@phdthesis{Kleineidam1999,
  author    = {Kleineidam, Christoph},
  title     = {Sensory Ecology of Carbon Dioxide Perception in Leaf-cutting Ants},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-1562},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {1999},
  abstract  = {The study examines the sensory ecology of CO2 perception in leaf-cutting ants. It begins with the ecological role of CO2 for leaf-cutting ants. Inside the subterranean nests of Atta vollenweideri large amounts of CO2 are produced by the ants and their symbiotic fungus. Measurements in field nest at different depths revealed that CO2 concentrations do not exceed 2 per cent in mature nests. These findings indicate effective ventilation even at depths of 2 m. Small colonies often face the situation of reduced ventilation when they close their nest openings as a measure against flooding. A simulation of this situation in the field as well as in the laboratory revealed increasing CO2 concentrations causing reduced colony respiration which ultimately might limit colony success. Wind-induced ventilation is the predominant ventilation mechanism of the nests of Atta vollenweideri, shown by an analysis of external wind and airflow in the channels. The mound architecture promotes nest ventilation. Outflow channels have their openings in the upper, central region and inflow channels had their openings in the lower, peripheral region of the nest mound. Air is sucked out through the central channels, followed by a delayed inflow of air through the peripheral channels. The findings support the idea that the nest ventilation mechanism used by Atta vollenweideri resembles the use of Bernoulli's principle in Venturi Tubes and Viscous Entrainment. CO2 is important in a second context besides microclimatic control. A laboratory experiment with Atta sexdens demonstrated that leaf-cutting ants are able to orientate in a CO2 gradient. Foragers chose places with higher CO2 concentration when returning to the nest. This effect was found in all homing foragers, but it was pronounced for workers carrying leaf fragments compared to workers without leaf fragments. The findings support the hypothesis that CO2 gradients are used as orientation cue inside the (dark) nest to find suited fungus chambers for unloading of the leaf fragments. After the importance of CO2 in the natural history of the ants has thus been demonstrated, the study identifies for the first time in Hymenoptera type and location of the sensory organ for CO2 perception. In Atta sexdens a single neuron associated with the sensilla ampullacea was found to respond to CO2. Since it is the only neuron of this sensillum, the sensillum characters can be assumed to be adapted for CO2 perception. A detailed description of the morphology and the ultrastructure allows a comparison with sensilla for CO2 perception found in other insects and provides more information about sensillum characters and their functional relevance. The CO2 receptor cells respond to increased CO2 with increased neural activity. The frequency of action potentials generated by the receptor cell shows a phasic-tonic time course during CO2 stimulation and a reduced activity after stimulation. Phasic response accomplished with a reduced activity after stimulation results in contrast enhancement and the ability to track fast fluctuations in CO2 concentration. The neurons have a working range of 0 to 10 per cent CO2 and thus are able to respond to the highest concentrations the ants might encounter in their natural environment. The most exciting finding concerning the receptor cells is that the CO2 neurons of the leaf-cutting ants do not adapt to continuous stimulation. This enables the ants to continuously monitor the actual CO2 concentration of their surroundings. Thus, the sensilla ampullacea provide the ants with the information necessary to orientate in a CO2 gradient (tracking of fluctuations) as well as with the necessary information for microclimatic control (measuring of absolute concentrations).},
  subject      = {Blattschneiderameisen},
  language  = {en}
}
@phdthesis{Spaethe2001,
  author    = {Spaethe, Johannes},
  title     = {Sensory Ecology of Foraging in Bumblebees},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-1179692},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2001},
  abstract  = {Pollinating insects exhibit a complex behavior while foraging for nectar and pollen. Many studies have focused on ultimate mechanisms of this behavior, however, the sensory-perceptual processes that constrain such behavior have rarely been considered. In the present study I used bumblebees (Bombus terrestris), an important pollinating insect, to investigate possible sensory constraints on foraging behavior. Additionally, I survey inter-individual variation in the sensory capabilities and behavior of bumblebees caused by the pronounced size polymorphism among members of a single colony. In the first chapter I have focused on the sensory-perceptual processes that constrain the search for flowers. I measured search time for artificial flowers of various sizes and colors, a key variable defining the value of a prey type in optimal foraging theory. When flowers were large, search times correlate well with the color contrast of the targets with their green foliage-type background, as predicted by a model of color opponent