99 research outputs found

    Desynchronization of pulse-coupled oscillators with delayed excitatory coupling

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    Collective behavior of pulse-coupled oscillators has been investigated widely. As an example of pulse-coupled networks, fireflies display many kinds of flashing patterns. Mirollo and Strogatz (1990) proposed a pulse-coupled oscillator model to explain the synchronization of South East Asian fireflies ({\itshape Pteroptyx malaccae}). However, transmission delays were not considered in their model. In fact, the presence of transmission delays can lead to desychronization. In this paper, pulse-coupled oscillator networks with delayed excitatory coupling are studied. Our main result is that under reasonable assumptions, pulse-coupled oscillator networks with delayed excitatory coupling can not achieve complete synchronization, which can explain why another species of fireflies ({\itshape Photinus pyralis}) rarely synchronizes flashing. Finally, two numerical simulations are given. In the first simulation, we illustrate that even if all the initial phases are very close to each other, there could still be big variations in the times to process the pulses in the pipeline. It implies that asymptotical synchronization typically also cannot be achieved. In the second simulation, we exhibit a phenomenon of clustering synchronization

    Thrips Settling, Oviposition and IYSV Distribution on Onion Foliage

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    Thrips tabaci Lindeman (Thysanoptera: Thripidae) adult and larval settling and oviposition on onion (Allium cepa L.) foliage were investigated in relation to leaf position and leaf length at prebulb plant growth stages under controlled conditions. In the laboratory, four and six adult females of T. tabaci were released on onion plants at three-leaf stage and six- to eight-leaf stage, respectively, and thrips egg, nymph, and adult count data were collected on each of the three inner most leaves at every 2-cm leaf segment. Thrips settling and oviposition parameters were quantified during the light period on the above ground portion of onion plants from the distal end of the bulb or leaf sheath “neck” through the tips of the foliage. Results from studies confirmed that distribution of thrips adults, nymphs, and eggs were skewed toward the base of the plant. The settling distributions of thrips adults and nymphs differed slightly from the egg distribution in that oviposition occurred all the way to the tip of the leaf while adults and nymphs were typically not observed near the tip. In a field study, the foliage was divided into three equal partitions, i.e., top, middle, basal thirds, and thrips adults by species, primarily Frankliniella fusca (Hinds) and T. tabaci, were collected from each partition to determine if there was a similar bias of all adult thrips toward the base of the plant. The results suggested that adults of different species appear to segregate along leaf length. Finally, thrips oviposition on 2-cm segments and Iris yellow spot virus positive leaf segments were quantified in the field, irrespective of thrips species. Both variables demonstrated a very similar pattern of bias toward the base of the plant and were significantly correlated

    The RNA polymerase II subunit RPB-9 recruits the integrator complex to terminate Caenorhabditis elegans piRNA transcription.

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    PIWI-interacting RNAs (piRNAs) are genome-encoded small RNAs that regulate germ cell development and maintain germline integrity in many animals. Mature piRNAs engage Piwi Argonaute proteins to silence complementary transcripts, including transposable elements and endogenous genes. piRNA biogenesis mechanisms are diverse and remain poorly understood. Here, we identify the RNA polymerase II (RNA Pol II) core subunit RPB-9 as required for piRNA-mediated silencing in the nematode Caenorhabditis elegans. We show that rpb-9 initiates heritable piRNA-mediated gene silencing at two DNA transposon families and at a subset of somatic genes in the germline. We provide genetic and biochemical evidence that RPB-9 is required for piRNA biogenesis by recruiting the Integrator complex at piRNA genes, hence promoting transcriptional termination. We conclude that, as a part of its rapid evolution, the piRNA pathway has co-opted an ancient machinery for high-fidelity transcription

