Growth Hormone Synthesis Research Articles

Calcium and other signalling pathways in neuroendocrine regulation of somatotroph functions

Relative to mammals, the neuroendocrine control of pituitary growth hormone (GH) secretion and synthesis in teleost fish involves numerous stimulatory and inhibitory regulators, many of which are delivered to the somatotrophs via direct innervation. Among teleosts, how multifactorial regulation of somatotroph functions are mediated at the level of post-receptor signalling is best characterized in goldfish. Supplemented with recent findings, this review focuses on the known intracellular signal transduction mechanisms mediating the ligand- and function-specific actions in multifactorial control of GH release and synthesis, as well as basal GH secretion, in goldfish somatotrophs. These include membrane voltage-sensitive ion channels, Na+/H+ antiport, Ca2+ signalling, multiple pharmacologically distinct intracellular Ca2+ stores, cAMP/PKA, PKC, nitric oxide, cGMP, MEK/ERK and PI3K. Signalling pathways mediating the major neuroendocrine regulators of mammalian somatotrophs, as well as those in other major teleost study model systems are also briefly highlighted. Interestingly, unlike mammals, spontaneous action potential firings are not observed in goldfish somatotrophs in culture. Furthermore, three goldfish brain somatostatin forms directly affect pituitary GH secretion via ligand-specific actions on membrane ion channels and intracellular Ca2+ levels, as well as exert isoform-specific action on basal and stimulated GH mRNA expression, suggesting the importance of somatostatins other than somatostatin-14.

Spotlight on Tesamorelin in HIV-Associated Lipodystrophy†

Tesamorelin (Egrifta™) is a synthetic analog of human growth hormone-releasing hormone (also known as growth hormone-releasing factor) that stimulates the synthesis and release of endogenous growth hormone. It is the first and, so far, only treatment indicated for the reduction of excess abdominal fat in patients with HIV-associated lipodystrophy. This article reviews the pharmacological properties, clinical efficacy and tolerability of tesamorelin in patients with HIV-associated central fat accumulation. Subcutaneous tesamorelin was effective in reducing visceral adipose tissue (VAT), but did not affect subcutaneous adipose tissue to a clinically significant extent in two 26-week, well designed, clinical trials in patients with HIV-associated central fat accumulation. This reduction in VAT was maintained in the longer term in patients who continued to receive tesamorelin until week 52 in the extension phases of the two trials. However, discontinuation of therapy during this period resulted in the reaccumulation of VAT. Tesamorelin therapy was also associated with significant improvements in other body composition measures (e.g. trunk fat and waist circumference) and improvements were generally seen in some body image parameters (e.g. belly image distress). Tesamorelin was generally well tolerated, with treatment-emergent serious adverse events occurring in <4% of patients during 26 weeks of therapy. Most of these events were injection-site reactions or events known to be associated with growth hormone therapy (e.g. arthralgia, headache and peripheral edema). Although long-term clinical experience is needed to further assess the benefits and risks of therapy, current evidence suggests that tesamorelin may be useful for reducing visceral adiposity in patients with HIV-associated lipodystrophy, thereby potentially improving self image.

Long-Term In Vivo Studies in Mice Unexpectedly Reveal That Prolonged Growth Hormone (GH) and Insulin/Insulin-Like Growth Factor-1 (IGF-1) Signaling Have a Negative Effect on Normal Bone Marrow Hematopoiesis – Implications for GH-Based “rejuvenation” Therapies,

