Refine
Year of publication
- 2018 (204) (remove)
Document Type
- Doctoral Thesis (204) (remove)
Has Fulltext
- yes (204) (remove)
Is part of the Bibliography
- no (204)
Keywords
- Lebensqualität (2)
- Spracherwerb (2)
- vascular endothelial cells (2)
- ABCE1 (1)
- ARFI (1)
- Adhärenz (1)
- Afghanistan (1)
- Allosteric inhibition (1)
- Anomalie <Medizin> (1)
- Anwendungsorientierte Forschung (1)
Institute
- Biochemie, Chemie und Pharmazie (44)
- Medizin (39)
- Biowissenschaften (34)
- Physik (21)
- Informatik und Mathematik (17)
- Gesellschaftswissenschaften (8)
- Sprach- und Kulturwissenschaften (8)
- Neuere Philologien (7)
- Biochemie und Chemie (3)
- Kulturwissenschaften (3)
The continuous conversion of natural wildlife habitats into agricultural areas, as well as the fragmentation of the last wildlife refuges, is increasing the interface between people and wildlife. When wildlife negatively impacts on people and vice versa, we speak about human-wildlife conflicts (HWCs). This definition includes losses on both sides and takes into consideration the rooting of most of these conflicts between different groups of interest, such as advocates for nature conservation and economic groups. The centres of highest biodiversity are located in developing countries, which are also characterized by poverty. In African and Asian countries, people living in the vicinity of national parks and other conservation areas mostly receive only little support through the government or conservation organisations. Especially for those people who are dependent on agriculture, damage to fields and harvests can have catastrophic consequences. If the species causing damage is protected by national or even international law, the farmer is not allowed to use lethal methods, but has to approach the authority in charge. If this agency, however, cannot offer appropriate support, resentment, anger or even hate develops, and the support for wildlife conservation activities declines. For this reason, HWCs were declared as one of the most important conservation topics today, being particularly relevant for large and threatened species such as the African and Asian elephant, hippopotamus and the greater one-horned rhino, as well as for large predators. Up to today, no general assessment scheme has been recommended for damage caused by protected wildlife species.
In my study, HWCs in Asia and Africa are compared, focussing on all herbivorous species identified which damaged crops. For the French NGO Awely, des animaux et des hommes, I developed a detailed assessment scheme suitable for all terrestrial ecosystems, and any type of HWCs and any species (Chapter 2). This HWC assessment scheme was used in four different study areas located in two African countries (South Luangwa/Zambia (SL), Tarangire/Tanzania (TA)) and two Asian countries (Bardia/Nepal (BA) and Manas/India (MA)). This scheme ran for six consecutive years (2009 to 2014) for Zambia, Nepal and India and two years (2010 to 2011) for Tanzania. To carry out the assessments, I trained local HWC officers (Awely Red Caps) to assess HWCs by field observations (measurement of damage, identification of species through signs of presence, landscape attributes etc.) and interviews with aggrieved parties (socio economic data). Results of this assessment are presented in Chapters 2-4.
To determine whether elephants prefer or avoid specific crop species, two field experiments were carried out, one in SL and one in BA (Chapter 5 and 6). For this, two test plots were set up and damage by elephants (and other herbivores) were quantified.
Within this doctoral thesis, 3306 damage events of 7408 aggrieved parties were analysed. In three out of the four study areas (SL, BA, MA), elephants caused the highest number of damage events compared to all other wildlife species, however, in TA, most fields were damaged by zebra. Furthermore, the greater one-horned rhino, hippopotamus, wild boar, bushpig, deer and antelope, as well as primates, caused damage to fields and harvests. Damage to houses and other property were nearly exclusively caused by elephants.
With this doctoral thesis I was able to show that season, crop availability, type and the phenological stage of the crop played an important role for crop damaging behavior of herbivores (Chapter 2). Elephants especially damaged rice, maize and wheat and preferred all crop types in a mature stage of growth. In contrast, rhinos preferred wheat to rice and similar to antelope and deer, they preferred crops at earlier stages of growth, before ripening. Crop damage by wildlife species varied strongly in size; most damages fell below 40% of the total harvest per farmer, but in several cases (3 to 8% depending on the study area), harvests were completely destroyed. Interestingly, during times of low nutritional availability in the natural habitat (dry season), crop damages in all four study areas were significantly less than during other seasons.
