A fundamental defense mechanism against pathogens is the recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs). These PRRs are integral components of the innate immune system. This recognition process initiates the interferon (IFN) response mechanism, triggering expression of interferon-stimulated genes (ISGs). Many of these ISGs possess antiviral properties that inhibit viruses, including HIV-1. The PPRs and their following signal pathways vary based on cell type. Publications have shown that an unknown pathway mediated over MAVS is activated by intron-containing RNA from HIV-1 in monocyte-derived macrophages (MDMs). However, the mechanism behind the sensing of the viral genomic RNA is yet unknown.
This work identified two distinct stages of immune recognition in MDMs triggered by HIV-1 infection. The first stage occurred prior to reverse transcription and was influenced by the stability of the viral capsid. In the second stage, characterized by a more robust immune response, a short peptide sequence encoded by the N-terminus of gag was crucial to inducing inflammatory responses. While partially spliced or full-length viral RNA in the cytoplasm was required for Gag protein translation, the myristoylation site of Gag was essential to induce innate sensing in MDMs. Furthermore, we examined whether THP-1 or U937 cells in differentiated state showed a similar phenotype to MDMs during HIV-1 infection to identify the molecular mechanisms involved in sensing the virus. We found that U937 cells exhibited robust innate response at a late-stage of virus replication, whereas pre-integration determinants, observed in MDMs, differ. Surprisingly, THP-1 cells exhibited minimal innate immune responses against HIV-1 and showed significant differences from the responses observed in MDMs and U937 cells. Our findings reveal that HIV-1 sensing in differentiated THP-1 and U937 cells does not parallel the responses seen in primary cells. These results enable new research targets in regard to find the cellular sensor, which induces HIV-1 chronic inflammation in MDMs and highlight the importance of research in primary cell systems.
Weniger anzeigenAntimicrobial peptides are an interesting class on ribosomally and non-ribosomally synthesised peptides found in all kingdoms of life. Among these is the underexplored class of bacteriocins: Short ribosomally synthesized and post-translationally modified peptides that often show high potency, and low toxicity. One subclass requires a glycosylation to show antimicrobial activity and thus have been termed glycoactive bacteriocins, Glycocins. The glycosylation of glycocins is installed by a specific subfamily of glycosyltransferases, part of the CaZy transferase family 2. Despite being in the same family, these glycosyltransferases show a remarkable diversity in terms of donor specificity, peptide specificity, acceptor selectivity and number of glycosylations that are carried out. I identified several putative Glycocins and their cognate transferases using bioinformatics. The recombinant production and purification of several glycosyltransferases was established. These were characterised in regard of the metal ion dependency and the carbonucleotide specificity. Using SPPS several glycocin-peptides were synthesized and their selective glycosylation by the cognate transferase could be proven. A facile and scalable method to obtain the mature, glycosylated, and folded glycocin by heterologous expression of the peptide and its transferase in E. coli was established. To investigate the molecular determinants for the observed differences in specificity in terms of preferred sugars and their acceptor selectivity, X-ray crystallography was used as method of choice. For four glycosyltransferases with noticeably different specificities, crystals could be obtained, and the structure could be solved. For the transferase of Enterocin 96 it was possible to obtain snapshots of the enzyme-substrate complex during its reaction.
Weniger anzeigenIn the 1990s, the economic downturn and hyperinflation in Brazil motivated many descendants of Japanese migrants (Nikkeijin) living in Brazil to ‘return’ to Japan, where an aging population and a booming economy had led to a labor shortage. Another incentive was the revision of the Japanese Immigration Law in 1990 that allowed Nikkeijin up to the third generation to obtain special permanent residency visa. Approximately 220.000 Latin American returnees arrived in the 1990s, and more than 200.000 Brazilians live in Japan today, constituting the fifth largest group of foreigners. As many have decided to stay in Japan for the time being, integration and multiculturalism have become important societal challenges, especially at the local level.
This dissertation examines the role of mediating institutions for the integration of Brazilian return migrants in Japan. Based on ethnographic field research in Hamamatsu, the Japanese city with the highest number of Brazilian residents, three research areas have been determined: everyday life and community, religion, and education. The relevant mediating institutions, such as cultural centers, libraries, churches, schools, and civil society institutions, were identified and their activities analyzed with regard to the research question of what role these institutions play for the process of integration into the host society and the relation to Japanese residents.
The analysis revealed that as spaces of interaction and encounter and as providers of knowledge, education, and information, mediating institutions serve as promoters of multiculturalism, mutual understanding, and integration. At the same time, they offer a space of belonging and creation of an ethnic support network, which facilitates the formation of a parallel society and exacerbates existing divisions. In other words, mediating institutions simultaneously foster and hinder integration processes.
Weniger anzeigenThe purpose of my project is to identify novel functions of circRNAs with a particular focus on the effects of RNA--RNA interactions (RRI) on RNA processing. Computational prediction of RRI has revealed the biological function and mechanism of action of multiple genes. However, computational RRI prediction is limited by 2 major challenges: knowing the full sequence of the transcript and a high false-positive rate. Discovering the full sequence identity of circRNA has been a challenging task for bioinformatics in the last decade. In addition, the lack of knowledge of the full sequence of the transcripts in a sample leads to skewed quantification based on RNA-seq data, as well as incorrect results from analyses of NGS-derived techniques (e.g., CLIP-seq, SPLASH etc.). The problem of false discovery of new RRIs can be mitigated by dedicated experimental datasets. To overcome the first hurdle of my project, I developed CYCLeR , a computational tool that compares ribo-depleted and circRNA enriched RNA-seq libraries and outputs a high-confidence set of circRNA transcripts. The true strength of CYCLeR is the quantification module that can robustly estimate the abundances of both circular and linear transcripts. I have shown the advantage of CYCLeR over alternative tools in terms of transcript assembly and quantification. I have also shown that CYCLeR has is the only tool suitable to search for the functional association of circRNA transcripts. The second part of my work focuses on predicting functional RRIs that influence pluripotency. A co-expression network based on the output of CYCLeR can show the association of circRNA with known biological pathways and significantly facilitate the discovery of the function of circRNA. In vivo RNA proximity ligation experiments provide information on the dynamics of RNA-RNA interaction inside the cell. The combination of RNA-seq and RNA interactome data allows me to significantly enhance the strength of computational predictions. I build a co-expression network based on time series experiment of H1ESC treated with retinoic acid. I combine the co-expression information with results from analysis of RNA-RNA proximity ligation data (SPLASH). The analysis is supplemented with localisation information based on RNA-seq libraries specific for nuclear localisation. The results two circRNAs that participate in functional RRIs. circFIRRE is significantly enriched in SPLASH data, indicating a high probability of interaction with other RNAs. Interestingly, circFIRRE is one of the few circRNAs specifically enriched in the nucleus. The enrichment can be explained by the binding site for the hnRNPU protein, which keeps the circRNA in the nucleus. Knockout of the circFIRRE locus in human leads to a viral response. Multiple interaction sites of circFIRRE with ALU-specific sequences indicate that the viral response is triggered by disruption of A-to-I editing in cells. circLARP7 is another nuclear-specific circRNA. circLARP7 is co-expressed with all major markers for pluripotency. It is also expressed in high proximity to MIR302CHG -- a microRNA host gene related to maintaining the pluripotent state. High complementarity and conservation of a duplex between the circLARP7 and the nascent MIR302CHG indicate that circLARP7 might be related to the processing of the microRNAs from the miR-302/367 cluster.
Weniger anzeigenThe Kupferschiefer district in the Southern Permian basin of central Europe hosts several sediment-hosted stratiform copper (SCC) deposits. The Cu and Zn-Pb sulfide mineralized rocks in the uppermost part of the terrestrial Rotliegend sandstones (S1), organic matter-rich marine Kupferschiefer mudstones (T1), and Zechstein Limestone (Ca1) units in the Kupferschiefer district are located at a major stratigraphic redox boundary. Various genetic models, including syngenetic, early diagenetic, and late diagenetic to epigenetic, have been proposed to explain the formation of stratabound-stratiform, fine-grained sulfide mineralization in the Kupferschiefer district. Most of these models were constructed based on bulk geochemical and isotopic data interpretations without complimentary detailed petrographic investigations.