Abstract 3422 Background:Growth hormone (GH) has been proposed as a rejuvenation factor that delays aging in older patients. The long-term results of such therapy, however, have recently become controversial. It is known that GH action is mediated by release of insulin-like growth factor-1 (IGF-1, also known as somatomedin C) from the liver. IGF-1 is an important factor affecting proliferation of several types of cells, including malignant hematopoietic blasts. A role for the GH-IGF-1 axis in normal hematopoiesis still remains controversial and some stimulatory effects to the clonogenicity of normal hematopoiteic stem/progenitor cells (HSPCs) have been described. We have previously reported that IGF-1 does not directly stimulate proliferation of normal clonogenic hematopoietic progenitors (J Clin Invest. 1994;94:320); however, it may promote erythroid differentiation and hemoglobinization of erythroblasts (Leukemia 1998;12:371). Aim of the study: Since long-term studies on the effect of GH-IGF-1 signaling on normal hematopoiesis in vivo have not been performed yet, we investigated the influence of these factors on the hematopoietic system in appropriate mouse models that express low or high levels of plasma GH and IGF-1. Experimental approach: We employed two mutant mouse strains that have low circulating plasma levels of IGF-1 due to a GH-receptor mutation (Laron dwarf mice) or to a defect in GH synthesis in the pituitary gland (Ames dwarf mice). We also employed transgenic mice that express the bovine GH gene (bGH), which results in a constitutively high level of circulating plasma IGF-1. In some experiments, normal wild type or Laron and Ames dwarf mice, with low circulating plasma IGF-1 levels, were injected for a prolonged period of time with recombinant GH or IGF-1. All these animals were analyzed by FACS for the presence of Sca-1+Lin–CD45+ HSPCs in bone marrow (BM) and the clonogenic growth of progenitors from all hematopoietic lineages monitored in standard methylcellulose (CFU-GM and BFU-E) and plasma clot (CFU-Meg) cultures. We also analyzed changes in peripheral blood count by Hemavet. The mice employed in our studies were at different ages (2 months, 6 months, and 2 years), and both female and male mice were analyzed. Results: We observed that Laron and Ames dwarf mice, with low circulating plasma levels of IGF-1, at the age of 1–2 years had ∼3–5 times more Sca-1+Lin–CD45+ in the BM than normal control littermates of the same age. Similarly, these mice also had ∼3–5 times more CFU-GM, BFU-E, and CFU-Meg in BM. The number of Sca-1+Lin–CD45+ cells and clonogenic progenitors from all lineages declined ∼5 fold in these animals (at 2 months and 8 months of age) after 4 weeks of treatment by daily injection of GH or IGF-1. However, interestingly, if this treatment was ceased the number of these cells showed over time a tendency to normalize. In another set of experiments, we evaluated the number of HSPCs in BM of 6-month- and 1-year-old mice that express the bovine GH transgene. We found that these mice have an ∼6-fold and ∼12-fold lower number in the BM of Sca-1+Lin–CD45+ and clonogenic progenitors, respectively, than control transgenic littermates expressing empty vector. Overall, a decrease in the number of HSPCs was accompanied by microcytic anemia. Conclusions: Our data, obtained from several in vivo animal models, show that prolonged exposure to GH-IGF-1 signaling depletes the number of HSPCs in the BM over time. This observation is highly relevant to GH rejuvenation therapies currently employed in humans. Our data indicate that this may lead to the premature depletion of HSPCs, and we also envision that prolonged stimulation of HSPCs by GH-IGF-1 may result in development of leukemias. In support of this notion, Laron dwarf mice and Laron dwarf patients do not develop hematological malignancies, while leukemias are often seen in bGH transgenic mice and in acromegalic patients. Disclosures:No relevant conflicts of interest to declare.

Transgenic mice expressing the human growth hormone gene provide a model system to study human growth hormone synthesis and secretion in non-tumor-derived pituitary cells: Differential effects of dexamethasone and thyroid hormone

Growth hormone (GH) is regulated by pituitary and hypothalamic factors as well as peripheral endocrine factors including glucocorticoids and thyroid hormone. Studies on human GH are limited largely to the assessment of plasma levels in endocrine disorders. Thus, insight into the regulation of synthesis versus secretion has come mainly from studies done on non-human GH and/or pituitary tumor cells. However, primate and non-primate GH gene loci have differences in their structure and, by extension, regulation. We generated transgenic (171hGH/CS-TG) mice containing the intact hGH1 gene and locus control region, including sequences required for integration-independent and preferential pituitary expression. Here, we show hGH co-localizes with mouse (m) GH in somatotrophs in situ and in primary pituitary cells. Dexamethasone treatment increased hGH and mGH, as well as GH releasing hormone (GHRH) receptor RNA levels, and hGH release was stimulated by GHRH treatment. By contrast, triiodothyronine decreased or had no effect on hGH and mGH production, respectively, and the negative effect on hGH was also seen in the presence of dexamethasone. Thus, 171hGH/CS-TG mouse pituitary cultures represent a model system to investigate hormonal control of hGH synthesis and secretion.

