Isolation and primary structure of urotensin II from the brain of a tetrapod, the frog Rana ridibunda

Urotensin II-related peptides, Urp1 and Urp2, control zebrafish spine morphology

The spine provides structure and support to the body, yet how it develops its characteristic morphology as the organism grows is little understood. This is underscored by the commonality of conditions in which the spine curves abnormally such as scoliosis, kyphosis, and lordosis. Understanding the origin of these spinal curves has been challenging in part due to the lack of appropriate animal models. Recently, zebrafish have emerged as promising tools with which to understand the origin of spinal curves. Using zebrafish, we demonstrate that the urotensin II-related peptides (URPs), Urp1 and Urp2, are essential for maintaining spine morphology. Urp1 and Urp2 are 10-amino acid cyclic peptides expressed by neurons lining the central canal of the spinal cord. Upon combined genetic loss of Urp1 and Urp2, adolescent-onset planar curves manifested in the caudal region of the spine. Highly similar curves were caused by mutation of Uts2r3, an URP receptor. Quantitative comparisons revealed that urotensin-associated curves were distinct from other zebrafish spinal curve mutants in curve position and direction. Last, we found that the Reissner fiber, a proteinaceous thread that sits in the central canal and has been implicated in the control of spine morphology, breaks down prior to curve formation in mutants with perturbed cilia motility but was unaffected by loss of Uts2r3. This suggests a Reissner fiber-independent mechanism of curvature in urotensin-deficient mutants. Overall, our results show that Urp1 and Urp2 control zebrafish spine morphology and establish new animal models of spine deformity.

Zebrafish: an important model for understanding scoliosis

Scoliosis is a common spinal deformity that considerably affects the physical and psychological health of patients. Studies have shown that genetic factors play an important role in scoliosis. However, its etiopathogenesis remain unclear, partially because of the genetic heterogeneity of scoliosis and the lack of appropriate model systems. Recently, the development of efficient gene editing methods and high-throughput sequencing technology has made it possible to explore the underlying pathological mechanisms of scoliosis. Owing to their susceptibility for developing scoliosis and high genetic homology with human, zebrafish are increasingly being used as a model for scoliosis in developmental biology, genetics, and clinical medicine. Here, we summarize the recent advances in scoliosis research on zebrafish and discuss the prospects of using zebrafish as a scoliosis model.

Characterization of four urotensin II receptors (UTS2Rs) in chickens

Urotensin II receptor (UTS2R) is suggested to mediate the actions of urotensin II (UTS2) and UTS2-related peptide (URP, also called UTS2B) in mammals. However, the information regarding the gene structure, functionality and tissue expression of UTS2/URP receptor remains largely unknown in non-mammalian vertebrates including birds. In this study, using RACE-PCR, we cloned the full-length cDNAs of four chicken UTS2/URP receptors and designated them as cUTS2R1, cUTS2R2, cUTS2R3 and cUTS2R5 respectively, according to their evolutionary origin. The cloned cUTS2R1, cUTS2R2, cUTS2R3 and cUTS2R5 are predicted to encode 7-transmembrane receptors of 382, 343, 331 and 363 amino acids respectively, which show 50-66 % amino acid sequence identity with human UTS2R. Using cell-based luciferase reporter assays and Western blot, we demonstrated that chicken UTS2Rs expressed in HEK293 cells could be effectively activated by synthetic chicken UTS2-12, UTS2-17 and URP peptides, and their activation can elevate intracellular calcium concentration and activate MAPK/ERK signaling cascade, indicating that the four UTS2Rs are functional and capable of mediating UTS2/URP actions in chickens. Quantitative real-time PCR revealed that the four receptors are widely, but differentially, expressed in adult chicken tissues, while cUTS2 and cURP are highly expressed in the hindbrain and spinal cord, and moderately/weakly expressed in other tissues examined including the spleen and gonads. Taken together, our data provide first piece of evidence that all four UTS2Rs are functional in an avian species and help to reveal the conserved roles of UTS2R signaling across vertebrates.

Identification and signaling characterization of four urotensin II receptor subtypes in the western clawed frog, Xenopus tropicalis

Urotensin II (UII) is involved, via the UII receptor (UTR), in many physiological and pathological processes, including vasoconstriction, locomotion, osmoregulation, immune response, and metabolic syndrome. In silico studies have revealed the presence of four or five distinct UTR (UTR1-UTR5) gene sequences in nonmammalian vertebrates. However, the functionality of these receptor subtypes and their associations to signaling pathways are unclear. In this study, full-length cDNAs encoding four distinct UTR subtypes (UTR1, UTR3, UTR4, and UTR5) were isolated from the western clawed frog (Xenopus tropicalis). In functional analyses, homologous Xenopus UII stimulation of cells expressing UTR1 or UTR5 induced intracellular calcoum mobilization and phosphorylation of extracellular signal-regulated kinase 1/2. Cells expressing UTR3 or UTR4 did not show this response. Furthermore, UII induced the phosphorylation of cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) through the UII-UTR1/5 system. However, intracellular cAMP accumulation was not observed, suggesting that UII-induced CREB phosphorylation is caused by a signaling pathway different from that involving Gs protein. In contrast, the administration of UII to cells increased the phosphorylation of guanine nucleotide exchange factor-H1 (GEF-H1) and myosin light chain 2 (MLC2) in all UTR subtypes. These results define four distinct UTR functional subtypes and are consistent with the molecular evolution of UTR subtypes in vertebrates. Further understanding of signaling properties associated with UTR subtypes may help in clarifying the functional roles associated with UII-UTR interactions in nonmammalian vertebrates.

Nitric Oxide and the Neuroendocrine Control of the Osmotic Stress Response in Teleosts

The involvement of nitric oxide (NO) in the modulation of teleost osmoresponsive circuits is suggested by the facts that NO synthase enzymes are expressed in the neurosecretory systems and may be regulated by osmotic stimuli. The present paper is an overview on the research suggesting a role for NO in the central modulation of hormone release in the hypothalamo-neurohypophysial and the caudal neurosecretory systems of teleosts during the osmotic stress response. Active NOS enzymes are constitutively expressed by the magnocellular and parvocellular hypophysiotropic neurons and the caudal neurosecretory neurons of teleosts. Moreover, their expression may be regulated in response to the osmotic challenge. Available data suggests that the regulatory role of NO appeared early during vertebrate phylogeny and the neuroendocrine modulation by NO is conservative. Nonetheless, NO seems to have opposite effects in fish compared to mammals. Indeed, NO exerts excitatory effects on the electrical activity of the caudal neurosecretory neurons, influencing the amount of peptides released from the urophysis, while it inhibits hormone release from the magnocellular neurons in mammals.

