Application of recombinant DNA technologies to studies on chicken growth hormone

Chicken growth hormone: further characterization and ontogenic changes of an N-glycosylated isoform in the anterior pituitary gland

Glycosylation is one of the post-translational modifications that growth hormone (GH) can undergo. This has been reported for human, rat, mouse, pig, chicken and buffalo GH. The nature and significance of GH glycosylation remains to be elucidated. This present study further characterizes glycosylated chicken GH (G-cGH) and examines changes in the pituitary concentration of G-cGH during embryonic development and post hatching growth. G-cGH was purified from chicken pituitaries by affinity chromatography (Concanavalin A-Sepharose and monoclonal antibody bound to Sepharose). Immunoreactive G-cGH has a MW of 26 kDa or 29 kDa as determined by SDS-PAGE, respectively, under non-reducing and reducing conditions. Evidence that it is N-glycosylated comes from its susceptibility to peptide N-glycosidase F, and its resistance to O-glycosidase. Based on the ability of G-cGH to bind Concanavalin A or wheat germ agglutinin but not other lectins and its susceptibility to peptide N-glycosidase F, a hybrid or biantennary type glycopeptide (GlcNac2, Man) structure is proposed. Some G-cGH can be observed in the pituitary at most ages examined (from 15-day embryo to adult). Moreover, electron microscopy revealed the presence of both immuno-reactive GH and Concanavalin A-reactive sites in the same secretory granules in the somatotrope. There were marked changes in the level and relative proportion of G-cGH in the pituitary gland during development and growth, the proportion of G-cGH rising during late embryonic development (e.g., between 15 and 18 days of development) and with further increases between 9 weeks and 15 weeks old. G-cGH was able to bind to chicken liver membrane preparations with less affinity than non-glycosylated monomer; on the other hand, however, G-cGH stimulated cell proliferation on Nb2 lymphoma bioassay whereas the non-glycosylated monomer was uncapable to do it.

Testicular growth hormone (GH): GH expression in spermatogonia and primary spermatocytes

Growth hormone (GH) gene expression is not restricted to pituitary somatotrophs and has recently been demonstrated in a variety of extrapituitary sites in mammals and the domestic chicken. The possibility that GH gene expression occurs in the male reproductive system of chickens was therefore examined, since GH has established roles in male reproductive function and GH immunoreactivity is present in the chicken testis. Using RT-PCR and oligonucleotide primers for pituitary GH cDNA, GH mRNA was shown to be present in the testes and vas deferens of adult cockerels. Although testicular GH mRNA was of low abundance (not detectable by Northern blotting), a 690 bp fragment of the amplified testicular GH cDNA was cloned and had a nucleotide sequence 99.6% homologous with pituitary GH cDNA. GH mRNA was localized by in situ hybridization in spermatogonia and primary spermatocytes of the seminiferous tubules, but unlike testicular GH-immunoreactivity, GH mRNA was not present in secondary spermatocytes, spermatids or spermatozoa. The presence of Pit-1 mRNA in the male reproductive tract may indicate Pit-1 involvement in GH expression in these tissues. The presence of GH receptor mRNA in the testis and vas deferens also suggests they are target sites for GH action. These results demonstrate, for the first time, expression of the pituitary GH gene in the testis, in which GH mRNA was discretely localized in primary spermatocytes. The local expression of the GH gene in these cells suggests autocrine or paracrine actions of GH during spermatogenesis.

Characterization of a bioactive 15 kDa fragment produced by proteolytic cleavage of chicken growth hormone

There is evidence for a cleaved form of GH in the chicken pituitary gland. A 25 kDa band of immunoreactive-(ir-)GH, as well as the 22 kDa monomeric form and some oligomeric forms were observed when purified GH or fresh pituitary extract were subjected to SDS-PAGE under nonreducing conditions. Under reducing conditions, the 25 kDa ir-GH was no longer observed, being replaced by a 15 kDa band, consistent with reduction of the disulfide bridges of the cleaved form. The type of protease involved was investigated using exogenous proteases and monomeric cGH. Cleaved forms of chicken GH were generated by thrombin or collagenase. The site of cleavage was found in position Arg133-Gly134 as revealed by sequencing the fragments produced. The NH2-terminal sequence of 40 amino acid residues in the 15 kDa form was identical to that of the rcGH and analysis of the remaining 7 kDa fragment showed an exact identity with positions 134-140 of cGH structure. The thrombin cleaved GH and the 15 kDa form showed reduced activity (0.8% and 0.5% of GH, respectively) in a radioreceptor assay employing a chicken liver membrane preparation. However, this fragment had a clear bioactivity in an angiogenic bioassay and was capable to inhibit the activity of deiodinase type III in the chicken liver.

Production of a recombinant newt growth hormone and its application for the development of a radioimmunoassay

