Partial biochemical and biological characterization of purified chicken growth hormone (cGH). Isolation of cGH charge variants and evidence that cGH is phosphorylated

Internalization and synaptogenic effect of GH in retinal ganglion cells (RGCs)

In the chicken embryo, GH gene expression occurs in the neural retina and retinal GH promotes cell survival and induces axonal growth of retinal ganglion cells. Neuroretinal GH is therefore of functional importance before the appearance of somatotrophs and the onset of pituitary GH secretion to the peripheral plasma (at ED15-17). Endocrine actions of pituitary GH in the development and function of the chicken embryo eye are, however, unknown. This possibility has therefore been investigated in ED15 embryos and using the quail neuroretinal derived cell line (QNR/D). During this research, we studied for the first time, the coexistence of exogenous (endocrine) and local GH (autocrine/paracrine) in retinal ganglion cells (RGCs). In ovo systemic injections of Cy3-labeled GH demonstrated that GH in the embryo bloodstream was translocated into the neural retina and internalized into RGC's. Pituitary GH may therefore be functionally involved in retinal development during late embryogenesis. Cy3-labelled GH was similarly internalized into QNR/D cells after its addition into incubation media. The uptake of exogenous GH was by a receptor-mediated mechanism and maximal after 30-60min. The exogenous (endocrine) GH induced STAT5 phosphorylation and increased growth associated protein 43 (GAP43) and SNAP-25 immunoreactivity. Ex ovo intravitreal injections of Cy3-GH in ED12 embryos resulted in GH internalization and STAT5 activation. Interestingly, the CY3-labeled GH accumulated in perinuclear regions of the QNR/D cells, but was not found in the cytoplasm of neurite outgrowths, in which endogenous retinal GH is located. This suggests that exogenous (endocrine) and local (autocrine/paracrine) GH are both involved in retinal function in late embryogenesis but they co-exist in separate intracellular compartments within retinal ganglion cells.

Characterization of pituitary growth hormone and its receptor in the green iguana (Iguana iguana)

Pituitary growth hormone (GH) has been studied in most vertebrate groups; however, only a few studies have been carried out in reptiles. Little is known about pituitary hormones in the order Squamata, to which the green iguana (gi) belongs. In this work, we characterized the hypophysis of Iguana iguana morphologically. The somatotrophs (round cells of 7.6-10 μm containing 250- to 300-nm secretory granules where the giGH is stored) were found, by immunohistochemistry and in situ hybridization, exclusively in the caudal lobe of the pars distalis, whereas the lactotrophs were distributed only in the rostral lobe. A pituitary giGH-like protein was obtained by immuno-affinity chromatography employing a heterologous antibody against chicken GH. giGH showed molecular heterogeneity (22, 44, and 88 kDa by SDS-PAGE/Western blot under non-reducing conditions and at least four charge variants (pIs 6.2, 6.5, 6.9, 7.4) by isoelectric focusing. The pituitary giGH cDNA (1016 bp), amplified by PCR and RACE, encodes a pre-hormone of 218 aa, of which 190 aa correspond to the mature protein and 28 aa to the signal peptide. The giGH receptor cDNA was also partially sequenced. Phylogenetic analyses of the amino acid sequences of giGH and giGHR homologs in vertebrates suggest a parallel evolution and functional relationship between the GH and its receptor.

Expression and function of chicken bursal growth hormone (GH)

Growth hormone (GH) has several effects on the immune system. Our group has shown that GH is produced in the chicken bursa of Fabricius (BF) where it may act as an autocrine/paracrine modulator that participates in B-cell differentiation and maturation. The time course of GH mRNA and protein expression in the BF suggests that GH may be involved in development and involution of the BF, since GH is known to be present mainly in B lymphocytes and epithelial cells. In addition, as GH is anti-apoptotic in other tissues, we assessed the possibility that GH promotes cell survival in the BF. This work focused on determining the mechanism by which GH can inhibit apoptosis of B cells and if the PI3K/Akt pathway is activated. Bursal cell cultures were treated with a range of GH concentrations (0.1-100nM). The addition of 10nM GH significantly increased viability (16.7±0.6%) compared with the control and decreased caspase-3 activity to 40.6±6.5% of the control. Together, these data indicate that GH is produced locally in the BF and that the presence of exogenous GH in B cell cultures has antiapoptotic effects and increases B cell survival, probably through the PI3k/Akt pathway.