Levodopa Induces Synthesis of Nerve Growth Factor and Growth Hormone in Patients With Parkinson Disease

Polyneuropathy is observed in treated patients with Parkinson disease. Peripheral axonal degeneration is related to nerve growth factor metabolism. The causes for this axonal degeneration and the role of levodopa itself are not known. Levodopa may experimentally exert supportive effects on nerve growth factor synthesis and on growth hormone production, a hormonal compound with regenerative potential. The objective of this study was to investigate the effects of soluble 250-mg levodopa/benserazide administration on plasma occurrence of levodopa, nerve growth factor, and growth hormone in patients with Parkinson disease over an interval of 60 minutes. Levodopa moderately increased bioavailability of nerve growth factor and growth hormone combined with the rise of levodopa. Nerve growth factor data and levodopa values correlated to each other. Axonal degeneration may not be due to levodopa itself, as levodopa supports production of nerve growth factor and of growth hormone. Both may complement each other for neuronal survival.

Tesamorelin

Tesamorelin (Egrifta™) is a synthetic analogue of human growth hormone-releasing hormone (also known as growth hormone-releasing factor) that stimulates the synthesis and release of endogenous growth hormone. It is the first and, so far, only treatment indicated for the reduction of excess abdominal fat in patients with HIV-associated lipodystrophy. This article reviews the pharmacological properties, clinical efficacy and tolerability of tesamorelin in patients with HIV-associated central fat accumulation. Subcutaneous tesamorelin was effective in reducing visceral adipose tissue (VAT), but did not affect subcutaneous adipose tissue to a clinically significant extent in two 26-week, well designed, clinical trials in patients with HIV-associated central fat accumulation. This reduction in VAT was maintained in the longer term in patients who continued to receive tesamorelin until week 52 in the extension phases of the two trials. However, discontinuation of therapy during this period resulted in the reaccumulation of VAT. Tesamorelin therapy was also associated with significant improvements in other body composition measures (e.g. trunk fat and waist circumference) and improvements were generally seen in some body image parameters (e.g. belly image distress). Tesamorelin was generally well tolerated, with treatment-emergent serious adverse events occurring in <4% of patients during 26 weeks of therapy. Most of these events were injection-site reactions or events known to be associated with growth hormone therapy (e.g. arthralgia, headache and peripheral oedema). Although long-term clinical experience is needed to further assess the benefits and risks of therapy, current evidence suggests that tesamorelin may be useful for reducing visceral adiposity in patients with HIV-associated lipodystrophy, thereby potentially improving self image.

Changes in Growth Hormone-Axis Function in Nutrient Excess or Deprivation

Growth hormone (GH) is produced in a select population of cells, somatotropes, located in the anterior pituitary gland. GH is released into the general circulation where it interacts with multiple peripheral tissues through its receptor, GH receptor, to regulate growth and metabolic function. GH-releasing hormone (GHRH) and somatostatin are the primary positive and negative regulators of GH secretion, respectively. More recently, ghrelin has emerged as an additional stimulatory hormone for GH release. In humans, GH levels decrease in states of nutrient excess, such as obesity, and increase in response to nutrient deprivation, such as fasting, type 1 diabetes, and anorexia nervosa. Considering that GH regulates metabolism of carbohydrate, lipid, and protein, clarifying the mechanisms by which metabolic changes alter pituitary GH synthesis and secretion will increase our knowledge on the pathophysiology and treatment of metabolic diseases. In this review, the effect of nutrient excess and nutrient deficiency on GHaxis function in humans and other mammals will be summarized, with particular emphasis on studies exploring the direct effects of systemic signals, including insulin-like growth factor 1 (IGF-1) and insulin, on somatotrope function. Additionally, new mouse models with somatotrope-specific knockout of IGF-1 and insulin receptors generated by using the Cre/loxP system will be discussed. (Endocrinol Metab 26:279-284, 2011)

Effect of glucocorticoid on the biosynthesis of growth hormone-containing secretory granules in pituitary cells