Complementary DNA (cDNA) encoding newt (Cynops pyrrhogaster) growth hormone (nGH) was cloned from a cDNA library constructed from mRNAs of newt pituitary glands and was expressed in Escherichia coli. Based on Northern blot analysis using the cDNA as a probe, the nGH mRNA was estimated to be 940 bases in length. The recombinant nGH (nGHr) had a molecular mass of 22 kDa as determined by SDS-PAGE and possessed considerable bioactivity as determined in a Xenopus cartilage assay. Using the nGHr, we produced a polyclonal antibody against nGHr. Western blot analysis of newt anterior pituitary gland homogenates revealed that this antiserum specifically detected a single 22-kDa band, and histological studies of newt pituitary gland sections showed that the cells that reacted immunologically by the anti-nGHr antiserum corresponded to those stained by an antiserum against rat GH. A radioimmunoassay (RIA) that is specific and sensitive for nGH was developed, employing the antiserum thus produced. The sensitivity of the RIA was 57 +/- 7 pg/100 microl assay buffer. Interassay and intraassay coefficients of variation were 1.22 and 2.70%, respectively. Serial dilutions of plasma and pituitary homogenate of C. pyrrhogaster yielded dose-response curves that were parallel to the standard curve. Plasma from hypophysectomized newts showed no cross-reactivity. Moreover, displacement curves obtained using pituitary homogenates of the sword-tailed newt (C. ensicauda) and the crested newt (Triturus carnifex) were also parallel to the standard curve. Mammalian and frog GHs and prolactins (PRLs), as well as newt PRL, showed no inhibition of binding, even at relatively high doses, in this RIA. The RIA was used to measure GH released from newt pituitaries in vitro. Enhancement of GH release by 10(-7) M thyrotropin-releasing hormone was observed in cultures of newt pituitaries.

Studies on the GH/SL gene family: cloning of African lungfish (Protopterus annectens) growth hormone and somatolactin and toad (Bufo marinus) growth hormone

The lungfishes (lobe-finned fish) occupy a unique position in vertebrate phylogeny, being regarded as the closest extant relatives to the tetrapods. The putative pituitary hormone somatolactin (SL) has hitherto been found only in teleost fishes, and the presence of this protein in tetrapods or lobe-finned fishes has not been ascertained. It was therefore of interest to determine the structure of SL in the African lungfish (Protopterus annectens), as this information would be useful for designing probes to facilitate the detection of SL genes in amphibians and other tetrapods. The structural relationships between SL, growth hormone (GH), and prolactin (PRL) strongly suggest that these proteins evolved from a common ancestor. To obtain a more complete picture of the evolution of these hormones in lungfish, African lungfish GH has been cloned and sequenced. The cDNA sequence of a toad (Bufo marinus) GH was determined to facilitate maximum parsimony analysis of GH sequences. Cladistic analysis confirmed that lungfish and amphibian GH sequences form a clade distinct from the GH sequences of ray-finned fishes. A distance matrix analysis of SL sequences indicated that lungfish SL had the lowest primary sequence identity with goldfish SL (47%) and the highest with flounder SL (66%). The detection of SL in a lungfish indicates that the gene duplication within the SL/GH/PRL family, which gave rise to SL, must have occurred in a common ancestor of the ray-finned fishes (Actinopterygii) and the lungfishes (Sarcopterygii) and tetrapods.

Baculovirus-mediated expression of chicken growth hormone

A full-length chicken growth hormone (cGH) cDNA was placed downstream from the Autograph californica nuclear polyhedron virus, AcNPV, polyhedron gene promoter and expressed in Sf9 insect cells. Secreted recombinant cGH levels averaged 2-10 micrograms/ml from day 5-10 postinfection. The recombinant cGH analyzed by SDS-PAGE gels and Western blotting consisted of a doublet with M(r) of 26.5 and 23.5 kDa. Analysis by 2-D electrophoresis of partially-purified recombinant cGH and purified native cGH revealed similar immunoreactive charge isoforms and M(r) variants. The recombinant hormone was biologically active in a homologous radioreceptor assay. The results show that cGH expressed in insect cells is biologically and immunologically active, and that a variety of isoforms are secreted which exhibit size and charge properties similar to those of pituitary-derived cGH.

Structure and function of bovine growth hormone. Bovine growth hormone as an experimental model for studies of protein-protein interactions

Growth hormone (GH) is a polipeptide that controls the differentiation, growth and metabolism of many cell types, and is secreted from the hypophysis of all vertebrate species tested so far. Despite the overlapping evolutionary, structural, immunological and biological properties, it is well-known that GHs from distinct mammalian species have significant species-specific characteristics. The main purpose of this review is to highlight bovine GH (bGH) structural features related to its species-specific properties. Novel interest in bGH is also aroused by the advent of biotechnological methods for production of recombinant proteins. In fact recombinant bGH will have a great importance in veterinary medicine research and as a 'high tech' drug that needs to be monitored in zootechnical productions.

Germline transmission of exogenous genes in chickens using helper-free ecotropic avian leukosis virus-based vectors

We have used vectors derived from avian leukosis viruses to transduce exogenous genes into early somatic stem cells of chicken embryos. The ecotropic helper cell line, Isolde, was used to generate stocks of NL-B vector carrying the Neo(r) selectable marker and the Escherichia coli lacZ gene. Microinjection of the NL-B vector directly beneath unincubated chicken embryo blastoderms resulted in infection of germline stem cells. One of the 16 male birds hatched (6.25%) from the injected embryos contained vector DNA sequences in its semen. Vector sequences were transmitted to G1 progeny at a frequency of 2.7%. Neo(r) and lacZ genes were transcribed in vitro in chicken embryo fibroblast cultures from transgenic embryos of the G2 progeny.

Ontogeny of pituitary and serum growth hormone in growing turkeys as measured by radioimmunoassay and radioreceptor assay

Some mammalian studies have revealed a wide discrepancy in pituitary and circulating growth hormone (GH) measurements determined by immunological and biological assay methods. Recent studies demonstrating that avian GH exists in numerous isoforms raise concerns that immunological measurement of GH may not accurately reflect the amount of biologically active hormone present. We sampled eight different male turkeys of a commercial strain weekly until 6 wk of age, and then biweekly until 20 wk. Total pituitary GH content and serum GH concentration were measured by avian GH RIA and radioreceptor assay (RRA). The highest mean serum GH concentration occurred at 3 wk, and the ontogeny of serum GH content from 1 to 8 wk was similar whether measured by RIA or RRA. Pituitary GH content was highest at 6 wk, but RIA and RRA estimates differed markedly throughout the study. Pituitary content of biologically active GH, as estimated by RRA, exceeded that of immunologically active GH from 2 to 10 wk, whereas the reverse was true at 14, 18, and 20 wk. We conclude that this avian GH RIA accurately measures bioactive circulating turkey GH, but that the pituitary of the young turkey may contain bioactive GH isoforms that have poor immunological activity in our RIA.

