TY - THES AB - The human ability to recognize objects in complex scenes has driven research in the computer vision field over couple of decades. This thesis focuses on the object recognition task in images. That is, given the image, we want the computer system to be able to predict the class of the object that appears in the image. A recent successful attempt to bridge semantic understanding of the image perceived by humans and by computers uses attribute-based models. Attributes are semantic properties of the objects shared across different categories, which humans and computers can decide on. To explore the attribute-based models we take a statistical machine learning approach, and address two key learning challenges in view of object recognition task: learning augmented attributes as mid-level discriminative feature representation, and learning with attributes as privileged information. Our main contributions are parametric and non-parametric models and algorithms to solve these frameworks. In the parametric approach, we explore an autoencoder model combined with the large margin nearest neighbor principle for mid-level feature learning, and linear support vector machines for learning with privileged information. In the non-parametric approach, we propose a supervised Indian Buffet Process for automatic augmentation of semantic attributes, and explore the Gaussian Processes classification framework for learning with privileged information. A thorough experimental analysis shows the effectiveness of the proposed models in both parametric and non-parametric views. AU - Sharmanska, Viktoriia ID - 1401 SN - 2663-337X TI - Learning with attributes for object recognition: Parametric and non-parametrics views ER - TY - THES AB - Cancer results from an uncontrolled growth of abnormal cells. Sequentially accumulated genetic and epigenetic alterations decrease cell death and increase cell replication. We used mathematical models to quantify the effect of driver gene mutations. The recently developed targeted therapies can lead to dramatic regressions. However, in solid cancers, clinical responses are often short-lived because resistant cancer cells evolve. We estimated that approximately 50 different mutations can confer resistance to a typical targeted therapeutic agent. We find that resistant cells are likely to be present in expanded subclones before the start of the treatment. The dominant strategy to prevent the evolution of resistance is combination therapy. Our analytical results suggest that in most patients, dual therapy, but not monotherapy, can result in long-term disease control. However, long-term control can only occur if there are no possible mutations in the genome that can cause cross-resistance to both drugs. Furthermore, we showed that simultaneous therapy with two drugs is much more likely to result in long-term disease control than sequential therapy with the same drugs. To improve our understanding of the underlying subclonal evolution we reconstruct the evolutionary history of a patient's cancer from next-generation sequencing data of spatially-distinct DNA samples. Using a quantitative measure of genetic relatedness, we found that pancreatic cancers and their metastases demonstrated a higher level of relatedness than that expected for any two cells randomly taken from a normal tissue. This minimal amount of genetic divergence among advanced lesions indicates that genetic heterogeneity, when quantitatively defined, is not a fundamental feature of the natural history of untreated pancreatic cancers. Our newly developed, phylogenomic tool Treeomics finds evidence for seeding patterns of metastases and can directly be used to discover rules governing the evolution of solid malignancies to transform cancer into a more predictable disease. AU - Reiter, Johannes ID - 1400 SN - 2663-337X TI - The subclonal evolution of cancer ER - TY - THES AB - This thesis is concerned with the computation and approximation of intrinsic volumes. Given a smooth body M and a certain digital approximation of it, we develop algorithms to approximate various intrinsic volumes of M using only measurements taken from its digital approximations. The crucial idea behind our novel algorithms is to link the recent theory of persistent homology to the theory of intrinsic volumes via the Crofton formula from integral geometry and, in particular, via Euler characteristic computations. Our main contributions are a multigrid convergent digital algorithm to compute the first intrinsic volume of a solid body in R^n as well as an appropriate integration pipeline to approximate integral-geometric integrals defined over the Grassmannian manifold. AU - Pausinger, Florian ID - 1399 SN - 2663-337X TI - On the approximation of intrinsic volumes ER - TY - THES AB - The co-evolution of hosts and pathogens is characterized by continuous adaptations of both parties. Pathogens of social insects need to adapt towards