Recent studies have suggested that treatment of glucocorticoid to immature growth hormone (GH)-producing cell line, MtT/S cells, dramatically induced the accumulation of GH-containing secretory granules in the cytosol and differentiated into mature GH-producing cells. However, the molecular mechanism of glucocorticoid-induced GH-containing secretory granule biogenesis in the MtT/S cells remains unknown. In the present study, we found that GH mRNA expression was facilitated by application of glucocorticoid. We artificially increased GH synthesis by transfection of green fluorescent protein-tagged GH (GH-GFP) gene. We found that the artificial elevation of GH expression in the cells did not accumulate the secretory granules in the cytosol, whereas glucocorticoid-induced the biogenesis of granules in GH-GFP-expressing MtT/S cells. We next performed DNA microarray and real-time RT-PCR analysis and found that glucocorticoid significantly altered the expression of membrane trafficking-related protein, syntaxin11 (Syx11). Immunocytochemical analysis further demonstrated that Syx11 positive structures were well colocalized with GH-containing granules in both MtT/S cells and rat anterior pituitary gland. Our findings indicate that glucocorticoid regulate the expression of Syx11 and facilitate the biogenesis and the trafficking of GH-containing granules in the MtT/S cells.

Methods for Enhancing Ring Closing Metathesis Yield in Peptides: Synthesis of a Dicarba Human Growth Hormone Fragment

Ruthenium-alkylidene catalysed ring closing metathesis (RCM) provides a convenient method for the synthesis of cyclic dicarba peptide analogues. Sequences devoid of turn-inducing residues, however, can often fail to cyclise. A combination of pseudoproline (ΨPro) insertion and microwave irradiation can be used to enhance RCM yield in these problematic sequences. This strategy is illustrated in the synthesis of a dicarba human growth hormone (hGH) fragment. The structural changes associated with cystine to dicarba replacement were found to change the metabolic profile of the peptide.

PRL and GH synthesis and release from the sea bream ( Sparus auratus L.) pituitary gland in vitro in response to osmotic challenge

The endocrine factors prolactin (PRL) and growth hormone (GH) are believed to have counteracting effects in the adaption of fish to changes in environmental salinity. In order to further investigate this interaction sea bream were challenged with full seawater (SW) or freshwater (FW) for 7 days and the response of pituitary glands cultured in vitro to an osmotic challenge (230, 275 and 320 mOsm/kg) was assessed. In vitro PRL secretion from pituitaries of SW-adapted fish was unaltered in response to an osmotic challenge, while GH secretion increased in the lowest osmolality (230 mOsm/kg). In contrast, both GH and PRL secretion by pituitaries from FW challenged fish was significantly increased ( p < 0.01) over that of pituitaries from SW fish at the highest osmolality (320 mOsm/kg). After FW challenge pituitary PRL content and de novo synthesised and released PRL were significantly increased ( p < 0.01), while total PRL secretion was not different from SW animals. GH pituitary content decreased in FW animals while total secretion and secretion of de novo synthesised protein were significantly increased ( p < 0.01). In addition, after transfer of fish to FW expression of PRL and GH increased 3- and 2-fold, respectively. Despite the increase in PRL expression, no increase in total PRL secretion occurred and although in gills a 2-fold increase in the osmoregulatory marker, Na +/K +-ATPase activity was detected, profound haemodilution and a cumulative mortality of 40% occurred in sea bream placed in FW. Taken together the results suggest that the sea bream pituitary gland fails to respond appropriately to the osmotic challenge caused by low salinity and the physiological response evoked in vivo is not enough to allow this species to withstand and adapt to FW.

The endocrine regulation network of growth hormone synthesis and secretion in fish: Emphasis on the signal integration in somatotropes

In teleosts, growth hormone (GH) production is governed by multiple neuroendocrine factors from the hypothalamus and other regulators from the pituitary and peripheral organs. Exploring the principles followed by pituitary somatotropes when differentiating and integrating the signals from these regulators at the cellular and intracellular level is essential for understanding the endocrine regulation network of growth hormone synthesis and secretion in fish. This paper discusses recent advances in the action mechanisms of GH regulation factors, including the neuroendocrine regulators, pituitary level factors and peripheral factors, primarily involved in their receptor systems as well as in post-receptor signal transduction pathways.

