Sequence of the growth hormone (GH) gene from the silver carp (Hypophthalmichthys molitrix) and evolution of GH genes in vertebrates

Isolation and Characterization of the Arapaima gigas Growth Hormone (ag-GH) cDNA and Three-Dimensional Modeling of This Hormone in Comparison with the Human Hormone (hGH)

In a previous work, the common gonadotrophic hormone α-subunit (ag-GTHα), the ag-FSH β- and ag-LH β-subunit cDNAs, were isolated and characterized by our research group from A. gigas pituitaries, while a preliminary synthesis of ag-FSH was also carried out in human embryonic kidney 293 (HEK293) cells. In the present work, the cDNA sequence encoding the ag-growth hormone (ag-GH) has also been isolated from the same giant Arapaimidae Amazonian fish. The ag-GH consists of 208 amino acids with a putative 23 amino acid signal peptide and a 185 amino acid mature peptide. The highest identity, based on the amino acid sequences, was found with the Elopiformes (82.0%), followed by Anguilliformes (79.7%) and Acipenseriformes (74.5%). The identity with the corresponding human GH (hGH) amino acid sequence is remarkable (44.8%), and the two disulfide bonds present in both sequences were perfectly conserved. Three-dimensional (3D) models of ag-GH, in comparison with hGH, were generated using the threading modeling method followed by molecular dynamics. Our simulations suggest that the two proteins have similar structural properties without major conformational changes under the simulated conditions, even though they are separated from each other by a >100 Myr evolutionary period (1 Myr = 1 million years). The sequence found will be used for the biotechnological synthesis of ag-GH while the ag-GH cDNA obtained will be utilized for preliminary Gene Therapy studies.

Polymorphisms of the growth hormone gene and their association with growth traits and sex in Sarcocheilichthys sinensis

The growth hormone gene (gh) of Sarcocheilichthys sinensis was cloned and characterized in this study. The cDNA length of gh was 973 bp, containing a 5'-UTR of 15 bp, a 3'-UTR of 325 bp and an open reading frame of 633 bp. The genomic DNA of gh was 2135 bp in length containing five exons and four introns. The precursor peptide of gh contained 210 amino acids (aa), including a signal peptide of 22 aa (Met¹-Ala²²) and a mature region of 188 aa (Ser²³-Leu²¹⁰). The similarity and identity ranges of the gh precursor peptide with those of other cyprinids were 88.6%-99.0% and 84.8%-98.6%, respectively. The gh of S. sinensis expressed at the highest level in the pituitary, and its expression was also detected in muscle and brain. Six polymorphic sites were detected in intron 1 (g.51InDel, g.64InDel and g.242InDel), intron 2 (g.864T>C), intron 3 (g.1017InDel) and intron 4 (g.1541A>G). Among these sites, g.242InDel was significantly associated with condition factor, g.1541A>G was associated with all six growth traits, while g.864T>C was associated with sex. The data obtained herein provide useful information for further studies on the regulation mechanisms of growth and sexual growth differences in S. sinensis.

Growth hormone from striped catfish (Pangasianodon hypophthalmus): genomic organization, recombinant expression and biological activity

Growth hormone is an essential polypeptide required for normal growth and development of vertebrates. In this report, striped catfish (Pangasianodon hypophthalmus) growth hormone gene and cDNA were isolated by reverse transcriptase-polymerase chain reaction. The striped catfish growth hormone (scGH) encoding gene contains 5 exons and 4 introns. The cDNA sequence of the scGH gene contains a 603bp open reading frame and encodes for a 200-aa protein consisting of a putative 22-aa signal peptide and the mature 178-aa protein. The recombinant histidine-tagged scGH protein which expressed in Escherichia coli as inclusion bodies was unfolded, refolded and purified to near-homogeneity by Ni(2+)-NTA chromatography. Analysis of the secondary structure content by CD spectroscopy showed that the α-helical content of the refolded scGH is 55%. Elucidation of the folding pathway of scGH by fluorescence spectroscopy showed that denaturation transition of scGH is coincident and cooperative, consistent with the two-state denaturation mechanism. The purified scGH was biologically active and exhibited growth-promoting activity in striped catfish, but not tilapia.

