Isolation of peptide hormones from the pancreas of the bullfrog (Rana catesbeiana). Amino acid sequences of pancreatic polypeptide, oxyntomodulin, and two glucagon-like peptides

Glucagon-like peptide-1 analogs: Miracle drugs are blooming?

Glucagon-like peptide-1 (GLP-1), secreted by L cells in the small intestine, assumes a central role in managing type 2 diabetes mellitus (T2DM) and obesity. Its influence on insulin secretion and gastric emptying positions it as a therapeutic linchpin. However, the limited applicability of native GLP-1 stems from its short half-life, primarily due to glomerular filtration and the inactivating effect of dipeptidyl peptidase-IV (DPP-IV). To address this, various structural modification strategies have been developed to extend GLP-1's half-life. Despite the commendable efficacy displayed by current GLP-1 receptor agonists, inherent limitations persist. A paradigm shift emerges with the advent of unimolecular multi-agonists, such as the recently introduced tirzepatide, wherein GLP-1 is ingeniously combined with other gastrointestinal hormones. This novel approach has captured the spotlight within the diabetes and obesity research community. This review summarizes the physiological functions of GLP-1, systematically explores diverse structural modifications, delves into the realm of unimolecular multi-agonists, and provides a nuanced portrayal of the developmental prospects that lie ahead for GLP-1 analogs.

In silico evaluation of the downstream effect of mutated glucagon is consistent with higher blood glucose homeostasis in Galliformes and Strigiformes

In contrast to mammals, glucagon is reported as a much more potent blood glucose modulator in birds. Interestingly, we have found p.Thr16Ser mutation, a variation in the highly conserved glucagon hormone, in Galliformes as well as Strigiformes. To check the effect of this mutation on the receptor binding of glucagon, we predicted the ancestral glucagon receptor sequence of all available Galliformes and Strigiformes species. Subsequently, we analysed their binding to the mutated and wild type glucagon (ancestral) by molecular dynamics simulation. At first, we made a model of ancestral glucagon receptor and ancestral mutated, and wild type glucagon in the order Galliformes and Strigiformes. Then we performed molecular dynamics for each Galliformes and Strigiformes receptor as well as each glucagon peptide, respectively. The final structures were used for docking simulation of glucagon to their receptors. The results of the docking simulations showed a stronger binding affinity of mutated glucagon to glucagon receptors. Afterward, we obtained blood glucose concentrations of all available Galliformes members, as well as all available members of its only taxonomic neighbour (order Anseriformes) in superorder Galloanserae. Interestingly the p.Thr16Ser mutation could finely cluster these two orders into two groups: higher blood glucose concentration (order Galliformes, 17.64 ± 1.66 mMol/L) and lower blood glucose concentration (order Anseriformes, 11.34 ± 1.11 mMol/L). Strigiformes which carry the mutated glucagon peptide show also high blood glucose concentrations (17.40 ± 1.51 mMol/L). Therefore, the results suggest this mutation, which leads to stronger binding affinity of mutated glucagon to its receptor, may be a driving force for higher blood glucose homeostasis in the related birds.

Glucagon Like Peptide 1 Receptor Agonists for Targeted Delivery of Antisense Oligonucleotides to Pancreatic Beta Cell

The extra hepatic delivery of antisense oligonucleotides (ASOs) remains a challenge and hampers the widespread application of this powerful class of therapeutic agents. In that regard, pancreatic beta cells are a particularly attractive but challenging cell type because of their pivotal role in diabetes and the fact that they are refractory to uptake of unconjugated ASOs. To circumvent this, we have expanded our understanding of the structure activity relationship of ASOs conjugated to Glucagon Like Peptide 1 Receptor (GLP1R) agonist peptide ligands. We demonstrate the key role of the linker chemistry and its optimization to design maleimide based conjugates with improved in vivo efficacy. In addition, truncation studies and scoping of a diverse set of GLP1R agonists proved fruitful to identify additional targeting ligands efficacious in vivo including native hGLP1(7-36)NH2. Variation of the carrier peptide also shed some light on the dramatic impact of subtle sequence differences on the corresponding ASO conjugate performance in vivo, an area which clearly warrant further investigations. We have confirmed the remarkable potential of GLP1R agonist conjugation for the delivery of ASOs to pancreatic beta cell by effectively knocking down islet amyloid polypeptide (IAPP) mRNA, a potential proapoptotic target, in mice.

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.

Using evolutionary information and ancestral sequences to understand the sequence-function relationship in GLP-1 agonists

Glucagon-like peptide-1 (GLP-1) is an incretin hormone with therapeutic potential for type 2 diabetes. A variety of GLP-1 sequences are known from amphibian species, and some of these have been tested here and found to be able to bind and activate the human GLP-1 receptor. While little difference was observed for the in vitro potency for the human GLP-1 receptor, larger differences were found in the enzymatic stability of these peptides. Two peptides showed increased enzymatic stability, and they group together phylogenetically, though they originate from Amphibia and Reptilia. We have used ancestral sequence reconstruction to analyze the evolution of these GLP-1 molecules, including the synthesis of new peptides. We find that the increased stability could not be observed in the resurrected peptides from the common ancestor of frogs, even though they maintain the ability to activate the human GLP-1 receptor. Another method, using residue mapping on evolutionary branches yielded peptides that had maintained potency towards the receptor and also showed increased stability. This represents a new approach using evolutionary data in protein engineering.

Analysis of pancreatic polypeptide cDNA from the house musk shrew, Suncus murinus, suggests a phylogenetically closer relationship with humans than for other small laboratory animal species

Pancreatic polypeptide was isolated and sequenced from endocrine cells of the pancreas from an insectivore, the house musk shrew, Suncus murinus. The primary sequence was APLEPAYPGD(10)NATPEQMAQY(20)AAELRKYINM(30)VTRPRYamide. This is the first polypeptide hormone to be characterised from this species and is typical of the primary sequences of pancreatic polypeptide of other animals, being a C-terminal-amidated peptide with 36 residues. Comparison with several vertebrate sequences shows that it has more in common with the human form than do the forms from common laboratory animals such as rabbits, rats, mice and guinea-pigs.

