Nuclei on the Move - Physical Aspects of Interkinetic Nuclear Migration

Embryonic development is a highly complex procedure, leading from initial, unspecialised cell types - the stem cells - to ever more specialised ones. In part, this process is regulated by genes; but interactions between cells, such as mechanical contacts and the exchange of diffusive signalling molecules, also play pivotal roles for the correct execution of developmental programmes. Therefore, unravelling the rules of cell differentiation requires insights from both biology and physics. In this dissertation, we focus on the process of interkinetic nuclear migration (IKNM). IKNM takes place in cells of so-called pseudostratified epithelia (PSE) during development. In these tissues, the nuclei of cells move in a cell cycle dependent manner and position themselves in a specific region of the cells for each cell division. The correct nuclear positioning has been shown to be crucial for proper development in PSE. And because organs like the brain and the spinal cord develop from pseudostratified epithelial tissues, IKNM appears to be of paramount importance for the entire embryo. The work presented here concerns IKNM in the retina, an experimentally accessible outgrowth of the brain, and relies on experimental data obtained from zebrafish. However, the conclusions are likewise relevant for understanding the development of many other PSE tissues. Based on the experimental data, two previously posed hypotheses on how the majority of nuclear movements might be driven can be tested. The data is consistent with the idea that nuclear movements depend on the build-up of a gradient in nuclear packing density across the retinal tissue. Consequently, we develop the first mathematical model for the distribution of nuclei across the retinal tissue as a function of time. Underlying this model is the notion that individual nuclear trajectories phenomenologically resemble random walks during most of the cell cycle. Therefore, we model the time evolution of the nuclear density using a diffusion equation with an effective diffusion constant to be determined from the data. Furthermore, we specifically account for the fact that nuclear divisions always take place in a defined region of the cells - leading to the aforementioned gradient in nuclear packing density. Finally, we also pay attention to the spherical geometry of the retinal tissue. Although the simplest linear model describes well the data from early in the experiments, it fails to do so for data from later stages in which nuclei approach close-packing. We hypothesise that the reason for this mismatch between model and data might result from the neglect of crowding. Therefore, we present a second, nonlinear model which now takes the volume of nuclei into account by introducing a maximum possible packing density. This enables us to replicate the experimental nuclear distribution across the whole range of experimental time points. We finally employ this second model to make statements about the influence of experimental parameters, specifically incubation temperature, on the dynamics of IKNM. The result also provides some indications for possible microscopic mechanisms underlying the nuclear movements. Having studied the distribution of nuclei across the retinal tissue, we aim to investigate the significance of our obtained results on the level of individual cells. First, we compare the mobility of nuclei during IKNM with the expected mobility in the cases of Brownian motion and membrane-hindered Brownian motion. We find that IKNM appears to be both membrane-hindered and additionally driven throughout the entire cell cycle. Assuming a stochastic driving force and calculating its typical strength we deduce IKNM to be consistent with cytoskeletal transport. We then devise possible Langevin models for individual nuclear movements which are consistent with the model for the distribution of nuclei derived previously. The numerical simulation of each of these Langevin models enables us to distinguish between them; we identify the model which most likely reflects the biological process in each individual cell. This again leads to predictions about the potential microscopic underpinnings of nuclear movements during IKNM. The apparent importance of the cell membrane in restricting nuclear mobility prompts us to examine the shape of PSE cells in closer detail. We numerically solve the Helfrich elastic model for lipid bilayers for increasingly large cell aspect ratios. In the case of long, slender cells and high membrane tension, we recover shapes not unlike those previously reported for membrane tethers. In contrast, shorter cells are almost cylindrical. The results of this systematic investigation into cell shapes might explain the different geometries of cells in various types of PSE. Furthermore, they might also be of relevance for more generally understanding peculiar cell shapes, such as those of neurons.EPSRC; Helen Stone Scholarship at the University of Cambridge (through the Cambridge Commonwealth, European & International Trust); The Cambridge Philosophical Society Research Studentshi

