Molecular evolution of the growth hormone-releasing hormone/pituitary adenylate cyclase-activating polypeptide gene family. Functional implication in the regulation of growth hormone secretion (original) (raw)
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Molecular and Cellular Endocrinology, 1995
Growth hormone-releasing hormone (GHRH) and pituitary adenylate cyclase activating polypeptide (PACAP) are two neuropeptides that are associated with the release of pituitary growth hormone. Here a cDNA of 2501 base pairs encoding both a PACAP and a GHRH-like peptide was isolated from a brain cDNA library made from Thai catfish (Clarius macrocephufur). The organization is unlike that of the mammalian gene where PACAP and PACAP-related peptide (PRP) are encoded in one gene, and the GI-IRH peptide is on a separate gene. Northern analysis of catfish brain mRNA indicated that PACAP/GHRH-like mRNA has three sixes; bands of 6000, 2500, and 1000 bases suggest alternative splicing of the gene. Reverse transcriptase/PCR assay detected PACAP/GHRH-like rnRNA in tissues from the brain, testis, ovary, and stomach, but not from the pancreas, pituitary, muscle, and liver. Our hypothesis that the two mammalian genes encoding GHRH or PACAP originated from a gene duplication between fish and tetrapods is supported by the present findings of similar mRNA organization and pattern of expression for the one fish gene and two mammalian genes.
Discovery of Growth Hormone-Releasing Hormones and Receptors in Nonmammalian Vertebrates
Proceedings of The National Academy of Sciences, 2007
In mammals, growth hormone-releasing hormone (GHRH) is the most important neuroendocrine factor that stimulates the release of growth hormone (GH) from the anterior pituitary. In nonmammalian vertebrates, however, the previously named GHRH-like peptides were unable to demonstrate robust GH-releasing activities. In this article, we provide evidence that these GHRH-like peptides are homologues of mammalian PACAP-related peptides (PRP). Instead, GHRH peptides encoded in cDNAs isolated from goldfish, zebrafish, and African clawed frog were identified. Moreover, receptors specific for these GHRHs were characterized from goldfish and zebrafish. These GHRHs and GHRH receptors (GHRH-Rs) are phylogenetically and structurally more similar to their mammalian counterparts than the previously named GHRH-like peptides and GHRH-like receptors. Information regarding their chromosomal locations and organization of neighboring genes confirmed that they share the same origins as the mammalian genes. Functionally, the goldfish GHRH dose-dependently activates cAMP production in receptor-transfected CHO cells as well as GH release from goldfish pituitary cells. Tissue distribution studies showed that the goldfish GHRH is expressed almost exclusively in the brain, whereas the goldfish GHRH-R is actively expressed in brain and pituitary. Taken together, these results provide evidence for a previously uncharacterized GHRH-GHRH-R axis in nonmammalian vertebrates. Based on these data, a comprehensive evolutionary scheme for GHRH, PRP-PACAP, and PHI-VIP genes in relation to three rounds of genome duplication early on in vertebrate evolution is proposed. These GHRHs, also found in flounder, Fugu, medaka, stickleback, Tetraodon, and rainbow trout, provide research directions regarding the neuroendocrine control of growth in vertebrates.
General and Comparative Endocrinology, 2001
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.
Neuroendocrinology, 2001
In mammals, growth hormone (GH) is under a dual hypothalamic control exerted by growth hormone-releasing hormone (GHRH) and somatostatin (SRIH). We investigated GH release in a pleuronectiform teleost, the turbot (Psetta maxima), using a serum-free primary culture of dispersed pituitary cells. Cells released GH for up to 12 days in culture, indicating that turbot somatotropes do not require releasing hormone for their regulation. SRIH dose-dependently inhibited GH release up to a maximal inhibitory effect of 95%. None of the potential stimulators tested induced any change in basal GH release. Also, neither forskolin, an activator of adenylate cyclase, nor phorbol ester (TPA), an activator of protein kinase C, were able to modify GH release, suggesting that spontaneous basal release already represents the maximal secretory capacity of turbot somatotropes. In contrast, forskolin and TPA were able to increase GH release in the presence of SRIH. In this condition (coincubation with SRIH), pituitary adenylate cyclase-activating polypeptide (PACAP) stimulated GH release, whereas none of the other neuropeptides tested (GHRHs; sea bream or salmon or chicken II GnRHs; TRH; CRH) had any significant effect. These data indicate that inhibitory control by SRIH may be the basic control of GH production in teleosts and lower vertebrates, while PACAP may represent the ancestral growth hormone-releasing factor in teleosts, a role taken over in higher vertebrates by GHRH.
