Expression and alternative processing of a chicken gene encoding both growth hormone-releasing hormone and pituitary adenylate cyclase-activating polypeptide

Investigating the potential role of the pituitary adenylate cyclase-activating polypeptide (PACAP) in regulating the ubiquitin signaling pathway in poultry

The physiological processes in animal production are regulated through biologically active molecules like peptides, proteins, and hormones identified through the development of the fundamental sciences and their application. One of the main polypeptides that plays an essential role in regulating physiological responses is the pituitary adenylate cyclase-activating polypeptide (PACAP). PACAP belongs to the glucagon/growth hormone-releasing hormone (GHRH)/vasoactive intestinal proteins (VIP) family and regulates feed intake, stress, and immune response in birds. Most of these regulations occur after PACAP stimulates the cAMP signaling pathway, which can regulate the expression of genes like MuRF1, FOXO1, Atrogin 1, and other ligases that are essential members of the ubiquitin system. On the other hand, PACAP stimulates the secretion of CRH in response to stress, activating the ubiquitin signaling pathway that plays a vital role in protein degradation and regulates oxidative stress and immune responses. Many studies conducted on rodents, mammals, and other models confirm the regulatory effects of PACAP, cAMP, and the ubiquitin pathway; however, there are no studies testing whether PACAP-induced cAMP signaling in poultry regulates the ubiquitin pathway. Besides, it would be interesting to investigate if PACAP can regulate ubiquitin signaling during stress response via CRH altered by HPA axis stimulation. Therefore, this review highlights a summary of research studies that indicate the potential interaction of the PACAP and ubiquitin signaling pathways on different molecular and physiological parameters in poultry species through the cAMP and stress signaling pathways.

Pituitary adenylate cyclase-activating polypeptide in the testis of the quail Coturnix coturnix: Expression, localization, and phylogenetic analysis

To evaluate the involvement of pituitary adenylate cyclase-activating polypeptide (PACAP)/receptors system in the control of testis activity, we have investigated the expression and localization of PACAP and the distribution of its receptors in the testis of mature samples of quail Coturnix coturnix, and we have performed a phylogenetic analysis of PACAP in birds. Using histological, molecular, and bioinformatics tools, we demonstrated that (a) PACAP messenger RNA shows a high sequence identity with that reported in other birds studied so far and in other vertebrates. Furthermore, we showed that purifying selection acts on PACAP; (b) the PACAP peptide is present only in Leydig cells, whereas its receptors are localized within both Leydig and germ cells; (c) the synthesis of PACAP does not take place in seminiferous tubules. The role of PACAP in the control of spermatogenesis and steroidogenesis in birds is discussed. Finally, we talk about the phylogenetic and evolutionary relationships between PACAP in birds and in other vertebrates.

Characterization and distribution of GHRH, PACAP, TRH, SST and IGF1 mRNAs in the green iguana

The somatotropic axis (SA) regulates numerous aspects of vertebrate physiology such as development, growth, and metabolism and has influence on several tissues including neural, immune, reproductive and gastric tract. Growth hormone (GH) is a key component of SA, it is synthesized and released mainly by pituitary somatotrophs, although now it is known that virtually all tissues can express GH, which, in addition to its well-described endocrine roles, also has autocrine/paracrine/intracrine actions. In the pituitary, GH expression is regulated by several hypothalamic neuropeptides including GHRH, PACAP, TRH and SST. GH, in turn, regulates IGF1 synthesis in several target tissues, adding complexity to the system since GH effects can be exerted either directly or mediated by IGF1. In reptiles, little is known about the SA components and their functional interactions. The aim of this work was to characterize the mRNAs of the principal SA components in the green iguana and to develop the tools that allow the study of the structural and functional evolution of this system in reptiles. By employing RT-PCR and RACE, the cDNAs encoding for GHRH, PACAP, TRH, SST and IGF1 were amplified and sequenced. Results showed that these cDNAs coded for the corresponding protein precursors of 154, 170, 243, 113, and 131 amino acids, respectively. Of these, GHRH, PACAP, SST and IGF1 precursors exhibited a high structural conservation with respect to its counterparts in other vertebrates. On the other hand, iguana's TRH precursor showed 7 functional copies of mature TRH (pyr-QHP-NH₂), as compared to 4 and 6 copies of TRH in avian and mammalian proTRH sequences, respectively. It was found that in addition to its primary production site (brain for GHRH, PACAP, TRH and SST, and liver for IGF1), they were also expressed in other peripheral tissues, i.e. testes and ovaries expressed all the studied mRNAs, whereas TRH and IGF1 mRNAs were observed ubiquitously in all tissues considered. These results show that the main SA components in reptiles of the Squamata Order maintain a good structural conservation among vertebrate phylogeny, and suggest important physiological interactions (endocrine, autocrine and/or paracrine) between them due to their wide peripheral tissue expression.

Central administration of chicken growth hormone-releasing hormone decreases food intake in chicks

Growth hormone-releasing hormone (GHRH) is well known as a stimulator of growth hormone (GH) secretion. GHRH not only stimulates GH release but also modifies feeding behavior and energy homeostasis in rodents. In chickens (Gallus gallus domesticus), on the other hand, two types of GHRH, namely, chicken GHRH (cGHRH) and cGHRH-like peptide (cGHRH-LP), have been identified. The purpose of the present study was to investigate the effect of central injection of cGHRH and cGHRH-LP on feeding behavior in chicks. Intracerebroventricular (ICV) injection of both cGHRH and cGHRH-LP (0.04 to 1 nmol) significantly decreased food intake without any abnormal behavior in chicks. Furthermore, the feeding-inhibitory effect was not abolished by co-injection of the antagonist for pituitary adenylate cyclase-activating polypeptide (PACAP) or corticotropin-releasing hormone (CRH) receptors, suggesting that the anorexigenic effect of cGHRH and cGHRH-LP might not be related to the PACAP and CRH systems in the brain of chicks. Finally, 24-h food deprivation increased mRNA expression of cGHRH but not cGHRH-LP in the diencephalon. These results suggest that central cGHRH is related to inhibiting feeding behavior and energy homeostasis in chicks.

Growth hormone (GH)-releasing activity of chicken GH-releasing hormone (GHRH) in chickens

Two peptides with sequence similarities to growth hormone releasing hormone (GHRH) have been identified by analysis of the chicken genome. One of these peptides, chicken (c) GHRH-LP (like peptide) was previously found to poorly bind to chicken pituitary membranes or to cloned and expressed chicken GHRH receptors and had little, if any, growth hormone (GH)-releasing activity in vivo or in vitro. In contrast, a second more recently discovered peptide, cGHRH, does bind to cloned and expressed cGHRH receptors and increases cAMP activity in transfected cells. The possibility that this peptide may have in vivo GH-releasing activity was therefore assessed. The intravenous (i.v.) administration of cGHRH to immature chickens, at doses of 3-100 μg/kg, significantly increased circulating GH concentrations within 10 min of injection and the plasma GH levels remained elevated for at least 30 min after the injection of maximally effective doses. The plasma GH responses to cGHRH were comparable with those induced by human (h) or porcine (p) GHRH preparations and to that induced by thyrotropin releasing hormone (TRH). In marked contrast, the i.v. injection of cGHRH-LP had no significant effect on circulating GH concentrations in immature chicks. GH release was also increased from slaughterhouse chicken pituitary glands perifused for 5 min with cGHRH at doses of 0.1 μg/ml or 1.0 μg/ml, comparable with GH responses to hGHRH1-44. In contrast, the perifusion of chicken pituitary glands with cGHRH-LP had no significant effect on GH release. In summary, these results demonstrate that cGHRH has GH-releasing activity in chickens and support the possibility that it is the endogenous ligand of the cGHRH receptor.

