An overview on kisspeptins in European sea bass

Abstract

Kisspeptin 1-10, encoded by the kiss1 gene has emerged as a major actor in the neuroendocrine regulation of the reproductive axis in mammals. Although the existence of two kiss genes (kiss1 and kiss2) and to kiss receptors (kissr1 and kissr2), issued fromearly whole genome duplication events, is well-documented in teleosts, the functions ofkisspeptins are still very unclear in fishes. This is partly due to the existence of several models species, belonging to orders that have diverged evolutionary over a long period of time. This lecture intends to summarize the information that we have obtained in a wellstudied fish model, the European seabass (Dicentrarchuslabrax)a fish of high commercial interest in Europe. In this species, the neuroanatomical distribution of kissneurons has been studied in details showing the widespread distribution in the forebrain, notably in the habenula the preoptic area and the mediobasal hypopthalamus.This expression is subject to changes according to the reproductive activity, which is not surprising as populations of kiss neurons express estrogen receptors. Interestingly, kiss2 fibres exhibit a widespread distribution that overlaps quite well with the distribution of kissr2. Kiss1. The relationships between the kiss systems and the GnRH neurons have received much attention showing that while kissr2are expressed in a variety of neurons, notably in somatostatinergic neurons, none of the GnRH1, GnRH2 or GnRH3 neurons was shown to express kissr2.This result is surprising as there is recent evidence that kiss2-12 given intracerebraly is able to stimulate gonadotrophin release and the expression of gnrh1. These results indicate that kissspeptins probably have a wide spectrum of actions in the brain of teleosts including some indirect actions on the reproductive axis that could involve intermediate neurons, potentially NO synthase expressing cells. On another hand, kiss1 mRNAs and kiss2 fibres are present in the pituitary where direct effects of kisspeptins on gonadotrophin release have been documented.