@phdthesis{Hoerr2008,
  author    = {H{\"o}rr, Verena},
  title     = {Methoden zur Evaluation von Zytotoxizit{\"a}t und Struktur-Wirkungs-Beziehungen an Trypanosoma brucei brucei},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-27543},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2008},
  abstract  = {Im Rahmen dieser Arbeit wurden potenzielle Wirksubstanzen zur Behandlung trypanosomaler und bakterieller Infektionen gesucht. W{\"a}hrend auf dem Gebiet der Trypanosomiasis das Ziel in der Testung großer Substanzbibliotheken auf antitrypanosomale Wirkung und in der Erstellung von Struktur-Wirkungs-Beziehungen bestand, lag im Bereich der bakteriellen Infektion der Schwerpunkt in der Entwicklung neuer Testmethoden. Die Untersuchungen erfolgten mittels Kapillarelektrophorese und magnetischer Kernresonanz.},
  subject      = {Trypanosomiase},
  language  = {de}
}
@phdthesis{Bartossek2018,
  author    = {Bartossek, Thomas},
  title     = {Structural and functional analysis of the trypanosomal variant surface glycoprotein using x-ray scattering techniques and fluorescence microscopy},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-144775},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {Trypanosoma brucei is an obligate parasite and causative agent of severe diseases affecting humans and livestock. The protist lives extracellularly in the bloodstream of the mammalian host, where it is prone to attacks by the host immune system. As a sophisticated means of defence against the immune response, the parasite's surface is coated in a dense layer of the variant surface glycoprotein (VSG), that reduces identification of invariant epitopes on the cell surface by the immune system to levels that prevent host immunity. The VSG has to form a coat that is both dense and mobile, to shield invariant surface proteins from detection and to allow quick recycling of the protective coat during immune evasion. This coat effectively protects the parasite from the harsh environment that is the mammalian bloodstream and leads to a persistent parasitemia if the infection remains untreated. The available treatment against African Trypanosomiasis involves the use of drugs that are themselves severely toxic and that can lead to the death of the patient. Most of the drugs used as treatment were developed in the early-to-mid 20th century, and while developments continue, they still represent the best medical means to fight the parasite. The discovery of a fluorescent VSG gave rise to speculations about a potential interaction between the VSG coat and components of the surrounding medium, that could also lead to a new approach in the treatment of African Trypanosomiasis that involves the VSG coat. The initially observed fluorescence signal was specific for a combination of a VSG called VSG'Y' and the triphenylmethane (TPM) dye phenol red. Exchanging this TPM to a bromo-derivative led to the observation of another fluorescence effect termed trypanicidal effect which killed the parasite independent of the expressed VSG and suggests a structurally conserved feature between VSGs that could function as a specific drug target against T. b. brucei. The work of this thesis aims to identify the mechanisms that govern the unique VSG'Y' fluorescence and the trypanocidal effect. Fluorescence experiments and protein mutagenesis of VSG'Y' as well as crystallographic trials with a range of different VSGs were utilized in the endeavour to identify the binding mechanisms between TPM compounds and VSGs, to find potentially conserved structural features between VSGs and to identify the working mechanisms of VSG fluorescence and the trypanocidal effect. These trials have the potential to lead to the formulation of highly specific drugs that target the parasites VSG coat. During the crystallographic trials of this thesis, the complete structure of a VSG was solved experimentally for the first time. This complete structure is a key component in furthering the understanding of the mechanisms governing VSG coat formation. X-ray scattering techniques, involving x-ray crystallography and small angle x-ray scattering were applied to elucidate the first complete VSG structures, which reveal high flexibility of the protein and supplies insight into the importance of this flexibility in the formation of a densely packed but highly mobile surface coat.},
  subject      = {Trypanosoma brucei brucei},
  language  = {en}
}
@phdthesis{MuellerHuebner2020,
  author    = {M{\"u}ller-H{\"u}bner, Laura},
  title     = {The role of nuclear architecture in the context of antigenic variation in Trypanosoma brucei},
  doi       = {10.25972/OPUS-18707},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-187074},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2020},
  abstract  = {Antigenic variation of surface proteins is a commonly used strategy among pathogens to evade the host immune response [63]. The mechanism underlying antigenic variation relies on monoallelic exclusion of a single gene from a hypervariable multigene family combined with repeated, systematic changes in antigen expression. In many systems, these gene families are arranged in subtelomeric contingency loci that are subject to both transcriptional repression and enhanced mutagenesis and recombination [16]. Eviction of a selected gene from a repressed antigen repertoire can be achieved e.g. by recombination into a dedicated, transcriptionally permissive site or by local epigenetic alterations in chromatin composition of the selected gene. Both processes are ultimately affected by genome architecture. Architectural proteins controlling antigenic variation have, however, remained elusive in any pathogen. The unicellular protozoan parasite Trypanosoma brucei evades the host immune response by periodically changing expression of a single variant surface glycoprotein (VSG) from a repertoire of ~3000 VSG genes - the largest mutually exclusively expressed gene family described today. To activate a selected VSG gene, it needs to be located in a dedicated expression site that becomes subject to relocation into a distinct, transcriptionally active subnuclear compartment, the expression site body (ESB). Whereas this emphasizes the importance of nuclear architecture in regulating antigen expression in T. brucei, the mechanisms underlying spatial positioning of DNA in T. brucei are not well understood. In this study I applied genome-wide chromosome conformation capture (Hi-C) to obtain a comprehensive picture of the T. brucei genome in three dimensions, both in procyclic and bloodstream form parasites. Hi-C revealed a highly structured nucleus with megabase chromosomes occupying distinct chromosome territories. Further, specific trans interactions between chromosomes, among which are clusters of centromeres, rRNA genes and procyclins became apparent. With respect to antigenic variation, Hi-C revealed a striking compaction of the subtelomeric VSG gene repertoire and a strong clustering of transcriptionally repressed VSG-containing expression sites. Further, Hi-C analyses confirmed the spatial separation of the actively transcribed from the silenced expression sites in three dimensions. I further sought to characterize architectural proteins mediating nuclear architecture in T. brucei. Whereas CTCF is absent in non-metazoans, we found cohesin to be expressed throughout the cell cycle, emphasizing a function beyond sister chromatid cohesion in S-phase. By Chromatin-Immunoprecipitation with sequencing (ChIPseq), I found cohesin enrichment to coincide with the presence of histone H3 vari- ant (H3.V) and H4 variant (H4.V). Most importantly, cohesin and the histone variants were enriched towards the VSG gene at silent and active expression sites. While the deletion of H3.V led to increased clustering of expression sites in three dimensions and increased chromatin accessibility at expression site promoters, the additional deletion of H4.V increased chromatin accessibility at expression sits even further. RNAseq showed that mutually exclusive VSG expression was lost in H3.V and H4.V single and double deletion mutants. Immunofluorescence imaging of surface VSGs, flow cytometry and single-cell RNAseq revealed a progressive loss of VSG-2 expression, indicative of an increase in VSG switching rate in the H3.V/H4.V double deletion mutants. Using long-read sequencing technology, we found that VSG switching occurred via recombination and concluded, that the concomitant increase in spatial proximity and accessibility among expression sites facilitated the recombination event. I therefore identified the histone variants H3.V and H4.V to act at the interface of global nuclear architecture and chromatin accessibility and to represent a link between genome architecture and antigenic variation.},
  subject      = {Trypanosoma brucei brucei},
  language  = {en}
}