Nibea coibor growth hormone gene: its phylogenetic significance, microsatellite variation and expression analysis

The growth hormone (GH) gene has been characterized for a number of fishes and used to establish phylogenetic relationships and as a candidate gene for studies of genetic variation in connection with growth traits. In this study, we report the genomic structure of Nibea coibor GH (designated as ncGH) including its 5'-flanking region, being cloned by homology-cloning and chromosome walking methods. The ncGH gene spans approximately 3.0 kb and consists of six exons and five introns, as found for all cloned teleost GH genes with the exception of carps and catfish. The 5'-flanking region contains consensus sequences for a TATA box, a CRE, a pit-1alpha, a TRE, two HNF-3, a ERE and a GRE. Five microsatellites are identified in the ncGH gene and three of them are polymorphic marker. The open reading frame (ORF) of ncGH is 615 bp in length encoding a polypeptide of 204 amino acids with an estimated molecular mass of 23.04 kDa and theoretical isoelectric point of 7.79. The precursor of ncGH consists of a 17 amino-acid signal peptide and a 187 amino-acid mature peptide. The four Cys residues are located at conserved positions (Cys(69), Cys(177), Cys(194) and Cys(202)), and One possible site for N-glycosylation (Asn-X-Ser/Thr motif) is present at Asn(201). The coding region sequence of ncGH is used to align with the sequences of 18 other species from Percoidei and one species from Anabantoidei using Clustal X. A matrix of 612 bp was used to construct the phylogenetic trees using neighbor-joining and maximum parsimony methods. The phylogenetic trees by two methods are identical in most of the clades with high bootstrap support. Every family all forms independent monophyly on the phylogenetic trees, in the family, the different species also forms the monophyly according to the different genera. The results are also identical to those from morphological data, and demonstrated that the GH gene is very suitable for phylogenetic relationship analysis of Percoidei. To validate the predicted exon/intron boundaries, ncGH cDNA is cloned using RT-PCR, and tissue distributions are investigated using semi-quantitative RT-PCR method. The results indicate that the predicted exon/intron is correct, the ncGH mRNA are mainly expressed in pituitary, and weakly expressed in ovary, brain, liver, gill, intestine, muscle and hear, but not expressed in spleen and kidney.

Gene structure and functional characterization of growth hormone in dogfish, Squalus acanthias

Dogfish (Squalus acanthias) growth hormone (GH) was identified by cDNA cloning and protein purification from the pituitary gland. Dogfish GH cDNA encoded a prehormone of 210 amino acids (aa). Sequence analysis of purified GH revealed that the prehormone is composed of a signal peptide of 27 aa and a mature protein of 183 aa. Dogfish GH showed 94% sequence identity with blue shark GH, and also showed 37-66%, 26%, and 48-67% sequence identity with GH from osteichtyes, an agnathan, and tetrapods. The site of production was identified through immunocytochemistry to be cells of the proximal pars distalis of the pituitary gland. Dogfish GH stimulates both insulin-like growth factor-I and II mRNA levels in dogfish liver in vitro. The dogfish GH gene consisted of five exons and four introns, the same as in lamprey, teleosts such as cypriniforms and siluriforms, and tetrapods. The 5'-flanking region within 1082 bp of the transcription start site contained consensus sequences for the TATA box, Pit-1/GHF-1, CRE, TRE, and ERE. These results show that the endocrine mechanism for growth stimulation by the GH-IGF axis was established at an early stage of vertebrate evolution, and that the 5-exon-type gene organization might reflect the structure of the ancestral gene for the GH gene family.

The growth hormone-encoding gene isolated and characterized from Labeo rohita Hamilton is expressed in CHO cells under the control of constitutive promoters in 'autotransgene' constructs

