1,720,960 research outputs found
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
Arsenite-induced aneuploidy following short and long-term exposure in mammalian cells
No full textWe studied the long-term progression of chromosomal instability in V79 cells treated acutely with arsenite (10mM, 24
hr) followed by growth in arsenic-free medium for 120 cell generations. Indirect immunostaining using anti-ß-tubulin
antibody showed severe alterations in spindle morphology after only 6 h treatment and cytogenetic investigations
carried out at the end of treatment revealed that the percentage of cells with 21 chromosomes (modal number of the cell
line) decreased, making way for aneuploid cells. The acquired instability remained and propagated within the cell
population. Moreover, we treated V79-derived G12 cells with sub-lethal doses (0.1-1.0 μM) of arsenite for 10 days
followed by growth in arsenite-free medium for 40 cell generations. Cytogenetic analysis at the end of treatment
showed concentration-dependent increase in aneuploid cells frequency that was even higher after 40 cell generations. In
addition to this finding a large amount of cells in anaphase and cells with chromosomes showing premature centromere
division was observed. Western blotting analysis showed dose-dependent upregulation of Mad2 that returns to normal
after 40 cell generations and persistent aberrant expression of the spindle assembly complex proteins p-BubR1 and
Cenp-E. Taken together, these results demonstrate that arsenic induces aneuploidy independently of mode of treatment;
in particular, results from chronic exposure to sub-lethal doses raise the possibility that arsenic induces bypass of the
spindle assembly checkpoints which may be mechanistically involved in the induction of cell transformation
Persistent dysregulation of DNA methylation in cells with arsenic-induced genomic instability
Full text linkThe mechanisms by which arsenic-induced genomic instability is initiated and maintained are poorly understood. In previous studies long-term progression of chromosomal instability was typified by increasing aneuploidy in Chinese hamster V79 and human keratinocyte cells treated with arsenite for a 24 hr exposure period followed by growth in arsenic-free medium for 40-120 cell generations. In the current study the role of progressive DNA methylation changes was evaluated in long-term cell cultures after brief arsenite treatments as above. We have found altered genomic methylation patterns in cells that were briefly exposed to arsenic with evidence for widespread dysregulation of CpG methylation that persists for many population doublings after the treatment.
In V79 cell populations, progressive aneuploidy increases were notable by 50 cell generations after a 24 hr exposure to 1-10 uM arsenite. Dicentric chromosomes and/or telomeric associations, as well as complex chromosome rearrangements, occurred by 90 cells generations post treatment; and mutator and transformed phenotypes began to appear thereafter. This increasing genomic instability correlated with modifications of global DNA methylation patterns in V79 cells evaluated by 5-methylcytosine antibody binding and MeSAP-PCR. The results show that short-term exposure to arsenite induced an apparent genome hypomethylating effect within a short time after exposure.
In identical protocols using human HaCaT keratinocytes exposed to low doses of arsenite (0.05-0.1 M) for 24 hr, genomewide methylation levels were measured by LINE1 pyrosequencing and gene-specific methylation status was assessed by Methylation-Specific-PCR for up to 40 generations post exposure. Global demethylation following treatment was supported by preliminary LINE-1 studies. Moreover, the study of gene-specific MSP and determination of expression levels by RT-PCR of several genes (p16, hMLH1, hMSH2, DNMT1, DNMT3a and DNMT3b) demonstrated that hMSH2 gene was epigenetically regulated by arsenite and that down regulation of DNMT3a and DNMT3b genes occurred in an arsenite dose-dependent manner.
The results reported here demonstrate that acute 24 hr arsenic exposure promptly induces genome wide DNA hypomethylation, and support the hypothesis that the cells continue to undergo epigenetic reprogramming both at the gene and genomic levels in the absence of further arsenite treatment; thus likely contributing to long-lasting genomic instability that manifests as aberrant chromosomal, mutator and cell transformation effects
Long-term exposure to submicromolar arsenite induces bypass of the spindle assembly checkpoint in mammalian cells
No full textMitosis is regulated by checkpoints that delay mitotic progression when chromosome segregation errors occur. Inaccuracy in checkpoint processes can lead to chromosome instability both in number and structure (CIN). Arsenic is reported to induce CIN by perturbing mitotic spindles and checkpoints, however, its carcinogenic mechanisms are poorly understood. We previously studied the long-term progression of chromosomal instability in V79 cells treated acutely with arsenite (10 M, 24 hr) followed by growth in arsenic-free medium for 120 cell generations, and found time-dependent increase of aneuploid cells. Here, we treated V79-derived G12 cells with sub-lethal doses (0.1-1.0 μM) of arsenite for 10 days followed by growth in arsenite-free medium for 40 cell generations. Cytogenetic analysis at the end of treatment showed concentration-dependent increases in the frequency of aneuploid cells that was even higher after 40 cell generations. Furthermore, the mitotic index (MI) of arsenite-exposed cells was higher than untreated cells at the end of the 10-day treatment or after 40 cell generations without arsenite. Surprisingly, we found that submicromolar 10-day arsenic exposure induced a large amount of cells in anaphase with premature centromere division. These aberrant mitotic figures dramatically increased after 40 cell generations. Taken together, these results raise the possibility that chronic exposure to sub-lethal arsenic doses induces bypass of the spindle assembly checkpoints and may be mechanistically involved in the induction of cell transformation
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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