Kisspeptins in the brain of the european sea bass

Abstract

Kisspeptins are considered the key players in the neuroendocrine control of puberty and reproduction in mammals. Kiss genes, as well as kiss receptor genes, are present in most classes of vertebrates and derived from an ancestral gene that underwent gene duplication followed by gene losses. In most fish species two kiss genes (kiss1 and kiss2) and two kiss receptor genes (kiss1r and kiss2r) are identified but the organization and the functions of these duplicated systems are still poorly understood. Whit Withthe aim to investigate whether both kiss genes are involved in the neuroendocrine control of reproduction in fish we have characterized the neuroanatomical organization of both systems in zebrafish (Danio rerio, Cyprinodontiform), and the European sea bass (Dicentrarchus labrax), a highly evolved Perciform fish intensively farmed in Southern Europe. We also have investigated whether Kiss neurons have any special relationships with the GnRH neurons and express estrogen receptors. Finally, the nature of the very abundant cells expressing kiss2r was studied using combination of in situ hybridization and immunohistochemistry. The main kiss1 expression site is the habenula, whereas kiss2 mRNA is mostly observed at the lateral recess in both species. No evident sexual dimorphism was observed but an additional kiss1 expressing cells population was reported into the mediobasal hypothalamus in sea bass during the spawning period. In both teleosts, few kiss2 cells of the preoptic region could make synaptic contact with the hypophysiotrophic GnRH neurons. In both species, the kiss population sensible to estrogens is the one placed into the ventral hypothalamus corresponding to a kiss1 cell population in sea bass and to kiss2 expression site in zebrafish. Altogether our findings suggest that kiss2 in zebrafish and kiss1 gene in sea bass would be more likely to participate in the regulation of reproduction through the mediobasal hypothalamus kiss population sensitive to estrogens.