Characterization of the neuropeptide Y system in the frog Silurana tropicalis (Pipidae): three peptides and six receptor subtypes

Neuropeptide Y and its related peptides PYY and PP (pancreatic polypeptide) are involved in feeding behavior, regulation of the pituitary and the gastrointestinal tract, and numerous other functions. The peptides act on a family of G-protein coupled receptors with 4-7 members in jawed vertebrates. We describe here the NPY system of the Western clawed frog Silurana (Xenopus) tropicalis. Three peptides, NPY, PYY and PP, were identified together with six receptors, namely subtypes Y1, Y2, Y4, Y5, Y7 and Y8. Thus, this frog has all but one of the ancestral seven gnathostome NPY-family receptors, in contrast to mammals which have lost 2-3 of the receptors. Expression levels of mRNA for the peptide and receptor genes were analyzed in a panel of 19 frog tissues using reverse transcriptase quantitative PCR. The peptide mRNAs had broad distribution with highest expression in skin, blood and small intestine. NPY mRNA was present in the three brain regions investigated, but PYY and PP mRNAs were not detectable in any of these. All receptor mRNAs had similar expression profiles with high expression in skin, blood, muscle and heart. Three of the receptors, Y5, Y7 and Y8, could be functionally expressed in HEK-293 cells and characterized with binding studies using the three frog peptides. PYY had the highest affinity for all three receptors (K(i) 0.042-0.34 nM). Also NPY and PP bound to the Y8 receptor with high affinity (0.14 and 0.50 nM). The low affinity of NPY for the Y5 receptor (100-fold lower than PYY) differs from mammals and chicken. This may suggest a less important role of NPY on Y5 in appetite stimulation in the frog compared with amniotes. In conclusion, our characterization of the NPY system in S. tropicalis with its six receptors demonstrates not only greater complexity than in mammals but also some interesting differences in ligand-receptor preferences.

Uneven evolutionary rates of bradykinin B1 and B2 receptors in vertebrate lineages

Bradykinin acts through two receptor subtypes in mammals and generates a variety of responses including pain, inflammation and hypotension. The evolutionary history of the bradykinin system has been unclear due to shortage of information outside mammals. We describe here two receptor subtypes and the bradykinin precursor in three species of bony fish (the zebrafish Danio rerio, the Japanese pufferfish Takifugu rubripes, and the green spotted pufferfish Tetraodon nigroviridis) and chicken and analyze the relationships to mammals by a combination of phylogeny, conserved synteny and exon-intron organization. All of these species have two receptor genes located close to each other in a tandem formation, with the B2 gene 5' to the B1 gene, in chromosomal regions displaying conserved synteny between the species (albeit conservation of synteny in zebrafish is still unclear due to poor genome assembly). The evolutionary rate differs between the two genes as well as between lineages leading to differing pharmacological properties for both B1 and B2 across vertebrate classes. Also the bradykinin precursor gene was identified in all of these species in a chromosome region with conserved synteny. The tissue distribution of mRNA in T. rubripes is similar for B1 and B2, suggesting more similar regulation for the two genes than in mammals. In conclusion, the receptor tandem duplication predates the divergence of ray-finned fish and tetrapods and no additional duplicates of the receptors or bradykinin seem to have survived the ray-finned fish tetraploidization.

Cloning and characterization of a zebrafish Y2 receptor

The NPY receptors belong to the superfamily of G-protein coupled receptors and in mammals this family has five members, named Y1, Y2, Y4, Y5, and Y6. In bony fish, four receptors have been identified, named Ya, Yb, Yc and Y7. Yb and Y7 arose prior to the split between ray-fined fishes and tetrapods and have been lost in mammals. Yc appeared as a copy of Yb in teleost fishes. Ya may be an ortholog of Y4, but surprisingly no unambiguous receptor ortholog to any of the mammalian subtypes has yet been identified in bony fishes. Here we present the cloning and pharmacological characterization of a Y2 receptor in zebrafish, Danio rerio. To date, this is the first Y2 receptor outside mammals and birds that has been characterized pharmacologically. Phylogenetic analysis and synteny confirmed that this receptor is orthologous to mammalian Y2. We show that the receptor is pharmacologically most similar to chicken Y2 which leads to the conclusion that Y2 has acquired several novel characteristics in mammals. Y2 from zebrafish binds very poorly to the Y2-specific antagonist BIIE0246. Our pharmacological characterization supports our previous conclusions regarding the binding pocket of BIIE0246 in the human Y2 receptor.

Molecular evolution of NPY receptor subtypes

The neuropeptide Y (NPY) system consists in mammals of three peptides and 4-5 G-protein-coupled receptors called Y receptors that are involved in a variety of physiological functions such as appetite regulation, circadian rhythm and anxiety. Both the receptor family and the peptide family display unexpected evolutionary complexity and flexibility as shown by information from different classes of vertebrates. The vertebrate ancestor most likely had a single peptide gene and three Y receptor genes, the progenitors of the Y1, Y2 and Y5 subfamilies. The receptor genes were probably located in the same chromosomal segment. Additional gene copies arose through the chromosome quadruplication that took place before the emergence of jawed vertebrates (gnathostomes) whereupon differential losses of the gene copies ensued. The inferred ancestral gnathostome gene repertoire most likely consisted of two peptide genes, NPY and PYY, and no less than seven Y receptor genes: four Y1-like (Y1, Y4/a, Y6, and Yb), two Y2-like (Y2 and Y7), and a single Y5 gene. Whereas additional peptide genes have arisen in various lineages, the most common trend among the Y receptor genes has been further losses. Mammals have lost Yb and Y7 (the latter still exists in frogs) and Y6 is a pseudogene in several mammalian species but appears to be still functional in some. One challenge is to find out if mammals have been deprived of any functions through these gene losses. Teleost fishes like zebrafish and pufferfish, on the other hand, have lost the two major appetite-stimulating receptors Y1 and Y5. Nevertheless, teleost fishes seem to respond to NPY with increased feeding why some other subtype probably mediates this effect. Another challenge is to deduce how Y2 and Y4 came to evolve an inhibitory effect on appetite. Changes in anatomical distribution of receptor expression may have played an important part in such functional switching along with changes in receptor structures and ligand preferences.