Structural and functional characterization of pituitary adenylyl cyclase-activating polypeptide (PACAP)/PACAP-related peptide (PRP) and its receptor in olive flounder (Paralichthys olivaceus)

We identified full-length cDNAs encoding pituitary adenylyl cyclase-activating polypeptide (PACAP), PACAP-related peptide (PRP), and PACAP-specific receptor (PAC1R) from olive flounder, Paralichthys olivaceus. Two variant mRNA forms were created by alternative splicing. Comparison of genomic and cDNA sequences of the PRP-PACAP precursor revealed that skipping of exon 4 within PRP resulted in two variant transcripts: a long form encoding both PRP and PACAP and a short form encoding PACAP only. Both transcripts were constitutively observed only in the brain, whereas the short form appeared in gut tissues, such as the intestine and pyloric cecum in fish challenged with a pathogen, but not in healthy fish. Furthermore, expression of the long PRP/PACAP transcript gradually increased in the intestine of flounder challenged with bacteria, suggesting that PRP and/or PACAP may serve as a regulator(s) of the immune system, especially in the gastrointestinal tract of olive flounder. The biological functions of PACAP and PRP were investigated by exogenous treatment of flounder embryogenic cells (hirame natural embryonic cells, HINAE cells) with synthetic peptides of fPACAP-38 and/or fPRP-45. Intracellular cyclic adenosine monophosphate (cAMP) production in PAC1R-overexpressing HINAE cells was regulated by fPACAP-38 in a concentration-dependent manner, but was not regulated by fPRP-45. Results from real-time quantitative polymerase chain reaction revealed that PAC1R mRNA was specifically induced by fPACAP-38 but not by fPRP-45; PACAP significantly increased TNF-α mRNA but not growth hormone (GH) mRNA in HINAE cells; however, PRP affected GH but not TNF-α mRNA expression. These results suggest that the expression ratio of PRP and PACAP is regulated at the transcriptional level depending on the tissues and conditions, and that the unique biological roles of PRP and PACAP differ from that of mammalian PRP.

Characterization of chicken secretin (SCT) and secretin receptor (SCTR) genes: a novel secretin-like peptide (SCT-LP) and secretin encoded in a single gene

Secretin and the secretin receptor have been reported to play an important role in regulating pancreatic water and bicarbonate secretion in mammals; however, little is known about their expression, structure, and biological functions in non-mammalian vertebrates including birds. In this study, the full-length cDNAs encoding secretin and secretin receptor have first been cloned from duodenum of adult chickens. The putative chicken secretin receptor (cSCTR) is 449 amino acids in length and shares high sequence identity (58-63%) with its mammalian counterparts. Interestingly, chicken secretin cDNA encodes not only the secretin peptide (cSCT), but also a novel secretin-like peptide (cSCT-LP), which shares high amino acid identity with chicken (56%) and mammalian (48-52%) secretin. Using a pGL3-CRE-luciferase reporter system, we further demonstrated that both cSCT (EC(50): 0.31nM) and cSCT-LP (EC(50): 1.10nM), but not other structurally-related peptides, could potently activate cSCTR expressed in CHO cells, suggesting that both peptides may function as potential ligands for cSCTR. Using RT-PCR, the expression of secretin and secretin receptor in adult chicken tissues was also examined. Secretin was detected to be predominantly expressed in small intestine, while the mRNA expression of cSCTR was restricted to several tissues including gastrointestinal tract, liver, testis, pancreas and several brain regions. Collectively, results from present study not only established a molecular basis to elucidate the physiological roles of SCT, SCT-LP and SCTR in chickens, but also provide critical insights into structural and functional changes of secretin and its receptor during vertebrate evolution.

Pituitary adenylate cyclase-activating peptide (PACAP) immunoreactivity distribution in the small intestine of the adult New Hampshire chicken

We conducted a study in which we demonstrated by means of immunoperoxidase and immunofluorescence methods the presence of pituitary adenylate cyclase-activating peptide 38 (PACAP-38) immunoreactivity in the small intestine of adult New Hampshire chickens and its co-localization with VIP. In particular we describe for the first time the presence of PACAP-positive cells in the epithelium of crypts and villi. Using double immunostaining, we observed that these two peptides were widely co-localized in the nerve structures of duodenum and jejunum with the exception of the ileum, where we noticed a faint co-localization regarding the nerve fibers of the lamina propria of the villi. Furthermore, the two peptides were occasionally co-stored in the epithelial cells of the mucosa. Our findings suggest that in the chicken small intestine, PACAP can be considered, not only as a neuromodulator released by nerve elements, but also as a gut hormone secreted by endocrine cells, and it appears likely to have a role in the regulation of important intestinal physiological functions.

Growth differences and differential expression analysis of pituitary adenylate cyclase activating polypeptide (PACAP) and growth hormone-releasing hormone (GHRH) between the sexes in half-smooth tongue sole Cynoglossus semilaevis

Pituitary adenylate cyclase activating polypeptide (PACAP) and growth hormone-releasing hormone (GHRH) are regulators of growth hormone secretion. In this article, we examined the difference in growth and mRNA expression of PACAP and GHRH between the sexes in half-smooth tongue sole, an important cultured fish species indicating sexually growth dimorphism in China. Firstly, a significant body weight difference between females and males was first observed at 7 months (P<0.05) and at 18 onths the mean body weight of the females (771.0±44.3 g) was as much as 4.9 times higher than that of males (130.6±6.0 g). As a result, half-smooth tongue sole, Cynoglossus semilaevis, is a good model to investigate the effects of growth-related genes expression on sexual growth dimorphism. Secondly, the cDNAs encoding PRP/PACAP and GHRH were isolated. Two differently processed mRNA transcripts of PRP/PACAP (PRP-encoding and PRP splice variant) were found. PACAP and GHRH mRNA was highly abundant in brain and less abundant in other tissues. However, PACAP mRNA was expressed in most brain regions, and was lower in the cerebellum. GHRH mRNA was predominantly expressed in the hypothalamus and weakly expressed in all areas of the brain examined. Ontogenetic expression analysis indicated that PACAP and GHRH mRNA was detected in the early stages of embryogenesis. Finally, differential expression showed that there was no significant difference of the expression level of PACAP or GHRH between the sexes before 8 months of age. However, between 9 and 12 months of age, the GHRH mRNA expression level in males was significantly higher than in females (P<0.05), which might be associated with GH deficiency in males. In contrast, the male PACAP mRNA expression level was not significantly higher than that in females even at 9 and 12 months of age. The present results provide important clues for understanding the sexual growth dimorphism mechanisms in half-smooth tongue sole.

The serendipitous origin of chordate secretin peptide family members

Background

The secretin family is a pleotropic group of brain-gut peptides with affinity for class 2 G-protein coupled receptors (secretin family GPCRs) proposed to have emerged early in the metazoan radiation via gene or genome duplications. In human, 10 members exist and sequence and functional homologues and ligand-receptor pairs have been characterised in representatives of most vertebrate classes. Secretin-like family GPCR homologues have also been isolated in non-vertebrate genomes however their corresponding ligands have not been convincingly identified and their evolution remains enigmatic.

Results

In silico sequence comparisons failed to retrieve a non-vertebrate (porifera, cnidaria, protostome and early deuterostome) secretin family homologue. In contrast, secretin family members were identified in lamprey, several teleosts and tetrapods and comparative studies revealed that sequence and structure is in general maintained. Sequence comparisons and phylogenetic analysis revealed that PACAP, VIP and GCG are the most highly conserved members and two major peptide subfamilies exist; i) PACAP-like which includes PACAP, PRP, VIP, PH, GHRH, SCT and ii) GCG-like which includes GCG, GLP1, GLP2 and GIP. Conserved regions flanking secretin family members were established by comparative analysis of the Takifugu, Xenopus, chicken and human genomes and gene homologues were identified in nematode, Drosophila and Ciona genomes but no gene linkage occurred. However, in Drosophila and nematode genes which flank vertebrate secretin family members were identified in the same chromosome.

Conclusions

Receptors of the secretin-like family GPCRs are present in protostomes but no sequence homologues of the vertebrate cognate ligands have been identified. It has not been possible to determine when the ligands evolved but it seems likely that it was after the protostome-deuterostome divergence from an exon that was part of an existing gene or gene fragment by rounds of gene/genome duplication. The duplicate exon under different evolutionary pressures originated the chordate PACAP-like and GCG-like subfamily groups. This event occurred after the emergence of the metazoan secretin GPCRs and led to the establishment of novel peptide-receptor interactions that contributed to the generation of novel physiological functions in the chordate lineage.