Preparation, Processing and Characterization of Noble Metal Nanoparticle-based Aerogels

New challenges in nanotechnology arise in the assembly of nanoobjects into three-dimensional superstructures, which may carry synergetic properties and open up new application fields. Within this new class of materials nanostructured, porous functional metals are of great interest since they combine high surface area, gas permeability, electrical conductivity, plasmonic behavior and size-enhanced catalytic reactivity. Even though a large variety of preparation pathways for the fabrication of porous noble metals has already been established, several limitations are still to be addressed by research developments. The new and versatile approach that is presented in this work makes use of a templatefree self-assembly process for the fabrication of highly porous, metallic nanostructures. Thereby, nanochains are formed by the controlled coalescence of noble metal NPs in aqueous media and their interconnection and interpenetration leads to the formation of a self-supported network with macroscopic dimensions. Subsequently, the supercritical drying technique is used to remove the solvent from the pores of the network without causing a collapse of the fragile structure. The resulting highly porous, low-weighted, three-dimensional nanostructured solids are named aerogels. The exceptional properties of these materials originate from the conjunction of the unique properties of nanomaterials magnified by macroscale assembly. Moreover, the combination of different metals may lead to synergetic effects regarding for example their catalytic activity. Therefore, the synthesis of multimetallic gels and the characterization of their structural peculiarities are in the focus of the investigations. In the case of the developed preparation pathways the gelation process starts from preformed, stable colloidal solutions of citrate capped, spherical noble metal (Au, Ag, Pt, Pd) NPs. In order to face various requirements several methods for the initiation of the controlled destabilization and coalescence of the nanosized building blocks were developed and synthesis conditions were optimized, respectively. Multimetallic structures with tunable composition are obtained by mixing different kinds of monometallic NP solutions and performing a joint gel formation. The characterization of the resulting materials by means of electron microscopy reveals the formation of a highly porous network of branched nanochains that provide a polycrystalline nature and diameters in the size range of the initial NPs. Furthermore, synthesis conditions for the spontaneous gel formation of glucose stabilized Au and Pd NPs were investigated. In order to gain a detailed knowledge of the structural properties of bimetallic aerogel structures a versatile set of characterization techniques was applied. A broad pore size distribution dominated by meso- and macropores and remarkably high inner surface areas were concluded from the N2 physisorption isotherms and density measurements. As investigated, a specific thermal treatment could be used to tune the ligament size of Au-Ag aerogels, whereas Au-Pd and Pt-Pd structures provide thermal stability under mild conditions. Further investigations aimed to the enlightenment of the elemental distribution and phase composition within the nanochains of multimetallic gel structures. The different approaches provide complementary and consistent results. Phase analyses based on XRD measurements revealed separated phases of each metal in the case of Ag-Pd and Au-Pd aerogels. They further proved the possibility of temperature induced phase modifications that lead to complete alloying of Au and Pd. In addition, separated domains of Pt and Pd were established from the EXAFS analysis of the corresponding aerogel. STEM EDX high resolution elemental mappings confirmed the separated domains of different metals in the case of Au-Pd and Pt-Pd aerogels. Moreover, a complete interdiffusion and alloy formation of Au and Ag within the corresponding aerogel structure is suggested from STEM EDX results. Finally, the presented investigations further promote the field of metallic aerogels by addressing the challenging issue of processability and device fabrication. Hybrid materials with organic polymers as well as various kinds of coatings on glass substrates and glassy carbon electrodes were prepared whereas the network structure was preserved throughout all processing steps. Moreover, it was illustrated that the NP-based aerogels carry metallic properties as expressed by their low Seebeck coefficients and high electrical conductivities

Anpassung von Gebäuden

Dies ist ein Faktenblatt aus dem REGKLAM-Vorhaben zum Thema "Anpassung von Gebäuden"