Novel neuropeptide Y Y2-like receptor subtype in zebrafish and frogs supports early vertebrate chromosome duplications

The Y receptors comprise a family of G-protein coupled receptors with neuropeptide Y-family peptides as endogenous ligands. The Y receptor family has five members in mammals and evolutionary data suggest that it diversified in the two genome duplications proposed to have occurred early in vertebrate evolution. If this theory holds true, it allows for additional family members to be present. We describe here the cloning, pharmacological characterization, tissue distribution, and chromosomal localization of a novel subtype of the Y-receptor family, named Y7, from the zebrafish. We also present Y7 sequences from rainbow trout and two amphibians. The new receptor is most similar to Y2, with 51-54% identity. As Y2 has also been cloned from some of these species, there clearly are two separate Y2-subfamily genes. Chromosomal mapping in zebrafish supports origin of Y7 as a duplicate of Y2 by chromosome duplication in an early vertebrate. Y7 has probably been lost in the lineage leading to mammals. The pharmacological profile of the zebrafish Y7 receptor is different from mammalian Y2, as it does not bind short fragments of NPY with a high affinity. The Y7 receptor supports the theory of early vertebrate genome duplications and suggests that the Y family of receptors is a result of these early genome duplications.

Chicken neuropeptide Y-family receptor Y4: a receptor with equal affinity for pancreatic polypeptide, neuropeptide Y and peptide YY

Within the neuropeptide Y (NPY) family of peptides, pancreatic polypeptide is the most divergent across species. It differs in 20 of 36 positions between human and chicken. In mammals, it binds primarily to the Y4 receptor, to which NPY and peptide YY (PYY) bind with lower affinities. Because of these large sequence differences in pancreatic polypeptide, we decided to characterise the chicken Y4 receptor. We report here that Y4 displays the least sequence conservation among the Y-family receptors, with only 57-60% overall amino acid identity between chicken and mammals, compared with 64-83% for the Y1, Y2 and Y5 receptors. After expression of the chicken Y4 receptor in COS-7 cells, (125)I-labelled porcine (p) PYY bound with a K(d) of 20 pM. In competition with (125)I-pPYY, chicken pancreatic polypeptide bound with high affinity at 140 pM. Interestingly, chicken PYY bound with even greater affinity at 68 pM. The affinity of NPY, 160 pM, was similar to that of pancreatic polypeptide. Chicken Y4 is less sensitive than is mammalian Y4 to truncation of the amino terminus of the NPY molecule. RT-PCR revealed expression in several peripheral organs, including adipose tissue and oviduct. In brain, Y4 mRNA was detected in the brainstem, cerebellum and hippocampus. In situ hybridisation to brain sections showed expression in the dorsal motor nucleus of the vagus in the brainstem. Thus the chicken Y4 receptor is less selective and anatomically more widespread than that in mammals, probably reflecting the original properties of the Y4 receptor.

A neuropeptide Y receptor Y1-subfamily gene from an agnathan, the European river lamprey. A potential ancestral gene

We report here the isolation and functional expression of a neuropeptide Y (NPY) receptor from the river lamprey, Lampetra fluviatilis. The receptor displays approximately 50% amino-acid sequence identity to all previously cloned Y1-subfamily receptors including Y1, Y4, and y6 and the teleost subtypes Ya, Yb and Yc. Phylogenetic analyses point to a closer relationship with Y4 and Ya/b/c suggesting that the lamprey receptor could possibly represent a pro-orthologue of some or all of those gnathostome receptors. Our results support the notion that the Y1 subfamily increased in number by genome or large-scale chromosome duplications, one of which may have taken place prior to the divergence of lampreys and gnathostomes whereas the second duplication probably occurred in the gnathostome lineage after this split. Functional expression of the lamprey receptor in a cell line facilitated specific binding of the three endogenous lamprey peptides NPY, peptide YY and peptide MY with picomolar affinities. Binding studies with a large panel of NPY analogues revealed indiscriminate binding properties similar to those of another nonselective Y1-subfamily receptor, zebrafish Ya. RT-PCR detected receptor mRNA in the central nervous system as well as in several peripheral organs suggesting diverse functions. This lamprey receptor is evolutionarily the most distant NPY receptor that clearly belongs to the Y1 subfamily as defined in mammals, which shows that subtypes Y2 and Y5 arose even earlier in evolution.

Site-directed mutagenesis of the 5-HT1B receptor increases the affinity of 5-HT for the agonist low-affinity conformation and reduces the intrinsic activity of 5-HT

The antagonist radioligand [3H]GR125743 and the agonist radioligand [3H]5-HT were used to investigate the pharmacological characteristics of the G protein uncoupled agonist low-affinity and G protein coupled agonist high-affinity conformations of the wild-type and mutant human 5-hydroxytryptamine 1B (5-HT1B) receptors. We found that substitution of phenylalanine 185 in transmembrane region IV by alanine or methionine resulted in a reduced number of receptors in the coupled conformation, as well as a reduced affinity of 5-HT for the uncoupled conformation. In contrast, substitution of phenylalanine 331 in transmembrane region VI by alanine increased the affinity of 5-HT for the uncoupled conformation 11-fold thus reducing the agonist low-affinity to agonist high-affinity (K(il)/K(ih)) ratio 5-fold. This reduced ratio was correlated with a significantly reduced intrinsic activity of 5-HT previously determined by its ability to inhibit forskolin-stimulated cAMP production. In conclusion, these results show that single amino acid substitutions can selectively change the affinity of 5-HT for the G protein uncoupled conformation of the 5-HT1B receptor and alter the intrinsic activity of the ligand.

Binding of chimeric NPY/galanin peptides M32 and M242 to cloned neuropeptide Y receptor subtypes Y1, Y2, Y4, and Y5

Ligand binding to neuropeptide Y (NPY) receptors Y1, Y2, Y4, and Y5 from guinea-pig was investigated using the two NPY-galanin hybrids M32 (galanin1-13-NPY25-36-amide) and M242 ([D-Trp(32)]M32). The affinity of M32 for Y1, Y2, and Y4 receptors was 13, 4, and 30nM, respectively, similar to that of NPY18-36 and NPY22-36 but 40-fold to 300-fold lower than the affinity of intact porcine NPY. M242 bound to the Y1, Y2, and Y4 receptors with 9-fold to 20-fold lower affinity than did M32. The affinities of M32 and M242 for Y5 were 400 and 800 nM, respectively. Thus, M32 seems to gain affinity relative to both of its constituent peptide portions although the NPY25-36 part may be sufficient for NPY-receptor recognition, especially at the Y2 receptor. This suggests that the galanin portion of M32 influences and/or stabilizes the conformation of the NPY portion, similar to the effect seen for the NPY portion of M32 in binding to galanin receptors.

