Abstract

Biogenic amines constitute an important group of neuroactive substances that control and modulate various neural circuits. These small organic compounds engage members of the guanine nucleotide-binding protein coupled receptor (GPCR) superfamily to evoke specific cellular responses. In addition to dopamine- and 5-hydroxytryptamine (serotonin) receptors, arthropods express receptors that are activated exclusively by tyramine and octopamine. These phenolamines functionally substitute the noradrenergic system of vertebrates Octopamine receptors that are the focus of this study are classified as either α- or β-adrenergic-like. Knowledge on these receptors is scarce for the American cockroach (Periplaneta americana). So far, only an α–adrenergic-like octopamine receptor that primarily causes Ca2+ release from intracellular stores has been studied from the cockroach (PaOctα1R). Here we succeeded in cloning a gene from cockroach brain tissue that encodes a β-adrenergic-like receptor and leads to cAMP production upon activation. Notably, the receptor is 100-fold more selective for octopamine than for tyramine. A series of synthetic antagonists selectively block receptor activity with epinastine being the most potent. Bioinformatics allowed us to identify a total of 19 receptor sequences that build the framework of the biogenic amine receptor clade in the American cockroach. Phylogenetic analyses using these sequences and receptor sequences from model organisms showed that the newly cloned gene is an β2-adrenergic-like octopamine receptor. The functional characterization of PaOctβ2R and the bioinformatics data uncovered that the monoaminergic receptor family in the hemimetabolic P. americana is similarly complex as in holometabolic model insects like Drosophila melanogaster and the honeybee, Apis mellifera. Thus, investigating these receptors in detail may contribute to a better understanding of monoaminergic signaling in insect behavior and physiology.

Highlights

  • Biogenic amines play a pivotal role in the regulation of physiology and behavior of most animals

  • We succeeded in cloning the complete cDNA encoding a PaOctβ2R by Polymerase chain reaction (PCR) on single stranded cDNA synthesized on mRNA isolated from adult cockroach brain tissue

  • The hydrophobicity profile according to Kyte and Doolittle [32] and prediction of transmembrane helices using TMHMM Server v.2.0 [33] suggest seven transmembrane (TM) domains (Figure 1A,B), a cognate feature of guanine nucleotide-binding protein coupled receptor (GPCR)

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Summary

Introduction

Biogenic amines play a pivotal role in the regulation of physiology and behavior of most animals. Besides the vinegar fly Drosophila melanogaster and the honeybee (Apis mellifera) as well-established model organisms for investigating the roles of biogenic amines on behavioral plasticity and social behavior [5–9], the cockroach (Periplaneta americana) is well suited as a model to examining the contribution of biogenic amines on physiology and neurobiology as well [10–12]. Both tyramine and octopamine bind to membrane proteins that belong to the superfamily of G protein-coupled receptors (GPCRs). Only two dopamine (PaDOP2A and PaDOP2B [27]) and one 5-hydroxytryptamine (serotonin) receptor (Pa5-HT1 [28]), two tyramine (PaTAR1A [29], PaTAR1B [30]) and one octopamine receptor (PaOctα1R [31]) have been functionally characterized

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