Fluid Secretion by Malpighian Tubules of Rhodnius prolixus: Neuroendocrine Control With New Insights From a Transcriptome Analysis

Abstract

Rhodnius prolixus (the kissing bug and a major vector of Chagas disease) is an obligate blood feeder that in the case of the fifth instar consumes up to 10 times its unfed body weight in a single 20-minute feed. A post-prandial diuresis is initiated, within minutes of the start of gorging, in order to lower the mass and concentrate the nutrients of the meal. Thus, R. prolixus rapidly excretes a fluid that is high in NaCl content and hypo-osmotic to the hemolymph, thereby eliminating 50% of the volume of the blood meal within 3 hours of gorging. In R. prolixus, as with other insects, the Malpighian tubules play a critical role in diuresis. Malpighian tubules are not innervated, and their fine control comes under the influence of the neuroendocrine system that releases amines and neuropeptides as diuretic or antidiuretic hormones. These hormones act upon the Malpighian tubules via a variety of G protein-coupled receptors linked to second messenger systems that influence ion transporters and aquaporins; thereby regulating fluid secretion. Much has been discovered about the control of diuresis in R. prolixus, and other model insects, using classical endocrinological studies. The post-genomic era, however, has brought new insights, identifying novel diuretic and antidiuretic hormone-signaling pathways whilst also validating many of the classical discoveries. This paper will focus on recent discoveries into the neuroendocrine control of the rapid post-prandial diuresis in R. prolixus, in order to emphasize new insights from a transcriptome analysis of Malpighian tubules taken from unfed and fed bugs.

Malpighian tubules of Rhodnius prolixus: More than post-prandial diuresis

“…In the unfed condition, R. prolixus are in a state of arrested development and can go several months without a blood meal, but when they take a blood meal it triggers short term and long term physiological events as mentioned earlier (see 1). A bioinformatic pipeline to process RNA-seq reads for mapping sequences, transcript quantification, differential expression analysis and Kyoto encyclopedia of genes and genomes (KEGG) enrichment as well as the validation of RNA-seq data, have been thoroughly detailed by Orchard et al (1) and Leyria et al (29,30). Here, we performed heatmap analysis to compare mRNA expression levels under the different feeding states presented by means of a color scale, showing the Fragments Per Kilobase Million (FPKM) values obtained by gene expression analysis after normalization.…”

“…When heatmaps of these clusters throughout the 3 experimental groups are analyzed, we can visually observe a nutrition-dependent pattern of physiological responses (Supplementary Figure 1). In the following sections we have performed an in-depth exploration of these DEG in Malpighian tubules, describing changes induced by blood gorging that are distinct from those associated with diuresis, which were previously covered in Orchard et al (1).…”

“…Several studies have examined the presence of transcripts for hormones and their receptors in insect Malpighian tubules, largely in the context of diuretic and antidiuretic hormones (1,(19)(20)(21). Similarly, a previous analysis of the R. prolixus transcriptome revealed the presence of G-protein coupled receptors for the known diuretic and antidiuretic hormones of R. prolixus (1).…”

“…(see 1,2). The ability to trigger and therefore precisely time these events was taken advantage of by Sir Vincent Wigglesworth (e.g.…”

“…These hormones regulate fluid secretion and reabsorption by the Malpighian tubules via a variety of receptors (G protein-coupled, tyrosine kinase, and guanylyl cyclase type receptors) linked to several second messenger systems that ultimately influence a V-type H + ATPase, ion transporters and aquaporins, among others (see 1, 14-17). Much has been discovered about the control of diuresis in R. prolixus, and other model insects, but the post-genomic era has brought new insights, enabling the identification of novel diuretic and antidiuretic hormone-signaling pathways whilst also validating many of the existing models (see 1,[16][17][18][19][20][21]. This era has also identified functions quite apart from diuresis for Malpighian tubules, and microarray and transcriptome analyses have revealed the major roles that Malpighian tubules play in immunity, detoxification, pesticide resistance, and in tolerance to overall stress (7,16,18,(20)(21)(22).…”