Natural and synthetic peptides in the cardiovascular diseases: An update on diagnostic and therapeutic potentials

Several peptides play an important role in physiological and pathological conditions into the cardiovascular system. In addition to well-known vasoactive agents such as angiotensin II, endothelin, serotonin or natriuretic peptides, the vasoconstrictor Urotensin-II (Uro-II) and the vasodilators Urocortins (UCNs) and Adrenomedullin (AM) have been implicated in the control of vascular tone and blood pressure as well as in cardiovascular disease states including congestive heart failure, atherosclerosis, coronary artery disease, and pulmonary and systemic hypertension. Therefore these peptides, together with their receptors, become important therapeutic targets in cardiovascular diseases (CVDs). Circulating levels of these agents in the blood are markedly modified in patients with specific CVDs compared with those in healthy patients, becoming also potential biomarkers for these pathologies. This review will provide an overview of current knowledge about the physiological roles of Uro-II, UCN and AM in the cardiovascular system and their implications in cardiovascular diseases. It will further focus on the structural modifications carried out on original peptide sequences in the search of analogues with improved physiochemical properties as well as in the delivery methods. Finally, we have overviewed the possible application of these peptides and/or their precursors as biomarkers of CVDs.

The G Protein-Coupled Receptor UT of the Neuropeptide Urotensin II Displays Structural and Functional Chemokine Features

The urotensinergic system was previously considered as being linked to numerous physiopathological states, including atherosclerosis, heart failure, hypertension, pre-eclampsia, diabetes, renal disease, as well as brain vascular lesions. Thus, it turns out that the actions of the urotensin II (UII)/G protein-coupled receptor UT system in animal models are currently not predictive enough in regard to their effects in human clinical trials and that UII analogs, established to target UT, were not as beneficial as expected in pathological situations. Thus, many questions remain regarding the overall signaling profiles of UT leading to complex involvement in cardiovascular and inflammatory responses as well as cancer. We address the potential UT chemotactic structural and functional definition under an evolutionary angle, by the existence of a common conserved structural feature among chemokine receptorsopioïdergic receptors and UT, i.e., a specific proline position in the transmembrane domain-2 TM2 (P2.58) likely responsible for a kink helical structure that would play a key role in chemokine functions. Even if the last decade was devoted to the elucidation of the cardiovascular control by the urotensinergic system, we also attempt here to discuss the role of UII on inflammation and migration, likely providing a peptide chemokine status for UII. Indeed, our recent work established that activation of UT by a gradient concentration of UII recruits Gαi/o and Gα13 couplings in a spatiotemporal way, controlling key signaling events leading to chemotaxis. We think that this new vision of the urotensinergic system should help considering UT as a chemotactic therapeutic target in pathological situations involving cell chemoattraction.

Effects of peripherally administered urotensin II and arginine vasotocin on the QT interval of the electrocardiogram in trout

The QT interval of the electrocardiogram (ECG) is a measure of the duration of the ventricular depolarization and repolarization. In fish as in human, the QT interval is positively correlated with the RR interval of the ECG, a measure of the cardiac cycle length. Urotensin II (UII) is a neuropeptide that has been highly conserved from fish to human, and UII and its receptor (UT) are expressed in cardiovascular tissues including the heart. Although UII exerts potent cardiovascular actions, its possible effects on the QT interval have never been investigated. The goal of the present study was to provide insight into the potential effect of UII on the QT interval in an established in vivo trout model. To this end, the effects of UII on dorsal aortic blood pressure (PDA), RR, QT intervals and corrected QT (QTc) for RR interval, were investigated after intra-arterial (IA) injection of 5, 50 and 100 pmol UII. The effects of UII were compared to those of two structurally UII-related peptides (URPs), URP1 and URP2, and to those of arginine vasotocin (AVT), homolog of the mammalian arginine vasopressin. IA injection of vehicle or 5 pmol UII had no effect on the various parameters. At the 50-pmol dose, UII evoked its usual increase in PDA with a peak value observed 15 min after the injection (+22% from baseline, P<0.001). This hypertensive effect of UII was accompanied by a significant increase in the RR interval (+18%, P<0.001), i.e. a bradycardia, and these effects remained constant until the end of the recording. The highest dose of UII evoked similar hypertensive and bradycardic effects. Of interest, the QT interval did not change during the bradycardic action of UII (50 and 100 pmol) but the QTc interval significantly decreased. In trout pre-treated with urantide, a peptidic antagonist of UT, the hypertensive and bradycardic actions of 50 pmol UII were reduced 3-fold and no change occurred in the QT and QTc intervals. In trout pre-treated with blockers of the autonomic nervous system, the hypertensive effect of UII was maintained but no change appeared in RR, QT and QTc intervals. IA injections of 50 pmol URPs were without action on the preceding parameters. IA administration of 50 pmol AVT provoked quite similar increase in PDA, and elevation of the RR interval to those evoked by IA injection of UII but, in contrast to UII, AVT injection induced a highly significant and sustained prolongation of the QT interval compared to baseline (+7%, P<0.001) without change in QTc. Our results are indicative of a lack of QT interval change during UII-evoked bradycardia but not after AVT-induced bradycardia and suggest for the first time that some compensatory mechanism specific for the UII peptide is working to stabilize the QT interval. Further research is needed to elucidate the mechanism involved in this action of UII. The potential for UII to prevent detrimental prolongation of cardiac ventricular repolarization might be questioned.

International Union of Basic and Clinical Pharmacology. XCII. Urotensin II, urotensin II-related peptide, and their receptor: from structure to function

Urotensin II (UII) is a cyclic neuropeptide that was first isolated from the urophysis of teleost fish on the basis of its ability to contract the hindgut. Subsequently, UII was characterized in tetrapods including humans. Phylogenetic studies and synteny analysis indicate that UII and its paralogous peptide urotensin II-related peptide (URP) belong to the somatostatin/cortistatin superfamily. In mammals, the UII and URP genes are primarily expressed in cholinergic neurons of the brainstem and spinal cord. UII and URP mRNAs are also present in various organs notably in the cardiovascular, renal, and endocrine systems. UII and URP activate a common G protein-coupled receptor, called UT, that exhibits relatively high sequence identity with somatostatin, opioid, and galanin receptors. The UT gene is widely expressed in the central nervous system (CNS) and in peripheral tissues including the retina, heart, vascular bed, lung, kidney, adrenal medulla, and skeletal muscle. Structure-activity relationship studies and NMR conformational analysis have led to the rational design of a number of peptidic and nonpeptidic UT agonists and antagonists. Consistent with the wide distribution of UT, UII has now been shown to exert a large array of biologic activities, in particular in the CNS, the cardiovascular system, and the kidney. Here, we review the current knowledge concerning the pleiotropic actions of UII and discusses the possible use of antagonists for future therapeutic applications.