In this thesis, work has been focused on samples from three drill holes (Sangerhausen, Allstedt, and Wallendorf) in the Saale subbasin, eastern Germany. All drill holes intersect the S1, T1, and Ca1 in different base metal zones which provides an opportunity to investigate their diagenetic and hydrothermal assemblages. The focus of this thesis is to determine the mineralogy and paragenesis of diagenetic assemblages that controlled fluid flow during ore-stage sulfide mineralization, constrain the processes responsible for the formation and distribution of the calcite cement and assess if hotter mineralizing fluids overprinted its isotopic signature, and constrain the timing between the ore-stage sulfides and pore-filling illite. This has been done using detailed petrography, quantitative mineralogy, bulk rock geochemistry, major element chemistry of carbonates, microanalyses of δ13C and δ18O values of calcite cement using secondary ion mass spectrometry (SIMS), and nanoscale investigations of pore-filling illite adjacent to ore-stage sulfides using ultrahigh-resolution transmission electron microscopy (TEM).
The results of this study showed Cu and Zn-Pb sulfide (bornite, sphalerite, and galena) mineralized rocks in the S1 and T1 formed primarily via the replacement of early diagenetic carbonate cement, mostly predating alteration of detrital clasts. The highest base metal grades were found in the carbonate-rich samples of the T1, deposited under reducing conditions. A minor part of the ore-stage sulfides in the S1 and T1 involved the replacement of detrital feldspar clasts. In the Ca1, the sulfides are dominantly formed in vuggy pores. Vein sulfides in the T1 and Ca1 are also formed as a replacement of calcite veins. The calcite cement in the three units has a similar cathodoluminescence response and major element chemistry, suggesting a common origin. Overlapping δ13C and δ18O values of calcite cement in samples from the S1 and T1 in the Sangerhausen and Wallendorf drill cores suggest that the calcite cement was derived from fluids of similar composition. The δ13C values indicate carbonate alkalinity sourced from seawater-derived fluids and organic matter degradation products. However, the high variability in the δ13C values in the calcite veins in the T1 without significant change in their δ18O values suggests that the alkalinity of the porewater during calcite precipitation in veins was derived from organic matter degradation. The δ18O values suggest the influence of alteration of detrital clasts, with a minor contribution from meteoric water and evaporitic fluids. Furthermore, in pores surrounding the ore-stage bornite, Cu chloride nanoparticles (CuCl NPs) are intergrown with pore-filling illite, which indicates illite precipitation during sulfide mineralization, and limited availability of aqueous reduced sulfur in certain microenvironments and steep chemical gradients between these pores.
Overall, this thesis demonstrates that the reduced nature of the T1 provided the necessary redox gradient for sulfide precipitation and the dissolution of carbonate cement was the main control on the lateral migration of mineralizing fluids in the Saale subbasin. This thesis also provides new constraints that the mineralizing fluid flux or temperature was not sufficient to overprint the isotopic composition of the calcite cement. Furthermore, the results in this study demonstrate that Cu was soluble as chloride complexes, in low-temperature brines that infiltrated the host units during burial diagenesis when both illite formation and organic maturation were active processes.
Weniger anzeigenCompliance ist in Deutschland der Ausdruck der Regeltreue im Unternehmen: Kapitalgesellschaften, die keine Handlungsfähigkeit besitzen, deren Haftung auf die Ziffer des Stamm- bzw. Grundkapitals beschränkt ist und deren Geschäftsleiter in aller Regel nicht den Dritten gegenüber haften, müssen rechtssystematisch für die Regeltreue ihrer Organe und Beschäftigten sorgen, anderenfalls würde ein Missbrauch des Privilegs der beschränkten Haftung vorliegen. So begründet im Innenverhältnis bereits der Sorgfaltsmaßstab eines deutschen Geschäftsleiters seine Compliance-Pflicht der Gesellschaft gegenüber. Im Außenverhältnis wird diese Pflicht durch delikts- und bußgeldrechtliche Vorschriften sowie durch allgemeine Verkehrspflichten flankiert. Darüber hinaus zwingen die wirtschaftliche Abhängigkeit und die Internationalisierung einige Kapitalgesellschaften zur freiwilligen Übernahme einer (zusätzlichen) Compliance-Pflicht als Selbstverpflichtung. In Russland ist die Rechtslage vergleichbar gestaltet. Auch dort lässt sich die Compliance-Pflicht aus dem Sorgfaltsmaßstab des Unternehmensleiters (des Einzelexekutivorgans) ableiten. Öffentlich-rechtliche, deliktsrechtliche und arbeitsrechtliche Normen erweitern die rechtliche Grundlage der Compliance-Pflicht und verdeutlichen die Notwendigkeit einer auf die Einhaltung rechtlicher Vorschriften gerichteten Unternehmensorganisation. Ebenso wie die deutschen werden auch russische Unternehmen von ihren internationalen Geschäftspartnern angehalten, sich selbst zur Errichtung einer Compliance-Organisation zu verpflichten.
Weniger anzeigenIn der vorliegenden Arbeit werden die Funktionen von Blicken und von Vorgängen des Sehens und Gesehenwerdens im Kontext der Klarissenklöster in Söflingen, Nürnberg und München vom 15. bis zum 17. Jahrhundert analysiert und die Lebenswelt frühneuzeitlicher Frauenklöster damit aus einer sinnes- und geschlechtergeschichtlichen Perspektive betrachtet. Vor dem Hintergrund raumtheoretischer Überlegungen werden Blicke und visuelle Wahrnehmungen als Handlungen begriffen und für eine Beschreibung der Beziehungen der Nonnen untereinander sowie zum klosterexternen Umfeld herangezogen. Über die Analyse von Blickoptionen, visuellen Zugänglichkeiten und tatsächlich erfolgten oder aber verhinderten Blickkontakten können Machtverhältnisse verdeutlicht werden, die sowohl innerhalb der Klöster als auch zwischen den Konventen und der Außenwelt wirkten. Ziel der Arbeit ist es, die Möglichkeiten und Grenzen des visuellen Handelns der Nonnen als Sehende und Gesehene nachzuvollziehen und damit eine neue Ebene von female agency zu erschließen. Vor dem Hintergrund der in den Klöstern durchgeführten Reformen und Visitationen, lässt sich veranschaulichen, dass männliche Obrigkeiten zwar wiederholt in visuelle Gegebenheiten und damit einhergehende Blickoptionen der Nonnen eingriffen, die Konvente ihre Sehgewohnheiten bis zu einem gewissen Grad jedoch auch behaupten konnten. Die Frage nach einem Wandel der Blickverhältnisse zwischen Kloster und Welt ermöglicht es dabei, das Verständnis für die konfessionellen Unterschiede im Umfeld der jeweiligen Konvente zu schärfen. Anders als im Falle des Söflinger Konvents ging in Nürnberg mit der visuellen Öffnung der Klausur des Klarissenklosters und dem Sichtbarwerden der Nonnen im Zuge der Reformation auch ein Bedeutungsverlust der gesellschaftlichen Stellung des Konvents einher. Im Münchner Konvent blieben die Klausur und daran gebundene visuelle Restriktionen als zentraler Bestandteil der Lebensweise der Schwestern bestehen und formten nicht nur die religiöse Identität des Konvents, sondern galten insbesondere nach dem Konzil von Trient auch als entscheidendes Distinktionsmerkmal gegenüber anderen weiblichen Klostergemeinschaften. Im Rahmen der Untersuchung der architektonischen Binnenstruktur und Raumnutzung im Inneren der Klöster wird aufgezeigt, dass das visuelle Erleben einzelner Nonnen entscheidend von der sozialen Hierarchie innerhalb der Konvente abhängig war und je nach individueller Stellung innerhalb der Gemeinschaft variierte. Über ihren Blick war jede Klosterfrau in das konventsinterne visuelle Überwachungsnetz eingebunden und partizipierte damit sowohl als Sehende als auch Gesehene an der Aufrechterhaltung der gemeinschaftlich befolgten Ordnung. Das mit Fragen des Sehens und Gesehenwerdens einhergehende Machtgefüge schlug sich darüber hinaus auch im Austausch zwischen den Klöstern und der Außenwelt nieder. Während die Konvente einerseits die Einsehbarkeit der Klausur unterbanden und die Blicke von Besuchern regulierten, waren Blickkontakte andererseits jedoch auch ein wichtiger Bestandteil der Beziehungen zum klosterexternen Umfeld. Wer die Nonnen sehen durfte und wer nicht, spiegelte dabei die machtpolitischen, wirtschaftlichen und familiären Interessen der Konvente sowie einzelner Schwestern wider. Ausgehend von den Handlungsmöglichkeiten, die sich Klosterfrauen als Sehende sowohl innerhalb der Klöster als auch in Bezug auf ihr Verhältnis zur Außenwelt boten, bricht die vorliegende Arbeit den Topos vom passiven, gesenkten oder abgewandten weiblichen Blick im Gegensatz zu einem aktiv schauenden männlichen Blick in der Frühen Neuzeit auf. Der Blick weiblicher Konventsmitglieder wird als wachsamer, maßregelnder, sinnstiftender, subversiver, grenzüberschreitender, machtergreifender und damit letztlich als ein höchst aktiver Blick beschrieben.
