Developmental expression of the growth hormone receptor gene in rabbit tissues

Identification of polymorphic loci in OSMR and GHR genes and analysis of their association with growth traits in sheep

The aim of this study was to analyze the effect of OSMR and GHR genes polymorphisms on growth traits in sheep. The single nucleotide polymorphisms of sheep OSMR and GHR genes were identified by DNA sequencing technology. A total of two intronic mutations g.2443 T > C and g.170196 A > G were identified in OSMR and GHR, respectively. Correlation analysis was carried out between the obtained genotypes and the growth traits of sheep. The results showed that at the OSMR g.2443 T > C locus, the body weight, chest circumference and cannon circumference of the TT genotype sheep were significantly higher than those of the CC genotype sheep (p < .05). At the GHR g.170196 A > G locus, the body weight, body length, chest circumference and cannon circumference of the AA genotype sheep were significantly higher than those of the AG genotype and GG genotype sheep (p < .05). Moreover, the body weight of sheep of combination TTOSMR/AAGHR genotype was significantly higher than that of other combination genotypes (p < .05). Therefore, we believe that the polymorphic sites identified in the OSMR and GHR genes can be used as candidate molecular markers for breeding good traits in sheep.

Growth Axis Somatostatin, Growth Hormone Receptor, and Insulin-like Growth Factor-1 Genes Express and Are Affected by the Injection of Exogenous Growth Hormone in Chinemys reevesii

In this study, to explore the effect of growth hormone changes on the related genes and regulatory roles of the turtle, PCR amplification, real-time fluorescence quantitative analysis, and enzyme cutting technology were used to clone and sequence the somatostatin (SS) gene, growth hormone receptor (GHR), and insulin-like growth factor-1 (IGF-I) sequence of Chinemys reevesii. The effects of human growth hormone on the mRNA expression of growth-axis-related genes SS, GHR, and IGF-1 in different sexes were observed. The study of the SS gene in turtles using real-time fluorescence quantitative PCR showed that the SS gene was mainly expressed in the nervous system and the digestive system, with the highest expression found in the brain, while the GHR gene and the IGF-I gene were expressed in all tissues of Chinemys reevesii. The SS gene was expressed in the brain, pituitary, liver, stomach, and intestine, with the highest expression in the brain and the lowest expression in the liver. Within 4 weeks of the injection of exogenous growth hormone, the expression level of the SS gene in the brain of both sexes first increased and then decreased, showing a parabolic trend, and the expression level of the experimental group was lower than that of the control group. After the injection of growth hormone (GH), the expression of the GHR gene in the liver of both sexes showed a significant increase in the first week, decreasing to the control group level in the second week, and then gradually increasing. Finally, a significant level of difference in the expression of the GHR gene was reached at 3 and 4 weeks. In terms of the IGF-I gene, the changing trend of the expression level in the liver was the same as that of the GHR gene. After the injection of exogenous growth hormone, although the expression of the SS gene increased the inhibition of the secretion of the GHR gene by the Reeves' turtle, exogenous growth hormone could replace the synthesis of GH and GHR, accelerating the growth of the turtle. The experiments showed that the injection of recombinant human growth hormone affects the expression of SS, GHR, and IGF-1 genes, and promotes the growth of the Reeves' turtle.

Detecting novel Indel variants within the GHR gene and their associations with growth traits in Luxi Blackhead sheep

The growth hormone is important in the regulation of metabolism and energy homeostasis and acts through a growth hormone receptor (GHR). In this work, genetic variations within the ovine GHR gene were identified and tested for associations with body morphometric traits in Chinese Luxi Blackhead (LXBH) sheep. Novel deletion loci in the LXBH GHR gene included P2-del-23 bp and P8-del-23 bp indel variants. The polymorphic information content (PIC) was 0.329 in P2-del-23 bp and 0.257 in P8-del-23 bp. Moreover, both indel polymorphisms were not at Hardy-Weinberg equilibrium (p < 0.05) in the LXBH population. Statistical analyses revealed that the P2-del-23 bp and P8-del-23 bp indels were significantly associated (p < 0.05) with several growth traits in rams and ewes, including body weight, body height, chest depth, chest width, chest circumference, cannon circumference, paunch girth and hip width. Among the tested sheep, the body traits of those with genotype DD were superior to those with II and ID genotypes, suggesting that the 'D' allele was responsible for the positive effects on growth traits. Thus, these results indicate that the P2-del-23 bp and P8-del-23 bp indel sites and the DD genotype can be useful in marker-assisted selection in sheep.

