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

Lidiya Misyura,Elia Grieco Guardian,Andrew Donini,Andrea Claire Durant,Dmitri Boudko

doi:10.1371/journal.pone.0234892

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.

Highlights

Aedes aegypti mosquitoes are arboviral vectors for human diseases including Zika, chikungunya, dengue, and yellow fever [1]
Larvae that developed in FW or brackish water (BW) had similar levels of AaAQP transcripts in the gastric caeca (GC), Malpighian tubules (MTs) and HG (Fig 1)
The abundance of AaAQP1 was higher in the GC of BW reared larvae relative to FW reared larvae, whereas there was no difference in AaAQP1 protein abundance in the MT and HG between BW and FW reared larvae

Summary

Introduction

Aedes aegypti mosquitoes are arboviral vectors for human diseases including Zika, chikungunya, dengue, and yellow fever [1]. Studies have demonstrated that changes in the structure and function of anal papillae of A. aegypti larvae from FW adapted populations occur when these larvae are transferred to BW [16,17,18] These alterations suggest a reduction in ion uptake activity when larvae are placed in BW; alterations of anal papillae size in response to BW depend on whether larvae come from a population adapted to FW or BW [18]. Differences in aquaporin (water channel) expression have been documented in the anal papillae of A. aegypti larvae that develop in BW compared with those in FW but the functional significance remains to be studied [19]. Information on aquaporin expression and function in other osmoregulatory organs of mosquito larvae in response to BW is lacking

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Discussion

Conclusion