Abstract
SIFamides are a family of highly conserved neuropeptides in arthropods, and in insects are mainly expressed in four medial neurons in the pars intercerebralis of the brain. Although SIFamide has been shown to influence sexual behavior, feeding, and sleep regulation in holometabolous insects such as Drosophila melanogaster, little is known about its role in hemimetabolous insects, including the blood-sucking bug, Rhodnius prolixus. In this study, we confirm the nucleotide sequence for R. prolixus SIFamide (Rhopr-SIFa) and find characteristic phenotypic expression of SIFamide in four cells of the pars intercerebralis in the brain. In addition to extensive SIFa projections throughout the entire central nervous system, SIFamidergic processes also enter into the corpus cardiacum, and project along the dorsal vessel, suggestive of Rhopr-SIFa acting as a neurohormone. Physiologically, Rhopr-SIFamide induces dose-dependent increases in heartbeat frequency in vitro suggesting the presence of peripheral receptors, and thereby indicating Rhopr-SIFa is released to act upon peripheral targets. We also explore the function of Rhopr-SIFa in R. prolixus, specifically in relation to feeding, since R. prolixus is a blood-gorging insect and a vector for Chagas disease. The intensity of SIFamide-like staining in the neurons in the brain is diminished 2 h following feeding, and restocking of those cells is finished 24 h later, indicating Rhopr-SIFa may be released at feeding. The results of temporal qPCR analysis were consistent with the immunohistochemical findings, showing an increase in Rhopr-SIFa transcript expression in the brain 2 h after feeding. We also observed enhanced feeding (size of meal) in insects injected with Rhopr-SIFa whereas insects with RNAi-mediated knockdown of the Rhopr-SIFa transcript consumed a significantly smaller blood meal relative to controls. These data suggest that the four SIFamidergic neurons and associated arborizations may play an important function in the neuronal circuitry controlling R. prolixus feeding, with Rhopr-SIFa acting as a central and peripheral neuromodulator/neurohormone.
Highlights
Neuropeptides constitute a functionally diverse class of neuroactive chemicals responsible for regulating physiological processes and behaviors such as ecdysis, reproduction, and feeding (Nässel, 2002; Nässel and Zandawala, 2019)
We have sequenced 608 base pairs of Rhopr-SIFa complementary DNA (cDNA), where the open reading frame (ORF) starts at base 171, and ends at base 393, yielding a prepropeptide consisting of 74 amino acids
The aim of this study was to investigate the possible role of Rhopr-SIFa, a member of a highly conserved family, in feeding in R. prolixus
Summary
Neuropeptides constitute a functionally diverse class of neuroactive chemicals responsible for regulating physiological processes and behaviors such as ecdysis, reproduction, and feeding (Nässel, 2002; Nässel and Zandawala, 2019). An interesting family of neuropeptides that contribute to flexibility and diversity in physiological and behavioral regulation is the SIFamide family. SIFamide Influences Feeding in Rhodnius identified in the gray fleshfly Neobellieria bullata, SIFamides have since been observed across arthropods, including the malaria mosquito Anopheles gambiae, the beetle Agelastica alni, the moth Galleria mellonella, the honeybee Apis mellifera, the giant tiger prawn Penaeus monodon, the Jonah crab Cancer borealis and the red swamp crayfish Procambarus clarkii (Janssen et al, 1996; Sithigorngul et al, 2002; Huybrechts et al, 2003; Verleyen et al, 2004; Yasuda et al, 2004). The presence of the peptide family has been reported in the nervous system of the desert locust Schistocerca gregaria (Gellerer et al, 2015) and in the kissing bug, Rhodnius prolixus (Ons et al, 2009)
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