In all four study areas, crop protection strategies, such as active guarding in the fields, chasing wildlife with noise or fire torches or erecting barriers, were used. In some cases protection strategies were combined. Analysis of data revealed that traditional protection strategies did not reduce the costs of damage (Chapter 3). In some cases, costs of damage, on protected fields were even higher than for unprotected fields. Only in MA did strategic and cohesive guarding significantly reduce crop damage by wildlife species.
Besides damage in the fields, elephants also caused damage to properties in the villages. In search for stored staple crops, they damaged houses, grain stores and kitchens. Such damage was analysed in three study areas (SL, BA, MA) (Chapter 4). Although property damage occurred less frequently compared to crop damage in the fields, the mean cost of this damage was found to be double in BA/MA and four times higher in SL, compared to the costs of crop damage in the fields. It is further remarkable that property damage significantly increased towards the dry season, when the harvest was brought into the villages.
The findings of this study underpin the assumption that wildlife herbivores, especially elephants, are lured to fields and crops because the highly nutritional food (crop) being readily available. Traditional crop protection is cost and labour intensive and does not reduce the costs of damage. For this reason, crop types, which are thought to be not consumed by elephants were systematically tested on their attractiveness in field experiments in SL and BA (Chapter 5 and 6). In SL, lemon grass, ginger and garlic were proven to be less attractive to African elephants than maize and in BA, basil, turmeric, chamomile, coriander, mint, citronella and lemon grass were found to be less attractive to Asian elephants than rice.
The results of this doctoral thesis are relevant for the management of wildlife conservation as they can lead to new approaches to the mitigation of HWCs in African and Asian countries. Finally, specific needs for more scientific research in this field have been identified.
Most of the elements in the universe are produced via charged-particle fusion reactions during the primordial nucleosynthesis and different stellar burning stages, as well as via neutron-capture reactions. Around 35 heavy, proton-rich isotopes are bypassed by those reaction paths, the p nuclei. A series of photo-disintegration reactions occurring in supernovae, called the γ process, was suggested as a mechanisms to produce the p nuclei. Numerical simulations of the γ process have been unable to reproduce the observed abundances of the light p isotopes. Recent models showed that a series of proton capture reactions could provide the observed abundances. Hence, the cross sections of the crucial capture reactions have to be measured in order to test those assumptions.
Radiative proton captures in addition to the γ-process could reproduce the observed abundance pattern. This thesis presents preparations of a proton capture measurement on the radioactive 91Nb in standard kinematics with a calorimetric 4π setup. The 91Nb(p,γ)92Mo reaction might be the key to explain the production of one of the most abundant p-nuclei, 92Mo. So far, no experimental data for this reaction is available.
We produced a sample of 91Nb, with a half-life of 680 yr, at the Physikalisch Technische Bundesanstalt in Braunschweig, Germany, by irradiating 92Mo with protons in the energy range of 12 – 20MeV. 91Nb was produced via the reaction 92Mo(p,2p)91Nb and via 92Mo(p,pn)91Mo, where 91Mo decays to 91Nb with a half-life of 15.5min. To predict the amount of produced 91Nb the cross section of 92Mo(p, 2p) was measured. It was found to be higher than the value given by theoretical calculations with TALYS. Finally, 91Nb was chemically separated from the molybdenum carried at Paul-Scherrer- Institut, Villigen, Switzerland.
In-beam total absorption cross-section measurement of the reaction 91Nb(p,γ)92Mo with 2 MeV protons at FRANZ is planed with the produced 91Nb. A 4π BaF2 detector consisting of 41 crystals will be used. During this experiment we will measure the sum energy and the multiplicity of each event. The freshly produced 91Nb constitutes only a minor component of the sample material. The sum energy and multiplicity are crucial to distinguish the desired 91Nb(p,γ) from all the other more dominant reactions. The expected multiplicity and the efficiency of the setup were carefully simulated with DICEBOX and GEANT4. It was possible to show that background reactions can be effectively suppressed. The most important background contributions could be identified and result from 92Mo(p,γ), 19F(p,γ), and 19F(p,α).
