1,720,995 research outputs found
On the origins of the extracellular matrix in vertebrates
No full textExtracellular matrix (ECM) is a key metazoan characteristic. In addition to providing structure and orientation to tissues, it is involved in many cellular processes such as adhesion, migration, proliferation and differentiation. Here we provide a comprehensive analysis of ECM molecules focussing on when vertebrate specific matrices evolved. We identify 60 ECM genes and 20 associated processing enzymes in the genome of the urochordate Ciona intestinalis. A comparison with vertebrate and protostome genomes has permitted the identification of both a core set of metazoan matrix genes and vertebrate-specific innovations in the ECM. We have identified a few potential cases of de novo vertebrate ECM gene innovation, but the majority of ECM genes have resulted from duplication of pre-existing genes present in the ancestral vertebrate. In conclusion, the modern complexity we see in vertebrate ECM has come about largely by duplication and modification of pre-existing matrix molecules. Extracellular matrix genes and their processing enzymes appear to be over-represented in the vertebrate genome suggesting that these genes played an active role enabling and underpinning the evolution of vertebrates
Back to basics - How the evolution of the extracellular matrix underpinned vertebrate evolution
No full textThe extracellular matrix (ECM) is a complex substrate that is involved in and influences a spectrum of behaviours such as growth and differentiation and is the basis for the structure of tissues. Although a characteristic of all metazoans, the ECM has elaborated into a variety of tissues unique to vertebrates, such as bone, tendon and cartilage. Here we review recent advances in our understanding of the molecular evolution of the ECM. Furthermore, we demonstrate that ECM genes represent a pivotal family of proteins the evolution of which appears to have played an important role in the evolution of vertebrates. © 2009 Blackwell Publishing Ltd
The characterisation of six ADAMTS proteases in the basal chordate Ciona intestinalis provides new insights into the vertebrate ADAMTS family
No full textADAMTS, constituting a recently discovered family of secreted zinc-dependent metalloproteases, have been shown to have critical physiological roles through identification of a number of natural animal and human gene mutations. The identification of six ADAMTS genes in the basal chordate Ciona intestinalis provides new insight into how, when and in what order the vertebrate orthologues have evolved. The phylogenetic assignments, based on sequences conserved across all genes, are supported by conserved domain structures within defined sub-families. The phylogeny and the frequent localisation of ADAMTS genes in paralogous regions of the genome are consistent with the vertebrate lineages having arisen by large scale or genome duplication. The high level of conservation in the protease active site of vertebrate orthologues within some sub-families suggests subfunctionalisation, whereas the greater divergence in others would favour the evolution of novel substrate specificities and these observations are borne-out where substrate-specificity is known. The expansion and sub-specialization of the ADAMTS family is a component of the increased complexity of extracellular matrix that is associated with the evolution of vertebrates. © 2005 Elsevier Ltd. All rights reserved
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
Fibrillar collagen: The key to vertebrate evolution? A tale of molecular incest
No full textFibril-forming (fibrillar) collagens are extracellular matrix proteins conserved in all multicellular animals. Vertebrate members of the fibrillar collagen family are essential for the formation of bone and teeth, tissues that characterise vertebrates. The potential role played by fibrillar collagens in vertebrate evolution has not been considered previously largely because the family has been around since the sponge and it was unclear precisely how and when those particular members now found in vertebrates first arose. We present evidence that the classical vertebrate fibrillar collagens share a single common ancestor that arose at the very dawn of the vertebrate world and prior to the associated genome duplication events. Furthermore, we present a model, 'molecular incest', that not only accounts for the characteristics of the modern day vertebrate fibrillar collagen family but demonstrates the specific effects genome or gene duplications may have on the evolution of multimeric proteins in general. © 2003 Wiley Periodicals, Inc
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
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