Since the discovery of KISS/GPR54 pair in mammals, distinct kisspeptin forms have been reported in non-mammalian vertebrates, including reptilian, amphibian and fish. There is also evidence that multiple forms of kisspeptin receptors, up to four GPR54 paralogs, appear to exist in vertebrates. In this context, placental mammals (human and opossum) and reptiles possess one form of ligand and kisspeptin receptor whereas two distinct kisspeptin genes exist in mammalian monotremes, such as platypus, and non-mammalian vertebrates such as several teleost fish. Presently among bony fish only the medaka, zebrafish, goldfish and sea bass have two forms of kisspeptin and gpr54 genes whereas other fish species possess one form of ligand and kisspeptin receptor. In the case of amphibians, three forms of kisspeptin and receptor genes have been identified. Noteworthy, kiss1 and kiss2 share only 7-16% identity in the amino acid sequences in vertebrates, whereas the sequences of gpr54 show higher percent amino acid identity. It is worth pointing out that these genes possess conserved structural organization, suggesting that ligands and receptors originated each gene from a common ancentral form. In support of this hypothesis, mapping of kiss and gpr54 genes have revealed conserved synteny within each gene across species. Recent data have also evidenced that when more than two genes co-exist in a same species, genes are located in different chromosomes. To date, results obtained in fish evidence the significance of this neuroendrocrine system in reproduction. In Dicentrarchus labrax, current research interests are focused on neuroanatomical localization, tissue distribution and gene expression of kisspeptin system in parallel with studies related to characterization of ligand selectivity of receptors, kisspeptin signalling and steroid regulation in the brain.

Trabajo presentado en el 8º Congreso de la Asociación Ibérica de Endocrinología Comparada celebrado en Madrid (España) del 5 al 7 septiembre 2011