128 research outputs found

    Generalised Indiscernibles, Dividing Lines, and Products of Structures

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    Generalised indiscernibles highlight a strong link between model theory and structural Ramsey theory. In this paper, we use generalised indiscernibles as tools to prove results in both these areas. More precisely, we first show that a reduct of an ultrahomogenous ℵ0\aleph_0-categorical structure which has higher arity than the original structure cannot be Ramsey. In particular, the only nontrivial Ramsey reduct of the generically ordered random kk-hypergraph is the linear order. We then turn our attention to model-theoretic dividing lines that are characterised by collapsing generalised indiscernibles, and prove, for these dividing lines, several transfer principles in (full and lexicographic) products of structures. As an application, we construct new algorithmically tame classes of graphs

    Dissecting Subsecond Cadherin Bound States Reveals an Efficient Way for Cells to Achieve Ultrafast Probing of their Environment

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    Cells continuously probe their environment with membrane receptors, achieving subsecond adaptation of their behaviour [1-3]. Recently, several receptors, including cadherins, were found to bind ligands with a lifetime of order of one second. Here we show at the single molecule level that homotypic C-cadherin association involves transient intermediates lasting less than a few tens of milliseconds. Further, these intermediates transitionned towards more stable states with a kinetic rate displaying exponential decrease with piconewton forces. These features enable cells to detect ligands or measure surrounding mechanical behaviour within a fraction of a second, much more rapidly than was previously thought

    Nucleotide diversity of the ZmPox3 maize peroxidase gene: Relationships between a MITE insertion in exon 2 and variation in forage maize digestibility

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    BACKGROUND: Polymorphisms were investigated within the ZmPox3 maize peroxidase gene, possibly involved in lignin biosynthesis because of its colocalization with a cluster of QTL related to lignin content and cell wall digestibility. The purpose of this study was to identify, on the basis of 37 maize lines chosen for their varying degrees of cell wall digestibility and representative of temperate regions germplasm, ZmPox3 haplotypes or individual polymorphisms possibly associated with digestibility. RESULTS: Numerous haplotypes with high diversity were identified. Frequency of nucleotide changes was high with on average one SNP every 57 bp. Nucleotide diversity was not equally distributed among site categories: the estimated π was on average eight times higher for silent sites than for non-synonymous sites. Numerous sites were in linkage disequilibrium that decayed with increasing physical distance. A zmPox3 mutant allele, carrying an insertion of a transposable element in the second exon, was found in lines derived from the early flint inbred line, F7. This element possesses many structural features of miniature inverted-repeat transposable elements (MITE). The mutant allele encodes a truncated protein lacking important functional sites. An ANOVA performed with a subset of 31 maize lines indicated that the transposable element was significantly associated with cell wall digestibility. This association was confirmed using an additional set of 25 flint lines related to F7. Moreover, RT-PCR experiments revealed a decreased amount of corresponding mRNA in plants with the MITE insertion. CONCLUSION: These results showed that ZmPox3 could possibly be involved in monolignol polymerisation, and that a deficiency in ZmPox3 peroxidase activity seemingly has a negative effect on cell wall digestibility. Also, genetic diversity analyses of ZmPox3 indicated that this peroxidase could be a relevant target for grass digestibility improvement using specific allele introgressions

    A novel inhibitor of p75-neurotrophin receptor improves functional outcomes in two models of traumatic brain injury.

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    The p75 neurotrophin receptor is important in multiple physiological actions including neuronal survival and neurite outgrowth during development, and after central nervous system injury. We have discovered a novel piperazine-derived compound, EVT901, which interferes with p75 neurotrophin receptor oligomerization through direct interaction with the first cysteine-rich domain of the extracellular region. Using ligand binding assays with cysteine-rich domains-fused p75 neurotrophin receptor, we confirmed that EVT901 interferes with oligomerization of full-length p75 neurotrophin receptor in a dose-dependent manner. Here we report that EVT901 reduces binding of pro-nerve growth factor to p75 neurotrophin receptor, blocks pro-nerve growth factor induced apoptosis in cells expressing p75 neurotrophin receptor, and enhances neurite outgrowth in vitro Furthermore, we demonstrate that EVT901 abrogates p75 neurotrophin receptor signalling by other ligands, such as prion peptide and amyloid-β. To test the efficacy of EVT901 in vivo, we evaluated the outcome in two models of traumatic brain injury. We generated controlled cortical impacts in adult rats. Using unbiased stereological analysis, we found that EVT901 delivered intravenously daily for 1 week after injury, reduced lesion size, protected cortical neurons and oligodendrocytes, and had a positive effect on neurological function. After lateral fluid percussion injury in adult rats, oral treatment with EVT901 reduced neuronal death in the hippocampus and thalamus, reduced long-term cognitive deficits, and reduced the occurrence of post-traumatic seizure activity. Together, these studies provide a new reagent for altering p75 neurotrophin receptor actions after injury and suggest that EVT901 may be useful in treatment of central nervous system trauma and other neurological disorders where p75 neurotrophin receptor signalling is affected

    The NOMAD experiment at the CERN SPS

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    The NOMAD experiment is a short base-line search for νμ→ντ\nu_{\mu}\rightarrow \nu_{\tau} oscillations in the CERN neutrino beam. The ντ\nu_{\tau}'s are searched for through their charged-current interactions followed by the observation of the resulting τ−\tau^{-} through its electronic, muonic or hadronic decays. These decays are recognized using kinematical criteria necessitating the use of a light target which enables the reconstruction of individual particles produced in the neutrino interactions. This paper describes the various components of the NOMAD detector: the target and muon drift chambers, the electromagnetic and hadronic calorimeters, the preshower and transition radiation detectors, and the veto and trigger scintillation counters. The beam and data acquisition system are also described. The quality of the reconstruction of individual particles is demonstrated through the ability of NOMAD to observe Ks0^0_{\rm s}'s, Λ0\Lambda^0's and π0\pi^0's. Finally, the observation of τ−\tau^{-} through its electronic decay being one of the most promising channels in the search, the identification of electrons in NOMAD is discussed
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