Characterization of the receptors for chicken GHRH and GHRH-related peptides: identification of a novel receptor for GHRH and the receptor for GHRH-LP (PRP)

Growth hormone-releasing hormone and its structurally related peptides, GHRH-like peptide (GHRH-LP) (also called PRP), peptide histidine-isoleucine (PHI), vasoactive intestinal polypeptide (VIP), and pituitary adenylate cyclase-activating polypeptide (PACAP), have been reported to play important physiological roles in pituitary and extrapituitary tissues of vertebrates; however, little is known about the identity of these GHRH-related peptide receptors in birds. In this study, 6 receptors for GHRH and GHRH-related peptides (cGHRHR(1), cGHRHR(2), cGHRH-LPR, cPAC(1), cVPAC(1), and cVPAC(2)) were cloned from chicken brain or pituitary, and their functionalities were examined in Chinese hamster ovary (CHO) cells using a pGL3-CRE-luciferase reporter system. Results showed that: (1) all receptors are G protein-coupled receptors functionally coupled to the intracellular PKA signaling pathway; (2) 2 GHRH receptors (cGHRHR(1) and cGHRHR(2)) were identified, and both receptors could be potently activated by cGHRH; (3) cGHRH-LP could activate its specific receptor cGHRH-LPR (cPRP-R), and it also activated cGHRHR(1) and cGHRHR(2); and (4) PACAP could potently activate its receptors cPAC(1), cVPAC(1) and cVPAC(2); however, cVPAC(1) and cVPAC(2) could also be effectively activated by cVIP and tPHI, indicating that they can serve as VIP receptors and potential PHI receptors. Using a reverse transcription polymerase chain reaction assay, we further examined the mRNA expression of these receptors in adult chicken tissues. The expressions of cGHRHR(1), cGHRHR(2), and cGHRH-LPR are restricted mainly to the pituitary and/or brain, whereas cPAC(1), cVPAC(1), and cVPAC(2) are expressed in most of the tissues examined. Collectively, our study identified the receptors for chicken GHRH and GHRH-related peptides, including a novel GHRH receptor (cGHRHR(2)), and established a basis to elucidate the roles of these peptides in target tissues.

Distribution of growth hormone-releasing hormone-like peptide: Immunoreactivity in the central nervous system of the adult zebrafish (Danio rerio)

The distribution of growth hormone-releasing hormone-like peptides (GHRH-LP) in the central nervous system of the zebrafish was investigated by using immunohistochemical techniques with polyclonal antibodies. ELISAs showed that the antiserum raised against salmon (s)GHRH-LP recognized both zebrafish GHRH-LP1 and -2, whereas the antiserum raised against carp (c)GHRH-LP was more sensitive but detected only zebrafish GHRH-LP1. Neither antiserum detected the true GHRH. Large cells in the nucleus lateralis tuberis were immunoreactive with both antisera, which suggests that they contained zebrafish GHRH-LP1, but not excluding GHRH-LP2. Also, immunoreactive fibers, which putatively originated from these hypothalamic neurons, were present in the hypophysis; both antisera detected fibers, although only sGHRH-LP antiserum stained fibers in the neurointermediate lobe. These fibers may have a neuroendocrine role. Candidates for a role in feeding include several areas in which both antisera labeled cells and fibers, implying a strong reaction for GHRH-LP1 and possibly GHRH-LP2. These areas include the isthmus with cells in the secondary gustatory/visceral nucleus, which were also calretinin immunoreactive. Numerous GHRH-LP-immunoreactive fibers (also labeled by both antisera) probably originate from the gustatory/visceral nucleus to innervate the ventral area of the telencephalon, preglomerular nuclei, torus lateralis and hypothalamic diffuse nucleus, habenula, torus semicircularis, and dorsolateral funiculus of the spinal cord. Present results in the zebrafish brain suggest involvement of GHRH-LP in both neuroendocrine and feeding-associated nervous circuits. The present data on the location of the two GHRH-LPs are the first clue to the possible functions of these two hormones.

Cloning, tissue distribution and effects of food deprivation on pituitary adenylate cyclase activating polypeptide (PACAP)/PACAP-related peptide (PRP) and preprosomatostatin 1 (PPSS 1) in Atlantic cod (Gadus morhua)

Full-length complementary deoxyribonucleic acid sequences encoding pituitary adenylate cyclase activating polypeptide (PACAP)/PACAP-related peptide (PRP) and preprosomatostatin 1 (PPSS 1) were cloned from Atlantic cod (Gadus morhua) hypothalamus using reverse transcription and rapid amplification of complementary deoxyribonucleic acid ends. Semi-quantitative reverse transcriptase polymerase chain reaction shows that PRP/PACAP mRNA and PPSS 1 mRNA are widely distributed throughout cod brain. During development, PRP/PACAP and PPSS 1 were detected at the 30-somite stage and pre-hatching stage, respectively, and expression levels gradually increased up to the hatched larvae. PPSS 1, but not PRP/PACAP, appeared to be affected by food availability during early development. In juvenile cod, PPSS 1 expression levels increased and remained significantly higher than that of control fed fish throughout 30 days of starvation and during a subsequent 10 days refeeding period. In contrast, PRP/PACAP expression levels were not affected by 30 days of food deprivation, but a significant increase in expression levels was observed during the 10 days refeeding period in the experimental food-deprived group as compared to the control fed group. Our results suggest that PRP/PACAP and PPSS 1 may be involved in the complex regulation of growth, feeding and metabolism during food deprivation and refeeding in Atlantic cod.

Distribution and molecular evolution of the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors in the lizard Podarcis sicula (Squamata, Lacertidae)

The presence of the pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors PAC(1), VPAC(1), and VPAC(2) was studied in the lizard Podarcis sicula gastrointestinal and respiratory tissues. The expression and distribution of this neuropeptide was investigated using RT-PCR, immunohistochemistry, and in situ hybridization techniques. RT-PCR showed that several tissues of this reptile synthesize an mRNA encoding for PACAP. Performing in situ hybridization and immunohistochemistry, we found a wide distribution of PACAP and its mRNA in intestine, stomach, liver, and lung. PACAP receptors possess a specific distribution in both gastrointestinal and respiratory system. Further, we analyzed the conservation of PACAP amino acid sequence demonstrating that this peptide in the lizard is very similar to that of other vertebrates. Our findings suggest that also in reptiles an effective PACAP system is present and that it could be implicated in some essential physiological functions as a result of its high conservation amongst vertebrates.

VPAC and PAC receptors: From ligands to function

Vasoactive intestinal peptide (VIP) and the pituitary adenylate cyclase activating polypeptides (PACAPs) share 68% identity at the amino acid level and belong to the secretin peptide family. Following the initial discovery of VIP almost four decades ago a substantial amount of knowledge has been presented describing the mechanisms of action, distribution and pleiotropic functions of these related peptides. It is now known that the physiological actions of these widely distributed peptides are produced through activation of three common G-protein coupled receptors (VPAC(1), VPAC(2) and PAC(1)R) which preferentially stimulate adenylate cyclase and increase intracellular cAMP, although stimulation of other intracellular messengers, including calcium and phospholipase D, has been reported. Using a range of in vitro and in vivo approaches, including cell-based functional assays, transgenic animals and rodent models of disease, VPAC/PAC receptor activation has been associated with numerous physiological processes (e.g. control of circadian rhythms) and clinical conditions (e.g. pulmonary hypertension), which underlies on-going research efforts and makes these peptides and their cognate receptors attractive targets for the pharmaceutical industry. However, despite the considerable interest in VPAC/PAC receptors and the processes which they mediate, there is still a paucity of selective and available, non-peptide ligands, which has hindered further advances in this field both at the basic research and clinical level. This review summarises the current knowledge of VIP/PACAP and the VPAC/PAC receptors with regard to their distribution, pharmacology, signalling pathways, splice variants and finally, the utility of animal models in exploring their physiological roles.