Temperature dependent action of growth hormone on somatic growth and testicular activities of the catfish, Clarias batrachus

Effects of growth hormone on somatic growth and testicular activities were studied during late quiescence and early recrudescence phases of the reproductive cycle of the catfish, Clarias batrachus. The administration of exogenous growth hormone (GH) during the late quiescence phase (December-January; ambient water temperature-15.2±1°C) did not influence the somatic growth as well as the testicular activity, as no change in body weight, testis weight, plasma level of insulin-like growth factor I (IGF-I) and testicular morphology was detected following GH treatment, though the plasma testosterone was marginally increased. While during the early recrudescence phase (March-April; ambient water temperature-28.1±2°C), GH treatment promoted the production of insulin like growth factor-I and testicular steroidogenic activity in a dose dependent manner, as was evident from the significant increase in the circulating levels of testosterone and estradiol-17β. GH treatment also increased body weight, testicular weight and gonadosomatic index, suggesting its involvement in testicular development. The GH treatment promoted spermatogonial proliferation and accelerated the spermatogenic process in the present catfish. These results, thus, suggest that GH influences the somatic growth and testicular activities depending on the temperature of the rearing water; warmer temperature and longer photoperiod promote testicular steroidogenic and spermatogenic activities in fish. This study has immense practical use in fisheries science.

The effects of type 1 IGF receptor inhibition in a mouse model of diabetic kidney disease

OBJECTIVE

We have recently shown increased sensitivity to IGF-I induced signal transduction in kidneys of diabetic mice. Accordingly we investigated the effects of PQ401, a novel diarylurea compound that inhibits IGF1R autophosphorylation in type I diabetes.

METHODS

Control (C) and Diabetic (D) mice were administered PQ401 (CP, DP) or vehicle (C, D) for 3weeks.

RESULTS

CP animals showed a decrease in renal phosphorylated (p-)AKT and p-IGF1R. However, PQ401 had no effect on diabetic state (hyperglycemia, weight loss) or renal disease parameters (hypertrophy, hyperfiltration and albuminuria). Type IV collagen as well as TGF-β mRNA increased in DP and D compared to C. In the CP group renal hypertrophy with fat accumulation in proximal tubuli and increased renal IGF-I, collagen IV and TGF-β mRNA were seen.

CONCLUSIONS

IGF1R inhibition by PQ401 exerted no significant effects on diabetic kidney disease parameters, arguing against a role for IGF-I in the pathogenesis of diabetic kidney disease. However, PQ401 affects normal kidneys, inducing renal hypertrophy as well as collagen and fat accumulation, with increased renal IGF-I mRNA, suggestive of a damage-regeneration process. Therefore, this diarylurea compound is not beneficial in early diabetic kidney disease. Its potential deleterious effects on kidney tissue need to be further investigated.

The conflicting effects of maternal nutrient restriction and early-life obesity on renal health

Epidemiological and animal studies have demonstrated that early-life nutrition alters the metabolic responses and generates structural changes in complex tissues, such as the kidneys, which may lead to a reduction in the offspring lifespan. Independently, obesity induces a spontaneous low-grade chronic inflammatory response by modulating several of the major metabolic pathways that ultimately compromise long-term renal health. However, the combined effects of maternal nutrition and early-life obesity in the development of renal diseases are far from conclusive. Previous results, using the ovine model, demonstrated that the combination of a reduction in fetal nutrition and juvenile obesity induced a series of adaptations associated with severe metabolic syndrome in the heart and adipose tissue. Surprisingly, exposure to an obesogenic environment in the kidney of those offspring produced an apparent reduction in glomerulosclerosis in relation to age- and weight-matched controls. However, this reduction in cellular apoptosis was accompanied by a rise in glomerular filtration rate and blood pressure of equal intensity when compared with obese controls. The intention of this review is to explain the adaptive responses observed in this model, based on insights into the mechanism of renal fetal programming, and their potential interactions with some of the metabolic changes produced by obesity.

