Molecular cloning and tissue-specific expression of a gonadotropin-releasing hormone receptor in the Japanese eel

Gonadotropin-releasing hormone (GnRH) is a key regulatory neuropeptide invo lved in the control of reproduction in vertebrates. In the Japanese eel, on e of the most primitive teleost species, two molecular forms of GnRH, mamma lian-type GnRH and chicken-II-type GnRH (cGnRH-II), have been identified. T his study has isolated a full-length cDNA for a GnRH receptor from the pitu itary of the eel. The 3233-bp cDNA encodes a 380-amino acid protein which c ontains seven hydrophobic transmembrane domains and N- and C-terminal regio ns. The exon/intron organization of the open reading frame of the eel GnRH receptor gene was also determined. The open reading frame consists of three exons and two introns. The exon-intron splice site is similar to that of t he GnRH receptor genes of mammals reported so far. Expression of the eel Gn RH receptor was detected in various parts of the brain, pituitary, eye, olf actory epithelium, and testis. This result suggests that GnRH has local fun ctions in these tissues in addition to its actions on gonadotropin synthesi s and release in the pituitary. This tissue-specific expression pattern is similar to that of the eel cGnRH-II. Furthermore, the present eel receptor shows very high amino acid identity with the catfish and goldfish GnRH rece ptors, which are highly selective for the cGnRH-II. These results suggest t hat the cGnRH-II acts through binding to the present receptor in the eel. ( C) 2000 Academic Press.