Recherches Aéropalynologiques À Paris Et Dans Sa Banlieue: Nouveaux Résultats

Des corrélations ont été établies entre certains facteurs météorologiques et le dépot pollinique observé à l'aide de capteurs gravimétriques placés en deux points de l'agglomération parisienne. L'étude menée de mars à juillet 1984 fait apparaître le rôle important des températures et des précipitations dans les quantités de pollen disséminé. Des différences dans la durée de pollinisation et les quantités sont observables pour plusieurs taxons entre le site parisien et celui situé en banlieue. Les deux stations présentent une forte proportion de pollen d'arbres jusqu'au 15 juin. Cette proportion s'inverse ensuite au profit des herbacées.

Correlations have been established between some meteorological factors and the pollen deposition observed with the help of gravimetric samplers situated at two different points in Paris. The study conducted between March and July 1984 emphasizes the importance of the role played by temperatures and precipitations in the quantities of disseminated pollen grains. Differences can be observed in the duration of pollen incidence as well as in the quantities for several taxa between the sites within Paris and the outskirts. Both these sites present high proportion of tree-pollen until June 15th. This proportion is later reversed to the benefit of herbaceous plants.     

EGTA induces the synthesis in Escherichia coli of three proteins that cross-react with calmodulin antibodies

Escherichia coli mutants, (verA, dilA) specifically resistant to the Ca²⁺ channel inhibitors verapamil and diltiazem, respectively, are hypersensitive to EGTA and BAPTA. We have shown, using 1-D and 2-D gel electrophoresis, that the synthesis of at least 25 polypeptides in the mutants was enhanced by treatment with Ca²⁺ chelators and the synthesis of at least 11 polypeptides was repressed. This pattern of induction was not observed in heat- or SDS-treated cells and therefore does not appear to be a general stress response. The majority of the induced proteins are low molecular weight, extremely heat stable and acidic, characteristic properties of calmodulin. Moreover, of the major induced species, three with apparent molecular masses of 12, 18, and 34kDa all cross-reacted with polyclonal and monoclonal antibodies to eukaryote calmodulins or calerythrin, a heat-resistant Ca²⁺-binding protein from Saccharo-polyspora erythraea. The verA, dilA mutants. In being hypersensitive to EGTA and to the Ca²⁺ ionophore A23187 + Ca²⁺, may be defective in the regulation of the level of free intracellular Ca²⁺.     

Characterization of BCAM0224, a Multifunctional Trimeric Autotransporter from the Human Pathogen Burkholderia cenocepacia

Members of the trimeric autotransporter adhesin (TAA) family play a crucial role in adhesion of Gram-negative pathogens to host cells. Moreover, these proteins are multifunctional virulence factors involved in several other biological traits, including invasion into host cells and evasion of the host immune system. In cystic fibrosis epidemic Burkholderia cenocepacia strain J2315, we identified a unique TAA (BCAM0224)-encoding gene, previously described as being implicated in virulence. Here, we characterized this multifunctional protein, trying to establish its role in B. cenocepacia pathogenicity. We show that BCAM0224 occurs on the bacterial surface and adopts a trimeric conformation. Furthermore, we demonstrated that BCAM0224 is needed for earlier stages of biofilm formation and is required for swarming motility. In addition, BCAM0224 plays an important role in evasion of the human innate immune system, providing resistance against the bactericidal activity of serum via the complement classical pathway. Finally, BCAM0224 mediates bacterial adhesion to and invasion of cultured human bronchial epithelial cells. Together, these data reveal the high versatility of the BCAM0224 protein as a virulence factor in the pathogenic bacterium B. cenocepacia.     

Diversity and floristic patterns of mediterranean grasslands: the relative influence of environmental and land management factors

Managed grasslands are normally ecosystems with high species diversity. They are associated with traditional extensive livestock grazing. Land-use changes, in particular gradual abandonment or grazing intensification, lead to major changes in floristic patterns of these grasslands, some included in priority habitats of the EU Habitats Directive. In order to analyse these patterns of change, Mediterranean grasslands of eastern areas of mainland Portugal were studied aiming to: (1) establish ecological gradients underlying their floristic patterns; (2) examine the relative importance of both environmental and land-use factors on their floristic composition; (3) assess how floristic composition and species richness are affected by land-use factors. Vegetation sampling was carried out from 2008 to 2009 following phytosociological procedures. Canonical Correspondence Analysis was applied. Variation partitioning was used to assess the relative influence of land-use variables. Richness, legumes cover, endemic species and bryophytes cover were compared in four land-management regimes: unmanaged; extensive grazing by sheep; extensive grazing by cattle and sheep; frequent soil tillage. Significant differences were found in floristic and diversity patterns, revealing the importance of grazing as a management tool for maintaining or improving floristic diversity. From our findings slight extensive grazing can contribute to both maintenance of species diversity and to the increase in legumes cover and thus to palatability and economic value of studied grasslands. Interactions between herbivores and grasslands, considering also their influences on soil properties, have an important role in the equilibrium states which promote biodiversity and conservation of the services of these ecosystems.     