Urotensin II upregulates migration and cytokine gene expression in leukocytes of the African clawed frog, Xenopus laevis

Urotensin II (UII) exhibits diverse physiological actions including vasoconstriction, locomotor activity, osmoregulation, and immune response via the UII receptor (UTR) in mammals. However, in amphibians the function of the UII-UTR system remains unknown. In the present study, we investigated the potential immune function of UII using leukocytes isolated from the African clawed frog, Xenopus laevis. Stimulation of male frogs with lipopolysaccharide increased mRNA expression of UII and UTR in leukocytes, suggesting that inflammatory stimuli induce activation of the UII-UTR system. Migration assays showed that both UII and UII-related peptide enhanced migration of leukocytes in a dose-dependent manner, and that UII effect was inhibited by the UTR antagonist urantide. Inhibition of Rho kinase with Y-27632 abolished UII-induced migration, suggesting that it depends on the activation of RhoA/Rho kinase. Treatment of isolated leukocytes with UII increased the expression of several cytokine genes including tumor necrosis factor-α, interleukin-1β, and macrophage migration inhibitory factor, and the effects were abolished by urantide. These results suggest that in amphibian leukocytes the UII-UTR system is involved in the activation of leukocyte migration and cytokine gene expression in response to inflammatory stimuli.

Comparative distribution and in vitro activities of the urotensin II-related peptides URP1 and URP2 in zebrafish: evidence for their colocalization in spinal cerebrospinal fluid-contacting neurons

Urotensin II (UII) is an evolutionarily conserved neuropeptide initially isolated from teleost fish on the basis of its smooth muscle-contracting activity. Subsequent studies have demonstrated the occurrence of several UII-related peptides (URPs), such that the UII family is now known to include four paralogue genes called UII, URP, URP1 and URP2. These genes probably arose through the two rounds of whole genome duplication that occurred during early vertebrate evolution. URP has been identified both in tetrapods and teleosts. In contrast, URP1 and URP2 have only been observed in ray-finned and cartilaginous fishes, suggesting that both genes were lost in the tetrapod lineage. In the present study, the distribution of urp1 mRNA compared to urp2 mRNA is reported in the central nervous system of zebrafish. In the spinal cord, urp1 and urp2 mRNAs were mainly colocalized in the same cells. These cells were also shown to be GABAergic and express the gene encoding the polycystic kidney disease 2-like 1 (pkd2l1) channel, indicating that they likely correspond to cerebrospinal fluid-contacting neurons. In the hindbrain, urp1-expressing cells were found in the intermediate reticular formation and the glossopharyngeal-vagal motor nerve nuclei. We also showed that synthetic URP1 and URP2 were able to induce intracellular calcium mobilization in human UII receptor (hUT)-transfected CHO cells with similar potencies (pEC50=7.99 and 7.52, respectively) albeit at slightly lower potencies than human UII and mammalian URP (pEC50=9.44 and 8.61, respectively). The functional redundancy of URP1 and URP2 as well as the colocalization of their mRNAs in the spinal cord suggest the robustness of this peptidic system and its physiological importance in zebrafish.

Dynamic expression pattern of corticotropin-releasing hormone, urotensin I and II genes under acute salinity and temperature challenge during early development of zebrafish

Corticotropin-releasing hormone (CRH), urotensin I (UI) and urotensin II (UII) are found throughout vertebrate species from fish to human. To further understand the role of crh, uI and uII in teleosts during development, we investigated the expression pattern of crh, uI, uIIα and uIIβ genes, and their response to acute salinity and temperature challenge during early development of zebrafish, Danio rerio. The results reveal that crh, uI, uIIα and uIIβ mRNA are detected from 0hpf, and the expression levels increase to a maximum at 6 days post fertilization (dpf), with the exception of uIIα that peak at 5dpf. Exposure of zebrafish embryos and larvae to acute osmotic (30ppt) stress for 15 min failed to modify expression levels of crh, uI, uIIα and uIIβ mRNA from levels in control fish except at 6dpf when uIIα and uIIβ were significantly (P < 0.05) modified. Exposure of embryos and larvae to a cold (18 °C) or hot stress (38 °C) generally down-regulated mRNA levels of crh, uI, uIIα and uIIβ apart from at 3dpf. The results indicate that the contribution of crh, uI, uIIα and uIIβ genes to the stress response in zebrafish may be stressor-specific during early development. Overall, the results from this study provide a basis for further research into the developmental and stressor-specific function of crh, uI, uIIα and uIIβ in zebrafish.

Molecular evolution of GPCRs: Somatostatin/urotensin II receptors

Somatostatin (SS) and urotensin II (UII) are members of two families of structurally related neuropeptides present in all vertebrates. They exert a large array of biological activities that are mediated by two families of G-protein-coupled receptors called SSTR and UTS2R respectively. It is proposed that the two families of peptides as well as those of their receptors probably derive from a single ancestral ligand-receptor pair. This pair had already been duplicated before the emergence of vertebrates to generate one SS peptide with two receptors and one UII peptide with one receptor. Thereafter, each family expanded in the three whole-genome duplications (1R, 2R, and 3R) that occurred during the evolution of vertebrates, whereupon some local duplications and gene losses occurred. Following the 2R event, the vertebrate ancestor is deduced to have possessed three SS (SS1, SS2, and SS5) and six SSTR (SSTR1-6) genes, on the one hand, and four UII (UII, URP, URP1, and URP2) and five UTS2R (UTS2R1-5) genes, on the other hand. In the teleost lineage, all these have been preserved with the exception of SSTR4. Moreover, several additional genes have been gained through the 3R event, such as SS4 and a second copy of the UII, SSTR2, SSTR3, and SSTR5 genes, and through local duplications, such as SS3. In mammals, all the genes of the SSTR family have been preserved, with the exception of SSTR6. In contrast, for the other families, extensive gene losses occurred, as only the SS1, SS2, UII, and URP genes and one UTS2R gene are still present.

Urotensin-II receptor is over-expressed in colon cancer cell lines and in colon carcinoma in humans

BACKGROUND

Urotensin (U)-II receptor (UTR) has been previously reported to be over-expressed in a number of tumours. Whether UTR-related pathway plays a role in colon carcinogenesis is unknown.

METHODS

We evaluated UTR protein and mRNA expression in human epithelial colon cancer cell lines and in normal colon tissue, adenomatous polyps and colon cancer. U-II protein expression was assessed in cancer cell lines. Moreover, we evaluated the effects of U-II(4-11) (an UTR agonist), antagonists and knockdown of UTR protein expression through a specific shRNA, on proliferation, invasion and motility of human colon cancer cells.

