The Jumpstart for Juniors grant allowed me to investigate the role of the immune system of the mosquito Aedes aegypti in resistance to infection by canine heartworm, Dirofilaria immitis.
Mosquitoes are vectors of several human and animal diseases. For disease transmission to occur, the mosquito must become infected. The mosquito immune system has been shown to play an important role in determining whether a mosquito becomes infected. Thus, it is important to understand mosquito immune responses to infection to develop new ways to combat the spread of disease. My project focuses on A. aegypti mosquito, responsible for transmission of myriad diseases including yellow fever, dengue fever, and Zika. A. aegypti is a powerful genetic model for understanding the interactions between mosquitoes and the nematode that causes canine heartworm, D. immitis. Previous work in the laboratory comparing strains of A. aegypti with differences in infection by D. immitis found strong upregulation of a set of immune genes in the refractory strain. My project is to functionally analyze a group of seven immune genes to determine whether silencing their expression using RNA interference renders the refractory mosquitoes susceptible to infection.
Infection was assessed 6 days after infection. At this time, there is a striking difference in D. immitis development in the Malpighian tubules (kidneys) of susceptible mosquitoes. In contrast, worms retain their initial morphology in refractory mosquitoes with a small proportion becoming melanized, an insect immune reaction where they are coated in pigment. My hypothesis is that if silencing of immune genes will then allow the worms to develop further and prevent worm melanization.
This research experience allowed me to develop my critical thinking skills. Gene silencing efficiency depends on mosquito age and timing during mosquito infection. Therefore, I developed better planning and preparation skills to ensure all the necessary proper steps were completed. For example, gene silencing requires exposing mosquitoes to double-stranded RNA (dsRNA) specific to a gene of interest. High quality dsRNA must be created. In addition, mosquitoes must be in the proper stage. The dsRNA is delivered to mosquitoes by microinjection and analysis of infection requires dissection of Malpighian tubules. This project provided me with a fundamental understanding of how each preparatory experiment worked and played a role in the overall goal.