1,721,028 research outputs found
Expression and regulation of Xenopus CRMP-4 in the developing nervous system.
Get PDFThe collaspin response mediator proteins (CRMPs) are a family of cytosolic phosphoproteins which play a critical role in the establishment of neuronal polarity and growth cone guidance. Here, we describe the temporal and spatial expression of CRMP-4 during early Xenopus embryogenesis. CRMP-4 transcripts were first detected by whole mount in situ hybridization at the end of gastrulation in the prospective neuroectoderm. During open neural plate stages, CRMP-4 was expressed broadly throughout the anterior neural plate and in the three bilateral stripes of the posterior neural plate where primary neurons arise. The expression in the territories of primary neurogenesis prefigures that of the post-mitotic neuronal marker N-tubulin. At tadpole stages, expression was maintained throughout the central nervous system and in the retina of the eye. Consistent with the observed expression, CRMP-4 transcripts are positively regulated by X-ngnr-1 and negatively by Notch signaling. The observed expression and regulation of CRMP-4 differ from that of the CRMP-2, which is induced by the events of neural induction.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe
The RNA-binding protein XSeb4R: a positive regulator of VegT mRNA stability and translation that is required for germ layer formation in Xenopus.
No full textVegT represents a localized maternal determinant essentially required for endoderm formation in Xenopus. Here, we report on the identification of the RNA-binding protein XSeb4R as a positive regulator of VegT. XSeb4R interacts directly with the 3'-untranslated region of VegT mRNA, stabilizes it, and stimulates translation. Ablation of XSeb4R activity results in impairment of endoderm and mesoderm formation, while ectopic expression of XSeb4R in ectodermal cells induces endodermal and mesodermal gene expression. These observations unravel a novel mode of VegT regulation at the post-transcriptional level that is essential for germ layer formation in Xenopus.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe
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
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
Characterization of Novel Genes Involved in Neurogenesis in Xenopus
No full textDer Südafrikanische Krallenfrosch Xenopus laevis ist ein gutes System für das Studium der Neurogenese in Vertebraten. Bereits früh, im offenen Neuralplattenstadium, wird das Gebiet der primären Neuronen durch eine Gruppe von neuralen Genen definiert, die in einem typischen Muster in Form von Streifen exprimiert werden und die drei bilaterale Zellgruppen definieren, aus denen jeweils Motorneuronen, Interneuronen und sensorische Neuronen hervorgehen. Eine Untergruppe enthält Gene, deren Expressionsmuster dem von N-tubulin, einem neuronalen Differenzierungsmarker, entspricht. Diese Untergruppe wird aufgrund der Beobachtung, dass Mitglieder dieser Gruppe bei der Differenzierung von primären Neuronen eine Funktion besitzen, als N-tubulin Synexpressionsgruppe bezeichnet. Eine andere Untergruppe, die als Delta Synexpressionsgruppe bezeichnet wird, beinhaltet Gene, deren Expressionsmuster dem von X-Delta-1 ähnelt. Mitglieder dieser Gruppe regulieren die lokalen Zell-Zell-Interaktionen, im Zusammenhang mit der primären Neurogenese bekannt als laterale Hemmung. Insgesamt sind solche Expressionsmuster ein wertvolles Kriterium für die Suche nach neuen Genen, die bei der primären Neurogenese eine Funktion besitzen. Wir haben 500 Klone aus einer Xenopus Schwanzknospenstadium Kopf cDNA Bank durch Verwendung einer systematischen Expressionsmusteranalyse untersucht. Aus der Fülle der neural exprimierten Gene werden fünf in Form von Streifen exprimiert. Drei dieser Gene sind in Xenopus bisher nicht beschrieben worden. Diese beeinhalten XPak3, eine Serin/Threonin Proteinkinase, und X-Mxi1, ein basisches Helix-Loop-Helix Leucin Zipper Protein, die beide zur N-tubulin Synexpressionsgruppe gehören, sowie XSeb4, ein RRM-Typ RNA bindendes Protein, das zur Delta Synexpressionsgruppe gehört. Basierend auf der Tatsache, dass XPak3 und XSeb4 regulatorische Moleküle mit unbekannter Funktion bei der Neurogenese definieren, wurde ihre funktionelle Charakterisierung durchgeführt. Durch Mikroinjektionsexperimente in Embryonen wurde gefunden, dass XPak3 und XSeb4 auf Transkriptionsebene durch den proneuralen Faktor X-Neurogenin related-1 (X-Ngnr-1) aktiviert und durch laterale Hemmung reprimiert wurden. Eine vergleichende Expressionsmusteranalyse zeigte, dass XPak3, aber nicht XPak1 und XPak2, eine neuronal exprimierte XPak Isoform ist. Interessanterweise induzierte die Überexpression einer konstitutiv aktiven Form von XPak3, XPak3-myr, vorzeitige neuronale Differenzierung, ein Phänotyp, der mit der Induktion von Zellzyklusarretierung korreliert. Umgekehrt blockierte der XPak3 Funktionsverlust, der durch Verwendung eines Morpholino-antisense-Oligonukleotids erzeugt wurde, die Bildung von primären Neuronen und induzierte eine gesteigerte Zellproliferation. Diese Hemmung der Neurogenese wurde durch Koinjektion von XPak3-myr wieder aufgehoben. Schlussfolgernd schlagen wir vor, dass XPak3 von Neurogenin induziert wird, um die Mitose neuronal programmierter Zellen zu inhibieren und so deren Differenzierung zu erlauben. Ektopische Expression hoher Konzentrationen (>150 pg) von XSeb4 hemmt die Bildung primärer Neuronen. Unerwarteterweise führte die Unterdrückung der XSeb4 Expression durch die Verwendung eines Morpholino-antisense-Oligonukleotids ebenfalls zur Hemmung der Neurogenese. Die Mikroinjektion niedriger Konzentrationen von XSeb4 mRNA zeigte keinen Effekt auf die Expression von N-tubulin. Diese widersprüchlichen Befunde erfordern weitere systematische Untersuchungen.The South African claw-toed frog, Xenopus laevis, is a good model to study neurogenesis in vertebrates. Early on, at the open neural plate stage, the territory of primary neurons is nicely defined by a set of neural genes expressed in a typical pattern in the form of stripes which define three bilateral groups of cells giving rise to motor neurons, interneurons, and sensory neurons, respectively. One subset comprises genes whose expression pattern mimics that of N-tubulin, a neuronal differentiation marker. This subset has been refered to as N-tubulin synexpression group, thanks to the observation that members of this group are involved in the differentiation of primary neurons. Another subset, designated Delta synexpression group, includes genes whose expression pattern is similar to that of X-Delta-1. Members of this group regulate the local cell-cell interactions in the context of primary neurogenesis known as lateral inhibition. Overall, these patterns of expression are a valuable criterion to search for novel genes involved in primary neurogenesis. We have analysed 500 clones from a Xenopus tailbud stage head cDNA library by use of a systematic expression pattern screen. From the panel of neurally expressed genes, five were expressed in form of stripes. Three of these genes have not been described in Xenopus. These genes are XPak3, a serine/threonine protein kinase, and X-Mxi1, a basic helix-loop-helix leucine zipper protein, both belonging to the N-tubulin synexpression group, and XSeb4, a RRM-type RNA binding protein, belonging to the X-Delta-1 synexpression group. Based on the fact that XPak3 and XSeb4 define regulatory molecules with unknown function in neurogenesis, their functional characterization was carried out. By embryo microinjection experiments, XPak3 and XSeb4 were found to be transcriptionally activated by the proneural factor X-Neurogenin related-1 (X-Ngnr-1) and repressed by lateral inhibition. Comparative expression pattern analysis showed that XPak3 but not XPak1 or XPak2 is a neuronally expressed XPak isoform. Interestingly, overexpression of a constitutively active form of XPak3, XPak3-myr, induced premature neuronal differentiation, a phenotype correlating with the induction of cell cycle arrest. Conversely, XPak3 loss-of-function, generated by using a morpholino antisense oligonucleotide, blocked the formation of primary neurons and induced increased cell proliferation. This inhibition of neurogenesis was rescued by coinjection of XPak3-myr. In conclusion, we propose that XPak3 is induced by neurogenin to inhibit the mitosis of neuronally programmed cells and thereby allowing for their differentiation. Ectopic expression of high concentrations (>150 pg) of XSeb4 inhibits the formation of primary neurons. Unexpectedly, the suppression of XSeb4 expression, using morpholino antisense oligonucleotide, also led to inhibition of neurogenesis. Microinjection of low concentrations of XSeb4 mRNA showed no effect on the expression of N-tubulin. These contradictory findings require further systematic investigations
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