A comparison of aquaporin expression in mosquito larvae (Aedes aegypti) that develop in hypo-osmotic freshwater and iso-osmotic brackish water

Abstract

The mosquito Aedes aegypti vectors the arboviral diseases yellow fever, dengue, Zika and chikungunya. Larvae are usually found developing in freshwater; however, more recently they have been increasingly found in brackish water, potential habitats which are traditionally ignored by mosquito control programs. Aedes aegypti larvae are osmo-regulators maintaining their hemolymph osmolarity in a range of ~ 250 to 300 mOsmol l -1 . In freshwater, the larvae must excrete excess water while conserving ions while in brackish water, they must alleviate an accumulation of salts. The compensatory physiological mechanisms must involve the transport of ions and water but little is known about the water transport mechanisms in the osmoregulatory organs of these larvae. Water traverses cellular membranes predominantly through transmembrane proteins named aquaporins (AQPs) and Aedes aegypti possesses 6 AQP homologues (AaAQP1 to 6). The objective of this study was to determine if larvae that develop in freshwater or brackish water have differential aquaporin expression in osmoregulatory organs, which could inform us about the relative importance and function of aquaporins to mosquito survival under these different osmotic conditions. We found that AaAQP transcript abundance was similar in organs of freshwater and brackish water mosquito larvae. Furthermore, in the Malpighian tubules and hindgut AaAQP protein abundance was unaffected by the rearing conditions, but in the gastric caeca the protein level of one aquaporin, AaAQP1 was elevated in brackish water. We found that AaAQP1 was expressed apically while AaAQP4 and AaAQP5 were found to be apical and/or basal in the epithelia of osmoregulatory organs. Overall, the results suggest that aquaporin expression in the osmoregulatory organs is mostly consistent between larvae that are developing in freshwater and brackish water. This suggests that aquaporins may not have major roles in adapting to longterm survival in brackish water or that aquaporin function may be regulated by other mechanisms like post-translational modifications.

Exploratory phosphoproteomics profiling of Aedes aegypti Malpighian tubules during blood meal processing reveals dramatic transition in function

“…Negatively charged Clions follow into the MT lumen to maintain electroneutrality [7,12,13]. These processes generate the osmotic gradient that powers the mass flow of water into the MT lumens both by paracellular movement and transcellular transport through aquaporins (AQPs) in SCs [7,12,13,[20][21][22]. Aquaporins (AQPs) are six transmembrane-domain proteins that facilitate the transport of water and small solutes across the cell membrane and are responsible for a large portion of the water excretion mediated by MTs [10,[23][24][25].…”

The genome of the brackish-water malaria vectorAnopheles aquasalis

“…melas) with a mean of 13,162 genes +-1,380 (23). Our results suggest that the size of the genome (162.9 Mb) and several coding proteins (12,446) of An. aquasalis is relatively similar to other anophelines.…”

“…Studies on the tolerance of An. albimanus to saltwater also suggest the importance of V-type ATPase, carbonic anhydrase, and K+/Na+ ATPase proteins to osmoregulation (8–12), and studies in other insects have shown the role of aquaporins in such process. Orthology searches suggest that An.…”

“…albimanus , when exposed to gradual changes in saline water, specialized non-dorsal anterior rectal (non-DAR) cells undergo changes in the localization of V-type ATPases and K+/Na+ ATPases proteins, allowing the production of super osmotic urine and disrupting the ion reabsorption system in non-DAR cells (8, 9). Other studies in mosquitoes have also suggested the importance of Carbonic Anhydrase (CA) and aquaporins to osmoregulation in saline environments (10, 12). We found that An.…”

“…albimanus (8,9). Other molecular and transcriptome studies also suggest that other genes, such as aquaporin and carbonic anhydrases, in conjunction with transcription modulation, are essential for mosquito survival in hyperosmotic or hypo-osmotic environments (10)(11)(12) Besides its peculiar ecological features, recent research recognized An. aquasalis as an important model for studying the interaction with human Plasmodium and murine models such as P. yoelii nigeriensis (13)(14)(15).…”