Characterization of peptides related to neuropeptide tyrosine and peptide tyrosine-tyrosine from the brain and gastrointestinal tract of teleost fish

Evolution of peptide YY analogs for the management of type 2 diabetes and obesity

Peptide YY (PYY) is a gastrointestinal hormone consisting of 36 amino acids, that is predominantly secreted by intestinal l-cells. Originally extracted from pig intestines, it belongs to the pancreatic polypeptide (PP) family, but has functions distinct from those of PP and neuropeptide Y (NPY). PYY is a potential treatment for type 2 diabetes mellitus (T2DM) because of its ability to delay gastric emptying, reduce appetite, decrease weight, and lower blood glucose. However, the clinical use of PYY is limited because it is rapidly cleared by the kidneys and degraded by enzymes. In recent years, researchers have conducted various structural modifications, including amino acid substitution, PEGylation, lipidation, and fusion of PYY with other proteins to prolong its half-life and enhance its biological activity. This study presents an overview of the recent progress on PYY, including its physiological functions, metabolites and structure-activity relationships.

Brain neuropeptides in central ventilatory and cardiovascular regulation in trout

Many neuropeptides and their G-protein coupled receptors (GPCRs) are present within the brain area involved in ventilatory and cardiovascular regulation but only a few mammalian studies have focused on the integrative physiological actions of neuropeptides on these vital cardio-respiratory regulations. Because both the central neuroanatomical substrates that govern motor ventilatory and cardiovascular output and the primary sequence of regulatory peptides and their receptors have been mostly conserved through evolution, we have developed a trout model to study the central action of native neuropeptides on cardio-ventilatory regulation. In the present review, we summarize the most recent results obtained using this non-mammalian model with a focus on PACAP, VIP, tachykinins, CRF, urotensin-1, CGRP, angiotensin-related peptides, urotensin-II, NPY, and PYY. We propose hypotheses regarding the physiological relevance of the results obtained.

Autonomic control of gut motility: a comparative view

Gut motility is regulated to optimize food transport and processing. The autonomic innervation of the gut generally includes extrinsic cranial and spinal autonomic nerves. It also comprises the nerves contained entirely within the gut wall, i.e. the enteric nervous system. The extrinsic and enteric nervous control follows a similar pattern throughout the vertebrate groups. However, differences are common and may occur between groups and families as well as between closely related species. In this review, we give an overview of the distribution and effects of common neurotransmitters in the vertebrate gut. While the focus is on birds, reptiles, amphibians and fish, mammalian data are included to form the background for comparisons. While some transmitters, like acetylcholine and nitric oxide, show similar distribution patterns and effects in most species investigated, the role of others is more varying. The significance for these differences is not yet fully understood, emphasizing the need for continued comparative studies of autonomic control.

Cloning and characterization of neuropeptide Y (NPY) and cocaine and amphetamine regulated transcript (CART) in Atlantic cod (Gadus morhua)

Neuropeptide Y (NPY) and cocaine and amphetamine regulated transcript (CART) are two neuropeptides involved in the regulation of feeding in both mammals and fish. NPY stimulates feeding whereas CART inhibits feeding. In this study, we have cloned the full-length cDNA and complete genomic DNA sequences for NPY and CART in Atlantic cod. Atlantic cod preproNPY share a 45-85% identity with preproNPY from other fish whereas preproCART shows a 70% identity to CART peptides from zebrafish and goldfish. RT-PCR revealed that NPY mRNA is expressed in brain, in particular the forebrain, and in peripheral tissues, including intestine and kidney. CART mRNA is expressed throughout the brain and in ovaries. In order to assess the role of these peptides in the regulation of feeding, we examined changes in mRNA expression in the forebrain before, during and after a meal. NPY and CART mRNA both undergo peri-prandial changes in expression, with NPY levels being elevated around meal time and CART showing a decline 2 h after a meal. Food deprivation for 7 days induced a decrease in CART mRNA expression in the brain but did not affect NPY mRNA expression. Overall, our results suggest that NPY and CART are conserved peptides that might be involved in the regulation of feeding and other physiological functions in Atlantic cod.