Prolactin-dependent modulation of organogenesis in the vertebrate: Recent discoveries in zebrafish

The scientific literature is replete with evidence of the multifarious functions of the prolactin (PRL)/growth hormone (GH) superfamily in adult vertebrates. However, little information is available on the roles of PRL and related hormones prior to the adult stage of development. A limited number of studies suggest that GH functions to stimulate glucose transport and protein synthesis in mouse blastocytes and may be involved during mammalian embryogenesis. In contrast, the evidence for a role of PRL during vertebrate embryogenesis is limited and controversial. Genes encoding GH/PRL hormones and their respective receptors are actively transcribed and translated in various animal models at different time points, particularly during tissue remodeling. We have addressed the potential function of GH/PRL hormones during embryonic development in zebrafish by the temporary inhibition of in vivo PRL translation. This treatment caused multiple morphological defects consistent with a role of PRL in embryonic-stage organogenesis. The affected organs and tissues are known targets of PRL activity in fish and homologous structures in mammalian species. Traditionally, the GH/PRL hormones are viewed as classical endocrine hormones, mediating functions through the circulatory system. More recent evidence points to cytokine-like actions of these hormones through either an autocrine or a paracrine mechanism. In some situations they could mimic actions of developmentally regulated genes as suggested by experiments in multiple organisms. In this review, we present similarities and disparities between zebrafish and mammalian models in relation to PRL and PRLR activity. We conclude that the zebrafish could serve as a suitable alternative to the rodent model to study PRL functions in development, especially in relation to organogenesis.

Maternal nutrient restriction alters renal development and blood pressure regulation of the offspring

Studies have shown that the risk of hypertension in adulthood can be affected by the in utero environment. It is established that hypertension is linked to compromised kidney function and that factors affecting organogenesis can increase the risk of later disease. Prostaglandins (PG) and growth factors are known to play an important role in regulating kidney function and renal organogenesis. The extent, however, to which global energy restriction (where all nutrients are reduced) of the mother can programme later blood pressure control or renal PG and growth factor status is unknown. A study is described that aimed to examine the long-term effects of maternal nutrient restriction (NR) and elucidate their relationship with compromised kidney development. First, it was necessary to establish animal models. A sheep model of 50% NR during specific stages of gestation was used to investigate fetal renal development, whilst a rat model of 50% NR throughout pregnancy was used to investigate postnatal kidney development and adult functioning. Molecular analysis has shown that expression of the growth hormone–insulin-like growth factor (GH–IGF) axis is affected by NR in the fetal sheep kidneys, and that changes are dependent on the timing of NR and whether the fetus is a singleton or a twin. Analysis of the kidneys from the rat model has shown nutritional differences in the expression of PG receptors and the enzymes responsible for PG synthesis and degradation that persist into adulthood. In conclusion, NR does affect the GH–IGF and PG axes, and these changes may be important in the nutritional programming of renal functioning and adult blood pressure control.

Impact of maternal undernutrition and fetal number on glucocorticoid, growth hormone and insulin-like growth factor receptor mRNA abundance in the ovine fetal kidney

Epidemiological and animal studies strongly indicate that the environment experienced in utero determines, in part, an individual's likelihood of developing cardiovascular disease in later life. This risk has been further linked to impaired kidney function, as a result of compromised development during fetal life. The present study therefore examined the influence of maternal nutrient restriction (NR), targeted at specific periods of kidney development during early to mid gestation, on the mRNA abundance of receptors for glucocorticoid (GCR), growth hormone (GHR) and insulin-like growth factors-I (IGF-IR) and -II (IGF-IIR), and the IGF-I and -II ligands. This was undertaken in both singleton and twin fetuses. At conception ewes were randomly allocated to either an adequately fed control group or one of four nutrient-restricted groups that were fed half the control amount from 0 to 30, 31 to 65, 66 to 110 or 0 to 110 days gestation. At 110 days gestation all ewes were humanely euthanased and fetal kidneys and surrounding adipose tissue sampled. There was no effect of NR or fetal number on kidney weight, shape or nephron number, but the surrounding fat mass was increased in singleton fetuses exposed to NR for 110 days. An increase in kidney mRNA abundance with NR only occurred in singleton fetuses where IGF-IR mRNA was enhanced with NR from 66-110 days gestation. In twin fetuses, NR had no effect on mRNA abundance. However, for all genes examined mRNA expression was lower in the kidneys of twin compared with singleton fetuses following NR, and the magnitude of the effect was dependent on the timing of NR. In conclusion, the abundance of mRNA for receptors which regulate fetal kidney development are lower in twin animals compared with singletons following periods of nutrient deficiency. This may impact on later kidney development and function.