Giant catfish Pangasianodon gigas growth hormone-encoding cDNA: cloning and sequencing by one-sided polymerase chain reaction

cDNA clones encoding giant catfish (Pangasianodon gigas) growth hormone (GH) have been isolated using a polymerase chain reaction (PCR) strategy. Pairwise combinations of degenerate and general primers allowed for the amplification of regions both 3' and 5' to the point of entry into the message. The amplified PCR products were cloned and sequenced. The cDNA sequence was found to encode a polypeptide of 200 amino acids (aa), including a putative signal peptide of 22 aa. The 5' and 3' untranslated regions of the message are 58 and 515 nucleotides long, respectively. The giant catfish GH displays the highest aa sequence homology with the carp GH, with 80% of sequence identity. Moreover, giant catfish GH has structural features in common with both mammalian and avian GH polypeptides, and also contains the domains of conserved sequence found in other GH.

Liver-specific expression of a phosphoenolpyruvate carboxykinase-neo gene in genetically modified chickens

In order to investigate the potential of the avian liver for the expression of recombinant proteins in vivo, replication-competent retroviral vectors were used to introduce a recombinant rat phosphoenolpyruvate carboxykinase promoter-driven neomycin resistance gene (PEPCKneo) into early Line 11 Leghorn embryos. After hatching, these birds possessed apparently intact PEPCKneo sequences in most tissues examined, however, the neo protein was expressed preferentially in the liver (up to .45% of total cellular protein). Therefore, the tissue specificity of the PEPCK promoter from the rat was retained in the chicken, although hormone responsiveness was not observed. Retroviral vectors used to transmit the genes were more stable during passage in either fibroblast cells or in the animal if the inserted genes were oriented in the same (sense) direction as the viral genome. After Geneticin drug selection in cultured cells, PEPCKneo mRNA was the predominant recombinant species observed on Northern blots, whereas embryos expressed mostly the RNA species originating in the retroviral long terminal repeats. The results demonstrate the potential usefulness of liver-specific gene expression in chickens, as well as the transcriptional effects observed when a foreign promoter is introduced into the replication-competent vector.

Purification, partial characterization, and radioimmunoassay of prolactin and growth hormone from the Bennett's wallaby

Bennett's wallaby prolactin (wPRL) and growth hormone (wGH) were purified from an aqueous extract of pituitary glands. The extract from 202 glands (6.5 g wet wt) was processed by gel filtration on Sephadex G-100, gel filtration on Sephadex G-100 SF, and then anion-exchange chromatography on DEAE-Sepharose CL-6B. The yields of wPRL and wGH were 5.2 and 15.7 mg, respectively. Since recovery of wPRL from the anion exchange column was 10%, anion exchange was performed in the presence of 20% acetonitrile in a subsequent purification. Recovery from this column was markedly increased to 42%. The purified hormones each gave a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with a molecular weight under reducing conditions of 21,000 and 23,000 for GH and PRL, respectively. Each hormone was positively identified by its N-terminal amino acid sequence, which showed high sequence identity with the equivalent eutherian hormone. Semianalytical gel filtration of purified hormone was used to demonstrate that each hormone remained as a monomer in aqueous solution. Each purified hormone was tested in the heterologous PRL radioimmunoassay (RIA) which has been used in many earlier studies to measure marsupial PRL. Highly purified wPRL was less potent than ovine prolactin (5.3 compared with 1.5 ng/ml at 50% displacement) and the cross-reaction of wGH was < 0.01%. Antibodies were raised against wPRL and wGH and a homologous RIA was developed for each hormone. The sensitivity of the wPRL assay was 0.8 ng/ml which is similar to that of the heterologous PRL assay. Cross-reaction with a number of eutherian pituitary hormones or wGH was < 0.07%. The wGH assay detected 0.8 ng/ml which is similar to that of the heterologous PRL assay. Cross-reaction with a number of eutherian pituitary hormones or wGH was < 0.07%. The wGH assay detected 0.8 ng/ml, cross-reacted with GH from several eutherian species, and showed low cross-reaction with wPRL (< 0.5). In both the wPRL and wGH assays, pituitary homogenates from several species of marsupial diluted in parallel with the wallaby standard, suggesting that these assays will be of use in studies of a number of marsupial species.

The primary structures of growth hormones of three cyprinid species: bighead carp, silver carp, and grass carp

The primary structures of growth hormone (GH) of three cyprinid species, bighead carp, silver carp, and grass carp, were determined by a chemical method and/or by molecular cloning. The bighead carp GH was extracted from pituitary tissue by use of an alkaline medium, then successively purified by gel filtration, hydrophobic interaction column chromatography, and reverse-phase high-pressure liquid chromatography. The primary structure of bighead carp GH determined chemically is identical to that deduced from the cDNA nucleotide sequence. By molecular cloning, the primary structures of silver carp and grass carp GHs were also determined. The GHs of these three cyprinid species all contain 188 amino acid residues and their sequences are identical. When four of the five cysteines of cyprinid GHs were arranged to match the same positions of cysteines of other vertebrate GHs, a maximally matched alignment was achieved. Among fishes, GHs are relatively conserved within the same order (82 to 100% identity) but they are more diversified between orders (49 to 68% identity). In further comparison, fish GHs are even more different from tetrapod GHs (37 to 58% identity). Although the primary structures of vertebrate GHs are relatively variable, four homologous sequences, notably one located at the C-terminal, are found.