coding using inputs from the bee's UV, blue, and green receptors. Targets which made poor color contrast with their backdrop, such as white, UV-reflecting ones, or red flowers, take longest to detect, even though brightness contrast with the background is pronounced. When searching for small targets, bumblebees change their strategy in several ways. They fly significantly slower and closer to the ground, so increasing the minimum detectable area subtended by an object on the ground. In addition they use a different neuronal channel for flower detection: instead of color contrast, they now employ only the green receptor signal for detection. I related these findings to temporal and spatial limitations of different neuronal channels involved in stimulus detection and recognition. Bumblebees do not only possess species-specific sensory capacities but they also exhibit inter-individual differences due to size. Therefore, in the next two chapters I have examined size-related effects on the visual and olfactory system of Bombus terrestris. Chapter two deals with the effect of scaling on eye architecture and spatial resolving power of workers. Foraging efficiency in bees is strongly affected by proficiency of detecting flowers. Both floral display size and bee spatial vision limit flower detection. In chapter one I have shown that search times for flowers strongly increases with decreasing floral display size. The second factor, bee spatial vision, is mainly limited by two properties of compound eyes: (a) the interommatidial angle {\c{C}}{\aa} and (b) the ommatidial acceptance angle {\c{C}}{\´a}. When a pollinator strives to increase the resolving power of its eyes, it is forced to increase both features simultaneously. Bumblebees show a large variation in body size. I found that larger workers with larger eyes possess more ommatidia and larger facet diameters. Large workers with twice the size of small workers (thorax width) have about 50 per cent more ommatidia, and a 1.5 fold enlarged facet diameter. In a behavioral test, large and small workers were trained to detect the presence of a colored stimulus in a Y-maze apparatus. The stimulus was associated with a sucrose reward and was presented in one arm, the other arm contained neither stimulus nor reward. The minimum visual angle a bee is able to detect was estimated by testing the bee at different stimuli sizes subtending angles between 30° and 3° on the bee's eye. Minimum visual detection angles range from 3.4° to 7.0° among tested workers. Larger bumblebees are able to detect objects subtending smaller visual angles, i.e. they are able to detect smaller objects than their small conspecifics. Thus morphological and behavioral findings indicate an improved visual system in larger bees. Beside vision, olfaction is the most important sensory modality while foraging in bees. Bumblebees utilize species-specific odors for detecting and identifying nectar and pollen rich flowers. In chapter three I have investigated the olfactory system of Bombus terrestris and the effect of scaling on antennal olfactory sensilla and the first olfactory neuropil in the bumblebee brain, the antennal lobes. I found that the pronounced size polymorphism exhibited by bumblebees also effects their olfactory system. Sensilla number (I measured the most common olfactory sensilla type, s. placodea), sensilla density, volume of antennal lobe neuropil and volume of single identified glomeruli correlate significantly with worker's size. The enlarged volume of the first olfactory neuropil in large individuals is caused by an increase in glomeruli volume and coarse neuropil volume. Additionally, beside an overall increase of brain volume with scaling I found that the olfactory neuropil increases disproportionately compared to a higher order neuropil, the central body. The data predict a higher odor sensitivity in larger bumblebee workers. In the last chapter I have addressed the question if scaling alters foraging behavior and rate in freely foraging bumblebees. I observed two freely foraging B. terrestris colonies and measured i) trip number, ii) trip time, iii) proportion of nectar trips, and iv) nectar foraging rate of different sized foragers. In all observation periods large foragers exhibit a significantly higher foraging rate than small foragers. None of the other three foraging parameters is affected by workers' size. Thus, large foragers contribute disproportionately more to the current nectar influx of their colony. To summarize, this study shows that understanding the mechanisms of visual information processing and additionally comprising inter-individual differences of sensory capabilities is crucial to interpret foraging behavior of bees.},
  subject      = {Hummeln},
  language  = {en}
}
@phdthesis{ContarAdolfi2017,
  author    = {Contar Adolfi, Mateus},
