Corticotropin-releasing hormone family evolution: five ancestral genes remain in some lineages.

The evolution of the peptide family consisting of corticotropin-releasing hormone (CRH) and the three urocortins (UCN1-3) has been puzzling due to uneven evolutionary rates. Distinct gene duplication scenarios have been proposed in relation to the two basal rounds of vertebrate genome doubling (2R) and the teleost fish-specific genome doubling (3R). By analyses of sequences and chromosomal regions, including many neighboring gene families, we show here that the vertebrate progenitor had two peptide genes that served as the founders of separate subfamilies. Then, 2R resulted in a total of five members: one subfamily consists of CRH1, CRH2, and UCN1. The other subfamily contains UCN2 and UCN3. All five peptide genes are present in the slowly evolving genomes of the coelacanth Latimeria chalumnae (a lobe-finned fish), the spotted gar Lepisosteus oculatus (a basal ray-finned fish), and the elephant shark Callorhinchus milii (a cartilaginous fish). The CRH2 gene has been lost independently in placental mammals and in teleost fish, but is present in birds (except chicken), anole lizard, and the nonplacental mammals platypus and opossum. Teleost 3R resulted in an additional surviving duplicate only for crh1 in some teleosts including zebrafish (crh1a and crh1b). We have previously reported that the two vertebrate CRH/UCN receptors arose in 2R and that CRHR1 was duplicated in 3R. Thus, we can now conclude that this peptide-receptor system was quite complex in the ancestor of the jawed vertebrates with five CRH/UCN peptides and two receptors, and that crh and crhr1 were duplicated in the teleost fish tetraploidization.

New insights into the evolution of vertebrate CRH (corticotropin-releasing hormone) and invertebrate DH44 (diuretic hormone 44) receptors in metazoans.

The corticotropin releasing hormone receptors (CRHR) and the arthropod diuretic hormone 44 receptors (DH44R) are structurally and functionally related members of the G protein-coupled receptors (GPCR) of the secretin-like receptor superfamily. We show here that they derive from a bilaterian predecessor. In protostomes, the receptor became DH44R that has been identified and functionally characterised in several arthropods but the gene seems to be absent from nematode genomes. Duplicate DH44R genes (DH44 R1 and DH44R2) have been described in some arthropods resulting from lineage-specific duplications. Recently, CRHR-DH44R-like receptors have been identified in the genomes of some lophotrochozoans (molluscs, which have a lineage-specific gene duplication, and annelids) as well as representatives of early diverging deuterostomes. Vertebrates have previously been reported to have two CRHR receptors that were named CRHR1 and CRHR2. To resolve their origin we have analysed recently assembled genomes from representatives of early vertebrate divergencies including elephant shark, spotted gar and coelacanth. We show here by analysis of synteny conservation that the two CRHR genes arose from a common ancestral gene in the early vertebrate tetraploidizations (2R) approximately 500 million years ago. Subsequently, the teleost-specific tetraploidization (3R) resulted in a duplicate of CRHR1 that has been lost in some teleost lineages. These results help distinguish orthology and paralogy relationships and will allow studies of functional conservation and changes during evolution of the individual members of the receptor family and their multiple native peptide agonists.

Evolution of complementary peptide systems: teneurin C-terminal-associated peptides and corticotropin-releasing factor superfamilies.

In chordates, the corticotropin-releasing factor (CRF) family of peptides consists of four paralogous lineages that include CRF, urocortin/urotensin-I, urocortin 2, and urocortin 3. Related to the CRF peptide family is the diuretic hormone family found in insects. This family consists of a number of paralogous lineages within the Insecta. The teneurin C-terminal-associated peptides (TCAP) are a recently described family of peptides with evolutionary origins around the same time as the CRF family. This family consists of four independent lineages in chordates that are orthologous to peptides in the Insecta. Like CRF, the peptides are 40 or 41 amino acids in length and share about 20% sequence identity to the CRF family members. Each of the four TCAP peptides is encoded by an exon that is closely associated with the teneurin gene. Recent studies indicate that TCAP can block CRF-mediated c-fos expression in the brain and modulate CRF-mediated behaviors. Thus, the TCAP family may act, in part, to modulate the physiological actions of the CRF family.