Weniger anzeigenTurbulence in stable boundary layers (SBL) is often accompanied by the presence of large patches of non-turbulent flow regions, even close to the wall, a phenomenon referred in literature as global intermittency. Understanding the physical processes and dynamics of this mode of rotating, stratified and intermittent turbulence is important for the improvement of existing and/or development of new parametrizations of the SBL, which in turn, may be useful for many applications, including but not limited to numerical weather prediction, modeling gas dispersion events and understanding the Arctic climate system. In this thesis, the SBL is investigated by establishing a detailed comparison with the well-studied neutrally stratified atmospheric boundary layer. The datasets examined here were inherited through the work of Ansorge (Dissertation, Springer 2016). They used a simplified physical configuration, namely, an Ekman flow over a smooth wall where global intermittency is known to occur beyond a certain stability despite the absence of surface heterogeneities and other external perturbations.
Comparisons between both regimes is accomplished with the help of coherent structures, particularly with their geometry. This is motivated from previous observations where a change in the geometry of these structures from hairpin vortices under neutral conditions to thermal plumes under unstable conditions (where there is a positive buoyancy flux) has been detected. However, very little is known about the geometry of these structures, especially their three-dimensional character, when buoyancy has a stabilizing effect. Since a well-accepted definition of a coherent structure has not yet surfaced, the classification of boundary layer structures introduced by Robinson (Dissertation, Stanford 1991), henceforth referred to as Robinson structures, is used to study the various structures identified in literature in an organized manner. Suitable scalar indicators are identified for all eight categories of Robinson structures and they are grouped as quantitative and qualitative, the former of which can be extracted and geometrically characterized.
First, a framework to characterize the geometry of quantitative Robinson structures is developed. There are two main steps: extraction and geometrical characterization. In the extraction step, individual structures are obtained by thresholding scalar indicators. An improvement to the neighbor scanning procedure of Moisy and Jimenez (J. Fluid Mech. 2004) with the marching cubes algorithm is developed to extract visualization accurate structures. Optimum thresholds are identified with the percolation analysis approach of del Alamo et al. (J. Fluid Mech. 2006). However, it is seen that this fails when the flow is strongly intermittent. Therefore, an extension of this method where percolation analysis is applied in an iterative manner is introduced. In the second step, noise-like structures are filtered out by discarding structures having a fractal dimension less than 1. The remaining structures are subjected to the non-local methodology of Bermejo-Moreno and Pullin (J. Fluid Mech. 2008) to classify a structure as blob-like, tube-like or sheet-like based on its location within a three-dimensional visualization space composed of two differential geometry parameters - shape index and curvedness, and a stretching parameter.
Next, the framework is applied to structures obtained from instantaneous neutral and stably stratified Ekman flow fields with increasing stability. Results are discussed by dividing the flow field into four layers in the wall-normal direction: viscous sublayer, buffer, inner and outer layers. Geometrical characterization reveals that the structures are moderately stretched tube-like or moderate to strongly stretched sheet-like regardless of the strength of stratification. Furthermore, in the strongly stratified case, it is shown that global intermittency has a direct impact in the viscous sublayer where a large portion of the domain is occupied by a single low-speed streak which is reminiscent of the non-turbulent region aloft. Conclusions derived from the geometrical characterization are also compared with those obtained from conditional one-point statistics. To this end, a new definition of intermittency factor based on coherent structures is proposed to segregate the flow into turbulent and non-turbulent parts.
Since global intermittency is known to exhibit spatio-temporal variability, it may have an impact on the dynamics of coherent structures which can induce changes in their geometry. The geometrical characterization framework is modified with the addition of a region-based tracking procedure where correspondence is determined by measuring the degree of spatial overlap. Starting with structures having a similar geometry, i.e., with similar shape index, curvedness and stretching parameters from the instantaneous Ekman fields analyzed previously, the Robinson structures are tracked in time and temporal changes in their geometry are recorded. Similar to previous observations, these results also suggest mostly tube-like and sheet-like geometry for all Ekman flow cases. While all these results indicate that the geometry is mostly unaffected for increasing stability, the presence of non-turbulent flow patches that extend throughout the vertical length of the flow alters the spatial organization of coherent structures. This is particularly visible for hairpin-like vortex structures, whose abundance increases with stability and at the strongest stratification the head regions of these structures appears to be oriented in similar directions in the turbulent patches.
Finally, the orientation and abundance of hairpin-like structures are investigated. The region-based tracking scheme is improved to overcome the limitation of using a constant threshold in time by dynamically adjusting the thresholds such that the feature can freely grow or shrink in time. This is used to track hairpin-like structures from both neutral and stably stratified cases. Results show that the hairpin-like structures experience longer lifetime and higher number of interactions with increasing stability and a link between the number of split events and the autogeneration mechanism is proposed to be the underlying cause of the abundance of hairpins with increasing stability. To gain a better understanding of the dynamics, hairpin-like structures are also studied with a slender vortex filament approach, i.e., a vortex filament whose diameter d is much smaller than its characteristic radius of curvature R. The corrected thin-tube model of Klein and Knio (J. Fluid Mech. 1995) is used to calculate the motion of these filaments with the mean velocity profiles of the Ekman flow as the background flow. These results suggest that orientation of the filament in the spanwise direction is linked to its initial starting height under stable stratification whereas no such dependency can be observed with the neutrally stratified background flow.
Weniger anzeigenThe process of cytokinesis ultimately results in the partitioning of a mother cell into two daughter cells. Cytokinesis is initiated through the formation of an actomyosin ring at the equatorial plane of the mother cell, which drives the ingression of a cleavage furrow. At this stage, the scaffolding protein anillin stabilizes the actomyosin ring, and recruits septins. Once the ingression of the cleavage furrow is completed, the furrow membrane anchors to the bundled microtubules of the cytokinetic bridge. This is achieved through the centralspindlin complex, which resides at the nascent midbody organelle. Subsequently, anillin and septins further regulate the maturation of an intercellular bridge (ICB), which will ultimately be resolved by the abscission machinery. The phospholipid phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] plays a crucial role in mammalian cytokinesis. It is essential for the anillin-dependent stabilization of the actomyosin ring at the cleavage furrow, and it is required for the centralspindlin-dependent tethering of bridge microtubules to the plasma membrane. Nevertheless, the molecular mechanisms orchestrating PI(4,5)P2 synthesis in space and time during cytokinesis have remained elusive so far. In this study we investigated the contribution of type I PIP-kinases (phosphatidylinositol-4-phosphate 5-kinases) to the progression of cytokinesis and unveiled a crucial role for PIPKIy at the ICB. We found that septins interact with a common splice insert of PIPKIy isoforms 3 and 5 (PIPKIy-i3/i5), and that both septins and PIPKIy form a complex with centralspindlin. SiRNA-mediated depletion of PIPKIy-i3/i5 resulted in the loss of septin association with ICB microtubules, scattering of anillin away from the ICB, reduction of centralspindlin at the midbody, and a shorter cytokinetic bridge. Notably, these defects were rescued by wild-type PIPKIy, but not by septin binding-deficient or catalytically inactive mutants. These data support a model wherein septins recruit specific PIPKIy isoforms to the nascent midbody and, at this locale, PIPKIy-i3/i5 synthetize a pool of PI(4,5)P2 required for maintaining anillin, centralspindlin, and septins in place. Super-resolution analysis via ultrastructure-expansion microscopy further confirmed the above-mentioned defects at cytokinetic bridges in cells depleted of PIPKIy-i3/i5. Furthermore, live cell imaging of endogenously tagged eGFP-SEPT6 revealed that the hindered association of septins with microtubules observed at cytokinesis persisted within the daughter cells. Notably, siRNA-mediated depletion of centralspindlin phenocopied the loss of septin association to microtubules in non-mitotic cells, pointing towards a role of centralspindlin in coordinating the translocation of septins to bridge microtubules and, thereby, the inheritance of microtubule-associated septin fibers by daughter cells. Taken together, our findings establish septin-associated PIPKIy isoforms as novel regulators of late cytokinesis and demonstrate that both septins and PIPKIy are essential during midbody assembly and maturation.
