Hagfish, Genome Duplications, and RFamide Neuropeptide Evolution

Superconserved receptors expressed in the brain: Expression, function, motifs and evolution of an orphan receptor family

GPR27, GPR85 and GPR173 constitute a small family of G protein-coupled receptors (GPCR) that share the distinctive characteristics of being highly conserved throughout vertebrate evolution and predominantly expressed in the brain. Accordingly, they have been coined as "Superconserved Receptors Expressed in the Brain" (SREB), although their expression profile is more complex than what was originally thought. SREBs have no known validated endogenous ligands and are thus labeled as "orphan" receptors. The investigation of this particular category of uncharacterized receptors holds great promise both in terms of physiology and drug development. In the largest GPCR family, the Rhodopsin-like or Class A, around 100 receptors are considered orphans. Because GPCRs are the most successful source of drug targets, the discovery of a novel function or ligand most likely will lead to significant breakthroughs for the discovery of innovative therapies. The high level of conservation is one of the characteristic features of the SREBs. We propose herein a detailed analysis of the putative evolutionary origin of this family. We highlight the properties that distinguish SREBs from other rhodopsin-like GPCRs. We present the current evidence for these receptors downstream signaling pathways and functions. We discuss the pharmacological challenge for the identification of natural or synthetic ligands of orphan receptors like SREBs. The different SREB-related scientific questions are presented with a highlight on what should be addressed in the near future, including the confirmation of published evidence and their validation as drug targets. In particular, we discuss in which pathological conditions these receptors may be of great relevance to solve unmet medical needs.

The evolutionary appearance of signaling motifs in PGRMC1

A complex PGRMC1-centred regulatory system controls multiple cell functions. Although PGRMC1 is phosphorylated at several positions, we do not understand the mechanisms regulating its function. PGRMC1 is the archetypal member of the membrane associated progesterone receptor (MAPR) family. Phylogentic comparison of MAPR proteins suggests that the ancestral metazoan "PGRMC-like" MAPR gene resembled PGRMC1/PGRMC2, containing the equivalents of PGRMC1 Y139 and Y180 SH2 target motifs. It later acquired a CK2 site with phosphoacceptor at S181. Separate PGRMC1 and PGRMC2 genes with this "PGRMC-like" structure diverged after the separation of vertebrates from protochordates. Terrestrial tetrapods possess a novel proline-rich PGRMC1 SH3 target motif centred on P64 which in mammals is augmented by a phosphoacceptor at PGRMC1 S54, and in primates by an additional S57 CK2 site. All of these phosphoacceptors are phosphorylated in vivo. This study suggests that an increasingly sophisticated system of PGRMC1-modulated multicellular functional regulation has characterised animal evolution since Precambrian times.

The vertebrate RCAN gene family: novel insights into evolution, structure and regulation

Recently there has been much interest in the Regulators of Calcineurin (RCAN) proteins which are important endogenous modulators of the calcineurin-NFATc signalling pathway. They have been shown to have a crucial role in cellular programmes such as the immune response, muscle fibre remodelling and memory, but also in pathological processes such as cardiac hypertrophy and neurodegenerative diseases. In vertebrates, the RCAN family form a functional subfamily of three members RCAN1, RCAN2 and RCAN3 whereas only one RCAN is present in the rest of Eukarya. In addition, RCAN genes have been shown to collocate with RUNX and CLIC genes in ACD clusters (ACD21, ACD6 and ACD1). How the RCAN genes and their clustering in ACDs evolved is still unknown. After analysing RCAN gene family evolution using bioinformatic tools, we propose that the three RCAN vertebrate genes within the ACD clusters, which evolved from single copy genes present in invertebrates and lower eukaryotes, are the result of two rounds of whole genome duplication, followed by a segmental duplication. This evolutionary scenario involves the loss or gain of some RCAN genes during evolution. In addition, we have analysed RCAN gene structure and identified the existence of several characteristic features that can be involved in RCAN evolution and gene expression regulation. These included: several transposable elements, CpG islands in the 5′ region of the genes, the existence of antisense transcripts (NAT) associated with the three human genes, and considerable evidence for bidirectional promoters that regulate RCAN gene expression. Furthermore, we show that the CpG island associated with the RCAN3 gene promoter is unmethylated and transcriptionally active. All these results provide timely new insights into the molecular mechanisms underlying RCAN function and a more in depth knowledge of this gene family whose members are obvious candidates for the development of future therapies.

Insight from the lamprey genome: glimpsing early vertebrate development via neuroendocrine-associated genes and shared synteny of gonadotropin-releasing hormone (GnRH)

Study of the ancient lineage of jawless vertebrates is key to understanding the origins of vertebrate biology. The establishment of the neuroendocrine system with the hypothalamic-pituitary axis at its crux is of particular interest. Key neuroendocrine hormones in this system include the pivotal gonadotropin-releasing hormones (GnRHs) responsible for controlling reproduction via the pituitary. Previous data incorporating several lines of evidence showed all known vertebrate GnRHs were grouped into four paralogous lineages: GnRH1, 2, 3 and 4; with proposed evolutionary paths. Using the currently available lamprey genome assembly, we searched genes of the neuroendocrine system and summarize here the details representing the state of the current lamprey genome assembly. Additionally, we have analyzed in greater detail the evolutionary history of the GnRHs based on the information of the genomic neighborhood of the paralogs in lamprey as compared to other gnathostomes. Significantly, the current evidence suggests that two genome duplication events (both 1R and 2R) that generated the different fish and tetrapod paralogs took place before the divergence of the ancestral agnathans and gnathostome lineages. Syntenic analysis supports this evidence in that the previously-classified type IV GnRHs in lamprey (lGnRH-I and -III) share a common ancestry with GnRH2 and 3, and thus are no longer considered type IV GnRHs. Given the single amino acid difference between lGnRH-II and GnRH2 we propose that a GnRH2-like gene existed before the lamprey/gnathostome split giving rise to lGnRH-II and GnRH2. Furthermore, paralogous type 3 genes (lGnRH-I/III and GnRH3) evolved divergent structure/function in lamprey and gnathostome lineages.

Evolution of vertebrate GnRH receptors from the perspective of a Basal vertebrate

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.