After entorhinal deafferentiation of the hippocampal dentate gyrus a reinnervation of the denervated neurons by axon collaterals can be observed. This process takes place in a matter of weeks. However, the overall functional effect on the hippocampal network is still unclear.
In an effort to investigate this effect of axonal sprouting on the neuronal network of the dentate gyrus we compared the electrophysiological response of the dentate gyrus after electric stimulation in wild-type mice (WT mice) with a normal post-lesion sprouting, with genetically modified mice with an overexpression of the growth-protein CAP23 (cytoskeleton-associated protein 23). CAP23 overexpressing mice (CAP23tg mice) are known to have an enhanced axonal growth and sprouting after lesion.
The mice (both the WT as well as the CAP23tg mice) were deeply anesthetized and a lesion of the perforant path was induced stereotactically with a wire knife. After that the mice were permitted to survive for 4-6 weeks for partial reinnervation of the dentate gyrus before they were again operated and evoked potentials were measured (extracellular recordings of evoked potentials in the dentate gyrus). Non-lesioned litter-mate mice were taken as reference. The sprouting and the correct position of the electrodes was confirmed histologically.
For electrophysiological investigation we assessed laminar profiles and calculated a current-source density (CSD). In lesioned CAP23tg mice compared to lesioned WT mice this CSD-analysis revealed a significant enhancement of the current sink in the area of deafferentiation (outer molecular layer) and a significant excitation in the granule-cell layer.
Our results show that axonal sprouting seems to enhance the excitability of granule-cells. Thus, even if an enhanced axonal sprouting might accelerate the reinnervation of denervated dendrites after lesion, but it also leads to posttraumatic hyperexcitability of the neuronal network. In a therapeutic approach of fascilitating axonal sprouting this hyperexcitability has to be taken into consideration.
Das menschliche Leben erscheint heute als in vielfältiger Weise mit seiner Umwelt verbunden. Bio- und neurowissenschaftliche Forschungen über die Interaktionsweisen mit der Umwelt verändern dabei das Bild des Körpers von einem hierarchisch aufgebauten Organismus zu einem organisch-kognitiv-verteilten Netzwerk. Nicht zuletzt Forschungen zur künstlichen Intelligenz haben gezeigt, dass das menschliche Gehirn nicht isoliert betrachtet werden kann, sondern verkörpert, vernetzt und damit in einer wechselwirkenden Abhängigkeit zu Körpern steht (embedded und extended mind). Epigenetische Forschungen haben ebenfalls auf die Umweltabhängigkeit auch genetischer Prozesse verwiesen (Postgenomik) und damit auf komplexe Wechselwirkungen zwischen Biotischem und Abiotischem aufmerksam gemacht. Diese komplexen Wechselwirkungen und Umweltabhängigkeiten zwischen Lebendigem und Nicht-Lebendigem werden inzwischen zusehends zum Gegenstand menschlicher Selbstorganisation. Sie tauchen in veränderter Form in den Plänen zu den sogenannten Industrien 4.0 auf, wenn es darum geht, intelligente Umgebungen mit dem Menschen interaktiv zu vernetzen. Die hierfür notwendigen digitalen Datenmengen stehen aber nur zur Verfügung, wenn Menschen sich aktiv vernetzen. Die Entstehung digitaler Daten- körper wird dadurch zu einem essentiellen Bestandteil sozialer Teilhabe, wodurch Soziales zum entwicklungsoffenen und unbestimmten Prozess wird. Wie sich Menschen wann und wo vernetzen, ist nicht vorherbestimmt. Digitalisierung ist dabei, so die These der Arbeit, sich zur grundlegenden Praxis menschlicher Vernetzung zu entwickeln.