Four novel PYFs: members of NPY/PP peptide superfamily from the eyestalk of the giant tiger prawn Penaeus monodon

An immunocytochemical method was used for localization of pancreatic polypeptide (PP) immunoreactive substances in the eyestalk of Penaeus monodon using anti-C-terminal hexapeptide of PP (anti-PP6) antiserum. Approximately 200 neuronal cell bodies were recognized in the ganglia between the medulla interna (MI) and medulla terminalis (MT) and surrounding MT in conjunction with the neuronal processes in medulla externa (ME), MI, MT and sinus gland. About half of the PP immunoreactive neurons were also recognized by a combination of three monoclonal antibodies raised against FMRFamide-like peptides. Isolation of the PP immunoreactive substances from the eyestalk was performed using 7500 eyestalks extracted in methanol/acetic acid/water (90/1/9) followed by five to six steps of RP-HPLC separation. Dot-ELISA with anti-PP6 antiserum was used to monitor PP-like substances in various fractions during the purification processes. Four new sequences of one hexapeptide; RARPRFamide, and three nonapeptides; YSQVSRPRFamide, YAIAGRPRFamide and YSLRARPRFamide were identified, and named as Pem-PYF1-4 due to their structural similarity to the PYF found in squid Loligo vulgaris. Each of the new peptides shares four to seven common residues with the C-terminus of the squid PYF and with the NPFs found in other invertebrates. The NPY/PP superfamily as well as the FMRFamide peptide family may be present throughout vertebrates and invertebrates.

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

Pancreatic polypeptide receptors: affinity, sodium sensitivity and stability of agonist binding

Cloned rat, human and guinea-pig Y4 pancreatic polypeptide (PP) receptors expressed in Chinese hamster ovary (CHO) cells, as well as the rabbit Y4-like PP receptor, show a selective sensitivity to Na+ over K+ ion in PP attachment, but little sensitivity to Na+ in dissociation of bound PP peptides. Agonist binding to Y4 receptors of intact CHO cells also shows much greater sensitivity to Na+ over K+, and a tenacious attachment of the bound agonist. Binding sensitivity to K+ is greatly enhanced upon receptor solubilization. Pancreatic polypeptide sites also show large sensitivity to modulators of Na+ transport such as N5-substituted amilorides and to RFamides, as different from Y1 or Y2 receptors. Thus, PP binding is modulated by cation-induced changes in site environment (with selectivity for Na+) and ultimately results in a blocking attachment. This would support receptor operation in the presence of ion gradients, as well as prolonged agonist-delimited signaling activity (which can include partial antagonism). Also, this could point to an evolutionary adaptation enabling small numbers of PP receptors to perform extensive metabolic tasks in response to low agonist signals.

Identification of a proglucagon cDNA from Rana tigrina rugulosa that encodes two GLP-1s and that is alternatively spliced in a tissue-specific manner

Glucagon plays a pivotal role in the regulation of metabolism. A glucagon receptor has been previously characterized in the frog, Rana tigrina rugulosa, and the frog and human glucagon receptors have been shown to possess similar binding affinities toward human glucagon. To study the structural evolution of glucagon peptide and its receptor in vertebrates, in the current study, a proglucagon cDNA from the same frog species was cloned. Interestingly, in contrast to the mammalian proglucagons that contain only one GLP-1 peptide, the frog proglucagon cDNA encodes two GLP-1 peptides (GLP-1A and GLP-1B) in addition to a glucagon peptide and a glucagon-like peptide 2 (GLP-2). By reverse transcriptase-PCR (RT-PCR) analysis, the proglucagon gene expression was widely detected in the brain, colon, small intestine, liver, lung, and pancreas, suggesting that the proglucagon-derived peptides have diverse functions in frogs. Moreover, tissue-specific alternative mRNA splicing was observed in the brain, colon, and pancreas. In these tissues, proglucagon transcripts with a 135 bp in frame deletion encoding GLP-1A were found. This splicing event in R. tigrina rugulosa is novel because it deletes a GLP-1 encoding sequence instead of the GLP-2 observed in other vertebrates. These findings should enhance understanding of the proglucagon evolution, structure, and expression in vertebrates.

Glucagon-like peptide isolated from the eel intestine: effects on atrial beating

A new glucagon-like peptide was isolated from the intestine of the eel Anguilla japonica. The primary structure was determined by sequence analysis after cleavage with lysyl endopeptidase, quantitative amino acid analysis and fast atom bombardment mass spectrometry as HSQGTFTNDY10SKYLETRRAQ20DFVQWLMNSK30RSGGPT. Since its structure is similar to that of oxyntomodulins (OXMs) reported in various vertebrates, we named this peptide eel oxyntomodulin (eOXM). We found that eOXM enhanced the contractile force and the beating rate of the eel atrium in a dose-dependent manner. These effects of eOXM were not inhibited by betaxolol, a β1-adrenoceptor antagonist, indicating that the actions of eOXM were independent of those of adrenaline. eOXM enhanced the intracellular Ca2+ concentration of the myocardium. The contractility of the eel atrium was greatly reduced after omitting Ca2+ from the bathing medium or after treatment with verapamil, a Ca2+ channel blocker. After inhibiting Ca2+ entry under these conditions, the inotropic effect of eOXM was markedly reduced, but the chronotropic effect was not altered significantly. These results indicate that the inotropic effect of eOXM is via a stimulation of Ca2+ influx but that the chronotropic effect may be independent of extracellular Ca2+.