Weiterbildungsstudiengänge im tertiären Bildungssystem Deutschlands nach der Bologna-Reform: eine erste fallbasierte Analyse anhand von Absolventen

Die Dissertation untersucht die Absolventen des bundesweit ersten Master of Business Administration [MBA]-Studiengangs mit Schwerpunkt Sportmanagement. In einem ersten Schritt findet die Vorstellung (ausgewählter) theoriegeleiteter Ansätze der Studien(fach)wahl mit besonderer Betrachtung von (möglichen) Einflussfaktoren statt. Darauf folgt eine strukturelle Einordnung von Weiterbildungsstudiengängen und ihren rechtlichen Vorgaben allgemein sowie die spezielle Studienform des MBAs betreffend in das deutsche Bildungssystem. Es erfolgt eine generelle Betrachtung des Bachelor- und des Masterstudiums sowie der Besonderheiten von weiterbildenden, berufsbegleitenden Masterstudiengängen. Anschließend wird die international bereits etablierte, in Deutschland jedoch vergleichsweise neue, Studienform der MBA-Studiengänge charakterisiert. Ferner wird der Forschungsstand zu Studenten und Absolventen relevanter Studienfächer sowie -formen beleuchtet. Nach einer Zusammenfassung der theoretischen Erkenntnisse wird im Anschluss zum empirischen Teil übergeleitet. Im Zentrum dessen steht folgende Frage: Welche Gründe und Erwartungen bewegen berufstätige Menschen dazu, sich für ein berufsbegleitendes MBA-Studium mit dem Schwerpunkt Sportmanagement zu entscheiden und wie lassen sich eben diese anhand von ausgewählten Merkmalen charakterisieren? Dieser Fragestellung wurde zunächst in einer quantitativen Erhebung mithilfe einer Online-Befragung nachgegangen und in einem zweiten Forschungsschritt wurden vertiefende Interviews geführt. Die Ergebnisse der beiden empirischen Studien werden ausführlich dargestellt. Nach der Interpretation und Diskussion der gewonnenen Erkenntnisse schließt die Arbeit mit Hinweisen auf Limitationen sowie einem Forschungsausblick.

Interkulturalität als Herzstück der Bildung für eine Menschlich begründete Gesellschaft

Fondé sur le concept d’identité (Dervin), le terme interculturalité est exploré par déclinaisons sémantiques dans des approches épistémologiques (Abdallah Pretceille, Devereux, Chalmel,) et empirique (Projet interculturel universitaire) au cœur du rapport sujet-culture. Celles-ci interrogent finalement les finalités éducatives (éduquer l’apprenant vers le développement de ses compétences ou de ses capabilités?), leurs enjeux et les limites du terme interculturalité dans un contexte des competences. (DIPF/Orig.)Basierend auf dem Identitätskonzept (Dervin) wird der Begriff Interkulturalität durch semantische Deklinationen in epistemologischen (Abdallah-Pretceille, Devereux, Chalmel) und empirischen Ansätzen (Universitäts-Interkulturelles Projekt) im Kern der Subjekt-Kultur-Beziehung untersucht. Sie fragen schließlich nach den Bildungszielen (Schulung des Lernenden zur Entwicklung seiner Kompetenzen oder Fähigkeiten?), ihren Herausforderungen und den Grenzen des Begriffs Interkulturalität im Kontext von Kompetenz. (DIPF/Orig.