The complete amino acid sequence of growth hormone from sturgeon (Acipencer guldenstadti)

The complete amino acid sequence of growth hormone (GH) from a chondrostean species, the sturgeon (Acipencer gludenstaditi), has been determined. Two variants of GH, termed GH I and GH II, were isolated from the pituitary by alkaline extraction, gel filtration on a Sephadex G-100 column, and reversed-phase high-performance liquid chromatography (rpHPLC) on a TSK gel ODS-120T column. The purified proteins were confirmed to be GHs by immunoblotting using bovine and chum salmon GH antisera. For determining of the primary structures, these GHs were digested with lysyl endopeptidase and cleaved with cyanogen bromide. The resulting fragments were separated by rpHPLC and subjected to sequence analysis on an automated gas-phase sequencer employing an Edman method. Both GHs consist of 190 amino acid residues, and contain two disulfide linkages at positions 52-163 and 180-188. The GHs differ from each other at only three positions. Sequence comparison with GHs from other vertebrates revealed that sturgeon GHs have greater sequence homology with tetrapod GHs (63-76%) than with teleost GHs (42-63%).

Lipolytic and diabetogenic effects of native and biosynthetic growth hormone in the chicken: A re-evaluation

1. There is controversy as to whether growth hormone (GH) is lipolytic and/or diabetogenic in vivo in chickens. The ability of GH to influence circulating concentrations of free fatty acids was examined in anaesthetized (suppressing endogenous GH secretion) adult and young chickens using three preparations of GH. 2. Plasma concentrations of free fatty acids were increased following the intravenous injection of native bovine GH (50 micrograms/kg to either young or adult chickens), recombinant chicken GH (American Cyanamid) (50 micrograms/kg to adult chickens) and recombinant chicken GH (Amgen) (50 micrograms/kg to young chickens). 3. Similarly, infusion of recombinant chicken GH was accompanied by a gradual increase (P less than 0.05, 90 min following start of infusion) in plasma concentrations of free fatty acids in both anaesthetized hypophysectomized and sham operated young chickens. 4. These data support an acute lipolytic role for GH in the chicken. 5. The injection of neither bovine nor chicken GH had any consistent effect on circulating concentrations of glucose. Moreover, if GH was administered in the presence of glucose, GH had no effect on plasma concentrations of glucose. 6. Further evidence for a lack of a diabetogenic role for GH comes from the inability of chronic administration of GH to influence the decline in plasma concentrations of glucose following challenge with the insulin secretagogue, tolabutamide.

Avian retroviral expression of luciferase

Biologically active replication-competent (subgroups A, B, and C) and replication-defective Rous sarcoma virus-derived vectors containing the cDNA encoding firefly luciferase as a reporter gene were constructed. In these retroviral vectors, luciferase is expressed from a spliced subgenomic mRNA. A biologically active replication-defective UR2 virus-derived vector expressing the reporter gene as a gag-luciferase fusion protein from an unspliced genomic mRNA was also constructed. The luciferase reporter gene was used because it lacks homology with chicken genomic sequences and because a rapid and sensitive direct enzymatic assay is available to monitor luciferase expression in retrovirus-infected cells. The levels of luciferase expression in luciferase recombinant retrovirus-infected chicken embryo fibroblasts are greater than 10(3) higher than that detected in uninfected cells or in cells infected with retroviral vectors carrying other genes. Endpoint dilution titration experiments demonstrated that one infected cell can be detected in a background of 10(3) uninfected cells. The vectors are stable in tissue culture and high level expression of the unselected luciferase reporter gene is maintained. The vectors were used to express luciferase in chicken embryos, demonstrating the potential utility of luciferase as a reporter in vivo.

Purification and electrophoretic analysis of glycosylated chicken growth hormone (G-cGH): evidence of G-cGH isoforms

It has been shown that chicken growth hormone (cGH) exhibits functional and molecular heterogeneity. Mass and charge variants have been described in fresh pituitary extracts and in pure preparations of the hormone. In an attempt to further study the molecular heterogeneity of cGH we have purified the glycosylated variant of this hormone by affinity chromatography and analyzed it by different electrophoretic methods. Purification was achieved by homogeneizing chicken pituitaries in a protease inhibitor solution (0.5 mM PMSF and aprotinin, 50 KIU/ml); the supernatant of the alkaline extract (pH 9.5) was precipitated with 0.15 M ammonium sulfate and metaphosphoric acid, pH 4.0. The supernatant from this step was further precipitated with 80% ammonium sulfate, pH 6.5. After dialysis and lyophilization, the extract was chromatographed in a Con A-Sepharose column. The fraction eluted with 10 mM alpha-methylmannoside (which contained the glycoproteins) was passed through an immunoaffinity column (anticGH). Glycosylated cGH (G-cGH) was obtained pure after this step. Pure G-cGH was analyzed by nondenaturing electrophoresis (ND-PAGE), SDS-PAGE, isoelectrofocusing (IEF), and bidimensional electrophoresis (2D-PAGE) followed by Western blot and staining either with a specific antibody or with peroxidated Con A. Results showed that monomeric G-cGH has a MW of 29 kDa (under reducing conditions) and is heterogeneous, showing at least three important charge variants with pIs 6.5, 6.7, and 7.2. Mass variants of G-cGH were also detected under nonreducing conditions. Bidimensional analysis revealed that the charge variants had a similar MW (29 kDa).

