Estimation des paramètres spatio-temporels d'un canal de propagation à trajets multiples

L'identification active de canaux de propagation à trajets multiples réduit le débit de la transmission. Nous proposons ici des algorithmes passifs, qui n'utilisent pas de séquence d'apprentissage. Nous avions proposé, dans une publication antérieure, des algorithmes procédant en deux étapes à partir des méthodes de déconvolution autodidacte. Nous utilisons ici la forme particulière des critères pour estimer conjointement les paramètres spatio-temporels (angles d'incidence et retards de groupe), et donnons leurs bornes de Cramer-Rao. Les propriétés de ces méthodes, ainsi que leurs liens avec l'approche au sens du maximum de vraisemblance, sont démontrées puis analysées par simulations

Identification and characterization of secreted and pathogenesis-related proteins in Ustilago maydis

Interactions between plants and fungal pathogens require a complex interplay at the plant–fungus interface. Extracellular effector proteins are thought to play a crucial role in establishing a successful infection. To identify pathogenesis-related proteins in Ustilago maydis we combined the isolation of secreted proteins using a signal sequence trap approach with bioinformatic analyses and the subsequent characterization of knock-out mutants. We identified 29 secreted proteins including hydrophobins and proteins with a repetitive structure similar to the repellent protein Rep1. Hum3, a protein containing both, a hydrophobin domain and a repetitive Rep1-like region, is shown to be processed during passage through the secretory pathway. While single knock-outs of hydrophobin or repellent-like genes did not affect pathogenicity, we found a strong effect of a double knock-out of hum3 and the repetitive rsp1. Yeast-like growth, mating, aerial hyphae formation and surface hydrophobicity were unaffected in this double mutant. However, pathogenic development in planta stops early after penetration leading to a complete loss of pathogenicity. This indicates that Hum3 and Rsp1 are pathogenicity proteins that share an essential function in early stages of the infection. Our results demonstrate that focusing on secreted proteins is a promising way to discover novel pathogenicity proteins that might be broadly applied to a variety of fungal pathogens

Intron Evolution: Testing Hypotheses of Intron Evolution Using the Phylogenomics of Tetraspanins

BACKGROUND: Although large scale informatics studies on introns can be useful in making broad inferences concerning patterns of intron gain and loss, more specific questions about intron evolution at a finer scale can be addressed using a gene family where structure and function are well known. Genome wide surveys of tetraspanins from a broad array of organisms with fully sequenced genomes are an excellent means to understand specifics of intron evolution. Our approach incorporated several new fully sequenced genomes that cover the major lineages of the animal kingdom as well as plants, protists and fungi. The analysis of exon/intron gene structure in such an evolutionary broad set of genomes allowed us to identify ancestral intron structure in tetraspanins throughout the eukaryotic tree of life. METHODOLOGY/PRINCIPAL FINDINGS: We performed a phylogenomic analysis of the intron/exon structure of the tetraspanin protein family. In addition, to the already characterized tetraspanin introns numbered 1 through 6 found in animals, three additional ancient, phase 0 introns we call 4a, 4b and 4c were found. These three novel introns in combination with the ancestral introns 1 to 6, define three basic tetraspanin gene structures which have been conserved throughout the animal kingdom. Our phylogenomic approach also allows the estimation of the time at which the introns of the 33 human tetraspanin paralogs appeared, which in many cases coincides with the concomitant acquisition of new introns. On the other hand, we observed that new introns (introns other than 1-6, 4a, b and c) were not randomly inserted into the tetraspanin gene structure. The region of tetraspanin genes corresponding to the small extracellular loop (SEL) accounts for only 10.5% of the total sequence length but had 46% of the new animal intron insertions. CONCLUSIONS/SIGNIFICANCE: Our results indicate that tests of intron evolution are strengthened by the phylogenomic approach with specific gene families like tetraspanins. These tests add to our understanding of genomic innovation coupled to major evolutionary divergence events, functional constraints and the timing of the appearance of evolutionary novelty

Comparative Genome Analysis of Filamentous Fungi Reveals Gene Family Expansions Associated with Fungal Pathogenesis

Fungi and oomycetes are the causal agents of many of the most serious diseases of plants. Here we report a detailed comparative analysis of the genome sequences of thirty-six species of fungi and oomycetes, including seven plant pathogenic species, that aims to explore the common genetic features associated with plant disease-causing species. The predicted translational products of each genome have been clustered into groups of potential orthologues using Markov Chain Clustering and the data integrated into the e-Fungi object-oriented data warehouse (http://www.e-fungi.org.uk/). Analysis of the species distribution of members of these clusters has identified proteins that are specific to filamentous fungal species and a group of proteins found only in plant pathogens. By comparing the gene inventories of filamentous, ascomycetous phytopathogenic and free-living species of fungi, we have identified a set of gene families that appear to have expanded during the evolution of phytopathogens and may therefore serve important roles in plant disease. We have also characterised the predicted set of secreted proteins encoded by each genome and identified a set of protein families which are significantly over-represented in the secretomes of plant pathogenic fungi, including putative effector proteins that might perturb host cell biology during plant infection. The results demonstrate the potential of comparative genome analysis for exploring the evolution of eukaryotic microbial pathogenesis