Die Arbeit geht Digitalisierung aus einer Perspektive koevolutionärer Entstehungs- und Entwicklungszusammenhänge nach und zeigt, dass digitale Praxen zu einer neuen Form menschlicher Selbstorganisation weltweit geworden sind. Angesprochen wird damit, dass Digitalisierung nicht als etwas dem Menschen Äußerliches betrachtet werden kann, sondern in einen größeren kulturellen Entstehungszusammenhang eingebettet werden muss, der bis zu den Anfängen der Menschheit zurückreicht. Um dies zu veranschaulichen, werden in der Arbeit drei verschiedene Wissensformationen benannt, die sich jeweils in unterschiedlicher Art und Weise mit den aktuellen Veränderungen digitalisierter Lebenswelten auseinandersetzen.
Die erste Wissensformation (Kapitel 2) benennt den Humanismus, der im Aufkommen neuer Medientechnologien eine Bedrohung für den Menschen sieht. Eine zweite Wissensformation (Kapitel 3) widmet sich dem „Ende des Humanismus“, indem Ansätze der Science and Technology Studies (STS), der Akteur-Network-Theory (ANT) und des Agentiellen Realismus von Karan Barad diskutiert werden. Mit einer „neuen Ökonomie für eine neue Menschheit“ wird eine dritte Wissensformation (Kapitel 4) benannt, die, von postoperaistischen Ansätzen ausgehend, die These eines „dritten“ oder „kognitiven Kapitalismus“ diskutiert. Hier geht es um die These des Zusammenfallens von Ökonomischem und Sozialem, aus dem neue offene Sozialformationen entstehen. Schließlich wird eine vierte Wissensformation (Kapitel 5) formuliert, die, ausgehend vom Ansatz einer Anthropologie des Medialen (AdM) und dem Modell der Erweiterung kultureller Kapazitäten (EECC) versucht, die als digitalen Wandel bezeichneten Veränderungen in einen größeren Zusammenhang zu stellen.
Mit beiden Ansätzen kann schließlich gezeigt werden, dass sich Veränderungen menschlicher Selbstorganisation immer in der biologischen, individuellen, kulturellen und historisch-sozialen Entwicklungsdimension zugleich vollziehen. Dies lässt sich auch für die Prozesse der Digitalisierung zeigen. Nämlich, dass sich der Mensch als Teil der Natur in einem fortwährenden koevolutionären Prozess befindet. Weder Kultur, noch Soziales, noch Technologien sind unnatürlich. Sie können als „indirekte Biologie“, als „Künstliches“ oder als „Kultur der Biologie“ bezeichnet werden, die der Natur aber nie entkommen. Die Erweiterung kultureller Kapazitäten ist deshalb nicht als eine Ausdehnung des Menschen in die Natur hinaus zu verstehen, sondern bezeichnet die im Laufe der Menschheitsgeschichte komplexer werdenden Reichweiten und Zeittiefen menschlicher Selbstorganisation, die immer auf den drei Ebenen von Phylogenese, Ontogenese, Technogenese und der damit verbundenen Soziogenese basieren.
G-protein coupled receptors (GPCRs) are a predominant class of cell-surface receptors in eukaryotic life. They are responsible for the perception of a broad range of ligands and involved in a multitude of physiological functions. GPCRs are therefore of crucial interest for biological and pharmaceutical research. Molecular analysis and functional characterisation of GPCRs is frequently hampered by challenges in efficient large-scale production, non-destructive purification and long-term stability. Cell-free protein synthesis (CFPS) provides new production platforms for GPCRs by extracting the protein synthesis machinery of the cell in an open system that allows target-oriented modulations of the synthesis process and direct access to the nascent polypeptide chain. CFPS is fast, reliable and highly adaptable. Unfortunately, highly productive cell-free synthesis of GPCRs is often opposed by low product quality. This thesis was aimed to adapt and improve some of the new possibilities for the cell-free production of GPCRs in high yield and quality for structural and pharmaceutical analysis. An E. coli based CFPS system was applied to synthesise various turkey and human Beta-adrenergic receptor (Beta1AR) derivatives as well as human Endothelin receptors type A and B (ETA and ETB) constructs. Both receptor families are important drug targets and pharmacologically addressed in the treatment of several cardiovascular diseases. CF-synthesis was mainly performed in presence of nanodiscs (ND), which are reconstituted high density lipoprotein particles forming discoidal bilayer patches with a diameter varyring from 6 to approx. 