Comparative genomics analysis coupled to functional assays uncovered evolutionarily conserved signaling pathways and provided important insights towards the understanding of insect immunity. However, extrapolating this approach to non-insect arthropods, such as the tick Ixodes scapularis, sometimes constitutes a problem because of the lack of distinguishable protein homologues and incorrect annotation of genes due to low sequence coverage or incompleteness of a particular genome. For instance, we observed that the immune deficiency (IMD) signaling pathway of the tick I. scapularis is critical for defense against the rickettsial agent Anaplasma phagocytophilum despite the absence of the adaptor molecule imd and the gene fadd on its genome. Moreover, we learned that the E3 ubiquitin ligase x-linked inhibitor of apoptosis protein (XIAP) is critical for activating the IMD pathway against A. phagocytophilum infection of I. scapularis ticks. Collectively, these findings led to ou central hypothesis stating that XIAP regulates the non-canonical tick IMD pathway in response to the rickettsial agent A. phagocytophilum. Accordingly, in Aim #1 of this proposal, we will characterize the functional interaction between XIAP and the E2-conjugating enzyme Bendless. We surmise a direct interaction between these two proteins based on structural docking and mass spectrometry analysis.
In Aim #2, we will identify XIAP substrates during pathogen colonization of ticks using stable isotope labeling with amino acids in cell culture (SILAC) and diglycine remnant affinity profiling combined with tandem mass spectrometry.
In Aim #3, we will validate the IMD network during A. phagocytophilum infection of I. scapularis ticks in vivo. We will ascertain the immune response following pathogen entry into the tick and evaluate the effect of the IMD signaling pathway during pathogen infection. The outcome of this research will be two-fold: (1) it will provide fundamental knowledge related to tick-pathogen interactions; and (2) it will uncover a novel immune pathway in arthropods with broad implications for the vector biology community.

Public Health Relevance

Tick-borne diseases are the most common vector-borne illnesses in the northern hemisphere. We will perform a systematic characterization of a distinct immune pathway in the tick I. scapularis by using the rickettsial pathogen A. phagocytophilum. Our research should open new venues of research for a better understanding and prevention of tick-borne diseases.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Vector Biology Study Section (VB)
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Costero-Saint Denis, Adriana
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University of Maryland Baltimore
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Shaw, Dana K; Tate, Ann T; Schneider, David S et al. (2018) Vector Immunity and Evolutionary Ecology: The Harmonious Dissonance. Trends Immunol 39:862-873
McClure Carroll, Erin E; Wang, Xiaowei; Shaw, Dana K et al. (2018) p47 licenses activation of the immune deficiency pathway in the tick Ixodes scapularis. Proc Natl Acad Sci U S A :
Shaw, Dana K; Wang, Xiaowei; Brown, Lindsey J et al. (2017) Infection-derived lipids elicit an immune deficiency circuit in arthropods. Nat Commun 8:14401
McClure, Erin E; Chávez, Adela S Oliva; Shaw, Dana K et al. (2017) Engineering of obligate intracellular bacteria: progress, challenges and paradigms. Nat Rev Microbiol 15:544-558
Oliva Chávez, Adela S; Shaw, Dana K; Munderloh, Ulrike G et al. (2017) Tick Humoral Responses: Marching to the Beat of a Different Drummer. Front Microbiol 8:223
Wang, Xiaowei; Shaw, Dana K; Sakhon, Olivia S et al. (2016) The Tick Protein Sialostatin L2 Binds to Annexin A2 and Inhibits NLRC4-Mediated Inflammasome Activation. Infect Immun 84:1796-1805
Shaw, Dana K; McClure, Erin E; Wang, Xiaowei et al. (2016) Deviant Behavior: Tick-Borne Pathogens and Inflammasome Signaling. Vet Sci 3:
Shaw, Dana K; Kotsyfakis, Michail; Pedra, Joao H F (2016) For Whom the Bell Tolls (and Nods): Spit-acular Saliva. Curr Trop Med Rep 3:40-50