Molecular and functional characterization of somatostatin-type signalling in a deuterostome invertebrate.

Ya Zhang,Maurice R Elphick,Luis Alfonso Yañez Guerra,Michaela Egertová,Cleidiane G Zampronio,Alexandra M Jones

doi:10.1098/rsob.200172

Ya Zhang, Maurice R Elphick + Show 4 more

Open Access

https://doi.org/10.1098/rsob.200172

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Abstract

Somatostatin (SS) and allatostatin-C (ASTC) are structurally and evolutionarily related neuropeptides that act as inhibitory regulators of physiological processes in mammals and insects, respectively. Here, we report the first molecular and functional characterization of SS/ASTC-type signalling in a deuterostome invertebrate—the starfish Asterias rubens (phylum Echinodermata). Two SS/ASTC-type precursors were identified in A. rubens (ArSSP1 and ArSSP2) and the structures of neuropeptides derived from these proteins (ArSS1 and ArSS2) were analysed using mass spectrometry. Pharmacological characterization of three cloned A. rubens SS/ASTC-type receptors (ArSSR1–3) revealed that ArSS2, but not ArSS1, acts as a ligand for all three receptors. Analysis of ArSS2 expression in A. rubens using mRNA in situ hybridization and immunohistochemistry revealed stained cells/fibres in the central nervous system, the digestive system (e.g. cardiac stomach) and the body wall and its appendages (e.g. tube feet). Furthermore, in vitro pharmacological tests revealed that ArSS2 causes dose-dependent relaxation of tube foot and cardiac stomach preparations, while injection of ArSS2 in vivo causes partial eversion of the cardiac stomach. Our findings provide new insights into the molecular evolution of SS/ASTC-type signalling in the animal kingdom and reveal an ancient role of SS-type neuropeptides as inhibitory regulators of muscle contractility.

Highlights

Somatostatin (SS) was first identified as a constituent of rat hypothalamus that inhibits growth hormone release [1] and a constituent of pigeon pancreatic islets that inhibits insulin release [2]
This peptide was identified in samples of extracts that were subjected to reduction and alkylation and the two cysteine residues were modified by carbamidomethylation, as seen in the MS/MS mass spectrum by higher-energy collisional dissociation (HCD) fragmentation
Analysis of A. rubens radial nerve cord extracts using mass spectrometry enabled determination of the mature structure of ArSS2, revealing that it is a 20-residue peptide (RAKNARCMADFWKGRGLVDC) that was identified as a 4+ charged precursor mass 603.55 m/z

Summary

Introduction

Somatostatin (SS) was first identified as a constituent of rat hypothalamus that inhibits growth hormone release [1] and a constituent of pigeon pancreatic islets that inhibits insulin release [2]. An N-terminally extended isoform (SS28) was identified [4], with both SS14 and SS28 being derived from the same precursor protein [5]. Five G-protein-coupled receptors, SSTR1, SSTR2, SSTR3, SSTR4 and SSTR5, mediate effects of SS in mammals as a regulator of a variety of physiological processes [6,7]. In addition to its effects as an inhibitor of hormone release, other actions of SS in mammals include inhibition of pancreatic exocrine secretion [8], regulation of gut motility [8,9] and neuromodulation in the central nervous system [10,11]. Behavioural effects of intracerebroventricular administration of SS in mammals include stimulation of food intake and drinking [12,13] and anxiolysis [14]

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