  title     = {Sex determination and meiosis in medaka: The role of retinoic acid},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-136335},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {Sex determination (SD) is a complex and diverse developmental process that leads to the decision whether the bipotential gonad anlage will become a testis or an ovary. This mechanism is regulated by gene cascades, networks and/or chromosomal systems, and can be influenced by fluctuations of extrinsic factors like temperature, exposure to hormones and pollution. Within vertebrates, the group of fish show the widest variety of sex determination mechanism. This whole diversity of processes and mechanisms converges to the formation of two different gametes, the eggs and the sperm, the first bigger and static, and the second smaller and motile. Meiosis is crucial for the formation of both types of gametes, and the timing of meiosis entry is one of the first recognizable differences between male and female in vertebrates. The germ cells go into meiosis first in female than in male, and in mammals, this event has been shown to be regulated by retinoic acid (RA). This small polar molecule induces in the germ cells the expression of the pre-meiotic marker Stra8 (stimulated by retinoic acid gene 8), which is necessary for meiosis initiation. Interestingly, genome analyzes have shown that the majority of fish (including medaka) lack the stra8 gene, adding a question mark to the role of RA in meiosis induction in this group. Since a role of RA in entry of meiosis and sexual development of fish is still far from being understood, I investigated in medaka (Oryzias latipes) a possible signaling function of RA during the SD period in embryos and in reproductively active gonads of adults. I generated a transgenic medaka line that reports responsiveness to RA in vivo. With this tool, I compared RA responsiveness with the expression of the main gene involved in the synthesis of RA. My results show that there is a de-correlation between the action of RA with its source. In adults, expression of the RA metabolizing enzymes show sexually dimorphic RA levels, with aldh1a2 levels being higher in testis, and cyp26a1 stronger in female gonad. In ovary, the responsiveness is restricted to the early meiotic oocytes. In testis, RA is acting directly in the pre-meiotic cells, but also in Sertoli and Leydig cells. Treatment experiments on testis organ culture showed that RA pathway activation leads to a decrease in meiosis markers expression levels. During the development, RA responsiveness in the germ cells was observed in both sexes much earlier than the first female meiosis entry. Treatments with RA-synthesis inhibitor show a decrease in meiosis markers expression levels only after the sex differentiation period in female. Expression analyzes of embryos treated with exogenous RA showed induction of dmrt1a at the gonad levels and an increase of amh levels. Both genes are not only involved in male formation, but also in the regulation of germ cell proliferation and differentiation. RA is important in meiosis induction and gametogenesis in adult medaka. However, there is no evidence for a similar role of RA in initiating the first meiosis in female germ cells at the SD stage. Moreover, contrary to common expectation, RA seems to induce sex related genes that are involved indirectly in meiosis inhibition. In this thesis, I showed for the first time that RA can be involved in both induction and inhibition of meiosis entry, depending on the sex and the developmental stage in a stra8-independent model organism.},
  subject      = {Japank{\"a}rpfling},
  language  = {en}
}
@phdthesis{Ostner2002,
  author    = {Ostner, Julia},
  title     = {Sex-specific reproductive strategies in redfronted lemurs (Eulemur fulvus rufus, Primates, Lemuridae)},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-5011},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2002},
  abstract  = {The number of males in animal groups is an essential determinant of male and female reproductive strategies. Females may benefit from living with several males, whereas males generally strive to monopolize a group of females. Due to male intrasexual competition, the sex ratio of groups of anthropoid primates is generally female-biased. Gregarious Malagasy lemurs deviate from theoretical expectations derived from sexual selection theory and from patterns found among anthropoids because they live in relatively small groups with an even or male-biased adult sex ratio and lack sexual dimorphism. The aim of this thesis was to investigate sex-specific reproductive strategies relating to the unusual group composition of redfronted lemurs (Eulemur fulvus rufus) by combining behavioral, demographic and endocrinological data. In the first of a set of four studies I investigated the applicability of non-invasive endocrine measurements for monitoring ovarian function in wild redfronted lemur females in order to evaluate the degree of estrus synchrony. Further, I tested the prediction that males living in multi-male groups rely on indirect mechanisms of intrasexual competition, such as physiological suppression of testicular function. Several possible benefits gained from living with many males have been proposed and the hypothesis that additional males improve social thermoregulation was tested in the third study. Finally, I examined the proximate determinants of the unusual sex ratio within groups, the variation in the adult sex ratio as well as possible social benefits of the high number of males for both sexes. The study was conducted in Kirindy Forest, Madagascar, between April 1999 and July 2000. I recorded >3000 hours of focal animal data on social and sexual behavior of all adult members of five groups. Additionally, >2200 fecal samples of males and females were collected for subsequent hormone analysis