Neuropeptide expression in rat paraventricular hypothalamic neurons that project to the spinal cord

The paraventricular hypothalamic nucleus (PVH) exerts many of its regulatory functions through projections to spinal cord neurons that control autonomic and sensory functions. By using in situ hybridization histochemistry in combination with retrograde tract tracing, we analyzed the peptide expression among neurons in the rat PVH that send axons to the spinal cord. Projection neurons were labeled by immunohistochemical detection of retrogradely transported cholera toxin subunit B, and radiolabeled long riboprobes were used to identify neurons containing dynorphin, enkephalin, or oxytocin mRNA. Of the spinally projecting neurons in the PVH, approximately 40% expressed dynorphin mRNA, 40% expressed oxytocin mRNA, and 20% expressed enkephalin mRNA. Taken together with our previous findings on the distribution of vasopressin-expressing neurons in the PVH (Hallbeck and Blomqvist [1999] J. Comp. Neurol. 411:201-211), the results demonstrated that the different PVH subdivisions display distinct peptide expression patterns among the spinal cord-projecting neurons. Thus, the lateral parvocellular subdivision contained large numbers of spinal cord-projecting neurons that express any of the four investigated peptides, whereas the ventral part of the medial parvocellular subdivision displayed a strong preponderance for dynorphin- and vasopressin-expressing cells. The dorsal parvocellular subdivision almost exclusively contained dynorphin- and oxytocin-expressing spinal cord-projecting neurons. This parcellation of the peptide-expressing neurons suggested a functional diversity among the spinal cord-projecting subdivisions of the PVH that provide an anatomic basis for its various and distinct influences on autonomic and sensory processing at the spinal level.

Origins of the many NPY-family receptors in mammals

The NPY system has a multitude of effects and is particularly well known for its role in appetite regulation. We have found that the five presently known receptors in mammals arose very early in vertebrate evolution before the appearance of jawed vertebrates 400 million years ago. The genes Y(1), Y(2) and Y(5) arose by local duplications and are still present on the same chromosome in human and pig. Duplications of this chromosome led to the Y(1)-like genes Y(4) and y(6). We find evidence for two occasions where receptor subtypes probably arose before peptide genes were duplicated. These observations pertain to the discussion whether ligands or receptors tend to appear first in evolution. The roles of Y(1) and Y(5) in feeding may differ between species demonstrating the importance of performing functional studies in additional mammals to mouse and rat.

Studies of the human, rat, and guinea pig Y4 receptors using neuropeptide Y analogues and two distinct radioligands

The neuropeptide Y-family receptor Y4 differs extensively between human and rat in sequence, receptor binding, and anatomical distribution. We have investigated the differences in binding profile between the cloned human, rat, and guinea pig Y4 receptors using NPY analogues with single amino acid replacements or deletion of the central portion. The most striking result was the increase in affinity for the rat receptor, but not for human or guinea pig, when amino acid 34 was replaced with proline; [Ahx(8-20),Pro(34)]NPY bound to the rat Y4 receptor with 20-fold higher affinity than [Ahx(8-20)]NPY. Also, the rat Y4 tolerates alanine in position 34 since p[Ala(34)]NPY bound with similar affinity as pNPY while the affinity for hY4 and gpY4 decreased about 50-fold. Alanine substitutions in position 33, 35, and 36 as well as the large loop-deletion, [Ahx(5-24)]NPY, reduced the binding affinity to all three receptors more than 100-fold. NPY and PYY competed with (125)I-hPP at Y4 receptors expressed in CHO cells according to a two-site model. This was investigated for gpY4 by saturation with either radiolabeled hPP or pPYY. The number of high-affinity binding-sites for (125)I-pPYY was about 60% of the receptors recognized by (125)I-hPP. Porcine [Ala(34)]NPY and [Ahx(8-20)]NPY bound to rY4 (but not to hY4 or gpY4) according to a two-site model. These results suggest that different full agonists can distinguish between different active conformations of the gpY4 receptor and that Y4 may display functional differences in vivo between human, guinea pig, and rat.

Cloning and characterization of the guinea pig neuropeptide Y receptor Y5

The Y5 receptor has been postulated to be the main receptor mediating NPY-induced food intake in rats, based on its pharmacological profile and mRNA distribution. To further characterize this important receptor subtype, we isolated the Y5 gene in the guinea pig, a widely used laboratory animal in which all other known NPY receptors (Y1, Y2, Y4, y6) [2,13,33,37] have recently been cloned by our group. Our results show that the Y5 receptor is well conserved between species; guinea pig Y5 displays 96% overall amino acid sequence identity to human Y5, the highest identity reported for any non-primate NPY receptor orthologue, regardless of subtype. Thirteen of the twenty substitutions occur in the large third cytoplasmic loop. The identities between the guinea pig Y5 receptor and the dog, rat, and mouse Y5 receptors are 93%, 89%, and 89% respectively. When transiently expressed in EBNA cells, the guinea pig Y5 receptor showed a high binding affinity to iodinated porcine PYY with a dissociation constant of 0.41 nM. Competition experiments showed that the rank order of potency for NPY-analogues was PYY = NPY = NPY2-36 > gpPP > rPP >> NPY 22-36. Thus the pharmacological profile of the guinea pig Y5 receptor agrees well with that reported for the Y5 receptor from other cloned species.