Structural analysis of pituitary adenylate cyclase-activating polypeptides bound to phospholipid membranes by magic angle spinning solid-state NMR

PACAP (pituitary adenylate cyclase-activating polypeptide) is a member of the VIP/secretin/glucagon family, which includes the ligands of class II G-protein coupled receptors. Since the recognition of PACAP by the receptor may involve the binding of PACAP to membranes, its membrane-bound structure should be important. We have carried out structural analysis of uniformly 13C,15N labeled PACAP27 and its C-terminal truncated form PACAP(1-21)NH2 (PACAP21) bound to membranes with high resolution solid-state NMR. Phosphatidylcholine bilayers and phosphatidylcholine/phosphatidylglycerol bilayers were used for PACAP27 and PACAP21, respectively. Most backbone signals were assigned for PACAP27 and PACAP21. TALOS analysis revealed that both peptides take on extended conformations on the membranes. Dilution of PACAP21 did not change the conformation of the major part. Selective polarization transfer experiment confirmed that PACAP27 is interacting with the membranes. It was concluded that the interaction of PACAP with the membrane surface causes their extended conformation. PACAP27 is reported to take an alpha-helical conformation in dodecylphosphocholine micelles and membrane-binding peptides usually take similar conformations in micelles and in membranes. Therefore, the property of PACAP27 changing its conformation in response to its environment is unique. Its conformational flexibility may be associated with its wide variety of functions.

PACAP, VIP and their receptors in the metazoa: insights about the origin and evolution of the ligand-receptor pair

The evolution, function and interaction of ligand-receptor pairs are of major pharmaceutical interest. Comparative sequence analysis approaches using data from phylogenetically distant organisms can provide insights into their origin and possible physiological roles. The present review focuses on the pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal polypeptide (VIP) and their receptors in the metazoa. A PACAP-like peptide is present in tunicates and chordates while VIP- and PACAP/VIP-specific receptors have only been isolated in the latter phyla. The apparently disparate evolution of the ligands and their specific receptors raises questions about their evolution during the metazoan radiation and also about how the ligands may have acquired new functions.

PACAP-related peptide (PRP)--molecular evolution and potential functions

PACAP-related peptide (PRP) and PACAP are structurally related peptides that are encoded in the same transcripts. In the past, it was believed that the mammalian PRPs are evolved from GHRHs in non-mammals. With the recent discovery of authentic GHRH and receptor genes in frog and fish, this review aims to (1) coin the name of all GHRH-like peptides in previous literature as PRPs and (2) provide the background for new research direction for PRP in vertebrates. As a goldfish receptor highly specific for PRP with distinct tissue distribution has previously been characterized, it is highly possible that PRP plays a physiological role in non-mammalian vertebrates and the function of PRP has somehow been lost in mammals as a consequence of the loss of its receptor in the genome. This information may provide clues to elucidate functions of PRP in the future.

Identification of the endogenous ligands for chicken growth hormone-releasing hormone (GHRH) receptor: evidence for a separate gene encoding GHRH in submammalian vertebrates

It is generally believed that hypothalamic GHRH activates GHRH receptor (GHRHR) to stimulate GH synthesis and release in the pituitary of mammals. However, the identity of the endogenous ligand of GHRHR is still unresolved in submammalian vertebrates including birds. In this study, we have successfully identified the chicken GHRH (cGHRH) gene, which consists of seven exons including two exons (exons 4 and 5) coding for the predicted mature GHRH peptide of 47 amino acids. Interestingly, the differential usage of splice donor sites at exon 6 results in the generation of two prepro-GHRHs (172 and 188 amino acids in length) with different C-terminal tails. Similar to mammals, cGHRH was detected to be predominantly expressed in the hypothalamus by RT-PCR assay. Using the pGL3-CRE-luciferase reporter system, we further demonstrated that both the synthetic cGHRH peptides (cGHRH(1-47) and cGHRH(1-31)) and conditioned medium from CHO cells expressing cGHRH could strongly induce luciferase activity via activation of cGHRHR, indicating that cGHRH could bind cGHRHR and activate downstream cAMP-protein kinase A signaling pathway. Using the same system, cGHRH-like peptide was also shown to be capable of activating cGHRHR in vitro. As in chicken, a conserved GHRH gene was identified in the genomes of lower vertebrate species including zebrafish, fugu, tetraodon, and Xenopus by synteny analysis. Collectively, our data suggest that GHRH, perhaps together with GHRH-like peptide (chicken/carp-like), may function as the authentic endogenous ligands of GHRHR in chicken as well as in other lower vertebrate species.

Molecular characterization and gene expression of the pituitary adenylate cyclase-activating polypeptide (PACAP) in the lizard brain

The pituitary adenylate cyclase-activating polypeptide (PACAP) is considered a pleiotropic neuropeptide in vertebrate physiology. The nucleotide sequence, the expression and the distribution of PACAP were determined in the brain of the lizard Podarcis sicula. RT-PCR showed that the brain of this reptile synthesizes an mRNA coding for PACAP. By performing in situ hybridization and immunohistochemistry techniques, a wide distribution of PACAP and its mRNA in neurons, nervous fibers and other cells was found. Phylogenetic sequence analysis indicates that lizard PACAP is highly conserved, resembling the vertebrate PACAP. Our data demonstrate that PACAP is not only highly preserved during vertebrate evolution but also suggest that PACAP could be implicated in a wide number of functions in the physiology of the reptile brain.

Identification of the chicken growth hormone-releasing hormone receptor (GHRH-R) mRNA and gene: regulation of anterior pituitary GHRH-R mRNA levels by homologous and heterologous hormones

GHRH stimulates GH secretion in chickens as in mammals. However, nothing is known about the chicken GHRH receptor (GHRH-R). Here we report the cDNA sequence of chicken GHRH-R. Comparison of the cDNA sequence with the chicken genome localized the GHRH-R gene to chicken chromosome 2 and indicated that the chicken GHRH-R gene consists of 13 exons. Expression of all exons was confirmed by RT-PCR amplification of pituitary mRNA. The amino acid sequence predicted by the GHRH-R cDNA is homologous to that in other vertebrates and contains seven transmembrane domains and a conserved hormone-binding domain. The predicted size of the GHRH-R protein (48.9 kDa) was confirmed by binding of (125)I-GHRH to chicken pituitary membranes and SDS-PAGE. GHRH-R mRNA was readily detected by RT-PCR in the pituitary but not in the hypothalamus, total brain, lung, adrenal, ovary, or pineal gland. Effects of corticosterone (CORT), GHRH, ghrelin, pituitary adenylate cyclase-activating peptide, somatostatin (SRIF), and TRH on GHRH-R and GH gene expression were determined in cultures of chicken anterior pituitary cells. GHRH-R and GH mRNA levels were determined by quantitative real-time RT-PCR. Whereas all treatments affected levels of GH mRNA, only CORT, GHRH, and SRIF significantly altered GHRH-R mRNA levels. GHRH-R gene expression was modestly increased by GHRH and suppressed by SRIF at 4 h, and CORT dramatically decreased levels of GHRH-R mRNA at 72 h. We conclude that adrenal glucocorticoids may substantially impact pituitary GH responses to GHRH in the chicken through modulation of GHRH-R gene expression.