using enzymeimmunoassay (EIA). Further, I analyzed demographic data from seven Eulemur fulvus rufus groups collected between 1996 and 2002. The analyses of fecal estrogen and progestogen excretion in wild and captive females revealed that monitoring ovarian function is principally possible in redfronted lemurs, as demonstrated by the analysis of samples from captive females. Characterization of ovarian cycles in wild females, however, was not possible, because of a high day-to-day variability in excreted hormones. Nevertheless, the study provided reliable information on gestation and cycle length as well as endocrine changes associated with gestation. Additionally, I established a method for prenatal sex determination using maternal fecal samples collected during late gestation. The excretion pattern of androgens in samples of males revealed no differences between dominant and subordinate males, indicating that dominant males did not suppress the endocrine function of subordinate rivals. High frequencies of matings in combination with large testes size suggest that male reproductive competition relies at least partly on sperm competition. Females did not benefit from the high number of males in their groups in terms of improved thermoregulation because surplus males did not participate frequently in huddling groups with females. Analysis of the demographic data revealed that birth and mortality rates were not sex-biased and that males migrated considerably more frequently than females, providing no proximate explanation for the unusual sex ratio. Females in this study may proximately regulate group composition by synchronizing their fertile periods, which were inferred indirectly from the temporal distribution of births within groups. Both males and females benefit from the high number of co-resident males because reduced male group size seemed to be the main predictor of take-over rate, and thus, infanticide risk. The results of these studies suggest that certain life history traits (fast maturation, short inter-birth intervals) may ultimately determine the high number of males and the lack of single-male groups seen in redfronted lemurs. An accelerated male life history may facilitate joint group transfers and take-overs of male coalitions without a transitional time outside bisexual groups. Because males and females both benefit from a high number of males the conflict of interests between the sexes is considerably defused.},
  subject      = {Rotstirnmaki},
  language  = {en}
}
@phdthesis{Streinzer2013,
  author    = {Streinzer, Martin},
  title     = {Sexual dimorphism of the sensory systems in bees (Hymenoptera, Apoidea) and the evolution of sex-specific adaptations in the context of mating behavior},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-78689},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2013},
  abstract  = {Bees have had an intimate relationship with humans for millennia, as pollinators of fruit, vegetable and other crops and suppliers of honey, wax and other products. This relationship has led to an extensive understanding of their ecology and behavior. One of the most comprehensively understood species is the Western honeybee, Apis mellifera. Our understanding of sex-specific investment in other bees, however, has remained superficial. Signals and cues employed in bee foraging and mating behavior are reasonably well understood in only a handful of species and functional adaptations are described in some species. I explored the variety of sensory adaptations in three model systems within the bees. Females share a similar ecology and similar functional morphologies are to be expected. Males, engage mainly in mating behavior. A variety of male mating strategies has been described which differ in their spatiotemporal features and in the signals and cues involved, and thus selection pressures. As a consequence, males' sensory systems are more diverse than those of females. In the first part I studied adaptations of the visual system in honeybees. I compared sex and caste-specific eye morphology among 5 species (Apis andreniformis, A. cerana, A. dorsata, A. florea, A. mellifera). I found a strong correlation between body size and eye size in both female castes. Queens have a relatively reduced visual system which is in line with the reduced role of visual perception in their life history. Workers differed in eye size and functional morphology, which corresponds to known foraging differences among species. In males, the eyes are conspicuously enlarged in all species, but a disproportionate enlargement was found in two species (A. dorsata, A. florea). I further demonstrate a correlation between male visual parameters and mating flight time, and propose that light intensities play an important role in the species-specific timing of mating flights. In the second study I investigated eye morphology differences among two phenotypes of drones in the Western honeybee. Besides normal-sized drones, smaller drones are reared in the colony, and suffer from reduced reproductive success. My results suggest that the smaller phenotype does not differ in spatial resolution of its visual system, but suffers from reduced light and contrast sensitivity which may exacerbate the reduction in reproductive success caused by other factors. In the third study I investigated the morphology of the visual