The growth hormone (GH) gene along with its regulatory sequences has been isolated from the blood and pituitary gland of Labeo rohita. This GH gene is approximately 2.8 kb long and consists of five exons and four introns of varying sizes with AG/TA in its exon-intron junctions. The promoter has a single cyclic AMP response unit (CRE) element, TATA, CAT and several Pit 1 binding sequences. The 1169-bp gene transcript starts 54 bp upstream of the ATG initiation codon and has two polyadenylation signals, ATTAAA, after the TAG stop codon. The mature mRNA has the poly (A) tail inserted 16 bp downstream of the second polyadenylation signal. Four chimeric 'autotransgenes' were constructed having either histone 3 or beta-actin promoter and cDNA or the total GH gene. The functionality of the individual components of the autotransgene was determined in the Chinese hamster ovary (CHO) cells by transfection experiments. Based on the results, the transcription of the GH gene is initiated at the transcription start signal of the respective promoters and terminates at the 3' regulatory sequence of the GH gene. Expression of GH in CHO cells shows that the fish promoters are active, the splicing signal is recognized, and the mRNA produced is stable and translated. The GH protein produced is effectively translocated and secreted into the medium. These results indicate the usefulness of CHO cells in determining the property of individual components of autotransgenes constructed from L. rohita and overall functional commonality between fish and mammal.

Neuroendocrine control of growth hormone in fish

The biological actions of growth hormone (GH) are pleiotropic, including growth promotion, energy mobilization, gonadal development, appetite, and social behavior. Accordingly, the regulatory network for GH is complex and includes many endocrine and environmental factors. In fish, the neuroendocrine control of GH is multifactorial with multiple inhibitors and stimulators of pituitary GH secretion. In fish, GH release is under a tonic negative control exerted mainly by somatostatin. Sex steroid hormones and nutritional status influence the level of brain expression and effectiveness of some of these GH neuroendocrine regulatory factors, suggesting that their relative importance differs under different physiological conditions. At the pituitary level, some, if not all, somatotropes can respond to multiple regulators. Therefore, ligand- and function-specificity, as well as the integrative responses to multiple signals must be achieved at the level of signal transduction mechanisms. Results from investigations on a limited number of stimulatory and inhibitory GH-release regulators indicate that activation of different but convergent intracellular pathways and the utilization of specific intracellular Ca(2+) stores are some of the strategies utilized. However, more work remains to be done in order to better understand the integrative mechanisms of signal transduction at the somatotrope level and the relevance of various GH regulators in different physiological circumstances.

Genomic structure of the sea lamprey growth hormone-encoding gene

Growth hormone (GH) belongs to a family of pituitary hormones together with prolactin and somatolactin. In our previous study, GH and its cDNA were identified in the pituitary gland of the sea lamprey, Petromyzon marinus, an extant representative of the most ancient class of vertebrates, and isolated GH stimulated expression of insulin-like growth factor in the liver. The evidence suggests that GH is the ancestral hormone in the molecular evolution of the GH/PRL/SL family and that the endocrine mechanism for growth stimulation was established at an early stage in the evolution of vertebrates. To further understand the molecular evolution of the GH/PRL/SL gene family, we report the genomic structure of sea lamprey GH including its 5'-flanking region, being cloned by PCR using specific primers prepared from its cDNA. The sea lamprey GH gene consists of 13,604 bp, making it the largest of all the GH genes. The 5'-flanking region within 697 bp contains consensus sequences for a TATA box, two Pit-1/GHF-1, three TRE, and a CRE. The sea lamprey GH gene consists of five exons and four introns, the same as in mammals, birds, and teleosts such as cypriniforms and siluriforms with the exception of some teleosts such as salmoniforms, percififorms, and tetradontiforms, in which there is an additional intron in the 5th exon. The 5-exon-type gene organization might reflect the structure of the ancestral gene for the GH/PRL/SL gene family.

