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Proliferative Signals Regulate Hemocyte Development and Intestinal Immunity in Drosophila melanogaster. Open Access


Other title
Platelet Derived Growth Factor
Innate Immunity
Vascular Endothelial Growth Factor
Type of item
Degree grantor
University of Alberta
Author or creator
Parsons, Brendon D
Supervisor and department
Foley, Edan (Medical Microbiology and Immunology)
Examining committee member and department
Simmonds, Andrew (Cell Biology)
Baldwin, Troy (Medical Microbiology and Immunology)
Harris, Tony (Cell & Systems Biology)
Ostergaard, Hanne (Medical Microbiology and Immunology)
Department of Medical Microbiology and Immunology
Date accepted
Graduation date
Doctor of Philosophy
Degree level
The innate immune system is an ancient line of resistance against intrusive microbial threats. This system integrates cellular, humoral, and barrier defenses to generate a protective immune response. These divisions are indispensable and conserved between Drosophila and mammals. Hemocytes are the immune cells of Drosophila, and they resemble vertebrate myeloid lineages in their ontogeny and function. Similar to tissue macrophages, the Drosophila hemocytes have roles in development, tissue homeostasis and defense against pathogens. Conserved constituents of the platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF) receptor tyrosine kinase (RTK) families have defined roles in these processes. Signaling through the PDGF/VEGF-related receptor (Pvr) mediates the establishment and dispersal of hemocytes during embryogenesis. The Pvr ligands, Pvf2 and Pvf3 are implicated in hemocyte cellular proliferation, size and chemotactic guidance of hemocyte. However, the precise role that Pvf2 and Pvf3 play in hemocytes is unclear due to the lack of available mutants. To determine Pvf functions in vivo, I generated a genomic deletion that simultaneously disrupts Pvf2 and Pvf3. From my studies, I identified contributions of Pvf2 and Pvf3 to the trophic maintenance of hemocytes. I uncovered a novel role for Pvfs in invasive migrations and found that Pvf2 and Pvf3 are not required as guidance cues during hemocyte migration, but act locally in epithelial cells to coordinate trans-epithelial movements. Additionally, I observed that Pvr activation in hemocytes attenuates immune signaling through the immune deficiency pathway (IMD). These observations redefined the role of growth factor signaling in Drosophila hemocyte migration and uncover novel roles for hemocyte invasive migration. I then assessed the role that proliferative and immune responses play in the Drosophila gut epithelium. Unlike the sterile hemolymph of the body cavity, the epithelial barriers of the Drosophila gut interface with a dense heterogeneous population of microbes. Cells of the epithelium must relay intrinsic and extrinsic signals to coordinate epithelial renewal programs and immune response. Pathogenic challenge of the epithelium drives a local humoral response through the IMD pathway and a burst of intestinal stem cell (ISC) proliferation to maintain barrier integrity. While Pvf-Pvr signaling and several additional intrinsic regulators are essential for ISC homeostatic proliferation, it is unclear if the microbiota impact these systems during infection. To this end, I assessed gut epithelial IMD and regenerative responses in Drosophila devoid of a microbiota. I found that in the absence of infection, the microbiota stimulate basal IMD signaling are essential to maintain the ISCs. I also found that during infection the gut microbiota dramatically enhance survival, support epithelial compensatory proliferation and exhibit a regulatory impact on the IMD response. Together my findings define growth factor signaling roles through Pvfs in hemocyte survival and invasive migration and identify roles for the microbiota in gut epithelial regeneration and immune responses during infection.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Brendon D. Parsons and Edan Foley. (2013) Journal of Biological Chemistry. 288:20173-20183.Kristina Petkau, Brendon D. Parsons, Aashna Duggal and Edan Foley. (2014) Journal of Biological Chemistry. 289(41):28719-29.Brendon D. Parsons, Anja Schindler, David H. Evans, Edan Foley. (2009) PLoS ONE. 4(12):e8471.

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