system in bumblebees. I explored the association between male eye size and mating behavior and investigated the diversity of compound eye morphology among workers, queens and males in 11 species. I identified adaptations of workers that correlate with distinct foraging differences among species. Bumblebee queens must, in contrast to honeybees, fulfill similar tasks as workers in the first part of their life, and correspondingly visual parameters are similar among both female castes. Enlarged male eyes are found in several subgenera and have evolved several times independently within the genus, which I demonstrate using phylogenetic informed statistics. Males of these species engage in visually guided mating behavior. I find similarities in the functional eye morphology among large-eyed males in four subgenera, suggesting convergent evolution as adaptation to similar visual tasks. In the remaining species, males do not differ significantly from workers in their eye morphology. In the fourth study I investigated the sexual dimorphism of the visual system in a solitary bee species. Males of Eucera berlandi patrol nesting sites and compete for first access to virgin females. Males have enlarged eyes and better spatial resolution in their frontal eye region. In a behavioral study, I tested the effect of target size and speed on male mate catching success. 3-D reconstructions of the chasing flights revealed that angular target size is an important parameter in male chasing behavior. I discuss similarities to other insects that face similar problems in visual target detection. In the fifth study I examined the olfactory system of E. berlandi. Males have extremely long antennae. To investigate the anatomical grounds of this elongation I studied antennal morphology in detail in the periphery and follow the sexual dimorphism into the brain. Functional adaptations were found in males (e.g. longer antennae, a multiplication of olfactory sensilla and receptor neurons, hypertrophied macroglomeruli, a numerical reduction of glomeruli in males and sexually dimorphic investment in higher order processing regions in the brain), which were similar to those observed in honeybee drones. The similarities and differences are discussed in the context of solitary vs. eusocial lifestyle and the corresponding consequences for selection acting on males.},
  subject      = {Biene},
  language  = {en}
}
@phdthesis{Feldmann2002,
  author    = {Feldmann, Kristina},
  title     = {Signal transduction of transforming growth factor-Beta in cytotoxic T cells},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-4912},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2002},
  abstract  = {Transforming-Growth-Factor-beta1 (TGF-b1) ist ein multifunktionelles Zytokin, welches insbesondere Zellwachstum und Zelldifferenzierung koordiniert. TGF-b ist vor allem daf{\"u}r bekannt, Zellen des Immunsystems zu beeinflussen. TGF-b steuert zum Beispiel die Differenzierung von T-Zellen und und deren Effektorfunktionen. Die Signaltransduktion von TGF-b wird vermittelt durch die Phosphorylierung von Rezeptor-assoziierten Smad-Proteinen (R-Smads). R-Smads werden vom Typ I Rezeptor aktiviert, der seinerseits vom hochaffinen Typ II Rezeptor phosphoryliert wird, sobald der Ligand bindet. Die phosphorylierten RSmads assoziieren darauf mit Co-Smads. Heterooligomere von R-Smads und Co-Smads wandern dann in den Zellkern, wo sie im Zusammenspiel mit Transkriptionsfaktoren wie CBP/p300 oder AP-1 die Transkription TGF-b-spezifischer Zielgene koordinieren. Neue Erkenntnisse lassen vermuten, daß die pleiotropen Effekte von TGF-b durch das Interagieren mit anderen Signalkaskaden entstehen, zum Beispiel mit dem MAP-Kinase-Weg oder der STAT-Kaskade. Wir beschreiben hier den Effekt von TGF-b auf die Effektorfunktionen unterschiedlich stimulierter prim{\"a}rer Maus-Milzzellen und aufgereinigten zytotoxischen CD8+ Maus-TZellen. Langzeitbehandlung mit TGF-b resultierte in der Unf{\"a}higkeit der Zellen, Smad2 ligandeninduziert zu phosphorylieren. Entweder wurde {\"u}berhaupt keine Phosphorylierung beobachtet, oder eine anhaltende Phosphorylierung von Smad2 unabh{\"a}ngig vom Vorhandensein des Liganden. Des weiteren stellten wir einen Zusammenhang zwischen anhaltender Smad2-Phosphorylierung und der Resistenz gegen{\"u}ber TGF-b induzierter Wachstumshemmung fest. Im Gegensatz dazu zeigen Zellen, die sensitiv sind gegen{\"u}ber TGF-b vermittelter Wachstumshemmung, keine Smad2-Phosphorylierung mehr. Bez{\"u}glich ihrer zytotoxische Aktivt{\"a}t waren allerdings beide Ph{\"a}notypen nicht mehr lytisch wirksam, unabh{\"a}ngig von der jeweiligen Smad2-Phosphorylierung. In dieser Arbeit zeigen wir auch die Notwendigkeit eines funktionalen MEK-1-Signalweges auf, der unabdingbar ist, damit TZellen keine Wachstumsinhibierung durch TGF-b mehr erfahren. Das Blockieren dieses Signalweges f{\"u}hrt dar{\"u}berhinaus bei diesen Zellen ebenfalls zu einem ver{\"a}nderten Smad2- Phosphorylierungsmuster. Bez{\"u}glich des JNK-Signalweges konnten wir feststellen, daß ein funktional aktiver JNK-Signalweg mit der Resistenz gegen{\"u}ber TGF-b vermittelter Wachstumsinhibierung einhergeht. Allerdings f{\"u}hrt die Zugabe von IFNg und/oder aCD28- Antik{\"o}rper nicht zu einer ver{\"a}nderten Sensitivit{\"a}t gegen{\"u}ber TGF-b. Im Gegensatz zuprim{\"a}ren Zellen k{\"o}nnen die beschriebenen Zusammenh{\"a}nge in Zellkulturen vom humanen und murinen T Zellen nicht beobachtet werden, und sind somit spezifisch f{\"u}r primare TZellen. Wir beschreiben auch die Klonierung eines chim{\"a}ren dominant-negativen Typ II Rezeptors, der an eine Kinase gekoppelt ist, die bei Aktivierung Zelltod ausl{\"o}st. Damit soll es in Zukunft m{\"o}glich sein, T-Zellen gegen{\"u}ber TGF-b Resistenz zu verleihen. Die hier geschilderten Ergebnisse vertiefen die Kenntnisse {\"u}ber molekulare Mechanismen der Wirkung von TGF-b auf T-Zellen und k{\"o}nnen vielleicht dazu beitragen, negative Effekte von TGF-b, zum Beispiel in der Tumortherapie, gezielt abzuwenden.},