RESULTS

Cancer cell lines expressed U-II protein and UTR protein and mRNA. By immunohistochemistry, UTR was expressed in 5-30% of epithelial cells in 45 normal controls, in 30-48% in 21 adenomatous polyps and in 65-90% in 48 colon adenocarcinomas. UTR mRNA expression was increased by threefold in adenomatous polyps and eightfold in colon cancer, compared with normal colon. U-II(4-11) induced a 20-40% increase in cell growth while the blockade of the receptor with specific antagonists caused growth inhibition of 20-40%. Moreover, the knock down of UTR with a shRNA or the inhibition of UTR with the antagonist urantide induced an approximately 50% inhibition of both motility and invasion.

CONCLUSIONS

UTR appears to be involved in the regulation of colon cancer cell invasion and motility. These data suggest that UTR-related pathway may play a role in colon carcinogenesis and that UTR may function as a target for therapeutic intervention in colon cancer.

UII and UT in grouper: cloning and effects on the transcription of hormones related to growth control

Urotensin II (UII) is a cyclic peptide that was originally extracted from the caudal neurosecretory system (CNSS) of fish. UII is well known to exhibit cardiovascular, ventilatory, and motor effects in vertebrates. Studies have reported that UII exerts mitogenic effects and can act as an autocrine/paracrine growth factor in mammals. However, similar information in fish is limited. In this study, the full-length cDNAs of UII and its receptor (UT) were cloned and characterized in the orange-spotted grouper. UII and UT were expressed ubiquitously in various tissues in grouper, and particularly high levels were observed in the CNSS, CNS, and ovary. A functional study showed that UT was coupled with intracellular Ca2+ mobilization in HEK293 cells. Studies carried out using i.p. injections of UII in grouper showed the following: i) in the hypothalamus, UII can significantly stimulate the mRNA expression of ghrh and simultaneously inhibit the mRNA expression of somatostatin 1 (ss1) and ss2 3 h after injection; ii) in the pituitary, UII also significantly induced the mRNA expression of gh 6 and 12  h after injection; and iii) in the liver, the mRNA expression levels of ghr1/ghr2 and igf1/igf2 were markedly increased 12 and 3  h after the i.p. injection of UII respectively. These results collectively indicate that the UII/UT system may play a role in the promotion of the growth of the orange-spotted grouper.

Impact of gene/genome duplications on the evolution of the urotensin II and somatostatin families

The present review describes the molecular evolution of two phylogenetically related families of neuropeptides, the urotensin II (UII) and somatatostatin (SS) families. The UII family consists of four paralogous genes called UII, URP, URP1 and URP2 and the SS family is composed of six paralogous genes named SS1, SS2, SS3, SS4, SS5 and SS6. All these paralogs are present in teleosts, while only four of them, UII, URP, SS1 and SS2 are detected in tetrapods. Comparative genomics showed that most of these genes, namely UII, URP, URP1 and URP2 on the one hand and SS1, SS2 and SS5 on the other hand arose through the 2R. In contrast, the teleost-specific 3R had a much more moderate impact since it only concerned the UII and SS1 genes, which once duplicated, generated a second UII copy and SS4, respectively. The two remaining genes, SS3 and SS6, arose through tandem duplications of the SS1 and SS2 genes respectively, probably in the stem lineage of actinopterygians, before the emergence of teleosts. The history of the UII and SS families has also been marked by massive gene lost, both in tetrapods and in teleosts, but only after the 3R in this latter lineage. Finally, ancestral UII and SS genes are thought to have arisen through tandem duplication of a single ancestral gene, largely before the 1R. An important challenge for the future will be to understand the physiological significance of the molecular diversity of these two families.

Urotensin II receptor (UTR) exists in hyaline chondrocytes: a study of peripheral distribution of UTR in the African clawed frog, Xenopus laevis

Urotensin II (UII) and UII-related peptide (URP) exhibit diverse physiological actions including vasoconstriction, locomotor activity, osmoregulation, and immune response through UII receptor (UTR), which is expressed in the central nervous system and peripheral tissues of fish and mammals. In amphibians, only UII has been identified. As the first step toward elucidating the actions of UII and URP in amphibians, we cloned and characterized URP and UTR from the African clawed frog Xenopus laevis. Functional analysis showed that treatment of UII or URP with Chinese hamster ovary cells transfected with the cloned receptor increased the intracellular calcium concentration in a concentration-dependent manner, whereas the administration of the UTR antagonist urantide inhibited UII- or URP-induced Ca(2+) mobilization. An immunohistochemical study showed that UTR was expressed in the splenocytes and leukocytes isolated from peripheral blood, suggesting that UII and URP are involved in the regulation of the immune system. UTR was also localized in the apical membrane of the distal tubule of the kidney and in the transitional epithelial cells of the urinary bladder. This result supports the view that the UII/URP-UTR system plays an important role in osmoregulation of amphibians. Interestingly, immunopositive labeling for UTR was first detected in the chondrocytes of various hyaline cartilages (the lung septa, interphalangeal joint and sternum). The expression of UTR was also observed in the costal cartilage, tracheal cartilages, and xiphoid process of the rat. These novel findings probably suggest that UII and URP mediate the formation of the cartilaginous matrix.

Urotensin-II Ligands: An Overview from Peptide to Nonpeptide Structures

Urotensin-II was originally isolated from the goby urophysis in the 1960s as a vasoactive peptide with a prominent role in cardiovascular homeostasis. The identification of human isoform of urotensin-II and its specific UT receptor by Ames et al. in 1999 led to investigating the putative role of the interaction U-II/UT receptor in multiple pathophysiological effects in humans. Since urotensin-II is widely expressed in several peripheral tissues including cardiovascular system, the design and development of novel urotensin-II analogues can improve knowledge about structure-activity relationships (SAR). In particular, since the modulation of the U-II system offers a great potential for therapeutic strategies related to the treatment of several diseases, like cardiovascular diseases, the research of selective and potent ligands at UT receptor is more fascinating. In this paper, we review the developments of peptide and nonpeptide U-II structures so far developed in order to contribute also to a more rational and detectable design and synthesis of new molecules with high affinity at the UT receptor.

Urotensin II in invertebrates: from structure to function in Aplysia californica

Neuropeptides are ancient signaling molecules that are involved in many aspects of organism homeostasis and function. Urotensin II (UII), a peptide with a range of hormonal functions, previously has been reported exclusively in vertebrates. Here, we provide the first direct evidence that UII-like peptides are also present in an invertebrate, specifically, the marine mollusk Aplysia californica. The presence of UII in the central nervous system (CNS) of Aplysia implies a more ancient gene lineage than vertebrates. Using representational difference analysis, we identified an mRNA of a protein precursor that encodes a predicted neuropeptide, we named Aplysia urotensin II (apUII), with a sequence and structural similarity to vertebrate UII. With in-situ hybridization and immunohistochemistry, we mapped the expression of apUII mRNA and its prohormone in the CNS and localized apUII-like immunoreactivity to buccal sensory neurons and cerebral A-cluster neurons. Mass spectrometry performed on individual isolated neurons, and tandem mass spectrometry on fractionated peptide extracts, allowed us to define the posttranslational processing of the apUII neuropeptide precursor and confirm the highly conserved cyclic nature of the mature neuropeptide apUII. Electrophysiological analysis of the central effects of a synthetic apUII suggests it plays a role in satiety and/or aversive signaling in feeding behaviors. Finding the homologue of vertebrate UII in the numerically small CNS of an invertebrate animal model is important for gaining insights into the molecular mechanisms and pathways mediating the bioactivity of UII in the higher metazoan.