The role of neuropeptide Y, orexins, cocaine and amphetamine-related transcript, cholecystokinin, amylin and leptin in the regulation of feeding in fish

In fish, as in all vertebrates, the brain is the primary center of regulation of food intake. Afferent signals continuously inform the central nervous system about changes in energy homeostasis. The brain interprets and integrates these signals and responds with efferent signals that help maintain a constant energy balance. Neuropeptides that originate from the hypothalamus regulate food intake either by stimulating (orexigenic factors) or inhibiting (anorexigenic factors) appetite. Studies using brain or peripheral peptide injections have shown that neuropeptide Y (NPY) and orexins are potent orexigenic factors in fish, whereas cocaine and amphetamine-related transcript (CART) peptides decrease food intake. Complex interactions exist between these central neuropeptide systems. For example, NPY and orexins have synergistic effects on food intake and they are both modulated by CART peptides. These systems are also influenced by endocrine factors from the periphery, including hormones from the gut, such as cholecystokinin (CCK), the pancreatic hormone amylin and the adipocyte hormone leptin. Fasting or ingestion of a meal induces changes in the mRNA expression of NPY, orexins and CART, suggesting that nutritional status modulates the action of these systems. This brief review will focus on our current knowledge on the structure and role of these six appetite-regulating peptides in fish.

Characterization of NPY receptor subtypes Y2 and Y7 in rainbow trout Oncorhynchus mykiss

We report the cloning and pharmacological characterization of two neuropeptide Y (NPY) receptor subtypes, Y2 and Y7, in rainbow trout (Oncorhynchus mykiss). These subtypes are approximately 50% identical to each other and belong to the Y2 subfamily of NPY receptors. The binding properties of the receptors were investigated after expression in human HEK-293 EBNA cells. Both receptors bound the three zebrafish peptides NPY, PYYa, and PYYb, as well as porcine NPY and PYY, with affinities in the nanomolar range that are similar to mammalian Y2. The affinity of the truncated porcine NPY fragments, NPY 13-36 and NPY 18-36 was markedly lower compared to mammalian and chicken Y2. This suggests that mammalian and chicken Y2 are unique among NPY receptors in their ability to bind truncated peptide fragments. The antagonist BIIE0246, developed for mammalian Y2, did not bind either of the two rainbow trout receptors. Our results support the proposed expansion of this gene family by duplications before the gnathostome radiation. They also reveal appreciable differences in the repertoire and characteristics of NPY receptors between fish and tetrapods stressing the importance of lineage-specific gene loss as well as sequence divergence after duplication.

Regulation of fish gonadotropins

Neurohormones similar to those of mammals are carried in fish by hypothalamic nerve fibers to regulate directly follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Gonadotropin-releasing hormone (GnRH) stimulates the secretion of FSH and LH and the expression of the glycoprotein hormone alpha (GPalpha), FSHbeta, and LHbeta, as well as their secretion. Its signal transduction leading to LH release is similar to that in mammals although the involvement of cyclic AMP-protein kinase A (cAMP-PKA) cannot be ruled out. Dopamine (DA) acting through DA D2 type receptors may inhibit LH release, but not that of FSH, at sites distal to activation of protein kinase C (PKC) and PKA. GnRH increases the steady-state levels of GPalpha, LHbeta, and FSHbeta mRNAs. Pituitary adenylate cyclase-activating polypeptide (PACAP) 38 and neuropeptide Y (NPY) potentiate GnRH effect on gonadotropic cells, and also act directly on the pituitary cells. Whereas PACAP increases all three subunit mRNAs, NPY has no effect on that of FSHbeta. The effect of these peptides on the expression of the gonadotropin subunit genes is transduced differentially; GnRH regulates GPalpha and LHbeta via PKC-ERK and PKA-ERK cascades, while affecting the FSHbeta transcript through a PKA-dependent but ERK-independent cascade. The signals of both NPY and PACAP are transduced via PKC and PKA, each converging at the ERK level. NPY regulates only GPalpha- and LHbeta-subunit genes whereas PACAP regulates the FSHbeta subunit as well. Like those of the mammalian counterparts, the coho salmon LHbeta gene promoter is driven by a strong proximal tripartite element to which three different transcription factors bind. These include Sf-1 and Pitx-1 as in mammals, but the function of the Egr-1 appears to have been replaced by the estrogen receptor (ER). The GnRH responsive region in tilapia FSHbeta 5' flanking region spans the canonical AP1 and CRE motifs implicating both elements in conferring GnRH responsiveness. Generally, high levels of gonadal steroids are associated with high LHbeta transcript levels whereas those of FSHbeta are reduced when pituitary cells are exposed to high steroid levels. Gonadal or hypophyseal activin also participate in the regulation of FSHbeta and LHbeta mRNA levels. However, gonadal effects are dependent on the gender and stage of maturity of the fish.

