Ultra-stable ring-type organosilicas with click modifiable groups : application as catalytic support and HPLC packing

Organosilicas or polysilsesquioxane frameworks are attractive alternatives for commonly applied silica-based materials. Within these hybrid materials, the structural properties and robustness of inorganic supports are combined with embedded organic functionalities. Due to their resulting hydrolytic stability and functional versatility, organosilicas have successfully been applied in many fields of research. In this work, a deliberate suggestion towards an ultimate organosilica precursor in terms of versatility and stability is made. Subsequently, this new precursor is transformed into two distinctly different but highly adapted materials for further application. To serve as a catalytic support, a Periodic Mesoporous Organosilica (PMO), possessing highly uniform and ordered pores, is developed. Employing ‘click’ chemistry this material is further converted into a solid ligand able to accomodate a Ru(III)-complex. Such heterogeneous catalyst is found active in alcohol oxidation reactions performed in water at room temperature. Next to this, multiple approaches were investigated to obtain spherical and porous particles used as ultra-stable reverse-phase HPLC packing. The unprecedented stability of the organosilica at both high and low pH holds high promise for the development of new chromatographic methods. Its high-temperature stability, on the other hand, offers opportunities for extremely fast separations with a reduced amount of organic modifier

A single cell based model for cell divisions with spontaneous topology changes

The development of multicellular organisms is accompanied by the formation of tis- sues of precise shapes, sizes and topologies. Remarkable similarities between tissue topologies, in particular proliferating epithelial topologies, in various species suggest that the mechanisms that govern the formation of tissues are conserved among species. To understand these mechanisms various models have been developed. In this thesis, we present a novel mechanical model for cell divisions and tissue for- mation. The model accounts for cell mechanics and cell-cell adhesion. In our model, each cell is treated individually, thus the changes in cell’s shape and its local rearrange- ments occur naturally as a response to the evolving cellular environment and cell-cell interactions. We introduce the processes of cell growth and divisions and numerically simulate tissue proliferation. As tissue grows starting from few cells, we follow the dynamics of the tissue growth and cell packing topologies. The outcomes are com- pared with experimental observations in Drosophila wing growth. Our model accounts for the exponential decay of the mitotic index and reproduces commonly observed cell packing topologies in proliferating epithelia. Next, we consider two biologically relevant division schemes, namely, division through asymmetric division plane and division by Hertwig’s rule. We study the im- pact of division planes on tissue growth and show that the division plane may affect cell packing topologies. Development of the tissue is accompanied by cellular rearrange- ments. We vary the extent of cellular rearrangements and analyse their effects on tissue topology. We find that when cells are allowed to move freely, more organized packing topologies emerge

Self-organized Growth in Developing Epithelia

The development of a multicellular organism, such as a human or an animal, begins with the fertilization of an egg cell. Thereupon the organism grows by repeated cell divisions until the adult size is reached and growth stops. Although it is known that intrinsic mechanisms determine the final size of developing organs and organisms, the basic principles of growth control are still poorly understood. However, there is strong evidence that certain morphogens, which are a special class of signaling molecules, act as growth factors and play a key role in growth control. In this work, growth control is studied from a mainly theoretical viewpoint. A discrete vertex model describing the organization of cells by a network of polygons is used, including a description of the cell cycle and a description of dynamical morphogen distributions. Self-organized growth is studied by introducing growth rules that govern cell divisions based on the local morphogen level. This discrete description is complemented by a continuum theory to gain further insight into the dynamics of self-organized growth processes. The theoretical description is applied to the developing wing of the fruit fly Drosophila melanogaster. In the developing wing, which is an epithelium consisting of single-layered cell sheets, the morphogen Decapentaplegic (Dpp) acts as a key growth factor. Experimental data shows that the Dpp distribution is dynamic and adapts to the size of the developing wing. Two mechanisms that rely on a regulatory molecule species and lead to such a dynamic behaviour of the Dpp distribution are studied. Several growth rules are tested and the resulting growth behaviour is quantitatively compared to experimental data of the developing wing. A particular growth rule, that triggers a cell division when the local morphogen level has increased by a certain relative amount, is found to be consistent with experimental observations under normal and several perturbed conditions. It is shown that mechanical stresses that arise due to spatial growth inhomogeneities can have a stabilizing effect on the growth process

Dissecting the molecular interplay between tomato spotted wilt virus and the insect vector, Frankliniella occidentalis

Doctor of PhilosophyDepartment of Plant PathologyAnna E. WhitfieldThe Bunyaviridae is a family of animal and plant viruses that pose a threat to human, animal, and plant health worldwide. In nature, the dissemination of these viruses is dependent on arthropod vectors (genera Orthobunyavirus, Nairovirus, Phlebovirus, and Tospovirus) or rodent vectors (genus Hantavirus). The genus Tospovirus is the only one within this virus family that is composed of plant-infecting viruses transmitted by thrips. Tomato spotted wilt virus (TSWV), the type species of the Tospovirus genus, is one of the ten most devastating plant viruses known. It is most efficiently transmitted by the western flower thrips, Frankliniella occidentalis Pergande, in a persistant propagative manner. The insect molecules associated with virus infection and transmission by the thrips vector remain unidentified to date. The aim of this work was to identify F. occidentalis larval thrips proteins that are differentially expressed during TSWV infection of the insect vector and those that directly interact with TSWV. To achieve these goals, I used two-dimensional (2-D) gel electrophoresis and mass spectrometry coupled with Mascot searches. I identified 26 protein spots that displayed differential abundances in response to TSWV infection, which contained 37 proteins. Sixty two percent of these proteins were down-regulated by the viral infection demonstrating a complex response. Moreover, 8 and 11 protein spots that directly interacted with purified TSWV virions and a TSWV glycoprotein (GN), respectively, were identified in overlay assays of larval thrips proteins resolved by 2-D gel electrophoresis. A total of five proteins were identified from these spots. These interacting proteins might play roles in attachment and entry, endocytosis/exocytosis, and escape from different tissues for transmission to occur. Injection of double-stranded RNA (dsRNA) into adult female thrips triggered an RNAi response that resulted in 23% reduction of the target gene transcript level. This significant reduction resulted in increased mortality and decreased fertility compared to insects injected with control dsRNA or water and non-injected insects as well. The work presented here provides new insights on the molecular basis of this virus-vector interaction and describes new tools to conduct functional genomic assays to study gene function and design control strategies of F. occidentalis