Characterization of the true ortholog of the urotensin II-related peptide (URP) gene in teleosts

It has been recently established that the urotensin II (UII) family consists of four distinct paralogs in bony vertebrates, namely UII, and the three UII-related peptides (URPs) called URP, URP1 and URP2. These four peptides are encoded by genes which arose from the two rounds of tetraploidization (2R) which took place early during vertebrate evolution. Up to now, three of them, UII, URP1 and URP2, have been identified in teleosts, while only two, UII and URP, have been reported in tetrapods. The fact that fish URP has not been found in previous studies led to the suggestion that the corresponding gene had been lost in the teleost lineage. In the present study, we show that this view is not correct. A search of the most recent release of the Ensembl genome database led us to identify a novel UII/URP-like gene in teleosts. Using synteny analysis, we demonstrate that this gene corresponds to the true ortholog of the tetrapod URP gene. Molecular cloning of the corresponding cDNA in medaka revealed that URP gene encodes a putative peptide, with the primary structure GEPCFWKYCV. In stickleback, tilapia and takifugu, URP exhibited the same sequence while, in tetraodon, it differed by only one amino acid substitution Gly ↔ Ser. In zebrafish, URP appeared totally divergent at its N-terminus with the structure DDTCFWKYCV. In conclusion, the occurrence of a true URP in teleosts shows that the quartet of UII-related genes which arose from 2R has been integrally preserved in this lineage.

Update on the urotensinergic system: new trends in receptor localization, activation, and drug design

The urotensinergic system plays central roles in the physiological regulation of major mammalian organ systems, including the cardiovascular system. As a matter of fact, this system has been linked to numerous pathophysiological states including atherosclerosis, heart failure, hypertension, diabetes as well as psychological, and neurological disorders. The delineation of the (patho)physiological roles of the urotensinergic system has been hampered by the absence of potent and selective antagonists for the urotensin II-receptor (UT). Thus, a more precise definition of the molecular functioning of the urotensinergic system, in normal conditions as well as in a pathological state is still critically needed. The recent discovery of nuclear UT within cardiomyocytes has highlighted the cellular complexity of this system and suggested that UT-associated biological responses are not only initiated at the cell surface but may result from the integration of extracellular and intracellular signaling pathways. Thus, such nuclear-localized receptors, regulating distinct signaling pathways, may represent new therapeutic targets. With the recent observation that urotensin II (UII) and urotensin II-related peptide (URP) exert different biological effects and the postulate that they could also have distinct pathophysiological roles in hypertension, it appears crucial to reassess the recognition process involving UII and URP with UT, and to push forward the development of new analogs of the UT system aimed at discriminating UII- and URP-mediated biological activities. The recent development of such compounds, i.e. urocontrin A and rUII(1-7), is certainly useful to decipher the specific roles of UII and URP in vitro and in vivo. Altogether, these studies, which provide important information regarding the pharmacology of the urotensinergic system and the conformational requirements for binding and activation, will ultimately lead to the development of potent and selective drugs.

Occurrence of two distinct urotensin II-related peptides in zebrafish provides new insight into the evolutionary history of the urotensin II gene family

The urotensin II (UII) family is currently known to consist of two paralogous peptides, namely UII and UII-related peptide (URP). In contrast to UII, which has been identified in all vertebrate classes so far, URP has only been characterized in tetrapods. We report here the occurrence of two distinct URP genes in teleosts, which we have named URP1 and URP2. Synteny analysis revealed that teleost URP1 and URP2 genes and tetrapod URP genes represent three distinct paralog genes that, together with the UII gene, probably arose from the two rounds of tetraploidization, which took place early in vertebrate evolution. The absence of URP in fish indicates that the corresponding gene has been lost in the teleost lineage, whereas it is likely that both the URP1 and URP2 genes have been lost in the tetrapod lineage. Quantitative RT-PCR analysis revealed that the URP2 gene is mainly expressed in the spinal cord and the brain in adult zebrafish. In situ hybridization experiments showed that in zebrafish embryos, URP2 mRNA-containing cells are located in the floor plate of the neural tube. In adult, URP2-expressing cells occur in close contact with the ventral side of the ependymal canal along the whole spinal cord, whereas in the brain, they are located below the fourth ventricle. These URP-expressing cells may correspond to cerebrospinal fluid-contacting neurons. In conclusion, our study reveals the occurrence of four distinct UII paralogous systems in vertebrates that may exert distinct functions, both in tetrapods and teleosts.

Urotensin II, from fish to human

The cyclic peptide urotensin II (UII) was originally isolated from the urophysis of teleost fish on the basis of its ability to contract intestinal smooth muscle. The UII peptide has subsequently been isolated from frog brain and, later on, the pre-proUII cDNA has been characterized in mammals, including humans. A UII paralog called urotensin II-related peptide (URP) has been identified in the rat brain. The UII and URP genes originate from the same ancestral gene as the somatostatin and cortistatin genes. In the central nervous system (CNS) of tetrapods, UII is expressed primarily in motoneurons of the brainstem and spinal cord. The biological actions of UII and URP are mediated through a G protein-coupled receptor, termed UT, that exhibits high sequence similarity with the somatostatin receptors. The UT gene is widely expressed in the CNS and in peripheral organs. Consistent with the broad distribution of UT, UII and URP exert a large array of behavioral effects and regulate endocrine, cardiovascular, renal, and immune functions.