Cloning of the chicken pituitary receptor for growth hormone-releasing hormone

Details of the regulation of GH in birds are unclear. In this report, a receptor was cloned from chicken pituitary cDNA with 61% amino acid sequence identity to the human pituitary GHRH receptor. Phylogenies inferred from sequence alignments support that this is the chicken counterpart of the GHRH receptor known in mammals. Northern blotting shows that this receptor message is expressed in chicken pituitary, with lesser amounts seen in hypothalamus and brain but not in liver. The recombinant chicken receptor binds human GHRH with high affinity and specificity and signals cAMP accumulation. Surprisingly, available peptides synthesized to the published sequence for chicken GHRH-like peptide (cGHRH-LP) were inactive at this receptor. To address this we recloned the cDNA for this cGHRH-LP from chicken hypothalami. The revised sequence encodes lysine at position 21, which is consistent with all reported GHRH sequences from other species but different from the originally published chicken sequence. When this revised cGHRH-LP sequence was synthesized, it had improved but still weak potency at the cloned receptor. Consistent with the activity at the cloned receptor, human GHRH was potent when assayed in live chickens or on chicken pituitary membranes, but cGHRH-LP was not. We conclude that we have cloned a putative GHRH receptor that is homologous to mammalian GHRH receptors and functionally expressed in chicken pituitary, but that the identity of the endogenous ligand remains unclear. The chicken GHRH receptor cloned in this study can serve as a tool to identify its ligand and to clarify the evolutionary development of the regulation of GH.

Expression profiles of growth hormone-releasing hormone and growth hormone-releasing hormone receptor during chicken embryonic pituitary development

Growth hormone-releasing hormone (GHRH) and its receptor (GHRHR) have long been regarded as the critical molecules for the stimulation of growth hormone (GH) synthesis and release, as well as the regulation of pituitary somatotroph expansion in vertebrates. However, little is known about their expression in the embryonic pituitaries of birds. In this study, the full-length cDNA for chicken GHRHR was cloned from the chicken pituitary. It encodes 419 amino acids and shares high homology with that of the human, rat, and mouse. As in those in mammals, chicken GHRHR is predominantly expressed in the pituitary and weakly expressed in several extra-pituitary tissues including brain, pancreas, testis, and kidney, among 12 tissues examined. Using semiquantitative reverse transcription-PCR, we further examined the expression of GH, GHRH, and GHRHR during embryonic pituitary development. The expression of GHRHR on embryonic d 8 was much lower, but abundant expression was noticed as early as embryonic d 12. In contrast, the level of pituitary GHRH mRNA peaked on d 8 and declined sharply afterwards. Interestingly, unlike those of pituitary GHRH and GHRHR, the higher expression levels of GH appeared much later (from d 16 to 20). The differential expressions of GHRH, GHRHR, and GH in the developing embryonic pituitaries not only imply that pituitary-derived GHRH (or pituitary adenylate cyclase-activating polypeptide) and GHRHR may have a paracrine/autocrine role in the expansion of undifferentiated somatotroph precursor cells, but also suggest that GHRHR is likely to be involved in the somatotroph differentiation occurring at the later developmental stages.

Pituitary adenylate cyclase activating polypeptide plays a role in olfactory memory formation in chicken

PACAP plays an important role during development of the nervous system and is also involved in memory processing. The aim of the present study was to investigate the function of PACAP in chicken embryonic olfactory memory formation by blocking PACAP at a sensitive period in ovo. Chicken were exposed daily to strawberry scent in ovo from embryonic day 15. Control eggs were treated only with saline, while other eggs received a single injection of the PACAP antagonist PACAP6-38 at day 15. The consumption of scented and unscented water was measured daily after hatching. Animals exposed to strawberry scent in ovo showed no preference. However, chickens exposed to PACAP6-38, showed a clear preference for plain water, similarly to unexposed chicken. Our present study points to PACAP's possible importance in embryonic olfactory memory formation.

Inhibitory effects of pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) on food intake in the goldfish, Carassius auratus

Pituitary adenylate cyclase-activating polypeptide (PACAP) has a similar structure to that of vasoactive intestinal peptide (VIP) and both the polypeptides belong to the same molecular group, the secretin-glucagon superfamily. PACAP and VIP have possible potency as hypothalamic factors mediating the release of pituitary hormones in the fish pituitary. However, the roles of PACAP and VIP in the central nervous systems of fish have not yet been made clear. Recently, it was reported that PACAP and/or VIP are involved in the feeding behavior of the mouse and chick. Therefore, we investigated the effects of intracerebroventricular (ICV) and intraperitoneal (IP) administration of synthetic PACAP and VIP on food intake in the goldfish, Carassius auratus. Cumulative food intake was significantly decreased by ICV injection of PACAP (11 or 22 pmol/g body weight) or VIP (11 or 22 pmol/g) during a 60-min observation period after treatment. IP administration of PACAP (44 or 88 pmol/g) or VIP (22 or 44 pmol/g) induced a significant decrease in food intake during a 60-min observation period after treatment. These results suggest that PACAP and VIP may be involved as feeding regulators in goldfish.

The release of growth hormone (GH): relation to the thyrotropic- and corticotropic axis in the chicken

In the chicken and other avian species, the secretion of GH is under a dual stimulatory and inhibitory control of hypothalamic hypophysiotropic factors. Additionally, the thyrotropin-releasing hormone (TRH), contrary to the mammalian situation, is also somatotropic and equally important in releasing GH in chick embryos and juvenile chicks compared to the (mammalian) growth hormone-releasing hormone (GHRH) itself. Consequently, the negative feedback loop for GH release not only involves the insulin-like growth factor IGF-I but also thyroid hormones. In adult chickens, TRH does no longer have a clear thyrotropic activity, whereas its somatotropic activity depends on the feeding status of the animal. In addition, as in mammals, the secretion of GH and glucocorticoids is stimulated by ghrelin, a novel peptide predominantly synthesized in the gastrointestinal tract. Two chicken isoforms of the ghrelin receptor have been identified, both of which are highly expressed in the hypothalamus and pituitary, suggesting that a stimulatory effect may be directed at these levels. GH and glucocorticoids control the peripheral thyroid hormone function by down-regulating the hepatic type III deiodinating enzyme (D3) in embryos (GH and glucocorticoids) and in juvenile and adult chickens (GH). Moreover, glucocorticoids help to regulate T3-homeostasis in the brain during embryogenesis by stimulating the type II deiodinase (D2) expression. This way not only a multifactorial release mechanism exists for GH but also a functional entanglement of activities between the somatotropic-, thyrotropic- and corticotropic axis.

Effects of in ovo treatment with PACAP antagonist on general activity, motor and social behavior of chickens

Pituitary adenylate cyclase activating polypeptide (PACAP) has been shown to influence nervous system development. The aim of the present study was to investigate the effects of in ovo treatment with the PACAP antagonist PACAP6-38 during embryonic life (E8 and E16) on motor activity and social behavior in chicken. Our results showed that a single injection of PACAP6-38 during the first half of embryonic life caused subtle transient changes in general behavior and motor control when compared to saline-treated controls. Increased activity and reduced anxiety were observed also in a novel environment at 2 days after hatching. However, most of these behavioral differences disappeared by 2 weeks. PACAP6-38-treatment during the first half of embryonic life resulted in markedly reduced social behavior, which was still present at 2 weeks of age. Treatment during the second half of embryonic life resulted in no behavioral differences between control and PACAP6-38-treated chicken. PACAP content in different brain areas was not different between control and PACAP6-38-treated chicken at 5 days or 3 weeks of age, but it decreased significantly with age in both groups. In summary, our results show that PACAP6-38 treatment at E8 caused transient changes in motor behavior, and long-lasting reduction in social behavior.

Pituitary adenylate cyclase-activating polypeptide in the brain, spinal cord and sensory organs of the zebrafish, Danio rerio, during development

The distribution of Pituitary adenylate cyclase-activating polypeptide (PACAP) was investigated in the brain, pituitary and sensory organs of the zebrafish, Danio rerio, during development, in juvenile and adult specimens, using the immunofluorescence method. In 24 h post fertilization (hpf) embryos, PACAP immunoreactive cells appeared in the rostral telencephalon, dorsal diencephalon, caudal and medial rhombencephalon, spinal cord and retina. At 48 hpf stage, positive cells were present in the dorsal diencephalon, medial rhombencephalon, spinal cord, retina and olfactory placode (Op). At 72 hpf stage, additional immunoreactive elements appeared in the medial telencephalon, hypothalamus, mesencephalic tegmentum, retina and otic sensory epithelium (Ose). At day 5, new immunoreactive cells were found in the anterior rhombencephalon and pituitary pars distalis. At day 13, positive cells were mainly concentrated in the mesencephalic tegmentum and spinal cord. In the telencephalon, diencephalon, rhombencephalon and pituitary, the distribution of positive cells was similar to that previously reported. At 1 month stage, positive cells were detected in the hypothalamus, nucleus of the medial longitudinal fascicle (nMlf), rhombencephalic griseum centrale (Gc) and pituitary pars distalis. At 2-3 month stages, immunoreactive elements were found in several hypothalamic nuclei, in the mesencephalic nucleus isthmi, cerebellum and pituitary. In adults, PACAP immunoreactivity was confined to a few brain regions and the pituitary. PACAP immunoreactivity was transiently expressed in several regions suggesting that the peptide may have a role in the control of cells differentiation and proliferation during zebrafish ontogeny. The finding of positive fibers in the pituitary from day 5 onward indicates that PACAP may function from this stage as a hypophysiotropic peptide.