Corticotropin-releasing factor and neuropeptide Y mRNA levels are elevated in the preoptic area of socially subordinate rainbow trout

The objectives of this study were to characterize rainbow trout (Oncorhynchus mykiss) corticotropin-releasing factor (CRF) and neuropeptide Y (NPY) cDNAs and to determine their mRNA levels in response to social stress. Standard cloning techniques were used to obtain cDNAs, sequences for trout NPY and two CRF isoforms. At the predicted amino acid level, our NPY sequence differs from the trout amino acid sequence reported by. A phylogenetic analysis suggests that the two CRF isoforms result from a gene duplication that occurred in a common ancestor of salmonids. A tissue distribution demonstrated that the mRNAs of both CRF isoforms are predominantly present in the preoptic area of the trout brain, whereas NPY mRNA is more abundant in the telencephalon. Pairs of sized-matched juvenile female trout were allowed to interact for 72 h and social ranks were assigned on the basis of behavioural observations. Mean plasma cortisol levels were 13-fold higher in subordinate than in dominant trout. As measured by ribonuclease protection assay, CRF1 and NPY mRNA levels were respectively 51 and 32% higher in the preoptic area of subordinate trout; in addition, CRF1 and NPY mRNA levels were positively correlated (R2=0.44). These results suggest that subordinate rainbow trout chronically maintain high levels of CRF mRNA during social stress and that NPY may be involved in the control of the stress axis in trout.

Neuropeptide tyrosine-like immunoreactive system in the brain, olfactory organ and retina of the zebrafish, Danio rerio, during development

The anatomical distribution of neuropeptide tyrosine (NPY)-like immunoreactivity was investigated in the brain, olfactory organ and retina of the zebrafish, Danio rerio, during development and in juvenile specimens, by using the indirect immunofluorescence and the peroxidase-antiperoxidase methods. In 60 h post fertilization (hpf) embryos, NPY-like immunoreactive cell bodies appeared in the hypothalamus, within the posterior periventricular nucleus. Few positive nerve fibers were found in the hypothalamus and in the tegmentum of the mesencephalon. In 72 hpf embryos, a new group of NPY-like immunoreactive cells was found in the olfactory pit. At day 4 of development, NPY-like immunoreactive cell bodies were detected between the olfactory pit and the olfactory organ. In the hypothalamus the location of positive cell bodies was similar to that reported in the previous developmental stages. A few positive nerve fibers appeared in the tegmentum of the rhombencephalon. At days 7 and 15 of development, the distribution of NPY-like immunoreactivity was very similar to that reported at day 4. However, at day 15, NPY-like immunoreactivity appeared for the first time in amacrine cells of the retina and in nerve fibers of the tectum of the mesencephalon. In 1-month/3-month-old animals, additional groups of NPY-like immunoreactive cell bodies appeared in the glomerular layer of the olfactory bulbs, the terminal nerve, the lateral nucleus of the ventral telencephalic area, the entopeduncular nucleus and in the medial region of the reticular formation of the rhombencephalon. These results show that NPY-like immunoreactive structures appear early during ontogeny of zebrafish. The distribution of the immunoreactive system increases during the ontogeny, the juvenile stages, and reaches the complete development in mature animals. The location of NPY-like immunoreactivity indicates that, during development, NPY could be involved in several neuromodulatory functions, including the processing of visual and olfactory information. In 1-month/3-month-old animals, NPY-like immunoreactive nerve fibers are present in the pituitary, suggesting that, from these stages onward, NPY may influence the secretion of pituitary hormones.

Neuropeptide Y effects on vasorelaxation and intestinal contraction in the Atlantic cod Gadus morhua

Neuropeptide Y (NPY) has prominent cardiovascular effects in mammals and sharks, but no such effect has previously been demonstrated in any teleost fish. In the Atlantic cod, we found that cod NPY (10(-10)-10(-6) M) relaxed celiac arteries precontracted with epinephrine, and weak contractions were elicited in intestinal ring preparations. A few NPY-immunoreactive nerve fibers were present along small gut arteries. The results suggest that cod NPY produces vasorelaxation both by a direct action on smooth muscle and by release of prostaglandins, but with no involvement of nitric oxide, leukotrienes, or endothelium-derived relaxing factors. An additional indirect effect involving another neurotransmitter may occur. Cod NPY (10(-7) M) and human NPY (10(-7) M) had identical effects on the vessels. Small differences only in the effects of porcine [Leu(31),Pro(34)]NPY, NPY-(13-36), and cod NPY suggest the presence of a Y(1) subfamily receptor, similar to the zebrafish Ya receptor. A physiological role for NPY in teleost vasculature is concluded, but surprisingly the effect, a vasodilation, is opposite to that in mammals and is mediated by prostaglandins.