Anomalous rates of evolution of pancreatic polypeptide and peptide tyrosine-tyrosine (PYY) in a tetraploid frog, Xenopus laevis (Anura:Pipidae)

The South African clawed frog Xenopus laevis is believed to have arisen as a result of a tetraploidization event occurring approximately 30 million years ago. Two molecular forms of pancreatic polypeptide (PP) have been isolated from an extract of the pancreas of this species and two molecular forms of peptide tyrosine-tyrosine (PYY) from the intestine. Despite the fact that the amino acid sequence of PP has, in general, been very poorly conserved during the evolution of tetrapods (only Pro(5), Pro(8), Gly(9), Ala(12), Tyr(27), Arg(33) and Arg(35) are invariant among species studied so far), the two Xenopus PPs differ by only a single amino acid substition (Asp(22)-->Glu). In contrast the two molecular forms of PYY differ by six amino acid substitutions (Glu(15)-->Gln, Thr(18)-->Ala, Leu(21)-->Met, Ile(22)-->Thr, Ile(28)-->Val, Val(31)-->Ile). The data imply that strong evolutionary pressure is acting to conserve the functional domain in both genes encoding PP and so suggest that PP may have an important physiological role in amphibians (although the nature of this role has yet to be determined). The more rapid mutation of the functional domain in the genes encoding PYY, a peptide whose amino acid sequence has been quite well conserved in tetrapods and whose physiological significance is well established, suggests that one of the PYY genes may be evolving towards a new function or towards becoming a pseudogene.

The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily

The pituitary adenylate cyclase-activating polypeptide (PACAP)/ glucagon superfamily includes nine hormones in humans that are related by structure, distribution (especially the brain and gut), function (often by activation of cAMP), and receptors (a subset of seven-transmembrane receptors). The nine hormones include glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, glucose-dependent insulinotropic polypeptide (GIP), GH-releasing hormone (GRF), peptide histidine-methionine (PHM), PACAP, secretin, and vasoactive intestinal polypeptide (VIP). The origin of the ancestral superfamily members is at least as old as the invertebrates; the most ancient and tightly conserved members are PACAP and glucagon. Evidence to date suggests the superfamily began with a gene or exon duplication and then continued to diverge with some gene duplications in vertebrates. The function of PACAP is considered in detail because it is newly (1989) discovered; it is tightly conserved (96% over 700 million years); and it is probably the ancestral molecule. The diverse functions of PACAP include regulation of proliferation, differentiation, and apoptosis in some cell populations. In addition, PACAP regulates metabolism and the cardiovascular, endocrine, and immune systems, although the physiological event(s) that coordinates PACAP responses remains to be identified.

Characterization of insulin and atypically processed proglucagon-derived peptides from the surinam toad Pipa pipa (Anura:Pipidae)

Electrospray mass spectrometry was used to identify insulin, glucagon and two peptides related to glucagon-like peptide-1 (GLP-1) in an extract of the pancreas of the Surinam toad, Pipa pipa, a species belonging to the same family as the African clawed frog, Xenopus laevis. Purification and characterization of the peptides established the primary structure of Pipa insulin as A-chain: GIVEQCCHSS(10)CTLLQLETYC(20) N and B-Chain: FSNQR LCGSH(10) LVEALHLVCG(20) DRGFFYYPKA(30). This amino acid sequence contains several substitutions (B5 His --> Arg, B16 Tyr --> His, A12 Ser --> Thr, A14 Tyr--> Leu, A18Asn --> Thr) of residues that have otherwise been quite strongly conserved during vertebrate evolution. Pipa glucagon comprises 37 amino acid residues (HSQGTFTSDY(10) SKYLDSRRAQ(20) DFVQWLMNTK(30)QSGGLSS) and the 29 amino-acid-residue peptide was not identified in the extract. In Xenopus and mammalian preproglucagons, the glucagon-29 sequence is followed by Lys-Arg which functions as a recognition site for a prohormone convertase. We propose that a point mutation in the gene encoding Pipa preproglucagon has transformed the Lys(30)-Arg(31) processing site into Lys-Gln with the result that the site in no longer recognized by the processing enzyme. In contrast, Pipa GLP-32 and GLP-37 are of the same molecular size as the corresponding peptides from Xenopus.

Islet hormones from the African bullfrog Pyxicephalus adspersus (Anura:Ranidae): structural characterization and phylogenetic implications

The African bullfrog Pyxicephalus adspersus is generally classified along with frogs of the genus Rana in the subfamily Raninae of the family Ranidae but precise phylogenetic relationships between species are unclear. Pancreatic polypeptide (PP), insulin, and glucagon-like peptide (GLP-1) were isolated from an extract of P. adspersus pancreas and characterized structurally. A comparison of the amino acid sequence of Pyxicephalus PP (APSEPQHPGG(10)QATPEQLAQY(20)YSDLYQYITF(30)ITRPRF++ +. NH(2)) with those of the known amphibian PP molecules in a maximum parsimony analysis generates a single phylogenetic tree in which Pyxicephalus is the sister to the clade comprising the members of the genus Rana. The three orders of living amphibians form discrete clades with the representative of the Gymnophiona appearing as sister to the Caudata-Anura. In contrast, Pyxicephalus insulin (A chain, GIVEQCCHSA(10)CSLYDLENYC(20)N; B-chain, LANQHLCGSH(10)LVEALYMVCG(20)ERGFFYYPKS(30)) and and GLP-1 (HAEGTFTSDM(10)TSYLEEKAAK(20)EFVDWLIKGR(30)PK) resemble more closely the corresponding peptides from the cane toad Bufo marinus than the peptides from any species of Rana. Cladistic analysis based upon the amino acid sequences of insulin produced a polyphyletic assemblage with the Gymnophiona nesting within an unresolved clade containing the non-ranid frogs. The data support the assertion that the amino acid sequence of PP, but not those of the other islet hormones, is of value as a molecular marker for inferring phylogenetic relationships between early tetrapod species.