Weniger anzeigenChapter 1: In this paper, I analyze the interplay between (European) monetary policy and energy prices. Employing a Bayesian proxy structural vector autoregressive model, I establish that the ECB’s decisions have material effects on global and local energy prices. This starkly contrasts the public communication and internal assumptions of the ECB. Through Lucas-critique robust counterfactuals, I demonstrate that the monetary-policy induced changes in energy prices play a crucial role in shaping the response of inflation and inflation expectations to monetary policy. By affecting fast-moving energy prices, monetary policy transmits quickly and more strongly to consumer prices. This turns energy prices from a foe to a friend that, when managed correctly, can assist monetary policy in achieving its objective of price stability. Finally, I ask how European monetary policy should optimally respond to an energy price shock and find that, historically, it has been too accommodative. My estimates suggest that the ECB could have largely avoided the latest energy-price-driven surge in inflation of 10% at the cost of a short-run and comparably small loss in output. I argue that this favorable outcome is precisely due to the ability of the ECB to affect fast-moving energy prices.
Chapter 2: This paper, which is joint work with Max Breitenlechner and Georgios Georgiadis, deals with the domestic repercussions of the global effects of the Federal Reserve’s decisions. In particular, it shows that these “spillovers” from US monetary policy entail “spillbacks” to the domestic economy. Applying counterfactual analyses in a Bayesian proxy structural vector-autoregressive model we find that spillbacks account for a non-trivial share of the slowdown in domestic real activity following a contractionary US monetary policy shock. Spillbacks materialize as a monetary policy tightening depresses foreign sales and valuations of US firms so that Tobin’s q/cash flow and stock market wealth effects impinge on investment and consumption. Net trade does not contribute to spillbacks because US monetary policy affects exports and imports similarly. Geographically, spillbacks materialize through advanced rather than emerging market economies.
Chapter 3: In this paper, which is joint work with Gernot Müller and Georgios Georgiadis, we analyze the interplay of changes in global risk and the appreciation of the US dollar. We identify global risk shocks using high-frequency asset-price surprises around narratively selected events. Global risk shocks appreciate the US dollar, induce tighter global financial conditions and a synchronized contraction of world economic activity. To isolate the role played by the appreciation of the US dollar we benchmark the estimated effects of these global risk shocks against counterfactuals in which the US dollar does not appreciate. By leveraging recent advances in sufficient statistics approaches to macroeconomic policy evaluation and building a rich two-country DSGE model we show that, in the absence of US-dollar appreciation, the contractionary impact of a global risk shock is much weaker. This holds true in the rest of the world as well as the US. For the rest of the world, contractionary financial channels thus dominate expansionary expenditure switching effects when global risk rises and the US dollar appreciates.
Chapter 4: In this paper Georgios Georgiadis and I develop the partial and asymmetric dominant-currency pricing (DCP) hypothesis and test for its empirical relevance. This hypothesis states that a large but not necessarily identical share of global export and import prices are sticky in US dollars and that this impacts the response of an economy to unexpected changes in the US dollar. We first set up a structural three-country New Keynesian dynamic stochastic general equilibrium model which nests DCP, producer-currency pricing (PCP), and local-currency pricing (LCP). Under DCP, the output spillovers from shocks that appreciate the US dollar decline with an economy’s export-import US dollar pricing share differential, i.e. the difference between the share of an economy’s export and import prices that are sticky in US dollar. Underlying this prediction is variation in an economy’s net exports in response to US dollar appreciation that arises because the shares of export and import prices that are sticky in US dollar are different. We then document that this prediction from partial and asymmetric DCP is consistent with the data. We do so by estimating impulse responses to different shocks that appreciate the US dollar for a sample of up to 45 advanced and emerging market economies. We document that our findings are robust to considering US demand, US monetary policy, and exogenous exchange rate shocks as a trigger of US dollar appreciation, zooming in on the responses of economies’ exports and imports, as well as accounting for the role of commodity trade in US dollar invoicing.
Weniger anzeigenImportant ecological und economic functions are performed by different pollinators. Apis mellifera being one of the most important ones, as it is managed by beekeepers worldwide. In recent years, the obligate ectoparasite Varroa destructor grew of importance as the impact on honey bee hives grew more apparent, as research has shown that it not only feeds on haemolymph and fatbody and therefore weakens brood and adults directly, but also transmits different viral, bacterial and fungal diseases. A common treatment against Varroa destructor is formic acid fumigation. The upsides include high efficacy against Varroa destructor and no resistance or cross resistance development, as it is the case in synthetic treatment options such as amides (e.g. Amitraz). Additionally formic acid is certified for organic farms application. The biggest downsides of the treatment include Apis mellifera mortality through all clades, as well as a narrow therapeutic index, as the treatment is reliant on humidity, bee density, temperature and mode of application. Even though the treatment has been used for many years, very little is known about the detoxification mechanism in Apis mellifera and Varroa destructor. Through recombinant expression of the 10-formyl-tetrahydrofolate dehydrogenase (10-FTHFDH), suspected to be involved in the detoxification of formic acid in Apis mellifera, the first study showed, that the enzyme is involved in the detoxification process, with similar activity known in mammalian counterparts. Additionally, as the sequence similarity of the insect 10-FTHFDH to the mammalian 10-FTHFDH is very low the second study focused on verifying the active residues and mode of action of the Apis mellifera enzyme. Through an interdisciplinary approach combining protein prediction, protein modelling and protein mutagenesis, it was verified, that the unsimilar proteins share the same active residues and function.
Weniger anzeigenThe massive consumption of fossil fuels and the severe greenhouse gas effect urgently require the development of renewable energy sources. Green hydrogen via water electrolysis powered by renewable energy sources such as solar or wind could drive the upcoming energy transition. While water electrolysis technology is commercially mature, its operation in corrosive electrolytes undoubtedly does not allow for future decentralized energy production by private individuals ("personalized energy"). Moreover, the high kinetic barrier of the water oxidation reaction (also known as oxygen evolution reaction, OER) limits the overall efficiency of water electrolyzer. Therefore, developing OER at neutral pH is crucial but it is typically hampered by low catalytic efficiency. Here, an electrocatalytic cobalt-phosphate system is chosen as a model system to study activity determinants and limiting factors in neutral-pH OER. Electrochemical experiments were used in combination with various in-situ/operando spectroscopic techniques (e.g. X-ray absorption spectroscopy (XAS), Raman spectroscopy (RM), UV spectroscopy) and total reflection X-ray fluorescence (TXRF) as well as mathematical simulations. As a result, project (a) found out the macroscopic proton transport in the bulk electrolyte dominating the rate limitation of neutral OER and it is facilitated by the diffusion of either phosphate ions (base pathway) or H3O+ ions (water pathway). A proof-of- principle experiment shows an achievable current density over 1 A cm−2 in neutral-pH OER. Project (b) verified the catalytic current of OER depending exponentially on the CoIV concentration for the volume-active CoCat material, irrespective of electrolyte pH or mass transport limitations. It is the chemical state of the equilibrated material that governs the rate of catalysis, rather than electric potentials or field strengths itself. Project (c) via a novel potassium XAS supports that the important charge-compensated ion flow is not realized by potassium ions but by protons. Project (d) revealed the pronounced local acidification close to the outer surface of CoCat for potential applied beyond the Tafel slope regime. A circular electrolyte flow between anode and cathode is verified and contributed to the buoyancy effect. The non-diffusive flows dominating proton transport may be technically relevant for water electrolyser. In summary, understanding limiting factors of neutral water oxidation facilitates the knowledge-guided design of efficient, technologically relevant catalysts and water electrolyzers. The new mechanism of OER catalytic rate governed by the chemical state of the equilibrium material may reveal a unifying concept for connecting the heterogeneous, homogeneous and biocatalysis.