Neuropeptide Y family of peptides: structure, anatomical expression, function, and molecular evolution

Evolutionary relationships between neuroendocrine peptides are often difficult to resolve across divergent phyla due to independent duplication events in different lineages. Thanks to peptide purification and molecular cloning in many different species, the situation is beginning to clear for the neuropeptide Y (NPY) family, which also includes peptide YY (PYY), the tetrapod pancreatic polypeptide (PP) and the fish pancreatic peptide Y (PY). It has long been assumed that the first duplication to occur in vertebrate evolution generated NPY and PYY, as both of these are found in all gnathostomes as well as lamprey. Evidence from other gene families show that this duplication was probably a chromosome duplication event. The origin of a second PYY peptide found in lamprey remains to be explained. Our recent cloning of NPY, PYY and PY in the sea bass proves that fish PY is a separate gene product. We favour the hypothesis that PY is a duplicate of the PYY gene and that it may have occurred late in fish evolution, as PY has so far only been found in acanthomorph fishes. Thus, this duplication seems to be independent of the one that generate PP from PYY in tetrapods, although both tetrapod PP and fish PY are expressed in the pancreas. Studies in the sea bass and other fish show that PY, in contrast to PP, is expressed in the nervous system. We review the literature on the distribution and functional aspects of the various NPY-family peptides in vertebrates.

Binding properties of three neuropeptide Y receptor subtypes from zebrafish: comparison with mammalian Y1 receptors

Neuropeptide Y (NPY) and peptide YY (PYY) are two related 36-amino-acid peptides found in all vertebrates and are involved in many physiological processes. Five receptor subtypes have been cloned in mammals (Y1, Y2, Y4, Y5, and y6). We have recently cloned three NPY/PYY receptor subtypes in zebrafish, called Ya, Yb, and Yc. Here we report on a direct comparison of the pharmacological properties of these three receptors in vitro using porcine NPY with alanine substitutions in positions 33-36 as ligands and three analogues with internal deletions: [Ahx(8-20)]NPY, [Ahx(8-20), Pro(34)]NPY, and [Ahx(5-24)]NPY. In all cases, the zYc receptor was the most sensitive to the modifications of the NPY molecule and zYa was the least sensitive (except for the Arg --> Ala replacement at position 33). Our data identified zYa as a receptor that can bind ligands specific for Y1, Y2, and Y4 receptors, while zYb and zYc were more Y1-like. All peptides with internal deletions bound to the zYa receptor with affinities similar to that of intact pNPY. Neither the Y1-selective antagonists BIBP3226 and SR120819A nor the Y2-selective BIIE0246 bound to any of the zebrafish receptors, although the amino acids identified as important for BIBP3226 binding were almost completely conserved. These results may prove helpful in molecular modeling of the three-dimensional receptor structure.

Molecular evolution of the neuropeptide Y (NPY) family of peptides: cloning of three NPY-related peptides from the sea bass (Dicentrarchus labrax)

Neuropeptide Y (NPY) is a 36-amino-acid peptide that is widely and abundantly expressed in the central nervous system of all vertebrates investigated. Related peptides have been found in various vertebrate groups: peptide YY (PYY) is present in gut endocrine cells of many species and pancreatic polypeptide (PP) is made in the pancreas of all tetrapods. In addition, a fish pancreatic peptide called PY has been reported in three species of fishes. The evolutionary relationships of fish PY have been unclear and it has been proposed to be the orthologue (species homologue) of each of the three tetrapod peptides. We demonstrate here with molecular cloning techniques that the sea bass (Dicentrarchus labrax), an acanthomorph fish, has orthologues of both NPY and PYY as well as a separate PY peptide. Sequence comparisons suggest that PY arose as a copy of the PYY gene, presumably in a duplication event separate from the one that generated PP from PYY in tetrapods. PY sequences from four species of fish indicate that, similar to PP, PY evolves much more rapidly than NPY and PYY. The physiological role of PY is unknown, but we demonstrate here that sea bass PY, like NPY and PYY but in contrast to the tetrapod PP, is expressed in brain.

Chicken neuropeptide Y receptor Y2: structural and pharmacological differences to mammalian Y2(1)

Here we report the molecular cloning of the chicken (Gallus gallus) neuropeptide Y (NPY) receptor Y2, the first non-mammalian Y2 receptor. It displays 75-80% identity to mammalian Y2 and has a surprisingly divergent cytoplasmic tail. Expression of the receptor protein in a cell line showed that the receptor did not bind the mammalian Y2 selective antagonist BIIE0246. Furthermore, porcine [Leu(31), Pro(34)]NPY, which binds poorly to mammalian Y2, exhibited an unexpectedly high affinity for chicken Y2. In situ hybridisation revealed expression in the hippocampus. Thus, the chicken Y2 receptor exhibits substantial differences with regard to sequence and pharmacological profile in comparison to mammalian Y2 receptors, while the expression pattern in the central nervous system resembles that observed in mammals.

Neuropeptide Y receptor gene y6: multiple deaths or resurrections?

The neuropeptide Y family of G-protein-coupled receptors consists of five cloned members in mammals. Four genes give rise to functional receptors in all mammals investigated. The y6 gene is a pseudogene in human and pig and is absent in rat, but generates a functional receptor in rabbit and mouse and probably in the collared peccary (Pecari tajacu), a distant relative of the pig family. We report here that the guinea pig y6 gene has a highly distorted nucleotide sequence with multiple frame-shift mutations. One evolutionary scenario may suggest that y6 was inactivated before the divergence of the mammalian orders and subsequently resurrected in some lineages. However, the pseudogene mutations seem to be distinct in human, pig, and guinea pig, arguing for separate inactivation events. In either case, the y6 gene has a quite unusual evolutionary history with multiple independent deaths or resurrections.

Zebrafish genes for neuropeptide Y and peptide YY reveal origin by chromosome duplication from an ancestral gene linked to the homeobox cluster

Neuropeptide Y (NPY) and peptide YY (PYY) are related 36-amino acid peptides. NPY is widely distributed in the nervous system and has several physiological roles. PYY serves as an intestinal hormone as well as a neuropeptide. We report here cloning of the npy and pyy genes in zebrafish (Danio rerio). NPY differs at only one to four amino acid positions from NPY in other jawed vertebrates. Zebrafish PYY differs at three positions from PYY from other fishes and at 10 positions from mammals. In situ hybridization showed that neurons containing NPY mRNA have a widespread distribution in the brain, particularly in the telencephalon, optic tectum, and rhombencephalon. PYY mRNA was found mainly in brainstem neurons, as reported previously for vertebrates as divergent as the rat and the lamprey, suggesting an essential role for PYY in these neurons. PYY mRNA was observed also in the telencephalon. These results were confirmed by immunocytochemistry. As in the human, the npy gene is located adjacent to homeobox (hox) gene cluster A (copy a in zebrafish), whereas the pyy gene is located close to hoxBa. This suggests that npy and pyy arose from a common ancestral gene in a chromosomal duplication event that also involved the hox gene clusters. As zebrafish has seven hox clusters, it is possible that additional NPY family genes exist or have existed. Also, the NPY receptor system seems to be more complex in zebrafish than in mammals, with at least two receptor genes without known mammalian orthologues.

