Molecular characterization of the Drosophila responses towards nematodes

Abstract: A sophisticated evolutionary conserved innate immune system has evolved in insects to fight pathogens and to restrict damage in harmful (danger) situations including cancer. A significant amount of knowledge about different infection models in Drosophila has been generated in past decades, which revealed functional resemblances and implications for vertebrate systems. However, how Drosophila responds towards multicellular parasitic nematodes and in danger situations is still little understood. Therefore, the aim of the thesis was to characterize multiple aspects of the host defense in the two important contexts mentioned above.We analyzed the transcriptome profiles of nematode-infected Drosophila larvae with uninfected samples. For this we employed the entomopathogenic nematode Heterorhabditis bacteriophora with its symbiont Photorhabdus luminescence to infect Drosophila larvae. We found 642 genes were differentially regulated upon infection. Among them a significant portion belonged to immune categories. Further functional analysis identified a thioester containing protein TEP3, a recognition protein GNBP-like 3, the basement membrane component protein Glutactin and several other small peptides. Upon loss or reduced expression of these genes hosts showed mortality during nematode infections. This study uncovers a novel function for several of the genes in immunity.Furthermore, we investigated the cellular response towards nematodes. When we eliminated hemocytes genetically (referred to as hml-apo) in Drosophila, we found hml-apo larvae are resistant to nematodes. Subsequent characterization of hml-apo larvae showed massive lamellocyte differentiation (another blood cell type which is rare in naïve larvae), emergence of melanotic masses, up- and down-regulation of Toll and Imd signaling respectively suggesting a pro-inflammatory response. Moreover, a striking defective leg phenotype in adult escapers from pupal lethality was observed. We identified nitric oxide (NO) as a key regulator of these processes. We also showed that imaginal disc growth factors 3 (IDGF3): (a) protects hosts against nematodes, (b) is a clotting component and (c) negatively regulates Wnt and JAK/STAT signaling. To follow larval behavior in the presence or absence of nematodes we monitored Drosophila larval locomotion behaviors using FIMtrack (a recently devised automated method) to elucidate evasive strategies of hosts. Finally, we characterized host defenses in three Drosophila leukemia models with and without nematode infection. Taken together, these studies shed light on host responses in two crucial circumstances, nematode infections and danger situations.