disease defences at two levels: 1) individual immunity of each colony member consisting of behavioural defence strategies as well as humoral and cellular immune responses and 2) social immunity that is collectively performed by all group members comprising behavioural, physiological and organisational defence strategies. To disentangle the selection pressure on pathogens by the collective versus individual level of disease defence in social insects, we performed an evolution experiment using the Argentine Ant, Linepithema humile, as a host and a mixture of the general insect pathogenic fungus Metarhizium spp. (6 strains) as a pathogen. We allowed pathogen evolution over 10 serial host passages to two different evolution host treatments: (1) only individual host immunity in a single host treatment, and (2) simultaneously acting individual and social immunity in a social host treatment, in which an exposed ant was accompanied by two untreated nestmates. Before starting the pathogen evolution experiment, the 6 Metarhizium spp. strains were characterised concerning conidiospore size killing rates in singly and socially reared ants, their competitiveness under coinfecting conditions and their influence on ant behaviour. We analysed how the ancestral atrain mixture changed in conidiospere size, killing rate and strain composition dependent on host treatment (single or social hosts) during 10 passages and found that killing rate and conidiospere size of the pathogen increased under both evolution regimes, but different depending on host treatment. Testing the evolved strain mixtures that evolved under either the single or social host treatment under both single and social current rearing conditions in a full factorial design experiment revealed that the additional collective defences in insect societies add new selection pressure for their coevolving pathogens that compromise their ability to adapt to its host at the group level. To our knowledge, this is the first study directly measuring the influence of social immunity on pathogen evolution. AU - Stock, Miriam ID - 1404 TI - Evolution of a fungal pathogen towards individual versus social immunity in ants ER - TY - THES AB - In this thesis I studied various individual and social immune defences employed by the invasive garden ant Lasius neglectus mostly against entomopathogenic fungi. The first two chapters of this thesis address the phenomenon of 'social immunisation'. Social immunisation, that is the immunological protection of group members due to social contact to a pathogen-exposed nestmate, has been described in various social insect species against different types of pathogens. However, in the case of entomopathogenic fungi it has, so far, only been demonstrated that social immunisation exists at all. Its underlying mechanisms r any other properties were, however, unknown. In the first chapter of this thesis I identified the mechanistic basis of social immunisation in L. neglectus against the entomopathogenous fungus Metarhizium. I could show that nestmates of a pathogen-exposed individual contract low-level infections due to social interactions. These low-level infections are, however, non-lethal and cause an active stimulation of the immune system, which protects the nestmates upon subsequent pathogen encounters. In the second chapter of this thesis I investigated the specificity and colony level effects of social immunisation. I demonstrated that the protection conferred by social immunisation is highly specific, protecting ants only against the same pathogen strain. In addition, depending on the respective context, social immunisation may even cause fitness costs. I further showed that social immunisation crucially affects sanitary behaviour and disease dynamics within ant groups. In the third chapter of this thesis I studied the effects of the ectosymbiotic fungus Laboulbenia formicarum on its host L. neglectus. Although Laboulbeniales are the largest order of insect-parasitic fungi, research concerning host fitness consequence is sparse. I showed that highly Laboulbenia-infected ants sustain fitness costs under resource limitation, however, gain fitness benefits when exposed to an entomopathogenus fungus. These effects are probably cause by a prophylactic upregulation of behavioural as well as physiological immune defences in highly infected ants. AU - Konrad, Matthias ID - 1395 SN - 2663-337X TI - Immune defences in ants: Effects of social immunisation and a fungal ectosymbiont in the ant Lasius neglectus ER - TY - THES AB - Phosphatidylinositol (Ptdlns) is a structural phospholipid that can be phosphorylated into various lipid signaling molecules, designated polyphosphoinositides (PPIs). The reversible phosphorylation of PPIs on the 3, 4, or 5 position of inositol is performed by a set of organelle-specific kinases and phosphatases, and the characteristic head groups make these molecules ideal for regulating