Drosophila melanogaster is an excellent model to study the molecular basis of anti-pathogen mechanisms. Currently, microbial pathogenesis in Drosophila and the insect antimicrobial immune response are well understood. However, our knowledge of nematode infections and anti-nematode immune mechanisms is still in its infancy. In this work, I investigated the interaction between the Drosophila immune response with the entomopathogenic nematode parasite, Steinernema carpocapsae. I report a new protocol for generating Steinernema nematodes lacking their mutualistic Xenorhabdus nematophila bacteria. Infection with Steinernema symbiotic (carrying Xenorhabdus ) or axenic (lacking Xenorhabdus) results in Drosophila larval death at the similar rates. Interestingly, the Drosophila immune response to Steinernema infection can be modulated by the presence of the endosymbiotic bacteria, Wolbachia and Spiroplasma. I report that presence of Wolbachia alone or together with Spiroplasma promote the survival of Drosophila larvae against Steinernema symbiotic nematodes. The presence or absence of endosymbiotic bacteria differentially modulate the immune signaling and phenoloxidase response, and alter the metabolic status and fat body lipid droplet size in the nematode infected larvae. These data demonstrate an interaction between the endosymbiotic bacteria, Wolbachia and Spiroplasma, and the Drosophila immune and metabolic responses in the context of Steinernema nematode infection.
Then, I investigated the transcriptomic profile of Drosophila larvae during infection with Steinernema symbiotic or axenic nematodes. I have found that infection with symbiotic nematodes induce genes associated with immune functions, whereas axenic nematodes induce genes associated with chitin binding and metabolic functions. I also report that the Drosophila genes with potential anti-nematode activity are conserved in the lepidopteran insect host, Manduca sexta , as well as in humans. These findings have led to the identification of genes with potential roles in nematode recognition and anti-nematode activity in Drosophila.
I also investigated the participation of the chitinase-like imaginal disc growth factor encoding genes, Idgf2 and Idgf3 , in the Drosophila response to Steinernema nematode infection. I report that Idgf2 and Idgf3 are upregulated in Drosophila larvae responding to Steinernema nematodes and inactivation of Idgf2 provides a survival advantage to the larvae against axenic nematodes. I show that Idgf2 or Idgf3 modulate distinct immune signaling pathways and inactivation of Idgf3 induces the recruitment of Drosophila larval hemocytes in response to Steinernema nematodes. These data demonstrate that Idgf2 and Idgf3 are involved in different yet crucial anti-nematode immune functions in Drosophila.
Next, I report the participation of Jonah66Ci that encodes a serine protease, in the Drosophila response to Steinernema infection. I show that Jonah66Ci is strongly upregulated in the gut of Drosophila larvae responding to Steinernema . Jonah66Ci differentially modulates Toll, Imd and Wnt/Wg signaling in the gut of Drosophila larvae upon Steinernema infection. Inactivation of Jonah66Ci increases the numbers of replicating cells in uninfected larvae and nematode infection reduces cell replication. These results indicate that Jonah66Ci is essential in maintaining homeostasis in Drosophila larvae during Steinernema nematode infection.
In conclusion, my work has demonstrated that Steinernema infection differentially regulates a large number of genes in Drosophila larvae, endosymbiotic bacteria participate in the interaction between the Drosophila immune system with the nematode parasites, and Idgf2, Idgf3 and Jonah66Ci genes encode factors with distinct yet important anti-nematode activity in Drosophila larvae against Steinernema challenge. These findings generate novel insights towards deciphering the molecular and functional basis of the Drosophila anti-nematode immune response and unraveling previously unknown aspects of the Drosophila innate immune system.
|Commitee:||Manier, Mollie, Nixon, Douglas F., O'Halloran, Damien, Smith, L. Courtney|
|School:||The George Washington University|
|School Location:||United States -- District of Columbia|
|Source:||DAI-B 79/12(E), Dissertation Abstracts International|
|Subjects:||Biology, Molecular biology, Immunology|
|Keywords:||Axenic, Drosophila, Host-pathogen, Steinernema, Symbiotic, Xenorhabdus|
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