15 nm. The supplementation of ND in the CF-synthesis reaction caused the co-translational solubilisation of the freshly synthesised GPCRs. The fraction of the solubilised GPCR that was correctly folded was analysed by the competence to bind its ligand alprenolol or Endothelin-1, respectively. Both the solubilisation efficiency and the ability to fold in a ligand binding competent state was strongly affected by the lipid composition of the supplied ND. Best results were generally achieved with lipids having phosphoglycerol headgroups and unsaturated fatty acid chains with 18 carbon atoms. Furthermore, thermostabilisation by introduction of point mutations had a large positive impact on the folding efficiency of both Beta1AR and ETB receptor. Formation of a conserved disulphide bridge in the extracellular region was additionally found to be crucial for the function of the ETB receptor. Disulphide bridge formation could be enhanced by applying a glutathione-based redox system in the CFPS. Further improvements in the quality of ETB receptor could be made by the enrichment of heat-shock chaperones in the CF-reaction. Depending on the receptor type and DNA-template, roughly 10 – 30 nmol (350 – 1500 µg) of protein could be synthesised in 1 ml of CF-reaction mixture. After the applied optimisation steps, the fractions of correctly folded receptor could be improved by several orders of magnitude and were finally in between 35% for the thermostabilised turkey Beta1AR, 9% for the thermostabilised ETB receptor, 6.5% for the non-stabilised ETB receptor, 1 - 5% for non-stabilised turkey Beta1AR and for human Beta1AR isoforms and 0.1% for ETA receptor. Therefore, between 2 and 120 µg of GPCR could be synthesised in a ligand binding competent form, depending on the receptor and its modifications. Correctly folded turkey Beta1AR and ETB receptors were thermostable at 30°C and could be stored at 4°C for several weeks after purification. Yields of the thermostabilised turkey Beta1AR were sufficient to purify the receptor in a two-step process by ligand-binding chromatography to obtain pure and correctly folded receptor in the lipid bilayer of a ND. Furthermore, a lipid dependent ligand screen could be demonstrated with the turkey Beta1AR and significant alterations in binding affinities to currently in-use pharmaceuticals were found. The established protocols are therefore suitable and highly competetive for a variety of applications such as screening of GPCR ligands, analysis of lipid effects on GPCR function or for the systematical biochemical characterisation of GPCRs. Most promising for future approaches appears to address the suspected bottlenecks of intial insertion of the GPCR-polypeptide chain in the ND bilayer and the thermal stability of the receptors. Nevertheless, the estabilised protocols for the analysed targets in this thesis are already highly competitive to previously published production protocols either in cell-based or cell-free systems with regard to yield of functional protein, speediness and costs. Moreover, the direct accessibility and other general characteristics of cell-free synthesis open a large variety of possible applications and this work can therefore contribute to the molecular characterisation of this important receptor type and to the development of new pharmaceuticals.
An die Soziologie werden zunehmend Fragen des ökonomischen Nutzens und der gesellschaftlichen Relevanz herangetragen. Ein Wissen um den gesellschaftlichen Impact soziologischen Wissens und die Artikulation eines Nutzens für die Praxis sind wertvolle Werkzeuge im Kampf um die Alimentation soziologischer Forschung. Aber wie wird soziologisches Wissen überhaupt angewendet? Um diese Frage zu beantworten, wird soziologisches Wissen definiert und dessen Anwendung expliziert. Unter Zuhilfenahme von Wissenschaftstheorie und Wissenssoziologie wird zunächst eine Definition erarbeitet. Anschließend werden Forschungsgebiete, die sich mit der Anwendung von (soziologischen) Wissen beschäftigen, vorgestellt – allen voran die soziologische Verwendungsforschung. Darauf aufbauend wird eine Explikation der Anwendung soziologischen Wissens erarbeitet, vor dessen Hintergrund aktuelle Bemühungen, soziologisches Wissen stärker anzuwenden, betrachtet werden. Die abschließende Diskussion beschäftigt sich mit den Möglichkeiten und Restriktionen der Anwendung soziologischen Wissens und betont die Rolle der Soziologie als kritische gesellschaftliche Aufklärungsinstanz.
