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An animal depends heavily on its sense of smell and its ability to form olfactory associations as this is crucial for its survival. This thesis studies in two parts about such associative olfactory learning in larval Drosophila. The first part deals with different aspects of odour processing while the second part is concerned with aspects related to memory and learning. Chapter I.1 highlights how odour intensities could be integrated into the olfactory percept of larval Drosophila. I first describe the dose-effect curves of learnability across odour intensities for different odours and then choose odour intensities from these curves such that larvae are trained at intermediate odour intensity, but are tested for retention with either that trained intermediate odour intensity, or with respectively HIGHer or LOWer intensities. I observe a specificity of retention for the trained intensity for all the odours used. Further I compare these findings with the case of adult Drosophila and propose a circuit level model of how such intensity coding comes about. Such intensity specificity of learning adds to appreciate the richness in 'content' of olfactory memory traces, and to define the demands on computational models of olfaction and olfactory learning. Chapter I.2 provides a behaviour-based estimate of odour similarity using four different types of experiments to yield a combined, task-independent estimate of perceived difference between odour-pairs. Further comparison of these perceived differences to published measures of physico- chemical difference reveals a weak correlation. Notable exceptions to this correlation are 3-octanol and benzaldehyde. Chapter I.3 shows for two odours (3-octanol and 1-octene-3-ol) that perceptual differences between these odours can either be ignored after non-discriminative training (generalization), or accentuated by odour-specific reinforcement (discrimination). Anosmic Or83b1 mutants have lost these faculties, indicating that this adaptive adjustment is taking place downstream of Or83b expressing sensory neurons. Chapter II.1 of this thesis deals with food supplementation with dried roots of Rhodiola rosea. This dose-dependently improves odour- reward associative function in larval Drosophila. Supplementing fly food with commercially available tablets or extracts, however, does not have a 'cognitive enhancing' effect, potentially enabling us to differentiate between the effective substances in the root versus these preparations. Thus Drosophila as a genetically tractable study case should now allow accelerated analyses of the molecular mechanism(s) that underlie this 'cognitive enhancement' conveyed by Rhodiola rosea. Chapter II.2 describes the role of Synapsin, an evolutionarily conserved presynaptic phosphoprotein using a combined behavioural and genetic approach and asks where and how, this protein affects functions in associative plasticity of larval Drosophila. This study shows that a Synapsin-dependent memory trace can be pinpointed to the mushroom bodies, a 'cortical' brain region of the insects. On the molecular level, data in this study assign Synapsin as a behaviourally- relevant effector of the AC-cAMP-PKA cascade.
A major goal of the main topics of ecology is to answer the question of how species can co-exist and maintain biodiversity. To understand how community dynamics operate in different spatio-temporal dimensions to govern biodiversity patterns requires a process-based knowledge. Thus, this study focused primarily on biodiversity patterns and ecological processes at both spatial and temporal scales. Spatially, the diversity and similarity of spider communities in high, intermediate, and low strata of beech trees represented a set of age-related effects: Old-growth trees provided unique and distinct resources to spiders and in turn possessed discrete spider compositions. Intra-annually, spider communities in different seasons showed a repeated, predictable temporal dynamics. Inter-annually, comparison revealed that neutral and niche models can operate in tandem, and that both are needed to fully explain the dynamics of arboreal spider assemblages among different canopy strata in this beech forest.
