1,721,083 research outputs found
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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Biochemical and structural studies of NOD-like receptors and their inhibition by small molecule inhibitors
No full textNOD-like receptors (NLRs) are innate immune sensors that can form inflammasomes driving pyroptosis. NLRP3 is the best studied member of the NLRs to date, and its dysregulation has been linked to human diseases relevant to our contemporary aging society. NLRP9 and NLRP12 are less well studied, but they have been described to form inflammasomes during infections. However, the existence of both inflammasomes has never been biochemically confirmed, and the mode of action of small molecule inhibitors is poorly understood. In this thesis, I show that recombinant human NLRP9 forms a defined and stable monomer in solution that is expected to adopt an ADP-bound and inactive conformation. Overexpression of NLRP9 in cells is not sufficient to nucleate ASC specks, which contradicts inflammasome formation and is in great contrast to NLRP3 or NLRP12. In line, the NLRP9 Pyrin domain (PYD) does not polymerize into filaments or interact with ASC. Based on a 1.95 Å crystal structure of NLRP9-PYD, these observations can be explained by finding several mismatches in residues that would otherwise form interfaces in a filament. Recombinant human NLRP12 associates with tubulin superfamily proteins, suggesting a role of microtubules in inflammasome formation. In addition, the detergent CHAPS can abrogate ATPase activity, which might indicate NLRP12 activation at lipid membranes. However, NLRP12PYD does not polymerize into filaments or interact with ASC, contradicting inflammasome formation. Based on a previously determined crystal structure of NLRP12PYD, this discrepancy was investigated but did not yield a clear explanation. Since recombinant NLRP12NACHT can assemble into oligomers, it is supposed that the NACHT domain acts as a scaffold for PYD polymerization. Crystals of NLRP12-NACHT have been generated under various conditions, but have not yet diffracted sufficiently for structure determination. The development of an optimized purification protocol allowed the determination of a 2.48 Å crystal structure of NLRP3 in complex with the prototypic inhibitor CRID3. NLRP3NACHT adopts an ADP-bound and inactive conformation stabilized by three intramolecular interdomain interfaces, each containing a disease-relevant mutation site. CRID3 binds NLRP3 with nanomolar affinity and inhibits ATPase activity. The binding site is formed by a cleft located on the backside of the Walker A motif and is also required to adopt the active state. In this way, CRID3 glues four subdomains of the NACHT domain together with the transition LRR and locks NLRP3 in the inactive conformation. Binding experiments demonstrated that CRID3 can be extended at the eastern side without loss of interaction, and that substitution of the furan moiety could be an option for the development of advanced NLRP3 inhibitors with lower hepatotoxicity. I anticipate that these data could pave the way for rational and structure-guided drug optimization in the future not only for NLRP3 but for all NOD-like receptors
Microglia derived from embryonic stem cells and its application in CNS diseases
Get PDFMicroglia are the resident immune cells of the central nervous system (CNS). They are known to have detrimental as well as beneficial effects. To overcome the limitations of primary microglia, embryonic stem cell derived microglia precursor cells (ESdM) were differentiated out of mouse embryonic stem cells. ESdM showed expression of microglial markers such as Iba1, CD45 or CD68, but lacked stem cell markers. Stimulation of ESdM with Interferon-γ (IFN- γ) or lipopolysaccharides leads to an up-regulation of inflammatory cytokines and to increased phagocytosis. Furthermore, ESdM migrate in a dose-dependent manner towards fractalkine CX3CL1. Gene expression of ESdM resembles that of primary microglia and preliminary data indicate that they can be subpolarized into a neuro-toxic or a neuro-protective subtype by IFN-γ or interleukin-4. After lentiviral transduction of ESdM with Neurotrophin 3 (NT3), they were applied to experimental autoimmune encephalomyelitis (EAE) afflicted mice to reveal possible therapeutic chances for the treatment of multiple sclerosis (MS). EAE mice treated with NT3-green fluorescent protein (GFP)-ESdM showed stable recovery of clinical symptoms, accompanied by less demyelination and less axonal damage in the spinal cord tissue. ESdM migrated to the lesions and promoted an anti-inflammatory cytokine profile. Furthermore, in close proximity to the NT3-GFP-ESdM, the axonal growth protein GAP-43 could be found, indicating neural regeneration due to the presence of NT3. To summarize, NT3-GFP-ESdM can be considered a promising tool for therapeutic approaches to EAE as a model of MS. ESdM were also applied in co-culture systems with glioma cells to determine their potential for therapeutical approaches. ESdM phagocytosed glioma cells and reduced glioma cell number in vitro. Phagocytosis and proliferation inhibition were enhanced through subpolarization of ESdM into M1 subtype. The anti-tumor effects were most likely mediated via DAP12 and the DAP12-associated receptors SiglecH and Trem2. Knockdown of these molecules decreased the anti-tumor activity of ESdM, while overexpression of DAP12 resulted in stronger anti-tumor effects. Thus, ESdM could provide functions to also fight glioma in vivo. In summary, ESdM might provide a broad range of possible applications in therapeutical approaches of CNS diseases
Erforschung und Etablierung von microRNA als forensischer Biomarker zur Identifikation biologischer Spurenarten
Get PDFSpuren von forensisch-biologischem Interesse sind kleine Antragungen von Blut, Sekreten oder Gewebefragmenten an oder auf Personen, Oberflächen oder Gegenständen. Ihre Analyse ermöglicht nicht nur den Rückschluss auf spurenlegende Personen (beispielsweise Täter oder Opfer) durch Individualisierung anhand von DNA-Profilen, sondern kann auch Informationen zu einem Handlungsablauf liefern, etwa durch die Klärung der körperlichen Herkunft der Spur. Da die ‚klassischen‘ Verfahren zur Spurenartidentifikation eine Reihe von Nachteilen aufweisen, werden seit einigen Jahren alternative, nukleinsäurebasierte Herangehensweisen erforscht. MiRNAs besitzen neben der Grundvoraussetzung zelltypspezifischer Expression und der Co-Analysierbarkeit mit DNA weitere Charakteristika – allem voran ihre intrinsisch hohe Widerstandsfähigkeit gegenüber Degradation – durch die sie in besonderem Maße für die Anwendung in typischerweise nur in geringen Mengen vorhandenem, beeinträchtigtem forensischen Spurenmaterial geeignet sind. Die in dieser Dissertationsschrift zusammengefassten Studien befassten sich daher mit der Identifikation robuster miRNA-Marker für die forensisch relevantesten Körperflüssigkeiten Blut, Speichel, Sperma, Vaginalsekret und Menstruationsblut sowie erstmalig mit der miRNA-basierten Identifikation der Organgewebe Gehirn, Lunge, Leber, Niere, Herzmuskel, Skelettmuskel und Haut im forensischen Kontext. Um reliable Aussagen zur Ausgangsmenge einer untersuchten miRNA zu erhalten und verlässlich nur wenig unterschiedliche Expressionsniveaus erfassen zu können, erfordert die angewendete RT-qPCR-Methode eine stringente, für die gegebenen Versuchsbedingungen optimierte Datennormalisierung zur Eliminierung nicht-biologischer Varianzen. Hierfür wurden zunächst in zwei separaten Studien jeweils eine Gruppe von Referenzgenen (unter den gegebenen Bedingungen zwischen den Körperflüssigkeiten beziehungsweise Organgeweben möglichst stabil exprimierte snoRNAs oder snRNAs) ermittelt und validiert. Eine unvoreingenommene Auswahl differentiell zwischen den untersuchten Körperflüssigkeiten beziehungsweise Organgewebe exprimierter miRNA-Kandidaten wurde mit Hilfe von Microarray-Experimenten getroffen und anschließend mittels RT-qPCR analysiert. Die Marker, die dabei in vereinigten Proben mehrerer Individuen die besten Trenneigenschaften aufwiesen, also in ihrer Zielspurenart deutlich höher exprimiert waren als in den verbleibenden Spurenarten, wurden anschließend in Einzelproben evaluiert, wodurch die Analyse durch die Ergänzung um die interindividuellen Unterschiede vervollständigt wurde. Mit der Entwicklung eines Entscheidungsalgorithmus unter Einsatz der Diskriminanzanalyse gelang es, alle fünf Körperflüssigkeiten anhand der Expressionsniveaus von vier miRNAs in Einzelquellproben zu unterscheiden. Der entwickelte Entscheidungsbaum wurde anschließend in bis zu 36 Jahre alten Spuren, verblindeten Proben und Mischungen mehrerer Körperflüssigkeiten getestet und zeigte auch hier, insbesondere