proteins (FREPs) from the mollusc Biomphalaria glabrata are an example of these putative immune receptors. They are known to be involved in reactions against trematode parasites. Following not yet well understood somatic mechanisms, the FREP repertoire varies considerably from one snail to another, showing a trend towards an individualization of the putative immune repertoire almost comparable to that described from vertebrate adaptive immune system. Nevertheless, their antigenic targets remain unknown. In this study, we show that a specific set of these highly variable FREPs from B. glabrata forms complexes with similarly highly polymorphic and individually variable mucin molecules from its specific trematode parasite S. mansoni (Schistosoma mansoni Polymorphic Mucins: SmPoMucs). This is the first evidence of the interaction between diversified immune receptors and antigenic variant in an invertebrate host/pathogen model. The same order of magnitude in the diversity of the parasite epitopes and the one of the FREP suggests co-evolutionary dynamics between host and parasite regarding this set of determinants that could explain population features like the compatibility polymorphism observed in B. glabrata/S. mansoni interaction. In addition, we identified a third partner associated with the FREPs/SmPoMucs in the immune complex: a Thioester containing Protein (TEP) belonging to a molecular category that plays a role in phagocytosis or encapsulation following recognition. The presence of this last partner in this immune complex argues in favor of the involvement of the formed complex in parasite recognition and elimination from the host.
Population Genetics of Duplicated Alternatively Spliced Exons of the Dscam Gene in Daphnia and Drosophila
Daniela Brites,Francisco Encinas-Viso,Dieter Ebert,Louis Du Pasquier,Christoph R. Haag
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0027947
Abstract: In insects and crustaceans, the Down syndrome cell adhesion molecule (Dscam) occurs in many different isoforms. These are produced by mutually exclusive alternative splicing of dozens of tandem duplicated exons coding for parts or whole immunoglobulin (Ig) domains of the Dscam protein. This diversity plays a role in the development of the nervous system and also in the immune system. Structural analysis of the protein suggested candidate epitopes where binding to pathogens could occur. These epitopes are coded by regions of the duplicated exons and are therefore diverse within individuals. Here we apply molecular population genetics and molecular evolution analyses using Daphnia magna and several Drosophila species to investigate the potential role of natural selection in the divergence between orthologs of these duplicated exons among species, as well as between paralogous exons within species. We found no evidence for a role of positive selection in the divergence of these paralogous exons. However, the power of this test was low, and the fact that no signs of gene conversion between paralogous exons were found suggests that paralog diversity may nonetheless be maintained by selection. The analysis of orthologous exons in Drosophila and in Daphnia revealed an excess of non-synonymous polymorphisms in the epitopes putatively involved in pathogen binding. This may be a sign of balancing selection. Indeed, in Dr. melanogaster the same derived non-synonymous alleles segregate in several populations around the world. Yet other hallmarks of balancing selection were not found. Hence, we cannot rule out that the excess of non-synonymous polymorphisms is caused by segregating slightly deleterious alleles, thus potentially indicating reduced selective constraints in the putative pathogen binding epitopes of Dscam.
Origin and Evolution of TRIM Proteins: New Insights from the Complete TRIM Repertoire of Zebrafish and Pufferfish
Pierre Boudinot, Lieke M. van der Aa, Luc Jouneau, Louis Du Pasquier, Pierre Pontarotti, Valérie Briolat, Abdenour Benmansour, Jean-Pierre Levraud
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0022022
Abstract: Tripartite motif proteins (TRIM) constitute a large family of proteins containing a RING-Bbox-Coiled Coil motif followed by different C-terminal domains. Involved in ubiquitination, TRIM proteins participate in many cellular processes including antiviral immunity. The TRIM family is ancient and has been greatly diversified in vertebrates and especially in fish. We analyzed the complete sets of trim genes of the large zebrafish genome and of the compact pufferfish genome. Both contain three large multigene subsets - adding the hsl5/trim35-like genes (hltr) to the ftr and the btr that we previously described - all containing a B30.2 domain that evolved under positive selection. These subsets are conserved among teleosts. By contrast, most human trim genes of the other classes have only one or two orthologues in fish. Loss or gain of C-terminal exons generated proteins with different domain organizations; either by the deletion of the ancestral domain or, remarkably, by the acquisition of a new C-terminal domain. Our survey of fish trim genes in fish identifies subsets with different evolutionary dynamics. trims encoding RBCC-B30.2 proteins show the same evolutionary trends in fish and tetrapods: they evolve fast, often under positive selection, and they duplicate to create multigenic families. We could identify new combinations of domains, which epitomize how new trim classes appear by domain insertion or exon shuffling. Notably, we found that a cyclophilin-A domain replaces the B30.2 domain of a zebrafish fintrim gene, as reported in the macaque and owl monkey antiretroviral TRIM5α. Finally, trim genes encoding RBCC-B30.2 proteins are preferentially located in the vicinity of MHC or MHC gene paralogues, which suggests that such trim genes may have been part of the ancestral MHC.
Unfertilized Xenopus Eggs Die by Bad-Dependent Apoptosis under the Control of Cdk1 and JNK
David Du Pasquier, Aude Dupré, Catherine Jessus
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0023672
Abstract: Ovulated eggs possess maternal apoptotic execution machinery that is inhibited for a limited time. The fertilized eggs switch off this time bomb whereas aged unfertilized eggs and parthenogenetically activated eggs fail to stop the timer and die. To investigate the nature of the molecular clock that triggers the egg decision of committing suicide, we introduce here Xenopus eggs as an in vivo system for studying the death of unfertilized eggs. We report that after ovulation, a number of eggs remains in the female body where they die by apoptosis. Similarly, ovulated unfertilized eggs recovered in the external medium die within 72 h. We showed that the death process depends on both cytochrome c release and caspase activation. The apoptotic machinery is turned on during meiotic maturation, before fertilization. The death pathway is independent of ERK but relies on activating Bad phosphorylation through the control of both kinases Cdk1 and JNK. In conclusion, the default fate of an unfertilized Xenopus egg is to die by a mitochondrial dependent apoptosis activated during meiotic maturation.
Two generalizations of the PRV conjecture
Pierre-Louis Montagard,Boris Pasquier,Nicolas Ressayre
Mathematics , 2010, DOI: 10.1112/S0010437X10005233
Abstract: Let G be a complex connected reductive group. The PRV conjecture, which was proved independently by S. Kumar and O. Mathieu in 1989, gives explicit irreducible submodules of the tensor product of two irreducible G-modules. This paper has three aims. First, we simplify the proof of the PRV conjecture, then we generalize it to other branching problems. Finally, we find other irreducible components of the tensor product of two irreducible G-modules that appear for "the same reason" as the PRV ones.
Generalizations of the PRV conjecture, II
Pierre-Louis Montagard,Boris Pasquier,Nicolas Ressayre
Mathematics , 2011,
Abstract: Let $G\subset\hat{G}$ be two complex connected reductive groups. We deals with the hard problem of finding sub-$G$-modules of a given irreducible $\hat{G}$-module. In the case where $G$ is diagonally embedded in $\hat{G}=G\times G$, S. Kumar and O. Mathieu found some of them, proving the PRV conjecture. Recently, the authors generalized the PRV conjecture on the one hand to the case where $\hat{G}/G$ is spherical of minimal rank, and on the other hand giving more sub-$G$-modules in the classical case $G\subset G\times G$. In this paper, these two recent generalizations are combined in a same more general result.
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