The Ecology and Population structure of the invasive Yelllow Crazy Ant Anoplolepis gracilipes
(2011)
The invasive Yellow Crazy Ant Anoplolepis gracilipes is a widespread tropical ant species which is particularly common in anthropogenically disturbed habitats in South-East Asia and the Indopacific region. Its native range is unknown, and there is little information concerning its social structure as a potential mechanism facilitating invasion as well as its ecology in one of the putative native ranges, South-East Asia. Using mitochondrial DNA sequences, I demonstrated that the majority of the current Indopacific colonies were likely introduced from South-East Asian populations, which in turn may have been introduced much earlier from a yet unidentified native range. By conducting behavioral, genetic and chemical analyses, I found that A. gracilipes supercolonies contain closely related individuals, thus resembling enlarged versions of monogynous, polydomous colonies of other ant species. Furthermore, mutually aggressive A. gracilipes supercolonies were highly differentiated both genetically and chemically, suggesting limited or even absent gene flow between supercolonies. Intranidal mating and colony-budding are most likely the predominant, if not the exclusive mode of reproduction and dispersal strategy of A. gracilipes. Consequently, a positive feedback between genetic, chemical and behavioral traits may further enhance supercolony differentiation though genetic drift and neutral evolution. This potential scenario led to the hypothesis that absent gene flow between different A. gracilipes supercolonies may drive them towards different evolutionary pathways, possibly including speciation. Thus, I examined one potential way by which gene flow between supercolonies of an ant species without nuptial flights may be maintained, i.e. the immigration of sexuals into foreign supercolonies. The results suggest that this option of maintaining gene flow between different supercolonies is likely impaired by severe aggression of workers towards allocolonial sexuals. Moreover, breeding experiments involving males and queens from different supercolonies suggest that A. gracilipes supercolonies may already be on the verge of reproductive isolation, which might lead to the diversification of A. gracilipes into different species. Regarding the ecological consequences of its potential introduction to NE-Borneo, I could show that A. gracilipes supercolonies may affect the local ant fauna. The ant community within supercolonies was less diverse and differed in species composition from areas outside supercolonies. My data suggest that the ecological dominance of A. gracilipes within local ant communities was facilitated by monopolization of food sources within its supercolony territory, achieved by a combination of rapid recruitment, numerical dominance and pronounced interspecific aggression. A. gracilipes’ distribution is almost exclusively limited to anthropogenically altered habitat, such as residential and agricultural areas. The rate at which habitat conversion takes place in NE-Borneo will provide A. gracilipes with a rapidly increasing abundance of suitable habitats, thus potentially entailing significant population growth. An potentially increasing population size and ecological dominance, however, are not features that are limited to invasive alien species, but may also occur in native species that become ‘pests’ in an increasing abundance of anthropogenically altered habitat. Lastly, I detected several ant guests in supercolonies of A. gracilipes. I subsequently describe the relationship between one of them (the cricket Myrmecophilus pallidithorax) and its ant host. By conducting behavioral bioassays and analyses of cuticular hydrocarbon (CHC) profiles, I revealed that although M. pallidithorax is attacked and consumed by A. gracilipes whenever possible, it may evade aggression from its host by a combination of supreme agility and, possibly, chemical deception. This thesis adds to our general understanding of biological invasions by contributing species-specific data on a previously understudied invasive organism, the Yellow Crazy Ant Anoplolepis gracilipes. Introductions which may have occurred a long time ago may make it difficult to determine whether a given species is an introduced invader or a native pest species, as both may have pronounced ecological effects in native species communities. Furthermore, this thesis suggests that supercolonialism in invasive ants may not be an evolutionary dead end, but that it may possibly give rise to new species due to reproductive boundaries between supercolonies evoked by peculiar mating and dispersal strategies.
Understanding a complex network’s structure holds the key to understanding its function. The physics community has contributed a multitude of methods and analyses to this cross-disciplinary endeavor. Structural features exist on both the microscopic level, resulting from differences between single node properties, and the mesoscopic level resulting from properties shared by groups of nodes. Disentangling the determinants of network structure on these different scales has remained a major, and so far unsolved, challenge. Here we show how multiscale generative probabilistic exponential random graph models combined with efficient, distributive message-passing inference techniques can be used to achieve this separation of scales, leading to improved detection accuracy of latent classes as demonstrated on benchmark problems. It sheds new light on the statistical significance of motif-distributions in neural networks and improves the link-prediction accuracy as exemplified for gene-disease associations in the highly consequential Online Mendelian Inheritance in Man database.