Effects of genetic variability of the dairy goat growth hormone releasing hormone receptor (GHRHR) gene on growth traits

Growth hormone-releasing hormone receptor (GHRHR) plays a critical role in growth hormone (GH) synthesis, release and regulation of pituitary somatotroph expansion in vertebrates. The objective of this study was to investigate variations in goat GHRHR gene and their associations with growth traits in 668 dairy goats. The results showed four novel single nucleotide polymorphisms (SNPs): NC_007302:g.5203C>T, 7307C>G, 9583G>A and 9668A>C. In detail, the novel SNP C>T in the 5203rd nucleotide identified a missense mutation: CCC (Pro)>TCC (Phe) at position 116aa of the goat GHRHR (423aa). Besides, 9583G>A and 9668A>C polymorphism were in complete linkage disequilibrium. The genetic diversity analysis revealed that the Guanzhong dairy goat possessed intermediate genetic diversity in P3 and P7 loci, and the Xinong Sannen dairy goat belonged to poor genetic diversity in P4 locus. Significant associations between the genotypes of P3 locus and body length, body height and chest circumference was observed in Guanzhong goat (P<0.05). However, in Xinong saanen population, significant statistical difference was only found in body height and body length (P<0.05). In P4 and P7 loci, no significant associations were detected between any variant sites and body length, body height and chest circumference, as well as for the milk traits (P>0.05). These results strongly suggested that the goat GHRHR gene is a candidate gene that influences growth traits in dairy goat.

In Situ Growth of Side-Chain PEG Polymers from Functionalized Human Growth Hormone—A New Technique for Preparation of Enhanced Protein−Polymer Conjugates

The application of atom transfer radical polymerization (ATRP) for preparation of a novel class of protein-polymer bioconjugates is described, exemplified by the synthesis of a recombinant human growth hormone (rh-GH) poly(ethylene glycol) methyl ether methacrylate (PEGMA) hybrid. The rh-GH protein was activated via a bromo-ester functionalized linker and used as a macroinitiator to polymerize the hydrophilic monomer PEGMA under solely aqueous conditions at 4 degrees C. ATRP conditions resulted in controlled polymer growth from rh-GH with low-polydispersity polyPEGMA chains. The rh-GH PEGMA product exhibited properties consistent with the presence of attached hydrophilic polymer chains, namely, high stability to denaturation and proteolysis. The polymerization conditions and conjugation proceeded with retention of the biological activity of the hormone. The rh-GH PEGMA was administered subcutaneously to rats and the activity compared to native rh-GH. The rh-GH PEGMA exhibited similar activity as the native rh-GH in vivo when a daily dose of 40 microg was administered. However, when a higher dose of 120 microg was administered with 3 days between injections the bioavailability of the rh-GH PEGMA was significantly better than that of the native. The results therefore demonstrate that ATRP can be successfully used as a general alternative approach to direct polymer conjugation, namely, PEGylation, to produce PEG-like protein conjugates. This technique can be exploited to design and synthesize protein-polymer derivatives with tailored therapeutic properties.

Reciprocal Regulation of MicroRNA-1 and Insulin-Like Growth Factor-1 Signal Transduction Cascade in Cardiac and Skeletal Muscle in Physiological and Pathological Conditions

MicroRNAs (miRNAs/miRs) are small conserved RNA molecules of 22 nucleotides that negatively modulate gene expression primarily through base paring to the 3' untranslated region of target messenger RNAs. The muscle-specific miR-1 has been implicated in cardiac hypertrophy, heart development, cardiac stem cell differentiation, and arrhythmias through targeting of regulatory proteins. In this study, we investigated the molecular mechanisms through which miR-1 intervenes in regulation of muscle cell growth and differentiation. On the basis of bioinformatics tools, biochemical assays, and in vivo models, we demonstrate that (1) insulin-like growth factor-1 (IGF-1) and IGF-1 receptor are targets of miR-1; (2) miR-1 and IGF-1 protein levels are correlated inversely in models of cardiac hypertrophy and failure as well as in the C2C12 skeletal muscle cell model of differentiation; (3) the activation state of the IGF-1 signal transduction cascade reciprocally regulates miR-1 expression through the Foxo3a transcription factor; and (4) miR-1 expression correlates inversely with cardiac mass and thickness in myocardial biopsies of acromegalic patients, in which IGF-1 is overproduced after aberrant synthesis of growth hormone. Our results reveal a critical role of miR-1 in mediating the effects of the IGF-1 pathway and demonstrate a feedback loop between miR-1 expression and the IGF-1 signal transduction cascade.

