Organization and expression study of the shrimp (Metapenaeus ensis) putative 5-HT receptor: up-regulation in the brain by 5-HT.

To study the mechanism of 5-HT action and the roles of its receptor in the control of reproduction, we have cloned and characterized the gene and the cDNA of a putative 5-HT receptor (5HT1) from the shrimp, Metapenaeus ensis. The 5HT1 gene is intronless in the coding region but consists of two introns in the 5' untranslated region. 5HT1 transcript is 1.8 kb in size and the cDNA consists of an open reading frame of 1230 bp encoding for a protein of 409 amino acid residues. The deduced 5HT1 consists of the characteristic seven hydrophobic transmembrane (TM1-TM7) domains, which share a high amino acid sequence homology to those of the GPCRs. The results from phylogenetic tree analyses indicate that 5HT1 is more closely related to the octopamine/tyramine of the insect and the 5-HT receptors of the vertebrates than to the other G-protein coupled receptors. Although there is no major difference in the tissues' expression pattern of 5-HT in both sexes, the expression level of 5HT1 is much lower in the females than that in the males. 5HT1 expression in the brain and in the eyestalk is also up-regulated in the 5-HT injected shrimp. By in situ hybridization, no difference in the expression pattern of 5-HT was recorded in the eyestalk of males and females, and the pattern of 5HT1 expression in the eyestalk remained unchanged after 5-HT injection. In the eyestalk, 5HT1 transcripts can be detected in neuronal globuli cells and X-organs. The up-regulation of 5HT1 in the eyestalk and brain may be important for the sustained action in the signal transduction pathway or the regulation of other genes. This may represent an auto-regulation of 5HT1 expression in shrimp by 5-HT. To our knowledge, this is the first demonstration of 5-HT stimulation of a putative 5HT1 gene expression in shrimp.