Proglucagon cDNAs from the leopard frog, Rana pipiens, encode two GLP-1-like peptides

We have isolated and characterized proglucagon cDNAs from the intestine and pancreas of the leopard frog Rana pipiens. R. pipiens proglucagon encodes glucagon, glucagon-like peptides 2 (GLP-2), and two glucagon-like peptide 1 (GLP-1) like sequences. The pancreatic and intestinal cDNAs were of identical structure and sequence suggesting that, unlike many other non-mammalian vertebrates, there is little or no alternative splicing of the proglucagon mRNA in this species. A phylogenetic analysis of the GLP-1 encoding sequences implies that the exon encoding GLP-1 was triplicated early in frog evolution, more than 150 million years ago, before the divergence of modern frogs.

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.

Characterization of pancreatic endocrine cells of the European common frog Rana temporaria

To characterize the endocrine cell types of the pancreas of Rana temporaria, conventional staining, silver impregnation, and immunocytochemical methods for light and electron microscopy have been applied to paraffin, thin and semithin sections, many of them serial pairs. Quantitative data on the frequency and distribution (insular, extrainsular among the exocrine cells, or within the pancreatic ducts) of each endocrine cell type are also reported. Four distinct endocrine cell types have been identified: insulin (B) cells, which are also immunoreactive for [Met]enkephalin; glucagon/PP (A/PP) cells, also immunoreactive for GLP1; somatostatin (D) cells; and a fourth endocrine-like cell type (X cells) of unknown content and function. X cells display characteristic ultrastructure and tinctorial traits but are nonimmunoreactive for all of the 37 antisera tested. The presence of [Met]enkephalin in amphibian pancreatic endocrine cells is now reported for the first time. Almost half (44.9 +/- 7.9) of the total endocrine cell population lies outside the islets, mainly spread among the exocrine cells. Approximately 37.2 +/- 4.6% of the total endocrine cell population was immunoreactive for insulin, 48.8 +/- 6.9% was immunoreactive for glucagon/PP, and 14.0 +/- 4.9% was immunoreactive for somatostatin; 79.2 +/- 6.4% of glucagon/PP cells are found within the exocrine parenchyma, representing the majority (86.4 +/- 4.3%) of extrainsular endocrine component. On the contrary, most B cells (94.2 +/- 2.1%) are located within the islets; 30.8 +/- 12.9% of D cells are found outside the islets.

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.

Functional studies of a glucagon receptor isolated from frog Rana tigrina rugulosa: implications on the molecular evolution of glucagon receptors in vertebrates

In this report, the first amphibian glucagon receptor (GluR) cDNA was characterized from the liver of the frog Rana tigrina rugulosa. Functional expression of the frog GluR in CHO and COS-7 cells showed a high specificity of the receptor towards human glucagon with an EC(50) value of 0.8+/-0.5 nM. The binding of radioiodinated human glucagon to GluR was displaced in a dose-dependent manner only with human glucagon and its antagonist (des-His(1)-[Nle(9)-Ala(11)-Ala(16)]) with IC(50) values of 12.0+/-3. 0 and 7.8+/-1.0 nM, respectively. The frog GluR did not display any affinity towards fish and human GLP-1s, and towards glucagon peptides derived from two species of teleost fishes (goldfish, zebrafish). These fish glucagons contain substitutions in several key residues that were previously shown to be critical for the binding of human glucagon to its receptor. By RT-PCR, mRNA transcripts of frog GluR were located in the liver, brain, small intestine and colon. These results demonstrate a conservation of the functional characteristics of the GluRs in frog and mammalian species and provide a framework for a better understanding of the molecular evolution of the GluR and its physiological function in vertebrates.

Insulin and proglucagon-derived peptides from the horned frog, Ceratophrys ornata (Anura:Leptodactylidae)

Insulin and peptides derived from the processing of proglucagon have been isolated from an extract of the pancreas of the South American horned frog, Ceratophrys ornata (Leptodactylidae). Ceratophrys insulin is identical to the insulin previously isolated from the toad, Bufo marinus (Bufonidae). Ceratophrys glucagon was isolated in two molecular forms with 29- and 36-amino acid residues in approximately equal amounts. Glucagon-29 is identical to glucagon from B. marinus and from the bullfrog, Rana catesbeiana (Ranidae) and contains only 1 amino acid substitution (Thr29 --> Ser) compared with glucagon from Xenopus laevis (Pipidae). Glucagon-36 comprises glucagon-29 extended from its C-terminus by Lys-Arg-Ser-Gly-Gly-Met-Ser. This extension is structurally dissimilar to the C-terminal octapeptide of mammalian oxyntomodulin and resembles more closely that found in C-terminally extended glucagons isolated from fish pancreata. Ceratophrys glucagon-like peptide-1 (GLP-1) (His-Ala-Asp-Gly-Thr-Tyr-Gln-Asn-Asp-Val10-Gln-Gln-Phe-Leu-Glu- Glu-Lys-Ala-Ala-Lys20-Glu-Phe-Ile-Asp-Trp-Leu-Ile-Lys-Gly- Lys30-Pro-Lys-Lys-Gln-Arg-Leu-Ser) contains 3 amino acid substitutions compared with the corresponding peptide from B. marinus, 8 substitutions compared with GLP-1 from R. catesbeiana, and between 4 and 11 substitutions compared with the three GLP-1 peptides identified in X. laevis proglucagon. GLP-2 was not identified in the extract of Ceratophrys pancreas. The data indicate that, despite its importance in the regulation of glucose metabolism, the primary structure of GLP-1 has been very poorly conserved during evolution, even among a single order such as the Anura.

