Looking for the bird Kiss: evolutionary scenario in sauropsids

AbstractBackgroundThe neuropeptide Kiss and its receptor KissR are key-actors in the brain control of reproduction in mammals, where they are responsible for the stimulation of the activity of GnRH neurones. Investigation in other vertebrates revealed up to 3Kissand 4KissRparalogs, originating from the two rounds of whole genome duplication in early vertebrates. In contrast, the absence ofKissandKissRhas been suggested in birds, as no homologs of these genes could be found in current genomic databases. This study aims at addressing the question of the existence, from an evolutionary perspective, of the Kisspeptin system in birds. It provides the first large-scale investigation of the Kisspeptin system in the sauropsid lineage, including ophidian, chelonian, crocodilian, and avian lineages.ResultsSauropsid Kiss and KissR genes were predicted from multiple genome and transcriptome databases by TBLASTN. Phylogenetic and syntenic analyses were performed to classify predicted sauropsid Kiss and KissR genes and to re-construct the evolutionary scenarios of both gene families across the sauropsid radiation.Genome search, phylogenetic and synteny analyses, demonstrated the presence of twoKissgenes (Kiss1andKiss2types) and of twoKissRgenes (KissR1andKissR4types) in the sauropsid lineage. These four genes, also present in the mammalian lineage, would have been inherited from their common amniote ancestor. In contrast, synteny analyses supported that the otherKissandKissRparalogs are missing in sauropsids as in mammals, indicating their absence in the amniote lineage. Among sauropsids, in the avian lineage, we demonstrated the existence of aKiss2-likegene in three bird genomes. The divergence of these avianKiss2-likesequences from those of other vertebrates, as well as their absence in the genomes of some other birds, revealed the processes ofKiss2gene degeneration and loss in the avian lineage.ConclusionThese findings contribute to trace back the evolutionary history of the Kisspeptin system in amniotes and sauropsids, and provide the first molecular evidence of the existence and fate of aKissgene in birds.