Trotz aller Unsicherheit und kritischer Infragestellung sind Kunstlandschaftsbezeichnungen – und damit auch der „Mittelrhein“ – als Hilfsbegriffe für die Lokalisierung der Kunstwerke noch immer gebräuchlich. Aber es ist ganz besonders problematisch, vom Mittelrhein um 1500 als „Kunstlandschaft“ zu sprechen. Schon die Umgrenzung der Region fällt unterschiedlich aus, und noch mehr sind die Kriterien schwankend, die im Vergleich zu anderen Regionen den Mittelrhein definieren sollen. Vorherrschend sind bei solchen Vergleichen nach wie vor Stilbegriffe, welche Vorbehalte gegenüber dem Begriff des Stils auch geäußert werden. So ist die Frage, ob die für den Mittelrhein vorgeschlagene Kennzeichnung „Stilheterogenität“ als Kriterium der Abgrenzung tauglich ist oder mehr eine methodische Verlegenheitslösung darstellt.
Die Untersuchung konzentriert sich auf das Schnitzretabel, das als Leitmedium der spätgotischen Kunst im deutschsprachigen Raum zu betrachten ist. Die analysierten Schnitzretabel sind als Fallstudien anzusehen, wobei hier vor allem jene analysiert worden sind, die einen guten Erhaltungszustand aufweisen. Zwar haben die wenigsten ihr ursprüngliches Aussehen bewahrt, aber entweder sind die Veränderungen nur minimal oder der originale Zustand ist gut rekonstruierbar, sodass die Werkgruppe trotz der Eingriffe als repräsentativ gelten kann. Neben den traditionellen Untersuchungsmethoden konnte die Infrarotreflektographie mit beweglicher Kamera (Osiris) eingesetzt werden. Es soll mit der Vorstellung einer Gattung ein Ausschnitt der in der Region präsenten Kunst ohne „mittelrheinische Vorentscheidungen“ gezeigt werden.
Die meisten analysierten Retabel entstammen der Rhein-Main-Region mit Frankfurt und Mainz als Oberzentren des Mittelrheins; Oberwesel, Speyer und Gelnhausen markieren die Grenze für die Auswahl. Die 27 Einzeluntersuchungen finden sich im Katalogteil der Arbeit, während deren zusammenfassende Darstellung – im Hinblick auf Methode, Standort, Auftraggeber, Künstler, Retabeltyp, Bildprogramm sowie Einflüsse – sowie Ergebnisse im Hauptteil besprochen werden.
This dissertation discusses the mutual influence between leaders and followers on perception, emotion and behavior, using an attachment theory perspective. Some individuals are more likely to be seen as leaders than others. On the one hand this is determined by the characteristics or attributes as well as skills of the person in question. However, on the other hand, followers’ perception and expectations play a big role as well, in particular which expectations of an ideal leader can be fulfilled by followers’ current leader. Although attachment theory and – styles have only recently entered the organizational psychology literature, this dissertation advances that literature by looking at the role of attachment orientations between leaders and followers. In doing so, this dissertation answers several recent research calls on this topic. The three main subsequent chapters discuss the predictive role of attachment orientations with regard to leader preferences, the transference of behavioural expectations from one leader to another, and the perception of leader prototypicality in groups. The first chapter discusses the connection between implicit leader preferences and attachment orientations as predictors. Results show that avoidant attached individuals prefer a more autonomous and independent leadership style, whereas anxious attached individuals prefer a supportive and team-oriented leadership style. In the second chapter I study the transference of behavioural expectations from one leader to another. Results show that avoidant attached individuals are more likely to engage in this transference process. In addition, I discuss and empirically test the influence of culture with regard to leader transference. In the final chapter, I examine the behavioural influence of attachment orientations on how likely someone is perceived to be a leader in groups. Based on 57 project groups, I find that team members actually perceive avoidant attached individuals to be the most leader-like. Put differently, given certain environmental conditions, insecure attachment orientations can be perceived as leaders. These results show that it is even more important that leaders somewhat adapt to their followers’ preferences and not commit to merely one particular leadership style.