Physiology, pharmacology, and therapeutic relevance of urocortins in mammals: ancient CRF paralogs.

Urocortins, three paralogs of the stress-related peptide corticotropin-releasing factor (CRF) found in bony fish, amphibians, birds, and mammals, have unique phylogenies, pharmacologies, and tissue distributions. As a result and despite a structural family resemblance, the natural functions of urocortins and CRF in mammalian homeostatic responses differ substantially. Endogenous urocortins are neither simply counterpoints nor mimics of endogenous CRF action. In their own right, urocortins may be clinically relevant molecules in the pathogenesis or management of many conditions, including congestive heart failure, hypertension, gastrointestinal and inflammatory disorders (irritable bowel syndrome, active gastritis, gastroparesis, and rheumatoid arthritis), atopic/allergic disorders (dermatitis, urticaria, and asthma), pregnancy and parturition (preeclampsia, spontaneous abortion, onset, and maintenance of effective labor), major depression and obesity. Safety trials for intravenous urocortin treatment have already begun for the treatment of congestive heart failure. Further understanding the unique functions of urocortin 1, urocortin 2, and urocortin 3 action may uncover other therapeutic opportunities.

Structural characterisation of a cyprinid (Cyprinus carpio L.) CRH, CRH-BP and CRH-R1, and the role of these proteins in the acute stress response.

We elucidated the structure of the principle factors regulating the initiation of the acute stress response in common carp: corticotrophin-releasing hormone (CRH), CRH-receptor 1 (CRH-R1) and CRH-binding protein (CRH-BP). Phylogenetic analyses reveal that these proteins are evolutionarily well conserved in vertebrates. CRH and CRH-BP expression are not co-localised in the same hypothalamic perikarya. On the contrary, CRH-BP expression is limited to the perimeter of the nucleus preopticus (NPO), but is abundant in other regions, including an area directly rostral from, and in close proximity to, the NPO. Despite the lack of co-expression, the nerve fibres projecting onto both the rostral pars distalis (rPD) as well as the large fibre bundles projecting onto the pars intermedia (PI) contain CRH as well as CRH-BP, suggesting that both ACTH release from the rPD as well as the release of PI melanotrope content is regulated via CRH and CRH-BP. Finally, we show via real-time quantitative PCR that expression of hypothalamic CRH and CRH-BP following a 24 h restraint significantly increases, whereas PD CRH-R1 expression decreases; this reflects desensitisation of the PD for hypothalamic CRH output. We conclude that these factors are actively involved in the regulation of acute stress responses in the teleost fish.

Corticotropin-releasing factor (CRF) can directly affect brain microvessel endothelial cells.

Stress activates the hypothalamic-pituitary-adrenal (HPA) axis through release of corticotropin releasing factor (CRF), leading to production of glucocorticoids that down regulate immune responses. However, acute stress via CRF also has pro-inflammatory effects. We previously showed that acute stress increases rat blood-brain barrier (BBB) permeability, an effect involving brain mast cells and CRF, as it was absent in W/W(v) mast cell-deficient mice and was blocked by the CRF-receptor antagonist, Antalarmin. We investigated if CRF could also have a direct action on brain microvessel endothelial cells (BMEC) isolated from rat and bovine brain. BMEC were cultured and identified by electron microscopy. Western blot analysis of cultured BMEC identified CRF receptor protein; stimulation with CRF, or it structural analogue urocortin (Ucn) showed that the receptor is functionally coupled to adenylate cyclase as it increased cyclic AMP (cAMP) levels by 2-fold. These findings suggest that CRF could affect BMEC structure or function, as reported for increased cAMP levels by other studies. It is, therefore, possible that CRF may directly regulate BBB permeability, in addition to any effect mediated via brain mast cells.