Production of transgenic birds

The avian embryo presents a tremendous challenge for those interested in accessing and manipulating the avian germ line. By far the most successful method of gene transfer is by retrovirus vector. The efficacy of retrovirus vectors has been demonstrated by germ line insertion of replication-competent retroviruses as well as the insertion of replication-defective retrovirus vectors carrying bacterial marker genes. Retroviral vectors have also been shown to be useful for the transfer and expression of genes in somatic cells. Further, germ line transgenesis has been reported in both the chicken and the Japanese quail. In addition, several alternative gene transfer methods are under development. These include transfection of avian sperm, development of germ line chimeras using primordial germ cells and blastodermal cells, and the development of embryonic stem cell lines. Potentially, basic research and the poultry industry will derive substantial benefit from this revolutionary technology.

Growth hormone and insulin-like growth factors in poultry growth: required, optimal, or ineffective?

With a continually expanding market for poultry meat products, increased production demands of as much as 50% by the Year 2000 have been predicted. Indications already exist that this magnitude of expansion is not likely to be met by increased production output and genetic selection alone, and that other methods of improving growth performance per bird via exogenous manipulation of the growth process are needed. Studies in mammalian species clearly demonstrate the importance of growth hormone (GH) and its potential for enhancing productivity in domestic mammals. However, the role of GH in growth of poultry appears to be much more complex. Taken collectively, studies to date indicate that significant, positive effects of GH on growth performance of normal, growing poultry are possible. Expression of such effects appear to be largely contingent on the period of posthatch development (late posthatch being more responsive than early), and the pattern of several key metabolic regulatory hormones resulting in response to GH. Such regulatory hormone responses are largely influenced by the pattern or magnitude of exposure (acute versus chronic) to GH in birds. At this time, the available information on the potential for insulin-like growth factors to enhance growth is limited, and further studies are needed before a definitive role for these peptides in growth and development of poultry can be assigned.

The complete amino acid sequence of growth hormone of the bullfrog (Rana catesbeiana)

The primary structure of growth hormone (GH) isolated from the adenohypophysis of the bullfrogs (Rana catesbeiana) was determined. The hormone was reduced, carboxymethylated and subsequently cleaved with cyanogen bromide. Intact bullfrog GH was also digested with lysyl endopeptidase and trypsin. The resulting fragments were separated by reverse-phase high-performance liquid chromatography and subjected to sequence analysis using an automated gas-liquid sequencer employing the Edman method. Bullfrog GH was found to consist of 190 amino acid residues. The amino acid sequence determined is in accord with that deduced from bullfrog GH cDNA by Pan and Chang (1988) except for nine residues at positions 43-48, 73, 80 and 87. Sequence comparisons revealed that bullfrog GH is more similar to tetrapod GHs (e.g., 69% homology with sea turtle GH, 66% with chicken GH and 61% with ovine GH) than to GHs of teleosts (e.g., 35% homology with chum salmon GH and 33% with bonito GH) except for eel (52% identity). Bullfrog GH and prolactin exhibit a sequence homology of 25%.

Monoclonal antibody based sandwich enzyme-linked immunosorbent assay for chicken growth hormone

1. Monoclonal antibodies which bind to different epitopes of chicken growth hormone (cGH) were used to develop a homologous sandwich enzyme-linked immunosorbent assay (ELISA). 2. The first antibody, which is species specific, was immobilised on microtitre plates and concentrations of cGH in biological fluids were estimated by revealing bound hormone using a second, biotinylated monoclonal antibody. 3. The sensitivity was 0.024 ng/ml, which is at least ten-fold greater than current radioimmunoassays (RIA) and there was no cross-reactivity to other chicken pituitary hormones or to growth hormone from other species. 4. The accuracy and precision of the assay were similar to RIA, and the growth hormone concentrations measured in plasma samples by both RIA and this new ELISA showed a high degree of correlation. 5. The assay takes only 4 h using pre-coated plates which can be stored at 4 degrees C in sucrose. The advantages of being rapid and non-isotopic make this method attractive to both research and industrial laboratories.

Distribution and characterization of immunoreactive growth hormone (GH) in the pituitary of the frog Rana ridibunda using an antiserum against purified bullfrog GH

The presence of growth hormone (GH) in the pituitary of the frog Rana ridibunda was investigated using an antiserum raised against purified bullfrog GH. The immunofluorescence technique revealed that GH-containing cells are exclusively located in the dorsal area of the distal lobe of the pituitary. The relative abundance of these GH-positive cells, which correspond to acidophilic type 2 cells, was 18 +/- 1% of the total population of endocrine cells of the pars distalis. Frontal sections of the distal lobe indicated that GH-producing cells are distributed in an arc of a circle occupying all of the dorsal part of the lobe. At the electron microscopic level, GH-immunoreactive material was sequestered in large polymorphic granules (200-700 nm). GH was quantified in R. ridibunda pituitary extracts using a radioimmunoassay for bullfrog GH. The displacement curves obtained with serial dilutions of pars distalis extracts were not strictly parallel to the standard curve made with purified bullfrog GH. In contrast, Western blot analysis revealed that GH from R. ridibunda had a molecular weight (22 kDa) similar to that of bullfrog GH. In the pars distalis, the apparent amount of GH was 0.61 +/- 0.14 microgram per lobe, corresponding to 0.92 +/- 0.17% of total proteins in the extracts. In contrast, frog neurointermediate lobe or hypothalamus did not contain significant concentrations of immunoreactive GH (less than 0.006% of total proteins in the extracts). Taken together, these results validate the use of an antiserum to bullfrog GH to investigate the regulation of GH secretion in R. ridibunda.

