1,720,978 research outputs found
Xenopus helveticus, an endangered species?
No full textThis review traces the history of Xenopus research in Switzerland, its worldwide beginnings and British chapters having been summarised previously (Gurdon and Hopwood, 2000). As in other countries, Xenopus was initially used in the pharmaceutical industry at Basel for pregnancy testing. Developmental biologists became interested in this peculiar amphibian because it may be induced to ovulate all year round. Swiss Xenopus research is reviewed over 50 years, from the introduction of Xenopus by Rudolf Weber to the University of Bern, the return from Great Britain of two Swiss expatriates, Michail Fischberg and Max Birnstiel through the numerous pupils of the founder labs to the independently arisen Xenopus research units in the country. Besides developmental biology, Swiss Xenopus research engaged in immunology, genetics and cell biology, the latter focusing mainly on the oocyte. It set highlights in molecular biology by isolating some of the first eukaryotic genes and analysing their transcriptional regulation and post-transcriptional modifications through 'surrogate genetic' approaches in the oocyte system. An important line of research applied this system to study nuclear trafficking. Presently, functional testing mainly serves to characterise the function of proteins produced from expression vectors injected into the oocyte. A main accent of developmental studies was, from the early beginnings and still today, set on molecular characterisation of gene function in the embryo
Lentivector-mediated transfer of Bmi-1 and telomerase in muscle satellite cells yields a Duchenne myoblast cell line with long-term genotypic and phenotypic stability
No full textConditionally immortalized human cells are valuable substrates for basic bilogic studies, as well as for the production of specific proteins and for the creation of bioartificial organs. We previously demonstrated that the lentivector-mediated transduction of immortalizing genes into human primary cells is an efficient method for obtaining such cell lines. Here, we used human muscle satellite cells as model targets to examine the impact of the transduced genes on the genotypic and phenotypic characteristics of the immortalized cells. The most commonly used immortalizing gene, the SV40 large T antigen (T-Ag), was extremely efficient at inducing the continuous growth of primary myoblasts, but the resulting cells rapidly accumulated major chromosomal aberrations and exhibited profound phenotypic changes. In contrast, the constitutive expression of telomerase and Bmi-1 in satellite cells from a control individual and from a patient suffering from Duchenne's muscular dystrophy yielded cell lines that remained diploid and conserved their growth factor dependence for proliferation. However, despite the absence of detectable cytogenetic abnormalities, clones derived from satellite cells of a control individual exhibited a differentiation block "in vitro". In contrast, a Duchenne-derived cell line exhibited all the phenotypic characteristics of its primary parent, including an ability to differentiate fully into myotubes when placed in proper culture conditions. This cell line should constitute a useful reagent for a wide range of studies aimed at this disease
The role of the "Yaa (Y-linked autoimmune acceleration)" mutation and the Fc gamma receptor type IIB (FcγRIIB) in the control of lupus-like autoimmune responses in mice
No full textLe lupus érythémateux disséminé (SLE) est considéré comme le prototype des maladies auto-immunes systémiques. Il est caractérisé par la présence de divers auto-anticorps, y compris anti-DNA, et le développement d'une glomérulonéphrite lupique. Dans la présente thèse, nous avons analysé dans la souris les conséquences de trois dysfonctionnements dans la régulation du signal dû au récepteur à l'antigène des cellules B (BCR) en terme de développement d'auto-immunité. Primo, nous avons trouvé qu'une mutation accélératrice du SLE, "Yaa", pourrait augmenter la signalisation à travers le BCR après liaison de l'antigène spécifique, et ainsi favoriser l'activation de cellules B auto-réactives. Secundo, nous avons montré que le récepteur inhibiteur FcγRIIB, qui contrôle la production d'anticorps, est crucial pour empêcher la production de facteurs rhumatoïdes. Tertio, nous avons trouvé que l'expression de la molécule CD22, qui régule le niveau de signalisation du BCR, est différente selon l'allotype et la sous population de cellules B choisis.</p
Properties of transcription factors regulating interleukin-2 gene transcription through the NFAT binding site in untreated or drug-treated naive and memory T-helper cells
No full textCombining in vitro DNA binding studies and functional transcription assays in the Xenopus oocyte, we have tested the presence and functional state of transcription factors controlling the interleukin-2 (IL-2) promoter through the NFAT binding site. In naive T-helper cells, the IL-2 gene is repressed by a silencer. After first mitogenic stimulation, this silencer becomes undetectable while an activator is newly synthesized. In resting memory cells, the activator has low DNA-binding affinity and is located in the cytoplasm. However, no silencer is formed. Upon renewed cellular activation, this pre-existing activator is again targeted to the nucleus and regains function in promoting transcription. Cyclosporin A and FK506 act on two distinct levels of the IL-2 control mechanism. They prevent nuclear transport and reactivation of the performed activator in memory cells and, in naive cells, they render the silencer resistant to displacement by the activator. DNA-binding of silencer and activator from T-helper, and NFAT-1 from Jurkat cells, requires the same three G residues, but cross-linking analyses show differences in their constituent subunits. Supershift experiments show that the activator contains fra-2 and junD, whereas the silencer reacts with none of the antibodies tested
DNAs of simian virus 40 and polyoma direct the synthesis of viral tumor antigens and capsid proteins in <i>Xenopus</i> oocytes
No full textPurified simian virus 40 and polyoma DNAs injected into nuclei of Xenopus oocytes were transcribed and subsequently translated into virus-specific tumor antigens and capsid proteins. Simian virus 40 large and small tumor antigens synthesized in the oocytes were indistinguishable, by gel electrophoresis and [35S]methionine-labeled tryptic peptide mapping, from the corresponding polypeptides synthesized in CV-1 African green monkey cells. The synthesis of large simian virus 40 tumor antigen implies the correct splicing of its mRNA, which is complementary to nonadjacent nucleotide sequences in the early region of the viral genome. Polyoma DNA directed synthesis of two polyoma tumor antigen polypeptides, 57,000 Mr and small tumor antigen, and of the main capsid protein
Interleukin 2 gene regulation at the Pud (NFAT) promoter element: the complex situation in primary T lymphocytes
No full textDNA-protein binding studies and trans-activation assays in the Xenopus oocyte were used to assess the presence and functional state of factors controlling interleukin 2 (IL-2) transcription in primary human T-lymphocytes. The work summarized here shows that in resting naive CD4+/CD45Ro-T cells, the IL-2 promoter is repressed by a silencer bound to a purine-rich element (Pud or NFAT binding site). Upon first mitogenic stimulation of these cells, a positive transcription factor (activator) is synthesized and activates the IL-2 gene by binding to the Pud element. In memory CD4+/CD45RO+ cells, the silencer does not reappear and IL-2 transcription is controlled exclusively by the transition from inactive to active state of the activator correlated with its cytoplasmic or nuclear location. In addition, we show that differences in size and function exist between the Pud-factors that regulate the IL-2 gene in normal T cells and in tumor cell line models such as the human leukemia Jurkat and the mouse thymoma EL4.</p
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
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