1,721,015 research outputs found
Analysis of a botryllid enriched-full-length cDNA library: insight into the evolution of spliced leader trans-splicing in tunicates.
Full text linkIn some animals, mRNA may be modified after transcription by the addition of a 5' spliced leader sequence. This is known as spliced leader (SL) trans-splicing, and is of uncertain function and evolutionary origin. Here, we report the identification of SL trans-splicing in the colonial ascidian Botryllus schlosseri. Combining our own expressed sequence tag (EST) data with additional data from GenBank, we identify the dominant spliced leader sequence and show it to be similar to that of other ascidians and to that of Oikopleura dioica, a basally diverging tunicate. Gene Ontology analysis of B. schlosseri ESTs with and without a 5' spliced leader shows that genes encoding ribosomal proteins tend not to be trans-spliced, a character shared with the ascidian Ciona intestinalis. We also examine individual cases of genes that produce mRNAs that are SL trans-spliced in B. schlosseri but not in C. intestinalis. We conclude that SL trans-splicing evolved early in the tunicate lineage and shows stability over considerable evolutionary time. However, SL trans-splicing may be gained or lost in individual genes
Gene expression during body muscle differentiation in the colonial ascidian Botryllus schlosseri.
No full textAscidians display three types of muscles during their life: striated in the larval tail and heart, and smooth in the post-metamorphic sessile phase. The larval and cardiac muscles have an arrangement of myofilaments like the striated muscle of vertebrates. Instead, the smooth body-wall musculature has intermediate characters between smooth and striated muscle of vertebrates. A great number of ascidians form colonies constituted of clonal individuals (blastozooids) originated by asexual reproduction. We studied the musculature in Botryllus schlosseri analysing its organization, differentiation with electron microscopy. Moreover, we followed gene expression of muscle actin and troponin T in the larva and during the development of blastozooids, beginning from the early bud stage to adult and regression stage. We isolated and characterised two transcripts from colonies that resulted homologous to muscle genes of solitary ascidians: a muscle-type actin (BsMA2), a cytoplasmic-type actin (BsCA1) and a troponin T (BsTnT-c). Moreover, we obtained also the genomic sequences coding for BsMA2 and BsCA1.
Phylogenetic analyses showed a close relationship between urochordates and vertebrates muscle genes. The BsMA2 and BsCA1 genomic sequences were compared in the exon-intron organization with other muscle and cytoplasmic–type actin genes of both invertebrates and vertebrates. Our data revealed that intron positions are conserved in ascidians and in the other deuterostomes.
We detected the expression of the two genes by in situ hybridization on section (ISH) throughout the blastogenetic cycle of B. schlosseri. The ISH, in parallel with phalloidin staining experiments, showed that the first diffuse signal of BsMA2 and BsTnT-c labels differentiating muscles which appear in the intersiphonal area of young buds. Then, the muscle fibres differentiate into the body-wall, while an intense expression only of BsMA2 marks the myocardium just when it begins contractions. Thus, all the phases of muscle development and regression were documented by an integrated study showing the close correspondence of in situ expression of BsMA2 and BsTnT-c, phalloidin signal and ultrastructure
Evolutionary conservation of the placodal transcriptional network during sexual and asexual development in chordates
Full text linkBackground: An important question behind vertebrate evolution is whether the cranial placodes originated de novo, or if their precursors were present in the ancestor of chordates. In this respect, tunicates are of particular interest as they are considered the closest relatives to vertebrates. They are also the only chordate group possessing species that reproduce both sexually and asexually, allowing both types of development to be studied to address whether embryonic pathways have been co-opted during budding to build the same structures. Results: We studied the expression of members of the transcriptional network associated with vertebrate placodal formation (Six, Eya, and FoxI) in the colonial tunicate Botryllus schlosseri. During both sexual and asexual development, each transcript is expressed in branchial fissures and in two discrete regions proposed to be homologues to groups of vertebrate placodes. Discussion: Results reinforce the idea that placode origin predates the origin of vertebrates and that the molecular network involving these genes was co-opted in the evolution of asexual reproduction. Considering that gill slit formation in deuterostomes is based on similar expression patterns, we discuss possible alternative evolutionary scenarios depicting gene co-option as critical step in placode and pharynx evolution. Developmental Dynamics 242:752-766, 2013. © 2013 Wiley Periodicals, Inc
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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