1,720,957 research outputs found
Platelet derived growth factor B gene expression in the Xenopus laevis developing central nervous system
Full text linkPlatelet-derived growth factor B (PDGF-B) belongs to the mitogen and growth factor family and like the other members it has many roles in cell differentiation, proliferation and migration during development, adult life and in pathological conditions. Among them it has been observed that aberrant PDGF signalling is frequently linked to glioma development and progression, and Pdgf-b over-expression in mouse neural progenitors leads to the formation of gliomas. Despite this evidence, the mechanisms underlying PDGF-B driven tumorigenesis and its role during brain development are not fully understood. In order to contribute to clarifying possible new roles of pdgf-b signalling, we present here the embryonic gene expression pattern of pdgf-b, so far unknown in early vertebrate development. By using Xenopus laevis as a model system we performed qRT-PCR and whole mount in situ hybridization. Pdgf-b mRNA is expressed in discrete regions of the developing central nervous system, in the cranial nerve placodes and in the notochord. We also compared the gene expression of pdgf-b with that of its receptor pdgfr-a suggesting so far unsuspected roles for this signalling pathway during the development of specific embryonic structures
Use of Xenopus laevis Neural Crest Cells to study the role of PDGF-B in gliomas tumor progression
No full textGliomas are the most common primary tumours of the central nervous system; one of their major features is the ability of individual cells to infiltrate the brain parenchyma, which renders these tumours also the most aggressive. Evidences gained from studies on animal models have firmly established a causal connection between aberrant PDGF-B signalling and the formation of some gliomas. The aim of my project is to unravel the mechanisms underlying PDGF-B driven gliomagenesis and tumour progression, especially focusing on alteration of motility and migration. For this purpose, I used the animal model Xenopus laevis and in particular I focused on Neural Crest Cells (NCC), considering the many similarities shared by this population with cancer cells.
I demonstrated that over-expression of human PDGF-B in Xenopus embryos, obtained by mRNA microinjection, can alter NCC behaviour in terms of migration and streams segregation, validating the system. I then analysed, in PDGF-B injected embryos, the expression of some of the key players known to regulate NCC development such as: Cadherins, Chemokines and their receptors, Neuropilins and Semaphorins and Wnt/PCP pathway members. The results obtained highlighted a significant down-regulation of neuropilin-2 and of wnt11, a Wnt/PCP pathway member, suggesting for the first time a link between their expression and the PDGF signalling. The discovery of these new putative targets of the PDGF-B signalling pathway opens new possible lines of investigations aimed to identify alternative therapeutic approaches for glioma treatment.
Interestingly, I also evidenced that the gene expression pattern of Xenopus pdgf-b during embryogenesis relies in domains close to NCC, suggesting a possible physiological role for it in NCC development. In this regard, I deeper characterised the spatial and temporal expression profile of Pdgf-b during Xenopus embryogenesis and I performed loss of function experiments that showed how NCC migration is affected after pdgf-b down-regulation. Furthermore, with an in vivo chemotaxis assay, I observed that PDGF-BB can act as a chemoattractant for NCC in vivo, suggesting a putative chemotactic role for it and strengthening the hypothesis that this growth factor might play a physiological role in NCC migration
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
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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