  subject      = {T-Lymphozyt},
  language  = {en}
}
@phdthesis{Hassel2005,
  author    = {Haßel, Sylke},
  title     = {Signal transduction via multiple BMP receptor complexes},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-13353},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2005},
  abstract  = {BMPs influence a variety of cellular processes. They have been shown to regulate proliferation, differentiation, migration and apoptosis and thus play central roles during developmental processes and tissue homeostasis. Ligand mediated signal transduction is transmitted via BMP type I and BMP type II receptors, both members of the serine/threonine kinase superfamily. The BMP receptor mediated signal transduction is not explored in detail. Therefore our aim was to address different aspects of BMP mediated signal transduction with main focus on BRII and its regulation. Due to the existence of two alternative splice variants, a long and a short form, the function of the two variants and the impact of the C-terminal extension are of general interest. Moreover, mutations in the BMPR2 gene were identified to be responsible for PPH, a autosomal dominant lung disease. In this thesis, BRII phosphorylation and signalling mediated by different receptor oligomers were investigated and multiple BRII associated proteins were identified. We could show that the oligomerization pattern of BMP receptors exhibits a higher degree of flexibility compared to other receptors of that superfamily. In the present work the BMP2 mediated signal transduction should be examined, depending on the receptor oligomerization pattern. Using kinase-deficient mutants, it could be demonstrated, that signalling via preformed BMP receptor complexes is mediated by the well characterized Smad1/5/8 pathway, whereas signalling initiated by BMP2 induced recruitment of the receptors activates the p38 pathway and leads to Alkaline Phosphatase production. To further study signalling events triggered directly from the BRII a proteomics-based screen for BRII associated proteins was performed. 53 associated proteins were found, the majority being signal transducing molecules, but in addition metabolic proteins, transcriptional regulators and others were identified. These proteins enable to gain a deeper insight in BMP mediated signalling. One of the interactors, the receptor tyrosine kinase c-kit, was characterized in more detail. It could be demonstrated, that BRII and c-kit form a complex in vitro and in vivo, and the interaction is enhanced upon BMP2 stimulation. 2D phosphopeptid mapping showed that BRII is phosphorylated at S757 upon activation of c-kit by SCF. Moreover, c-kit and its ligand SCF are modulating BMP2 pathways, by enhancing Smad1/5 phosphorylation, Smad-transcriptional activity, Alkaline Phosphatase production and expression of Cbfa1. All these pathways hint towards modulation of the osteoblast development via c-kit. Thus, we were able to develop a novel paradigm for the BMP2 meditated signalling. One of the initial triggers for BRII is the auto-phosphorylation of BRII. Here we analyze ligand-independent as well as ligand-dependent phosphorylation of BRII. Some phosphorylation sites in BRII were identified. The general phosphorylation occurs mostly on serines. S815, S818 and Y825 are identified targets of phosphorylation whose function is still unclear. However phosphorylation of S336 is demonstrated to be essential for BRII activation. The elucidation of BMP receptor phosphorylation and oligomerization as well as the impact of a number of BRII associated proteins (such as c-kit), demonstrated in this thesis that BMP signalling has to be regulated precisely on multiple levels. This can be useful for the development of selective signalling inhibitors for basic research and therapeutic approaches of PPH and other diseases.},
  subject      = {Knochen-Morphogenese-Proteine},
  language  = {en}
}
@phdthesis{Meiser2023,
  author    = {Meiser, Elisabeth},
  title     = {Single-molecule dynamics at a bottleneck: a systematic study of the narrow escape problem in a disc},