PACAP promotes sensory neuron differentiation: blockade by neurotrophic factors

Developing neurons encounter a panoply of extracellular signals as they differentiate. A major goal is to identify these extrinsic cues and define the mechanisms by which neurons simultaneously integrate stimulation by multiple factors yet initiate one specific biological response. Factors that are known to exert potent activities in the developing nervous system include the NGF family of neurotrophic factors, ciliary neurotrophic factor (CNTF), and pituitary adenylate cyclase-activating peptide (PACAP). Here we demonstrate that PACAP promotes the differentiation of nascent dorsal root ganglion (DRG) neurons in that it increases both the number of neural-marker-positive cells and axonogenesis without affecting the proliferation of neural progenitor cells. This response is mediated through the PAC1 receptor and requires MAP kinase activation. Moreover, we find that, in the absence of exogenously added PACAP, blockade of the PAC1 receptor inhibits neuronal differentiation. These data coupled with our finding that both PACAP and the PAC1 receptor are expressed during the peak period of neuronal differentiation in the DRG suggest that PACAP functions in vivo to promote the differentiation of nascent sensory neurons. Interestingly, we also demonstrate that the neurotrophic factors NT-3 and CNTF completely block the PACAP-induced neuronal differentiation. This points to the intricate integration of cellular signals by nascent neurons and, to our knowledge, is the first evidence for neurotrophic factor abrogation of a pathway regulated by G-protein-coupled receptors (GPCRs).

PACAP maintains cell cycling and inhibits apoptosis in chick neuroblasts

We previously reported that pituitary adenylate cyclase-activating polypeptide (PACAP) increased cAMP in neuroblast-enriched cultures from embryonic day 3.5 chick brain. Also, the neuroblasts expressed the mRNA, peptide, and receptor for PACAP. Here, we investigated downstream effects of increased cAMP by examining PACAP's role in regulating cell numbers during brain development. Using flow cytometry, we quantified proliferating cell nuclear antigen and DNA, and compared apoptotic cells and cells in cell cycle compartments under differing conditions. Untreated cultures showed high proliferative activity with little apoptosis. Addition of exogenous PACAP had no effect on this pattern. However, blocking endogenous PACAP with a receptor antagonist increased cell cycle exit, then increased apoptosis. We conclude that chick neuroblasts require production of PACAP to inhibit apoptosis and maintain full proliferative activity during early brain development.

[The regulatory mechanism for neuron specific expression of PACAP gene]

Pituitary adenylate cyclase-activating polypeptide (PACAP), a pleiotropic neuropeptide, is present abundantly in the central nervous system. In the 5'-flanking region of the PACAP gene, we found and characterized two negative regulatory elements, which are homologous to the neural-restrictive silencer element (NRSE). Their sequence and position were significantly conserved among mouse, human, and rat PACAP genes. NRSE is a crucial negative-acting DNA regulatory element for neuron-specific gene expression. NRSE acts through the transcription factor known as neural-restrictive silencer factor (NRSF). In non-neuronal cells, NRSF suppresses the expression of neuron-specific genes. On the other hand, in neuronal cells, NRnV, a NRSF truncated form, repress their expressions in a dominant negative manner. The electrophoretic mobility shift assay with 3T3 cells extract demonstrated the identical complexes among NRSLE-1, NRSLE2, and the NRSE of rat type II sodium channel gene. In the luciferase reporter assay, NRSLEs suppressed SV40 promoter activity in 3T3 cells, but not in PC12 cells. RT-PCR analysis revealed that PACAP and NRnV mRNAs are expressed in neuronal cells (differentiated PC12), but not in non-neuronal cells (3T3 or C6). These results suggested that the NRSE-NRSF system might be involved in the regulatory mechanism of neuron-specific expression of the PACAP gene.

Receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide in turkey cerebral cortex: characterization by [125I]-VIP binding and effects on cyclic AMP synthesis

Receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) in turkey cerebral cortex were characterized using two approaches: (1) in vitro radioreceptor binding of [125I]-VIP, and (2) effects of peptides from the PACAP/VIP/secretin family on cyclic AMP formation. The binding of [125I]-VIP to turkey cortical membranes was rapid, stable, and reversible. Saturation analysis resulted in a linear Scatchard plot, suggesting binding to a single class of high affinity receptor binding sites with a Kd of 0.70 nM and a Bmax of 52 fmol/mg protein. Various peptides displaced the specific binding of 0.12 nM [125I]-VIP to turkey cerebral cortical membranes in a concentration-dependent manner. The relative rank order of potency of the tested peptides to inhibit [125I]-VIP binding to turkey cerebrum was: PACAP38 approximately PACAP27 approximately chicken VIP approximately mammalian VIP >>> PHI >> secretin, chicken VIP16-28 (inactive). About 65% of specific [125I]-VIP binding sites in turkey cerebral cortex was sensitive to Gpp(NH)p, a nonhydrolysable analogue of GTP. PACAP38, PACAP27, chicken VIP and, to a lesser extent, mammalian VIP potently stimulated cyclic AMP formation in turkey cerebral cortical slices in a concentration-dependent manner, displaying EC50 values of 8.7 nM (PACAP38), 21.3 nM (PACAP27), 67.4 nM (chicken VIP), and 202 nM (mammalian VIP). On the other hand, PHI and secretin very weakly affected the nucleotide production. The obtained results indicate that cerebral cortex of turkey contains VPAC type receptors that are positively linked to cyclic AMP-generating system and are labeled with [125I]-VIP.

PAC1 receptors in chick cerebral cortex: characterization by binding of pituitary adenylate cyclase-activating polypeptide, [125I]-PACAP27

In this study we characterized receptors for pituitary adenylate cyclase-activating polypeptide (PACAP) in chick cerebral cortex by in vitro binding technique, using [125I]-PACAP27 as a ligand. The specific binding of [125I]-PACAP27 to chick cerebral cortical membranes was found to be rapid, stable, saturable, and of high affinity. Scatchard analysis suggested binding to a single class of receptor binding sites with high affinity (K(d)=0.41+/-0.08 nM) and high capacity (B(max)=457+/-35 fmol/mg protein). The relative rank order of potency of the tested peptides to inhibit [125I]-PACAP27 binding to chick cerebrum was: PACAP38 approximately PACAP27>PACAP6-27 approximately PACAP6-38 >> chicken VIP >> mammalian VIP >> secretin (inactive). It is concluded that the cerebral cortex of chick, in addition to VPAC recognition sites, contains a large population of PAC(1)-type receptor binding sites.

Developmental changes in the expression of growth hormone-releasing hormone and pituitary adenylate cyclase-activating polypeptide in zebrafish

Growth hormone-releasing hormone (GHRH) and pituitary adenylate cyclase-activating polypeptide (PACAP) are structurally and functionally related members of the glucagon superfamily, a group of hormones important in development, growth, and metabolism. Our objectives were to determine the developmental expression pattern of the ghrh-pacap1 gene using the zebrafish model. The temporal and spatial expression pattern of the ghrh-pacap1 gene was examined by RT-PCR and in situ hybridization. In zebrafish, the ghrh-pacap1 mRNA transcript was expressed throughout development beginning at the transition between the blastula and gastrula periods. During midgastrulation, alternative splicing resulted in the generation of a novel transcript lacking the cryptic peptide. During the segmentation period, expression was localized to the neural tube, developing eye, and neural crest; strong expression was found in the developing cerebellum. Later in development, expression was localized in the hatching gland and developing pharyngeal arches. The temporal and spatial expression pattern of the ghrh-pacap1 transcript suggests that these hormones may modulate patterning during development.