Evolution of the neuropeptide Y receptor family: gene and chromosome duplications deduced from the cloning and mapping of the five receptor subtype genes in pig

Neuropeptide Y (NPY) receptors mediate a variety of physiological responses including feeding and vasoconstriction. To investigate the evolutionary events that have generated this receptor family, we have sequenced and determined the chromosomal localizations of all five presently known mammalian NPY receptor subtype genes in the domestic pig, Sus scrofa (SSC). The orthologs of the Y(1) and Y(2) subtypes display high amino acid sequence identities between pig, human, and mouse (92%-94%), whereas the Y(4), Y(5), and y(6) subtypes display lower identities (76%-87%). The lower identity of Y(5) is due to high sequence divergence in the large third intracellular loop. The NPY1R, NPY2R, and NPY5R receptor genes were localized to SSC8, the NPY4R to SSC14, and NPY6R to SSC2. Our comparisons strongly suggest that the tight cluster of NPY1R, NPY2R, and NPY5R on human chromosome 4 (HSA4) represents the ancestral configuration, whereas the porcine cluster has been split by two inversions on SSC8. These 3 genes, along with adjacent genes from 14 other gene families, form a cluster on HSA4 with extensive similarities to a cluster on HSA5, where NPY6R and >13 other paralogs reside, as well as another large cluster on HSA10 that includes NPY4R. Thus, these gene families have expanded through large-scale duplications. The sequence comparisons show that the NPY receptor triplet NPY1R-NPY2R-NPY5R existed before these large-scale duplications.

Inhibition of neurotransmitter release in the lamprey reticulospinal synapse by antibody-mediated disruption of SNAP-25 function

Exocytosis - syntaxin - synaptobrevin - SNARE synaptic vesicle The lamprey giant reticulospinal synapse can be used to manipulate the molecular machinery of synaptic vesicle exocytosis by presynaptic microinjection. Here we test the effect of disrupting the function of the SNARE protein SNAP-25. Polyclonal SNAP-25 antibodies were shown in an in vitro assay to inhibit the binding between syntaxin and SNAP-25. When microinjected presynaptically, these antibodies produced a potent inhibition of the synaptic response. Ba2+ spikes recorded in the presynaptic axon were not altered, indicating that the effect was not due to a reduced presynaptic Ca2+ entry. Electron microscopic analysis showed that synaptic vesicle clusters had a similar organization in synapses of antibody-injected axons as in control axons, and the number of synaptic vesicles in apparent contact with the presynaptic plasma membrane was also similar. Clathrin-coated pits, which normally occur at the plasma membrane around stimulated synapses, were not detected after injection of SNAP-25 antibodies, consistent with a blockade of vesicle cycling. Thus, SNAP-25 antibodies, which disrupt the interaction with syntaxin, inhibit neurotransmitter release without affecting the number of synaptic vesicles at the plasma membrane. These results provide further support to the view that the formation of SNARE complexes is critical for membrane fusion, but not for the targeting of synaptic vesicles to the presynaptic membrane.

Identification of an amino acid residue important for binding of methiothepin and sumatriptan to the human 5-HT(1B) receptor

Site-directed mutagenesis of the human 5-HT1B receptor was performed to investigate the role of the amino acid residues cysteine 326 and tryptophan 327 in transmembrane region VI and aspartic acid 352 in transmembrane region VII in ligand binding. Binding studies were performed with the antagonist radioligand [3H]GR125743 on mutant and wild-type receptors stably expressed in Chinese hamster ovary cells (CHO)-K1 cells. Substitution of tryptophan 327 by alanine resulted in decreased affinities of all ligands tested. The most prominent changes in affinity were observed for the antagonist methiothepin and the antimigraine drug sumatriptan, which were reduced approximately 300- and 60-fold, respectively. Nevertheless, the affinity of 5-HT remained the same. Replacement of the aspartic acid 352 by alanine reduced high-affinity binding of 5-HT. Substitution of cysteine 326 by alanine had minor effects on ligand binding. Some of these results agree with the results from mutagenesis studies of the corresponding amino acids in other receptors. However, some notable differences also emerge showing that functional roles of individual amino acid residues must be tested experimentally in each receptor subtype.

Characterization of the cloned atlantic cod neuropeptide Y-Yb receptor: peptide-binding requirements distinct from known mammalian Y receptors

Five members of the neuropeptide Y (NPY) receptor family have been cloned in mammals. The recently cloned NPY receptor in the Atlantic cod seems to be distinct from the mammalian subtypes as it has only 50% identity to Y1, Y4, and y6 and only 30% to Y2 and Y5. In most of the other families of G-protein-coupled receptors, species homologues have 65-90% identity between fishes and mammals. The functional expression and detailed pharmacological characterization of this cod NPY receptor, designated Yb, is reported. Membranes of cells transiently transfected with cod Yb showed saturable [(125)I]PYY binding with a K(d) of 45 pM. The pharmacological profile is similar to those of both the zebrafish Yb and Yc receptors and distinct from those of the mammalian NPY receptors. In competition experiments the cod Yb receptor had the following rank order of potencies: porcine PYY = porcine NPY = p[Leu(31), Pro(34)]NPY > zebrafish PYY > zebrafish NPY >> NPY2-36 = NPY3-36 > NPY18-36 > bovine PP = [D-Trp(32)]NPY > BIBP3226. This is in sharp contrast to the high selectivity of BIBP3226 for the Y1 receptor from all mammalian species. Together with the low amino acid identity of cod Yb with the mammalian Y1, Y4, and y6 receptors, this is further support for the notion that fish Yb constitutes a distinct NPY receptor subtype.