Weniger anzeigenKünstliche Intelligenz (KI) ist nicht mehr aus unseren privaten und beruflichen Leben wegzudenken. In Form von persönlichen Assistenten unterstützen sie uns dabei Aufgaben zu erfüllen oder nehmen sie uns komplett ab. Implementiert in Entscheidungsunterstützungssystemen kann KI dazu beitragen, dass menschliche Entscheidungsträger:innen informierte Entscheidungen treffen können. Weiterhin kann KI vielseitige Dimensionen wie die kognitive Anstrengung oder Belastung und die Leistung positiv beeinflussen oder auch zu Zeitersparnissen führen. Spätestens die Veröffentlichung von ChatGPT hat gezeigt, wie mächtig aktuelle KI-Ansätze sein können und welche weitreichenden Konsequenzen sowie Implikationen KI-Systeme entstehen lassen. Doch viele dieser mächtigen KI-Ansätze teilen sich eine kritische Eigenschaft, welche zu großen Herausforderungen für die Gestaltung, Evaluierung und Nutzung von KI-Systemen führen kann. Dabei handelt es sich um das Blackbox-Problem. Viele neuartige und hochleistungsfähige KI-Ansätze basieren auf komplexen Architekturen und beinhalten viele nicht-lineare Berechnungen, wodurch diese an Intransparenz gewinnen und daher häufig als opak beschrieben werden. Durch diesen Umstand wissen wir, welche Daten in die KI als Eingabe eingegangen sind und bspw. im Falle einer Klassifikation erhalten wir eine Ausgabe in Form einer Klasse. Das Blackbox-Problem liegt zwischen der Ein- und Ausgabe. In Blackbox-KI-Ansätzen können wir nur schwer nachvollziehen, welche Merkmale der Eingabedaten besonders wichtig oder unwichtig für die Ausgabe waren. Wir können nicht einschätzen, ob die KI für uns sinnvolle oder unerwünschte Merkmale für die Entscheidungsfindung nutzt, welche bspw. zu Diskriminierung oder einer kognitiven Verzerrung führen können. In unkritischen Aufgaben wie bspw. der Sentiment-Klassifizierung von Rezensionen in positiv und negativ, sind die Auswirkungen des Blackbox-Problems eher gering. Wenn KI aber in eher kritischen Bereichen eingesetzt wird wie im Bereich der Gesundheitsversorgung, im Personal- oder Finanzwesen, steigen die potenziellen Risiken, welche aus dem Blackbox-Problem entstehen und können weitreichende Folgen haben.
Das Forschungsfeld erklärbare KI (EKI) widmet sich diesem Blackbox-Problem. In diesem Forschungsfeld werden Methoden entwickelt, welche Blackbox-KI erklärbar machen sollen, bspw. durch die Generierung von Erklärungen für individuelle KI-Ausgaben. Gleichermaßen wird daran geforscht, transparente KI-Modelle und Architekturen zu entwickeln, um das Blackbox-Problem erst gar nicht aufkommen zu lassen. Ein weiterer wichtiger Forschungsfokus im Bereich EKI besteht darin, zu untersuchen und verstehen, wie Erklärungen gestaltet und wahrgenommen werden. Forschung hat bereits gezeigt, dass es keine allgemeingültige Lösung gibt, welche für alle EKI-Systeme gleichermaßen funktionieren. Denn es gibt eine Vielzahl von Branchen und Anwendungsszenarien für EKI, wobei die Nutzer:innen sehr individuelle Bedürfnisse, Vorkenntnisse und Erwartungen an Erklärungen stellen können. Es gibt also eine große Anzahl von Aspekten, welche die Wahrnehmung von Erklärungen und die Interaktionserfahrung beeinflussen können. Diese Herausforderung wird dadurch verstärkt, dass Erklärungen in den unterschiedlichsten Formaten für Nutzer:innen gestaltet werden können, wie bspw. Erklärungen in natürlicher Sprache, die grafische Hervorhebung relevanter Eingabedaten oder auch die Visualisierung in Form von Diagrammen. In diesem Spannungsfeld gibt es viele Möglichkeiten, mittels wissenschaftlicher Erkenntnisgewinnung einen wertvollen Beitrag zu leisten. Denn das Forschungsfeld EKI wird in der Forschung häufig dadurch charakterisiert, dass mehr human-zentrierte Evaluierungen sowie dazugehöriges Designwissen fehlt.
Die Aspekte der humanzentrierten Gestaltung und Evaluierung wurden in dieser Dissertation erforscht. Als Fokus wurden die User Interfaces (UIs) von EKI-Systemen ausgewählt, da sie ein elementarer Bestandteil der Interaktionserfahrung darstellen und hier die Erklärungen den Nutzer:innen bereitgestellt werden. Diese Klasse der UIs wird Explanation UI (XUI) genannt. XUIs sind jene UIs, welche Informationen über die Ausgabe eines EKI-Systems präsentieren und einen besonderen Fokus auf die Erklärungen legen. So präsentieren XUIs bspw. die Eingabedaten, die Ausgabe, eine oder mehrere Erklärungen und weitere Informationen, welche bei der Interpretation der Erklärungen unterstützen. Die Erforschung der human-zentrierten Gestaltung und Evaluierung von XUIs wurde in dieser Dissertation maßgeblich mittels des Design Science Research Paradigmas durchgeführt. In den individuellen Forschungsarbeiten, welche Teil dieser Dissertation sind, wurde die Gestaltung und Wahrnehmung von XUIs in unterschiedlichen Domänen untersucht. Dazu gehören Domänen wie die Gesundheitsbranche, Mobilitätsbranche, soziale Medien oder Personalmanagement. Neben den unterschiedlichen Branchen wurden viele verschiedene Akteure in die Gestaltung von human-zentrierten XUIs involviert. Hierzu gehören bspw. Domänenexpert:innen, Nutzer:innen oder von EKI-Ausgaben betroffene Personen. Durch die Involvierung von diversen Akteuren fließen vielseitige Erwartungshaltungen, Informationsbedürfnisse und Vorerfahrungen in den Gestaltungsprozess von XUIs ein. Im Rahmen des Gestaltungsprozesses wurden die Akteure auch in human-zentrierten Evaluierungen involviert. Dabei kamen unterschiedliche Forschungsmethoden zum Einsatz. Einerseits wurden qualitative Methoden verwendet und insbesondere semi-strukturierte Interviews durchgeführt. Andererseits wurden quantitative Methoden wie Onlineexperimente und Umfragen durchgeführt. Durch diese human-zentrierten Evaluierungen konnten viele tiefgehende Erkenntnisse gewonnen werden. Die gewonnenen Erkenntnisse beziehen sich auf die Problemidentifizierung mit existierenden vergleichbaren Systemen, Verbesserungspotenziale für die gestalteten XUIs, die Wahrnehmung sowie Effekte der gestalteten XUIs auf Nutzer:innen und die Wiederverwendbarkeit des entwickelten Designwissens.