The genome of Burkholderia cenocepacia J2315, an epidemic pathogen of cystic fibrosis patients

Bacterial infections of the lungs of cystic fibrosis (CF) patients cause major complications in the treatment of this common genetic disease. Burkholderia cenocepacia infection is particularly problematic since this organism has high levels of antibiotic resistance, making it difficult to eradicate; the resulting chronic infections are associated with severe declines in lung function and increased mortality rates. B. cenocepacia strain J2315 was isolated from a CF patient and is a member of the epidemic ET12 lineage that originated in Canada or the United Kingdom and spread to Europe. The 8.06-Mb genome of this highly transmissible pathogen comprises three circular chromosomes and a plasmid and encodes a broad array of functions typical of this metabolically versatile genus, as well as numerous virulence and drug resistance functions. Although B. cenocepacia strains can be isolated from soil and can be pathogenic to both plants and man, J2315 is representative of a lineage of B. cenocepacia rarely isolated from the environment and which spreads between CF patients. Comparative analysis revealed that ca. 21% of the genome is unique in comparison to other strains of B. cenocepacia, highlighting the genomic plasticity of this species. Pseudogenes in virulence determinants suggest that the pathogenic response of J2315 may have been recently selected to promote persistence in the CF lung. The J2315 genome contains evidence that its unique and highly adapted genetic content has played a significant role in its success as an epidemic CF pathogen.     

The Ability of GAP1IP4BP To Function as a Rap1 GTPase-Activating Protein (GAP) Requires Its Ras GAP-Related Domain and an Arginine Finger Rather than an Asparagine Thumb