Neuropeptide Y receptor subtype with unique properties cloned in the zebrafish: the zYa receptor

Neuropeptide Y (NPY) belongs to a family of structurally related neuroendocrine peptides for which five different G-protein-coupled receptor subtypes have been cloned in mammals. To identify additional subtypes we have performed PCR with degenerate primers in different species. We describe here the cloning and pharmacological profile of a unique NPY receptor subtype in the zebrafish that has tentatively been called the zYa receptor. It has 46-50% amino acid identity to the mammalian Y1, Y4 and y6 receptors and the previously cloned zebrafish receptors zYb and zYc, and only about 27% to Y2 and Y5. The zYa receptor binds NPY and PYY from mammals as well as zebrafish with high affinities and has a K(d) of 28 pM for porcine (125)I-PYY. It has a unique binding profile displaying some features in common with each of the mammalian Y1, Y2 and Y5 receptors. In a microphysiometer assay the receptor responds with extracellular acidification. Chromosomal mapping in the zebrafish genome of zYa, zYb and zYc receptor genes indicates a possible orthologous relationship between zYc and mammalian y6, but identifies no obvious mammalian ortholog for zYa (zYb is a recent copy of zYc in the fish lineage). These results imply that previous studies of NPY in fishes, which have striven to interpret the effects within the framework of mammalian Y1, Y2, and Y5 receptors, need to be reevaluated. Thus, the sequence comparisons, pharmacological properties, and chromosomal localization suggest that the zYa receptor is a novel NPY receptor subtype which is likely to be present also in mammals.

Perturbation of the synaptic release machinery in hippocampal neurons by overexpression of SNAP-25 with the Semliki Forest virus vector

We have examined whether the Semliki Forest virus (SFV) expression vector can be used to manipulate the exocytotic machinery in cultured hippocampal neurons. Autaptic responses were recorded in individually identified neurons which overexpressed either a non-synaptic protein, the transferrin receptor, or the synaptic SNARE protein SNAP-25 (synaptosomal-associated protein of 25 kDA). In neurons overexpressing the transferrin receptor, autaptic responses occurred in a similar proportion and had similar amplitudes (12-18 h postinfection) as in uninfected control neurons. With increasing time after the infection, an increasing proportion of the transferrin receptor-overexpressing neurons showed changes in the shape of the cell body, but the autaptic responses appeared normal as long as recordings could be performed (up to 30 h postinfection). In contrast, in SNAP-25-overexpressing neurons, the proportion of responding cells was reduced 12-18 h after the infection, and the amplitude of the autaptic current in responding neurons was also reduced. The sensitivity to exogenously applied glutamate was, however, unchanged. Biochemical analysis showed that 50% of the overexpressed SNAP-25 was palmitoylated. The levels of two other SNAREs, syntaxin and synaptobrevin (also called vesicle-associated membrane protein), were not affected. Our results indicate that the SFV vector can provide an effective tool to study the function of proteins participating in neurotransmitter release.

Cloning the neuropeptide Y exon 2 from sea bass (Dicentrarchus labrax)

A partial genomic library of sea bass DNA was constructed and screened with a goldfish NPY cDNA probe. Two identical clones were isolated and sequenced. The clones contain a segment with high identity to exon 2 of the NPY gene in tetrapods. This segment encodes a 62-amino acid peptide consisting of a signal peptide of 28 amino acids and the main portion of the mature NPY (34 amino acids). In the latter extension, sea bass NPY shows high identity with the human and deduced ancestral gnathostome sequences (88 and 91%, respectively). The open reading frame is followed by a consensus splice donor site. Northern blot hybridization to examine tissue distribution detected a 1-kb RNA transcript restricted to brain tissue. These data show that the NPY gene of this teleost fish has the same intron positions as tetrapods for at least two of the gene's three introns. In addition, the high evolutionary conservation of NPY is corroborated since sea bass NPY exhibits the same identity to both goldfish and human NPY.

The cloned guinea pig neuropeptide Y receptor Y1 conforms to other mammalian Y1 receptors

We have cloned the guinea pig neuropeptide Y (NPY) Y1 receptor and found it to be 92-93% identical to other cloned mammalian Y1 receptors. Porcine NPY and peptide YY (PYY) displayed affinities of 43 pM and 48 pM, respectively. NPY2-36 and NPY3-36 had 6- and 46-fold lower affinity, respectively, than intact NPY. Functional coupling was measured by using a microphysiometer. Human NPY and PYY were equipotent in causing extracellular acidification with EC50 values of 0.59 nM and 0.69 nM, respectively, whereas NPY2-36 and NPY3-36 were about 15-fold and 500-fold less potent, respectively, than NPY. The present study shows that the cloned guinea pig Y1 receptor is very similar to its orthologues in other mammals, both with respect to sequence and pharmacology. Thus, results from previous studies on guinea pig NPY receptors might imply the existence of an additional Y1-like receptor sensitive to B1BP3226.

The highly conserved synapse protein SNAP-25 displays sequence variability in the cockroach Leucophaea maderae

SNAP-25 (synaptosome-associated protein of 25 kD) is attached to the intracellular side of presynaptic membranes where it serves as a target receptor for the vesicle docking machinery prior to release of neurotransmitter. SNAP-25 displays a high degree of sequence conservation between vertebrates and Drosophila melanogaster. To obtain more information about conserved regions of SNAP-25, we have isolated cDNA clones from the cockroach Leucophaea maderae. One clone (Lm1) encoded a full-length SNAP-25 protein and its deduced amino acid sequence is 77% identical to Drosophila SNAP-25. Surprisingly, the cockroach protein is 17 amino acids shorter than Drosophila SNAP-25 at the carboxy terminus. Four other cDNA clones encode parts of SNAP-25 and each clone has distinct characteristics, including amino acid replacements and unique carboxy termini. Thus, the highly conserved protein SNAP-25 displays unexpected sequence variability in the cockroach that may indicate specialized SNAP-25 isoforms.

Cloning of two loci for synapse protein Snap25 in zebrafish: comparison of paralogous linkage groups suggests loss of one locus in the mammalian lineage

Synaptosome-associated protein of 25 kDa (Snap25) is an intracellular protein that is defined as a target receptor for synapse vesicles prior to neurotransmitter release. Snap25 is highly conserved, with 61% identity between human and Drosophila melanogaster. Whereas mammals and chicken have a single locus for Snap25, the tetraploid goldfish has at least three loci. We report that the zebrafish has two loci with 91% amino acid identity to each other. The alternative splicing of exon 5 arose before the gene duplication. The expression patterns of the two loci are virtually identical in adult zebrafish. The two zebrafish snap25 loci are located in paralogous linkage groups that seem to correspond to human chromosome 20, which harbors the SNAP locus, and human chromosome 14. Because no additional Snap25 homologue has been reported for any mammal or chicken, snap25.2 may have been lost in the amniote or even tetrapod lineage.