Characterization and comparison of avian and murine helper cell lines for production of replication-defective retroviruses for avian transformation

Several approaches were taken to identify improved helper cell lines for the production of replication-defective avian retroviral vectors for avian transformation. Both QT6 and D17 cells were engineered to become helper cell lines for the production of reticuloendotheliosis virus vectors. The results showed that the majority of lines from the D17, QT6, and D17C3 cells produced titers in the 10(2) to 10(3) cfu/mL range, with one QT6 line producing 10(5) cfu/mL. This high producer line was relatively free of helper virus when restricted to low passage. An amphotropic murine cell line produced a 6- to 10-fold higher amount of virus and had a comparable higher titer on chicken cells, suggesting possible application to avian transformation.

Gene expression from heterologous promoters in a replication-defective avian retrovirus vector in quail cells

Avian retrovirus vectors, with potential for use in avian transformation, were constructed to evaluate the relative efficiency of promoters placed internal to the viral long terminal repeats (LTR). The vectors are replication-defective reticuloendotheliosis plasmids that contain the neomycin phosphotransferase gene under control of the 5' LTR and an internal promoter that directs expression of the chloramphenicol acetyltransferase gene. The internal promoters were the SV40 early, the mouse metallothionein I, and the human cytomegalovirus immediate early (HCMV-IE) promoters. Under transient conditions in QT6 cells, the HCMV-IE promoter construct was by far the strongest. However, expression dropped greatly from the HCMV-IE promoter after integration into the quail cell genome. Evidence suggests that the HCMV-IE promoter is selectively suppressed by methylation after stable transfection but not after infection.

Amino acid sequence of growth hormone isolated from medium of incubated pituitary glands of tilapia (Oreochromis mossambicus)

The amino acid sequence of tilapia (Oreochromis mossambicus) growth hormone (GH) was determined directly by Edman degradation of peptide fragments generated by lysyl endopeptidase and trypsin digestion. The N-terminal residue was deduced to be pyroglutamic acid through the use of pyroglutamyl aminopeptidase; its removal allowed amino acid sequence determination of the remainder of the N-terminal trypsin peptide by Edman degradation. Tilapia GH is composed of 187 amino acid residues and shows high similarity to other perciform GHs. Sequence identities are: 89% with tuna GH, 83% with bonito GH, 85% with yellowtail GH, 89% with red sea bream GH, and 34% with bovine GH. The two asparagine residues (Asn-148 and Asn-184) were recovered by Edman degradation, suggesting the absence of N-glycosylation.

The complete amino acid sequences of two variants of growth hormone from Atlantic cod (Gadus morhua)

The complete amino acid sequences of two variants of cod growth hormone (GH) have been determined. The GHs, which have apparent molecular weights of 20K and 22K in SDS-PAGE, consist of 185 amino acids and have calculated molecular weights of 20,733 and 20,805, respectively. Comparison of the two sequences showed only one amino acid difference between the variants, with Lys at position 151 in the 22K GH changed to Gly in the 20K GH. The substitution of a charged amino acid by one which contains no sidechain might be expected to be reflected in the isoelectric point of the molecule. However, the observed pI for both the 20K and 22K GHs was 5.8. The difference in apparent molecular weights by SDS-PAGE suggests the existence of a conformational difference between the variants which is attributable to the observed substitution. This conclusion is in agreement with our previous data obtained from radioimmunoassay studies where the 20K GH shows only 25% cross-reactivity in an assay developed for the 22K GH. Alignment of the cod GH sequence with those of other teleost GHs reveals cod GH to be most similar to advanced marine fish such as tuna, sea bream, bonito, and yellowtail (76-83% identity), whereas it is 62-66% identical to flounder and chum salmon GH.

Nucleotide sequence of the complementary DNA for turkey growth hormone

Near-full length complementary DNA (cDNA) clones encoding turkey growth hormone (GH) have been isolated from a pituitary library. The longer of the two turkey GH cDNA clones that were sequenced is 803 base pairs (bp) in length and contains 41 nucleotides of the 5'-untranslated region (UTR), an open reading frame of 648 bp that encodes a 25 amino acid leader polypeptide segment as well as a 191 amino acid mature turkey GH protein, and a 3'-UTR that is 92 bp long followed by a 22 bp poly A tract. Comparison of the turkey GH nucleotide sequence to that of other avian GH clones shows the coding region to be greater than 93% homologous while the homology to mammalian GH sequences is between 68 and 78%. Northern blot analysis showed an approximate 800 bp turkey GH processed mRNA transcript that hybridized to the turkey GH cDNA probe. A large up-regulation of turkey GH transcription occurred when intact cultured pituitaries were treated with 1 nM human growth hormone releasing hormone but only modest changes were observed when cultures were treated with thyroid releasing hormone or somatostatin.

The adenohypophysis of the Australian lungfish, Neoceratodus forsteri--an immunocytological study

The cell types in the adenohypophysis of Neoceratodus resemble closely those already described for Lepidosiren and Protopterus. Four of these were immunocytochemically identified as prolactin cells, gonadotropes, corticotropes, and melanotropes. Antiserum to bullfrog growth hormone could not distinguish between prolactin cells and somatotropes. Anti-bullfrog prolactin, however, did selectively stain the prolactin cells, which allowed the identification of the somatotropes. The presumptive thyrotropes, as the only remaining cell type in the pars distalis, can then be tentatively identified by default. Likewise a PAS-positive cell type in the pars intermedia had no immunoreactivity to any of the antisera used. The functional significance of this cell remains to be demonstrated. One of the more unexpected findings was the presence of large numbers of cells immunoreactive to alpha-MSH in the proximal pars distalis. The implications of the presence of these cells in adult lungfish are discussed. The distribution of cell types within the pituitary of Neoceratodus showed more regionalization than is present in the other lungfish and corresponded more closely to that described for primitive actinopterygian fish. The general structure of the pituitary of Neoceratodus also resembled primitive actinopterygian fish more closely than it did amphibians, unlike the pituitaries of Lepidosiren and Protopterus. The evolutionary significance of this is also discussed.

