Transcriptional profiling and pathway analysis reveal differences in pituitary gland function, morphology, and vascularization in chickens genetically selected for high or low body weight

Background

Though intensive genetic selection has led to extraordinary advances in growth rate and feed efficiency in production of meat-type chickens, endocrine processes controlling these traits are still poorly understood. The anterior pituitary gland is a central component of the neuroendocrine system and plays a key role in regulating important physiological processes that directly impact broiler production efficiency, though how differences in pituitary gland function contribute to various growth and body composition phenotypes is not fully understood.

Results

Global anterior pituitary gene expression was evaluated on post-hatch weeks 1, 3, 5, and 7 in male broiler chickens selected for high (HG) or low (LG) growth. Differentially expressed genes (DEGs) were analyzed with gene ontology categorization, self-organizing maps, gene interaction network determination, and upstream regulator identification to uncover novel pituitary genes and pathways contributing to differences in growth and body composition. A total of 263 genes were differentially expressed between HG and LG anterior pituitary glands (P ≤ 0.05 for genetic line-by-age interaction or main effect of line; ≥1.6-fold difference between lines), including genes encoding four anterior pituitary hormones. Genes involved in signal transduction, transcriptional regulation, and vesicle-mediated transport were differentially expressed and are predicted to influence expression and secretion of pituitary hormones. DEGs involved in immune regulation provide evidence that inflammation and response to cellular stressors may compromise pituitary function in LG birds, affecting their ability to adequately produce pituitary hormones. Many DEGs were also predicted to function in processes that regulate organ morphology and angiogenesis, suggesting pituitary gland structure differs between the divergently selected lines.

Conclusions

The large number of DEGs within the anterior pituitary gland of birds selected for high or low body weight highlights the importance of this gland in regulating economically important traits such as growth and body composition in broiler chickens. Intracellular signaling, transcriptional regulation, and membrane trafficking are important cellular processes contributing to proper hormone production and secretion. The data also suggest that pituitary function is intimately tied to structure, and organization of the gland could influence hypothalamic and systemic metabolic inputs and delivery of hormones regulating growth and metabolism into peripheral circulation.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5670-9) contains supplementary material, which is available to authorized users.

Transcriptional profiling of liver during the critical embryo-to-hatchling transition period in the chicken (Gallus gallus)

Background

Although hatching is perhaps the most abrupt and profound metabolic challenge that a chicken must undergo; there have been no attempts to functionally map the metabolic pathways induced in liver during the embryo-to-hatchling transition. Furthermore, we know very little about the metabolic and regulatory factors that regulate lipid metabolism in late embryos or newly-hatched chicks. In the present study, we examined hepatic transcriptomes of 12 embryos and 12 hatchling chicks during the peri-hatch period—or the metabolic switch from chorioallantoic to pulmonary respiration.

Results

Initial hierarchical clustering revealed two distinct, albeit opposing, patterns of hepatic gene expression. Cluster A genes are largely lipolytic and highly expressed in embryos. While, Cluster B genes are lipogenic/thermogenic and mainly controlled by the lipogenic transcription factor THRSPA. Using pairwise comparisons of embryo and hatchling ages, we found 1272 genes that were differentially expressed between embryos and hatchling chicks, including 24 transcription factors and 284 genes that regulate lipid metabolism. The three most differentially-expressed transcripts found in liver of embryos were MOGAT1, DIO3 and PDK4, whereas THRSPA, FASN and DIO2 were highest in hatchlings. An unusual finding was the “ectopic” and extremely high differentially expression of seven feather keratin transcripts in liver of 16 day embryos, which coincides with engorgement of liver with yolk lipids. Gene interaction networks show several transcription factors, transcriptional co-activators/co-inhibitors and their downstream genes that exert a ‘ying-yang’ action on lipid metabolism during the embryo-to-hatching transition. These upstream regulators include ligand-activated transcription factors, sirtuins and Kruppel-like factors.

Conclusions

Our genome-wide transcriptional analysis has greatly expanded the hepatic repertoire of regulatory and metabolic genes involved in the embryo-to-hatchling transition. New knowledge was gained on interactive transcriptional networks and metabolic pathways that enable the abrupt switch from ectothermy (embryo) to endothermy (hatchling) in the chicken. Several transcription factors and their coactivators/co-inhibitors appear to exert opposing actions on lipid metabolism, leading to the predominance of lipolysis in embryos and lipogenesis in hatchlings. Our analysis of hepatic transcriptomes has enabled discovery of opposing, interconnected and interdependent transcriptional regulators that provide precise ying-yang or homeorhetic regulation of lipid metabolism during the critical embryo-to-hatchling transition.