Phylogenetic evolution of the neuroendocrine control of growth hormone: Contribution from teleosts
Growth hormone (GH) is involved in many physiological functions such as growth, metabolism, reproduction and immunity. In mammals, it is well established that GH release is under a dual hypothalamic control, stimulatory by somatoliberin (GHRH) and inhibitory by somatostatin (sRIH). Peripheral hormones such as the insulin-like growth factors (IGfs) and the thyroid hormones (TH) can also regulate GH release. In non-mammalian vertebrates, a great variability of hypothalamic neuropeptides involved in GH stimulation seems to occur. This review underlines the important contribution of teleost models in the phylogenetic study of GH control.
Tracing the Origins of the Pituitary Adenylate-Cyclase Activating Polypeptide (PACAP)
Frontiers in Neuroscience, 2020
Pituitary adenylate cyclase activating polypeptide (PACAP) is a well-conserved neuropeptide characteristic of vertebrates. This pluripotent hypothalamic neuropeptide regulates neurotransmitter release, intestinal motility, metabolism, cell division/differentiation, and immunity. In vertebrates, PACAP has a specific receptor (PAC 1) but it can also activate the Vasoactive Intestinal Peptide receptors (VPAC 1 and VPAC 2). The evolution of the vertebrate PACAP ligand-receptor pair has been well-described. In contrast, the situation in invertebrates is much less clear. The PACAP ligand-receptor pair in invertebrates has mainly been studied using heterologous antibodies raised against mammalian peptides. A few partial PACAP cDNA clones sharing >87% aa identity with vertebrate PACAP have been isolated from a cnidarian, several protostomes and tunicates but no gene has been reported. Moreover, current evolutionary models of the peptide and receptors using molecular data from phylogenetically distinct invertebrate species (mostly nematodes and arthropods) suggests the PACAP ligand and receptors are exclusive to vertebrate genomes. A basal deuterostome, the cephalochordate amphioxus (Branchiostoma floridae), is the only invertebrate in which elements of a PACAP-like system exists but the peptides and receptor share relatively low sequence conservation with the vertebrate homolog system and are a hybrid with the vertebrate glucagon system. In this study, the evolution of the PACAP system is revisited taking advantage of the burgeoning sequence data (genome and transcriptomes) available for invertebrates to uncover clues about when it first appeared. The results suggest that elements of the PACAP system are absent from protozoans, non-bilaterians, and protostomes and they only emerged after the protostome-deuterostome divergence. PACAP and its receptors appeared in vertebrate genomes and they probably shared a common ancestral origin with the cephalochordate PACAP/GCG-like system which after the genome tetraploidization events that preceded the vertebrate radiation generated the PACAP ligand and receptor pair and also the other members of the Secretin family peptides and their receptors.
Molecular and Cellular Endocrinology, 2000
The purpose of this research was to isolate and characterize the gene encoding growth hormone-releasing hormone (GRF) and pituitary adenylate cyclase-activating polypeptide (PACAP) from the zebrafish. The gene is comprised of five exons with two distinct peptides encoded on separate exons, GRF on exon 4 and PACAP on exon 5. Our evidence indicates that the zebrafish genome contains a single copy of the GRF-PACAP gene. The tissue distribution pattern of the mRNA transcript shows expression in the brain, eye, gastrointestinal tract, ovary and testis; each transcript was sequenced and found to be identical to the gene. This is the first report of GRF-PACAP mRNA expression in the eye of a non-mammalian species. Evidence that a duplication of the PACAP gene gave rise to the vasoactive intestinal peptide (VIP) gene is supported by the high amino acid sequence identity between PACAP in zebrafish and VIP in other fish species.
Endocrinology, 1997
In mammals, GRF and pituitary adenylate cyclase-activating polypeptide (PACAP) are encoded in separate genes. We report here that in the salmon a 4.5-kilobase gene contains five exons that encode the biologically active part of the GRF-like peptide (amino acids 1-32) on exon 4 and PACAP on exon 5. Analysis of two fish messenger RNAs reveals that a long precursor containing GRF and PACAP and a short precursor containing only PACAP are both expressed in the brain of at least five species of salmon, whereas mice express only the long precursor encoded by the PACAP gene. Synthetic salmon PACAP-38 and salmon GRF-like peptide-45 both stimulated GH release from cultured salmon pituitary cells; PACAP stimulated a concentrationdependent release of GH at both 4 and 24 h of incubation, whereas GRF-like peptide did not. Alternative splicing, resulting in the short precursor in which GRF-32 is excised, may provide a means for differential control of GH secretion with higher production of the more potent PACAP. A duplication of the GRF-like/PACAP gene in evolution after the divergence of fish and tetrapods would explain separate genes and regulation for GRF and PACAP in mammals. (Endocrinology 138: 414-423, 1997)
Endocrinology, 2007
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 pep-tides (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 cAMPprotein 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. (Endocrinology 148: 2405-2416, 2007)