Preprocholecystokinin mRNA-expressing neurons in the rat parabrachial nucleus: subnuclear localization, efferent projection, and expression of nociceptive-related intracellular signaling substances

The pontine parabrachial nucleus (PB) is a major target for ascending fibers from nociresponsive dorsal horn neurons. Several different neuropeptides have been identified in the PB. By using double-labeling methods that combine in situ hybridization histochemistry with retrograde tract tracing and immunohistochemistry, we have examined the subnuclear localization of preprocholecystokinin mRNA (ppCCK)-containing neurons, investigated their efferent projection, and analyzed their expression of intracellular signaling substances that may be of importance for nociceptive processing. The results show that neurons containing ppCCK are preferentially localized to the superior lateral subnucleus (PBsl), whereas other subnuclei, such as the dorsal lateral, external lateral, central lateral, and ventral lateral subnuclei, and the Kölliker-Fuse nucleus, contain only moderate to small numbers of such neurons. Injections of the retrograde tracer cholera toxin subunit b into the ventromedial hypothalamus demonstrated that ppCCK-containing neurons in PBsl were projection neurons. Following nociceptive stimulation, the ppCCK-containing neurons expressed FOS protein as well as phosphorylated cyclic AMP-responsive element-binding protein (CREB). In addition, Ca2+/calmodulin-dependent kinase II (CaMKII) was heavily and rather selectively expressed in PBsl and was co-localized to ppCCK-containing neurons. These observations show that nociceptive stimuli activate a cholecystokinin pathway from the parabrachial nucleus to the ventromedial hypothalamus that may be important for homeostatic responses to tissue damage, and point to a putative intracellular route for Ca2+-mediated FOS transcription via CaMKII and CREB for the regulation of ppCCK transcription.

Cloning of a neuropeptide Y/peptide YY receptor from the Atlantic cod: the Yb receptor

Neuropeptide Y (NPY) belongs to a family of structurally related neuroendocrine peptides that bind to G protein-coupled receptors. Five different receptor subtypes have recently been cloned in mammals and we have found another three receptor genes in the zebrafish, called zYa, zYb, and zYc, that appear to be distinct subtypes as deduced from their widely different sequences. To elucidate the evolutionary relationships between the mammalian and zebrafish receptors, we have used the zebrafish probes to isolate genomic clones from another teleost fish, the Atlantic cod, Gadus morhua. We present here the sequence of the cod Yb gene, whose deduced protein sequence is equally identical to the zebrafish Yb (69%) and Yc proteins (66%). The two zebrafish receptors are 76% identical to each other, suggesting that they arose by gene duplication in the zebrafish lineage after divergence from the cod lineage. The five cloned mammalian NPY-family receptors and the three cloned zebrafish NPY receptors indicate that this is the largest receptor family among all peptide receptors that belong to the superfamily of G protein-coupled receptors.

The cloned guinea pig pancreatic polypeptide receptor Y4 resembles more the human Y4 than does the rat Y4

Pancreatic polypeptide (PP) is involved in gastrointestinal functions and forms, together with neuropeptide Y (NPY) and peptide YY (PYY), the PP-fold family of peptides. The PP-binding receptor subtype Y4 has so far been cloned in human, rat, and mouse, and displays extensive species differences regarding sequence, pharmacology, and distribution. To explore this variability further, we have cloned the Y4 receptor in the guinea pig, which is evolutionarily equally distantly related to both humans and rodents. The guinea pig Y4 receptor is 84% identical to the human Y4 receptor, but only 74-75% identical to the rat and mouse receptors. The two latter are 75-76% identical to human Y4. The guinea pig Y4 receptor bound 125I-hPP with a dissociation constant (Kd) of 29+/-3 pM. The pharmacological profile of guinea pig Y4 has the following rank order of potencies: PP > NPY approximately = PYY approximately = LP-NPY approximately = LP-PYY > NPY2-36 >> [D-Trp32]NPY. Thus, the guinea pig receptor is more similar to the human Y4 than to the rat Y4 both in sequence and pharmacology. This agrees with the greater identity between guinea pig and human PP compared to rat PP. These comparisons suggest that the rodent PPs and Y4 receptors have an accelerated replacement rate.

Cloning and functional expression of the guinea pig neuropeptide Y Y2 receptor

Five neuropeptide Y (NPY) receptor subtypes have been cloned in mammals. The degree of sequence conservation differs considerably between subtypes as well as between evolutionary lineages. To shed further light on this, we have cloned the five NPY receptors in the guinea pig. Here, we report the cloning of the guinea pig Y2 receptor. The Y2 receptor is generally highly conserved, with 90-95% identity between different orders of mammals, including the guinea pig. The guinea pig receptor has a divergent cytoplasmic tail, indicating possible differences in regulation of signalling and/or down regulation. COS-7 cells transiently transfected with the gpY2 receptor show saturable 125I-PYY binding with a Kd = 6 pM. In displacement experiments, the gpY2 receptor was similar to the human and rat receptors with the following rank order of potencies: pNPY > pPYY > pNPY13-36 = pNPY22-36 >> [Leu31Pro34]NPY > BIBP3226. Thus, the guinea pig Y2 receptor is well conserved in comparison with human and rat with regard to both amino acid sequence and pharmacological profile.