Effect of sitagliptin on cardiovascular outcomes in type 2 diabetes

BACKGROUND: Data are lacking on the long-term effect on cardiovascular events of adding sitagliptin, a dipeptidyl peptidase 4 inhibitor, to usual care in patients with type 2 diabetes and cardiovascular disease. METHODS: In this randomized, double-blind study, we assigned 14,671 patients to add either sitagliptin or placebo to their existing therapy. Open-label use of antihyperglycemic therapy was encouraged as required, aimed at reaching individually appropriate glycemic targets in all patients. To determine whether sitagliptin was noninferior to placebo, we used a relative risk of 1.3 as the marginal upper boundary. The primary cardiovascular outcome was a composite of cardiovascular death, nonfatal myocardial infarction, nonfatal stroke, or hospitalization for unstable angina. RESULTS: During a median follow-up of 3.0 years, there was a small difference in glycated hemoglobin levels (least-squares mean difference for sitagliptin vs. placebo, -0.29 percentage points; 95% confidence interval [CI], -0.32 to -0.27). Overall, the primary outcome occurred in 839 patients in the sitagliptin group (11.4%; 4.06 per 100 person-years) and 851 patients in the placebo group (11.6%; 4.17 per 100 person-years). Sitagliptin was noninferior to placebo for the primary composite cardiovascular outcome (hazard ratio, 0.98; 95% CI, 0.88 to 1.09; P<0.001). Rates of hospitalization for heart failure did not differ between the two groups (hazard ratio, 1.00; 95% CI, 0.83 to 1.20; P = 0.98). There were no significant between-group differences in rates of acute pancreatitis (P = 0.07) or pancreatic cancer (P = 0.32). CONCLUSIONS: Among patients with type 2 diabetes and established cardiovascular disease, adding sitagliptin to usual care did not appear to increase the risk of major adverse cardiovascular events, hospitalization for heart failure, or other adverse events

Estimation de la matrice de covariance et méthodes d'identification à haute résolution

Les méthodes courantes d'identification non biaisées,à haute résolution utilisent la décomposition en valeurs singulière de la matrice de covariance. Cette dernière estimée à partir d'un nombre fini d'échantillons n'a pas une structure de Toeplitz. Le but de cette communication est de présenter une nouvelle méthode de calcul de la matrice de covariance sous forme Toeplitz qui n'introduit pas de biais sur l'estimation de l'espace signal.Les performan ces de ces méthodes seront discutées

Autocalibration robuste en traitement d'antenne : Resolution, correlation et regularisation

Les méthodes de localisation de sources à haute résolution se dégradent fortement lorsque le modèle qu'elles utilisent s' éloigne i de la réalité. En présence d' incertitudes sur les paramètres du modèle il faut donc autocalibrer. Un algorithme d'autocalibration a été proposé par B.Friedlander mais il n'est pas robuste vis à vis de fortes incertitudes sur le modèle. L'objet de cet article est d'en améliorer la robustesse. Dans le cas de sources proches de puissances différentes et fortement corrélées un algorithme original d'autocalibration du maximum de vraisemblance est introduit

Séparation de sources correlées voisines par les méthodes spectrales à haute résolution

Le problème considéré est celui de la séparation de sources voisines par une antenne linéaire, en particulier dans le cas de sources corrélées (phénomène d'écho). La séparation est effectuée par les méthodes spectrales à haute résolution analogues à celles utilisées pour la recherche de fréquences pures dans un signal temporel. Ces méthodes reposent sur les propriétés de la matrice interspectrale. En particulier les M vecteurs propres relatifs aux plus grandes valeurs propres engendrent le même sous-espace que les M vecteurs sources. On examinera d'une part la répartition des valeurs propres relatives au signal, d'autre part l'influence des incertitudes de mesure sur l'estimation de la matrice interspectrale ; ces résultats permettent de calculer la variance sur l'estimation des fréquences et de discuter le choix des paramètres d'estimation. En ce qui concerne la répartition des valeurs propres signal, on trouve que dans le cas de sources voisines la matrice devient mal conditionnée, particulièrement dans le cas de sources corrélées. Pour deux sources séparées de0 la forme asymptotique du rapport des valeurs propres est calculée ; ce rapport varie en θ-2 pour des sources non corrélées, en θ-4 pour des sources corrélées. Ces résultats seront réutilisés ultérieurement, mais ils donnent déjà une idée des limitations du pouvoir séparateur des méthodes haute résolution. En présence de bruits additifs décorrélés et de même variance les valeurs propres relatives au bruit ont même espérance mathématique. En fait pour la matrice spectrale estimée la répartition n'est plus uniforme. Une forme approchée linéaire de cette répartition est calculée et vérifiée par simulation. Ce résultat peut être utilisé pour séparer la plus faible valeur propre signal de la plus grande valeur propre de bruit. L'effet des incertitudes de mesure sur l'estimation des vecteurs propre signal est ensuite étudiée, dans le cas d'une seule source. Ces résultats permettent de calculer la variance sur l'estimation de la fréquence, pour différentes méthodes de mesure et de discuter le choix des paramètres d'estimation