title: A novel inhibitory gonadotropin-releasing hormone-related neuropeptide in the ascidian, Ciona intestinalis.
abstract: The gonadotropin-releasing hormone (GnRH) family peptides are most widely distributed neuropeptides and/or neurophysial hormones. GnRH is involved in diverse neuroendocrine, paracrine, autocrine, and neurotransmitter/neuromodulatory functions in the central and peripheral nervous system as well as peripheral tissues. In the present study, we show the identification of a novel GnRH-related peptide, Ci-GnRH-X, in the ascidian, Ciona intestinalis. Intriguingly, Ci-GnRH-X possesses a unique primary sequence consisting of 16 amino acids, although typical GnRH family peptides are composed of 10 amino acids. On the other hand, Ci-GnRH-X shares the GnRH consensus motifs, including the N-terminal pQHWS ('pQ' indicates a pyro-glutamic acid) and C-terminal Gly-amide. Reverse transcription (RT)-PCR analysis shows that the Ci-GnRH-X gene is expressed exclusively in the central nervous system. Moreover, in situ hybridization demonstrated that the Ciona GnRH-1 gene encoding Ciona GnRHs (t-GnRH-3, -5 and -6) was co-expressed with the Ci-GnRH-X gene in neurons of the cerebral ganglion. Of particular interest is that Ci-GnRH-X exhibited moderate (10-50%) inhibitory activity against t-GnRHs at their cognate receptors. Ci-GnRH-X repressed the elevation of the intracellular calcium and cAMP production by t-GnRH-6 at Ci-GnRHR-1, and cAMP production by t-GnRH-3, and t-GnRH-5 via Ci-GnRHR-3 was also inhibited by Ci-GnRH-X. In contrast, no inhibitory effect of Ci-GnRH-X at Ci-GnRHR-2 was observed. The localization and biochemical assays revealed that Ci-GnRH-X acts as an endogenous antagonist for the Ciona GnRHergic system. This is the first molecular and functional characterization of an endogenous inhibitor of GnRHs in an animal species.
authors.affiliation: Suntory Institute for Bioorganic Research, Mishima-gun, Osaka 618-8503, Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Kawada
authors.forename: Masato
authors.initials: M
authors.lastname: Aoyama
authors.forename: Iyo
authors.initials: I
authors.lastname: Okada
authors.forename: Tsubasa
authors.initials: T
authors.lastname: Sakai
authors.forename: Toshio
authors.initials: T
authors.lastname: Sekiguchi
authors.forename: Michio
authors.initials: M
authors.lastname: Ogasawara
authors.forename: Honoo
authors.initials: H
authors.lastname: Satake
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002938:Ciona intestinalis / Q000235:genetics / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D005786:Gene Expression Regulation; D007987:Gonadotropin-Releasing Hormone / Q000037:antagonists & inhibitors*; D006801:Humans; D017403:In Situ Hybridization; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009479:Neuropeptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D009479:Neuropeptides; D007987:Gonadotropin-Releasing Hormone; D000242:Cyclic AMP; D002118:Calcium