Development of neuropeptide Y-related peptides in the digestive organs during the larval stage of Japanese flounder, Paralichthys olivaceus

cDNAs encoding three neuropeptide Y (NPY)-related peptides were identified from the Japanese flounder. One peptide corresponds to NPY, and its mRNA was expressed in the brain and retina. The second peptide corresponds to peptide YY (PYY), and its mRNA was expressed in the brain but surprisingly not in the digestive organs. This suggests that PYY lacks function as a digestive hormone in flounder. The third peptide corresponds to peptide Y (PY), and its mRNA occupied the brain and the endocrine cells of the intestine and the pancreatic accessory islets, but not of the principal islet. This suggests that PY has a dual role as a neuropeptide and a digestive hormone. In flounder larvae, PY cells appear in the intestinal epithelia at 3 days posthatching (dph), when larvae start feeding, in contrast to the endocrine pancreas at 30 dph. Therefore, the endocrine system of PY, which probably regulates the pancreatic enzyme secretion, develops synchronously with the start of feeding in the intestine but about 1 month later in the endocrine pancreas in flounder.

The origin and evolution of peptide YY (PYY) and pancreatic polypeptide (PP)

It is generally accepted that the neuropeptide Y (NPY) family of homologous peptides arose as a result of a series of gene duplication events. Recent advances in comparative genomics allow to formulate a hypothesis that explains, at least in part, the complexity of the family. Chromosome mapping studies reveal that the gene encoding PYY may have arisen from a common ancestral gene (termed NYY) in an ancient chromosomal duplication event that also involved the hox gene clusters. A tandem duplication of the PYY gene concomitant with or just before the emergence of tetrapods generated the PPY gene encoding PP. In the primate and ungulate lineages, the PYY-PPY gene cluster has undergone a more recent gene duplication event to create a PYY2-PPY2 gene cluster on the same chromosome. In the human and baboon, this cluster probably does not encode functional NPY family peptides but expression of the bovine PYY2 gene generates seminalplasmin, a major biologically active component of bull semen. An independent duplication of the PYY gene in the lineage of teleost fish has generated peptides of the PY family that are synthesized in the pancreatic islets of Acanthomorpha. The structural organization of the biosynthetic precursors of PYY and PP (preproPYY and preproPP) has been quite well preserved during the evolution of vertebrates but conservative pressure on individual domains in the proteins has not been uniform. The duplication of the PYY gene that generated the PPY gene appears to have resulted in a relaxation of conservative pressure on the functional domain with the result that the amino acid sequences of tetrapod PYYs are more variable than the PYYs of jawed fish. Although the primary structure of PP has been quite strongly conserved in mammals, with the exception of the rodents, the extreme variability in the sequences of amphibian and reptilian PPs means that the peptide is a useful molecular marker to study the branching order in early tetrapod evolution

Evolution of vertebrate neuropeptides

This review describes some of the most typical features in the evolution of neuropeptides. Neuropeptides are synthesized like other polypeptides and proteins, with an amino acid sequence determined by the DNA sequence of the corresponding gene. Mutations of bases in the coding regions of the DNA lead to changes in amino acid sequence, and explain the differences in amino acid sequence of a certain neuropeptide in different animal species. The more distantly related two species are, the more substitutions can be found in one and the same neuropeptide. The biologically active part of the neuropeptide is usually the most conserved part. Neuropeptides also form families of closely related peptides, where several members may occur in one animal species. This is due to gene or exon duplications followed by mutations. Gene splicing and posttranslational processing decides the gene product in a single cell. Difference in sequence may cause difference in function, but more often than not, members of a family appear to produce the same effect. Three neuropeptide families, the tachykinins, the neuropeptide Y family, and the vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating peptide family will be described in more detail.

Gastroenteropancreatic hormones (insulin, glucagon, somatostatin, and multiple forms of PYY) from the pallid sturgeon, Scaphirhynchus albus (Acipenseriformes)

Insulin, glucagon, somatostatin-14, and three structurally related molecular forms of peptide tyrosine-tyrosine (PYY) were isolated from an extract of the combined pancreas and gastrointestinal tract of the pallid sturgeon, Scaphirhynchus albus. Pallid sturgeon insulin was identical to insulin from the Russian sturgeon, Acipenser guldenstaedti, and to insulin-2 from the paddlefish, Polyodon spathula, and was approximately twofold less potent than human insulin in inhibiting the binding of [3-[(125)I] iodotyrosine-A14] human insulin to the soluble human insulin receptor. The sturgeon glucagon (HSQGMFTNDY(10)-SKYLEEKLAQ(20) EFVEWLKNGK(30)S), like the two paddlefish glucagons, contains 31 rather than 29 amino acid residues, indicative of an anomalous pathway of posttranslational processing of proglucagon. Pallid sturgeon somatostatin, identical to human somatostatin-14, was also isolated in a second molecular form containing an oxidized tryptophan residue, but [Pro(2)]somatostatin-14, previously isolated from the pituitary of A. guldenstaedti, was not identified. Sturgeon PYY (FPPKPEHPGD(10)DAPAEDVAKY(20)YTALRHYINL(30) ITRQRY.HN(2)) was also isolated in variant forms containing the substitutions (Phe(1) --> Ala) and (Ala(18) --> Val), indicative of at least two gene duplications occurring within the Acipenseriformes lineage. The amino acid sequences of the pallidsturgeon PYY peptides are appreciably different from the proposed "ancestral" PYY sequence that has otherwise been very strongly conserved among the actinopterygian and elasmobranch fish.

cNeuropeptide 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.