Growth hormone as an early embryonic growth and differentiation factor

In this review we consider the evidence that growth hormone (GH) acts in the embryo as a local growth, differentiation, and cell survival factor. Because both GH and its receptors are present in the early embryo before the functional differentiation of pituitary somatotrophs and before the establishment of a functioning circulatory system, the conditions are such that GH may be a member of the large battery of autocrine/paracrine growth factors that control embryonic development. It has been clearly established that GH is able to exert direct effects, independent of insulin-like growth factor-I (IGF-I), on the differentiation, proliferation, and survival of cells in a wide variety of tissues in the embryo, fetus, and adult. The signaling pathways behind these effects of GH are now beginning to be determined, establishing early extrapituitary GH as a bona fide developmental growth factor.

The role of growth hormone in fetal development

Studies across several species, particularly the mouse, show that growth hormone (GH, somatotrophin) is an important determinant of litter size, and to a lesser extent, of birth length. GH acts at all stages of development, from ovulation through preimplantation development to the late fetus, with actions on both embryo/fetus and mother contributing to successful fetal development. The fact that these are not more obvious in vivo is likely a result of redundancy of cytokine hormone action, particularly in relation to prolactin, which shares common actions and receptor locations with GH.

Co-expression of GH and GHR isoforms in prostate cancer cell lines

Prostate cancer is a significant cause of morbidity and mortality in Western males. While it is known that androgens play a central role in prostate cancer development and progression, other hormones and growth factors are also involved in prostate growth. Insulin-like growth factor-I (IGF-I) plasma levels have been associated with prostate cancer risk, and growth hormone (GH), a major factor regulating IGF levels, also appears to have a role in prostate cancer cell growth. Most significantly, GH has been shown to increase the rate of cell proliferation in prostate cancer cell lines. We have now demonstrated the co-expression of GH and GH receptor (GHR) mRNA isoforms in the ALVA41, PC3, DU145, LNCaP prostate cancer cells by reverse transcription polymerase chain reaction. Sequence analysis has confirmed that these cell lines express the pituitary form of GH mRNA and also the placental mRNA isoform. These prostate cancer cell lines also express the full-length mRNA for the GHR and the exon 3 deleted isoform. We have also demonstrated the presence of GH and GHR proteins in these cell lines by immunohistochemistry. GH expression has not been described previously in human prostate cancer cells. The co-expression of GH and its receptor would enable an autocrine-paracrine pathway to exist in the prostate that would be capable of stimulating prostate growth, either directly via the GHR or indirectly via IGF production. The GH axis in the prostate could therefore be an important additional target for the future development of prostate cancer therapies.

Characterization of the growth hormone receptor in human dermal fibroblasts and liver during development

Human tissues express growth hormone receptors (hGHR) by the 3rd mo of gestation. We assessed developmental changes in hGHR function in fibroblasts and liver, testing binding and hormonal response. Fetal cells showed low but reproducible hGH binding. No age-related changes occurred in fibroblasts (9 wk-34 yr). In contrast, there was a fourfold increase in hGH binding in postnatal liver, with a sixfold increase in hGHR mRNA. Both full-length and truncated hGHR mRNAs were detected in all livers. Cross-linking revealed a larger hGH/receptor complex in fetal liver. Fetal hepatocytes produced 10 times more insulin-like growth factor (IGF)-II than IGF-I, and responded to hGH (150 ng/ml) with a significant increase in IGF-II. Fetal hepatocytes secreted three IGF-binding proteins (IGFBPs), including IGFBP1, but not IGFBP3. hGH did not alter fetal hepatocyte IGFBPs but stimulated glucose uptake. Exposure of fibroblasts to hGH decreased hGH binding only in >1-yr postnatal fibroblasts, whereas treatment with dexamethasone (100-400 nM) increased binding only in postnatal cells. Thus, although fetal hepatocytes and fibroblasts possess functional hGHR, these receptors (and/or their signaling pathways) are immature or have adapted to the in utero environment.