Co-localized neuropeptide Y and GABA have complementary presynaptic effects on sensory synaptic transmission

We have examined the morphological relationship of neuropeptide Y (NPY) and GABAergic neurons in the lamprey spinal cord, and the physiological effects of NPY and GABA(B) receptor agonists on afferent synaptic transmission. NPY-containing fibres and cell bodies were identified in the dorsal root entry zone. NPY immunoreactive (-ir) fibres made close appositions with primary afferent axons. Co-localization of NPY and GABA-ir was found in the dorsal horn and dorsal column. Fifty-two per cent of NPY-ir profiles showed immunoreactivity to GABA at the ultrastructural level. Electron microscopic analysis showed that NPY-immunoreactivity was present throughout the axoplasm, including over dense core vesicles, whereas GABA-immunoreactivity was mainly found over small synaptic vesicles. Synthetic lamprey NPY, and the related peptide, peptide YY, reduced the amplitude of monosynaptic afferent EPSPs in spinobulbar neurons. NPY had no significant effect on the postsynaptic input resistance or membrane potential, the electrical component of the synaptic potential, or the response to glutamate, but it could reduce the duration of presynaptic action potentials, suggesting that it was acting presynaptically. NPY also reduced the excitability of the spinobulbar neurons, suggesting at least one postsynaptic effect. Because NPY and GABA colocalize, we compared the effects of NPY and the GABA(B) agonist baclofen. Both presynaptically reduced EPSP amplitudes, baclofen having a larger effect and a faster onset and recovery than NPY. The GABA(B) antagonist phaclofen reduced the effect of baclofen, but not that of NPY. We conclude that NPY and GABA are colocalized in terminals in the dorsal spinal cord of the lamprey, and that they have complementary actions in modulating sensory inputs.

Mutagenesis of the human 5-HT1B receptor: differences from the closely related 5-HT1A receptor and the role of residue F331 in signal transduction

We have used a combination of sequence comparisons, computer-based modeling and site-directed mutagenesis to investigate the molecular interactions involved in ligand binding and signal transduction of the human 5-HT1B receptor. Two amino acid residues, S212 in transmembrane region (TM) V and F331 in TM VI, were replaced by alanines. These amino acids are conserved in many G protein-coupled receptors and therefore likely to be important for receptor function. The mutant receptors were expressed in Chinese hamster ovary cells. The 5-HT-like agonist 5-carboxamido-tryptamine (5-CT) bound with 15-fold lower affinity to the S212A mutant as compared to wild-type receptor and the antagonist methiothepin bound with 17-fold lower affinity to the F331A mutant. No reduction in the affinity of 5-HT was seen for the S212A mutant, although an equivalent mutation in the 5-HT1A receptor resulted in a 100-fold reduction of 5-HT binding. The inhibition of forskolin-stimulated cyclic AMP production by 5-HT was significantly reduced in cells expressing the F331A mutant, even though the endogenous ligand 5-HT bound with somewhat increased affinity. Methiothepin acted as an inverse agonist and increased the forskolin-stimulated cyclic AMP production at both the wild-type receptor and the mutants, and the effect was stronger on the F331A mutant. These results suggest that F331 is involved in the conformational changes necessary for signal transduction.

Site-directed mutagenesis of the human 5-HT1B receptor

Site-directed mutagenesis was used to investigate the molecular interactions involved in ligand binding to the human 5-HT1B receptor. Six mutants were constructed at four positions and expressed in Chinese hamster ovary cells. Substitution of the amino acid F185 in transmembrane region IV by an alanine increased the affinities of sumatriptan, methysergide and 8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT) 3-4-fold and substitution by a methionine increased the affinities of methysergide and methiothepin 2- and 3-fold, respectively. Substitution of amino acid S334 in transmembrane region VI by an alanine increased the affinity of 8-OH-DPAT 5-fold. In accordance with this, the EC50 value of 8-OH-DPAT was decreased 7-fold. This suggests that the serine at position 334 causes steric hindrance for 8-OH-DPAT binding that is lost in the S334A mutant. Mutation of F354 in transmembrane region VII, which differs between receptor subtypes, increased the affinity of methiothepin 2-3-fold but the affinities of the other compounds tested were essentially unchanged.

Vertebrate genome evolution and the zebrafish gene map

In chordate phylogeny, changes in the nervous system, jaws, and appendages transformed meek filter feeders into fearsome predators. Gene duplication is thought to promote such innovation. Vertebrate ancestors probably had single copies of genes now found in multiple copies in vertebrates and gene maps suggest that this occurred by polyploidization. It has been suggested that one genome duplication event occurred before, and one after the divergence of ray-finned and lobe-finned fishes. Holland et al., however, have argued that because various vertebrates have several HOX clusters, two rounds of duplication occurred before the origin of jawed fishes. Such gene-number data, however, do not distinguish between tandem duplications and polyploidization events, nor whether independent duplications occurred in different lineages. To investigate these matters, we mapped 144 zebrafish genes and compared the resulting map with mammalian maps. Comparison revealed large conserved chromosome segments. Because duplicated chromosome segments in zebrafish often correspond with specific chromosome segments in mammals, it is likely that two polyploidization events occurred prior to the divergence of fish and mammal lineages. This zebrafish gene map will facilitate molecular identification of mutated zebrafish genes, which can suggest functions for human genes known only by sequence.

Multiplicity of neuropeptide Y receptors: cloning of a third distinct subtype in the zebrafish

Five different receptor subtypes for neuropeptide Y (NPY) have recently been cloned in mammals. We have discovered three distinct subtypes by PCR in the zebrafish, Danio rerio, and describe here one of these called zYc. The protein sequence identity is 46-51% to mammalian subtypes Y1, Y4 and Y6 and to zebrafish Ya, i.e., the same degree of identity as these subtypes display to one another. The identity to zYb is higher, 75%, indicating that zYb and zYc share a more recent ancestor. The zYc receptor binds NPY and PYY (peptide YY) from mammals as well as zebrafish with high affinities and has a Kd of 16 pM for 125I-pPYY. The pharmacological profile is similar to, but distinct-from, mammalian Y1. zYc inhibits cAMP synthesis. This work suggests that NPY has more receptor subtypes than any other peptide that binds to G protein-coupled receptors. Work is in progress to see if the zebrafish receptors are present in mammals.

Embryonic expression of the mRNA for the rat homologue of the fusin/CXCR-4 HIV-1 co-receptor

We have previously cloned a human receptor recently shown to be a cofactor for entry of T-tropic HIV-1 strains into CD4+ cells, now named fusin. Stromal derived factor-1 (SDF-1) is an endogenous ligand for fusin, also called CXCR-4. Here we show the distribution of fusin/CXCR-4 mRNA during ontogeny in the rat. The onset of mRNA expression is around embryonic day 9 and the mRNA expression is high in the thymus as well as proliferative areas of the brain during development. Our results suggest: (1) that fusin/CXCR-4 might have a dual role in both brain development and the immune system; (2) that SDF-1 has a role in brain development or that additional physiological ligands exist for this receptor; (3) co-expression of CD4 and fusin/CXCR-4 may make fetuses susceptible to HIV infection during development.