Key words: neuropeptide Y, pancreatic polypeptide, fish pancreatic peptide, gene duplication.

Neuropeptide families and their receptors: evolutionary perspectives

Examination of families of neuropeptides and their receptors can provide information about phyletic relationships and evolutionary processes. Within an individual a given signal molecule may serve many diverse functions, mediated via subtypes of the receptor which may be coupled to their transduction mechanisms in different ways. The rate of evolution of a peptide may reflect or be reflected in the rate of evolution of its receptor. For example, in the neuropeptide Y (NPY) family, pancreatic polypeptide (PP) shows significant structural diversity, while NPY is highly conserved. Molecular forms of a given subtype of NPY receptor that is selectively activated by NPY (Y1 or Y2 or Y5) are also highly conserved, but the subtype that is primarily activated by PP (Y4), shows remarkable diversity. Also, between receptor subtypes there can be remarkable diversity. This is evident in several neuropeptide families, where a neuropeptide sequence is highly conserved across a wide range of species but where the receptor homology of subtypes with species tends to be much lower than homology between species. For example, human and rat vasopressin are identical, but the human V(1)- or V(2)-vasopressin receptors are approximately 80% homologous with rat V(1)- or V(2)-receptors, but within humans or rats the V(1)-receptor is less than 50% homologous with the V(2)-receptor. Furthermore, duplication of an ancestral gene is thought to have led to the co-presence in eutherian mammals of oxytocin and vasopressin, which have maintained a close structural similarity, yet in many species the oxytocin receptor is only 30 to 50% homologous with vasopressin receptors. Thus it appears that there has been greater evolutionary pressure to conserve the signal molecule, than to conserve the structure of the receptor. Evaluation of the evolution of neuropeptides and their receptors may be useful in determining phyletic relationships. Traditional classification places the guinea pig as a hystricomorph rodent within the same order (Rodentia) as the muriform or myomorph rat and mouse. However, molecular analyses of polypeptides have led to the suggestion that guinea pigs belong to a distinct order. Analysis of several neuropeptide sequences and the Y4 receptor supports this view. In general terms for both neuropeptides and receptors, sequence homology reflects phylogeny and taxonomy as based on morphological features. Within the oxytocin/vasopressin family in which peptides and receptors have been characterised in invertebrate representatives as well as fish and amphibia in addition to mammals, the molecular diversity correlates well with evolutionary diversity.

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.

Molecular evolution of peptide tyrosine--tyrosine: primary structure of PYY from the lampreys Geotria australis and Lampetra fluviatilis, bichir, python and desert tortoise

Peptide tyrosine-tyrosine (PYY) has been isolated from the intestines of two species of reptile, the desert tortoise Gopherus agassizii (Testudines) and the Burmese python Python molurus (Squamata), from the primitive Actinopterygian fish, the bichir Polypterus senegalis (Polypteriformes) and from two agnathans, the Southern-hemisphere lamprey Geotria australis (Geotriidae) and the holarctic lamprey Lampetra fluviatilis (Petromyzontidae). The primary structure of bichir PYY is identical to the proposed ancestral sequence of gnathostome PYY (YPPKPENPGE10/DAPPEELAKY20/YSALR HYINL30/ITRQRY). Tortoise and python PYY differ by six and seven residues, respectively, from the ancestral sequence consistent with the traditional view that the Testudines represent an earlier divergence from the primitive reptilian stock than the Squamates. The current views of agnathan phylogeny favor the hypothesis that the Southern-hemisphere lampreys and the holarctic lampreys arose from a common ancestral stock but their divergence is of a relatively ancient (pre-Tertiary) origin. The Geotria PYY-related peptide shows only two amino acid substitutions (Pro10-->Gln and Leu22-->Ser) compared with PYY from the holarctic lamprey Petromyzon marinus. This result was unexpected as Petromyzon PYY differs from Lampetra PYY deduced from the nucleotide sequence of a cDNA (Söderberg et al. J. Neurosci. Res. 1994;37:633-640) by 10 residues. However, a re-examination of an extract of Lampetra intestine revealed the presence of a PYY that differed in primary structure from Petromyzon PYY by only one amino acid residue (Pro10-->Ser). This result suggests that the structure of PYY has been strongly conserved during the evolution of Agnatha and that at least two genes encoding PYY-related peptides are expressed in Lampetra tissues.

