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Institut für Biologie

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Browsing Institut für Biologie by Subject "Aggregation"

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    Effects of N-terminal mutations of human androgen receptor on polyglutamine toxicity
    (2008) Funderburk, Sarah F.; Cato, Andrew C. B.
    Nine neurodegenerative diseases are caused by polyglutamine (polyQ) tract amplification in different proteins. The cytotoxicity of each of these proteins is associated with a misfolding of the mutant protein, resulting in the subsequent alteration of cellular processes and interactions as well as the interrelated formation of insoluble aggregates and other conformationally toxic species. However, the diseases differ in their pathology and tissue specificity of action, which may be due to protein context/regions neighboring the polyQ stretch. For the purpose of the studies presented in ths work, the polyQ containing human androgen receptor (AR) that causes the disorder spinal and bulbar muscular atrophy (SBMA) was used to model polyQ toxicity. In previous investigations, two putative phosphorylation sites of the AR were identified, and it was demonstrated that mutation of these sites appeared to cause conformational change in the protein. Therefore, these N-terminal serine residues were exchanged to alanine in the wild type AR (ARQ22/ARQ22dm) or a receptor with an amplified polyQ stretch (ARQ77/ARQ77dm). These mutants were then used to characterize variance in types of aggregates and the associated toxic profiles due to the different protein conformations that arose from the serine mutations. Evaluating changes in aggregation and toxicity in cultured cells and in a Drosophila model of SBMA, it was found that the effects of the conformational changes differed depending on the length of the polyQ stretch. Mutations in the ARQ22 resulted in a marked increase in aggregation as well as decreased survival rates and altered locomotion behavior in Drosophila. These results were similar but not as severe as the ARQ77/SBMA model. In quite the opposite manner, mutations in the ARQ77 caused a decrease in aggregation and a lessened toxic effect in Drosophila. Moreover, it was found that inhibitor compounds used to ameliorate polyQ toxicity were not as efficient in inhibiting the varied toxicities exhibited by both the ARQ22dm and ARQ77dm. Therefore, two distinct amino acid sites that profoundly modulate polyQ toxicity in the AR have been identified. These results can be further utilized to understand the conformational changes in the AR that lead to aggregation as well as the types of aggregates that lead to toxicity.
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    Reproduktionsbiologie und olfaktorisches Verhalten des Kleinen Beutenkäfers Aethina tumida MURRAY 1867 (Nitidulidae)
    (2014) Mustafa, Sandra Gabriele; Steidle, Johannes
    This dissertation aimed to investigate the olfactory behaviour and reproductive biology of the small hive beetle (Aethina tumida, Nitidulidae). Our investigations focused on the second part of the small hive beetle life cycle, after beetles emerged from the ground and invaded a honeybee (Apis mellifera) hive. Once in the hive, beetles show strong developed aggregation behaviour and start reproducing. We suspected the involvement of aggregation- and/or sexual pheromones in these social interactions. Our goal was to identify or at least to prove the existence of the latter. Three laboratory bioassays were developed on this purpose: aggregation-assay, filter-assay and choice-assay. Gender and age independent aggregation behaviour was revealed by the aggregation assay. The choice assay revealed a gender and age dependent preference for the opposite sex in both genders. The involvement of chemical substances in this system was proved by the filter-assay. Pieces of filter paper, which were left with certain beetle stages to leave marks on, proved to be attractive when offered to other beetles. A detailed description of the mating behaviour was supposed to reveal further information about chemical communication in the small hive beetle. Therefore an ethogram and flow diagram were compiled through video analysis of the mating behaviour. Several behaviours observed before, after and during copulation indicated chemical communication on tactile level; this included tapping, thrilling or rubbing of the cuticle surface of fellow mates. Electron microscopy pictures showed a high density of sensillae and pores on the areas involved in frequent behavioural interactions. The description of the mating behaviour revealed several indications for cryptic female choice mechanisms. One was the distinct aggressive behaviour of females in contrast to males. They pushed other beetles in high frequency and often interrupted matings this way. Comparison of matings in single pairs and aggregations showed that small hive beetles only copulate in aggregations and sexual behaviours reaches its peak at the ages from two to three weeks. It is further the only age in which more hetero- than homosexual matings occur. All these facts added up indicated female pheromone emission from the age of two weeks on. This feature might be seen as an extraordinary and unique adaption to their honey bee host. Single pairs would never be able to compete with the hygienic behaviour of the honeybees and all their offspring and eggs would be cleaned out immediately. It further helps in synchronizing reproduction of all beetles in an aggregation which in turn favours mass reproduction and surrendering the host. The central role of this mass reproduction strategy became further obvious when investigating the susceptibility of small nucleus hives to invasion of the small hive beetle. Nucleus hives were far more vulnerable to invasion of the small hive beetle than full sized colonies. After a four week study period under moderate invasion pressure, half of all 24 nucleus colonies showed signs of small hive beetle reproduction, namely they either collapsed or were infected with larvae in their final development stage. In contrast, none of the full-sized colonies showed any symptoms. Beekeepers in affected areas should consider this in their daily tasks and avoid using too-small nucleus colonies for queen rearing or colony propagation. The small hive beetle depends on the collapse of the colony to ensure its reproduction in contrast to many other parasites which try to keep their host alive as long as possible. In the first stage of the adult live cycle, after pupation and emergence from the ground, foraging and host-finding behaviour have first priority. Volatiles from fermenting honey might be a key trigger during this time. Infection with larvae incites fermentation of honey and pollen which produces the typical slimy combs in the end. Colonies in the stage between collapse and symptom-free infestation are supposed to be the most attractive. There are still food resources available but the honey bee host is already weak and vulnerable. In a preliminary trial under canvas we investigated the effect of various ferment products. They seemed to be attractive and could be considered as lure for traps in the field after further experiments. In conclusion one can say that it was possible to prove the existence of chemical- probably chemotactical communication via pheromones in the small hive beetle A. tumida. Olfactory orientation is present in all stages of the life cycle and aggregation and a mass reproduction strategy is closely connected to it on the reproductive and behavioural level. Thereby, this effective mass reproduction strategy may be the key to the success of this invasive species.