Endocrine pancreatic cells from Xenopus laevis: light and electron microscopic studies

Insulin, glucagon, pancreatic polypeptide (PP), peptide tyrosine tyrosine (PYY), somatostatin (SST)-28 (1-12), salmon (s) SST-25, and SST-14 immunoreactivities were demonstrated in the pancreatic endocrine cells of Xenopus laevis using light and electron microscopic immunocytochemistry. Insulin-, SST-28 (1-12)/SST-14-, and PYY-immunoreactive (ir) cells were found throughout the pancreas either isolated in small clusters of a single cell type or, except in the case of PYY-ir cells, forming islets consisting of various cell types. Anti-sSST-25 serum detected the invariant SST-14 form. Cells that were only immunoreactive to glucagon were isolated or clustered in the duodenal lobe, while in the splenic lobe cells immunoreactive to both glucagon and PP were observed in isolation, clustered, or in the periphery of the islets. There were no cells that were immunoreactive only to PP or to NPY. Ultrastructurally, the endocrine cells were characterized by their secretory granules, which were immunogold labeled with the corresponding antisera. Insulin cells had large round secretory granules with a round, irregular, or crystalline-like dense core. Glucagon-ir cells had round secretory granules with a dense core and a clear halo. Glucagon/PP- and PYY-ir cells showed round, ovoid, or pear-shaped secretory granules, which were larger and less electron dense in the latter cell type. The secretory granules of SST-ir cells were ovoid or bacillary with a medium electron-dense content. A sixth cell type with very small secretory granules could only be characterized by conventional electron microscopy, since it did not immunoreact with any of the antisera applied in this study.

Amino acid sequence diversity of pancreatic polypeptide among the amphibia

It has been suggested that the amino acid sequence of pancreatic polypeptide (PP) may provide a useful molecular marker with which to study evolutionary relationships between tetrapods but few PP sequences from amphibia are available to test this hypothesis. PPs have been purified from the pancreata of five species belonging to the different orders of amphibians. Their amino acid sequences were established as: APSEPEHPGD10 NASPDELAKY20 YSDLWQYITF30 VGRPRY for the lesser siren, Siren intermedia (Caudata); GPTEPIHPGK10 DATPEELTKY20 YSDLYDYITL30 VGRSRW for the caecilian, Typhlonectes natans (Gymnophiona); and TPSEPQHPGD10 QASPEQLAQY20 YSDLWQYITF30 VTRPRF for the cane toad, Bufo marinus (Anura). The structure of Rana sylvatica PP is the same as that of Rana catesbeiana PP whereas PP from the green frog Rana ridibunda contains one substitution (His6 --> Gln). The data provide further support for the conclusion that the amino acid sequence of PP has been poorly conserved during evolution with only 17 residues invariant among the eight species of amphibia yet studied and only 8 residues (Pro5, Pro8, Gly9, Ala12, Leu24, Tyr27, Arg33, and Arg35) invariant among all tetrapods. A maximum parsimony analysis based upon the amino acid sequence of PP and using the sequence of frog PYY as outgroup to polarize the in-group taxa generates a consensus phylogenetic tree in which the Amniota and Amphibia form two distinct clades. However, such a tree does not permit valid conclusions to be drawn regarding branching order within the Amphibia.

Neuropeptide families: evolutionary perspectives

Examination of neuropeptide families can provide information about phyletic relationships and evolutionary processes. In this article the oxytocin/vasopressin family, growth hormone releasing factor (GRF) superfamily and the substance P/tachykinin family have been considered in detail because they have been isolated from an extraordinarily diverse array of species from several vertebrate classes and invertebrate phyla. More important is that the nucleotide sequence of mRNA or cDNA encoding many of these peptides has been determined, which has allowed evolutionary distances to be estimated based on the DNA mutation rate. The origin of a given family lies in a primordial gene that arose many millions of years ago, and through time, exon duplication and insertion, gene duplication, point mutation and exon loss, the family developed into the forms that are now recognised. For example, in birds, GRF and pituitary adenylate cyclase activating peptide (PACAP) are encoded by the same gene, which probably arose as a result of exon duplication and tandem insertion of the ancestral GRF gene. In mammals GRF is the sole product on one gene, and PACAP is the product of a gene that also produces PACAP-related peptide (PRP), which is homologous to GRF. Thus it appears that between birds and mammals the GRF/PACAP gene duplicated: exon loss gave rise to the mammalian GRF gene, while mutation led to the formation of the mammalian PRP/PACAP gene. The neuropeptide Y superfamily is considered briefly, as is cionin, which is an invertebrate peptide that is closely related to the mammalian gastrin/cholecystokinin family.

Purification and characterization of islet hormones (insulin, glucagon, pancreatic, polypeptide and somatostatin) from the Burmese python, Python molurus

Insulin was purified from an extract of the pancreas of the Burmese python, Python molurus (Squamata:Serpentes) and its primary structure established as: A Chain: Gly-Ile-Val-Glu-Gln-Cys-Cys-Glu-Asn-Thr10-Cys-Ser-Leu-Tyr-Glu-Leu- Glu-Asn-Tyr-Cys20-Asn. B-Chain: Ala-Pro-Asn-Gln-His-Leu-Cys-Gly-Ser-His10-Leu-Val-Glu-Ala-Leu-Tyr- Leu-Val-Cys-Gly20-Asp-Arg-Gly-Phe-Tyr-Tyr-Ser-Pro-Arg-Ser30. With the exception of the conservative substitution Phe --> Tyr at position B25, those residues in human insulin that comprise the receptor-binding and those residues involved in dimer and hexamer formation are fully conserved in python insulin. Python insulin was slightly more potent (1.8-fold) than human insulin in inhibiting the binding of [125I-Tyr-A14] insulin to the soluble full-length recombinant human insulin receptor but was slightly less potent (1.5-fold) than human insulin for inhibiting binding to the secreted extracellular domain of the receptor. The primary structure of python glucagon contains only one amino acid substitution (Ser28 --> Asn) compared with turtle/duck glucagon and python somatostatin is identical to that of mammalian somatostatin-14. In contrast, python pancreatic polypeptide (Arg-Ile-Ala-Pro-Val-Phe-Pro-Gly-Lys-Asp10-Glu-Leu-Ala-Lys-Phe- Tyr20-Thr-Glu-Leu-Gln-Gln-Tyr-Leu-Asn-Ser-Ile30-Asn-Arg-Pro-Arg -Phe.NH2) contains only 35 instead of the customary 36 residues and the amino acid sequence of this peptide has been poorly conserved between reptiles and birds (18 substitutions compared with alligator and 20 substitutions compared with chicken).

