1,721,669 research outputs found
Toward a better understanding of composition and functions of the salivary secretions of the African malaria mosquito Anopheles gambiae.
No full textSeveral parasitic and viral diseases that represent a severe threat to human health are transmitted through the bites of arthropod vectors. The mosquito Anopheles gambiae is the most important vector of human malaria, a disease that is a global public health problem and one of the leading causes of mortality in Sub-saharan Africa. The Plasmodium parasite undergoes through complex developmental transitions in the mosquito vector and, as a final step, invades the salivary glands and can be transmitted to the vertebrate host during the next blood meals. The salivary glands of arthropod disease vectors are an interesting object of study not only in virtue of their role in pathogen transmission but also in view of the large variety of pharmacological activities that they secrete. Indeed, hematophagous arthropods saliva contains anti-hemostatic factors, that are essential for an efficient blood-feeding, as well as immuno-modulators, that interfere with the host immune response and that may enhance the transmission of pathogens (as shown for Leishmania by sandflies or for different viruses by mosquitoes and ticks). Moreover, salivary antigens may be strongly immunogenic inducing intense allergic reactions or evoking delayed-type hypersensitivity responses. Because of their immunogenic potential the use of salivary antigens as possible vaccine components is presently being evaluated (Valenzuela et al, 2001 J Exp Med, 194: 331-342). We started a few years ago a molecular study on the An. gambiae salivary glands with a special emphasis on secreted factors and potential sporozoite receptors. For this reason we used the Signal Sequence Trap (SST), a method that would allow for the isolation of cDNAs encoding secreted and transmembrane proteins independently from their functions. In two different rounds of SST screening (Arcà et al, 1999 Proc Natl Acad Sci USA, 96: 1516-1521; Lanfrancotti et al, 2002 FEBS Letters, in press) we identified 22 novel genes which are either specifically expressed in the salivary glands (10 female gland-specific, 6 expressed both in male and female glands) or whose expression is highly enriched in female glands. We studied to a certain extent the platelet inhibitor apyrase (Lombardo F et al, 2000 J Biol Chem, 275: 23861-23868) and a family of D7-related (D7r) genes (Arcà B et al, 2002 Insect Mol Biol, 11:47-55), however, several other proteins such as an Antigen 5 family member (gVAG), putative anticoagulants (cE5, gSG6, gSG7) and a novel family of proteins that we named glandins were identified. A striking result is that we could not assign a possible function to most of the genes identified; this observation underlines the complexity of mosquito saliva and points out that we have identified several novel activities. The accompanying abstracts by Lanfrancotti A et al. and by Lombardo F et al. report in detail some of the main outcome of our study. We summarize below the main properties of the An. gambiae D7r protein family. The D7r represent a cluster of four genes located in a region of approximately 6 kb on chromosome arm 3R. Tissue and developmental RT-PCR expression analysis showed that they are specifically and abundantly expressed in the An. gambiae adult female salivary glands, suggesting that they may play some essential role in blood-feeding. They are similar in sequence to D7, a salivary gene of unknown function previously isolated from the mosquito Aedes aegypti. Sequence analysis shows that the D7r deduced proteins are significantly shorter in comparison to D7 suggesting that the D7 family may include two type of proteins, long and short forms. A high degree of divergence within this protein family is also confirmed by Southern analysis on a few representative mosquito species of the culicine and anopheline subfamilies. The D7r proteins can be aligned, in virtue of four highly conserved cysteine residues, to an heterogeneous group of insect proteins that includes odorant- and pheromone-binding proteins, as well as several other proteins secreted in acqueous media as different as hemolymph, saliva or seminal fluid. The structure of two of these proteins, the Tenebrio molitor THP12 and the Bombyx mori pheromone-binding protein have been determined. They contain six alfa-helix folded to delimit a pocket where small hydrophobic ligands can bind. Secondary structure prediction analysis suggests that the D7r proteins may have a very similar tridimensional structure and that, therefore, they may function as carriers or binders of small hydrophobic molecules
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
The Anopheles gambiae D7-related are a cluster of salivary genes involved in blood feeding and belong to the insect odorant-binding protein superfamily.
No full textThe salivary glands of the mosquito Anopheles gambiae, the most important vector of human malaria, are an interesting target organ for molecular entomology studies both in virtue of their role in pathogen transmission and for the large variety of pharmacological activities which they secrete (anti-hemostatics, immuno-modulators, etc.). We started a few years ago a detailed molecular analysis of the An. gambiae salivary glands and, using the Signal Sequence Trap (SST) technique, we identified 22 novel genes which are either specifically expressed in the salivary glands or whose expression is highly enriched in female glands (1, 2). Among these are the platelet inhibitor apyrase (3), putative anticoagulants (cE5, gSG6, gSG7), a novel family of proteins that we named glandins, an insect Antigen 5 family member (gVAG) and a group of four D7-related salivary proteins (4). The D7-related (D7r) are similar in sequence to the Aedes aegypti D7 and form a cluster of closely linked genes located in a 6 kb region on chromosome arm 3R. Their function is still unknown but they are specifically and abundantly expressed in adult female salivary glands, suggesting that they probably play some essential role in blood-feeding. The D7r belong to a highly divergent family of proteins that is widely spread in blood-sucking Diptera (5) and they can be aligned, in virtue of four highly conserved cysteine residues, to an heterogeneous group of insect proteins belonging to the odorant-binding proteins superfamily. Despite the low sequence identity two members of this family, the Tenebrio molitor THP12 and the Bombyx mori pheromone-binding protein, share a similar tridimensional structure and are organized in six alfa-helices folded to delimit a pocket where small hydrophobic ligands can bind. Sequence comparison and secondary structure prediction analysis suggest that the D7r proteins may adopt a very similar folding and, therefore, may facilitate blood feeding by carrying or binding small hydrophobic molecules. (1) Arcà B et al, 1999 PNAS USA, 96: 1516-21. (2) Lanfrancotti A et al, 2002 FEBS Letters, 517: 67-71. (3) Lombardo F et al, 2000 JBC, 275: 23861-68. (4) Arcà B et al, 2002 Insect Mol Biol, 11:47-55. (5) Valenzuela J et al, 2002 Insect Mol Biol, 11: 149-155
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Asymmetric equilibria of two nested elastic rings
Full text linkThe packing of soft elastic structures is an important and challenging problem due to the possibility of multiple discrete and continuous zones of contact between different parts of the material. To address this problem, we consider the simplest possible packing problem of a thin elastic ring confined within another shorter flexible ring. The elastic properties as well as the dimensionality of both structures, combined with the contact condition yield a wide a variety of possible equilibrium shapes. When the rings are assumed to be inextensible and unshearable, the equilibrium shapes depend only on their relative bending stiffness κ, and on their relative length μ. Whereas the symmetric equilibria for such a problem have been completely determined, the possibility of asymmetric equilibria with lower energy has not yet been considered. For a fixed value of the relative bending stiffness, we explore these symmetry-breaking equilibria as the length of the inner ring increases. We show that, for μ ≃ 1.9 there is a symmetry-breaking bifurcation and asymmetric equilibria are preferred in order to relax the elastic energy
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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