Nucleotide sequence of cDNA and primary structure for hard tail growth hormone

Full-length cDNA for hard tail growth hormone (htGH) has been cloned, and the nucleotide and deduced amino acid sequences have been analyzed. htGH is composed of 188 amino acid residues, and it shows 79, 74, 72, 59, 56, 37, 33 and 30% identity of amino acid with yellow tail, tuna, sea bream, flounder, salmon, blue shark, bullfrog and human GHs, respectively.

Half-life and metabolic clearance rate of recombinant-derived chicken growth hormone and purified turkey growth hormone in intact and hypophysectomized turkeys

The half-life and metabolic clearance rate (MCR) of natural turkey growth hormone (tGH) were compared with those of recombinant-derived chicken growth hormone (rcGH) in intact and hypophysectomized (hypox) turkey poults at 8 and 13 wk of age. The hypox poults used were all hypophysectomized at 8 wk of age. The purpose of the experiment was to determine whether the source of growth hormone (GH) or the physiological changes associated with hypophysectomy might affect the disappearance of the hormone from the circulation and, hence, alter the biological response of the bird to exogenous GH. The mean half-life of GH in the growing turkey was 12.88 +/- .54 (SE) min. The source of GH had no effect on half-life, and GH half-life did not vary significantly between poults sampled at 8 and 13 wk. Hypophysectomy significantly (P less than .01) increased the half-life of administered GH from 11.21 +/- .50 min in intact poults to 14.70 +/- .84 min in hypox poults. The MCR of GH in hypox poults 2 days following hypophysectomy was markedly lower than that of intact birds (1.08 versus 2.95 mL/min; P less than .001). The GH clearance in hypox birds increased during the 5 wk following hypophysectomy but still remained somewhat lower than that of intact birds (2.55 versus 3.00 mL/min; P = .06). The MCR of GH did not change in intact birds between 8 and 13 wk of age, and the MCR of rcGH and tGH did not differ.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular characterization of the Spirometra mansonoides genome: renaturation kinetics, methylation, and hybridization to human cDNA probes

High molecular weight DNA from pleroceroid larvae of the tapeworm Spirometra mansonoides was purified from isolated nuclei by conventional techniques. The DNA so isolated has a melting temperature (Tm) of 87 degrees C and a guanine plus cytosine (G/C) content of 44%. 5-Methyl cytosine could not be detected in plerocercoid DNA by HPLC analysis of DNA hydrolysates, by radiolabeling 5'-termini of MspI digests with polynucleotide kinase, or by comparing restriction patterns generated by MspI and HpaII. Renaturation kinetics demonstrated that the genome of S. mansonoides contains repetitive as well as single copy sequences and has a genome size estimated at approx. 1.6 X 10(9) bp. Hybridization was carried out between plerocercoid DNA and cDNAs for human beta-actin, alpha-tubulin and growth hormone (hGH). Rationale for this analysis was based on known homologies among actin and tubulin genes in numerous species and on apparent similarities between hGH and a plerocercoid growth factor that may be reflected in similar DNA sequence. Scanning densitometry of dot blots demonstrated that the hGH probe annealed to the same extent at low stringency (1 M NaCl, 55 degrees C) to DNA from plerocercoids, rat liver and chicken erythrocytes; but this interaction was less than to DNA from human lymphocytes, calf thymus and mouse skin. Similar results were obtained when restriction endonuclease digests of these DNAs were analyzed by Southern transfer. Little or no hybridization of the growth hormone probe to plerocercoid DNA was evident at higher stringency (1 M NaCl, 65 degrees C). In contrast, human tubulin and actin probes showed extensive hybridization to pleroceroid restriction fragments under the high stringency conditions.

Porcine growth hormone: molecular cloning of cDNA and expression in bacterial and mammalian cells

Porcine growth hormone (PGH) precursor cDNAs were cloned from a pituitary cDNA library constructed in lambda gt11 by immunoscreening. One of the three clones characterized contained an entire nucleotide sequence for the 216-amino-acid precursor molecule. The deduced amino-acid sequence of PGH confirmed the sequence previously reported for that of the genomic DNA of PGH except for one base difference in the coding sequence. Expression of the full-length PGH cDNA was achieved in bacteria and mammalian cells. The mammalian cell line, COS-1, produced the GH molecule which processed the signal peptide and had the same molecular weight as standard PGH, in contrast to the higher molecular weight of the bacterial product. Radioimmunoassay of the recombinant PGH produced in COS-1 cells also revealed an inhibition curve similar to that of the standard PGH.

Phosphorylation of chicken growth hormone

The possibility that chicken growth hormone (cGH) can be phosphorylated has been examined. Both native and biosynthetic cGH were phosphorylated by cAMP-dependent protein kinase (and gamma -32P-ATP). The extent of phosphorylation was however less than that observed with ovine prolactin. Under the conditions employed, glycosylated cGH was not phosphorylated. Chicken anterior pituitary cells in primary culture were incubated in the presence of 32P-phosphate. Radioactive phosphate was incorporated in vitro into the fraction immunoprecipitable with antisera against cGH. Incorporation was increased with cell number and time of incubation. The presence of GH releasing factor (GRF) increased the release of 32P-phosphate labelled immunoprecipitable GH into the incubation media but not content of immunoprecipitable GH in the cells. The molecular weight of the phosphorylated immunoreactive cGH in the cells corresponded to cGH dimer.