für die Identifikation von Sperma und Blut im allgemeinen Sinne (venöses Blut und Menstruationsblut) gute Ergebnisse. Eine statistisch valide Unterscheidung der Gehirn-, Leber-, Nieren-, Herzmuskel-, Skelettmuskel- und Hautproben von den jeweils anderen Organgewebeproben gelang durch die Anwendung binär logistischer Regressionsanalysen. Mit kleinen Einschränkungen konnte das erarbeitete Klassifikationsmodell im Anschluss auf gealterte Organabriebproben, verwesendes Organgewebematerial, Mischungen mehrerer Organgewebe und Asservate von simulierten Gewaltdelikten mit Einsatz von Stich- und Schusswaffen erfolgreich angewendet werden. Zudem wurde die vollständige Kompatibilität mit dem DNA-Arbeitsablauf gezeigt. Die in dieser Dissertationsschrift zusammengefassten Arbeiten stellen mit ihren höchsten Standards genügenden, gemäß den MIQE-Richtlinien dokumentierten miRNA-Expressionsmessungen sowie dem bias-freien, statistisch reliablen Auswertungsgang die Grundlage für den Ausbau der Methode bis hin zu einer angestrebten Anwendung in der forensisch-genetischen Fallarbeit dar
Complement-mediated neuronal loss by sialic acid glycocalyx alterations
Get PDFEvery neuronal cell is covered with a dense structure of glycoconjugates, the glycocalyx. Sialic acids form the terminal ends of the glycocalyx and thus, are more accessible for the cellular environment. Microglia, the brain macrophages constantly survey the brain parenchyma and can sense small alterations in the glycocalyx. Recently, it was demonstrated in murine and human neuron-microglia/macrophage co-cultures that healthy neurons with reduced surface-bound sialic acids were removed by microglia/macrophages in a complement-dependent manner. Although microglial phagocytosis is considered as beneficial, the role of microglia in recognizing sialic acids in neurodegenerative and neuroinflammatory processes is still not fully understood. In this study, the situation of a desialylated glycocalyx in vivo was mimicked by using a mouse heterozygous for the bifunctional enzyme glucosamine-2-epimerase/N-acetylmannosamine kinase (GNE; GNE+/-- mice). It was shown that gne transcription was reduced in the brain of young and old GNE+/-- mice and a reduced sialylation status was confirmed. In accordance with the in vitro data, an increased age-dependent neuronal loss was found in different brain regions of GNE+/-- mice compared to their wildtype littermates. Histological staining indicated morphological changes in microglia but not in astrocytes. Furthermore, only very minor inflammatory changes were observed in the transcriptome data of the brain pointing towards a homeostatic removal of neurons in GNE+/-- mice by microglia. Based on the in vitro studies, the GNE+/-- mice were crossbred with mice deficient for the complement component 3 (C3), the central player of the complement cascade, to confirm the involvement of the complement system. The C3-deficiency was able to rescue the neuronal loss in the GNE+/-- mice. Thus, this study successfully showed that the complement system is involved in microglial removal of neurons in vivo. The in vivo data demonstrate the importance of microglial sensing of small alterations in the glycocalyx. Sialic acids seem to play an essential role in maintaining brain homeostasis and might also be in involved in synaptic plasticity. However, oxidative stress or aging can lead to a decrease of sialic acids that then might lead to unwanted reactivation of developmental synaptic pruning and consequently to the loss of neurons in the brain. Thus, targeting the neuronal glycocalyx could be a beneficial therapy in age-dependent neuronal loss and neurodegenerative diseases.Komplement-vermittelter Verlust der Nervenzellen durch Sialinsäure-Veränderungen der GlykokalyxIm Alter nimmt die Häufigkeit an neurodegenerativen Erkrankungen zu, die mit einem generellen oder zelltypspezifischen Abbau von Nervenzellen einhergehen. Mikroglia, die Gehirnmakrophagen, stehen im ständigen Kontakt mit Nervenzellen, um kleinste Veränderungen wahrnehmen zu können. Dies geschieht über die zelluläre Glykokalyx, ein Geflecht aus verschiedenen Zuckern mit Sialinsäuren als terminaler Zucker. In der vorliegenden Studie wurde der Einfluss einer veränderten Glykokalyx im Gehirn in vivo untersucht. In vitro-Experimente zeigten bereits, dass die Entfernung der Sialinsäuren von der neuronalen Glykokalyx