Expression of growth hormone and its receptor in the placental and feto-maternal environment during early pregnancy in sheep

In a previous study we showed the existence of GH in the ovine placenta. We now supplement the information available on placental GH and describe the presence and distribution of GH receptor (GH-R) messenger RNA (mRNA) in uterine, fetal, and placental tissues during early pregnancy. GH mRNA was not detected in the placenta before day 27 (d27). Its expression peaked between d40 and d45 and fell after d55. GH mRNA was localized in the trophectoderm and syncytium. During the d35-d50 period, concentrations of GH in the maternal circulation were not increased. In umbilical blood, however, GH was detected from d35 and was presumed to be of placental origin, because GH mRNA was not detected in the fetal pituitary gland on d40. We report on GH-R mRNA expression in the placenta between d20-d120. The relative abundance of GH-R transcripts increased significantly between d25-d43. In the endometrium, GH-R mRNA was detected from d8-d120 of pregnancy and from d4-d16 of the cycle. GH-R mRNA was localized in the trophectoderm, fetal mesoderm, and maternal uterine stroma. In the fetal liver, GH-R mRNA was first detectable on d35. The results of this study indicate that between d35-d50 of pregnancy, the endometrium, placenta, and fetus are all potential targets for the placental GH.

Activation of the adult mode of ovine growth hormone receptor gene expression by cortisol during late fetal development

The developmental and tissue-specific regulation of growth hormone receptor (GHR) mRNA expression is complex and involves alternate leader exon usage. The transcript composition of hepatic GHR mRNA has therefore been determined in fetal sheep during late gestation and after experimental manipulation of fetal plasma cortisol levels by fetal adrenalectomy and exogenous cortisol infusion, using RNase protection assays and a riboprobe containing exons 1A, 2, and 3 of the ovine GHR gene. Expression of the adult liver-specific GHR mRNA transcript containing exon 1A was not detected earlier than 138 days of gestation (term 145 +/-2 days). Thereafter, expression of this leader exon increased and accounted for 25-30% of the total GHR mRNA in the fetal liver at term. Hepatic GHR mRNA derived from leader exons other than 1A was detectable at 97 days and increased in abundance toward term in parallel with the normal prepartum rise in fetal plasma cortisol. Abolition of this cortisol surge by fetal adrenalectomy prevented both the activation of exon 1A expression and the prepartum rise in GHR mRNA derived from the other leader exons in fetal ovine liver. Conversely, raising cortisol levels by exogenous infusion earlier in gestation prematurely activated exon 1A expression and enhanced the abundance of GHR mRNA transcripts derived from the other leader exons. Cortisol therefore appears to activate the adult mode of GHR gene expression in fetal ovine liver during late gestation. These observations have important implications for the maturation of the somatotrophic axis and for the onset of GH-dependent growth after birth.

Generation of chicken growth hormone-binding proteins by proteolysis

A soluble protein that specifically bound growth hormone (GH) was characterized in culture medium of a COS-7 cell line transfected with the cDNA of the full-length chicken GH receptor (cGHR). Incubation of culture medium with 125I-labeled human GH resulted in the formation of a single specific complex with high affinity (KD = 0.36 nM) and apparent molecular weight of 75 kDa. The production of large quantities of GH-binding protein (GHBP) amounting to, per hour, 23% of the cell's GHR, points to the importance of partial proteolysis for GHR turnover. Considerable amounts of GHBP were also detected in a cytosolic fraction. These results strongly suggest that in chicken, as in rabbit and monkey, the GHBP is generated, at least partially, by proteolytic cleavage of the membrane-anchored GHR.

Growth hormone. A paracrine growth factor?

A number of tissues, including the brain, pituitary, immune system, placenta, mammary gland, and testis, may be self-contained units of GH regulation, production, and action. The production of GH and GH-releasing factors outside the hypothalamo-pituitary axis complements, rather than replaces, the traditional endocrine interactions between GH-releasing factors, GH, and its target tissues.

Rat growth hormone receptor/growth hormone-binding protein mRNAs with divergent 5'-untranslated regions are expressed in a tissue-specific manner

