Molecular cloning and functional expression of the 5-HT7 receptor in Chinese mitten crab (Eriocheir sinensis)

Serotonin (5-HT) regulates numerous physiological functions and processes, such as light adaptation, food intake and ovarian maturation, and plays the role through 5-HT receptors. To our knowledge, this is the first study to isolate and characterize the serotonin receptor 7 (5-HT7 receptor) cDNA encoded in Eriocheir sinensis, an economically important aquaculture species in China, by performing rapid-amplification of cDNA ends. The full-length of 5-HT7 receptor gene cDNA is 2328 bp and encodes a polypeptide with 590 amino acids that are highly homologous with other crustaceans 5-HT7 receptor genes. Analysis of the deduced amino acid sequence of the 5-HT7, including 7 transmembrane domains and some common features of G protein-coupled receptors (GPCRs), indicated that 5-HT7 receptor was a member of GPCRs family. A gene expression analysis of the 5-HT7 receptor by RT-PCR revealed that the 5-HT7 receptor transcripts were widely distributed in various tissues, in which high expression levels were observed in the cranial ganglia, thoracic ganglia and intestines. Further study about the effects of photoperiods on the 5-HT7 expression in the tissues showed that a significantly increasing expression of the 5-HT7 receptor was observed in the thoracic ganglia induced by constant light. In addition, in the eyestalks, the expression levels of 5-HT7 mRNA in constant darkness and constant light were lower than control treatment. Then, the expression levels of the 5-HT7 receptor in three feeding statuses displayed that there were significantly increasing expressions in the hepatopancreas and intestines after feeding, compared with before feeding and during the feeding period. Finally, the 5-HT7 mRNA expression levels in stage III and stage IV were higher than the levels in stage I of ovarian development. Our experimental results showed that the 5-HT7 receptor structurally belongs to GPCRs, and the thoracic ganglia and eyestalks are the important tissues of the 5-HT7 receptor for light adaptation. The 5-HT7 receptor may also be involved in the physiological regulation of the hepatopancreas and intestines after ingestion in E. sinensis. In addition, the 5-HT7 receptor is involved in the process of ovarian maturation. The study provided a foundation for further research of light adaptation, digestive functions and ovarian maturation of the 5-HT7 receptor in Decapoda.