45.4 Thursday, Jan. 5 Evolutionary Origin of Gonadotropin-Inhibitory Hormone (GnIH): Isolation, localization and Biological Activity of Lamprey GnIH Ortholog SOWER, Stacia *; OSUGI, Tomohiro; DAUKSS, Dana; GAZDA, Kristen; UBUKA, Takayoshi; KOSUGI, Takayoshi; TSUTSUI, Kazuyoshi; Univ. New Hampshire, Durham, USA; Waseda University, Japan; Univ. New Hampshire, Durham, USA; Univ. New Hampshire, Durham, USA; Waseda University, Japan; Univ. New Hampshire, Durham, USA; Waseda University, Japan email@example.com
Gonadotropin-inhibitory hormone (GnIH) is a novel hypothalamic neuropeptide that regulates pituitary hormone secretion in various vertebrates. GnIH has a LPXRFamide (X = L or Q) motif at the C-terminal that has been identified in representative species of gnathostomes. On the other hand, neuropeptide FF, has a PQRFamide motif at the C-terminal. A controversy exists as to the evolutionary origin of these two peptide groups, i.e., LPXRFamide group and PQRFamide group. In this study, we identified a LPXRFamide peptide orthologous gene in the brain of sea lamprey, the Agnatha, the most ancient vertebrate species. Subsequently, we purified three mature orthologous peptides that all have the PQRFamide motif at the C-termini. In situ hybridization revealed that the lamprey LPXRFamide peptide precursor mRNA was expressed in the bed nucleus of the tract of the postoptic commissure in the hypothalamus. One of the identified lamprey LPXRFamide orthologs stimulated the peptide expression of lamprey GnRH-III in the hypothalamus and mRNA expression of gonadotropin beta in the pituitary. The lamprey GnIH ortholog may thus act as a stimulatory factor on GnRH neurons in the lamprey, an agnathan, unlike in gnathostomes, suggesting the diverse functions of LPXRFamide peptides among vertebrate species. Therefore, we hypothesize that the identified LPXRFamide peptide may be an ancestral form of GnIH. Supported by Grants-in-Aid for Scientific Research, Japan (18107002, 22132004 and 22227002 to K.T.); NSF Grant (IOS-0849569 to SAS, and UNH SURF to K.G. and D.D.) and by NHAES to SAS.