Functional characterization of aquaporins in the disease vectors Aedes aegypti and Culex quinquefasciatus

Female mosquitoes require the uptake of blood for egg production and as a result, they transmit disease pathogens to humans. It is essential for mosquitoes to possess an efficient excretion system to shed excess water and sodium ions and retain nutrients from the blood. After a blood meal females excrete excessive amounts of urine through their excretory organs, the Malpighian tubules (MT). Aquaporins (AQPs) are a family of membrane transporters that regulate the flow of water, glycerol and other small molecules across cellular membranes in both prokaryotic and eukaryotic cells. Our aim was to identify aquaporins that function as water channels and mediate transcellular water transport in MTs of adult female Ae. aegypti and Culex quinquefasciatus. We surveyed genome databases and identified six putative AQPs in the genome of Ae. aegypti and Culex, respectively. Quantitative PCR and in situ hybridization assays showed that four of the AQPs are expressed in the MTs of both species. RNAi-mediated knockdown of the MT-expressed AQPs resulted in significantly reduced diuresis. Expression of Ae. aegypti AQPs in Xenopus eggs resulted in significant increase in water permeability of their cell membranes and subsequent swelling proving that these proteins are indeed water channels.