Glucagon- and NPY-related peptide-immunoreactive cells in the gut of sea bass (Dicentrarchus labrax L.): a light and electron microscopic study

Glucagon and peptide of the neuropeptide Y (NPY) family immunoreactivities were studied in the gut of sea bass (Dicentrarchus labrax) using antisera against bovine/porcine glucagon, porcine glucagon, glicentin (10-30), bovine pancreatic polypeptide (PP), peptide tyrosine tyrosine (PYY), salmon PYY (sPYY), and NPY. Glucagon-, glicentin-, PYY-, and NPY-immunoreactive (ir) cells were detected in the stomach, and glucagon-, PP-, PYY-, sPYY-, and NPY-ir cells in the intestine. PP, PYY, and NPY immunoreactivities coexisted in intestinal endocrine cells (NPY-like peptide containing cells), in some of which there was also glucagon immunoreactivity. Preabsorption tests indicated that different products of the glucagon gene(s) are probably expressed in the stomach and intestine of sea bass and that the peptides belonging to the NPY family in the endocrine cells of the intestine are more similar to NPY than to other peptides of this family. Glucagon-ir cells in the stomach, and glucagon/NPY-like containing cells in the intestine, were characterized by conventional and immunogold electron-microscopic techniques. The glucagon cells had secretory granules with a clotted content, the gold particles being observed in both the core and the halo. Glucagon/NPY-like cells showed two types of secretory granules differing in size, both of which were immunogold labeled with anti-NPY and anti-sPYY; the smaller granules were weakly immunogold labeled with anti-glucagon.

Cholecystokinin, neuropeptide Y and galanin modulate the release of pancreatic somatostatin-25 and somatostatin-14 in vitro

The direct effects of cholecystokinin (CCK), neuropeptide Y (NPY) and galanin on somatostatin-14 (SS-14) and somatostatin-25 (SS-25), containing [Tyr7, Gly10]-SS-14 at its carboxy terminus and presumably derived from a different gene than that giving rise to SS-14, were evaluated on principal islets (Brockmann bodies) removed from rainbow trout, Oncorhynchus mykiss. The potential for peptidergic action was deduced from the extensive neural network innervating the Brockmann body and confirmed by immunohistochemistry. Immunopositive CCK-like staining was located around the periphery of principal islets as well as in centrally-located nerve tracts. Mammalian CCK-33 stimulated SS-25 release at a dose of 10(-11) M in the presence of 1, 3 and 10 mM glucose. CCK-33 inhibited the release of SS-14 at concentrations of 10(-11) and 10(-7) M only in the presence of high (10 mM) glucose. Mammalian NPY stimulated SS-25 release in a dose-related manner in the presence of low (1 mM) glucose; the efficacy of this effect decreased at higher glucose concentrations. SS-14 release was inhibited by NPY in the presence of 10 mM glucose. Mammalian galanin generally inhibited the secretion of SS-25, but stimulated the release of SS-14 at 10(-7) M in the presence of 3 mM glucose. These results suggest that CCK, NPY and galanin modulate the release of the somatostatins present within the trout pancreas. Furthermore, glucose may mediate the overall responsiveness of somatostatin-secreting cells to these peptides.

Evolution of neuropeptide Y, peptide YY and pancreatic polypeptide

The neuropeptide Y family of peptides consists of neuropeptide Y (NPY), which is expressed in the central and peripheral nervous systems, and peptide YY (PYY) and pancreatic polypeptide (PP) which are gut endocrine peptides. All three peptides are 36 amino acids long and act on G-protein-coupled receptors. NPY and PYY are present in all vertebrates, whereas PP probably arose as a copy of PYY in an early tetrapod ancestor. NPY is one of the most conserved peptides during evolution and no gnathostome (jawed) species differs from the ancestral gnathostome sequence at more than five positions. PYY is more variable, particularly in mammals which have nine differences to the gnathostome ancestor. PP may be the most rapidly evolving neuroendocrine peptide among tetrapods with only 50% identity between mammals, birds, and amphibians. Ancestral gnathostome NPY and PYY seem to have differed at only four positions, suggesting that the gene duplication occurred shortly before the appearance of the gnathostomes. The two peptides differ from one another at 9-12 positions in tetrapod species and share at least two receptor subtypes in mammals. In bony and cartilaginous fishes, NPY and PYY have only 5-6 differences which, together with more extensive neuronal localization of PYY, indicate an even greater functional overlap between the two peptides in these animal groups. The emergence of sequence information for several receptor subtypes from various species will shed additional light on the evolution of the functions of the NPY-family peptides.