Characterization of urotensin II, distribution of urotensin II, urotensin II-related peptide and UT receptor mRNAs in mouse: evidence of urotensin II at the neuromuscular junction

Urotensin II (UII) and UII-related peptide (URP) are paralog neuropeptides whose existence and distribution in mouse have not yet been investigated. In this study, we showed by HPLC/RIA analysis that the UII-immunoreactive molecule in the mouse brain corresponds to a new UII(17) isoform. Moreover, calcium mobilization assays indicated that UII(17) and URP were equally potent in stimulating UII receptor (UT receptor). Quantitative RT-PCR and in situ hybridization analysis revealed that in the CNS UII and URP mRNAs were predominantly expressed in brainstem and spinal motoneurons. Besides, they were differentially expressed in the medial vestibular nucleus, locus coeruleus and the ventral medulla. In periphery, both mRNAs were expressed in skeletal muscle, testis, vagina, stomach, and gall bladder, whereas only URP mRNA could be detected in the seminal vesicle, heart, colon, and thymus. By contrast, the UT receptor mRNA was widely expressed, and notably, very high amounts of transcript occurred in skeletal muscle and prostate. In the biceps femoris muscle, UII-like immunoreactivity was shown to coexist with synaptophysin in muscle motor end plate regions. Altogether these results suggest that (i) UII and URP may have many redundant biological effects, especially at the neuromuscular junction; (ii) URP may more specifically participate to autonomic, cardiovascular and reproductive functions.

Urotensin II: a new pharmacologic target in the treatment of cardiovascular disease

Urotensin II was first identified over 30 years ago as a potent vasoconstrictor, and the identification of its receptor in the heart, lungs, blood vessels, and brain have made it a potential target for human pharmacotherapy. Current research would suggest that urotensin II plays a major role in the pathophysiology of various cardiovascular disease entities. This article discusses the biologic effects of urotensin under normal and pathophysiologic conditions, and reviews the research experiences with synthetic urotensin blockers in the treatment of various cardiovascular illnesses.

New insight into the molecular evolution of the somatostatin family

The present review describes the molecular evolution of the somatostatin family and its relationships with that of the urotensin II family. Most of the somatostatin sequences collected from different vertebrate species can be grouped as the products of at least four loci. The somatostatin 1 (SS1) gene is present in all vertebrate classes from agnathans to mammals. The SS1 gene has given rise to the somatostatin 2 (SS2) gene by a segment/chromosome duplication that is probably the result of a tetraploidization event according to the 2R hypothesis. The somatostatin-related peptide cortistatin, first identified in rodents and human, is the counterpart of SS2 in placental mammals. In fish, the existence of two additional somatostatin genes has been reported. The first gene, which encodes a peptide usually named somatostatin II (SSII), exists in almost all teleost species investigated so far and is thought to have arisen through local duplication of the SS1 gene. The second gene, which has been characterized in only a few teleost species, encodes a peptide also named SSII that exhibits a totally atypical structure. The origin of this gene is currently unknown. Nevertheless, because the two latter genes are clearly paralogous genes, we propose to rename them SS3 and SS4, respectively, in order to clarify the current confusing nomenclature. The urotensin II family consists of two genes, namely the urotensin II (UII) gene and the UII-related peptide (URP) gene. Both UII and URP exhibit limited structural identity to somatostatin so that UII was originally described as a "somatostatin-like peptide". Recent comparative genomics studies have revealed that the SS1 and URP genes, on the one hand, and the SS2 and UII genes, on the other hand, are closely linked on the same chromosomes, thus confirming that the SS1/SS2 and the UII/URP genes belong to the same superfamily. According to these data, it appears that an ancestral somatostatin/urotensin II gene gave rise by local duplication to a somatostatin ancestor and a urotensin II ancestor, whereupon this pair was duplicated (presumably by a segment/chromosome duplication) to give rise to the SS1-UII pair and the SS2-URP pair.

Another ligand fishing for G protein-coupled receptor 14. Discovery of urotensin II-related peptide in the rat brain

Urotensin II (UII), which was originally isolated from the teleost urophysis, was identified as an endogenous ligand for orphan G protein-coupled receptor 14 (GPR14). The structure of mammalian UII was confirmed by isolation from spinal cord in porcine, or was easily predicted from the sequence of prepro-UII in human. For rat and mouse, however, only the tentative sequences of UII peptides have been demonstrated because the typical processing sites are absent from the amino-terminal region of the mature peptides. Isolation of UII-like immunoreactivity in rat brain revealed the presence of a novel peptide, designated urotensin II-related peptide (URP). URP binds and activates the human and rat urotensin II receptors (GPR14) and has a hypotensive effect when administrated to anesthetized rats. Based on the DNA sequences of the cloned prepro-URP gene, the amino acid sequences of mature URP for mouse and human are identical to that for rat URP. These results suggest that URP is the endogenous and functional ligand for urotensin II receptor in the rat and mouse, and possibly in the human.

Structure-activity relationships of urotensin II and URP

Urotensin II (U-II) and urotensin II-related peptide (URP) are the endogenous ligands for the orphan G-protein-coupled receptor GPR14 now renamed UT. At the periphery, U-II and/or URP exert a wide range of biological effects on cardiovascular tissues, airway smooth muscles, kidney and endocrine glands, while central administration of U-II elicits various behavioral and cardiovascular responses. There is also evidence that U-II and/or URP may be involved in a number of pathological conditions including heart failure, atherosclerosis, renal dysfunction and diabetes. Because of the potential involvement of the urotensinergic system in various physiopathological processes, there is need for the rational design of potent and selective ligands for the UT receptor. Structure-activity relationship studies have shown that the minimal sequence required to retain full biological activity is the conserved U-II(4-11) domain, in particular the Cys5 and Cys10 residues involved in the disulfide bridge, and the Phe6, Lys8 and Tyr9 residues. Free alpha-amino group and C-terminal COOH group are not necessary for the biological activity, and modifications of these radicals may even increase the stability of the analogs. Punctual substitution of native amino acids, notably Phe6 and Trp7, by particular residues generates analogs with antagonistic properties. These studies, which provide crucial information regarding the structural and conformational requirements for ligand-receptor interactions, will be of considerable importance for the design of novel UT ligands with increased selectivity, potency and stability, that may eventually lead to the development of innovative drugs.

Nonpeptide Urotensin-II receptor agonists and antagonists: review and structure-activity relationships

Human Urotensin-II (hU-II) is a cyclic 11-amino acid peptide that plays a role in cardiovascular homeostasis. Its receptor is a member of the class A of G-protein-coupled receptors, called GPR14. In recent years, several nonpeptide ligands have been reported in the literature. Most were identified by high-throughput screening and optimized by medicinal chemistry methods. Other nonpeptide ligands were discovered starting from the 3D structure of hU-II or other ligands. They were identified by a virtual screening approach based on a 3D pharmacophore or by structural similarity with others cyclic peptides. In this review, nonpeptide agonists and antagonists are presented in relation to structure-activity relationships.

