Receptor Characterization and Functional Activity of Pyrokinins on the Hindgut in the Adult Mosquito, Aedes aegypti.

Aryan Lajevardi,Jean-Paul V Paluzzi

doi:10.3389/fphys.2020.00490

Abstract

Pyrokinins are structurally related insect neuropeptides, characterized by their myotropic, pheromonotropic and melanotropic roles in some insects, but their function is unclear in blood-feeding arthropods. In the present study, we functionally characterized the pyrokinin-1 and pyrokinin-2 receptors (PK1-R and PK2-R, respectively), in the yellow fever mosquito, Aedes aegypti, using a heterologous cell system to characterize their selective and dose-responsive activation by members of two distinct pyrokinin subfamilies. We also assessed transcript-level expression of these receptors in adult organs and found the highest level of PK1-R transcript in the posterior hindgut (rectum) while PK2-R expression was enriched in the anterior hindgut (ileum) as well as in reproductive organs, suggesting these to be prominent target sites for their peptidergic ligands. In support of this, PRXa-like immunoreactivity (where X = V or L) was localized to innervation along the hindgut. Indeed, we identified a myoinhibitory role for a PK2 on the ileum where PK2-R transcript was enriched. However, although we found that PK1 did not influence myoactivity or Na+ transport in isolated recta, the PRXa-like immunolocalization terminating in close association to the rectal pads and the significant enrichment of PK1-R transcript in the rectum suggests this organ could be a target of PK1 signaling and may regulate the excretory system in this important disease vector species.

Highlights

Neuropeptides regulate an array of physiological processes in insects, including feeding, metamorphosis, diapause, and reproduction (Nässel and Winther, 2010)
PK2-R was abundant in the anterior ileum and significantly enriched in reproductive organs relative to the whole body (Figure 1), and demonstrated significantly higher expression compared to PK1-R levels in these organs, which was consistent across all biological replicates
We have characterized the functional activation of A. aegypti PK1 and PK2 receptors in response to various PKs and related neuropeptides

Summary

Introduction

Neuropeptides regulate an array of physiological processes in insects, including feeding, metamorphosis, diapause, and reproduction (Nässel and Winther, 2010). Related PKs have been identified in other insects and shown to regulate cuticle melanization, pupariation, and feeding behavior (Matsumoto et al, 1990; Zdarek et al, 1997; Verleyen et al, 2004; Bader et al, 2007) The existence of another PK subfamily with the highly conserved WFGPRL-NH2 C terminus was revealed with the characterization of the diapause hormone (DH) that regulates the onset of embryonic diapause in the silkworm Bombyx mori (Yamashita, 1996). The role of DH in diapause has been identified in some lepidopteran species (Xu and Denlinger, 2003), and more recently in Locusta migratoria (Hao et al, 2019) Other peptides with this conserved sequence have been identified in Diptera (Predel et al, 2004; Predel et al, 2010), but their physiological roles remain unclear. PK-producing neurons localized in these ganglia have axons extending to perisympathetic organs, where peptides either act on the nervous system or are released into the hemolymph to exert their actions at peripheral targets (Choi et al, 2001; Hellmich et al, 2014)

Methods

Results

Conclusion