Die individuellen Forschungsprojekte und das zuvor beschriebene Vorgehen führten dazu, dass ein umfangreiches Wissen hinsichtlich der human-zentrierten Gestaltung und Evaluierung entwickelt wurde. Die Forschungsergebnisse haben gezeigt, wie Erklärungen in XUIs bspw. die Vertrauenswürdigkeit, Nützlichkeit, Interaktivität, Nutzerbindung oder Zufriedenheit positiv beeinflussen können. Weiterhin wurde das entwickelte Designwissen in Form von Designprinzipien zusammen mit Praktiker:innen evaluiert. Dabei lag der Fokus auf der Wiederverwendbarkeit und die Evaluierungen haben gezeigt, dass sie als sehr hoch bewertet wird. Zusätzlich gaben die Nutzer:innen stets einen hohen Zuspruch hinsichtlich der Akzeptanz der Designprinzipien für eigene Projekte an oder sie Kollegen zu empfehlen. Die in den individuellen Projekten generierten Erkenntnisse und Wissensbeiträge wurden im Rahmen der kumulativen Dissertationsschrift zusammengeführt. Um dies zu erreichen, werden die übergeordneten Forschungsfragen präsentiert, welche sich in den individuellen Forschungsarbeiten widerspiegeln. Es werden die Wissensbasis und das Begründungswissen präsentiert, welche die Basis der durchgeführten und präsentierten Forschung darstellen. Die in den unterschiedlichen Projekten verwendeten Forschungsmethoden werden ebenfalls präsentiert. Anschließend werden alle im Rahmen der Dissertation gewonnen wissenschaftlichen Erkenntnisse mit einem Bezug zu human-zentrierter Gestaltung und Evaluierung von XUIs in einer Information Systems Design Theory (ISDT) zusammengefasst. Durch die entwickelte ISDT werden die erarbeiteten Erkenntnisse zusammengeführt und zugänglich gemacht. Hierdurch entstehen vielfältige Wissensbeiträge mit Relevanz für die Forschung und Praxis. Dazu gehören bspw. die in der ISDT enthaltenen Designprinzipien, welche Wissen dazu bereitstellen, wie sich konkrete Designkonfigurationen von XUIs implementieren lassen. Hinzu kommen die empirischen Erkenntnisse, welche einen Einblick hinsichtlich der Effekte von unterschiedlichen Designkonfigurationen auf die Interaktionserfahrung für Nutzer:innen mit XUIs gewähren.
Weniger anzeigenInfluenza A viruses and SARS-CoV-2 continue to pose a severe threat to public health. Both are zoonotic pathogens, having arisen from the close human-animal interface. For both viruses vaccines are available, however their continuous evolution leads to immune escape so that the vaccines need to be continuously evaluated, updated and re-administered. For influenza viruses, immunity is mainly directed against the head of the viral surface protein HA, which is continuously changing due to drift processes, resulting in strain-specific responses. For SARS-CoV-2, the spike glycoprotein on the surface, which facilitates receptor-binding is the target of current vaccines. For both viruses, the interest lies in the development of broadly reactive vaccines which can protect against current and future variants. A concept that has gained interest in the development of vaccines is the induction of non-neutralizing antibodies that can activate cellular effector-functions, like ADCC. Another important aspect is the induction of mucosal antibodies, in regard to the infection route of both viruses. New delivery platforms have also been evaluated and gained momentum during the SARS-CoV-2 pandemic, for example vector vaccines (e.g. Vakzevria®), or mRNA-based vaccines (e.g. Comirnaty®). New vaccine candidates are also continuously developed and evaluated, for example the nucleoprotein-based vaccine by Leroux-Roels et al. (2023), which is currently in clinical trials. The AAV-vectors used in this thesis have shown to be safe for the use in humans and have already been successfully evaluated for the use as vaccine vectors. Intriguingly, they can be repeatedly administered via the respiratory tract, following the natural infection route. For IAV, this thesis aimed to assess a possible synergistic effect of an AAV-vector vaccine combining the HA and NP antigens of the influenza virus A/California/7/2009pdm. Furthermore, it was hypothesized that, opposed to WIV vaccination, the AAV-vaccine could induce broadly reactive responses. Additionally, an AAV-vector vaccine carrying the HA of the group 2 virus A/Aichi/2/68 (H3N2) was assessed regarding the hypothesis of the induction of a broadened immune response in combination with the group 1 HA of A/California/7/2009pdm. Furthermore, the induction of a mucosal immune response along the route of application in the respiratory tract was evaluated. To measure these responses, humoral, i.e. neutralizing, broadly reactive, and FcγR-activating responses were evaluated in the sera of immunized C57BL/6 mice, mucosal responses were assessed in nasal washes and lung samples, and T-cells were measured in spleens. The protective efficiency was assessed by an experimental challenge of mice with homologous, heterologous and heterosubtypic virus. Here, it was shown that a bivalent AAV-HA/NP vaccine was superior to WIV immunization. In the serum of mice immunized with AAV-HA/NP, broadly reactive antibodies and FcγR-activating responses could be detected, while in nasal washes and lung samples mucosal antibodies were present. After a prime-boost i.n. application the vaccine was also capable of protecting mice from viral challenge of homologous, heterologous and heterosubtypic virus, which WIV did not. An AAV-vector vaccine containing a group 2 HA (H3) was evaluated for the first time in vivo and proved to be successful in inducing strain-specific antibodies and protecting against homologous challenge but did not induce broadly reactive antibodies. Another aim of this thesis was the design and evaluation of an AAV-vector vaccine against SARS-CoV-2, because earlier studies evaluating a similar AAV-vector vaccine against SARS-CoV showed promising results. In the course of this thesis, the vaccine was further adapted to the emerging VOCs. In addition to the overall immunogenicity, the hypothesized cross-reactivity and broadly reactive responses induced by the AAV-vaccines against the wildtype virus and the different VOCs were evaluated. The AAV-S-RBD vaccine was initially evaluated in mammalian cell culture models before the in vivo analyses were conducted. Initially, different mouse strains were evaluated, and for subsequent analyses BALB/c and NMRI mice were used. Sera, nasal washes, lung samples and spleens were analysed as mentioned for the mice in the IAV experiment. No viral challenge was conducted. For this part, an induction of variant-specific antibodies by the designed AAV-S-RBD vector could be shown, but it wasn’t robust. Interestingly, non-neutralizing antibodies induced by the AAV-S-RBD BA.2 vector could be shown to induce FcγR-activating responses. Overall, in this thesis AAV-vectors have been demonstrated to be promising vaccine candidates for the induction of broadly reactive immune responses against influenza viruses and SARS-CoV-2.
Weniger anzeigenThe research field of spintronics emerges as a promising solution to address the core challenges posed by charge-based electronic information processing, aiming to reduce power dissipation while delivering lasting endurance and robust read and write capabilities. Spintronic circuits have already made their mark, finding practical applications in commercially accessible magnetic random-access memories. However, to effectively compete with future complementary metal–oxide–semiconductor (CMOS) and photonic technologies, fundamental spin operations speed should ideally extend to terahertz (THz) frequencies. In this respect, an exciting discovery is a new class of highly efficient and broadband THz emitters based on magnetic heterostructures, harnessing spintronic effects at terahertz frequencies.
This work is dedicated to addressing a series of fundamental questions, for example: What is the primary driving force for spin currents in spintronic THz emitters (STEs)? How do these spin currents relate to other processes such as ultrafast demagnetization dynamics? How do spin currents propagate through different material systems? What are the maximum speeds of spin current propagation? How can the spin conductance of various materials be quantified? Finally, how can the amplitude of the THz radiation from STEs be maximized to values exceeding 1 MV/cm?