Expression, cellular distribution, and heterogeneity of growth hormone in the chicken cerebellum during development

Although growth hormone (GH) is mainly synthesized and secreted by pituitary somatotrophs, it is now well established that the GH gene can be expressed in many extrapituitary tissues, including the central nervous system (CNS). Here we studied the expression of GH in the chicken cerebellum. Cerebellar GH expression was analyzed by in situ hybridization and cDNA sequencing, as well as by immunohistochemistry and confocal microscopy. GH heterogeneity was studied by Western blotting. We demonstrated that the GH gene was expressed in the chicken cerebellum and that its nucleotide sequence is closely homologous to pituitary GH cDNA. Within the cerebellum, GH mRNA is mainly expressed in Purkinje cells and in cells of the granular layer. GH-immunoreactivity (IR) is also widespread in the cerebellum and is similarly most abundant in the Purkinje and granular cells as identified by specific neuronal markers and histochemical techniques. The GH concentration in the cerebellum is age-related and higher in adult birds than in embryos and juveniles. Cerebellar GH-IR, as determined by Western blot under reducing conditions, is associated with several size variants (of 15, 23, 26, 29, 35, 45, 50, 55, 80 kDa), of which the 15 kDa isoform predominates (>30% among all developmental stages). GH receptor (GHR) mRNA and protein are also present in the cerebellum and are similarly mainly present in Purkinje and granular cells. Together, these data suggest that GH and GHR are locally expressed within the cerebellum and that this hormone may act as a local autocrine/paracrine factor during development of this neural tissue.

Growth hormone expression in stromal and non-stromal cells in the bursa of Fabricius during bursal development and involution: Causal relationships?

Growth hormone (GH) is expressed in the chicken bursa of Fabricius (BF), an organ that undergoes three distinct developmental stages: rapid growth (late embryogenesis until 6-8 weeks of age [w]), plateaued growth (between 10 and 15w), and involution (after 18-20w). The distribution and abundance of GH-immunoreactivity (GH-IR) and GH mRNA expression in stromal and non-stromal bursal cells during development, as well as the potential anti-apoptotic effect of GH in bursal cell survival were the focus of this study. GH mRNA expression was mainly in the epithelial layer and in epithelial buds at embryonic day (ED) 15; at 2w it was widely distributed within the follicle and in the interfollicular epithelium (IFE); at 10w it clearly diminished in the epithelium; whereas at 20w it occurred in only a few cortical cells and in the connective tissue. Parallel changes in the relative proportion of GH mRNA expression (12, 21, 13, 1%) and GH-IR (19, 18, 11, <3%) were observed at ED 15, 2w, 10w, and 20w, respectively. During embryogenesis, GH-IR co-localized considerably with IgM-IR, but scarcely with IgG-IR, whereas the opposite was observed after hatching. Significant differences in bursal cell death occurred during development, with 9.3% of cells being apoptotic at ED 15, 0.4% at 2w, 0.23% at 10w, and 21.1% at 20w. Addition of GH increased cultured cell survival by a mechanism that involved suppression (up to 41%) of caspase-3 activity. Results suggest that autocrine/paracrine actions of bursal GH are involved in the differentiation and proliferation of B lymphocytes and in BF growth and cell survival in embryonic and neonatal chicks, whereas diminished GH expression in adults may result in bursal involution.