Electronic supplementary material

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Transcriptional profiling of liver in riboflavin-deficient chicken embryos explains impaired lipid utilization, energy depletion, massive hemorrhaging, and delayed feathering

BACKGROUND

A strain of Leghorn chickens (rd/rd), unable to produce a functional riboflavin-binding protein, lays riboflavin-deficient eggs, in which all embryos suddenly die at mid-incubation (days 13-15). This malady, caused by riboflavin deficiency, leads to excessive lipid accumulation in liver, impaired β-oxidation of lipid, and severe hypoglycemia prior to death. We have used high-density chicken microarrays for time-course transcriptional scans of liver in chicken embryos between days 9-15 during this riboflavin-deficiency-induced metabolic catastrophe. For comparison, half of rd/rd embryos (n = 16) were rescued from this calamity by injection of riboflavin just prior to incubation of fertile eggs from rd/rd hens.

RESULTS

No significant differences were found between hepatic transcriptomes of riboflavin-deficient and riboflavin-rescued embryos at the first two ages (days 9 and 11). Overall, we found a 3.2-fold increase in the number of differentially expressed hepatic genes between day 13 (231 genes) and day 15 (734 genes). Higher expression of genes encoding the chicken flavoproteome was more evident in rescued- (15 genes) than in deficient-embryos (4 genes) at day 15. Diminished activity of flavin-dependent enzymes in riboflavin-deficient embryos blocks catabolism of yolk lipids, which normally serves as the predominant source of energy required for embryonic development.

CONCLUSIONS

Riboflavin deficiency in mid-stage embryos leads to reduced expression of numerous genes controlling critical functions, including β-oxidation of lipids, blood coagulation and feathering. Surprisingly, reduced expression of feather keratin 1 was found in liver of riboflavin-deficient embryos at e15, which could be related to their delayed feathering and sparse clubbed down. A large number of genes are expressed at higher levels in liver of riboflavin-deficient embryos; these up-regulated genes control lipid storage/transport, gluconeogenesis, ketogenesis, protein catabolism/ubiquitination and cell death.

Transcriptional analysis of abdominal fat in chickens divergently selected on bodyweight at two ages reveals novel mechanisms controlling adiposity: validating visceral adipose tissue as a dynamic endocrine and metabolic organ

Background

Decades of intensive genetic selection in the domestic chicken (Gallus gallus domesticus) have enabled the remarkable rapid growth of today’s broiler (meat-type) chickens. However, this enhanced growth rate was accompanied by several unfavorable traits (i.e., increased visceral fatness, leg weakness, and disorders of metabolism and reproduction). The present descriptive analysis of the abdominal fat transcriptome aimed to identify functional genes and biological pathways that likely contribute to an extreme difference in visceral fatness of divergently selected broiler chickens.

Methods

We used the Del-Mar 14 K Chicken Integrated Systems microarray to take time-course snapshots of global gene transcription in abdominal fat of juvenile [1-11 weeks of age (wk)] chickens divergently selected on bodyweight at two ages (8 and 36 wk). Further, a RNA sequencing analysis was completed on the same abdominal fat samples taken from high-growth (HG) and low-growth (LG) cockerels at 7 wk, the age with the greatest divergence in body weight (3.2-fold) and visceral fatness (19.6-fold).

Results

Time-course microarray analysis revealed 312 differentially expressed genes (FDR ≤ 0.05) as the main effect of genotype (HG versus LG), 718 genes in the interaction of age and genotype, and 2918 genes as the main effect of age. The RNA sequencing analysis identified 2410 differentially expressed genes in abdominal fat of HG versus LG chickens at 7 wk. The HG chickens are fatter and over-express numerous genes that support higher rates of visceral adipogenesis and lipogenesis. In abdominal fat of LG chickens, we found higher expression of many genes involved in hemostasis, energy catabolism and endocrine signaling, which likely contribute to their leaner phenotype and slower growth. Many transcription factors and their direct target genes identified in HG and LG chickens could be involved in their divergence in adiposity and growth rate.

Conclusions

The present analyses of the visceral fat transcriptome in chickens divergently selected for a large difference in growth rate and abdominal fatness clearly demonstrate that abdominal fat is a very dynamic metabolic and endocrine organ in the chicken. The HG chickens overexpress many transcription factors and their direct target genes, which should enhance in situ lipogenesis and ultimately adiposity. Our observation of enhanced expression of hemostasis and endocrine-signaling genes in diminished abdominal fat of LG cockerels provides insight into genetic mechanisms involved in divergence of abdominal fatness and somatic growth in avian and perhaps mammalian species, including humans.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-4035-5) contains supplementary material, which is available to authorized users.

