@phdthesis{Lisowski2022,
  author    = {Lisowski, Clivia},
  title     = {Maturation of the \(Salmonella\) containing vacuole is compromised in G1 arrested host cells},
  doi       = {10.25972/OPUS-18523},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-185239},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {The interaction of bacterial pathogens and the human host is a complex process that has shaped both organisms on a molecular, cellular and population level. When pathogenic bacteria infect the human body, a battle ensues between the host immune system and the pathogen. In order to escape an immune response and to colonize the host, pathogenic bacteria have developed diverse virulence strategies and some pathogens even replicate within host cells. For survival and propagation within the dynamic environment of a host cell, these bacteria interfere with the regulation of host pathways, such as the cell cycle, for their own benefit. The intracellular pathogen Salmonella Typhimurium invades eukaryotic cells and resides and replicates in a modified vacuolar compartment in which it is protected from the innate immune response. To this end, it employs a set of virulence factors that help to invade cells (SPI-1 effectors) and to hijack and modify the host endolysosomal system, in order to stabilize and mature its vacuolar niche (SPI-2 effectors). Previous studies have shown that Salmonella arrests host cells in G2/M phase and that Salmonella infected cells progress faster from G1 into S phase, suggesting that the G1 phase is disadvantageous for Salmonella infection. In fact, it has already been observed that Salmonella replication is impaired in G1 arrested cells. However, the reason for this impairment remained unclear. The current study addressed this question for the first time and revealed that the highly adapted, intracellular lifestyle of Salmonella is drastically altered upon G1 arrest of the host cell. It is shown that proteasomal degradation in G1 arrested cells is delayed and endolysosomal and autophagosomal trafficking is compromised. Accordingly, processing of lysosomal proteins is insufficient and lysosomal activity is decreased; resulting in uneven distribution and accumulation of endolysosomes and autophagosomes, containing undegraded cargo. The deregulation of these cellular signaling pathways affects maturation of the Salmonella containing vacuole (SCV). For the first time it is shown that acidification of SCVs is impaired upon G1 arrest. Thus, an important environmental factor for the switch from SPI-1 to SPI-2 gene expression is missing and the SPI-2 system is not activated. Consequently, targeting and modification of host cell structures by SPI-2 effectors e.g. recruitment of endolysosomal membrane proteins, like LAMP1, or exchange of endosomal cargo, is compromised. In addition, degradation of Salmonella SPI-1 effectors by the host proteasome is delayed. Their prolonged presence sustained the recruitment of early endosomes and contributed to the SCV remaining in an early, vulnerable maturation stage. Finally, it was shown that SCV membrane integrity is compromised; the early SCV ruptures and bacteria are released into the cytoplasm. Depending on the host cell type, SPI-2 independent, cytoplasmic replication is promoted. This might favor bacterial spreading, dissemination into the tissue and provide an advantage in host colonization. Overall, the present study establishes a link between host cell cycle regulation and the outcome of Salmonella infection. It fills the gap of knowledge as to why the host cell cycle stage is of critical importance for Salmonella infection and sheds light on a key aspect of host-pathogen interaction.},
  subject      = {Salmonella Typhimurium},
  language  = {en}
}
@phdthesis{BergmannBorges2023,
  author    = {Bergmann Borges, Alyssa},
  title     = {The endo-lysosomal system of \(Trypanosoma\) \(brucei\): insights from a protist cell model},
  doi       = {10.25972/OPUS-32924},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-329248},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {Most of the studies in cell biology primarily focus on models from the opisthokont group of eukaryotes. However, opisthokonts do not encompass the full diversity of eukaryotes. Thus, it is necessary to broaden the research focus to other organisms to gain a comprehensive understanding of basic cellular processes shared across the tree of life. In this sense, Trypanosoma brucei, a unicellular eukaryote, emerges as a viable alternative. The collaborative efforts in genome sequencing and protein tagging over the past two decades have significantly expanded our knowledge on this organism and have provided valuable tools to facilitate a more detailed analysis of this parasite. Nevertheless, numerous questions still remain. The survival of T. brucei within the mammalian host is intricately linked to the endo-lysosomal system, which plays a critical role in surface glycoprotein recycling, antibody clearance, and plasma membrane homeostasis. However, the dynamics of the duplication of the endo-lysosomal system during T. brucei proliferation and its potential relationship with plasma membrane growth remain poorly understood. Thus, as the primary objective, this thesis explores the endo-lysosomal system of T. brucei in the context of the cell cycle, providing insights on cell surface growth, endosome duplication, and clathrin recruitment. In addition, the study revisits ferritin endocytosis to provide quantitative data on the involvement of TbRab proteins (TbRab5A, TbRab7, and TbRab11) and the different endosomal subpopulations (early, late, and recycling endosomes, respectively) in the transport of this fluid-phase marker. Notably, while these subpopulations function as distinct compartments, different TbRabs can be found within the same region or structure, suggesting a potential physical connection between the endosomal subpopulations. The potential physical connection of endosomes is further explored within the context of the cell cycle and, finally, the duplication and morphological plasticity of the lysosome are also investigated. Overall, these findings provide insights into the dynamics of plasma membrane growth and the coordinated duplication of the endo-lysosomal system during T. brucei proliferation. The early duplication of endosomes suggests their potential involvement in plasma membrane growth, while the late duplication of the lysosome indicates a reduced role in this process. The recruitment of clathrin and TbRab GTPases to the site of endosome formation supports the assumption that the newly formed endosomal system is active during cell division and, consequently, indicates its potential role in plasma membrane homeostasis. Furthermore, considering the vast diversity within the Trypanosoma genus, which includes ~500 described species, the macroevolution of the group was investigated using the combined information of the 18S rRNA gene sequence and structure. The sequence-structure analysis of T. brucei and other 42 trypanosome species was conducted in the context of the diversity of Trypanosomatida, the order in which trypanosomes are placed. An additional analysis focused on Trypanosoma highlighted key aspects of the group's macroevolution. To explore these aspects further, additional trypanosome species were included, and the changes in the Trypanosoma tree topology were analyzed. The sequence-structure phylogeny confirmed the independent evolutionary history of the human pathogens T. brucei and Trypanosoma cruzi, while also providing insights into the evolution of the Aquatic clade, paraphyly of groups, and species classification into subgenera.},
  subject      = {Endocytose},
  language  = {en}
}