Cells within a tissue form highly complex, cellular interactions. This architecture is lost in two-dimensional (2D) cell cultures. To close the gap between 2D cell cultures and in vivo tissues, three-dimensional (3D) cell cultures such as spheroids or embryoid bodies were developed. To fully take advantage of the third dimension, imaging techniques are essential. The emerging field of "image-based systems biology" exploits the information in images and builds a connection between experimental and theoretical investigation of biological processes. Such interdisciplinary approaches strongly depend on the development of protocols to establish 3D cell cultures, innovations in sample preparation, well-suited imaging techniques and quantitative segmentation methods.
Although 3D cell cultures and image-based systems biology provide a great potential, 2D methods are still not completely replaced by 3D methods. This is mainly due to methodical and technical hurdles. Therefore, this thesis provides a significant contribution to overcome these hurdles and to further develop 3D cell cultures. I established computational and experimental methods related to 3D aggregates and investigated fundamental, cellular processes such as adhesion, growth and differentiation.
The automatic segmentation method "PAS" and "LoS" were developed in the context of this thesis. They extract essential biological properties such as the projected area or features of cell nuclei from 2D or 3D images of 3D aggregates. Both algorithms show their accuracy robustly over image data from different samples and different microscopes. In addition, the superior performance of PAS and LoS was proven in a comparison with state-of-the-art methods.
The PAS approach served as an essential basis for investigating cellular processes such as adhesion and growth which are tightly regulated to contribute to tissue integrity. These processes are involved in the formation of spheroids. The temporally resolved data of spheroid formation of three mammary epithelial cell lines revealed differences in their formation dynamics as well as in the onset of spheroid formation phases (aggregation, compaction and growth). Despite these differences, adhesion- and growth-associated proteins such as E-cadherin, actin, microtubules, and the focal adhesion kinase show similar importance in a particular phase. Notably, certain proteins (e.g. E-Cadherin) contribute differently to spheroid formation of cells from different cell types in terms of cell adhesion and growth. Overall, analyses of the individual phases of spheroid formation revealed the temporal coordination of fundamental tissue-specific processes. The results contribute to a better understanding of the maintenance and disruption of tissue integrity.
An important but yet unknown process is how cells accomplish to arrange themselves against the gravitational force to form a spheroid. Live imaging with light sheet-based microscopy provides the best solution for a temporally and in particular spatially resolved investigation of spheroid formation. Although the imaging possibilities increase with this particular microscopy technique, available sample preparation methods are rare. Therefore, I have significantly optimized "agarose beaker" as preparation method for 3D long-term imaging of spheroid formation. The data show that upward movement of the cells takes place early. This movement is initiated in the centre of the initially flat cell layer. Subsequently, the cells move from the periphery of the cell layer toward the centre. Cells rearrange within the spheroid which is followed by growth. It is very likely that 3D aggregates form by adopting an energetically favoured, spherical shape by increasing cell-cell or cell-matrix contacts.
Besides the knowledge gained from the examination of the self-assembly process in different contexts, fully formed cellular aggregates can serve as basis to investigate differentiation processes. Differentiation guide cell fate specification during early embryonic development (i.e. preimplantation) and is not fully understood yet. Due to the lack of an in vitro system for preimplantation, I have developed "blastoids". These are 3D multicellular aggregates of mouse embryonic stem cells which represent important phases of preimplantation and beyond. In qualitative and quantitative analyses, a strong similarity was proven between blastoids and the inner cell mass of in vivo mouse embryos. Further results strongly suggest that both, the cell number and the trophectoderm play a subordinate role for cell fate decision during preimplantation. Furthermore, 3D neighbourhood analyses have shown that both, blastoids and mouse embryos, do not show a random "salt-and-pepper" pattern during differentiation. Instead, they show a yet unknown local clustering of cells with identical fates, suggesting local cell interactions that influence cell fate decision. Furthermore, the data indicate that the maturation of the epiblast in the later stages of preimplantation is initiated by an interaction between cells of the epiblast and the primitive endoderm.
Using image-based systems biology, I have investigated fundamental cellular processes such as adhesion, growth and differentiation in the context of tissue integrity and early embryonic development using 3D cellular aggregates. This highly interdisciplinary work is a major contribution to 3D cell biology and demonstrates how cells bind and interact within a complex system. The main methods developed in this thesis as well as the biological findings can be used not only in further biological but also in medical and pharmacological studies. They have the potential to advance our understanding of complex biological systems and to provide new opportunities for practical applications.