Mapping of leptin and its syntenic genes to chicken chromosome 1p

Background

Misidentification of the chicken leptin gene has hampered research of leptin signaling in this species for almost two decades. Recently, the genuine leptin gene with a GC-rich (~70%) repetitive-sequence content was identified in the chicken genome but without indicating its genomic position. This suggests that such GC-rich sequences are difficult to sequence and therefore substantial regions are missing from the current chicken genome assembly.

Results

A radiation hybrid panel of chicken-hamster Wg3hCl2 cells was used to map the genome location of the chicken leptin gene. Contrary to our expectations, based on comparative genome mapping and sequence characteristics, the chicken leptin was not located on a microchromosome, which are known to contain GC-rich and repetitive regions, but at the distal tip of the largest chromosome (1p). Following conserved synteny with other vertebrates, we also mapped five additional genes to this genomic region (ARF5, SND1, LRRC4, RBM28, and FLNC), bridging the genomic gap in the current Galgal5 build for this chromosome region. All of the short scaffolds containing these genes were found to consist of GC-rich (54 to 65%) sequences comparing to the average GC-content of 40% on chromosome 1. In this syntenic group, the RNA-binding protein 28 (RBM28) was in closest proximity to leptin. We deduced the full-length of the RBM28 cDNA sequence and profiled its expression patterns detecting a negative correlation (R = − 0.7) between the expression of leptin and of RBM28 across tissues that expressed at least one of the genes above the average level. This observation suggested a local regulatory interaction between these genes. In adipose tissues, we observed a significant increase in RBM28 mRNA expression in breeds with lean phenotypes.

Conclusion

Mapping chicken leptin together with a cluster of five syntenic genes provided the final proof for its identification as the true chicken ortholog. The high GC-content observed for the chicken leptin syntenic group suggests that other similar clusters of genes in GC-rich genomic regions are missing from the current genome assembly (Galgal5), which should be resolved in future assemblies of the chicken genome.

Electronic supplementary material

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Identifying specific proteins involved in eggshell membrane formation using gene expression analysis and bioinformatics

Background

The avian eggshell membranes surround the egg white and provide a structural foundation for calcification of the eggshell which is essential for avian reproduction; moreover, it is also a natural biomaterial with many potential industrial and biomedical applications. Due to the insoluble and stable nature of the eggshell membrane fibres, their formation and protein constituents remain poorly characterized. The purpose of this study was to identify genes encoding eggshell membrane proteins, particularly those responsible for its structural features, by analyzing the transcriptome of the white isthmus segment of the oviduct, which is the specialized region responsible for the fabrication of the membrane fibres.

Results

The Del-Mar 14 K chicken microarray was used to investigate up-regulated expression of transcripts in the white isthmus (WI) compared with the adjacent magnum (Ma) and uterine (Ut) segments of the hen oviduct. Analysis revealed 135 clones hybridizing to over-expressed transcripts (WI/Ma + WI/Ut), and corresponding to 107 NCBI annotated non-redundant Gallus gallus gene IDs. This combined analysis revealed that the structural proteins highly over-expressed in the white isthmus include collagen X (COL10A1), fibrillin-1 (FBN1) and cysteine rich eggshell membrane protein (CREMP). These results validate previous proteomics studies which have identified collagen X (α-1) and CREMP in soluble eggshell extracts. Genes encoding collagen-processing enzymes such as lysyl oxidase homologs 1, 2 and 3 (LOXL1, LOXL2 and LOXL3), prolyl 4 hydroxylase subunit α-2 and beta polypeptide (P4HA2 and P4HB) as well as peptidyl-prolyl cis-trans isomerase C (PPIC) were also over-expressed. Additionally, genes encoding proteins known to regulate disulfide cross-linking, including sulfhydryl oxidase (QSOX1) and thioredoxin (TXN), were identified which suggests that coordinated up-regulation of genes in the white isthmus is associated with eggshell membrane fibre formation.

Conclusions

The present study has identified genes associated with the processing of collagen, other structural proteins, and disulfide-mediated cross-linking during eggshell membrane formation in the white isthmus. Identification of these genes will provide new insight into eggshell membrane structure and mechanisms of formation that will assist in the development of selection strategies to improve eggshell quality and food safety of the table egg.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2013-3) contains supplementary material, which is available to authorized users.