    Novel multiple sclerosis susceptibility loci implicated in epigenetic regulation

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    We conducted a genome-wide association study (GWAS) on multiple sclerosis (MS) susceptibility in German cohorts with 4888 cases and 10,395 controls. In addition to associations within the major histocompatibility complex (MHC) region, 15 non-MHC loci reached genome-wide significance. Four of these loci are novel MS susceptibility loci. They map to the genes L3MBTL3, MAZ, ERG, and SHMT1. The lead variant at SHMT1 was replicated in an independent Sardinian cohort. Products of the genes L3MBTL3, MAZ, and ERG play important roles in immune cell regulation. SHMT1 encodes a serine hydroxymethyltransferase catalyzing the transfer of a carbon unit to the folate cycle. This reaction is required for regulation of methylation homeostasis, which is important for establishment and maintenance of epigenetic signatures. Our GWAS approach in a defined population with limited genetic substructure detected associations not found in larger, more heterogeneous cohorts, thus providing new clues regarding MS pathogenesis

    Deciphering the Biology of \u3ci\u3eCryptophyllachora eurasiatica\u3c/i\u3e gen. et sp. nov., an Often Cryptic Pathogen of an Allergenic Weed, \u3ci\u3eAmbrosia artemisiifolia\u3c/i\u3e

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    A little known, unculturable ascomycete, referred to as Phyllachora ambrosiae, can destroy the inflorescences of Ambrosia artemisiifolia, an invasive agricultural weed and producer of highly allergenic pollen. The fungus often remains undetectable in ragweed populations. This work was conducted to understand its origin and pathogenesis, a prerequisite to consider its potential as a biocontrol agent. The methods used included light and transmission electron microscopy, nrDNA sequencing, phylogenetic analyses, artificial inoculations, and the examination of old herbarium and recent field specimens from Hungary, Korea, Ukraine and USA. The Eurasian and the North American specimens of this fungus were to represent two distinct, although closely related lineages that were only distantly related to other lineages within the Ascomycota. Consequently, we describe a new genus that includes Cryptophyllachora eurasiatica gen. et sp. nov. and C. ambrosiae comb. nov., respectively. The pathogenesis of C. eurasiaticawas shown in A. artemisiifolia. No evidence was found for either seed-borne transmission or systemic infection. Two hypotheses were developed to explain the interaction between C. eurasiatica and A. artemisiifolia: (i) as yet undetected seed-borne transmissions and latent, systemic infections; or (ii) alternative hosts

    Elemental Composition of Natural Nanoparticles and Fine Colloids in European Forest Stream Waters and Their Role as Phosphorus Carriers

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    "This is the peer reviewed version of the following article: Gottselig, N., W. Amelung, J. W. Kirchner, R. Bol, W. Eugster, S. J. Granger, C. Hernández-Crespo, et al. 2017. Elemental Composition of Natural Nanoparticles and Fine Colloids in European Forest Stream Waters and Their Role as Phosphorus Carriers. Global Biogeochemical Cycles 31 (10). American Geophysical Union (AGU): 1592 1607. doi:10.1002/2017gb005657, which has been published in final form at https://doi.org/10.1002/2017GB005657. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."[EN] Biogeochemical cycling of elements largely occurs in dissolved state, but many elements may also be bound to natural nanoparticles (NNP, 1-100 nm) and fine colloids (100-450 nm). We examined the hypothesis that the size and composition of stream water NNP and colloids vary systematically across Europe. To test this hypothesis, 96 stream water samples were simultaneously collected in 26 forested headwater catchments along two transects across Europe. Three size fractions (similar to 1-20 nm, >20-60 nm, and >60 nm) of NNP and fine colloids were identified with Field Flow Fractionation coupled to inductively coupled plasma mass spectrometry and an organic carbon detector. The results showed that NNP and fine colloids constituted between 2 +/- 5% (Si) and 53 +/- 21% (Fe; mean +/- SD) of total element concentrations, indicating a substantial contribution of particles to element transport in these European streams, especially for P and Fe. The particulate contents of Fe, Al, and organic C were correlated to their total element concentrations, but those of particulate Si, Mn, P, and Ca were not. The fine colloidal fractions >60 nm were dominated by clay minerals across all sites. The resulting element patterns of NNP <60 nm changed from North to South Europe from Fe-to Ca-dominated particles, along with associated changes in acidity, forest type, and dominant lithology.The authors gratefully acknowledge the assistance of the following people in locating suitable sampling sites, contacting site operators, performing the sampling, and providing data: A. Avila Castells (Autonomous University of Barcelona), R. Batalla (University of Lleida), P. Blomkvist (Swedish University of Agricultural Sciences), H. Bogena (Julich Research Center), A.K. Boulet (University of Aveiro), D. Estany (University of Lleida), F. Garnier (French National Institute of Agricultural Research), H.J. Hendricks-Franssen (Research Center Julich), L. JacksonBlake (James Hutton Institute, NIVA), T. Laurila (Finnish Meteorological Institute), A. Lindroth (Lund University), M.M. Monerris (Universitat Politecnica de Valencia), M. Ottosson Lofvenius (Swedish University of Agricultural Sciences), I. Taberman (Swedish University of Agricultural Sciences), F. Wendland (Research Center Julich), T. Zetterberg (Swedish University of Agricultural Sciences and The Swedish Environmental Research Institute, IVL) and further unnamed contributors. The Swedish Infrastructure for Ecosystem Science (SITES) and the Swedish Integrated Monitoring, the latter financed by the Swedish Environmental Protection Agency, and ICOS Sweden have supported sampling and provided data for the Swedish sites. J.J.K. gratefully acknowledges the support from CESAM (UID/AMB/50017/2013), funded by the FCT/MCTES (PIDDAC) with cofunding by FEDER through COMPETE. N.G. gratefully acknowledges all those who contributed to organizing and implementing the continental sampling. The raw data can be found at http://hdl.handle.net/2128/14937. This project was partly funded by the German Research Foundation (DFG KL2495/1-1).Gottselig, N.; Amelung, W.; Kirchner, J.; Bol, R.; Eugster, W.; Granger, S.; Hernández Crespo, C.... 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    DeepWAS: multivariate genotype-phenotype associations by directly integrating regulatory information using deep learning