Expression and localization of growth hormone and its receptors in the chicken ovary during sexual maturation

Roles of pituitary growth hormone (GH) in female reproduction are well established. Autocrine and/or paracrine actions of GH in the mammalian ovary have additionally been proposed, although whether the ovary is an extra-pituitary site of GH expression in the laying hen is uncertain. This possibility has therefore been assessed in the ovaries of Hy-Line hens before (between 10-16 weeks of age) and after (week 17) the onset of egg laying. Reverse transcription/polymerase chain reaction (RT-PCR) analysis has consistently detected a full-length (690 bp) pituitary GH cDNA in ovarian stroma from 10 weeks of age, although GH expression is far lower than that in the pituitary gland or hypothalamus. GH mRNA is also present in small (>1-4 mm diameter) follicles after their ontogenetic appearance at 14 weeks of age and in all other developing follicles after 16 weeks of age (>4-30 mm diameter). Immunoreactivity for GH is similarly present in the ovarian stroma from 10 weeks of age and in small (<4 mm diameter) and large (>4-30 mm) follicles from 14 and 16 weeks of age, respectively. The relative intensity of GH staining in the ovarian follicles is consistently greater in the granulosa cells than in the thecal cells and is comparable with that in the follicular epithelium. A 321-bp fragment of GH receptor (GHR) cDNA, coding for the intracellular domain of the receptor, has also been detected by RT-PCR in the ovary and is present in stromal tissue by 10 weeks of age, in small follicles (<4 mm diameter) by 14 weeks of age, and in larger follicles (>4-30 mm diameter) from 16 weeks. GHR immunoreactivity has similarly been detected, like GH, in the developing ovary and in all follicles and is more intense in granulosa cells than in the theca interna or externa. The expression and location of the GH gene therefore parallels that of the GHR gene during ovarian development in the laying hen, as does the appearance of GH and GHR immunoreactivity. These results support the possibility that GH has autocrine and/or paracrine actions in ovarian function prior to and after the onset of lay in hens.

Enhanced Yield and Homogeneity of Buffalo Growth Hormone by an Improved Chromatographic Protocol

Loss of buffalo Growth Hormone (buGH) in the various side fractions of standard buGH purification protocol has been determined quantitatively by direct binding ELISA and qualitatively by SDS-PAGE and Western blot analysis. Accounting result indicated that there was a considerable loss of buGH in the side fractions. An alternative protocol to prevent loss and to obtain a high yield of buGH has been developed by introducing anion exchange chromatography, QAE-Sephadex. This has resulted in a simple, reproducible three-step protocol. In this protocol, an extract obtained at 250 mM (NH4)2 SO4, pH 5.5, was loaded onto the QAE-Sephadex column in 0.1 M NH4 HCO3. At this salt concentration, the bulk of the buGH came as QAE unbound fraction. Some amount of buGH, together with contaminating proteins, was bound to QAE-Sephadex and these could be eluted with 1 M KCl. The immunopotency of the enriched buGH preparation "QUB" (QAE unbound fraction) in a direct binding ELISA was similar to that of the semi-pure buGH (ECS/APECS) preparation obtained using the standard protocol, but the yield was 4 times higher. The SDS-PAGE data showed that the banding pattern of standard semi-pure buGH and QUB were quite similar and QUB can be loaded onto the Sephacryl S-200 gel filtration chromatography to yield a highly purified buGH. SDS-PAGE and Western blot analyses showed the major band of buGH in QUB at the same position as in the case of standard buGH. It has also been demonstrated here that it is possible to separate buffalo prolactin (buPRL) and buGH on QAE-Sephadex.

Heterogeneity of growth hormone immunoreactivity in lymphoid tissues and changes during ontogeny in domestic fowl