Chicken growth hormone: cDNA-synthesis and base sequence

1. Growth hormone (GH)-cDNA was synthesized from poly A(+)-mRNA extracts of chicken pituitary glands. 2. Chicken-cDNA library was cloned into E. coli. 3. Base sequence analysis of chicken GH-cDNA revealed only 70% similarity compared with duck GH-cDNA, and 97% similarity with a previously published chicken GH-cDNA sequence. 4. Dissimilarities in base sequences are primarily observed in the 3'-non-coding region of GH-cDNAs (chicken and duck). 5. Comparisons of amino acid sequences of chicken and duck GH exhibit only three substitutions, while the amino acid sequences of GHs of chicken are identical.

Replication-defective vectors of reticuloendotheliosis virus transduce exogenous genes into somatic stem cells of the unincubated chicken embryo

Replication-defective vectors derived from reticuloendotheliosis virus were used to transduce exogenous genes into early somatic stem cells of the chicken embryo. One of these vectors transduced and expressed the chicken growth hormone coding sequence. The helper cell line, C3, was used to generate stocks of vector containing about 10(4) transducing units per ml. Injection of 5- to 20-microliters volumes of vector directly beneath the blastoderm of unincubated chicken embryos led to infection of somatic stem cells. Infected embryos and adults contained unrearranged integrated proviral DNAs. Embryos expressed the transduced chicken growth hormone gene and contained high levels of serum growth hormone. Blood, brain, muscle, testis, and semen contained from individuals injected as embryos contained vector DNA. Replication-defective vectors of the reticuloendotheliosis virus transduced exogenous genes into chicken embryonic stem cells in vivo.

Carp growth hormone: molecular cloning and sequencing of cDNA

cDNA clones of the fish Cyprinus carpio growth hormone (GH) mRNA have been isolated from a cDNA library prepared from carp pituitary gland poly(A)+RNA. The nucleotide sequence of one of the carp GH cDNA clones containing an insert of 1164 nucleotides (nt) was determined. The cDNA sequence was found to encode a polypeptide of 210 amino acids (aa) including a signal peptide of 22 aa and to contain 5' and 3' untranslated regions of the mRNA of 36 and 498 nt, respectively. The carp GH presents a 63% amino acid sequence homology with the salmon GH, has structural features common with other GH polypeptides of mammalian or avian origin and contains domains of conserved sequence near the N- and C-terminal regions. Southern blot hybridization of carp genomic DNA with GH cDNA probes shows the presence of at least two GH-coding sequences in the fish genome.

The complete nucleotide sequence of the growth-hormone gene from Atlantic salmon (Salmo salar)

We report here the complete genomic nucleotide sequence for the Atlantic salmon growth-hormone gene (asGH), including 600 bp of 5' flanking sequences. The primary transcription (3651 nt) is significantly longer than that of the mammalian genes, mainly because of larger intron sizes, but also because the asGH gene contains an additional intron (intron 5). The coding regions of the asGH gene have been compared to the corresponding regions from rainbow trout (cDNA and genomic), coho salmon (cDNA) and chum salmon (cDNA). With the exception of the rainbow trout cDNA sequence, all results were in agreement with current classification of the four species. The results of a similar comparison with the mRNA leader and trailer regions were also consistent with current classification. Sequences upstream from the transcription start point have been compared to the corresponding regions from rainbow trout and mammalian GH gene (maGH) upstream sequences. The results showed that the upstream sequences in the two fish species were very similar, while short stretches similar to conserved upstream sequences in the maGH genes were also found. Some of these conserved sequences are known to be involved in the specificity of expression of the mammalian genes.

Purification and characterization of bullfrog growth hormone

A highly purified growth hormone (GH) was isolated from an unadsorbed fraction obtained by subjecting acid acetone extract of bullfrog pituitary glands to DEAE-cellulose column chromatography, a side fraction obtained during the purification of prolactin, by cation-exchange chromatography on CM-Toyopearl and high-performance liquid chromatography on ODS with a yield of 5.6 mg/g protein of the starting material. Intraperitoneal injections of GH to hypophysectomized Xenopus resulted in a considerable elevation of chondroitin sulfate synthesis in the xiphisternal cartilage as measured in vitro. The bullfrog GH had a molecular weight of 22,000 Da as determined by sodium dodecyl sulfate-gel electrophoresis. The isoelectric point of bullfrog GH was estimated to be 7.8 by gel electrofocusing. The partial amino acid sequences of bullfrog GH at both terminal regions were determined.

Avian retroviral vectors derived from avian defective leukemia virus: role of the translational context of the inserted gene on efficiency of the vectors

We have constructed retroviral vectors derived from the genome of avian erythroblastosis virus ES4 (AEV ES4). The neo selectable gene was substituted for the original v-erbA or v-erbB oncogenes of AEV, either in the same or in a different reading frames. Recombinant retrovirus were rescued and used to infect chicken embryo fibroblasts or quail QT6 cells. When the neo gene was inserted in the same reading frame as the original oncogene, we obtained (1) a high level of expression of the neo gene, (2) a balanced ration of both genomic and subgenomic RNAs, and (3) high titer recombinant viruses. Conversely, when the neo gene was inserted in a reading frame different from that of the original oncogene, we observed (1) a very low level of expression of the neo protein, (2) a predominance of the viral transcript used as translational template for the neo protein synthesis, and (3) low titer recombinant viruses. One of the vectors was used to transfer a human delta-globin gene into avian cells in culture without detectable rearrangement of this gene, but exhibited a deletion within the conserved noncoding region located between the two original oncogenes. Our data provide information for further construction of double expression vectors. Furthermore, three of the vectors would provide helpful tools to identify genetic elements of the virus genome involved in splicing regulation.