Abstract
This minireview provides the current status on gonadotropin-releasing hormone receptors (GnRH-R) in vertebrates, from the perspective of a basal vertebrate, the sea lamprey, and provides an evolutionary scheme based on the recent advance of whole genome sequencing. In addition, we provide a perspective on the functional divergence and evolution of the receptors. In this review we use the phylogenetic classification of vertebrate GnRH receptors that groups them into three clusters: type I (mammalian and non-mammalian), type II, and type III GnRH receptors. New findings show that the sea lamprey has two type III-like GnRH receptors and an ancestral type GnRH receptor that is more closely related to the type II-like receptors. These two novel GnRH receptors along with lGnRH-R-1 share similar structural features and amino acid motifs common to other known gnathostome type II/III receptors. Recent data analyses of the lamprey genome provide strong evidence that two whole rounds of genome duplication (2R) occurred prior to the gnathostome-agnathan split. Based on our current knowledge, it is proposed that lGnRH-R-1 evolved from an ancestor of the type II receptor following a vertebrate-shared genome duplication and that the two type III receptors resulted from a duplication within lamprey of a gene derived from a lineage shared by many vertebrates.
Highlights
The study of gonadotropin-releasing hormone (GnRH) receptors in basal and later-evolved vertebrates can provide insight into the evolution and molecular mechanisms of signaling of this receptor family
Based on our current knowledge, it is proposed that lGnRH-R-1 evolved from an ancestor of the type II receptor following a vertebrate-shared genome duplication and that the two type III receptors resulted from a duplication within lamprey of a gene derived from a lineage shared by many vertebrates
On the premise that lGnRH-R-1 evolved from a common ancestor of the type II GnRH receptor, we propose that identification of key motifs can assist in the elucidation of these motifs/residues in terms of evolutionary stringency. lGnRH-R-2 and lGnRH-R3 which likely occurred due to a local gene duplication in the lamprey lineage may provide evidence of plasticity in amino acid residue functionality
Summary
The study of gonadotropin-releasing hormone (GnRH) receptors in basal and later-evolved vertebrates can provide insight into the evolution and molecular mechanisms of signaling of this receptor family. Vertebrate type I GnRH-Rs are represented in teleosts, amphibians, reptiles, and avian species and in mammals. The type II GnRH-Rs include receptors from amphibians, reptiles, and mammals; type II GnRH-Rs are inactivated in most mammals studied to date (Stewart et al, 2009). Unlike the type II GnRH-Rs, the type III GnRH-Rs include sequences from teleost fish, amphibians, reptiles, and avian species but do not occur in mammals. Based on our current knowledge, it is proposed that lGnRH-R-1 evolved from an ancestor of the type II receptor following a vertebrate-shared genome duplication and that the two type III receptors resulted from a duplication within lamprey of a gene derived from a lineage shared by many vertebrates. Lampreys, which express three hypothalamic peptides of GnRH, lamprey GnRH-I, -II, and -III are important to our understanding of the reproductive endocrinology of the first vertebrates and are likely to have retained key characteristics of the ancestral GnRH and GnRH receptor from which modern GnRH isoforms and GnRH receptors arose, as reviewed (Sower et al, 2009)
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