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

• Published in: Journal of experimental zoology. Part A, Ecological and integrative physiology Ecological and integrative physiology, 2021-03, Vol.335 (3), p.367-380
• Main Authors: Zhang, Bing, Yang, Jing‐Wen, Han, Tao, Huang, De‐Xiang, Zhao, Zi‐Hao, Feng, Jia‐Qian, Zhou, Nai‐Ming, Xie, Hong‐Qing, Wang, Tian‐Ming
• Format: Article
• Language: English
• Subjects: Apostichopus japonicus; functional interaction; G protein‐coupled receptor; second messenger; serotonin
• ISSN: 2471-5638; 2471-5646
• DOI: 10.1002/jez.2450

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. Apostichopus japonicus 5‐HT4/6 receptor mediated Gs coupled signaling pathway. Research Highlights A novel 5‐hydroxytryptamine receptor (5‐HTR) (Aj5‐HT4/6) was identified in sea cucumber with 1290 bp open reading frame. The bioinformatic and pharmacological analyses indicated that Aj5‐HT4/6 was Gs protein coupled GPCR and classified into 5‐HTR class 4 or 6 family. The transcriptional investigation of Aj5‐HT4/6 suggested its functional involvement in the movement and metabolism.