Growth hormone expression and neuroprotective activity in a quail neural retina cell line

We have previously shown that growth hormone (GH) is produced within cells of the chick embryo retina where it appears to act as an autocrine/paracrine anti-apoptotic factor in the regulation of programmed cell death during retinal development. These investigations were carried out on cultured chick embryo retinal ganglion cells (RGCs) as well as on the chick embryo retina in ovo, using GH protein knock-down by immunoneutralization. We have now investigated the putative neuroprotective actions of GH using a quail embryo neural retina cell line (QNR/D) treated with GH siRNA to silence the local synthesis of GH. We now show that knock-down of GH by gene silencing in cells of this cultured embryonic neural retina cell line, using NR-cGH-1 siRNA, correlates with the increased appearance in the cultures of cells with apoptotic nuclear morphology. This result is consistent with our previous results using protein knock-down by immunoneutralization. We thus validate, using different technology and a different culture system, our contention that GH, produced locally by cells of the neural retina acts in an autocrine or paracrine manner to regulate cell survival in the retina.

Activation of the GH/IGF-1 axis by CJC-1295, a long-acting GHRH analog, results in serum protein profile changes in normal adult subjects

Objective To identify biomarkers of growth hormone (GH) and insulin-like growth factor 1 (IGF-1) action in human serum. Background The search for new markers of GH activity has received extensive attention given that the current biomarkers (IGF-1, IGFBP-3 and collagen peptides) show substantial variability in the population, and are not reliably predictive of either the physiologic effects of GH therapy or the detection of GH abuse by athletes. GH releasing hormone (GHRH) is a polypeptide synthesized in the hypothalamus that binds to receptors on pituitary somatotropes to promote the synthesis and release of GH. Serum GH and IGF-1 levels have been shown to increase with administration of GHRH or CJC-1295, a long-acting GHRH analog. Design Sera from 11 healthy young adult men before and one week after CJC-1295 injection were analyzed by two-dimensional gel electrophoresis for proteomic changes. Serum proteins displaying significant changes before and after treatment were subsequently identified using mass spectrometry. In addition, correlations between these proteins and GH or IGF-1 levels were evaluated. Results Two protein spots that displayed decreased intensities after treatment were identified as an apolipoprotein A1 isoform and a transthyretin isoform. Three protein spots upregulated by CJC-1295 treatment included beta-hemoglobin, a C-terminal fragment of albumin, and a mix of an immunoglobulin fragment and another C-terminal albumin fragment. A linear relationship was found between the spot containing immunoglobulin and albumin fragments and IGF-1 levels. Conclusions Although the molecular mechanisms linking the identified proteins to GH and IGF-1 biological activity remain to be clarified, the results suggest that they represent potential biomarkers of GH and/or IGF-1 action.

Inhibitory effect of leptin on growth hormone secretion of GH3 cells: Involvement of cell proliferation, apoptosis and intracellular free Ca 2+

Recent studies have identified leptin and leptin receptors in the pituitary of different species, which suggest that there may be endocrine and paracrine regulatory roles between leptin-producing cells and cells with leptin receptor in pituitary, including growth and secretion of GH cells. The aim of this study was to investigate the effects of leptin on growth hormone (GH) secretion of GH3 cell. GH3 cells were cultured and treated with leptin. Cell proliferation was evaluated by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay, distribution of cell cycle and rate of apoptosis determined by flow cytometry and fluorescence microscopy, and intracellular free Ca 2+ levels ([Ca 2+] i) of single GH3 cells measured by a laser scanning confocal microscope. Leptin (10 −9–10 −7 mol/L) at 1 day or longer of treatment inhibited the basal growth hormone secretion of GH3 cells ( P < 0.05), but had no significant effect on short-term treatment. Leptin inhibited cell proliferation, reduced the proportion of cells in DNA synthesis period (S phase) to inhibit DNA synthesis of GH3 cells, and accelerated cell apoptosis of GH3 cells. Furthermore, the level of [Ca 2+] i of single GH3 cell was found to decrease immediately upon the addition of leptin (10 −8 mol/L). Leptin inhibits the basal GH secretion of GH3 cells, which may be due to the inhibition of proliferation, DNA synthesis and advanced apoptosis of GH3 cell. The inhibition of leptin on GH synthesis and secretion may be related to intracellular free Ca 2+ level.