In the rat, the growth hormone receptor (GH-R) gene generates two transcripts, one encoding the transmembrane GH-R, and a shorter one encoding the GH-binding protein (GH-BP). These transcripts exhibit a high degree of heterogeneity in their 5'-untranslated regions (5'-UTRs). Some of the exons encoding these 5'-UTR variants may be flanked by distinct promoter regions whose activity would result in the tissue-specific expression of the GH-R gene. To assess this possibility, we used single-sided polymerase chain reaction (PCR) amplification to characterize 5'-UTR variants in rat GH-R cDNAs, and by using 5'-UTR-specific probes, we determined their pattern of expression in several tissues. Besides two previously described variants (V1 and V2), three new 5'-UTR variants were identified, extending 56 nucleotides (V3), 135 nucleotides (V4), and 209 nucleotides (V5) upstream of the ATG translation initiation codon. The expression of GH-R and GH-BP transcripts was clearly tissue specific. In the liver, GH-BP mRNA was the predominant transcript, whereas in other tissues, there was equivalent expression of both transcripts or predominant expression of GH-R mRNA. With respect to the tissue distribution of the 5'-UTR variants in particular, variants V1 and V5 exhibited a pattern of expression closely resembling that seen with an exon 2 probe, with the overall expression of variant V1 being much higher than that of variant V5. The V2 species was exclusively expressed in liver. Variant V3 was expressed at low levels in liver, muscle, heart, and kidney; in muscle and heart, it was preferentially associated with GH-BP transcripts. Variant V4, although present in liver, was more abundant in extrahepatic tissues and predominantly found in GH-R mRNA transcripts. Southern blot analyses were consistent with exon 2 and the exons encoding the V1 and V2 sequences being in proximity, with the other 5'-UTR sequences being encoded by exons located further upstream of exon 2. These findings support the concept that different 5'-UTR variants are the result of the different promoters acting in a tissue-specific manner. The association of specific 5'-UTR variants with either GH-R or GH-BP transcripts raises the possibility that the alternative splicing process that generates GH-BP mRNA in the rat might be controlled by the 5'-flanking region regulating the expression of specific leader exons.

Estradiol inhibits growth hormone receptor gene expression in rabbit liver

We studied the ontogeny of GH receptor mRNA levels and the effect of exogenous estradiol administration on GH receptor mRNA levels in rabbit liver. A solution hybridization-RNase protection assay revealed a predominant 370-base long protected band corresponding to the mRNA encoding the transmembrane GH receptor, and a 241-base long protected band, representing about 9.0%, with the predicted size for the truncated form of the GH receptor. To study the developmental profile of GH receptor expression, we studied 12 female rabbits, at ages 1, 3, 5 and 7 months. Maximal GH receptor mRNA levels were observed in 3-month-old animals and decreased in 7-month-old animals. To investigate the effect of estradiol, 8-week-old immature female rabbits were randomly divided into five groups, and received subcutaneous pellets containing either placebo or estradiol at doses of 0.1, 0.5, 1.5 and 5.0 mg for 3 weeks. Exogenous administration of estradiol, at doses that resulted in physiological circulating levels, induced a reduction in GH receptor expression, measured both by GH binding (36 and 46%), and GH receptor mRNA levels (38 and 87%), in animals receiving pellets containing 1.5 and 5.0 mg of estradiol, respectively. We conclude that estradiol decreases GH receptor expression in rabbit liver. The results of our study suggest that there is an inverse relationship between circulating estrogen concentrations and liver GH receptor expression.

Developmental expression of the growth hormone receptor gene in the rat hypothalamus

The ontogeny of growth hormone receptor (GHR) gene expression was studied in the rat hypothalamus. Total RNA from the hypothalamus of rats at different developmental stages (embryonic day 15-56 days of age) was characterized using a 32P-labeled RNA probe derived from the extracellular domain of the rat GHR cDNA. Two RNA species, 4.5 kilobases (kb) encoding for GHR and 1.2 kb encoding for GH-binding protein, were detected in hypothalamic tissue from embryonic day 15 to 56 days of age. Their levels were low at embryonic day 15 and increased toward 3 days of age. The level of 4.5-kb transcript preferentially increased from 7 days after birth, and it was maintained until 35 days of age. Thereafter, the level of 4.5-kb transcript declined. The ratio between the 4.5- and 1.2-kb transcripts was less than 2.0 from embryonic day 15 to 3 days after birth, while it was larger than 4 after 7 days of age. There was no sex difference in the levels or the ratios of the transcripts of the GHR gene from 7 to 56 days of age. The findings indicate that the 4.5-kb transcript preferentially processed postnatally in the rat hypothalamus.