Platelet activation and adhesion results in thrombus formation that is essential for normal hemostasis, but can also cause irreversible vessel occlusion leading to myocardial infarction or stroke. The C-type lectin-like receptor 2 (CLEC-2) was recently identified to be expressed on the platelet surface, however, a role for this receptor in hemostasis and thrombosis had not been demonstrated. In the current study, the involvement of CLEC-2 in platelet function and thrombus formation was investigated using mice as a model system. In the first part of the thesis, it was found that treatment of mice with a newly generated monoclonal antibody against murine CLEC-2 (INU1) led to the complete and highly specific loss of the receptor in circulating platelets (a process termed “immunodepletion”). CLEC-2-deficient platelets were completely unresponsive to the CLEC-2-specific agonist rhodocytin, whereas activation induced by all other tested agonists was unaltered. This selective defect translated into severely decreased platelet aggregate formation under flow ex vivo; and in vivo thrombosis models revealed impaired stabilization of formed thrombi with enhanced embolization. Consequently, CLEC-2 deficiency profoundly protected mice from occlusive arterial thrombus formation. Furthermore, variable bleeding times in INU1-treated mice indicated a moderate hemostatic defect. This reveals for the first time that CLEC-2 significantly contributes to thrombus stability in vitro and in vivo and plays a crucial role in hemostasis and arterial thrombosis. Thus, CLEC-2 represents a potential novel anti-thrombotic target that can be functionally inactivated in vivo. This in vivo down-regulation of platelet surface receptors might be a promising approach for future anti-thrombotic therapy. The second part of the work investigated the effect of double-immunodepletion of the immunoreceptor tyrosine-based activation motif (ITAM)- and hemITAM-coupled receptors, platelet glycoprotein (GP) VI and CLEC-2, on hemostasis and thrombosis using a combination of the GPVI- and CLEC-2-specific antibodies, JAQ1 and INU1, respectively. Isolated targeting of either GPVI or CLEC-2 in vivo did not affect expression or function of the respective other receptor. However, simultaneous treatment with both antibodies resulted in the sustained loss of GPVI and CLEC-2 signaling in platelets, while leaving other activation pathways intact. In contrast to single deficiency of either receptor, GPVI/CLEC-2 double-deficient mice displayed a dramatic hemostatic defect. Furthermore, this treatment resulted in profound impairment of arterial thrombus formation that far exceeded the effects seen in single-depleted animals. Importantly, similar results were obtained in Gp6-/- mice that were depleted of CLEC-2 by INU1-treatment, demonstrating that this severe bleeding phenotype was not caused by secondary effects of combined antibody treatment. These data suggest that GPVI and CLEC-2 can be independently or simultaneously down-regulated in platelets in vivo and reveal an unexpected functional redundancy of the two receptors in hemostasis and thrombosis. Since GPVI and CLEC-2 have intensively been discussed as potential anti-thrombotic targets, these results may have important implications for the development of novel, yet save anti-GPVI or anti-CLEC-2-based therapies.
In this thesis we consider a reactive transport model with precipitation dissolution reactions from the geosciences. It consists of PDEs, ODEs, algebraic equations (AEs) and complementary conditions (CCs). After discretization of this model we get a huge nonlinear and nonsmooth equation system. We tackle this system with the semismooth Newton method introduced by Qi and Sun. The focus of this thesis is on the application and convergence of this algorithm. We proof that this algorithm is well defined for this problem and local even quadratic convergent for a BD-regular solution. We also deal with the arising linear equation systems, which are large and sparse, and how they can be solved efficiently. An integral part of this investigation is the boundedness of a certain matrix-valued function, which is shown in a separate chapter. As a side quest we study how extremal eigenvalues (and singular values) of certain PDE-operators, which are involved in our discretized model, can be estimated accurately.
No abstract avDendritic cells (DC) are the most important antigen presenting cells and play a pivotal role in host immunity to infectious agents by acting as a bridge between the innate and adaptive immune systems. Monocyte-derived immature DCs (iDC) were infected with viable resting conidia of Aspergillus fumigatus (Af293) for 12 hours at an MOI of 5; cells were sampled every three hours. RNA was extracted from both organisms at each time point and hybridised to microarrays. iDC cell death increased at 6 h in the presence of A. fumigatus which coincided with fungal germ tube emergence; .80% of conidia were associated with iDC. Over the time course A. fumigatus differentially regulated 210 genes, FunCat analysis indicated significant up-regulation of genes involved in fermentation, drug transport, pathogenesis and response to oxidative stress. Genes related to cytotoxicity were differentially regulated but the gliotoxin biosynthesis genes were down regulated over the time course, while Aspf1 was up-regulated at 9 h and 12 h. There was an up-regulation of genes in the subtelomeric regions of the genome as the interaction progressed. The genes up-regulated by iDC in the presence of A. fumigatus indicated that they were producing a pro-inflammatory response which was consistent with previous transcriptome studies of iDC interacting with A. fumigatus germ tubes. This study shows that A. fumigatus adapts to phagocytosis by iDCs by utilising genes that allow it to survive the interaction rather than just up-regulation of specific virulence genes.
