Identification and characterization of a novel 5-hydroxytryptamine receptor in the sea cucumber Apostichopus japonicus (Selenka)

J Exp Zool A Ecol Integr Physiol. 2021 Mar;335(3):367-380. doi: 10.1002/jez.2450. Epub 2021 Mar 2.

Abstract

Serotonin (5-hydroxytryptamine [5-HT]) receptors (5-HTRs) mediate neuroendocrine signaling via interactions with the ligand serotonin (5-HT). The 5-HT signaling system has been well studied in vertebrates, but rarely known in invertebrate animals, especially in the marine invertebrates. In this study, we identified and characterized a novel 5-HTR from the sea cucumber Apostichopus japonicus (Aj5-HT4/6 ). The cloned Aj5-HT4/6 open reading frame comprised 1290 bp and encoded 429 amino acids. Bioinformatic analysis of the receptor indicated that it was a member of the class A of the G protein-coupled receptor family. Further experiments using Aj5-HT4/6 -transfected HEK293 cells demonstrated that treatment with 5-HT could induce rapid internalization of Aj5-HT4/6 fused with enhanced green fluorescent protein from the cell surface into the cytoplasm and triggered a significant increase in levels of the second messenger cAMP as well as mitogen-activated protein kinase phosphorylation in a 5-HT dose-dependent manner. Quantitative real time-polymerase chain reaction demonstrated that Aj5-HT4/6 was predominantly expressed in the muscle and respiratory tree, and its expression was significantly decreased during estivation. Taken together, these results imply that Aj5-HT4/6 is potentially involved in the movement and metabolism of the sea cucumber.

Keywords: Apostichopus japonicus; G protein-coupled receptor; functional interaction; second messenger; serotonin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Gene Expression Regulation
  • HEK293 Cells
  • Humans
  • Models, Molecular
  • Phylogeny
  • Protein Conformation
  • Protein Transport
  • Receptors, Serotonin / chemistry
  • Receptors, Serotonin / genetics
  • Receptors, Serotonin / metabolism*
  • Sea Cucumbers / chemistry
  • Sea Cucumbers / metabolism*

Substances

  • Receptors, Serotonin