Gonadotropin-releasing hormones (GnRHs) in a primitive teleost, the arowana: Phylogenetic evidence that three paralogous lineages of GnRH occurred prior to the emergence of teleosts

Multiple molecular forms of gonadotropin-releasing hormone (GnRH) are prese nt in a single vertebrate species. To extend the knowledge on GnRH evolutio n and the number of GnRH forms in one organism, GnRH cDNAs have been isolat ed and characterized from one of the most primitive teleosts, the arowana S cleropages jardini. This species had two molecular forms of GnRH: salmon-ty pe GnRH (sGnRH) and chicken-II-type GnRH (cGnRH-II). Sequence comparison be tween the prepro-GnRHs of the arowana and those of other teleosts indicated that sGnRH represented a paralogue separate from any other forms of GnRH. Consistently, subsequent phylogenetic analysis showed that known forms of G nRH in teleosts fell into three paralogous lineages: sGnRH alone on one lin eage, cGnRH-II on another, and many other forms on the other. These results suggest that an ancestral GnRH gene duplicated twice prior to the emergenc e of teleosts and, therefore, that teleosts, and probably also tetrapods, w ould possess three paralogous forms of GnRH in individual brains. (C) 2001 Academic Press.