The dawn and evolution of hormones in the adenohypophysis

The adenohypophysial hormones have been believed to have evolved from several ancestral genes by duplication followed by evolutionary divergence. To understand the origin and evolution of the endocrine systems in vertebrates, we have characterized adenohypophysial hormones in an agnathan, the sea lamprey Petromyzon marinus. In gnathostomes, adrenocorticotropin (ACTH) and melanotropin (MSH) together with beta-endorphins (beta-END) are encoded in a single gene, designated as proopiomelanocortin (POMC), however in sea lamprey, ACTH and MSH are encoded in two distinct genes, proopoicortin (POC) gene and proopiomelanotropin (POM) gene, respectively. The POC and POM genes are expressed specifically in the rostral pars distalis (RPD) and the pars intermedia (PI), respectively. Consequently, the final products from both tissues are the same in all vertebrates, i.e., ACTH from the PD and MSH from the PI. The POMC gene might have been established in the early stages of invertebrate evolution by internal gene duplication of the MSH domains. The ancestral gene might be then inherited in lobe-finned fish and tetrapods, while internal duplication and deletion of MSH domains as well as duplication of whole POMC gene took place in lamprey and gnathostome fish. Sea lamprey growth hormone (GH) is expressed in the cells of the dorsal half of the proximal pars distalis (PPD) and stimulates the expression of an insulin-like growth factor (IGF) gene in the liver as in other vertebrates. Its gene consists of 5 exons and 4 introns spanning 13.6 kb, which is the largest gene among known GH genes. GH appears to be the only member of the GH family in the sea lamprey, which suggests that GH is the ancestral hormone of the GH family that originated first in the molecular evolution of the GH family in vertebrates and later, probably during the early evolution of gnathostomes. The other member of the gene family, PRL and SL, appeared by gene duplication. A beta-chain cDNA belonging to the gonadotropin (GTH) and thyrotropin (TSH) family was cloned. It is expressed in cells of the ventral half of PPD. Since the expression of this gene is stimulated by lamprey gonadotropin-releasing hormone, it was assigned to be a GTHbeta. This GTHbeta is far removed from beta-subunits of LH, FSH, and TSH in an unrooted tree derived from phylogenetic analysis, and takes a position as an out group, suggesting that lampreys have a single GTH gene, which duplicated after the agnathans and prior to the evolution of gnathostomes to give rise to LH and FSH.

Seasonal modulation of growth hormone mRNA and protein levels in carp pituitary: evidence for two expressed genes

Adaptation of eurythermal fish to naturally varying environmental conditions involves modulation of expressions of various factors in the hypothalamo-hypophyseal axis. Here we used three complementary approaches to assess the seasonal variation of growth hormone (GH) protein and mRNA levels in pituitary glands of acclimatized carp fish. First, a polyclonal antibody raised against an oligopeptide derived from the carp GH sequence was used for immunohistochemistry; second, oligonucleotides specific for GH transcripts were used for in situ hybridization. Specific immunodetection of GH coincides with visualization of GH mRNA in the proximal pars distalis, the specific location of somatotroph cells in carp pituitary gland. Finally, competitive RT-PCR analyses confirmed that GH expression exhibits seasonal cyclical reprogramming with higher levels in summer- than in winter-adapted fish. The expression pattern suggests an important role for GH in the molecular mechanisms underlying the acclimatization process. In parallel, amplification of sequences from the fourth intron and adjacent sites from exons IV and V demonstrates the existence of a new GH gene previously undescribed. The detection of transcripts corresponding to each gene suggests that both GH gene copies are active in the duplicated carp genome and that they are similarly affected by seasonal adaptation.

Isolation and characterization of two distinct growth hormone cDNAs from the tetraploid smallmouth buffalofish (Ictiobus bubalus)

The growth hormone (GH) gene has been characterized for a number of fishes and used to establish phylogenetic relationships and population structures. Analysis of tetraploid fishes, such as salmon and some Asian cyprinids, has shown the presence of two GH genes. Fishes in the sucker family (Catostomidae, Cypriniformes) are also tetraploid, and the present study reports the isolation and characterization of two GH cDNAs from a representative species, the smallmouth buffalofish (Ictiobus bubalus). The GH cDNAs of smallmouth buffalofish are 1272 and 1273nt in length, and each codes for a polypeptide of 210 amino acids, predicted to be cleaved to a final product of 188 aa. The GH cDNAs of smallmouth buffalofish are 6% divergent in nt sequence in the coding region, and there are 16 differences in predicted aa sequence. Because the cDNAs have distinct sequences in coding regions and in UTRs, which differed by more than 10%, they were identified as GHI and GHII. The predicted GHI protein contains 4 Cys residues, homologous to other vertebrate GH sequences. On the other hand, GHII has 5 Cys residues, homologous to other ostariophysan sequences. GHI and GHII are most similar to other cypriniform fishes for both nt and protein sequences. Phylogenetically, the sequences of smallmouth buffalofish GH consistently grouped with Asian cyprinids, but not loaches, consistent with morphological evidence suggesting that suckers are most closely related to minnows.