Solution structure of urotensin-II receptor extracellular loop III and characterization of its interaction with urotensin-II

Urotensin-II (U-II) is a vasoactive hormone that acts through a G-protein-coupled receptor named UT. Recently, we have shown, using the surface plasmon resonance technology that human U-II (hU-II) interacts with the hUT(281-300) fragment, a segment containing the extracellular loop III (EC-III) and short extensions of the transmembrane domains VI and VII (TM-VI and TM-VII). To further investigate the interaction of UT receptor with U-II, we have determined the solution structure of hUT(281-300) by high-resolution NMR and molecular modeling and we have examined, also using NMR, the binding with hU-II at residue level. In the presence of dodecylphosphocholine micelles, hUT(281-300) exhibited a type III beta-turn (Q285-L288), followed by an -helical structure (A289-L299), the latter including a stretch of transmembrane helix VII. Upon addition of hU-II, significant chemical shift perturbations were observed for residues located just on the N-terminal side of the beta-turn (end of TM-VI/beginning of EC-III) and on one face of the -helix (end of EC-III/beginning of TM-VII). These data, in conjunction with intermolecular NOEs, suggest that the initiation site of EC-III, as well as the upstream portion of helix VII, would be involved in agonist binding and allow to propose points of interaction in the ligand-receptor complex.

Effect of GABA A receptor activation on UT-coupled signaling pathways in rat cortical astrocytes

Cultured rat cortical astrocytes express two types of urotensin II (UII) binding sites: a high affinity site corresponding to the UT (GPR14) receptor and a low affinity site that has not been fully characterized. Activation of the high affinity site in astroglial cells stimulates polyphosphoinositide (PIP) turnover and provokes an increase in intracellular calcium concentration. We have hypothesized that the existence of distinct affinity sites for UII in rat cortical astrocytes could be accounted for by a possible cross-talk between UT and the ligand-gated ion channel GABA(A) receptor (GABA A R). Exposure of cultured astrocytes to UII provoked a bell-shaped increase in cAMP production, with an EC50 stimulating value of 0.83+/-0.04 pM, that was totally blocked in the presence of the adenylyl cyclase inhibitor SQ 22,536. In contrast, UII was found to inhibit forskolin-induced cAMP formation. In the presence of the specific PKA inhibitor H89, UII provoked a sustained stimulation of cAMP formation. Inhibition of PKA by H89 strongly reduced the stimulatory effect of UII on PIP metabolism. GABA and the GABA A R agonist isoguvacine provoked a marked inhibition of UII-induced cAMP synthesis and a significant reduction of UII-evoked PIP turnover. These data suggest that functional interaction between UT and GABA(A)R negatively regulates coupling of UT to the classical PLC/IP(3) signaling cascade as well as to the adenylyl cyclase/PKA pathway.

[Orn5]URP acts as a pure antagonist of urotensinergic receptors in rat cortical astrocytes

Cultured rat astrocytes, which express functional urotensin II (UII)/UII-related peptide (URP) receptors (UT), represent a very suitable model to investigate the pharmacological profile of UII and URP analogs towards native UT. We have recently designed three URP analogs [D-Trp4]URP, [Orn5]URP and [D-Tyr6]URP, that act as UT antagonists in the rat aortic ring bioassay. However, it has been previously reported that UII/URP analogs capable of inhibiting the contractile activity of UII possess agonistic activity on UT-transfected cells. In the present study, we have compared the ability of URP analogs to compete for [125 I]URP binding and to modulate cytosolic calcium concentration ([Ca2+]c) in cultured rat astrocytes. All three analogs displaced radioligand binding: [D-Trp4]URP and [D-Tyr6]URP interacted with high- and low-affinity sites whereas [Orn5]URP only bound high-affinity sites. [D-Trp4]URP and [D-Tyr6]URP both induced a robust increase in [Ca2+]c in astrocytes while [Orn5]URP was totally devoid of activity. [Orn5]URP provoked a concentration-dependent inhibition of URP- and UII-evoked [Ca2+]c increase and a rightward shift of the URP and UII dose-response curves. The present data indicate that [D-Trp4]URP and [D-Tyr6]URP, which act as UII antagonists in the rat aortic ring assay, behave as agonists in the [Ca2+]c mobilization assay in cultured astrocytes, whereas [Orn5]URP is a pure selective antagonist in both rat aortic ring contraction and astrocyte [Ca2+]c mobilization assays.

Evidence for endogenous urotensin-II as an inhibitor of insulin secretion. Study in the perfused rat pancreas

In the perfused rat pancreas, infusion of urotensin-II (UII), a somatostatin-like peptide, inhibits glucose-induced insulin secretion. We have resorted to specific antagonists of the UII receptor (UT), palosuran and urantide, to investigate whether endogenous UII also behaves as an inhibitor of beta-cell secretion. The insulinostatic effect of UII was counteracted by palosuran and by urantide but not by a somatostatin-receptor antagonist (cyclo-somatostatin). Furthermore, the insulinostatic effect of somatostatin was not reversed by palosuran. These results suggest that UII and somatostatin blocked beta-cell secretion via distinct receptors. Finally, in the absence of exogenous UII, both palosuran and urantide potentiated glucose-induced insulin release, thus supporting the concept that endogenous UII is an insulinostatic peptide. By virtue of their insulinotropic effect, UT antagonists may be considered potential drugs for treating the impaired insulin secretion characteristic of type 2 diabetic patients.

Liberation of urotensin II from the teleost urophysis: an historical overview

During the past 20 years, urotensin II (UII) has progressed from being a peptide synthesized only in the urophysis of the caudal neurosecretory system of teleost fish to being considered an important physiological regulator in mammals with implications for the pathogenesis of a range of human cardiovascular and renal diseases. The "liberation" of UII from the urophysis was a gradual process and involved the sequential realization that (a) UII is present not only in the urophysis but also in the central nervous systems (CNS) of teleosts, (b) UII peptides, similar in structure to the urophysial peptides, are present in the diffuse caudal neurosecretory systems and/or CNS of species less evolutionarily advanced than teleosts, including Agnatha, thereby showing that UII is a phylogenetically ancient peptide, (c) UII is present in the brain and spinal cord of a tetrapod, the green frog Rana ridibunda, and (d) the UII gene and its specific receptor (GPR14/UT) are expressed in the CNS and certain peripheral tissues of mammals, including the human. The discovery that the genomes of mammals contain an additional gene encoding a UII-related peptide (URP) and the availability of highly effective peptide and non-peptide antagonists to investigate the role of UII in human physiology and pathophysiology ensure that the peptide will remain "center stage" for several years to come.

