1,721,010 research outputs found
Stearylated octaarginine and artificial virus-like particles for transfection of siRNA into primary rat neurons
No full textRNA interference (RNAi) provides a powerful experimental tool for sequence-specific gene silencing, allowing efficient analysis of gene function in a multitude of cell types. However, application of RNAi in primary mammalian neurons has been limited by low-transfection efficiency and considerable toxicity of conventional transfection methods. In this study, we evaluated a peptide-mediated and a polymer/lipid-based cellular delivery method for siRNA into rat primary neurons and compared the results with a commonly used liposomal transfection reagent. Stearylated octaarginine (Stearyl-R8) was used as polypeptide and artificial virus-like particles (AVPs) were used as a combined liposomal-polymeric vector, since both reagents have been previously shown to successfully transfect DNA into cell lines. Stearyl-R8 and AVPs both promoted siRNA transfection into primary hippocampal neurons via the endosomal pathway. SiRNA-mediated gene silencing could be effectively induced in primary neuron cultures. In comparison with the commonly used cationic liposome transfection agent, both novel reagents were less detrimental to cell metabolic activity. We conclude that these novel transfection methods yield performances comparable to cationic liposome-mediated transfection for siRNA, while being less cytotoxic in primary neurons. Stearyl-R8 and AVPs may therefore represent novel and more cost-efficient alternatives to conventional siRNA-transfection reagents
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
Characterization and optimization of the non-viral gene transfer vehicle Artificial viral particles (AVP)
Full text linkIn this work the non-viral gene transfer vehicle artificial viral particles (AVP) was characterized in greater detail, improved and used for new cell culture applications. The former conception of AVP as filled particle with a liposomal hull was expanded. The described filled particles with a smooth liposomal hull are contained in AVP but they are not the only particle species. Ultracentrifugation in combination with cell culture experiments showed that a mix of those filled particles with small PEI-DNA particles is responsible for transfection success. AVP could be traced on their way into the cell by electron microscopy and confocal laser scanning microscopy. Results indicated that AVP are able to escape from endosomes and supported the “proton sponge” theory. Transfer of AVP preparation from manual pipetting to a mini mixer system is possible, allowing production upscale. AVP prove that they are a successful transfection system also suitable for new applications such as siRNA transfection and stable expression of a recombinant protein. They have a potential as they can be optimized for their specific task by selection of the proper condensation agent and type of AVE liposomes. However, AVP in their presently characterized form will have their main field of application in cell culture
Hydrodynamic analysis of macromolecular and colloidal systems by analytical ultracentrifugation and related methods
Full text linkIn the last decades, the studies in the field of macromolecular chemistry resulted in the appearance of numerous different polymeric and colloidal systems, which are capable for the intra and inter molecular complexation. One of the main goals of polymer characterization is to be able to predict certain physical/chemical properties of the macromolecules based on their conformational characteristics. The accuracy of the estimation of the molecular and conformational characteristics increases with the simultaneous study and comparison of the data obtained by different hydrodynamic methods. The main scope of the current thesis is investigation of complex macromolecular and colloidal systems by the methods of molecular hydrodynamics, in particular, analytical ultracentrifugation, intrinsic viscosity and translation diffusion
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
19F-Festkörper-NMR-Untersuchungen zur Orientierung und Dynamik des antimikrobiellen Peptids PGLa in Lipidmembranen
Full text linkDas antimikrobielle Peptid PGLa (21 Aminosäuren) aus der Haut des Krallenfroschs Xenopus laevis ist für die Permeabilisierung von Bakterienmembranen verantwortlich. Als Ansatz zur Aufklärung seines Wirkmechanismus wurde die Orientierung der [alpha]-helikalen Peptidstruktur relativ zur Membran und ihre Dynamik mit Hilfe der sensitiven 19F-Festkörper-NMR anhand von fünf verschiedenen 4-CF3-Phenylglycin-Markierungen in orientierten Proben untersucht. Nach der Peptid-Festphasensynthese, der Aufreinigung durch RP-HPLC ihrer Identifizierung durch ESI- bzw. MALDI-Massenspektrometrie bestätigten CD-Spektroskopie und antimikrobielle Wachstumsassays sowohl den geringen strukturellen Einfluss der CF3-Phenylglycin-Substitutionen als auch die vergleichbare biologische Wirksamkeit der Analoga zum Wildtyp-PGLa, mit Ausnahme der Substitution an Position Ala8. Eine X2-Analyse der gesammelten 19F-Dipolaufspaltungen ergab die Orientierung der idealisierten PGLa [alpha]-Helix in Bezug auf orientierte Lipidmembranen. Interessanterweise wurden zwei unterschiedliche Zustände je nach experimentellen Bedingungen (Konzentration und Temperatur) und Membranumgebung (DMPC, DLPC, DPPC, DOPC, DMPC:DPMG, DMPG:DMPE, E. coli-Lipidextrakte) gefunden: 1. im S-Zustand (S = surface) bei niedriger Peptidkonzentration legt sich die PGLa-Helix parallel auf die Membranoberfläche, und die Lysin-Seitenketten sind vom hydrophoben Membraninneren weg gerichtet; 2. im T-Zustand (T = tilt) bei hoher Peptidkonzentration (Lipid-Peptid-Verhältnisse von 50:1 bis 20:1) neigt sich die Helix um 30° gegen die Membranebene und dreht sich 25° um ihre Achse. Ein derartiger T-Zustand wird in der vorliegenden Arbeit erstmals beschrieben, und eine plausible Erklärung für die 30°-Orientierung liefert ein Dimerisierungsmodell zweier gegeneinander verkippter antiparalleler PGLa-Helices auf der Membranoberfläche.PGLa, a 21-residue member of the magainin family of antibiotic peptides isolated from frog skin of Xenopus laevis, is known to be responsible for permeabilizing bacterial membranes. In order to elucidate its mechanism of action, the orientation of the [alpha]-helical peptide structure with respect to the membrane and its dynamics were investigated by sensitive 19F-solid-state NMR measurements through five 4-CF3-phenylglycine labels in oriented samples. After solid-phase peptide synthesis, purification by RP-HPLC and their identification by ESI and MALDI mass spectrometry, CD spectroscopy confirmed the insignificant structural interference of the CF3-phenylglycine substitutions, and antimicrobial growth assays resulted in biological activity comparable to wild-type PGLa, with the exception of the substitution in position Ala8. A X2 analysis of 19F-dipolar couplings yielded the orientational state of the idealized PGLa helix with respect to the membrane surface of lipid membranes. Interestingly, this was found to differ depending on the experimental conditions (concentration and temperature) and membrane composition (DMPC, DLPC, DPPC, DOPC, DMPC:DPMG, DMPG:DMPE, E. coli-lipid extracts): 1. in the S-state (S = surface) at low peptide concentration the PGLa helix assumes a flat orientation on the membrane surface with the lysine side chains directed away from the hydrophobic membrane interior; 2. in the T-state (T = tilt) at high peptide concentration (lipid-to-peptide ratio from 50:1 to 20:1) the helix tilt changes by 30° relative to the membrane plane accompanied by a 25° rotation around its axis. The present thesis describes such a T-state for the first time, and a plausible explanation for the 30°-orientation may be provided by a dimeric model of two tilted PGLa helices aligned antiparallel and located on the membrane surface
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