First, we compare two central phenomena in femtomagnetism: ultrafast demagnetization and ultrafast spin currents in magnetic heterostructures. Strikingly, our findings unveil that both phenomena are driven by the same force, a generalized spin voltage, i.e., the excess of magnetization relative to equilibrium. We conclude that the spin voltage is genuinely ultrafast, and the decay of the spin voltage is predominantly due to spin-flip processes inside the ferromagnet, with only a minor fraction of spins contributing to the transport. Subsequently, we explore spin current propagation in copper and MgO tunnel junctions. Our results reveal that spin currents in copper propagate at high speed, reaching the Fermi velocity vF = 1.1 nm/fs with velocity-relaxation time of of τ =4 fs, and we separate ballistic and diffusive modes of spin transport. Furthermore, we introduce the new concept of THz spin-conductance spectroscopy. We apply this method to measure the spin conductance of an MgO tunnel junction, allowing to separate different spin-transport contributions, including coherent tunneling and incoherent resonant spin tunneling mediated through MgO defects. Finally, based on these findings, we significantly improve the STE performance by optimizing the heat management and maximizing the THz outcoupling. Our proposed Si-based STE design outperforms previous glass-based STEs by a factor of six, achieving a peak electric field of 1.7 MV/cm. Eventually, Si-STEs prove to be highly effective in inducing nonlinear effects such as the THz Kerr effect in diamond or Zeeman torque in magnets. In conclusion, this work demonstrates the significant potential of terahertz spin transport that can shape the future of ultrafast circuits.
Weniger anzeigenThis thesis presents the synthesis metal complexes with a variety of fluorinated ligand systems, featuring tripodal, terpiridine and azobenzene ligands. The resulting compounds thereof show various characteristics and therefore were investigated in terms of their geometric and electronic structures by single crystal X-ray diffraction, cyclic voltammetry, superconducting quantum interference device (SQUID) magnetometry and/or (spectro- )electrochemical methods. The first part of this thesis addresses new compounds of the form [M(L)2](BF4)2 (M = cobalt(II), iron(II); L = fluorinated tripodal ligand) and the influence of fluorine specific interactions in the secondary coordination sphere on the spin state of the central metal ion. For this purpose, a combined study by single X-ray diffraction analysis and SQUID magnetometry measurements was performed to investigate the spin states of the metal centers. It could be shown, that for the ligand, which contains either a pentrafluoro-benzyl or a 4-fluorobenzyl substituents, an effect of the fluorine specific interactions was observed. The complexes bearing the pentafluorobenzyl substituents do not display the expected!⋯! interactions, but an edge-to-face interaction. However, this leads to a change of the spin state for the iron(II) complex, while the corresponding cobalt(II) complexes remain in the low spin state. For the other substituent a partial spin crossover (SCO) behavior was observed for one cobalt(II) complex, depending on the co-crystallizing solvent, while the iron(II) complex displays a complete SCO. These results were obtained by a combination of X-ray diffraction analysis, SQUID magnetometry, electron paramagnetic resonance (EPR) spectroscopy and theoretical calculations. In the second part terpyridine ligands bearing different fluorinated backbones were implemented with cobalt(II) and iron(II) and the differences within the complexes were investigated primarily by SQUID magnetometry and EPR studies. The cobalt(II) complexes, where the tpy ligands bear a long fluorinated alkyl chain, show fluorine specific interactions that have an impact on the EPR spectra. Furthermore, ruthenium(II) complexes combining a mesoionic carbene and a terpyridine ligand were employed for electrocatalytic reduction of CO2. The complexes show a high selectivity towards CO and a faradaic efficiency of 92%. The final part deals with a series of platinum(II) donor-acceptor complexes bearing different azobenzene and bridging quinone ligands. The complexes exhibit strong electrochromic behavior and were studied towards the influence of different (perfluorinated) alkyl chains on the azobenzene ligands on the electrochemical behavior. In the present thesis the impact of fluorine on different ligand systems and its influence on the physical and electrochemical properties of the resulting metal complexes are highlighted, which can be useful for estimating the properties of potential target compounds.
Weniger anzeigenCurrent genetic testing of patients performed to identify the molecular cause and potentially drive therapy decisions is predominately focused on small variation affecting coding regions due to the limitations of the underlying experimental methods. Long-read sequencing approaches have been shown to overcome these limitations allowing the detection of the entire spectrum of larger genomic alterations i.e. structural variants (SVs) with an unprecedented resolution potentially revealing previously undetected disease-causing mechanisms. In this thesis, we discuss the potential of long-read sequencing in combination with a functional annotation-based framework to identify non-coding pathogenic SVs in a cohort of limb malformation patients. In the process, we developed a pipeline that combines short- and long-read sequencing data, filters the detected SVs based on allele frequency, and applies an extensive functional annotation-based prioritization resulting in sets of candidate SVs for all involved patients. We also conduct a comprehensive comparison of callers and technologies highlighting the superior performance of long-read sequencing for SV detection and an evaluation of an automated prioritization method indicating superior performance to comparable approaches. The results of this thesis suggest the potential of performing an extended analysis of SVs as part of clinical diagnostics workflows and the relevance of non-coding functional annotation during variant prioritization.
Weniger anzeigenSmall- and medium-sized enterprises (SMEs) are an important force for promoting innovation in China as they represent the bulk of China’s industrial fabric and have the most innovative vitality and potential due to entrepreneurial dynamism, organizational flexibility, and fast responsiveness. However, SMEs generally lack financial, technological, and human resources to develop innovation. Furthermore, innovation gives rise to externalities, which could reduce the incentive of SMEs to engage in innovation. Therefore, public aids are needed in support of SME innovation. In light of the variety of innovation behavior among SMEs, innovation policies should be designed to target certain SMEs and support them according to their specific characteristics. In addition, with a strong focus on formal R&D and main types of technological innovation (i.e., product and process innovation), prior research restricts a comprehensive understanding of diverse innovation activities, especially non-R&D activities, and different innovation types, especially non-technological innovation. Given the need for targeted innovation policies and the under-researched heterogeneity among innovating SMEs, this dissertation aims to deepen the understanding of SME innovation heterogeneity from a perspective of the following innovation process: innovation activities – innovation types – SME overall performance. This dissertation is organized into five chapters. Chapter 1 introduces research motivations, theoretical background, research design, and an overview of the three articles presented in Chapters 2, 3, and 4. Three empirical articles in Chapters 2, 3, and 4 constitute the core of this dissertation and they are summarized as follows. The first article in Chapter 2 empirically analyzes SME heterogeneity in innovation activities based on the input stage of the aforementioned innovation process (innovation activities – innovation types), especially by disentangling the varying effects of innovation activities on technological types of innovation. This article, focusing mainly on non-R&D sources of innovation, compares non-R&D and R&D SMEs with respect to the separate and combined effects of non-R&D activities on product and process innovation. Drawing on a database collected from 1,392 manufacturing SMEs in China, empirical result reveals heterogeneous importance of non-R&D activities to product and process innovation for non-R&D and R&D SMEs. Specifically, non-R&D SMEs rely mainly on embodied knowledge to introduce technological innovation, while R&D SMEs can access external knowledge from customers and scientific sources to develop product innovation and also from suppliers to introduce process innovation. In addition, substitutability is found between internal and external innovation strategies composed of non-R&D activities, which is limited to product innovation for non-R&D SMEs and process innovation for R&D SMEs. The second article in Chapter 3 contributes to the empirical analysis of SME heterogeneity in innovation types based on the output stage of the process (innovation types – SME overall performance), especially by exploring different combinations of innovation types and their effects on SME performance. This article investigates SMEs’ combined use of different innovation types as well as the effect of the combination of innovation types on SME performance. The empirical analysis is based on data from 1,139 Chinese manufacturing SMEs. The results of factor analysis imply a tendency of combining product, quality, and organizational innovation and the other tendency of combining efficiency and flexibility innovation. A conditional approach to supermodularity is used to test for the relationship between different types of innovation. The results show that product, quality, and organizational innovation are neither complements nor substitutes, meaning that their combination generates only additive effects on SME performance. It is also found that substitutability between efficiency and flexibility exists without organizational innovation but it disappears with organizational innovation, which suggests that simultaneous organizational innovation is required for better use of efficiency and flexibility innovation in combination. The third article in Chapter 4 synthesizes SME innovation heterogeneity through the identification of SME innovation patterns according to the inputs and outputs (i.e., innovation activities and innovation types) of the innovation process. Based on a sample of 1,127 Chinese manufacturing SMEs, this article identifies SME patterns of innovation activities and of innovation types and uses the identified innovation patterns to analyze the relationship between innovation and SME performance, contributing to a comprehensive analysis of the whole innovation process. The innovation activities associated with internal and external knowledge sourcing characterize three innovation sourcing patterns, namely internal sourcing group, low sourcing group, and open sourcing group, which differ in activeness and openness of knowledge sourcing. The innovation types involving technological and non-technological types of innovation profile three innovation introducing patterns, namely production innovators, product innovators, and multifaceted innovators, which differ in the variety of innovation types introduced. Regarding the relationship between innovation sourcing and introducing patterns, being active in innovation activities increases the likelihood of introducing various innovation types and being open is most likely to capture a variety of innovation types. The results for the relationship between innovation introducing patterns and SME performance show that production innovators combining efficiency and flexibility innovation experience decreased performance while product innovators focusing on product innovation and multifaceted innovators combining technological and non-technological innovation achieve better performance. Chapter 5 concludes by discussing the contributions to innovation research, innovation policy, and innovation management, along with the limitations of this dissertation and the directions for future research.