Investigating the Performance and Energy Saving Potential of Chinese Commercial Building Benchmark Models for the Hot Humid and Severe Cold Climate Regions

The demand for energy in China is growing at an alarming rate. Buildings have become a significant component of the energy-demand mix accounting for nearly one-quarter of the country's total primary energy consumption. This study compares the building code standards for office and hotel buildings in the hot humid and severe cold climate regions of China and the United States. Benchmark office and hotel building models have been developed for Guangzhou and Harbin, China that meets China's minimum national and regional building energy codes with the integration of common design and construction practices for each region. These models are compared to the ASHRAE standard based US reference building models for Houston, Texas and Duluth, Minnesota which have similar climate conditions. The research further uses a building energy optimization tool to optimize the Chinese benchmarks using existing US products to identify the primary areas for potential energy savings. In the case of the Harbin models, an economic analysis has also been performed to determine the economic feasibility of alternative building designs. The most significant energy-saving options are then presented as recommendations for potential improvements to current China building energy codes

Dissection and optimization of Adeno-associated virus (AAV) DNA family shuffling technology: The journey is the reward

Viral vectors based on Adeno-associated viruses (AAV) have a broad application spectrum including gene therapy and basic research. However, because naturally occurring AAV capsids are rarely sufficiently efficient and/or specific for a given application, techniques were developed to broaden the existing capsid repertoire. A prototype technology is DNA family shuffling where, in a first step, homologous cap genes encoding capsid subunits are fragmented and recombined, yielding a viral library which can then be subjected to selection in order to enrich promising variants. The aim of the present study was to dissect and improve four critical steps along this procedure. Firstly (1), two different methodologies for production of cap gene fragments were compared, resulting in the identification of DNase I based fragmentation as the most robust approach. Interestingly, cap DNA concatamer formation during nested PCR was observed, leading to amendment of the PCR purification protocol. Next (2), we studied the impact of chimerism on the essential assembly-activating protein (AAP) that is encoded in an alternative open reading frame within cap and is recombined as well during DNA family shuffling. Importantly, by performing a battery of complementary experiments, we were able to show that shuffling of AAP is not impairing its function, i.e. the support of particle assembly. Furthermore, no influence on titers was observed for wild-type and most chimeric vector productions, altogether relieving long-standing concerns about a potential rate-limiting role of AAP for AAV vector generation and evolution. Thirdly (3), we established a pioneering in vivo AAV library selection strategy in which, unlike most previously reported schemes, we selected novel capsids in specific cell types within an organ instead of the organ as a whole. Specifically, we were motivated by the facts that liver disease is wide-spread in humans and that hepatic stellate cells (HSC) are known to drive liver fibrosis, thus contributing to disease progression. Alas, tools to genetically manipulate HSCs are limited. Therefore, a library encompassing 10 capsid variants was selected in HSC by AAV injection into mice, HSC isolation and PCR rescue using purified total DNA. Following multiple selection rounds, in vivo bulk validation was performed based on next-generation sequencing. In total, 157 capsid variants were screened in parallel and again, the liver was segregated into the single cell types, i.e. hepatocytes, HSC, Kupffer cells and liver sinusoidal endothelial cells. Notably, this revealed that the selection was successful as hepatocyte-detargeted vectors were identified that showed a strong co-transduction of HSC and Kupffer cells. Intriguingly, we noted differences in vector specificity and efficiency on the DNA versus the RNA level. In order to even further restrict the new vectors to a given cell type, vector cassettes were generated bearing cell-type specific promoters and miRNA binding sites to suppress off-targeting in cells expressing these miRNAs. Testing of these constructs in vitro gave promising results especially for the miRNA-based detargeting strategy. Finally (4), we implemented improvements during the selection and analysis steps, including the use of PacBio/SMRT sequencing technology to monitor AAV sequence enrichments throughout the course of selection. Additionally, we managed to increase the stringency of the PCR rescue of cap genes, by incorporating sample-specific barcodes, i.e., short, unique nucleotide stretches, into the AAV library genomes. By using these barcodes as a primer during sample recovery, we could isolate single libraries out of a complex library mixture, as validated in vitro. In the future, this original strategy could be exploited to track individual libraries in vivo upon injection of a mixture of libraries, which should in turn help to accelerate the identification of top-performing variants for validation studies. In summary, different steps along the powerful methodology of DNA family shuffling were improved advancing future vector development and the lingering concern about AAP impairment upon shuffling was dispersed