Gonadotropin-releasing hormone-like gene in the cephalopod, Sepia pharaonis: characterization, expression analysis, and localization in the brain

Abstract

ABSTRACT Gonadotropin-releasing hormone (GnRH), a decapeptide secreted by hypothalamic neurons, is a key signalling molecule of the hypothalamic–pituitary–gonadal axis for the control of reproduction in vertebrates. In this study, a full-length cDNA of GnRH-like gene from the cuttlefish Sepia pharaonis (denoted as SpGnRH, GenBank Accession NO. QPB69198.1) was cloned, which is 432 bp and the open reading frame (ORF) encodes a protein of 90 aa. Multi-sequence alignment revealed high homology of SpGnRH with GnRH from other cephalopod species: 99%, 91%, 86% and 71% similarity with Sepia lycidas, Sepiella japonica, Uroteuthis edulis and Octopus vulgaris, respectively. Phylogenetic analysis supported the finding that SpGnRH was a new member of the GnRH protein family, which was clustered into a group with octopus, squid, and other cuttlefish species. Tissue distribution analysis revealed that SpGnRH mRNA was highly expressed in the brain at three developmental stages (stage III, stage IV, and stage V). In situ hybridization showed that SpGnRH was localized throughout several different functional brain lobes, suggesting SpGnRH might be involved in physiological regulations such as reproduction and feeding. This study might provide a useful theoretical basis for studying reproductive regulation, genetic resource conservation, and artificial breeding.