Anti-diuresis in the Blood-gorging Bug, Rhodnius prolixus: The Role of CAPA Peptides

CAPA-related peptides belong to a family of neuropeptides localized to the central nervous system that can function in diverse roles in the regulation of water and salt homeostasis in insects. These peptides are known to stimulate fluid secretion by Malpighian tubules (MTs) in Dipteran species, thus serving a diuretic function. In contrast, this thesis demonstrates that members of this family of peptides in Rhodnius prolixus serve an anti-diuretic role and have multiple tissue targets, whereby they oppose the activity of diuretic hormones such as serotonin (5-Hydroxytryptamine hydrochloride; 5-HT). I have identified two genes each encoding three peptides in R. prolixus, suggesting this insect is capable of producing a greater number of CAPA-peptides compared to other insects that contain only a single CAPA gene. Interestingly, while the second peptide encoded in each R. prolixus gene (RhoprCAPA-α2/-β2) inhibits the stimulatory effects of serotonin on tissues such as the anterior midgut and Malpighian tubules, it appears the other CAPA-related and pyrokinin-related peptides do not play a major role in inhibiting the effects of serotonin on these tissues. More specifically, serotonin-stimulated fluid secretion by MTs and fluid absorption by the anterior midgut are reduced by the anti-diuretic peptide, RhoprCAPA-α2. In addition, I have also identified a G protein-coupled receptor which likely mediates the anti-diuretic effect associated with RhoprCAPA-α2 and have functionally characterized this receptor in Chinese hamster ovary cells. Spatial transcript expression analysis in fifth-instars reveals a wide distribution of the receptor in tissues associated with the rapid post-gorging diuresis. Thus, my findings suggest that numerous tissues are regulated by the CAPA peptides in R. prolixus. Gene structure and phylogenetic analyses demonstrate that this receptor is the orthologue of the D. melanogaster capa receptor (CG14575) with homologs in other insects. Taken together, my thesis demonstrates that the RhoprCAPA peptides play an integral role in the coordination and maintenance of anti-diuresis in R. prolixus. This mechanism is necessary following the rapid diuresis associated with blood-feeding by this medically-important insect.Ph