1,721,013 research outputs found
Inhibition of polyoma gene expression in transformed mouse cells by hypermethylation
No full textThe evolution of mouse cells transformed by a recombinant plasmid containing the genome of the tsA mutant of polyoma virus (Py) cloned at the BamHI site into the plasmid pML, whose sequences therefore interrupt the Py late region, has been studied. Clones of transformed cells were selected at 39 degrees (nonpermissive temperature for large T antigen). Under these conditions viral DNA integration is stable and the cells display a uniformed transformed phenotype. Also studied in detail was the evolution of one of these cell lines (A4) upon shift to a temperature permissive for large T-Ag function (33 degrees); immediately after shift, 90% of the population became intensely positive for T-Ag and a considerable amount of free-viral DNA was produced, accompanied by a clear cytopathic effect. Surviving cells proliferated actively after 4 weeks at 33 degrees and showed a decreased expression of large T-Ag (only 2-3% of the population was T-Ag positive by immunofluorescence), a drastic reduction in the amount of free-viral DNA produced, but no apparent change in the pattern of integration of Py DNA in the host chromosomes. Analysis of the high-molecular-weight DNA with the restriction enzymes HpaII and MspI revealed that the cytosines in the recognition sequences of these enzymes were methylated. Accordingly, treating the cells with 5-Azacytidine, a methylation inhibitor, results in the expression of viral T-Ags in more than 80% of the cell population. Analysis of DNA transcription revealed a dramatic reduction of virus-specific poly(A)+ mRNA in the methylated cells; in addition, the phenotype of the 33 degrees A4 populations was much less transformed than that of the original cultures. The block of Py expression by methylation is not complete; approximately 2% of the cells remain T-Ag positive and viral transcription is not completely suppressed. This could be explained by an incomplete methylation which randomly leaves unmethylated sequences essential for Py gene expression, or by the fact that methylation is not sufficient to block transcription completely. Possible mechanisms underlying this type of evolution are discussed
New rat cell line that is highly susceptible to transformation by several oncogenes.
Full text linkWe describe here a new cell line, EL2, which spontaneously arose from primary rat embryo fibroblasts and has the distinctive property of being highly susceptible to a number of different transforming genes. The high susceptibility is expressed not only in high transformation frequencies but, most importantly, in an unusually high rate of growth of EL2 transformants under selective conditions, i.e., in soft agar or as foci. The biological characteristics of EL2 cells greatly accelerate the isolation of transformants from known oncogenes and could be useful to detect new transforming genes
Mechanisms underlying differential responses to FGF signaling.
No full textFibroblast growth factors (FGFs) are key regulators of several developmental processes in which cell fate and differentiation to various tissue lineages are determined. The importance of the proper spatial and temporal regulation of FGF signals is evident from human and mouse genetic studies which show that mutations leading to the dysregulation of FGF signals cause a variety of developmental disorders including dominant skeletal diseases and cancer. The FGF ligands signal via a family of receptor tyrosine kinases and, depending on the cell type or stage of maturation, produce diverse biological responses that include proliferation, growth arrest, differentiation or apoptosis. A central issue in FGF biology is to understand how these diverse cellular responses are determined and how similar signaling inputs can generate distinct patterns of gene expression that govern the specificity of the cellular response. In this review we draw upon studies from the past fifteen years and attempt to construct a molecular picture of the different levels of regulation by which such specific cellular responses could be achieved by FGF signals. We discuss whether specificity could lie in the nature of the ligand, the particular receptor, the signal transduction pathways utilized, or the transcriptional regulation of specific genes. Finally, we also discuss how the interplay of FGF signals with other signaling systems could contribute to the cellular response. In particular we focus on the interaction with the Wnt pathway since FGF/Wnt cross-talk is emerging as an important nexus in regulating a variety of biological processes
cis- and trans-Acting elements involved in amino acid regulation of asparagine synthetase gene expression
Full text linkWe have previously shown that asparagine synthetase (AS) mRNA expression can be dramatically upregulated by asparagine deprivation in ts11 cells, mutants of BHK hamster cells which encode a temperature-sensitive AS. The expression of AS mRNA was also induced upon starvation for one of several essential amino acids in HeLa cells. We also showed that regulation of AS mRNA expression by amino acid concentration has both transcriptional and posttranscriptional components. Here we report the analysis of the elements in the human AS promoter region important for its basal activity and activation by amino acid starvation. Our results indicate that a DNA fragment spanning from nucleotides -164 to +44 of the AS promoter is sufficient for uninduced and induced gene expression. Mutations in a region located 15 to 30 bp downstream from the major transcription start site that shows good homology to a sequence in the first exon of c-fos implicated as a negative regulatory element resulted in a significant increase in basal gene expression but did not affect regulation. Interestingly, this region binds single-stranded-DNA-binding proteins that are specific for the AS coding strand. Mutations in either one of two putative binding sites for transcription factor Sp1, in a region of approximately 60 bp where many minor RNA start sites are located, or at the major transcription start site decreased promoter activity, but significant induction by amino acid starvation was still observed. Strikingly, mutations centered around nucleotide -68 not only decreased the basal promoter activity but also abolished amino acid regulation. This DNA region contains the sequence 5'- CATGATG-3', which we call the amino acid response element (AARE), that can bind a factor(s) present in HeLa cells nuclear extracts that is not capable of binding to an AS promoter with mutations or deletions of the AARE. This finding is in line with the hypothesis that transcriptional activation of AS gene expression is mediated through the binding of a positive regulatory element. We did not detect changes in the level of binding of this factor to the AARE by using nuclear extracts from HeLa cells grown under starved conditions, suggesting that activation of this factor(s) results from posttranslational modification or complexing with other proteins that do not affect its DNA-binding properties
INNOVATIVE FULL SCALE APPROACH TO HRSG DUCT DESIGN FOR PRESERVING CCPP GLOBAL PERFORMANCE
No full textGoing 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
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