Recombinant goldfish growth hormones (gfGH-I and -II) expressed in Escherichia coli have similar biological activities

Complementary DNA regions coding for two different mature goldfish growth hormones (gfGH-I and gfGH-II) with four and five cysteine residues were cloned into the bacterial expression vector, pRSETA. The recombinant gfGH-I (five cysteines) and -II (four cysteines) were produced in Escherichia coli as the fusion proteins carrying N-terminal 6XHis tag, which facilitates purification by using metal chelating affinity chromatography under denaturing condition with urea. The recombinant hormones were further refolded by gradually removing the urea. Native gfGH was also purified from goldfish pituitary glands and served as a positive control in the present study. The native and recombinant hormones were tested in goldfish hepatic radioreceptor assay and in vitro Spi 2.1 promoter activation assay. Our results showed that the two recombinant gfGHs are biologically active, and they have similar biological activities despite their having different cysteine contents.

Genomic structure and sequence of the gilthead seabream (Sparus aurata) growth hormone-encoding gene: identification of minisatellite polymorphism in intron I

The growth hormone (GH) gene of the gilthead seabream (Sparus aurata) (saGH) has been cloned, sequenced, and characterized. The saGH gene spans approximately 4.3 kb and consists of six exons and five introns, as found for all cloned teleost GH genes with the exception of carps and catfish. The first and third introns contain long stretches of repetitive tandem repeats. The second intron, which is unusually long compared with that in other teleosts (and other vertebrates) spans 1747 nucleotides (nt) and contains several inverted repeats. Intron-targeted polymerase chain reaction (PCR) analysis identified length polymorphism of the first intron. Sequence analysis of four variants (405, 424, 636, and 720 nt) out of many variants found revealed that the variation in length is due to differences in the number of repeat monomers (17-mer or 15-mer) as well as minor changes in their length. This repeat unit contains the consensus half-site motif of the thyroid hormone response element (TRE) and estrogen response element (ERE). Polymorphism was found also in the third intron. This is the first report of such high polymorphism of the first intron of GH gene in a vertebrate.

Structure and functional analysis of a tilapia (Oreochromis mossambicus) growth hormone gene: activation and repression by pituitary transcription factor Pit-1

A gene encoding the Tilapia mossambica (Oreochromis mossambicus) growth hormone (tiGH) was isolated and sequenced. The gene spans 5.6 kb, including 3.7 kb of 5' and 0.2 kb of 3' flanking sequences and a 1.7-kb transcription unit comprised of six exons and five introns. The gene and the 5' flanking region contain several potential binding sites for Pit-1, a key transcription activator of mammalian GH genes. One of these (-57/-42) is highly conserved in fish GH genes. It activates transcription in pituitary cells and binds Pit-1. Transfection of luciferase reporter plasmids containing either the -3602/+19 tiGH sequence or one of its 5' deletion mutants (-2863/, -1292/, and -463/+19) resulted in strong activity in Pit-1-producing rat pituitary GC cells. A dose-dependent activation of the tiGH promoter was achieved in nonpituitary fish EPC and monkey COS cells cotransfected with a rat Pit-1 expression vector, demonstrating the crucial role played by Pit-1 as an activator of the tiGH gene. Fusion of the tiGH promoter with the beta-galactosidase gene led to transient expression specifically in the nervous system of microinjected zebrafish embryos. The activity of the tiGH promoter in GC and EPC cells was strongly repressed by extending its 3' end from +19 to +40, a sequence in which a Pit-1-binding site was identified using gel retardation assays. Point mutations of the site that suppressed Pit-1 binding in vitro restored full tiGH promoter activity. Thus, a Pit-1-binding site located in the 5' untranslated region mediates Pit-1-dependent repression of the tiGH gene.