Characterization of the pancreatic hormones from the Brockmann body of the tilapia: implications for islet xenograft studies

The Brockmann body of the teleost fish, the tilapia (Oreochromis nilotica) has been considered as a potential source of islet xenograft tissue for patients with insulin-dependent diabetes. This study describes the purification from an extract of tilapia Brockmann bodies of insulin and several peptides arising from different pathways of post-translational processing of two proglucagons, two prosomatostatins and proPYY. The primary structure of tilapia insulin is similar to insulins from other teleosts (particularly the anglerfish, Lophius americanus) except that the strongly conserved glutamine residue at position 5 in the A-chain, a residue that is important in the binding of insulin to its receptor, is replaced by glutamic acid. In common with other teleosts, the tilapia Brockmann body expresses two non-allelic glucagon genes. Alternative pathways of post-translational processing lead to glucagons with 29 and 36 amino acid residues derived from proglucagon I and glucagons with 29 and 32 residues derived from proglucagon II. Glucagon-like peptides with 30 and 34 residues derived from proglucagon II were also isolated. In each case, the longer peptide is a C-terminally extended form of the shorter. Tilapia peptide tyrosine-tyrosine (PYY) was isolated in a C-terminally alpha-amidated from with 36 amino acid residues that is structurally similar (89% sequence identity) to anglerfish PYY. A 30-amino acid peptide, representing the C-terminal flanking peptide of PYY, was also isolated that shows only 53% sequence identity with the corresponding anglerfish peptide. Tilapia somatostatin-14 is identical to mammalian somatostatin but the [Tyr7, Gly10] somatostatin-containing peptide derived from prosomatostatin II contains the additional substitution (Phe11-->Leu) compared with the corresponding peptide from other teleosts.

Gene duplication of the human peptide YY gene (PYY) generated the pancreatic polypeptide gene (PPY) on chromosome 17q21.1

Neuropeptide Y (NPY), peptide YY (PYY), and pancreatic polypeptide (PP) are structurally related but functionally diverse peptides, encoded by separate genes and expressed in different tissues. Although the human NPY gene has been mapped to chromosome 7, we demonstrate here that the genes for human PYY and PP (PPY) are localized only 10 kb apart from each other on chromosome 17q21.1. The high degree of homology between the members of this gene family, both in primary sequence and exon/intron structure, suggests that the NPY and the PYY genes arose from an initial gene duplication event, with a subsequent tandem duplication of the PYY gene being responsible for duplication of the PYY gene being responsible for the creation of the PPY gene. A second weaker hybridization signal also found on chromosome 17q11 and results obtained by Southern blot analysis suggest that the entire PYY-PPY region has undergone a further duplication event.

Characterization of trout galanin and its distribution in trout brain and pituitary

Galanin was purified from an extract of the stomach of the rainbow trout, Oncorhynchus mykiss, and its primary structure was established as Gly-Trp-Thr-Leu-Asn-Ser- Ala-Gly-Tyr-Leu10-Leu-Gly-Pro-His-Gly-Ile-Asp-Gly-His-Arg20- Thr-Leu-Ser-Asp- Lys-His-Gly-Leu-Ala. Trout galanin shows six amino acid substitutions compared with pig galanin, but the N-terminal region (residues 1-14) has been fully conserved. The distribution of galanin-immunoreactive (GAL-IR) structures in the trout brain and pituitary was studied via immunohistochemistry. GAL-IR cell bodies were observed only in the caudal telencephalon, the preoptic region, and the mediobasal hypothalamus. GAL-IR fibers, however, are widely distributed throughout the brain, with a much lower density in the midbrain and posterior brain than in the tel- and diencephalon. Particularly dense innervation of the mediobasal hypothalamus, the ventral and supracommissuralis parts of the caudal telencephalon, and the region above and below the anterior commissure was observed. A heavy innervation of the pituitary was consistently detected. GAL-IR fibers were present in neurohypophyseal digitations of both the anterior and intermediate lobes with highest density in the region of the proximal pars distalis, where growth hormone and gonadotropic cells are located. Fibers were also seen in digitations of the rostral pars distalis, in particular between the prolactin follicles. The distribution of GAL-IR neurons in the central nervous system and pituitary of the trout suggests that the peptide may exercise an important role in the regulation of neuroendocrine functions, particularly those related to reproduction.