Structure-activity relationships of a novel series of urotensin II analogues: identification of a urotensin II antagonist

Urotensin II (U-II) is a potent vasoconstrictor peptide which has been identified as the endogenous ligand for the orphan G protein-coupled receptor GPR14 now renamed UT receptor. As the C-terminal cyclic hexapeptide of U-II (U-II(4-11), H-Asp-Cys-Phe-Trp-Lys-Tyr-Cys-Val-OH) possesses full biological activity, we have synthesized a series of U-II(4-11) analogues and measured their binding affinity on hGPR14-transfected CHO cells and their contractile activity on de-endothelialized rat aortic rings. The data indicate that a free amino group and a functionalized side-chain at the N-terminal extremity of the peptide are not required for biological activity. In addition, the minimal chemical requirement at position 9 of U-II(4-11) is the presence of an aromatic moiety. Most importantly, replacement of the Phe6 residue by cyclohexyl-Ala (Cha) led to an analogue, [Cha6]U-II(4-11), that was devoid of agonistic activity but was able to dose-dependently suppress the vasoconstrictor effect of U-II on rat aortic rings. These new pharmacological data, by providing further information regarding the structure-activity relationships of U-II analogues, should prove useful for the rational design of potent and nonpeptidic UT receptor agonists and antagonists.

Biochemical and functional characterization of high-affinity urotensin II receptors in rat cortical astrocytes

The urotensin II (UII) gene is primarily expressed in the central nervous system, but the functions of UII in the brain remain elusive. Here, we show that cultured rat astrocytes constitutively express the UII receptor (UT). Saturation and competition experiments performed with iodinated rat UII ([(125)I]rUII) revealed the presence of high- and low-affinity binding sites on astrocytes. Human UII (hUII) and the two highly active agonists hUII(4-11) and [3-iodo-Tyr9]hUII(4-11) were also very potent in displacing [(125)I]rUII from its binding sites, whereas the non-cyclic analogue [Ser5,10]hUII(4-11) and somatostatin-14 could only displace [(125)I]rUII binding at micromolar concentrations. Reciprocally, rUII failed to compete with [(125)I-Tyr0,D-Trp8]somatostatin-14 binding on astrocytes. Exposure of cultured astrocytes to rUII stimulated [(3)H]inositol incorporation and increased intracellular Ca(2+) concentration in a dose-dependent manner. The stimulatory effect of rUII on polyphosphoinositide turnover was abolished by the phospholipase C inhibitor U73122, but only reduced by 56% by pertussis toxin. The GTP analogue Gpp(NH)p caused its own biphasic displacement of [(125)I]rUII binding and provoked an affinity shift of the competition curve of rUII. Pertussis toxin shifted the competition curve towards a single lower affinity state. Taken together, these data demonstrate that rat astrocytes express high- and low-affinity UII binding sites coupled to G proteins, the high-affinity receptor exhibiting the same pharmacological and functional characteristics as UT.

Localization of the urotensin II receptor in the rat central nervous system

The vasoactive peptide urotensin II (UII) is primarily expressed in motoneurons of the brainstem and spinal cord. Intracerebroventricular injection of UII provokes various behavioral, cardiovascular, motor, and endocrine responses in the rat, but the distribution of the UII receptor in the central nervous system (CNS) has not yet been determined. In the present study, we have investigated the localization of UII receptor (GPR14) mRNA and UII binding sites in the rat CNS. RT-PCR analysis revealed that the highest density of GPR14 mRNA occurred in the pontine nuclei. In situ hybridization histochemistry showed that the GPR14 gene is widely expressed in the brain and spinal cord. In particular, a strong hybridization signal was observed in the olfactory system, hippocampus, olfactory and medial amygdala, hypothalamus, epithalamus, several tegmental nuclei, locus coeruleus, pontine nuclei, motor nuclei, nucleus of the solitary tract, dorsal motor nucleus of the vagus, inferior olive, cerebellum, and spinal cord. Autoradiographic labeling of brain slices with radioiodinated UII showed the presence of UII-binding sites in the lateral septum, bed nucleus of the stria terminalis, medial amygdaloid nucleus, anteroventral thalamus, anterior pretectal nucleus, pedunculopontine tegmental nucleus, pontine nuclei, geniculate nuclei, parabigeminal nucleus, dorsal endopiriform nucleus, and cerebellar cortex. Intense expression of the GPR14 gene in some hypothalamic nuclei (supraoptic, paraventricular, ventromedian, and arcuate nuclei), in limbic structures (amygdala and hippocampus), in medullary nuclei (solitary tract, dorsal motor nucleus of the vagus), and in motor control regions (cerebral and cerebellar cortex, substantia nigra, pontine nuclei) provides the anatomical substrate for the central effects of UII on behavioral, cardiovascular, neuroendocrine, and motor functions. The occurrence of GPR14 mRNA in cranial and spinal motoneurons is consistent with the reported autocrine/paracrine action of UII on motoneurons.

Comparative genomics provides evidence for close evolutionary relationships between the urotensin II and somatostatin gene families

Although urotensin II (UII) and somatostatin 1 (SS1) exhibit some structural similarities, their precursors do not show any appreciable sequence identity and, thus, it is widely accepted that the UII and SS1 genes do not derive from a common ancestral gene. The recent characterization of novel isoforms of these two peptides, namely urotensin II-related peptide (URP) and somatostatin 2 (SS2)/cortistatin (CST), provides new opportunity to revisit the phylogenetic relationships of UII and SS1 using a comparative genomics approach. In the present study, by radiation hybrid mapping and in silico sequence analysis, we have determined the chromosomal localization of the genes encoding UII- and somatostatin-related peptides in several vertebrate species, including human, chicken, and zebrafish. In most of the species investigated, the UII and URP genes are closely linked to the SS2/CST and SS1 genes, respectively. We also found that the UII-SS2/CST locus and the URP/SS1 locus are paralogous. Taken together, these data indicate that the UII and URP genes, on the one hand, and the SS1 and SS2/CST genes, on the other hand, arose through a segmental duplication of two ancestral genes that were already physically linked to each other. Our results also suggest that these two genes arose themselves through a tandem duplication of a single ancestral gene. It thus appears that the genes encoding UII- and somatostatin-related peptides belong to the same superfamily.

Urotensin II: Ancient Hormone with New Functions in Vertebrate Body Fluid Regulation

Urotensin II (UII), described in many fish species, is secreted by the caudal neurosecretory system, a unique fish neuroendocrine structure. We have examined UII secretion and its control in euryhaline fish, supporting a proposed role in osmoregulation. However, it is now apparent that UII is present in other vertebrates, including mammals. The 12-amino-acid peptide has been highly conserved and the key cyclic region is common from fish to humans. Our UII radioimmunoassay for flounder, directed to this cyclic region, has shown circulating UII levels in humans and rats comparable with those in fish. In mammals, UII cardiovascular effects vary between species, with vasoconstriction only evident in specific vascular beds. The kidney expresses UII receptors and responds to UII administration by a reduction in glomerular filtration rate, urine flow, and excretion of the major ions. Interestingly, plasma levels of UII are chronically elevated in rat models of hypertension. These observations imply an unforeseen role for this ancient fish hormone in the physiological and perhaps pathophysiological regulation of body fluids in higher vertebrates, including humans.