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    Genome-wide association studies (GWAS) identify genetic variants associated with traits or diseases. GWAS never directly link variants to regulatory mechanisms. Instead, the functional annotation of variants is typically inferred by post hoc analyses. A specific class of deep learning-based methods allows for the prediction of regulatory effects per variant on several cell type-specific chromatin features. We here describe "DeepWAS", a new approach that integrates these regulatory effect predictions of single variants into a multivariate GWAS setting. Thereby, single variants associated with a trait or disease are directly coupled to their impact on a chromatin feature in a cell type. Up to 61 regulatory SNPs, called dSNPs, were associated with multiple sclerosis (MS, 4,888 cases and 10,395 controls), major depressive disorder (MDD, 1,475 cases and 2,144 controls), and height (5,974 individuals). These variants were mainly non-coding and reached at least nominal significance in classical GWAS. The prediction accuracy was higher for DeepWAS than for classical GWAS models for 91% of the genome-wide significant, MS-specific dSNPs. DSNPs were enriched in public or cohort-matched expression and methylation quantitative trait loci and we demonstrated the potential of DeepWAS to generate testable functional hypotheses based on genotype data alone. DeepWAS is available at https://github.com/cellmapslab/DeepWAS

    Deciphering the biology of Cryptophyllachora eurasiatica gen. et sp. nov., an often cryptic pathogen of an allergenic weed, Ambrosia artemisiifolia

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    A little known, unculturable ascomycete, referred to as Phyllachora ambrosiae, can destroy the inflorescences of Ambrosia artemisiifolia, an invasive agricultural weed and producer of highly allergenic pollen. The fungus often remains undetectable in ragweed populations. This work was conducted to understand its origin and pathogenesis, a prerequisite to consider its potential as a biocontrol agent. The methods used included light and transmission electron microscopy, nrDNA sequencing, phylogenetic analyses, artificial inoculations, and the examination of old herbarium and recent field specimens from Hungary, Korea, Ukraine and USA. The Eurasian and the North American specimens of this fungus were to represent two distinct, although closely related lineages that were only distantly related to other lineages within the Ascomycota. Consequently, we describe a new genus that includes Cryptophyllachora eurasiatica gen. et sp. nov. and C. ambrosiae comb. nov., respectively. The pathogenesis of C. eurasiatica was shown in A. artemisiifolia. No evidence was found for either seed-borne transmission or systemic infection. Two hypotheses were developed to explain the interaction between C. eurasiatica and A. artemisiifolia: (i) as yet undetected seed-borne transmissions and latent, systemic infections; or (ii) alternative hosts
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