Skin peptide tyrosine-tyrosine, a member of the pancreatic polypeptide family: isolation, structure, synthesis, and endocrine activity

Pancreatic polypeptide, peptide tyrosine-tyrosine (PYY), and neuropeptide tyrosine (NPY), three members of a family of structurally related peptides, are mainly expressed in the endocrine pancreas, in endocrine cells of the gut, and in the brain, respectively. In the present study, we have isolated a peptide of the pancreatic polypeptide family from the skin of the South American arboreal frog Phyllomedusa bicolor. The primary structure of the peptide was established as Tyr-Pro-Pro-Lys-Pro-Glu-Ser-Pro-Gly-Glu10-Asp-Ala-Ser-Pro-Glu-Glu- Met-Asn- Lys-Tyr20-Leu-Thr-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu30-Val-Thr- Arg-Gln-Arg-Tyr-NH2 . This unusual peptide, named skin peptide tyrosine-tyrosine (SPYY), exhibits 94% similarity with PYY from the frog Rana ridibunda. A synthetic replicate of SPYY inhibits melanotropin release from perifused frog neurointermediate lobes in very much the same way as NPY. These results demonstrate the occurrence of a PYY-like peptide in frog skin. Our data also suggest the existence of a pituitary-skin regulatory loop in amphibians.

Distribution of PACAP (pituitary adenylate cyclase-activating polypeptide)-like and helospectin-like peptides in the teleost gut

Pituitary adenylate cyclase-activating polypeptide (PACAP) and helospectin are two vasoactive intestinal polypeptide (VIP)-related neuropeptides that have recently been demonstrated in the mammalian gut; the aim of this study was to reveal their occurrence and localisation in the gastrointestinal tract, swimbladder, urinary bladder and the vagal innervation of the gut of teleosts, using immunohistochemical methods on whole-mounts and sections of these tissues from the Atlantic cod, Gadus morhua and the rainbow trout, Oncorhynchus mykiss. Both PACAP-like and helospectin-like peptides were present in the gut wall of the two species. Immunoreactive nerve fibres were found in all layers but were most frequent in the myenteric plexus and along the circular muscle fibres. Immunoreactivity was also demonstrated in nerves innervating the swimbladder wall, the urinary bladder and blood vessels to the gut. Immunoreactive nerve cell bodies were found in the myenteric plexus of the gut and in the muscularis mucosae of the swimbladder. In the vagus nerve, non-immunoreactive nerve cells were surrounded by PACAP-immunoreactive fibres. Double staining revealed the coexistence of PACAP-like and helospectin-like peptides with VIP in all visualized nerve fibres and in some endocrine cells. It is concluded that PACAP-like and helospectin-like peptides coexist with VIP in nerves innervating the gut of two teleost species. The distribution suggests that both PACAP and helospectin, like VIP, are involved in the control of gut motility and secretion.

Purification of a neuropeptide Y-related peptide from the brain of the sea lamprey and its effect on steroidogenesis

A peptide with neuropeptide Y-like immunoreactivity was identified by radioimmunoassay in an extract of the brain of the sea lamprey, Petromyzon marinus using an antiserum raised against the conserved COOH-terminal region of mammalian neuropeptide Y. Purification of the peptide and determination of its primary structure showed that it was identical to peptide methionine-tyrosine (PMY), previously isolated from the intestine of the same species. Intraperitoneal injection of synthetic PMY (0.15 micrograms/g) into female lampreys undergoing final maturation before spawning produced a significant (P < 0.05) decrease in plasma concentrations of estradiol compared with control lampreys injected with vehicle only. These data suggest the hypothesis that the observed decrease in the concentration of PMY-containing cells in the intestines of lampreys during upstream migration may correlate with the increase in circulating estradiol concentrations and final maturational processes.

Evolution of neuropeptide Y and its related peptides

1. The neuropeptide Y (NPY) family of peptides includes also the gut endocrine peptide YY (PYY), tetrapod pancreatic polypeptide (PP), and fish pancreatic peptide-tyrosine (PY). All peptides are 36 amino acids long. 2. Sequences from many types of vertebrates show that NPY has remained extremely well conserved throughout vertebrate evolution with 92% identity between mammals and cartilaginous fishes. 3. PYY has 97-100% identity between cartilaginous fishes and bony fishes, but is less conserved in amphibians and mammals (83% identity between amphibians and sharks and 75% identity between mammals and sharks). 4. NPY and PYY share 70-80% identity in most species. 5. Both NPY and PYY were present in the early vertebrate ancestor because both peptides have been found in lampreys. 6. The tissue distribution appears to have been largely conserved between phyla, except that PYY has more widespread neuronal expression in lower vertebrates. 7. Pancreatic polypeptide has diverged considerably among tetrapods leaving only 50% identity between mammals, birds/reptiles and frogs. 8. Several lines of evidence suggest that the PP gene arose by duplication of the PYY gene, probably in the early evolution of the tetrapods. 9. The pancreatic peptide PY found in anglerfish and daddy sculpin may have resulted from an independent duplication of the PYY gene. 10. The relationships of the recently described mollusc and worm peptides NPF and PYF with the NPY family still appear unclear.