  doi       = {10.25972/OPUS-31965},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-319650},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {Diffusion facilitates numerous reactions within the biological context of a cell. It is remarkable how the cost-efficient random process of Brownian motion promotes fast reactions. From the narrow escape theory, it is possible to determine the mean first passage time of such processes based on their reaction space and diffusion coefficient. The narrow escape theory of Brownian particles is characterized by a confining domain with reflective boundaries and a small reaction site. In this thesis, the mean first passage time was systematically tested in a disc as a function of the escape opening size in vitro and in silico. For the in vitro experiments, a model system of patterned supported-lipid bilayers (SLB) was established. Such a model is prepared by a combined colloid metalization approach, where a gold scaffold on glass facilitates assembly of SLB patches of distinct sizes through vesicle fusion. The model setup was evaluated and found to match all necessary requirements to test the nar- row escape problem in vitro. In particular, the reflectivity of the boundaries, the unhindered, free diffusion of the tracer lipids, and the distinct area were assessed. Observed results of the mean first passage time agreed with the theory of the narrow escape problem. There was excellent agreement in both absolute values and across a range of small escape opening sizes. Additionally, I developed a straightforward method, a correction factor, to calculate the mean first passage time from incomplete experimental traces. By re-scaling the mean first passage time to the fraction of particles that escaped, I was able to overcome the lifetime limitations of fluorescent probes. Previously inaccessible measurements of the mean first passage time relying on fluorescent probes will be made possible through this approach. The in vitro experiments were complemented with various in silico experiments. The latter were based on random walk simulations in discs, mimicking the in vitro situation with its uncertainties. The lifetime of single particles was either set sufficiently long to allow all particles to escape, or was adjusted to meet the lifetime limitations observed in the in vitro experiments. A comparison of the mean first passage time from lifetime-unlimited particles to the corrected, lifetime-limited particles did support the use of the correction factor. In agreement with the narrow escape theory, it was experimentally found that the mean first passage time is independent of the start point of the particle within the domain. This is when the particle adheres to a minimum distance to the escape site. In general, the presented random walk simulations do accurately represent the in vitro experiments in this study. The required hardware for the establishment of an astigmatism-based 3D system was installed in the existing microscope. The first attempts to analyze the obtained 3D imaging data gave insight into the potential of the method to investigate molecule dynamics in living trypanosome cells. The full functionality will be realized with the ongoing improvement of image analysis outside of this thesis.},
  subject      = {Freies Molek{\"u}l},
  language  = {en}
}
@phdthesis{Glogger2018,
  author    = {Glogger, Marius},
  title     = {Single-molecule fluorescence microscopy in live \(Trypanosoma\) \(brucei\) and model membranes},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-169222},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {Der eukaryotische Parasit Trypanosoma brucei hat komplexe Strategien entwickelt um der Immunantwort eines Wirtes zu entkommen und eine persistente Infektion innerhalb dessen aufrechtzuerhalten. Ein zentrales Element seiner Verteidigungsstrategie st{\"u}tzt sich auf die Schutzfunktion seines Proteinmantels auf der Zelloberfl{\"a}che. Dieser Mantel besteht aus einer dichten Schicht aus identischen, Glykosylphosphatidylinositol (GPI)-verankerten variablen Oberfl{\"a}chenglykoproteinen (VSG). Der VSG Mantel verhindert die Erkennung der darunterliegenden, invarianten Epitope durch das Immunsystem. Obwohl es notwendig ist die Funktionsweise des VSG Mantels zu verstehen, vor allem um ihn als m{\"o}gliches Angriffsziel gegen den Parasiten zu verwenden, sind seine biophysikalischen Eigenschaften bisher nur unzureichend verstanden. Dies ist vor allem der Tatsache geschuldet, dass die hohe Motilit{\"a}t der Parasiten mikroskopische Studien in lebenden Zellen bisher weitestgehend verhinderten. In der vorliegenden Arbeit wird nun hochmoderne Einzelmolek{\"u}l-Fluoreszenzmikroskopie (EMFM) als M{\"o}glichkeit f{\"u}r mikroskopische Untersuchungen im Forschungsbereich der Trypanosomen vorgestellt. Die Arbeit umfasst Untersuchungen der VSG Dynamik unter definierten Bedingungen k{\"u}nstlicher Membransysteme. Es wurde zuerst der Einfluss der lateralen Proteindichte auf die VSG Diffusion untersucht. Experimente mittels Fluoreszenz- Wiederkehr nach irreversiblem Photobleichen und komplement{\"a}re Einzelmolek{\"u}l- Verfolgungs Experimente offenbarten, dass ein molekularer Diffusionsschwellenwert existiert. {\"U}ber diesem Schwellenwert wurde eine dichteabh{\"a}nige Reduzierung des Diffusionskoeffizienten gemessen. Eine relative Quantifizierung der rekonstituierten VSGs verdeutlichte, dass der Oberfl{\"a}chenmantel der Trypanosomen sehr nahe an diesem Schwellenwert agiert. Der VSG Mantel ist optimiert um eine hohe Proteindichte bei gleichzeitiger hoher Mobilit{\"a}t der VSGs zu gew{\"a}hrleisten. Des Weiteren wurde der Einfluss der VSG N-Glykosylierung auf die Diffusion des Proteins quantitativ untersucht. Die Messungen ergaben, dass die N-Glykosylierung dazu beitr{\"a}gt eine hohe Mobilit{\"a}t bei hohen Proteindichten aufrechtzuerhalten. Eine detaillierte Analyse von VSG Trajektorien offenbarte, dass zwei unterschiedliche Populationen frei diffundierender VSGs in der