RNA-Seq Comparison of Larval and Adult Malpighian Tubules of the Yellow Fever Mosquito Aedes aegypti Reveals Life Stage-Specific Changes in Renal Function

Abstract

Introduction: The life history of Aedes aegypti presents diverse challenges to its diuretic system. During the larval and pupal life stages mosquitoes are aquatic. With the emergence of the adult they become terrestrial. This shifts the organism within minutes from an aquatic environment to a terrestrial environment where dehydration has to be avoided. In addition, female mosquitoes take large blood meals, which present an entirely new set of challenges to salt and water homeostasis.Methods: To determine differences in gene expression associated with these different life stages, we performed an RNA-seq analysis of the main diuretic tissue in A. aegypti, the Malpighian tubules. We compared transcript abundance in 4th instar larvae to that of adult females and analyzed the data with a focus on transcripts that encode proteins potentially involved in diuresis, like water and solute channels as well as ion transporters. We compared our results against the model of potassium- and sodium chloride excretion in the Malpighian tubules proposed by Hine et al. (2014), which involves at least eight ion transporters and a proton-pump.Results: We found 3,421 of a total number of 17,478 (19.6%) unique transcripts with a P < 0.05 and at least a 2.5 fold change in expression levels between the two groups. We identified two novel transporter genes that are highly expressed in the adult Malpighian tubules, which have not previously been part of the transport model in this species and may play important roles in diuresis. We also identified candidates for hypothesized sodium and chloride channels. Detoxification genes were generally higher expressed in larvae.Significance: This study represents the first comparison of Malpighian tubule transcriptomes between larval and adult A. aegypti mosquitoes, highlighting key differences in their renal systems that arise as they transform from an aquatic filter-feeding larval stage to a terrestrial, blood-feeding adult stage.

Activation of mosquito immunity blocks the development of transmission-stage filarial nematodes

“…aegypti demonstrated that refractory hemolymph is inhibitory to development of B. malayi (53). Regardless of whether larvae are restricted autonomously by activation of Toll signaling in their site of development or by activation of Toll signaling in another tissue, existing suitable tissue-selective expression systems for fat body (26) or indirect flight muscle (54), or newly generated expression systems for the Malpighian tubules identified using the transcriptomic information generated in this study and others (55), could be used to promote tissue-specific activation.…”

Identification of Candidate Iron Transporters From the ZIP/ZnT Gene Families in the Mosquito Aedes aegypti

“…AaeZIP11 transcripts were also found to be enriched in the Malpighian tubules, particularly following a bloodmeal, suggesting a potential role in excretion. As the key organ for insect excretion and detoxification, Malpighian tubules may play a critical role in excretion of excess iron accumulated in the hemolymph (Folwell et al, 2006 ; Beyenbach et al, 2010 ; Li et al, 2017 ). As a candidate exporter, AaeZIP11 may function in concert with AaeZnT7 (candidate importer) to transfer iron from the hemolymph to the MT lumen for excretion, and we are actively investigating this possibility.…”

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

“…The differences in expression of AaAQP1 between larvae and adults is therefore not surprising. Substantial differences in the transcriptome of MTs of mosquito larvae and adults have been reported and suggested to be related to the different functions the MTs need to play in larvae versus adults [ 47 ].…”

“…An alternative, or additional, function of AaAQP4 and AaAQP5 on the basal membrane is for trehalose uptake from the hemolymph to support metabolic functions of MTs cells as suggested for the GC (see above). In addition, AaAQP2 transcript levels in MTs of larvae are substantially high and warrant a thorough investigation at the protein level when an antibody is available [ 15 , 47 ].…”