Growth hormone (GH) expression is not confined to the pituitary and occurs in many extrapituitary tissues. Here, we describe the presence of GH-like moieties in chicken lymphoid tissues and particularly in the bursa of Fabricius. GH-immunoreactivity (GH-IR), determined by ELISA, was found in thymus, spleen, and in bursa of young chickens, but at concentrations <1% of those in the pituitary gland. Although the GH concentration in the spleen and bursa was approximately 0.82 and 0.23% of that in the pituitary at 9-weeks of age, because of their greater mass, the total GH content in the spleen, bursa, and in thymus were 236, 5.18, and 31.5%, respectively, of that in the pituitary gland. This GH-IR was associated with several proteins of different molecular size, as in the pituitary gland, when analyzed by SDS-PAGE under reducing conditions. While most of the GH-IR in the pituitary was associated with the 26 kDa monomer (40%), the putatively glycosylated 29 kDa variant (16%), the 52 kDa dimer (14%) and the 15 kDa submonomeric isoform (16%), GH-IR in the lymphoid tissues was primarily associated (27-36%) with a 17 kDa moiety, although bands of 14, 26, 29, 32, 37, 40, and 52 kDa were also identified in these tissues. The heterogeneity pattern and relative abundance of bursal GH-IR bands were determined during development between embryonic day 13 (ED13) and 9-weeks of age. The relative proportion of the 17 kDa GH-like band was higher (45-58%) in posthatched birds than in the 15 and 18-day old embryos (21 and 19%, respectively). The 26 kDa isoform was minimally present in embryos (<4% of total GH-IR) but in posthatched chicks it increased to 12-20%. Conversely, while GH-IR of 37, 40, and 45 kDa were abundantly present in embryonic bursa ( approximately 30% at ED13 and approximately 52-55% at ED15 and ED18, respectively), in neonatal chicks and juveniles they accounted for less than 5%. These ontogenic changes were comparable to those previously reported for similar GH-IR proteins in the chicken testis during development. In summary, these results demonstrate age-related and tissue-specific changes in the content and composition of GH in immune tissues of the chicken, in which GH is likely to be an autocrine or paracrine regulator.

Growth hormone in the male reproductive tract of the chicken: heterogeneity and changes during ontogeny and maturation

Growth hormone (GH) gene expression is not confined to pituitary somatotrophs and occurs in many extrapituitary tissues. In this study, we describe the presence of GH moieties in the chicken testis. GH-immunoreactivity (GH-IR), determined by ELISA, was found in the testis of immature and mature chickens, but at concentrations <1% of those in the pituitary gland. The immunoassayable GH concentration in the testis was unchanged between 4 and 66 weeks of age, and approximately 10-fold higher than that at 1-week of age and 25-fold higher than that in 1-day-old chicks and perinatal (embryonic day 18) embryos. This immunoreactivity was associated with several proteins of different molecular size, as in the pituitary gland, when analyzed by SDS-PAGE under reducing conditions. However, while most of the GH-IR in the pituitary ( approximately 40 and 15%, respectively) is associated with monomer (26 kDa) or dimer (52 kDa) GH moieties GH-IR in the testis is primarily (30-50%) associated with a 17 kDa moiety. GH bands between 32 and 45 kDa are also relatively more abundant in the testis than in the pituitary. During ontogeny the relative abundance of a 14 kDa GH and 40 kDa GH moieties in the testis significantly declined, whereas the relative abundance of the 17 and 45 kDa moieties increased with advancing age. In adult birds, GH-IR was widespread and intense in the seminiferous tubules. Although the GH-IR was not present in the basal compartment of Sertoli cells, nor in spermatogonia and primary spermatocytes, it was abundantly present in secondary spermatocytes and spermatids in the luminal compartments of the tubules as well as in some surrounding myocytes and interstitial cells. In summary, immunoreactive GH moieties are present in the chicken testis but at concentrations far less than in the pituitary. Age-related changes in the relative abundance of testicular GH variants may be related to local (autocrine/paracrine) actions of testicular GH. The localization of GH in spermatocytes and spermatids suggests hitherto unsuspected roles in gamete development.

