Identification and characterization of the adipokinetic hormone/corazonin-related peptide signaling system in Rhodnius prolixus.

The mammalian gonadotropin-releasing hormone is evolutionarily related to the arthropod adipokinetic hormone and the recently discovered adipokinetic hormone/corazonin-related peptide (ACP). The function of the ACP signaling system in arthropods is currently unknown. In the present study, we identify and characterize the ACP signaling system in the kissing bug Rhodnius prolixus. We isolated the complete cDNA sequence encoding R. prolixus ACP (Rhopr-ACP) and examined its expression pattern. Rhopr-ACP is predominantly expressed in the central nervous system. In particular, it is found in both the brain and corpus cardiacum (CC)/corpora allata (CA) complex. To gain an insight into its role in R. prolixus, we also isolated and functionally characterized cDNA sequences of three splice variants (Rhopr-ACPR-A, B and C) encoding R. prolixus ACP G protein-coupled receptor (Rhopr-ACPR). Rhopr-ACPR-A has only five transmembrane domains, whereas Rhopr-ACPR-B and C have all seven domains. Interestingly, Rhopr-ACPR-A, B and C were all activated by Rhopr-ACP, albeit at different sensitivities, when expressed in Chinese hamster ovary cells stably expressing the human G-protein G16 (CHO/G16). To our knowledge, this is the first study to isolate a truncated receptor cDNA in invertebrates that is functional in a heterologous expression system. Moreover, Rhopr-ACPR-B and C but not Rhopr-ACPR-A can be coupled with Gq α subunits. Expression profiling indicates that Rhopr-ACPR is highly expressed in the central nervous system, as well as the CC/CA complex, suggesting that it may control the release of other hormones found in the CC in a manner analogous to gonadotropin-releasing hormone. Temporal expression profiling shows that both Rhopr-ACP and Rhopr-ACPR are upregulated after ecdysis, suggesting that this neuropeptide may be involved in processes associated with post-ecdysis.

Myoinhibitors controlling oviduct contraction within the female blood-gorging insect, Rhodnius prolixus.

Muscle activity can be regulated by stimulatory and inhibitory neuropeptides allowing for contraction and relaxation. There are various families of neuropeptides that can be classified as inhibitors of insect muscle contraction. This study focuses on Rhodnius prolixus and three neuropeptide families that have been shown to be myoinhibitors in insects: A-type allatostatins, myoinhibiting peptides (B-type allatostatins) and myosuppressins. FGLa/AST-like immunoreactive axons and blebs were found on the anterior of the dorsal vessel and on the abdominal nerves. FGLa/AST-like immunoreactive axons were also seen in the trunk nerves and on the bursa. The effects of RhoprAST-2 (FGLa/AST or A-type allatostatins) and RhoprMIP-4 (MIP/AST or B-type allatostatins) were similar, producing dose-dependent inhibition of R. prolixus spontaneous oviduct contractions with a maximum of 70% inhibition and an EC50 at approximately 10(-8)M. The myosuppressin of R. prolixus (RhoprMS) has an unusual FMRFamide C-terminal motif (pQDIDHVFMRFa) as compared to myosuppressins from other insects. Quantitative PCR results show that the RhoprMS receptor transcript is present in adult female oviducts; however, RhoprMS does not have an inhibitory effect on R. prolixus oviduct contractions, but does have a dose-dependent inhibitory effect on the spontaneous contraction of Locusta migratoria oviducts. SchistoFLRFamide, the myosuppressin of Schistocerca gregaria and L. migratoria, also does not inhibit R. prolixus oviduct contractions. This implies that FGLa/ASTs and MIP/ASTs may play a role in regulating egg movement within the oviducts, and that the myosuppressin although myoinhibitory on other muscles in R. prolixus, does not inhibit the contractions of R. prolixus oviducts and may play another role in the reproductive system.