The aim of this thesis was the study of the origin and evolution of the kisspeptin system, a new actor in the control of reproduction. The analysis of genomes from vertebrate species of key phylogenetical positions allowed us to re-evaluate the diversity of kisspeptins (Kiss) and their receptors (Kissr). From these data, we could propose a new classification of Kiss and Kissr families, based on phylogenetic and syntenic criteria. Moreover, we showed that both Kiss and Kissr diversities resulted from the two whole genomic duplication rounds (1R & 2R) which occurred in the vertebrate ancestors. Gene losses led, then, to the reduction of the numbers of Kiss and Kissr in vertebrates. In particular, these losses suppressed the impact of the teleost-specific 3R on the current gene numbers. The results of this thesis revealed complex evolutionary histories that have resulted in the loss or the conservation of different Kiss and Kissr, according to vertebrate lineages. In order to address the evolutionary mechanisms that may have driven the conservation of multiple Kiss and Kissr in a given organism, we investigated the European eel which presents, as we demonstrated, two Kiss and three Kissr. The study of this model highlighted a new function of kisspeptin system in vertebrates, with the discovery of an in vitro inhibition of LHβ expression by pituitary cells, while a classical stimulatory role could be exerted on GnRH at the brain level. In conclusion, this study contributed to illustrate the complexity of the kisspeptin system in vertebrates, and to clarify the classifications and the evolutionary histories of its components