The Xenopus proglucagon gene encodes novel GLP-1-like peptides with insulinotropic properties

The proglucagon gene encodes several hormones that have key roles in the regulation of metabolism. In particular, glucagon-like peptide (GLP-1), a potent stimulus of insulin secretion, is being developed as a therapy for the treatment of non-insulin-dependent diabetes mellitus. To define structural moieties of the molecule that convey its insulinotropic activity, we have cloned and characterized the proglucagon gene from the amphibian, Xenopus laevis. Unexpectedly, these cDNAs were found to encode three unique glucagon-like-1 peptides, termed xenGLP-1A, xenGLP-1B, and xenGLP-1C in addition to the typical proglucagon-derived hormones glucagon and GLP-2. xenGLP-1A, -1B, and -1C were synthesized and tested for their ability to bind and activate the human GLP-1 receptor (hGLP-1R), and to stimulate insulin release from rat pancreas. All three Xenopus GLP-1-like peptides bind effectively to the hGLP-1R and stimulate cAMP production. Surprisingly, xenGLP-1B(1-30) demonstrated higher affinity for the hGLP-1R than hGLP-1 (IC50 of 1.1 +/- 0.4 nM vs. 4.4 +/- 1.0 nM, respectively, P < 0.02) and was equipotent to hGLP-1 in stimulating cAMP production (EC50 of 0.17 +/- 0.02 nM vs. 0.6 +/- 0. 2 nM, respectively, P > 0.05). Further studies demonstrated that hGLP-1, xenGLP-1A, -1B, and -1C stimulate comparable insulin release from the pancreas. These results demonstrate that despite an average of nine amino acid differences between the predicted Xenopus GLPs and hGLP-1, all act as hGLP-1R agonists.

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.

Glucagon and glucagon-like peptides in fishes

Glucagon and glucagon-like peptides (GLPs) are coencoded in the vertebrate proglucagon gene. Large differences exist between fishes and other vertebrates in gene structure, peptide expression, peptide chemistry, and function of the hormones produced. Here we review selected aspects of glucagon and glucagon-like peptides in vertebrates with special focus on the contributions made by analysis of piscine systems. Our topics range from the history of discovery to gene structure and expression, through primary structures and regulation of plasma concentrations to physiological effects and message transduction. In fishes, the pancreas synthesizes glucagon and GLP-1, while the intestine may contribute oxyntomodulin, glucagon, GLP-1, and GLP-2. The pancreatic gene is short and lacks the sequence for GLP-2. GLP-1, which is produced exclusively in its biologically active form, is a potent metabolic hormone involved in regulation of liver glycogenolysis and gluconeogenesis. The responsiveness of isolated hepatocytes to glucagon is limited to high concentrations, while physiological concentrations of GLP-1 effectively regulate hepatic metabolism. Plasma concentrations of GLP-1 are higher than those of glucagon, and liver is identified as the major site of removal of both hormones from fish plasma. Ultimately, GLP-1 and glucagon exert effects on glucose metabolism that directly and indirectly oppose several key actions of insulin. Both glucagon and GLP-1 show very weak insulinotropic activity, if any, when tested on fish pancreas. Intracellular message transduction for glucagon, especially at slightly supraphysiological concentrations, involves cAMP and protein kinase A, while pathways for GLP are largely unknown and may involve a multitude of messengers, including cAMP. In spite of fundamental differences in GLP-1 function between fishes and mammals, fish GLP-1 is as powerful an insulinotropin for mammalian B-cells as mammalian GLP-1 is a metabolic hormone if tested on piscine liver.

Humoral regulation of intestinal adaptation

After the loss of small bowel through disease or surgery the residual bowel adapts by increasing its functional capacity. This process of adaptation involves dilatation, hypertrophy and mucosal hyperplasia, particularly distal to the area of bowel loss or disease. The response of the residual bowel is mediated by a complex interplay of factors including luminal nutrition, pancreaticobiliary secretions, luminal or local growth factors and also humoral or endocrine factors. The experimental model commonly used to characterize the adaptive response, massive small bowel resection (MSBR), involves 80% resection of the small bowel in the rat. Of the various putative humoral factors, most work has focused on the products of the ileal L cells: enteroglucagon and peptide YY. Plasma levels of both hormones are increased after MSBR and indeed their mRNA levels are also increased as a result of an increase in the amount of message per L cell. Whilst PYY probably serves as an 'ileal brake' to slow the movement of the luminal contents and hence increase their mucosal contact time, the role of the enteroglucagon is unresolved. The molecular cloning of the proglucagon gene has revealed, firstly, that there are a number of biologically active peptides which derive from the propeptide and, secondly, that tissue-specific differential processing occurs. Most studies do not clearly define which of these products of proglucagon is being measured and is termed as glucagon-like or enteroglucagon immunoreactivity. The insulin-like growth factors (IGF) have a potent mitogenic action on the bowel. Their role after MSBR is likely to be largely paracrine. Though IGF-I mRNA levels do not increase after MSBR, the precipitous and early fall in ileal IGF-binding protein-3 (IGFBP-3) mRNA levels suggests a fall in IGFBP-3 levels may increase local IGF-I bioactivity. Polyamine synthesis is a critical component of the adaptive response, although the stimulus to their dramatic increase in synthesis after MSBR remains to be elucidated. Other humoral factors such as cholecystokinin, neurotensin and bombesin probably have minor indirect roles in the adaptive response. Components of the epidermal growth factor/transforming growth factor alpha response pathway family of growth factors may be involved as paracrine regulators. There is thus strong evidence that humoral factors play an important role in intestinal adaptation; characterization of the nature of the humoral factors and their relationship with other influences such as luminal nutrition and pancreatic biliary secretions may facilitate the development of new therapeutic strategies for the short bowel syndromes.