Differential secretion of chicken growth hormone variants after growth hormone-releasing hormone stimulation in vitro

Variants of growth hormone (GH) are present in most vertebrates. Chicken GH (cGH) undergoes posttranslational modifications that contribute to its structural diversity. Although the 22-kDa form of GH is the most abundant, some other variants have discrete bioactivities that may not be shared by others. The proportion of cGH variants changes during ontogeny, suggesting that they are regulated differentially. The effect of growth hormone-releasing hormone (GHRH) on the release of cGH variants was studied in both pituitary gland and primary cell cultures, employing sodium dodecyl sulfate polyacrylamide gel electrophoresis, Western blotting, and densitometry. GHRH (2 nM, 2 h) stimulated the secretion of most of the size variants of cGH although the amplitude of increase was not equal for each one. A differential effect on the secretion of GH size variants, particularly on the 22- (monomer) and 26-kDa (putatively glycosylated) cGH isoforms was found in both systems. In the whole pituitary culture, the proportion of the 26-kDa immunoreactive cGH increased 35% while the 22 kDa decreased 31% after GHRH treatment in comparison with the controls. In the primary cell culture system, the proportion of the glycosylated variant increased 43% whereas the monomer and the dimer decreased 22.26 and 29%, respectively, after GHRH stimulation. Activators of intracellular signals such as 1 mM 8-bromo-cAMP and 1 microM phorbol myristate acetate had a similar effect to that obtained with GHRH. The data support the hypothesis that GH variants may be under differential control and that GHRH promotes the release of a glycosylated cGH variant that has an extended half-life in circulation.

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.

Growth hormone size variants: changes in the pituitary during development of the chicken

There is considerable evidence for the existence of structural variants of growth hormone (GH). The chicken is a useful model for investigating GH heterogeneity as both size and charge immunoreactive-(ir) variants have been observed in the pituitary and plasma. The present study examined the size distribution of ir-GH in the pituitary gland of chicken, from late embryogenesis through adulthood. Pituitaries were homogenized in the presence of protease inhibitor, and the GH size variants were separated by SDS-PAGE, transferred by Western blotting, immunostained with a specific antiserum to chicken GH, and quantitated by chemiluminescence followed by laser densitometry (chemiluminescent assay). Under nonreducing conditions ir-GH bands of 15, 22, 25, 44, 50, 66, 80, 98, 105 and >110 kDa were observed. Both the relative proportion of the GH size variants and the total pituitary content varied with developmental stage and age. The proportion of the 15-kDa fragment was greatest in the embryonic stage, and then it decreased. The proportion of the monomeric 22-kDa form was lowest at 18 days of embryogenesis (dE) and highest at 20 dE. In contrast, the high MW forms (>/=66 kDa) were lowest in embryos, and they increased (P < 0.05) after hatching. The 22-, 44-, 66-, and 80-kDa forms were assayed for activity by radioreceptor assay following isolation by semipreparative SDS-PAGE. Only the 22-kDa GH variant showed radioreceptor activity. Under reducing conditions for SDS-PAGE, ir-GH bands of 13, 15, 18, 23, 26, 36, 39, 44, 48, 59 and 72 kDa were oberved, but most of the high MW form disappeared. There was a concomitant increase in the proportion of the monomeric band and of several submonomeric forms. The present data indicate that the expression, processing, and/or release of some if not all size variants are under some differential control during growth and development of the chicken.

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.

Angiogenic activity of anterior pituitary tissue and growth hormone on the chick embryo chorio-allantoic membrane: a novel action of GH

A useful system to evaluate the angiogenic activity of hormones and growth factors is the chorioallantoic membrane (CAM) of chick embryos. The present studies examined the angiogenic activity of chicken anterior pituitary glands and both fibroblast growth factor (FGF) and growth hormone (GH). Grafts of anterior pituitary gland evoked an angiogenic response on the CAM which was lost if the adenohypophyseal tissue was first boiled. The magnitude of the angiogenic response to anterior pituitary glands increased with the age of the donor (from a minimum 15 days of embryonic development to a maximum between 2 and 6 weeks old). In view of the similarity of the profile of the angiogenic response and the reported changes in GH secretion, the angiogenic activity of GH was then examined. Considerable angiogenic responses were observed with GH; there being increases (P < 0.05) in number of new blood vessels on the CAM of chick embryos on which native chicken GH or native bovine GH or recombinant bovine GH were added. These data support GH having an angiogenic action.

