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.

Keywords: Aedes aegypti; Malpighian tubules; RNAseq; detoxification; diuresis; mosquito.

Figure 1

Volcano plot generated with larval vs. adult transcript data. Transcripts altered at a less than log 2 fold level are in red, transcripts altered at a greater than log 2 fold level, but with a P < 0.05 are in blue. Transcripts with an expression level altered more than log 2 fold and have a P > 0.05 are in black.

Figure 2

Model of NaCl and KCl excretion. Expression levels of transporters hypothesized to be involved in excretion of NaCl and KCl in Aedes aegypti. Shown is the log scale transcript expression of each transporter we found to be expressed, larvae in red, adults in blue. The cellular localization of several of these transporters has not been determined and is therefore hypothetical. PC, principal cell; SC, stellate cell; v, vesicle.

Figure 3

Conversion of nitrogen in waste products. Log scale expression of transcripts for enzymes involved in the synthesis of nitrogen waste products in A. aegypti MTs. In general, in the classical urea cycle, transcripts are lower in larvae compared to adults, with the exception of argininosuccinate lyase. In the alternative urea pathway, transcripts are higher in larvae compared to adults with the exception of allantoicase. Shown is the log scale transcript expression of each transporter we found to be expressed, larvae in red, adults in blue.