1,720,977 research outputs found
Expressing Hoxa2 across the entire endochondral skeleton alters the shape of the skeletal template in a spatially restricted fashion
No full textHox genes control morphogenesis along the antero-posterior axis. The skeleton of vertebrates offers an exemplar readout of their activity: Hox genes control the morphology of the skeleton by defining type of vertebrae, and structure of the limbs. The head skeleton of vertebrates is formed by cranial neural crest (CNC), and mainly by a Hox-free domain of the CNC. Ectopic expression of anterior Hox genes in the CNC prevents the formation of the facial skeleton. These inhibitory effects on skeletogenesis are at odds with the recognized function of Hox genes in patterning the developing skeleton. To clarify these controversial effects, we overexpressed Hoxa2 across the entire developing endochondral skeleton in mouse. This gave rise to strong and spatially restricted effects: the most noticeable abnormalities were detected in the cranial base and consisted in a failure of bones to form or in a transformed morphology of bones. The rest of the skeleton exhibited milder defects, which never consisted in the absence or the transformation of any skeletal components. Analyses at early stages of endochondral bone development showed disorganized cell condensations in the cranial base of Col2a1-Hoxa2 transgenic embryos. We show that the distribution of Hoxa2-positive cells in Col2a1-Hoxa2 embryos does not match the wild-type developing cartilages. The Hoxa2-positive cells detected in atypical, non-chondrogenic location in the cranial base, remain as chondrocytes and lay down cartilage, indicating that Hoxa2 does not alter the fate of chondrocytes, but interferes with their spatial distribution. We propose that the ability of Hoxa2 to change the spatial distribution of cells accounts for the different phenotypes observed in Col2a1-Hoxa2 embryos; it also provides an explanation for the apparent inconsistency between the inhibitory effects of Hoxa2 on skeletal development, and the ability of Hox genes to establish the morphology of the vertebrate skeleton. © 2009 International Society of Differentiation
OTX2 homeodomain protein binds a DNA element necessary for interphotoreceptor retinoid binding protein gene expression
No full textA single cis-acting element in a short promoter segment of the gene encoding the interphotoreceptor retinoid-binding protein confers tissue- specific expression
No full textA single cis-acting element in a short promoter segment of the gene encoding the Interphotoreceptor Retinoid Binding Protein (IRBP) confers tissue-specific expression
No full text
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
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