Characterization of rainbow trout (Oncorhynchus mykiss) growth hormone 1 gene and the promoter region of growth hormone 2 gene

Studies by Agellon et al. (Mol. Reprod. Dev. 1, 11-17) showed the presence of two growth hormone (rtGH1 and rtGH2) mRNA species in pituitary glands of adult rainbow trout (Oncorhynchus mykiss). In this study, we have detected rtGH1 and rtGH2 mRNAs in pituitary glands of rainbow trout from fry to 2 years of age. The level of rtGH1 mRNA is notably higher than that of rtGH2 mRNA in 10-day-old fry and 2-year-old females. These results suggest differential expression of rtGH1 and rtGH2 genes in different sexes and developmental stages. As a step toward elucidating the mechanism of differential expression of both GH genes, DNA fragments encoding rtGH1 gene and the promoter/regulatory region of rtGH2 gene were isolated and characterized. Rainbow trout GH genes span approximately 4.5 kb and are composed of six exons and five introns. The 5'-flanking region of both genes contain consensus sequences for TATA boxes and several Pit-1 binding sequences. Consensus sequences related to the cAMP response element, thyroid hormone response element, retinoic acid response element, estrogen response element (ERE), and glucocorticoid response element are present not only in the 5'-flanking region, but also in introns and exons in rtGH1 gene. These hormone response elements, except ERE, are also present in rtGH2 gene.

Genomic structure and sequence of the pufferfish (Fugu rubripes) growth hormone-encoding gene: a comparative analysis of teleost growth hormone genes

A nested polymerase chain reaction (PCR) technique for amplifying a fragment of the gene (GH) encoding teleost growth hormone has been developed. Using this technique, a fragment of the pufferfish, Fugu rubripes and Arothron maculatus, dwarf gourami, Colisa lalia; guppy, Poecilia reticulata; and goldfish, Carassius auratus GH genes were cloned. The Fugu rubripes (Fugu) gene fragment was used to isolate the GH gene from a Fugu genomic library. The complete nucleotide sequence of a 8.5-kb SacI genomic fragment containing the Fugu GH gene has been determined. The GH gene spans 2.5 kb from the first codon to polyadenylation signal, and contains six exons and five introns similar to the GH genes of salmonids, tilapia, barramundi, flounder and yellowtail. The GH introns contain microsatellite and satellite sequences. The microsatellites found in the fifth intron of the GH gene are also present in the corresponding introns of tilapia, barramundi and flounder GH genes. Southern analysis revealed that the GH gene is a single-copy gene in the Fugu. The promoter region of the Fugu GH gene contains conserved sequences that are likely to be involved in the pituitary-specific expression of the gene. A phylogenetic tree of nucleotide (nt) sequences of all known teleost GH genes has been inferred using the distance matrix method. The topology of this tree reflects the major phylogenetic groupings of teleosts. The intron patterns and repetitive sequences of GH genes can serve as useful natural markers for the classification and phylogenetic studies of teleosts.

Sequence of the flounder (Paralichthys olivaceus) growth hormone-encoding gene and its promoter region

The flounder (Paralichthys olivaceus) growth hormone (GH)-encoding gene (fGH) and its promoter region were cloned and sequenced following amplification of genomic DNA by the polymerase chain reaction. The fGH gene is 2.1-kb long and consists of six exons and five introns. In the 5'-flanking region of the determined transcription start point, a potential TATA box is located at -24, and Pit-1/GHF-1-binding site candidates are located in the -70 to -53 and -133 to -141 regions.

Cloning of the barramundi growth hormone-encoding gene: a comparative analysis of higher and lower vertebrate GH genes

In this work the growth hormone-encoding gene (GH) from the fish barramundi (Lates calcarifer) was characterized by nucleotide (nt) sequence analysis and comparative studies on higher and lower vertebrate GH were performed. The barramundi GH contains six exons and five introns. A putative transcription start point 21 nt downstream from a potential TATAAA box was determined, with a modified primary transcript size of 1615 nt predicted. cis-Acting elements potentially important for transcriptional regulation at the basal, hormone-responsive and pituitary gland-specific levels were identified. Several microsatellite and minisatellite repetitive sequences were shown to be present within noncoding portions of this gene. Repeat sequences similar to the deca- and undeca-minisatellites of the barramundi GH were observed in the corresponding introns of the tilapia, but not other teleost GH. Comparative studies on the Osteichthyes, Mammalia and Aves vertebrate class GH promoters suggested that the TATAAA box was the only conserved region between these sequences. Conserved sequences, however, were identified within the GH promoters of different species from the Osteichthyes or Mammalia classes. The Osteichthyes A + T-rich sequence (consensus GATRMATYWAAWCA, where R = A or G; M = A or C, Y = C or T and W = A or T) is the only conserved region identified between teleost GH promoters, and is most likely involved in the pituitary gland-specific expression of these genes.