1,720,967 research outputs found
Reorganization of sea urchin gene regulatory networks at least 268 million years ago as revealed by oldest fossil cidaroid echinoid
Full text linkEchinoids, or sea urchins, are rare in the Palaeozoic fossil record, and thus the details regarding the early diversification of crown group echinoids are unclear. Here we report on the earliest probable crown group echinoid from the fossil record, recovered from Permian (Roadian-Capitanian) rocks of west Texas, which has important implications for the timing of the divergence of crown group echinoids. The presence of apophyses and rigidly sutured interambulacral areas with two columns of plates indicates this species is a cidaroid echinoid. The species, Eotiaris guadalupensis, n. sp. is therefore the earliest stem group cidaroid. The occurrence of this species in Roadian strata pushes back the divergence of cidaroids and euechinoids, the clades that comprise all living echinoids, to at least 268.8 Ma, ten million years older than the previously oldest known cidaroid. Furthermore, the genomic regulation of development in echinoids is amongst the best known, and this new species informs the timing of large-scale reorganization in echinoid gene regulatory networks that occurred at the cidaroid-euechinoid divergence, indicating that these changes took place by the Roadian stage of the Permian
Ancestral state reconstruction by comparative analysis of a GRN kernel operating in echinoderms
No full textDiverse sampling of organisms across the five major classes in the phylum Echinodermata is beginning to reveal much about the structure and function of gene regulatory networks (GRNs) in development and evolution. Sea urchins are the most studied clade within this phylum, and recent work suggests there has been dramatic rewiring at the top of the skeletogenic GRN along the lineage leading to extant members of the euechinoid sea urchins. Such rewiring likely accounts for some of the observed developmental differences between the two major subclasses of sea urchins—cidaroids and euechinoids. To address effects of topmost rewiring on downstream GRN events, we cloned four downstream regulatory genes within the skeletogenic GRN and surveyed their spatiotemporal expression patterns in the cidaroid Eucidaris tribuloides. We performed phylogenetic analyses with homologs from other non-vertebrate deuterostomes and characterized their spatiotemporal expression by quantitative polymerase chain reaction (qPCR) and whole-mount in situ hybridization (WMISH). Our data suggest the erg–hex–tgif subcircuit, a putative GRN kernel, exhibits a mesoderm-specific expression pattern early in Eucidaris development that is directly downstream of the initial mesodermal GRN circuitry. Comparative analysis of the expression of this subcircuit in four echinoderm taxa allowed robust ancestral state reconstruction, supporting hypotheses that its ancestral function was to stabilize the mesodermal regulatory state and that it has been co-opted and deployed as a unit in mesodermal subdomains in distantly diverged echinoderms. Importantly, our study supports the notion that GRN kernels exhibit structural and functional modularity, locking down and stabilizing clade-specific, embryonic regulatory states
Juvenile skeletogenesis in anciently diverged sea urchin clades
Full text linkAbstractMechanistic understanding of evolutionary divergence in animal body plans devolves from analysis of those developmental processes that, in forms descendant from a common ancestor, are responsible for their morphological differences. The last common ancestor of the two extant subclasses of sea urchins, i.e., euechinoids and cidaroids, existed well before the Permian/Triassic extinction (252 mya). Subsequent evolutionary divergence of these clades offers in principle a rare opportunity to solve the developmental regulatory events underlying a defined evolutionary divergence process. Thus (i) there is an excellent and fairly dense (if yet incompletely analyzed) fossil record; (ii) cladistically confined features of the skeletal structures of modern euechinoid and cidaroid sea urchins are preserved in fossils of ancestral forms; (iii) euechinoids and cidaroids are among current laboratory model systems in molecular developmental biology (here Strongylocentrotus purpuratus [Sp] and Eucidaris tribuloides [Et]); (iv) skeletogenic specification in sea urchins is uncommonly well understood at the causal level of interactions of regulatory genes with one another, and with known skeletogenic effector genes, providing a ready arsenal of available molecular tools. Here we focus on differences in test and perignathic girdle skeletal morphology that distinguish all modern euechinoid from all modern cidaroid sea urchins. We demonstrate distinct canonical test and girdle morphologies in juveniles of both species by use of SEM and X-ray microtomography. Among the sharply distinct morphological features of these clades are the internal skeletal structures of the perignathic girdle to which attach homologous muscles utilized for retraction and protraction of Aristotles׳ lantern and its teeth. We demonstrate that these structures develop de novo between one and four weeks after metamorphosis. In order to study the underlying developmental processes, a method of section whole mount in situ hybridization was adapted. This method displays current gene expression in the developing test and perignathic girdle skeletal elements of both Sp and Et juveniles. Active, specific expression of the sm37 biomineralization gene in these muscle attachment structures accompanies morphogenetic development of these clade-specific features in juveniles of both species. Skeletogenesis at these clade-specific muscle attachment structures displays molecular earmarks of the well understood embryonic skeletogenic GRN: thus the upstream regulatory gene alx1 and the gene encoding the vegfR signaling receptor are both expressed at the sites where they are formed. This work opens the way to analysis of the alternative spatial specification processes that were installed at the evolutionary divergence of the two extant subclasses of sea urchins
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
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