Weniger anzeigenDuring mammalian corticogenesis, a wide diversity of neural stem cells (NSCs) orchestrate the development and organization of the cortex. The pool of NSCs initially expands through proliferative symmetric divisions, and sequentially starts dividing asymmetrically to give rise to the diverse cell types residing within the cortical layers. Throughout this process, cortical NSCs undergo extensive modifications in their transcriptomic profile and chromatin landscape contributing to the formation of heterogeneous progenitor populations. Although much progress has been made towards understanding cell-fate specification during human corticogenesis the mechanisms responsible for the temporal lineage specification of NSCs remain largely unknown. Understanding the variability of these distinct NSC populations is key for developing an in vitro system that allows for the homogeneous and unlimited culture of the desired NSC type which is crucial for cell replacement-based therapies. Hence, one of the main aims in our lab is to identify and discern these distinct NSC types which sequentially appear during cortical development with the objective to better understand these cell stages and, eventually, being able to manipulate them in vitro. In order to address this question, my project is focused on developing a strategy to isolate the early cortical NSC population for its characterization and potential manipulation. The main approach is to identify a cell surface marker to enable the isolation of these cells from our in vitro culture by fluorescence-activated cell sorting. By profiling our hiPSC-derived cortical progenitors at different stages by means of single-cell RNA sequencing, we selected potential candidate markers that were validated using immunofluorescence and sequencing methods. In this study, we identify Protogenin (PRTG) as a novel surface marker for early human cortical NSCs that can be used to isolate this population in vitro. We provide evidence that early expression of the novel marker correlates with cortical lineage specification. Furthermore, by sorting for such marker at early stages of neural induction we can prospectively isolate three distinct cortical subpopulations, resulting in highly pure subtype-specific NSC cultures. These findings illustrate the utility of PRTG cell-surface sorting for enriching early cortical NSCs in culture and, thus, aiding to develop a more robust and homogenous differentiation protocol. Ultimately, such knowledge should facilitate the generation of highly pure stage- and region-specific NSC populations from patient-derived samples which would provide a reliable source for cell replacement and regenerative therapies.
Weniger anzeigenChemical synapses are fundamental for fast and reliable synaptic transmission and proves as fundamental basis needed for cognitive functions in higher organisms as well as in humans. The ability of synapses to communicate with each other by synaptic vesicle release of neurotransmitters enables them to create a big neuronal network responsible for information relay to other parts of the body. Communication from neuron to neuron happens through release of neurotransmitter-containing synaptic vesicles from presynapse to postsynapse. Synaptic vesicles must be tethered, primed, and then fused with the presynaptic membrane to fulfil their purpose. This is orchestrated by a complex proteinaceous machinery at dedicated cytomatrix sites at the presynapse, known as active zone (AZ). These active zones are essential for synaptic vesicle release and specific scaffolding proteins are needed to assemble and maintain this complex machinery. This synaptic vesicle release machinery has been observed in Drosophila melanogaster’s glutamatergic type I terminals and can be observed as an electron-dense structure in ultrastructural images. This is not the case for the smaller type II synaptic terminals that emerge from neuromodulatory ventral unpaired median (VUM) neurons in the ventral nerve cord (VNC). These VUM neurons extend their synaptic terminals towards the peripheric larval body wall muscles of Drosophila and innervate those muscles. The synapses of these neurons are in proximity of glutamatergic type I terminal neurons and are known to act neuromodulatory on the muscle. Contrary to type I terminals, type II terminals don’t possess an electron-dense structure and the synaptic vesicle release machinery is still widely unknown. Previously it has been shown that the presynaptic active zone protein BRP is present in type I as well as in type II terminals. This thesis can confirm the presence of BRP in the neuromodulatory type II terminals via stimulated emission depletion (STED) microscopy and shows through larval locomotion analyser “IMBA” that other known type I terminal active zone proteins such as Unc13A, Unc13B and RBP are present in those neurons. The use of RNAi lines allowed for a knockdown (KD) of the tested AZ proteins, where different larval locomotive microbehaviour parameters were tested. Analysis of these data have shown that Unc13A, Unc13B and RBP KD mutants show an increased crawling speed via a decrease in “step interval”, while BRP KD mutants showed no such increase. Additionally, Unc13A and Unc13B KD mutants show an increase in lateral head movement that precedes a reorientation event, also known as head cast (HC) in Drosophila larvae. Furthermore, STED microscopy was used to check for the tested proteins in better resolution with immunohistochemical approaches , but this remained unsuccessful. STED images confirmed the presence of BRP spots in type II boutons, which were previously only seen through confocal microscopy. Overexpression and KD of BRP in octopaminergic/tyraminergic (OA/TA) neurons didn’t alter type II bouton morphology, but number of BRP spots per bouton. Additionally, this thesis inspects the possible interaction between type I and type II terminal neurons during pupal stages throughout the metamorphosis. Immunohistochemical approaches showed no obvious dependence on each other during metamorphosis for innervation target finding. In the second part of my thesis, we extended our research from our master’s thesis and started working from there. Aging is a process that remains mainly ununderstood. Few theories have been proposed, and one of them is the “free radical theory of aging and radiation chemistry” by D. Harman, suggesting the involvement of reactive oxygen species (ROS) in aging. ROS are O2-derived free radicals that are, in high amount, capable of causing several intracellular damages ultimately leading to cell death. Most of the ROS are produced in mitochondria and are within physiological levels, used for intracellular signalling. To maintain a healthy intracellular redox equilibrium, redox couples to scavenge ROS are used in the cell. One of the dominant redox couples is the tripeptide glutathione (GSH) and its oxidized form glutathione disulphide (GSSG). The distribution of GSH/GSSG in cells are around 90% in the cytoplasm, 10% in the mitochondria and a low percentage in the endoplasmic reticulum. Mitochondria are very well known as “the powerhouse of the cell” as they are the main energy producer within cells and are an organelle with their own mitochondrial DNA (mtDNA). With age, mtDNA accumulates mutations, leading to defect in the respiratory chain and ultimately resulting into cell death. To counteract an accumulation of defective mitochondria, mitochondria are transported back to the soma for degradation through mitophagy. Axonal transport declines with age and impaired mitochondrial transport are a key pathogenic change in aging associated neurodegenerative diseases. Spermidine is a polyamine that has been shown to mediate anti-aging effects through boosting autophagy and acts as an amino-butyl group donor for hypusination of the eukaryotic initiation factor 5A (eIF5A) which has been shown to be involved in spermidine-mediated protection of mitochondrial functionality. Here, we show through the use of in vivo imaging of adult fly wings, that mitochondrial transport and transport velocity were not affected with age in flies, regardless of dietary spermidine supplementation. We also showed that mitochondrial GSH/GSSG ratio was not affected with age or spermidine supplementation, through the use of an engineered green fluorescent protein (roGFP), containing a disulfide switch with different excitation maxima depending on its oxidation status. Lastly, we used the same construct investigate mitochondrial glutathione redox status to measure the effects of a deoxyhypusine synthase (DHPS) knockdown mutant on mitochondrial GSH/GSSG equilibrium. We saw no significant changes in our control groups, but a significant increase in mid-aged flies when DHPS was genetically reduced, which absent in flies with dietary spermidine supplementation.
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