The Physiology of Ammonia Transport in the Disease Vector Mosquito Aedes Aegypti: Ammonia Transporter Localization, Function and Characterization
Durant, Andrea Claire
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The formation of ammonia (NH3/NH4+) through protein metabolism is ubiquitous in ani-mals. However, ammonia is typically destined for conversion and/or elimination from the body be-cause the toxicological consequences of systemic ammonia accumulation are grave. Specialized ammonia transporters regulate excretion of ammonia by moving it across biological membranes. The yellow fever mosquito, Aedes aegypti, possess four ammonia transporters: two Rhesus glyco-proteins (Rh proteins, AeRh50-1 and AeRh50-2) and two ammonium transporters (Amt proteins, AeAmt1 and AeAmt2), but functionally they are poorly understood in this medically important dis-ease vector. This presents a serious gap in knowledge, in particular because aquatic larvae of A. ae-gypti can inhabit ammonia-rich sewage, intensifying the possibility of vector success in regions where poorly maintained septic systems are used for sewage treatment. My studies sought to ad-vance our understanding of Rh and Amt proteins in A. aegypti by examining their function in (1) larvae residing in high environmental ammonia (HEA) and (2) hematophagous adult females that are naturally loaded with high ammonia while handling a blood meal. In larvae, all four ammonia transporters are expressed in the anal papillae (AP), structures that are in direct contact with the ex-ternal environment. Rh proteins and AeAmt2 are involved in ammonia excretion across the AP but decrease in abundance upon HEA exposure. The AP are still critical sites of ammonia excretion when larvae are in HEA, evidenced by enhanced NH4+ efflux. Rh proteins may also play a role in acid-base balance as protein levels of Rh significantly increase in conditions that challenge blood pH regulation. Of particular importance was that laboratory observations of ammonia transport physi-ology of larvae in HEA reconciled with observations of wild A. aegypti larvae collected from am-monia-rich septic tanks. In adult A. aegypti, Rh proteins are expressed in the excretory organs and facilitate NH4+ secretion via the urine. Novel observations of AeAmt1 being almost exclusively ex-pressed in the spermatozoa of males revealed a vital role for this protein in sperm survival and suc-cessful egg fertilization. Collectively, my studies significantly advance our mechanistic understand-ing of ammonia transport proteins in A. aegypti by revealing their broad and critical roles.