Quorum-sensing effects in the antagonistic rhizosphere bacterium Serratia plymuthica HRO-C48

The rhizosphere-associated bacterium Serratia plymuthica HRO-C48 is not only able to suppress symptoms caused by soil-borne pathogens but is also able to stimulate growth of plants. Detailed knowledge about the underlying mechanisms and regulation are crucial for the application in biocontrol strategies. To analyse the influence of N-acyl homoserine lactone (AHL)-mediated communication on the biocontrol activity, the AHL-degrading lactonase AiiA was heterologously expressed in the strain, resulting in abolished AHL production. The comparative analysis of the wild type and AHL negative mutants led to the identification of new AHL-regulated phenotypes. In the pathosystem Verticillium dahliae-oilseed rape, the essential role of AHL-mediated signaling for disease suppression was demonstrated. In vitro, the regulatory function of AHLs in the synthesis of the plant growth hormone indole-3-acetic acid is shown for the first time. Additionally, swimming motility was found to be negatively AHL regulated. In contrast, production of extracellular hydrolytic enzymes is shown to be positively AHL-regulated. HRO-C48 emits a broad spectrum of volatile organic compounds that are involved in antifungal activity and, interestingly, whose relative abundances are influenced by quorum sensing (QS). This study shows that QS is crucial for biocontrol activity of S. plymuthica and discusses the impact for the application of the strain as a biocontrol agent.

Association of polymorphisms of the &amp;lt;i&amp;gt;GHRHR&amp;lt;/i&amp;gt; gene with growth traits in cattle (Brief report)

Abstract. The hypothalamic hormone, growth hormone-releasing hormone (GHRH), is the principal stimulator of pituitary growth hormone (GH) synthesis and secretion. Its pituitary receptor is well characterized as a member of the superfamily of G protein-coupled receptors (MAYO et al., 1992). GHRH and its receptor provide important functions in the regulation of the GH axis and in the development and proliferation of pituitary somatotropes (LIN-SU et al., 2002). By now, polymorphisms of bovine GHRHR were not reported. In the present experiment the 5' flanking region, the coding region and partially introns of GHRHR were screened to detect the SNPs in the predominant cattle breeds of China.

급격한 염분변화에 따른 담수어 3종의 프로락틴 및 성장호르몬 유전자 발현변화

The changes in osmolality and the gene expression profiles of prolactin (PRL) and growth hormone (GH) with rapid changes in salinity were compared in the eel (Anguilla japonica), crucian carp (Carassius carassius), and masu salmon (Oncorhynchus masou). Fish stocked in freshwater (FW) were abruptly transferred to experimental tanks containing FW, 50% seawater (50% SW), or 100% SW (SW). Blood samples and pituitary glands were collected 2 and 24 hrs after the exposure. No mortality was observed in SW eel (n=6), whereas all of the crucian carp (n=6) and two masu salmon (n=6) exposed to SW died after land 24 hrs, respectively. The PRL mRNA levels of the eel and masu salmon decreased in 50% SW and SW compared to those of the fish kept in FW after 24 hrs, whereas the PRL levels of crucian carp were higher in 50% SW than in FW. Unlike the PRL mRNA levels, the GH mRNA levels of the eel did not differ significantly among three different salinities, while the GH mRNA levels of crucian carp and masu salmon increased significantly in 50% SW and SW after 24 hrs. The serum osmolalities increased marginally in the eel and masu salmon in 50% SW at 24 hrs (19% and 9%, respectively), whereas those of crucian carp increased abruptly in 50% SW (50% increase). These results suggest that the synthesis of PRL and GH is important in relation to the osmoregulatory system with environmental changes in salinity.