1,720,995 research outputs found
MEK/ERK regulation by the ephrin pathway during neural development in ascidian Ciona intestinalis
No full textDurant ma thèse, j’ai participé à une étude fonctionnelle qui a démontré que p120-RasGAP, une protéine appartenant à la famille GAP (GTPase-activating protein), est le médiateur cytoplasmique de l’éphrine lors de l’atténuation d’ERK1/2. Pour confirmer cela, j’ai réalisé une expérience de co-immunoprécipitation et j’ai démontré que p120-RasGAP s’associe au récepteur de l’éphrine, Eph3, quand celui-ci est activé par un ligand éphrine. Ce résultat indique fortement que les signaux FGF et éphrine convergent au niveau de Ras et qu’ils contrôlent de manière antagoniste son activité. Dès lors, j’ai analysé les autres événements de spécification cellulaire impliquant l’antagonisme FGF/éphrine. Chez l’embryon d’ascidie, le signal FGF est décrit comme inducteur du destin neural dans les cellules ectodermiques qui, en absence du signal FGF, adoptent le destin épidermique. L’induction neurale des ascidies a lieu au stade 32 cellules et se traduit par la spécification de quatre précurseurs neuraux (ERK+) parmi les 16 cellules ectodermiques. J’ai démontré que le signal éphrine/Eph/RasGAP antagonise le signal FGF pour générer une activation d’ERK1/2 de type tout ou rien parmi les cellules ectodermiques. Enfin, en collaboration avec Philip Abitua, doctorant dans le laboratoire du Dr. Mike Levine (UC Berkeley), nous démontrons que l’antagonisme entre les signaux éphrine et FGF est impliqué dans la régionalisation antéro-postérieure de la plaque neuraleDuring my thesis study, I was involved in functional studies to demonstrate that p120-RasGAP, a GTPase-activating-protein (GAP), is a cytoplasmic mediator of the ephrin-mediated ERK attenuation. To confirm this notion, I conducted a co-immunoprecipitation experiment and demonstrated that p120-RasGAP associates with an ephrin receptor, Eph3, when the latter is activated by an ephrin ligand in ascidian embryos. These results strongly indicate that FGF and ephrin signals converge at the level of Ras and control its activity antagonistically. Following this finding, I looked for other cell fate specification events controlled by the antagonism between ephrin and FGF signals. In ascidian embryos, FGF signals are known to induce neural fates in ectodermal cells which otherwise adopt epidermal fates. Ascidian neural induction takes place at the 32-cell stage, resulting in specification of specific four cells as ERK1/2-active neural precursors among 16 ectodermal cells. I was able to demonstrate that ephrin/Eph/RasGAP signals counterbalance FGF neural inducing signals to generate the ON-OFF response of ERK activation among the ectodermal cells. Finally, in collaboration with a PhD student in Dr. Mike Levine’s lab (UC Berkeley), the antagonism between ephrin and FGF signals plays a role in regionalisation of the neural plate along the anterior-posterior axis
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Patterning across the ascidian neural plate by lateral Nodal signalling sources
No full textInternational audienc
Spécification de destinées cellulaires dans l'embryon de l'ascidie Ciona intestinalis (étude de la ségrégation des destinées neurale et notochorde)
No full textL'embryogénèse précoce est un processus complexe au cours duquel divers types cellulaires sont spécifiés de manière contrôlée dans l'espace et dans le temps. Les embryons présentant un lignage cellulaire fixe permettent de suivre la ségrégation des destinées cellulaires à un niveau de résolution cellulaire individuel. Les embryons d'ascidie représentent de ce point de vue un modèlé idéal et nous utilisons l'ascidie Ciona intestinalis pour étudier la manière dont les destinées notochorde et neurale sont ségrégées à partir des progéniteurs communs. A la fin du stade 32 cellules dans ces embryons, deux blastomères végétatifs (A6.2 et A6.4) subissent une division cellulaire au cours de laquelle ils donnent chacun naissance à un précurseur de la notochorde et un précurseur neural. L'événement central dans la ségrégation des destinées neurale et notochorde est une activation différentielle de la MAP kinase ERK1/2 entre les deux cellules filles : les cellules qui présentent une activation de ERK1/2 adoptent une destinée notochorde tandis que les cellules qui ne présentent pas d'activation ERK1/2 adoptent une destinée neurale. L'activation de ERK1/2 est sous contrôle du ligand FGF9/16/20 exprimé dans tout l'hémisphère végétatif. Au cours de ma thèse, j'ai pu montrer qu'un ligand membranaire de type ephrin, appelé ephrin-Ad, est exprimé de manière localisée dans les cellules de l'hémisphère animal faisant contact avec la lignée neurale mais pas avec la lignée notochorde. Ce ligand, au travers d'un récepteur à activité tyrosine kinase EPH, est responsable de l'inhibition spécifique de ERK1/2 dans les cellules de destinée neurale. De plus, nous avons démontré que cette voie de signalisation ephrin/EPH est responsable de la polarisation de la cellule mère notochorde/neurale qui acquière ainsi une capacité intrinsèque à se diviser de manière asymétrique avant la cytocinèse. Enfin, j'ai montré que la protéine Ras-GAP est vraisemblablement impliquée dans l'inhibition de la voie des MAPK en aval de la signalisation ephrin/EPH.Early embryogenesis is a complex process during which diverse cell type precursors are specified in a defined spatio-temporal pattern. Embryos with a fixed cell lineage allow the segregation of cell fates to be precisely followed during embryogenesis. The invertebrate chordate embryos of ascidians are, from that point of view, an ideal model and we are using the ascidian Ciona intestinalis to study how notochord and neural fates become segregated. Using a morpholino knockdown strategy, we have shown that inhibition of ERK1/2 in the neural lineage is mediated by an ephrin membrane-bound ligand, namely ephrin-Ad. Ephrin-Ad is expressed in the animal cells, which are in contact with cells of the neural lineage but not those of the notochord lineage. Using dominant negative forms, we have also shown that this ephrin is mediated via an Eph receptor and the Ci-p120-Ras-GAP, leading to the selective inhibition of ERK1/2 in the neural lineage.NICE-BU Sciences (060882101) / SudocSudocFranceF
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
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