Salinity responsive aquaporins in the anal papillae of the larval mosquito, Aedes aegypti

The larvae of the mosquito, Aedes aegypti normally inhabit freshwater (FW) where they face dilution of body fluids by osmotic influx of water. In response, the physiological actions of the anal papillae result in ion uptake while the Malpighian tubules and rectum work in concert to excrete excess water. In an apparent paradox, the anal papillae express aquaporins (AQPs) and are sites of water permeability which, if AQPs are expressed by the epithelium, apparently exaggerates the influx of water from their dilute environment. Recently, naturally breeding populations of A. aegypti were found in brackish water (BW), an environment which limits the osmotic gradient. Given that salinization of FW is an emerging environmental issue and that these larvae would presumably need to adjust to these changing conditions, this study investigates the expression of AQPs in the anal papillae and their response to rearing in hypo-osmotic and near isosmotic conditions. Transcripts of all six Aedes AQP homologs were detectable in the anal papillae and the transcript abundance of three AQP homologs in the papillae was different between rearing conditions. Using custom made antibodies, expression of two of these AQP homologs (AQP4 and AQP5) was localized to the syncytial epithelium of the anal papillae. Furthermore, the changes in transcript abundance of these two AQPs between the rearing conditions, were manifested at the protein level. Results suggest that AQP4 and AQP5 play an important physiological role in larval responses to changes in environmental salinity.