k{\"u}nstlichen Membran vorlagen. K{\"u}rzlich wurde entdeckt, dass VSGs zwei strukturell unterschiedliche Konformationen annehmen k{\"o}nnen. Die Messungen in der Arbeit stimmen mit diesen Beschreibungen {\"u}berein. Die Ergebnisse der EMFM in k{\"u}nstlichen Membranen wurden durch VSG Einzelmolek{\"u}l- Verfolgungs Experimente auf lebenden Zellen erg{\"a}nzt. Es wurde eine hohe Mobilit{\"a}t und Dynamik einzelner VSGs gemessen, was die allgemein dynamische Natur des VSG Mantels verdeutlicht. Dies f{\"u}hrte zu der Schlussfolgerung, dass der VSG Mantel auf lebenden Trypanosomen ein dichter und dennoch dynamischer Schutzmantel ist. Die F{\"a}higkeit der VSGs ihre Konformation flexibel anzupassen, unterst{\"u}tzt das Erhalten der Fluidit{\"a}t bei variablen Dichten. Diese Eigenschaften des VSG Mantels sind elementar f{\"u}r die Aufrechterhaltung einer presistenden Infektion eines Wirtes. In dieser Arbeit werden des Weiteren verschiedene, auf Hydrogel basierende Einbettungsmethoden vorgestellt. Diese erm{\"o}glichten die Zellimmobilisierung und erlaubten EMFM in lebenden Trypanosomen. Die Hydrogele wiesen eine hohe Zytokompatibilit{\"a}t auf. Die Zellen {\"u}berlebten in den Gelen f{\"u}r eine Stunde nach Beginn der Immobilisierung. Die Hydrogele erf{\"u}llten die Anforderungen der Superresolution Mikroskopie (SRM) da sie eine geringe Autofluoreszenz im Spektralbereich der verwendeten Fluorophore besaßen. Mittels SRM konnte nachgewiesen werden, dass die Hydrogele die Zellen effizient immobilisierten. Als erstes Anwendungsbeispiel der Methode wurde die Organisation der Plasmamembran in lebenden Trypanosomen untersucht. Die Untersuchung eines fluoreszenten Tracers in der inneren Membranschicht ergab, dass dessen Verteilung nicht homogen war. Es wurden spezifische Membrandom{\"a}nen gefunden, in denen das Molek{\"u}l entweder vermehrt oder vermindert auftrat. Dies f{\"u}hrte zu der Schlussfolgerung, dass diese Verteilung durch eine Interaktion des Tracers mit Proteinen des zellul{\"a}ren Zytoskeletts zustande kam. Die in dieser Arbeit pr{\"a}sentierten Ergebnisse zeigen, dass EMFM erfolgreich f{\"u}r verschiedene biologische Untersuchungen im Forschungsfeld der Trypanosomen angewendet werden kann. Dies gilt zum Beispiel f{\"u}r die Untersuchung von der VSG Dynamik in k{\"u}nstlichen Membransystemen, aber auch f{\"u}r Studien in lebenden Zellen unter Verwendung der auf Hydrogelen basierenden Zelleinbettung.},
  subject      = {Trypanosoma brucei},
  language  = {en}
}
@phdthesis{Wolter2014,
  author    = {Wolter, Steve},
  title     = {Single-molecule localization algorithms in super-resolution microscopy},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-109370},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {Lokalisationsmikroskopie ist eine Methodenklasse der superaufl{\"o}senden Fluoreszenzmikroskopie, deren Methoden sich durch stochastische zeitliche Isolation der Fluoreszenzemission auszeichnen. Das Blinkverhalten von Fluorophoren wird so ver{\"a}ndert, dass gleichzeitige Aktivierung von einander nahen Fluorophoren unwahrscheinlich ist. Bekannte okalisationsmikroskopische Methoden umfassen dSTORM, STORM, PALM, FPALM, oder GSDIM. Lokalisationsmikroskopie ist von hohem biologischem Interesse, weil sie die Aufl{\"o}sung des Fluoreszenzmikroskops bei minimalem technischem Aufwand um eine Gr{\"o}ßenordnung verbessert. Der verbundene Rechenaufwand ist allerdings erheblich, da Millionen von Fluoreszenzemissionen einzeln mit Nanometergenauigkeit lokalisiert werden m{\"u}ssen. Der Rechen- und Implementationsaufwand dieser Auswertung hat die Verbreitung der superaufl{\"o}senden Mikroskopie lange verz{\"o}gert. Diese Arbeit beschreibt meine algorithmische Grundstruktur f{\"u}r die Auswertung lokalisationsmikroskopischer Daten. Die Echtzeitf{\"a}higkeit, d.h. eine Auswertegeschwindigkeit oberhalb der Datenaufnahmegeschwindigkeit an normalen Messaufbauten, meines neuartigen und quelloffenen Programms wird demonstriert. Die Geschwindigkeit wird auf verbrauchermarktg{\"a}ngigen Prozessoren erreicht und dadurch spezialisierte Rechenzentren oder der Einsatz von Grafikkarten vermieden. Die Berechnung wird mit dem allgemein anerkannten Gaussschen Punktantwortmodell und einem Rauschmodell auf Basis der gr{\"o}ßten Poissonschen Wahrscheinlichkeit durchgef{\"u}hrt. Die algorithmische Grundstruktur wird erweitert, um robuste und optimale Zweifarbenauswertung zu realisieren und damit korrelative Mikroskopie zwischen verschiedenen Proteinen und Strukturen zu erm{\"o}glichen. Durch den Einsatz von kubischen Basissplines wird die Auswertung von dreidimensionalen Proben vereinfacht und stabilisiert, um pr{\"a}zisem Abbilden von mikrometerdicken Proben n{\"a}her zu kommen. Das Grenzverhalten von Lokalisationsalgorithmen bei hohen Emissionsdichten wird untersucht. Abschließend werden Algorithmen f{\"u}r die Anwendung der Lokalisationsmikroskopie auf verbreitete Probleme der Biologie aufgezeigt. Zellul{\"a}re Bewegung und Motilit{\"a}t werden anhand der in vitro Bewegung von Myosin-Aktin-Filamenten studiert. Lebendzellbildgebung mit hellen und stabilen organischen Fluorophoren wird mittels SNAP-tag-Fusionsproteinen realisiert. Die Analyse des Aufbaus von Proteinklumpen zeigt, wie Lokalisationsmikroskopie neue quantitative Ans{\"a}tze jenseits reiner Bildgebung bietet.},
  subject      = {Fluoreszenzmikroskopie},
  language  = {en}
}