GAP1^IP4BP is a member of the GAP1 family of Ras GTPase-activating proteins (GAPs) that includes GAP1^m, CAPRI, and RASAL. Composed of a central Ras GAP-related domain (RasGRD), surrounded by amino-terminal C2 domains and a carboxy-terminal PH/Btk domain, these proteins, with the notable exception of GAP1^m, possess an unexpected arginine finger-dependent GAP activity on the Ras-related protein Rap1 (S. Kupzig, D. Deaconescu, D. Bouyoucef, S. A. Walker, Q. Liu, C. L. Polte, O. Daumke, T. Ishizaki, P. J. Lockyer, A. Wittinghofer, and P. J. Cullen, J. Biol. Chem. 281:9891-9900, 2006). Here, we have examined the mechanism through which GAP1^IP4BP can function as a Rap1 GAP. We show that deletion of domains on either side of the RasGRD, while not affecting Ras GAP activity, do dramatically perturb Rap1 GAP activity. By utilizing GAP1^IP4BP/GAP1^m chimeras, we establish that although the C2 and PH/Btk domains are required to stabilize the RasGRD, it is this domain which contains the catalytic machinery required for Rap1 GAP activity. Finally, a key residue in Rap1-specific GAPs is a catalytic asparagine, the so-called asparagine thumb. By generating a molecular model describing the predicted Rap1-binding site in the RasGRD of GAP1^IP4BP, we show that mutagenesis of individual asparagine or glutamine residues that lie in close proximity to the predicted binding site has no detectable effect on the in vivo Rap1 GAP activity of GAP1^IP4BP. In contrast, we present evidence consistent with a model in which the RasGRD of GAP1^IP4BP functions to stabilize the switch II region of Rap1, allowing stabilization of the transition state during GTP hydrolysis initiated by the arginine finger.The Ras-like family of small GTPases are ubiquitously expressed, evolutionarily conserved proteins that, by undergoing conformational changes in response to the alternate binding of GDP and GTP, function as binary switches (28, 31, 35). The GDP-bound “off” state and the GTP-bound “on” state recognize distinct effector proteins, thereby allowing the regulation of a variety of downstream signaling events (28, 31, 35). While Ras is the best-known and best-studied Ras-like GTPase, Rap1 has recently attracted considerable attention (reviewed in reference 20).Rap1 was originally identified through its ability, when overexpressed, to reverse the phenotype of K-Ras-transformed NIH 3T3 cells (19). As Ras and Rap1 have very similar effector regions, the ability of Rap1 to reverse the transformed phenotype appeared to arise through an ability to compete with K-Ras effectors. For example, Rap1 binds the Ras effector Raf1 but this does not lead to its activation (11). This is consistent with a simple model in which Rap1 functions as a Ras antagonist (6, 37). However, recent work has challenged this view. Increasing evidence points to Rap1 interacting with its own panel of effectors through which it controls cell-cell adhesion and cell-matrix interactions (reviewed in reference 20).Like that of other GTPases, the activation of Ras and Rap1 is regulated through guanine nucleotide exchange factors, which control activation by stimulating the exchange of GDP for GTP. Inactivation is driven by GTPase-activating proteins (GAPs). These enhance the intrinsic GTPase activity of Ras and Rap1, thereby leading to GTP hydrolysis. A wide variety of guanine nucleotide exchange factors and GAPs specific for these GTPases have been identified (14). Through the arrangement of different modular domains, these proteins are regulated following the activation of cell surface receptors. This occurs either through direct association with the activated receptor or indirectly through second messengers (4, 5, 14, 41).Mammalian proteins capable of functioning as Ras GAPs include NF1 (3, 27, 40), p120^GAP (38), the semaphorin 4D receptor plexin-B1 (29), and members of the GAP1 (reviewed in reference 41) and SynGAP (DAB2IP, nGAP, and SynGAP) families (10, 18, 39). These function as Ras GAPs by supplying a catalytic arginine residue—the arginine finger—into the active site of Ras. This stabilizes the transition state of the GTPase reaction, increasing the reaction rate by more than 1,000-fold (1, 33, 34).Rap1 GAPs include Rap GAPs I and II, the SPA-1 family (SPA-1, SPAR, SPAL, and E6TP1), and tuberin (16, 17, 26, 32). Unlike Ras, Rap1 does not possess the catalytic glutamine residue that is critical for GTP hydrolysis in Ras. This fundamental difference means that the mechanisms by which Ras and Rap1 GAPs function are distinct. Rap1 GAPs do not employ a catalytic arginine residue (8, 9); instead, they provide a catalytic asparagine—the asparagine thumb—to stimulate GTP hydrolysis (15). Here the asparagine carboxamide side chain has a function similar to that of the glutamine residue in Ras, stabilizing the position of the nucleophilic water and γ-phosphate in the transition complex (15, 36).Given such distinct catalytic mechanisms, surprisingly, some Ras GAPs, while having no detectable sequence homology with any Rap1 GAPs, are capable of stimulating the GTPase activity of Rap1. The first protein found to display such dual activities was GAP1^IP4BP (13) (also known as RASA3, GAPIII, and R-Ras GAP). This is a member of the GAP1 family, which also comprises GAP1^m, CAPRI, and RASAL (2, 23-25). These proteins are characterized by a domain architecture comprising amino-terminal tandem C2 domains, a highly conserved central Ras GAP-related domain (RasGRD), and a carboxy-terminal pleckstrin homology (PH) domain that is associated with a Bruton''s tyrosine kinase (Btk) motif (41). Consistent with the presence of the RasGRD, all proteins display Ras GAP activity, although each is differentially regulated following receptor stimulation (41). With the notable exception of GAP1^m, all GAP1 proteins also possess efficient Rap1 GAP activity (22). Such dual specificity is not restricted solely to GAP1 proteins. Recently, C2 domain-containing SynGAP—a neuronal Ras GAP—has also been shown to display Rap1 GAP activity (21), an activity that appears to require, alongside the RasGRD, the presence of a single C2 domain (30).Here we have examined the mechanism behind the dual Ras and Rap1 GAP activities of GAP1^IP4BP. Through the generation of a series of GAP1^IP4BP/GAP1^m chimeras, we have established that while the C2 domains of GAP1^IP4BP are required to stabilize the RasGRD, these domains do not supply catalytic residues required for Rap1 GAP activity. Rather, the Rap1 GAP catalytic machinery appears to reside solely within the RasGRD. By the site-directed mutagenesis of selected asparagine and glutamine residues within this domain—selected following the generation of a predicted molecular model of the GAP1^IP4BP RasGRD-Ras(Rap1) complex—we establish that the ability of GAP1^IP4BP to function as a Rap1 GAP does not occur via a mechanism that utilizes a classic asparagine thumb. Rather, we suggest that the GAP1^IP4BP RasGRD functions to stabilize the switch II region of Rap1 in a manner that allows a catalytic arginine finger from GAP1^IP4BP to drive the hydrolysis of GTP.     

Visual neglect in posterior cortical atrophy

Background  

In posterior cortical atrophy (PCA), there is a progressive impairment of high-level visual functions and parietal damage, which might predict the occurrence of visual neglect. However, neglect may pass undetected if not assessed with specific tests, and might therefore be underestimated in PCA. In this prospective study, we aimed at establishing the side, the frequency and the severity of visual neglect, visual extinction, and primary visual field defects in an unselected sample of PCA patients.