After a century of its retreat from political and social stages in East Asia, Confucianism eventually found its revival together with the economic industrialization in the region. The awakening consciousness of the traditional Confucian values leads to a reconsideration of their implication on a modern society. Despite the criticism on the actual relevance of Confucianism and modernization, there are precious elements within the Confucian values which provide the relevance of Confucianism to the future, such as an ethic of responsibility and the understanding of the humanistic meaning of life.
The pathogenic yeast Candida albicans can develop resistance to the widely used antifungal agent fluconazole, which inhibits ergosterol biosynthesis, by the overexpression of genes encoding multidrug efflux pumps or ergosterol biosynthesis enzymes. Zinc cluster transcription factors play a central role in the transcriptional regulation of drug resistance. Mrr1 regulates the expression of the major facilitator MDR1, Tac1 controls the expression of the ABC transporters CDR1 and CDR2, and Upc2 regulates ergosterol biosynthesis (ERG) genes. Gain-of-function mutations in these transcription factors result in constitutive overexpression of their target genes and are responsible for fluconazole resistance in many clinical C. albicans isolates. The transcription factor Ndt80 contributes to the drug-induced upregulation of CDR1 and ERG genes and also binds to the MDR1 and CDR2 promoters, suggesting that it is an important component of all major transcriptional mechanisms of fluconazole resistance. However, we found that Ndt80 is not required for the induction of MDR1 and CDR2 expression by inducing chemicals. CDR2 was even partially derepressed in ndt80D mutants, indicating that Ndt80 is a repressor of CDR2 expression. Hyperactive forms of Mrr1, Tac1, and Upc2 promoted overexpression of MDR1, CDR1/CDR2, and ERG11, respectively, with the same efficiency in the presence and absence of Ndt80. Mrr1- and Tac1-mediated fluconazole resistance was even slightly enhanced in ndt80D mutants compared to wild-type cells. These results demonstrate that Ndt80 is dispensable for the constitutive overexpression of Mrr1, Tac1, and Upc2 target genes and the increased fluconazole resistance of strains that have acquired activating mutations in these transcription factors.
Background: Gene function analysis of the obligate intracellular bacterium Chlamydia pneumoniae is hampered by the facts that this organism is inaccessible to genetic manipulations and not cultivable outside the host. The genomes of several strains have been sequenced; however, very little information is available on the gene structure and transcriptome of C. pneumoniae. Results: Using a differential RNA-sequencing approach with specific enrichment of primary transcripts, we defined the transcriptome of purified elementary bodies and reticulate bodies of C. pneumoniae strain CWL-029; 565 transcriptional start sites of annotated genes and novel transcripts were mapped. Analysis of adjacent genes for cotranscription revealed 246 polycistronic transcripts. In total, a distinct transcription start site or an affiliation to an operon could be assigned to 862 out of 1,074 annotated protein coding genes. Semi-quantitative analysis of mapped cDNA reads revealed significant differences for 288 genes in the RNA levels of genes isolated from elementary bodies and reticulate bodies. We have identified and in part confirmed 75 novel putative non-coding RNAs. The detailed map of transcription start sites at single nucleotide resolution allowed for the first time a comprehensive and saturating analysis of promoter consensus sequences in Chlamydia. Conclusions: The precise transcriptional landscape as a complement to the genome sequence will provide new insights into the organization, control and function of genes. Novel non-coding RNAs and identified common promoter motifs will help to understand gene regulation of this important human pathogen.