Identification of growth hormone molecular variants in chicken serum

It has been described that pituitary growth hormone shows molecular and functional heterogeneity. In birds, size and charge variants of chicken growth hormone (cGH) have been shown in the chicken pituitary gland and in purified preparations of the hormone. Here we demonstrate the existence of cGH molecular isoforms in chicken serum, thus suggesting that they are secreted from the gland. The isolation of total cGH present in sera was performed by immunoaffinity chromatography employing a specific monoclonal antibody against cGH. Different analytical electrophoretic methods (SDS-polyacrylamide gel electrophoresis, isoelectric focusing, bidimensional polyacrylamide gel electrophoresis) followed by Western blot and immunostaining were employed to characterize the serum cGH isoforms, and compared to those present in a fresh pituitary extract. Several identical immunoreactive bands comigrated in both serum and the gland extract in the different systems (SDS-PAGE, MW 16, 22, 26, 29, 52, 62, 66 kDa; IEF, pIs 8.1, 7.5, 7.1, 6.8, 6.2), thus revealing a high correspondence of molecular isoforms of the hormone in the two tissues. Additionally, a glycosylated variant of chicken growth hormone (G-cGH) was also revealed in the serum after concanavalin A-Sepharose chromatography.

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).

Immunoaffinity purification and partial characterization of sea bass (Dicentrarchus labrax) growth hormone

Growth hormone (GH) was isolated from sea bass (Dicentrarchus labrax) pituitary extract by a simple one-step procedure involving immunoaffinity chromatography. A monoclonal antibody raised against chicken GH and found to immunostain very specifically the GH cells in the pituitary of the sea bass was coupled to CNBr-activated Sepharose 4B. Sea bass pituitary extracts were run on the affinity column, and the eluted material was analyzed on reversed-phase HPLC and found to consist of one single peak. The yield of purified hormone was 2.4 mg/g pituitary. Two monomeric forms (MW = 20,000 and 22,000 Da) of sea bass GH were identified by gel electrophoresis. Gel electrofocusing revealed apparent isoelectric points of 6.15, 6.50, and 6.95. Amino acid composition is consistent with other vertebrate GHs. The immunological relatedness was tested by immunoblotting using antisera raised against GH of different species. Polyclonal antisera raised against the isolated hormone exhibited a specific labeling of the GH cells in sea bass pituitary sections as well as of the immunoblotted purified GH.

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.

Molecular isoforms of chicken growth hormone (cGH): different bioactivities of cGH charge variants

It has been suggested that the functional diversity of growth hormone (GH) is related to its molecular complexity. Here we report a characterization of charge and mass variants of chicken growth hormone (cGH) through a variety of electrophoretic systems [nondenaturing (ND-PAGE), denaturing (SDS-PAGE), under reducing and nonreducing conditions, isoelectrofocusing (IEF), and bidimensional electrophoresis] followed by Western blot and immunostaining with a specific antibody directed against pure cGH. We also report the biological properties of two charge variants on two homologous assays. The studies were carried out with purified cGH and with fresh chicken pituitary extracts. Three charge variants were obtained by ND-PAGE (Rf = 0.23, 0.30, and 0.35), which showed the same molecular weight (26 kDa), while in IEF eight isoforms were observed, the most conspicuous being those with pI = 6.86, 7.5, 7.9, 8.05, and 8.18. In SDS-PAGE under reducing conditions four immunoreactive bands were observed: the monomer (26 kDa), a dimer (52 kDa), a fragment (16 kDa), and a minor band at 22 kDa. Higher MW variants were found under nonreducing conditions. Bidimensional analysis also showed several charge variants for the monomer and the dimer. Bioactivity of two charge variants (0.23 and 0.3) was evaluated with a lipolytic and an antilipolytic assay on chicken adipose tissue explants. It was shown that variant 0.23 was mainly lipolytic, in a dose-dependent response, but lacked antilipolytic effect. On the other hand, variant 0.30 did not show lipolytic effect but presented a clear antilipolytic activity.

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.