Pituitary adenylate cyclase-activating polypeptide and growth hormone-releasing hormone-like peptide in sturgeon, whitefish, grayling, flounder and halibut: cDNA sequence, exon skipping and evolution

To better understand the evolution of pituitary adenylate cyclase-activating polypeptide (PACAP) and growth hormone-releasing hormone (GHRH), we isolated the cDNAs encoding these peptides from the brains of five species of fish: sturgeon, whitefish, grayling, flounder and halibut. Both hormones are encoded in tandem in full-length cDNAs. We compared the phylogenetic relationship among these and other known sequences encoding PACAP. In closely related species, transcripts encoding PACAP and GHRH are strongly conserved in the hormone coding regions, moderately conserved in the signal peptide, cryptic peptide and 3'-untranslated regions, but are most varied in the 5'-untranslated regions.Next, we compared the deduced amino acid sequences for the peptides to known sequences. Sturgeon and whitefish have a PACAP(38) peptide sequence that is 92% conserved compared to human PACAP(38), the highest for a fish reported to date. GHRH is the lesser conserved of the two peptides with only 39% to 45% conservation between fish and human.Each of the five fish species had a second cDNA encoding a short precursor lacking GHRH(1-32), the bioactive portion of GHRH. This suggests that exon skipping in GHRH-PACAP transcripts may be an important mechanism for regulating the ratio of PACAP to GHRH peptides.

Ontogenetic development and neuroanatomical localization of growth hormone-releasing hormone (GHRH) in the brain and pituitary gland of pejerrey fish Odontesthes bonariensis

The presence and distribution of growth hormone-releasing hormone (GHRH) were studied by immunocytochemistry in adult and developing pejerrey fish, Odontesthes bonariensis (Atheriniformes). A few perikarya and fibers with immunoreactivity to GHRH (ir-GHRH) were identified in the olfactory bulbs at hatching. One week later, scattered ir-GHRH cell bodies were observed in the preoptic area and some fibers were detected entering the pituitary gland. Isolated ir-GHRH perikarya were revealed in the hypothalamus and in the medulla oblongata (MO) 3 weeks after hatching. Seven weeks after hatching, ir-GHRH cells were also identified in the nucleus of the lateral lemniscus and the cerebellum. Both nuclei presented strong ir-GHRH projections extending rostro-ventrally. At 11 weeks after hatching another group of ir-GHRH cells were revealed in the midbrain tegmentum. After that time the pattern of distribution of ir-GHRH structures remained unchanged. At 1 week after hatching and later, the pituitary gland consistently revealed ir-GHRH cells and fibers mainly in the proximalis pars distalis and in a minor proportion of the pars intermedia since week 1. The pineal gland showed ir-GHRH cells projecting into the pineal lumen, at week 6 after hatching and later. The pineal stalk and the subcomissural organ also presented ir-GHRH structures. Additionally, ir-GHRH material was found from week 3 to the adult stage in the following extraneural organs: gills, gut, kidney and hepatopancreas. These results represent the anatomical substrate for understanding the physiology of GHRH peptide in pejerrey, adding information on the ontogeny of neural structures expressing GHRH.

Mouse pituitary adenylate cyclase-activating polypeptide (PACAP): gene, expression and novel splicing

PACAP is a conserved neuropeptide present in all vertebrates. In the mouse, the PACAP gene and various mRNAs have been isolated. To further characterize the mouse PACAP gene (Adcyap1), we have confirmed its sequence, identified its chromosomal location on distal chromosome 17 and used RT-PCR and 5'RACE in various tissues to identify eight PACAP mRNAs, four of which are novel. Three of these novel transcripts have alternate 5'UTRs, whereas the fourth is altered within the coding region. This is the first report of alternate splicing within the coding region of the PACAP gene. The expression pattern of PACAP in the mouse during embryonic development and adulthood is known. Here, expression of PACAP in the mouse at four postnatal stages in 12 tissues is assessed. We identify continuous expression of PACAP in the brain and eye and stage-specific expression in the gonads and thymus. The complex splicing of PACAP transcripts may regulate the tissue-and stage-specific expression.

Targeted disruption of the pituitary adenylate cyclase-activating polypeptide gene results in early postnatal death associated with dysfunction of lipid and carbohydrate metabolism

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a hormone belonging to the glucagon superfamily of hormones. These hormones are known to play important roles in metabolism and growth. PACAP is a neuropeptide that causes accumulation of cAMP in a number of tissues and affects the secretion of other hormones, vasodilation, neural and immune functions, as well as the cell cycle. To determine whether PACAP is essential for survival and to evaluate its function(s), we have generated mice lacking the PACAP gene via homologous recombination. We found that most PACAP null mice died in the second postnatal week in a wasted state with microvesicular fat accumulation in liver, skeletal muscle, and heart. Gas chromatography-mass spectrometry showed that fatty acid beta-oxidation in liver mitochondria of PACAP(-/-) mice was not blocked based on the distribution of 3-hydroxy-fatty acids (C6-16) in the plasma. Instead, increased metabolic flux through the beta-oxidation pathway was suggested by the presence of ketosis. Also, serum triglycerides and cholesterol were significantly higher (2- to 3-fold) in PACAP null mice than littermates. In the fed state, both serum insulin and blood glucose were normal in 5-d-old null mice compared with their littermates. In contrast, fasted PACAP null pups had a significant increase in insulin, but a decrease in blood glucose compared with littermates. Glycogen in the liver was reduced. These results suggest PACAP is a critical hormonal regulator of lipid and carbohydrate metabolism.

Distribution and daily variations of PACAP in the chicken brain

Levels of PACAP38 were measured in different areas of the chicken brain under various lighting conditions by radioimmunoassay (RIA). Selected groups of animals were maintained under light for 14 h alternating with 10 h of darkness (LD), reversed lighting conditions (DL) and constant light (LL) or constant dark (DD). Daily variations of PACAP levels were observed in the brainstem, diencephalon, telencephalon and retina. In the brainstem and diencephalon, levels of PACAP increased during subjective nighttime, except in the DL group where levels were elevated between 15-21 h. In the telencephalon, the lowest level of PACAP was measured between 12-21 h except in the DL group where two peaks occurred at 18 and 03 h. In the retina, all 4 groups showed a similar level and pattern, with lowest levels during midday hours. No daily variation was observed in the pineal gland. According to the present observations, it is suggested that PACAP levels differ in several areas of the chicken brain under various lighting conditions and photic stimuli do not appear to be the main regulators of the circadian variations of PACAP.

Developmental expression, alternative splicing and gene copy number for the pituitary adenylate cyclase-activating polypeptide (PACAP) and growth hormone-releasing hormone (GRF) gene in rainbow trout

Both growth hormone-releasing hormone (GRF) and pituitary adenylate cyclase-activating polypeptide (PACAP) are encoded on the same gene in fish, but not in mammals. Our objective was to examine the onset and pattern of expression for the grf/pacap gene and to determine whether there is more than one gene in rainbow trout. The results show that grf/pacap mRNA is first expressed at 4 days after fertilization and continues through to hatching. Alternative splicing at all developmental stages produces a full-length transcript and one lacking exon four, which encodes GRF. Thus, independent regulation of the hormones occurs throughout development. Southern analysis shows that two grf/pacap genes exist in trout, but only one gene is responsible for the two identified transcripts. Overexpression of the grf/pacap gene in transgenic fish was attempted, but did not succeed. We conclude that the early and continued expression of grf/pacap mRNA in trout embryos and regulation of the neuropeptide ratio suggests they have a role in early brain development apart from their later role in releasing pituitary hormones.

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.