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.

Metabolic and endocrine functions of glucagon-like peptides - evolutionary and biochemical perspectives

In amphibians and mammals, the preproglucagon gene encodes two related GLPs - GLP-1(37 residues) and GLP-2 (34 residues). The physiologically functional GLPs, however, are GLP-17-36amide, or similar, truncated forms of GLP-1. While the liver is devoid of GLP receptors and fails to respond metabolically, brain, gastric cells and pancreatic cells have been identified as potential target sites. These tissues possess specific binding sites for truncated GLP-1, and generally, cells respond to truncated GLPs with increases in CAMP. In mammalian pancreas, truncated GLPs function as powerful insulinotropins, while also increasing insulin gene transcription and inhibiting glucagon release. Full length GLP-1 is a weak insulinotropin only. To date, neither metabolic nor endocrine actions have been assigned to GLP-2.Following processing of preproglucagon gene products, fish pancreas and intestine contain only one GLP (31 residues) displaying considerable sequence homology with GLP-17-36. Applied in low nanomolar concentrations, fish GLPs, together with GLP-17-36, activate hepatic glycogenolysis, gluconeogenesis and lipolysis in fishes. Thousand-fold higher levels of GLP-17-37 are required to elicit comparable metabolic effects. Generally, the metabolic actions of GLPs are similar to those for glucagon, but GLPs tend to be more potent in their specific actions. Fish livers possibly contain GLP receptors distinct from glucagon receptors. Message transduction in some, but not all fish species, may involve adenylyl cyclase and CAMP, but correlation between metabolic activation and cAMP levels is generally poor. Fish GLP seems to be a very weak insulinotropin in Brockmann bodies.

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

Neuropeptide Y was isolated from the brain of the Atlantic cod, Gadus morhua and its primary structure established as Tyr-Pro-Ile*-Lys-Pro-Glu*-Asn-Pro-Gly-Glu10-Asp-Ala-Pro-Ala-Asp*-G lu*-Leu*-Ala- Lys*-Tyr20-Tyr-Ser-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu30-Ile-Thr -Arg-Gln-Arg-Tyr- CONH2. Residues denoted by an asterisk are different from the corresponding sequence of human neuropeptide Y. A structurally similar peptide was isolated from the brain of the trout, Oncorhynchus mykiss. Trout neuropeptide Y contains four substitutions (Ile3-->Val, Ala14-->Thr, Asp15-->Glu and Ser22-->Thr) compared with cod neuropeptide Y. A second peptide of the neuropeptide Y family was identified in the trout brain and this component was structurally similar to peptide tyrosine-tyrosine previously isolated from frog intestine (six amino acid substitutions) and identical to a peptide isolated from the pancreas of the closely related species, Oncorhynchus kisutch (Coho salmon). Peptide tyrosine-tyrosine, with the same primary structure as the brain peptide, was also isolated from an extract of the trout stomach. The data indicate that a peptide analogous to mammalian neuropeptide Y is present in the brain of teleost fish and a peptide analogous to mammalian peptide tyrosine-tyrosine is present in brain, gastrointestinal tissue and pancreas. We speculate, therefore, that the putative gene duplication that led to pancreatic polypeptide in the higher vertebrates took place after the time of divergence of fish and tetrapods.

Rainbow trout (Oncorhynchus mykiss) neuropeptide Y

Neuropeptide Y (NPY) has been isolated from brain extracts of the rainbow trout (Oncorhynchus mykiss) and subjected to structural analyses. Plasma desorption mass spectroscopy estimated the molecular mass of the purified peptide as 4303.9 Da. Automated Edman degradation unequivocally established the sequence of a 36 amino acid residue peptide as: Tyr-Pro-Pro-Lys-Pro-Glu-Asn-Pro-Gly-Glu-Asp-Ala-Pro-Pro-Glu-Glu-Leu-Ala- Lys- Tyr-Tyr-Thr-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu-Ile-Thr-Arg-Gln-Arg-Tyr. The molecular mass calculated from this sequence (4304 Da) is consistent with that obtained by mass spectroscopy. The presence of a C-terminal amide was established by radioimmunoassay. Rainbow trout NPY is identical in primary structure to coho salmon (Oncorhynchus kisutch) pancreatic polypeptide (PP). These data may indicate that, in this group of salmonid fishes, a single member of the NPY/PP peptide family is expressed in both neurons and peripheral endocrine cells.

The development of neuropeptide Y immunoreactive neurons in cat visual cortical areas

The development of NPY-ir neurons and fibers in cat striate and extrastriate cortex was studied to determine whether temporal changes in the morphology, distribution and density of NPY-ir neurons during development would provide clues to the emergence of specific cortical areas. No differences in the number or distribution of NPY-ir neurons were observed at any age among the five visual cortical areas examined, area 17, 18, 19, posteromedial lateral suprasylvian and posterolateral lateral suprasylvian cortex. The number of NPY-ir neurons in cat visual cortical areas was higher in adult animals than in kittens. The proportion of NPY-ir neurons found in layer VIb was constant throughout life, suggesting that NPY immunoreactivity is not a marker for the transient neurons of the subplate. NPY-ir neuronal morphology was seen to 'flatten' in older animals with the development of sulci and increasing density of the brain. In contrast to the pattern observed with NPY-ir neurons, NPY-ir processes exhibited area-dependent differences during development. NPY-ir fibers grew into area 17 earlier and with a radial orientation which was not consistently observed laterally. This radial orientation was still apparent in adult brains in layer IV of area 17, though there was no orientation of fibers in the other laminae or other visual areas of the adult.