biological processes in time and space. In yeast and mammals, Ptdlns3P and Ptdlns(3,5)P2 play crucial roles in trafficking toward the lytic compartments, whereas the role in plants is not yet fully understood. Here we identified the role of a land plant-specific subgroup of PPI phosphatases, the suppressor of actin 2 (SAC2) to SAC5, during vauolar trafficking and morphogenesis in Arabidopsis thaliana. SAC2-SAC5 localize to the tonoplast along with Ptdlns3P, the presumable product of their activity. in SAC gain- and loss-of-function mutants, the levels of Ptdlns monophosphates and bisphosphates were changed, with opposite effects on the morphology of storage and lytic vacuoles, and the trafficking toward the vacuoles was defective. Moreover, multiple sac knockout mutants had an increased number of smaller storage and lytic vacuoles, whereas extralarge vacuoles were observed in the overexpression lines, correlating with various growth and developmental defects. The fragmented vacuolar phenotype of sac mutants could be mimicked by treating wild-type seedlings with Ptdlns(3,5)P2, corroborating that this PPI is important for vacuole morphology. Taken together, these results provide evidence that PPIs, together with their metabolic enzymes SAC2-SAC5, are crucial for vacuolar trafficking and for vacuolar morphology and function in plants. AU - Marhavá, Petra ID - 1402 SN - 2663-337X TI - Molecular mechanisms of patterning and subcellular trafficking in Arabidopsis thaliana ER - TY - THES AB - A variety of developmental and disease related processes depend on epithelial cell sheet spreading. In order to gain insight into the biophysical mechanism(s) underlying the tissue morphogenesis we studied the spreading of an epithelium during the early development of the zebrafish embryo. In zebrafish epiboly the enveloping cell layer (EVL), a simple squamous epithelium, spreads over the yolk cell to completely engulf it at the end of gastrulation. Previous studies have proposed that an actomyosin ring forming within the yolk syncytial layer (YSL) acts as purse string that through constriction along its circumference pulls on the margin of the EVL. Direct biophysical evidence for this hypothesis has however been missing. The aim of the thesis was to understand how the actomyosin ring may generate pulling forces onto the EVL and what cellular mechanism(s) may facilitate the spreading of the epithelium. Using laser ablation to measure cortical tension within the actomyosin ring we found an anisotropic tension distribution, which was highest along the circumference of the ring. However the low degree of anisotropy was incompatible with the actomyosin ring functioning as a purse string only. Additionally, we observed retrograde cortical flow from vegetal parts of the ring into the EVL margin. Interpreting the experimental data using a theoretical distribution that models the tissues as active viscous gels led us to proposen that the actomyosin ring has a twofold contribution to EVL epiboly. It not only acts as a purse string through constriction along its circumference, but in addition constriction along the width of the ring generates pulling forces through friction-resisted cortical flow. Moreover, when rendering the purse string mechanism unproductive EVL epiboly proceeded normally indicating that the flow-friction mechanism is sufficient to drive the process. Aiming to understand what cellular mechanism(s) may facilitate the spreading of the epithelium we found that tension-oriented EVL cell divisions limit tissue anisotropy by releasing tension along the division axis and promote epithelial spreading. Notably, EVL cells undergo ectopic cell fusion in conditions in which oriented-cell division is impaired or the epithelium is mechanically challenged. Taken together our study of EVL epiboly suggests a novel mechanism of force generation for actomyosin rings through friction-resisted cortical flow and highlights the importance of tension-oriented cell divisions in epithelial morphogenesis. AU - Behrndt, Martin ID - 1403 TI - Forces driving epithelial spreading in zebrafish epiboly ER - TY - THES AB - Motivated by the analysis of highly dynamic message-passing systems, i.e. unbounded thread creation, mobility, etc. we present a framework for the analysis of depth-bounded systems. Depth-bounded systems are one of the most expressive known fragment of the π-calculus for which interesting verification problems are still decidable. Even though they are infinite state systems depth-bounded systems are well-structured, thus can be analyzed algorithmically. We give an interpretation of depth-bounded systems as graph-rewriting systems. This gives more flexibility and ease of use to apply depth-bounded systems to other type of systems like shared memory concurrency. First, we develop an adequate domain of limits for depth-bounded systems, a prerequisite for the effective representation of downward-closed