Evidence for two kisspeptins in vertebrate non-mammalian species: a particular study of KiSS-1 system in the European sea bass, Dicentrarchus labrax

Resumen del trabajo presentado en la 1st World Conference on Kisspeptin Signaling in the Brain, celebrada en Córdoba (España), del 8 al 10 de octubre de 2008The physiological relevance of the KiSS-1 system has revolutionized the reproduction area in vertebrates. Despite remarkable data in mammals, little information of this system exists in non-mammalian species. Evidence for KiSS-1 cDNA sequences has been recently described in some fish species and Xenopus. Here, we present a study focused in a teleost fish, the sea bass, an important marine aquacultured species. We report the cloning, tissue expression, and functional activity of two KiSS-1-like genes in this species. To amplify fragments of sea bass KiSS-1, degenerate PCR primers were designed based on 12 conserved amino acids including the kisspeptin-10 sequence from Fugu, medaka and zebrafish genes. PCR amplifications were performed using a genome walking approach and the complete cDNAs were obtained from a sea bass brain cDNA library. Sequencing analyses evidenced that two KiSS-1-like genes exist in sea bass, each containing 2 coding exons with open reading frames of 309 and 366 nucleotides. Their sequence is highly divergent, except for the kisspeptin-10 region. Based on those 10 conserved amino acids, one of the genes was predicted as a mammalian form and was named as sea bass KiSS-1, whereas the other is a non-mammalian form and was named KiSS-2. Searches in different genome databases showed that both genes are also present in other vertebrate non-mammalian species. Phylogenetic and genome mapping analyses suggest that KiSS-1 and KiSS-2 exist since early in vertebrate evolution, although KiSS-2 is lost in mammals. Expression patterns of both genes showed a marked expression in the brain and gonadal tissues of pubertal sea bass, medaka and zebrafish, although expression in other tissues was also observed. In prepubertal male and female sea bass, both genes are expressed in the brain, testis and ovary. During the reproductive season of sea bass, temporal tissue expression of both genes in the brain and gonadal tissues showed a lack of any developmental stage or sex-specificity. Finally, we examined the effect of intramuscular administration of the two kisspeptins on circulating luteininzing hormone (LH) and follicle-stimulating hormone (FSH) in prepubertal sea bass. Results evidenced that both kisspeptins stimulated LH and FSH secretion, although KiSS-2 showed a more noticeable response in the activation of gonadotropin secretion in comparison to KiSS-1. The different stimulatory action of both kisspeptins is under investigation to elucidate a potential diverse functional role in fish compared to that in mammals.Funded by GV06/268 to A.G. A.F. supported by a Ramón y Cajal contract from MEC of Spain