The primary structure and tissue distribution of an amphibian neuropeptide Y

Neuropeptide Y (NPY) has been isolated and sequenced from brain extracts of the European common frog, Rana temporaria. Plasma desorption mass spectroscopy of the purified peptide indicated a molecular mass of 4243.3 Da which was in agreement with that deduced from the sequence (4243.7 Da), incorporating a C-terminal amide. The primary structure of frog NPY was established as: YPSKPDNPGEDAPAEDMAKYYSALRHYINLITRQRY-NH2. Frog NPY contains a single, highly-conservative amino acid substitution (Lys for Arg at residue 19) with respect to human NPY. NPY immunoreactivity was localised exclusively in nerves within the brain, pancreas and gastrointestinal tract and reverse-phase HPLC of extracts of these tissues resolved a single immunoreactive peptide of identical retention time in each case. The primary structure of NPY has therefore been highly-conserved over a considerable evolutionary time-span.

Primary structure of frog PYY: implications for the molecular evolution of the pancreatic polypeptide family

A peptide belonging to the pancreatic polypeptide (PP) family was isolated in pure form from the intestine of the European green frog (Rana ridibunda). The primary structure of the peptide was established as: Tyr-Pro-Pro-Lys-Pro-Glu-Asn-Pro-Gly-Glu10-Asp-Ala- Ser-Pro-Glu-Glu-Met-Thr-Lys-Tyr20-Leu-Thr-Ala-Leu-Arg-His-Tyr-Ile- Asn-Leu30-Val - Thr-Arg-Gln-Arg-Tyr-NH2. This amino acid sequence shows moderate structural similarity to human PYY (75% identity) but stronger similarity to the PP family peptides isolated from the pancreas of the salmon (86%) and dogfish (83%). The data suggest that the two putative duplications of an ancestral PP family gene that have given rise to PP, PYY and NPY in mammals had already taken place by the time of the appearance of the amphibia. In fish, however, only a single duplication has occurred, giving rise to NPY in nervous tissue and a PYY-related peptide in both pancreas and gut.

Isolation and partial sequencing of a pancreatic polypeptide-like neuropeptide from the liver fluke, Fasciola hepatica

1. A pancreatic polypeptide (PP)-immunoreactive neuropeptide has been isolated and partially sequenced from the liver fluke, Fasciola hepatica. 2. Gel permeation chromatography of an acid ethanol extract of cattle flukes showed that the peptide is similar in size to mammalian (bovine) PP. 3. The Fasciola peptide was purified to homogeneity by means of reverse-phase HPLC, employing different column chemistries. 4. The purified peptide was sequenced using automated gas-phase Edman degradation and the first 24 amino acid residues determined.

The complete primary structure of pancreatic polypeptide from the European common frog, Rana temporaria

Using an antiserum directed against the highly-conserved C-terminal hexapeptide amide of mammalian pancreatic polypeptide (PP), numerous immunoreactive endocrine cells were identified within the pancreas of the European common frog, R. temporaria. An acidified ethanolic extract of pancreatic tissue (0.859 g, n = 35) contained 26.2 nmol equivalents/g of tissue. Gel permeation chromatography of the extract resolved a single peak of immunoreactivity co-eluting with synthetic bovine PP standard. Reverse phase HPLC of this material resolved a single peak of immunoreactivity which was purified to homogeneity following chromatography on a semipreparative C-18 column and an analytical C-8 column. Plasma desorption mass spectrometry (PDMS) of the purified peptide resolved a single component with a molecular mass of 4240.9 Da. Direct gas phase sequencing established the sequence of the first 26 residues. Following incubation of the peptide with endopeptidase Asp-N and direct application of the digest to the sequencer, the entire primary structure of the peptide was established as: APSEPHHPGDQATQDQLAQYYSDLYQYITFVTRPRF. The derived molecular mass of this peptide, incorporating a C-terminal amide, was 4240.6 Da which is entirely consistent with that obtained by PDMS.

Glucagon stimulates the cardiac Ca2+ current by activation of adenylyl cyclase and inhibition of phosphodiesterase

Glucagon exerts positive inotropic and chronotropic effects in the heart. Like its glycogenolytic effect in liver cells, the cardiac effects of glucagon are often correlated with adenylyl cyclase stimulation. Therefore, cyclic AMP-dependent phosphorylation of L-type Ca2+ channels might be involved in the inotropic effect of glucagon. There have been no reports, however, of the effects of glucagon on the cardiac Ca2+ current (ICa). Also, the physiological effects of glucagon could involve mechanisms other than stimulation of adenylyl cyclase. Here we show that glucagon enhances ICa in frog and rat ventricular myocytes. The effect of glucagon in rats resulted from a stimulation of adenylyl cyclase. In frogs, however, the effect of glucagon on ICa was smaller and occurred at a concentration tenfold lower than in rats, and adenylyl cyclase was not modified. In addition, cAMP potentiated the effect of glucagon on ICa in frog ventricle, which correlated with the observed inhibition by glucagon of low-Km cAMP phosphodiesterase activity. Therefore, this is an example of a hormone that affects cardiac function in a similar way to a variety of synthetic cardiotonic compounds, such as milrinone and Ro-20-1724. Inhibition of phosphodiesterase activity by glucagon may be essential in animals in which glucagon increases cardiac contractility but does not effectively stimulate adenylyl cyclase.

Isolation and structural characterization of insulin, glucagon and somatostatin from the turtle, Pseudemys scripta

The chelonians occupy an important position in phylogeny representing a very early branching from the ancestral reptile stock. Hormonal polypeptides in an extract of the pancreas of the red-eared turtle were purified to homogeneity by reversed phase HPLC and their primary structures were determined. Turtle insulin is identical to chicken insulin. Turtle glucagon differs from chicken glucagon by the substitution of a serine by a threonine residue at position 16 and from mammalian glucagon by an additional substitution of an asparagine by a serine residue at position 28. Turtle pancreatic somatostatin is identical to mammalian somatostatin-14. The crocodilians are phylogenetically much closer to the birds than are the chelonians. Alligator insulin, however, contains three amino acid substitutions relative to chicken insulin. Thus, caution is required when inferring phylogenetic relationships based upon a comparison of amino acid sequences of homologous peptides.