zur Komplementrezeptor 3-vermittelten Phagozytose der Nervenzellen durch Mikroglia/Makrophagen führt. Dieser Mechanismus wurde nun erfolgreich in ein Mausmodell übertragen. Als Modell wurde eine Maus verwendet, die heterozygot für das bifunktionelle Enzym UDP-N-Acetylglucosamin-2-Epimerase/N-Acetylmannosaminkinase (GNE+/--Maus) ist und dadurch eine niedrigere Sialylierung aufweist. Diese Mäuse zeigten einen Verlust von Nervenzellen in verschiedenen Gehirnregionen, der sich mit dem Alter weiter verstärkte. Parallel dazu wurde gezeigt, dass vor allem die langkettigen Polysialinsäuren reduziert waren. Trotz kontinuierlichem Nervenzellabbau konnten keine Entzündungsreaktionen im Gehirn festgestellt werden. Sowohl eine Transkriptom-Analyse, als auch eine Astrozyten- und Mikrogliaanalyse im Gehirn zeigten keine großen Auffälligkeiten. Lediglich die stärkere Exprimierung eines Mikroglia-/Makrophagenmarkers deutete auf eine erhöhte Mikroglia-Aktivität hin und lässt auf eine homöostatische Phagozytose schließen. Wichtige Erkenntnisse brachte die Kreuzung der GNE+/--Maus mit einer Komplementfaktor C3-defizienten Maus. Durch die vollständige Inhibierung des Komplementsystems konnte der Nervenzellabbau selbst bei alten GNE+/--Mäusen verhindert und dadurch die Involvierung des Komplementsystems auch in vivo nachgewiesen werden. Somit zeigt die vorliegende Arbeit, dass Sialinsäuren auch im komplexen Organismus eine zentrale Funktion in der Mikroglia-Nervenzell-Kommunikation einnehmen. Eine reduzierte Sialylierung führt zu einer Komplement-vermittelten Phagozytose der Nervenzellen durch Mikroglia. Das untersuchte Mausmodell, sowie die daraus gewonnenen Erkenntnisse bilden eine sehr gute Grundlage um den altersabhängigen Nervenzellverlust weiter zu untersuchen und geeignete Therapieansätze zur Vermeidung von neurodegenerativen Erkrankungen zu entwickeln
Establishment of anti-apoptotic brakes in human neurons during maturation
No full textNeurons represent a highly specialised cell population of the central and peripheral nervous system, which is responsible for spreading information throughout the body. They are born during embryonic development and persist throughout the entire life span of an individual. Since during the development of the nervous system an excess of neurons is produced, some neurons undergo apoptosis to guarantee the correct number of neurons required for the formation of neuronal networks. In immature neurons cell death pathways are freely active, while in mature neurons apoptosis is highly controlled. They have developed elaborated strategies to protect themselves against stress and apoptosis. This study set out to decipher, whether mature neurons are more resistant toward stress than their immature counterparts and to elucidate which pathways and proteins promote the stress resistance. Experiments reveal that during the time course of maturation, iPS cell-derived neurons become increasingly resistant to several types of cellular stressors. This goes along with a failure to activate caspase3 and a downregulation of caspase9. Comparative gene expression analysis was performed to develop deeper insights into the different stress resistance between immature and mature neurons. In mature neurons upregulated protective genes, converging into the AKT pathway, were identified. The elevated activity of the AKT pathway in mature neurons was supported by Western blot analysis. Additionally, the small heat shock protein Cryab upregulated in mature neurons was of interest. Western blot analysis confirmed its expression and upregulation upon stress. Cryab was of special interest because the common heat shock response is attenuated in mature neurons. In line with this, a downregulation of Hsp70 and Hsp27 was shown. To investigate the contribution of Cryab to the stress resistance of mature neurons, Cryab knockout neural stem cells were generated using CRISPR/Cas9-mediated gene editing. The disruption of Cryab increased the susceptibility of mature neurons especially to redox- and autophagy stress. Together this points out that mature neurons are equipped with several strategies: the downregulation of pro apoptotic proteins, the activation of a pro survival pathway and the upregulation of protective proteins, to protect against stress
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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