Expression of a functional porcine growth hormone receptor cDNA in mouse L cells

Porcine (p) growth hormone receptor (GHR) complementary DNA (cDNA) has been cloned and the primary amino acid structure was deduced from the nucleotide sequence. A comparison of pGHR to other GHRs revealed an approximately 70% similarity in amino acid sequence (Cioffi et al., 1990). Hybridization of this receptor cDNA to RNA samples isolated from various porcine tissues revealed a single RNA band of 4.2 kb. The full-length pGHR cDNA was subcloned into an eukaryotic expression vector, transcription of which was directed by the mouse metallothionein-I transcriptional regulatory sequence. Stable mouse L cell lines which express the pGHR cDNA were established. Approximately 80% of the cell lines were found to possess pGHR mRNA (approximately 2 kb) which corresponds to the length of the cloned pGHR cDNA. Binding studies showed that the stable cell lines were capable of specifically binding 125I-labeled pGH with a dissociation constant (Kd) of approximately 1.0 nM. The apparent molecular mass of the receptor, as determined by cross-linking studies, was found to be 118 kDa. Also, the receptor-ligand complex could be internalized. These results suggest that an active form of pGHR had been cloned and stably expressed in mouse L cells.

Molecular cloning of the bovine prolactin receptor and distribution of prolactin and growth hormone receptor transcripts in fetal and utero-placental tissues

We have isolated a bovine prolactin (bPRL) receptor cDNA from an endometrial cDNA library, which predicts a 557 amino acid transmembrane protein similar to the long forms of other characterized prolactin receptors. The predicted cytoplasmic domain is slightly truncated primarily by a stop codon located 36 codons 5' from the stop utilized in the human hepatic transcript. When expressed in COS cells, this cDNA was shown to encode a protein which bound bovine placental lactogen (bPL) and bPRL with nearly equal affinity (KD for bPL, 2.03 x 10(-10) M; bPRL, 3.07 x 10(-10) M). Northern analysis demonstrated multiple transcripts, with maternal liver, corpus luteum, intestine, endometrium and fetal liver containing a major transcript of about 3.8 kb, and maternal corpus luteum and endometrium, a second sized transcript of apparently equal abundance of 4.4 kb. This difference did not appear to be within the coding region. Primer extension analysis of maternal hepatic and endometrial transcripts revealed considerable heterogeneity. Examination of the distribution of prolactin and growth hormone receptor transcripts at mid-pregnancy by semi-quantitative reverse transcriptase polymerase chain reaction showed that both are widespread in bovine fetal and placental tissues. This isolation of bovine prolactin receptor cDNA, and description of receptor distribution will facilitate study of the action of the placental and pituitary members of this gene family during pregnancy.

Developmental expression of hepatic growth hormone receptor and insulin-like growth factor-I mRNA in the chicken

We have examined the ontogeny of expression of growth hormone (GH) receptor (GHR) and insulin-like growth factor-I (IGF-I) mRNA in chicken liver from day 13 of incubation until 31 weeks of age. The profiles of GHR and IGF-I mRNA levels were compared to developmental changes in body weight and plasma levels of GH and IGF-I. In the embryo, hepatic GHR mRNA was not detectable until day 15, highest on days 17 and 19, and then declined at hatching (day 21). Following an initial 2-week delay after hatching, there was a progressive increase in hepatic GHR mRNA which continued after the birds reached mature body weight. Plasma GH reached peak levels at 3-4 weeks of age and then fell sharply until maintenance of a low basal level after 10 weeks of age. Thus, there appears to be a strong inverse relationship between expression of the GHR and basal plasma GH levels in the prepubertal chicken. Although IGF-I mRNA was undetectable in embryonic liver by Northern blot analysis, there is a good correlation between expression of hepatic IGF-I mRNA and the plasma IGF-I profile during post-hatching development in the chicken. The highest levels of IGF-I mRNA were reached at 4 weeks of age which was followed by a slow decline to the basal levels maintained after 10 weeks of age. It appears that the decline in plasma IGF-I lags considerably behind the sharp fall in plasma GH levels and expression of hepatic IGF-I mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum binding proteins for growth hormone: origins, regulation of gene expression and possible roles

The above discussion highlights the heterogeneity of the family of GH receptors/GHBPs and their mRNAs. Considerable uncertainty still exists as to the interrelationships between the various forms, the specific mechanisms for their generation and their possible significance in terms of modulating GH action and receptor function. Collectively, the regulatory data indicate that while the mRNAs encoding the membrane and soluble GH receptors/GHBPs in the rat are expressed by the same broad distribution of tissues, they can be differentially regulated. Such regulated expression implies a functional basis for production of GHBP. The wide tissue distribution of GHBP mRNA also suggests a role for GHBP as a paracrine/autocrine effector molecule, perhaps in addition to an endocrine role. Additional studies, both in vitro and in vivo, perhaps utilizing highly purified recombinant GHBP, will be required to provide more definitive information as to the true physiological role(s) of the circulating GHBPs.