Role of Toll-NF-kappaB Signaling in Inflammation and Immune Homeostasis in Drosophila melanogaster
Item
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Title
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Role of Toll-NF-kappaB Signaling in Inflammation and Immune Homeostasis in Drosophila melanogaster
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Identifier
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d_2009_2013:d295f9e64ece:11091
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identifier
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11303
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Creator
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Paddibhatla, Indira,
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Contributor
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Shubha Govind
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Date
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2011
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Language
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English
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Publisher
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City University of New York.
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Subject
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Molecular biology | Immunology | Cellular biology | Cancer | Inflammation | Spatzle | Sumoylation | Toll | tumor
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Abstract
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Inflammation is defined as a localized reaction in response to injury or tissue destruction. It serves to contain or sequester the causative agent. Fundamentally important to human health, inflammation and its aberrant regulation underlie many diseases including cancer, diabetes and heart disease. Like humans, fruit flies respond to infection by coordinating complex defense responses. Parasitic wasps are natural enemies of Drosophila and attack larvae or pupae. They inject one or more eggs, each approximately 100 mum in size, into the hemocoel of the fly larva. Oviposition results either in the development of the wasp larva that gradually eats the Drosophila host tissue, or the host's blood cells encapsulate the wasp egg. In the latter scenario, circulating host blood cells surround the wasp egg and inhibit its development.;In addition to the activation and aggregation of the host blood cells in response to wasp attack, infected larvae also activate gene expression in the fat body. A number of antimicrobial peptides and other immune-related proteins are secreted into the hemolymph. The humoral arm is activated within the first couple of hours of infection, although the significance of this activation is not understood. It is also not clear how the encapsulation reaction is so tightly controlled or how it is terminated.;Previous studies from our laboratory have focused on the role of Toll-NF-kappaB signaling in hematopoiesis. Larvae deficient in either IkappaB/ cactus or the SUMO-conjugating enzyme, Ubc9, exhibit hematopoietic defects (overproliferation and abnormal differentiation of the blood cells) accompanied with aggregation and microtumor formation. These mutants also express antimicrobial peptides such as Drosomycin from the fat body even in the absence of infection. Given that both the humoral and cellular immune systems of these mutants are hyperactive, we hypothesized that changes induced after wasp infection represent acute inflammation, and these effects become chronic in cactus or Ubc9 mutants.;Studies in the first chapter explore the cellular and molecular parallels between wasp-induced gene expression and encapsulation versus constitutive gene expression and encapsulation (in microtumors) of Ubc9 mutants. We show that several core components (including SPE, Toll , and cactus) of the Toll-Dorsal pathway are activated in each case. However, while gene expression after wasp infection shows acute phase profile (activation followed by downregulation), expression in mutants remains high.;We show that the cytokine Spatzle (the Toll ligand) is expressed in the immune cells, hemocytes and the fat body. Spatzle protein levels are higher after wasp infection and in Ubc9 mutants. Misexpression of either SPE or Spz protein in immune tissues of wild type larvae leads to blood cell proliferation, differentiation, infiltration of the fat body tissue and melanized microtumors. We propose a pro-inflammaotry role for SPE/Spatzle whose downregulation is essential for limiting acute inflammation. Accordingly, loss of spz suppresses Ubc9- defects and loss of SPE in the immune cells fails to encapsulate the parasitic egg.;In contrast to the pro-inflammatory role of SPE/Spz, SUMO conjugating enzyme, Ubc9, and IkappaB homologue, Cactus, are anti-inflammatory agents. RNAi knockdown of Ubc9, or even Uba2/Aos1 subunits of SUMO activating enzymes leads to systemic chronic inflammation. Affected animals activate Drosomycin in the fat body in the absence of infection. Blood cells infiltrate the fat body and these changes are accompanied with microtumor development.;Extensive staining of fat body and blood cells reveals that while cactus transcription and protein levels increase after infection, Ubc9 mutants cannot sustain normal cytoplasmic levels of Cactus protein. These studies demonstrate the existence of a sumoylation dependent Ubc9/IkappaB modulated immune homeostasis mechanism that balances the pro- and anti-inflammatory factors in the hosts.;This study on Drosophila inflammatory responses complements the existing mammalian models for cancer inflammation. Knowledge gained from our system should be highly relevant in developing novel strategies for medical and agricultural pest control.
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Type
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dissertation
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Source
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2009_2013.csv
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degree
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Ph.D.
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Program
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Biology
