Prevertebrate local gene duplication facilitated expansion of the neuropeptide GPCR superfamily

In humans, numerous genes encode neuropeptides that comprise a superfamily of more than 70 genes in approximately 30 families and act mainly through rhodopsin-like G protein-coupled receptors (GPCRs). Two rounds of whole-genome duplication (2R WGD) during early vertebrate evolution greatly contributed to proliferation within gene families; however, the mechanisms underlying the initial emergence and diversification of these gene families before 2R WGD are largely unknown. In this study, we analyzed 25 vertebrate rhodopsin-like neuropeptide GPCR families and their cognate peptides using phylogeny, synteny, and localization of these genes on reconstructed vertebrate ancestral chromosomes (VACs). Based on phylogeny, these GPCR families can be divided into five distinct clades, and members of each clade tend to be located on the same VACs. Similarly, their neuropeptide gene families also tend to reside on distinct VACs. Comparison of these GPCR genes with those of invertebrates including Drosophila melanogaster, Caenorhabditis elegans, Branchiostoma floridae, and Ciona intestinalis indicates that these GPCR families emerged through tandem local duplication during metazoan evolution prior to 2R WGD. Our study describes a presumptive evolutionary mechanism and development pathway of the vertebrate rhodopsin-like GPCR and cognate neuropeptide families from the urbilaterian ancestor to modern vertebrates.