sets. Downward-closed sets are needed by forward saturation-based algorithms to represent potentially infinite sets of states. Then, we present an abstract interpretation framework to compute the covering set of well-structured transition systems. Because, in general, the covering set is not computable, our abstraction over-approximates the actual covering set. Our abstraction captures the essence of acceleration based-algorithms while giving up enough precision to ensure convergence. We have implemented the analysis in the PICASSO tool and show that it is accurate in practice. Finally, we build some further analyses like termination using the covering set as starting point. AU - Zufferey, Damien ID - 1405 SN - 2663-337X TI - Analysis of dynamic message passing programs ER - TY - THES AB - Epithelial spreading is a critical part of various developmental and wound repair processes. Here we use zebrafish epiboly as a model system to study the cellular and molecular mechanisms underlying the spreading of epithelial sheets. During zebrafish epiboly the enveloping cell layer (EVL), a simple squamous epithelium, spreads over the embryo to eventually cover the entire yolk cell by the end of gastrulation. The EVL leading edge is anchored through tight junctions to the yolk syncytial layer (YSL), where directly adjacent to the EVL margin a contractile actomyosin ring is formed that is thought to drive EVL epiboly. The prevalent view in the field was that the contractile ring exerts a pulling force on the EVL margin, which pulls the EVL towards the vegetal pole. However, how this force is generated and how it affects EVL morphology still remains elusive. Moreover, the cellular mechanisms mediating the increase in EVL surface area, while maintaining tissue integrity and function are still unclear. Here we show that the YSL actomyosin ring pulls on the EVL margin by two distinct force-generating mechanisms. One mechanism is based on contraction of the ring around its circumference, as previously proposed. The second mechanism is based on actomyosin retrogade flows, generating force through resistance against the substrate. The latter can function at any epiboly stage even in situations where the contraction-based mechanism is unproductive. Additionally, we demonstrate that during epiboly the EVL is subjected to anisotropic tension, which guides the orientation of EVL cell division along the main axis (animal-vegetal) of tension. The influence of tension in cell division orientation involves cell elongation and requires myosin-2 activity for proper spindle alignment. Strikingly, we reveal that tension-oriented cell divisions release anisotropic tension within the EVL and that in the absence of such divisions, EVL cells undergo ectopic fusions. We conclude that forces applied to the EVL by the action of the YSL actomyosin ring generate a tension anisotropy in the EVL that orients cell divisions, which in turn limit tissue tension increase thereby facilitating tissue spreading. AU - Campinho, Pedro ID - 1406 SN - 2663-337X TI - Mechanics of zebrafish epiboly: Tension-oriented cell divisions limit anisotropic tissue tension in epithelial spreading ER - TY - THES AB - CA3 pyramidal neurons are important for memory formation and pattern completion in the hippocampal network. These neurons receive multiple excitatory inputs from numerous sources. Therefore, the rules of spatiotemporal integration of multiple synaptic inputs and propagation of action potentials are important to understand how CA3 neurons contribute to higher brain functions at cellular level. By using confocally targeted patch-clamp recording techniques, we investigated the biophysical properties of rat CA3 pyramidal neuron dendrites. We found two distinct dendritic domains critical for action potential initiation and propagation: In the proximal domain, action potentials initiated in the axon backpropagate actively with large amplitude and fast time course. In the distal domain, Na+-channel mediated dendritic spikes are efficiently evoked by local dendritic depolarization or waveforms mimicking synaptic events. These findings can be explained by a high Na+-to-K+ conductance density ratio of CA3 pyramidal neuron dendrites. The results challenge the prevailing view that proximal mossy fiber inputs activate CA3 pyramidal neurons more efficiently than distal perforant inputs by showing that the distal synapses trigger a different form of activity represented by dendritic spikes. The high probability of dendritic spike initiation in the distal area may enhance the computational power of CA3 pyramidal neurons in the hippocampal network. AU - Kim, Sooyun ID - 2964 SN - 2663-337X TI - Active properties of hippocampal CA3 pyramidal neuron dendrites ER - TY - THES AB - Chemokines organize immune cell trafficking by inducing either directed (tactic) or random (kinetic) migration and by activating integrins in order to support surface adhesion (haptic). Beyond that the same chemokines can establish clearly defined functional areas in secondary lymphoid organs. Until now it is unclear how chemokines can fulfill such diverse functions. One decisive prerequisite to explain these capacities is to know how chemokines are presented in tissue. In theory chemokines could occur either soluble or immobilized, and could be distributed either homogenously or as a concentration gradient. To dissect if and how the presenting mode of chemokines influences immune cells, I tested the response of dendritic cells (DCs) to differentially displayed chemokines. DCs are antigen presenting cells that reside in the periphery and migrate into draining lymph nodes (LNs) once exposed to inflammatory stimuli to activate naïve T cells. DCs are guided to and within the LN by the chemokine receptor CCR7, which has two ligands, the chemokines CCL19 and CCL21. Both CCR7 ligands are expressed by fibroblastic reticular cells in the LN, but differ in their ability to bind to heparan sulfate residues. CCL21 has a highly charged C-terminal extension, which mediates binding to anionic surfaces, whereas CCL19 is lacking such residues and likely distributes as a soluble molecule. This study shows that surface-bound CCL21 causes random, haptokinetic DC motility, which is confined to the chemokine coated area by insideout activation of β2 integrins that mediate cell binding to the surface. CCL19 on the other hand forms concentration gradients which trigger directional, chemotactic movement, but no surface adhesion. In addition DCs can actively manipulate this system by recruiting and activating serine proteases on their surfaces, which create - by proteolytically removing the adhesive C-terminus - a solubilized variant of CCL21 that functionally resembles CCL19. By generating a CCL21 concentration gradient DCs establish a positive feedback loop to recruit further DCs from the periphery to the CCL21 coated region. In addition DCs can sense chemotactic gradients as well as immobilized haptokinetic fields at the same time and integrate these signals. The result is chemotactically biased haptokinesis - directional migration confined to a chemokine coated track or area - which could explain the dynamic but spatially tightly controlled swarming leukocyte locomotion patterns that have been observed in lymphatic organs by intravital microscopists. The finding that DCs can approach soluble cues in a non-adhesive manner while they attach to surfaces coated with immobilized cues raises the question how these cells transmit intracellular forces to the environment, especially in the non-adherent migration mode. In order to migrate, cells have to generate and transmit force to the extracellular substrate. Force transmission is the prerequisite to procure an expansion of the leading edge and a forward motion of the whole cell body. In the current conceptions actin polymerization at the leading edge is coupled to extracellular ligands via the integrin family of transmembrane receptors, which allows the transmission of intracellular force. Against the paradigm of force transmission during migration, leukocytes, like DCs, are able to migrate in threedimensional environments without using integrin transmembrane receptors (Lämmermann et al., 2008). This reflects the biological function of leukocytes, as they can invade almost all tissues, whereby their migration has to be independent from the extracellular environment. How the cells can achieve this is unclear. For this study I examined DC migration in a defined threedimensional environment and highlighted actin-dynamics with the probe Lifeact-GFP. The result was that chemotactic DCs can switch between integrin-dependent and integrin- independent locomotion and can thereby adapt to the adhesive properties of their environment. If the cells are able to couple their actin cytoskeleton to the substrate, actin polymerization is entirely converted into protrusion. Without coupling the actin cortex undergoes slippage and retrograde actin flow can be observed. But retrograde actin flow can be completely compensated by higher actin polymerization rate keeping the migration velocity and the shape of the cells unaltered. Mesenchymal cells like fibroblast cannot balance the loss of adhesive interaction, cannot protrude into open space and, therefore, strictly depend on integrinmediated force coupling. This leukocyte specific phenomenon of “adaptive force transmission” endows these cells with the unique ability to transit and invade almost every type of tissue. AU - Schumann, Kathrin ID - 3275 SN - 2663-337X TI - The role of chemotactic gradients in dendritic cell migration ER - TY - THES AU - Maître, Jean-Léon ID - 3273 SN - 2663-337X TI - Mechanics of adhesion and de‐adhesion in zebrafish germ layer progenitors ER - TY - THES AU - Pflicke, Holger ID - 3962 SN - 2663-337X TI - Dendritic cell migration across basement membranes in the skin ER -