Acute myeloid leukemia (AML) is a clonal malignancy of hematopoietic stem cells (HSCs) characterized by expansion of myeloid blasts in the bone marrow. It has been shown that autophagy is a degradative process, which delivers cytoplasmic components to lysosomes to prevent malignant transformation by maintaining HSC integrity. Besides its function as a bulk degradation machinery to recycle cytoplasmic components during limited energy supply, autophagy also serves as an intracellular quality control mechanism. Selective autophagy requires autophagy receptors such as p62 to specifically bridge the targeted cargos into autophagosomes. p62 is known as a central signaling hub involved in pro-oncogenic signaling pathways and autophagic degradation pathways. However, little is known about the role of p62 as a selective autophagy receptor in AML. This study aims to elucidate the precise function of p62 as an autophagy receptor in leukemia development and maintenance.
In silico analysis revealed that high p62 expression was significantly associated with poor overall survival of adult patients with de novo AML, suggesting that p62 may promote leukemia maintenance. To address the functional role of p62 in leukemia, genome editing by CRISPR/Cas9 was used to knockout p62 in four human AML cell lines. Importantly, p62 loss reduced cell proliferation in all four cell lines. This observation could be transferred to a murine leukemia cell model in which leukemic transformation of lineage-depleted bone marrow (ldMBM) cells was induced by overexpression of the human transcriptional coactivator MN1. Knockdown of p62 by shRNA in MN1-driven leukemia cells impaired proliferation and decreased colony forming ability without altering apoptosis. This indicates that p62 is crucial for leukemia proliferation in vitro. To further characterize the role of p62 in leukemia development and maintenance a murine AML transplantation model was established. Therefore, ldMBM cells isolated from WT and p62-/- mice were transduced with MN1 and transplanted into lethally irradiated mice. As expected, all mice developed fatal myeloid proliferation. Notably, p62 loss in MN1-driven leukemia significantly prolonged survival in mice and caused a more immature phenotype. Consistent with the in vitro results, ex vivo analysis of p62-/- leukemic cells displayed decreased colony-forming ability, although p62 loss did not affect composition and function of HSCs. Moreover, re-transplantation of primary MN1-driven leukemia cells attenuated leukemia progression upon p62 loss. These findings support a decisive role of p62 in leukemia development and maintenance.
To gain molecular insight into the function of p62 during myeloid transformation an interactome analysis of murine MN1-driven leukemia cells was performed. This revealed first that p62 predominantly interacts with mitochondrial proteins and second that inhibition of autophagic degradation causes accumulation of p62-bound mitochondria. This leads to the first assumption that loss of p62 may provoke mitochondrial accumulation with increasing mitochondrial damage and second that p62 may mediate degradation of mitochondria by mitophagy. Indeed, in the absence of p62, accumulation of dysfunctional mitochondria was detected by morphological changes of the mitochondria, increased mitochondrial ROS and impaired mitochondrial respiration capacity. Furthermore, induction of PINK1/Parkin-independent mitophagy revealed that loss of p62 caused impaired degradation of mitochondrial proteins and reduced translocation of damaged mitochondria into autophagosomes. Taken together, p62 is required for effective degradation of dysfunctional mitochondria by mitophagy in AML.
Due to the fact that p62 is a multifunctional protein, rescue experiments with different mutants of p62 were performed to clarify if p62-mediated mitophagy contributes to leukemia proliferation. Notably, the autophagy-deficient mutant (disabled to bind autophagosomes) reduced cell growth and colony-forming ability to the same extent as knockdown of p62, as the clustering-deficient mutant (disabled to form aggregates) displayed an intermediate phenotype. Strikingly, only the autophagy-deficient mutant failed to rescue mitophagy.
In conclusion, this study demonstrates the prominent role of p62 as a selective autophagy receptor for mitochondrial quality control which contributes to leukemia development and maintenance. Therefore, targeting selective autophagy opens new venues in the treatment of AML.