Pituitary adenylate cyclase-activating polypeptide and its receptors in amphibians

Pituitary adenylate cyclase-activating polypeptide (PACAP), a novel peptide of the secretin/glucagon/vasoactive intestinal polypeptide superfamily, has been initially characterized in mammals in 1989 and, only 2 years later, its counterpart has been isolated in amphibians. A number of studies conducted in the frog Rana ridibunda have demonstrated that PACAP is widely distributed in the central nervous system (particularly in the hypothalamus and the median eminence) and in peripheral organs including the adrenal gland. The cDNAs encoding the PACAP precursor and 3 types of PACAP receptors have been cloned in amphibians and their distribution has been determined by in situ hybridization histochemistry. Ontogenetic studies have revealed that PACAP is expressed early in the brain of tadpoles, soon after hatching. In the frog Rana ridibunda, PACAP exerts a large array of biological effects in the brain, pituitary, adrenal gland, and ovary, suggesting that, in amphibians as in mammals, PACAP may act as neurotrophic factor, a neurotransmitter and a neurohormone.

Sequence and expression of a cDNA encoding both pituitary adenylate cyclase activating polypeptide and growth hormone-releasing hormone-like peptide in channel catfish (Ictalurus punctatus)

In nonmammalian vertebrates, pituitary adenylate cyclase activating polypeptide (PACAP) and a putative growth hormone-releasing hormone (GHRH-like peptide) are encoded by a single mRNA transcript. Both PACAP and GHRH have been implicated in the control of fish growth. Although the gene encoding PACAP and GHRH-like peptide (GHRHLP) has been cloned in other fishes, characterization of this gene in the commercially important channel catfish (Ictalurus punctatus) has not been previously reported. In this study, the GHRHLP/PACAP cDNA was cloned from channel catfish hypothalamic tissue and a brain cDNA library. Two cDNA variants of the GHRHLP/PACAP precursor gene were identified as a result of alternative splicing, a long form encoding both PACAP and GHRHLP and a short form encoding only PACAP. Both the long and the short forms of the GHRHLP/PACAP precursor cDNA were identified in channel catfish brain, pituitary, fat, gastrointestinal tract, ovary, testes, and muscle by RT-PCR detection. This study is the first to demonstrate mRNA expression of this gene in fat or skeletal muscle of fish. By characterizing the GHRHLP/PACAP gene and its distribution in channel catfish, we have developed essential tools to investigate the roles of these peptides in the regulation of catfish growth.

Early expression of pituitary adenylate cyclase-activating polypeptide and activation of its receptor in chick neuroblasts

To investigate the involvement of pituitary adenylate cyclase- activating polypeptide (PACAP) and GH-releasing factor (GRF) during early chick brain development, we established neuroblast- enriched primary cell cultures derived from embryonic day 3.5 chick brain. We measured increases in cAMP generated by several species-specific forms of the peptides. Dose-dependent increases up to 5-fold of control values were measured in response to physiological concentrations of human/salmon, chicken, and tunicate PACAP27. Responses to PACAP38 were more variable, ranging from 5-fold for human PACAP38 to 4-fold for chicken PACAP38, to no significant response for salmon PACAP38, compared with control values. The responses to PACAP38 may reflect a greater difference in peptide structure compared with PACAP27 among species. Increases in cAMP generated by human, chicken, and salmon/carp GRF were not statistically significant, whereas increases in response to lower-range doses of tunicate GRF27-like peptide were significant, but small. We also used immunocytochemistry and Western blot to show synthesis of the PACAP38 peptide. RT-PCR was used to demonstrate that messenger RNAs for PACAP and GRF and a PACAP-specific receptor were present in the cells. This is a first report suggesting an autocrine/paracrine system for PACAP in early chick brain development, based on the presence of the ligand, messages for the ligand and receptor, and activation of the receptor in neuroblast-enriched cultures.

Intracerebroventricular injection of ghrelin and growth hormone releasing factor inhibits food intake in neonatal chicks

Growth hormone releasing factor (GRF) is known to stimulate feeding of rats. Ghrelin, a novel growth hormone (GH)-releasing acylated peptide, was recently isolated from rat stomach. It also stimulates the release of GH from the anterior pituitary through the GH secretagogue receptor (GHS-R) and feeding in the rat. We have investigated the effects of ghrelin and GRF on food intake of the neonatal chick. In Experiment 1, 0, 1.25, 2.5 and 5 microg of ghrelin were administered intracerebroventricularly (i.c.v.) to ad libitum fed birds. In Experiment 2, the effect of (i.c.v.) injection of 0, 1.25, 2.5 and 5 microg of GRF was investigated. Both peptides strongly inhibited food intake of the chick during the 2-h post-injection period. In the third experiment, 0, 0.5, 1 and 2 microg of ghrelin was injected i.c.v. in chicks previously deprived of food for 3 h. Food intake was again inhibited by ghrelin in a dose-dependent manner. These results suggest that the mechanisms for feeding of the neonatal chick through GH release are different from mammals.

Ontogeny of pituitary adenylate cyclase-activating polypeptide (PACAP) in the frog (Rana ridibunda) tadpole brain: immunohistochemical localization and biochemical characterization

The anatomic distribution and biochemical characteristics of the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) were investigated in the central nervous system of the frog, Rana ridibunda, during development. Three to four days after hatching, at stages IV-VII, PACAP-immunoreactive perikarya were detected in the dorsal thalamus within the anterior ventral area, and a few fibers were found in the medial pallium. Positive cell bodies were first observed in the hypothalamus at stages VIII-IX, at the level of the dorsal and ventral infundibular nuclei. In these regions, the number of positive perikarya increased during ontogeny. In tadpoles, during the mid- and late premetamorphosis, a more complex organization of the PACAP-immunoreactive system was found in the thalamus with the appearance, at stages IX-XII, of two additional groups of positive neurons in the ventrolateral area and posterocentral nucleus. At stages XIII-XVIII of larval development and subsequent larval stages, PACAP-immunoreactive fibers were found in the median eminence. In newly metamorphosed animals, several additional groups of positive perikarya appeared in the medial pallium, the preoptic nucleus, the torus semicircularis, the tegmentum of the mesencephalon, and the cerebellum. The immunoreactive peptide contained in the tadpole brain was characterized by high performance liquid chromatography analysis combined with radioimmunoassay quantification. At all stages investigated, the predominant form of PACAP-immunoreactive material coeluted with synthetic frog PACAP38. The occurrence of PACAP soon after hatching indicates that the peptide may exert neurotrophic activities. The existence of immunoreactive elements in several thalamic regions at mid- and late premetamorphic stages suggests that PACAP may act as a neurotransmitter, neuromodulator, or both, during ontogenesis. Finally, the presence of PACAP-immunoreactive perikarya in hypothalamic nuclei and nerve fibers in the median eminence supports the view that PACAP may play a role in the control of pituitary hormone secretion during larval development.

Molecular cloning and characterization of alternatively spliced transcripts of the turkey pituitary adenylate cyclase-activating polypeptide

Pituitary adenylate cyclase-activating polypeptide (PACAP) increases the release of growth hormone (GH) and prolactin (PRL) in mammals. However, the evolutionary and functional relationships of PACAP, GH, and PRL are not clear. To understand how PACAP is regulated in the turkey, a turkey PACAP (tPACAP) cDNA has been cloned by the combination of reverse transcription-polymerase chain reaction and the rapid amplification of cDNA 5'- and 3'-ends. The deduced amino acid sequence of tPACAP-38 and turkey PACAP-related peptide (tPRP) displayed 87-97 and 52-63% similarity when compared to a variety of known PACAP-38 and PRP sequences, respectively. Two major transcripts (1.3 and 3.0 kb) of tPACAP were detected by Northern blot analysis. The highest levels of tPACAP mRNA were shown to be expressed in the hypothalamus, the cerebellum, and the cerebrum. In contrast, most of the other tissues tested expressed relatively low steady-state levels of tPACAP mRNA. Alternative splicing of tPACAP resulted in the expression of two different isoforms. The smaller form of tPACAP was expressed in the hypothalamus during early embryonic development and decreased significantly in later stages.

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.