RNA-Seq Analysis of Abdominal Fat in Genetically Fat and Lean Chickens Highlights a Divergence in Expression of Genes Controlling Adiposity, Hemostasis, and Lipid Metabolism

Genetic selection for enhanced growth rate in meat-type chickens (Gallus domesticus) is usually accompanied by excessive adiposity, which has negative impacts on both feed efficiency and carcass quality. Enhanced visceral fatness and several unique features of avian metabolism (i.e., fasting hyperglycemia and insulin insensitivity) mimic overt symptoms of obesity and related metabolic disorders in humans. Elucidation of the genetic and endocrine factors that contribute to excessive visceral fatness in chickens could also advance our understanding of human metabolic diseases. Here, RNA sequencing was used to examine differential gene expression in abdominal fat of genetically fat and lean chickens, which exhibit a 2.8-fold divergence in visceral fatness at 7 wk. Ingenuity Pathway Analysis revealed that many of 1687 differentially expressed genes are associated with hemostasis, endocrine function and metabolic syndrome in mammals. Among the highest expressed genes in abdominal fat, across both genotypes, were 25 differentially expressed genes associated with de novo synthesis and metabolism of lipids. Over-expression of numerous adipogenic and lipogenic genes in the FL chickens suggests that in situ lipogenesis in chickens could make a more substantial contribution to expansion of visceral fat mass than previously recognized. Distinguishing features of the abdominal fat transcriptome in lean chickens were high abundance of multiple hemostatic and vasoactive factors, transporters, and ectopic expression of several hormones/receptors, which could control local vasomotor tone and proteolytic processing of adipokines, hemostatic factors and novel endocrine factors. Over-expression of several thrombogenic genes in abdominal fat of lean chickens is quite opposite to the pro-thrombotic state found in obese humans. Clearly, divergent genetic selection for an extreme (2.5-2.8-fold) difference in visceral fatness provokes a number of novel regulatory responses that govern growth and metabolism of visceral fat in this unique avian model of juvenile-onset obesity and glucose-insulin imbalance.

Discovery and characterization of the first genuine avian leptin gene in the rock dove (Columba livia)

Leptin, the key regulator of mammalian energy balance, has been at the center of a great controversy in avian biology for the last 15 years since initial reports of a putative leptin gene (LEP) in chickens. Here, we characterize a novel LEP in rock dove (Columba livia) with low similarity of the predicted protein sequence (30% identity, 47% similarity) to the human ortholog. Searching the Sequence-Read-Archive database revealed leptin transcripts, in the dove's liver, with 2 noncoding exons preceding 2 coding exons. This unusual 4-exon structure was validated by sequencing of a GC-rich product (76% GC, 721 bp) amplified from liver RNA by RT-PCR. Sequence alignment of the dove leptin with orthologous leptins indicated that it consists of a leader peptide (21 amino acids; aa) followed by the mature protein (160 aa), which has a putative structure typical of 4-helical-bundle cytokines except that it is 12 aa longer than human leptin. Extra residues (10 aa) were located within the loop between 2 5'-helices, interrupting the amino acid motif that is conserved in tetrapods and considered essential for activation of leptin receptor (LEPR) but not for receptor binding per se. Quantitative RT-PCR of 11 tissues showed highest (P < .05) expression of LEP in the dove's liver, whereas the dove LEPR peaked (P < .01) in the pituitary. Both genes were prominently expressed in the gonads and at lower levels in tissues involved in mammalian leptin signaling (adipose; hypothalamus). A bioassay based on activation of the chicken LEPR in vitro showed leptin activity in the dove's circulation, suggesting that dove LEP encodes an active protein, despite the interrupted loop motif. Providing tools to study energy-balance control at an evolutionary perspective, our original demonstration of leptin signaling in dove predicts a more ancient role of leptin in growth and reproduction in birds, rather than appetite control.

Discovery of the elusive leptin in birds: identification of several 'missing links' in the evolution of leptin and its receptor

Leptin is a pleiotropic protein best known for regulation of appetite and fat storage in mammals. While many leptin orthologs have been identified among vertebrates, an authentic leptin in birds has remained elusive and controversial. Here we identify leptin sequence from the Peregrine falcon, Falco peregrinus (pfleptin), and identify sequences from two other birds (mallard and zebra finch), and 'missing' vertebrates (elephant shark, alligator, Indian python, Chinese soft-shelled turtle, and coelacanth). The pattern of genes surrounding leptin (snd1, rbm28) is syntenic between the falcon and mammalian genomes. Phylogenetic analysis of all known leptin protein sequences improves our understanding of leptin's evolution. Structural modeling of leptin orthologs highlights a highly conserved hydrophobic core in the four-helix cytokine packing domain. A docked model of leptin with the leptin receptor for Peregrine falcon reveals several conserved amino acids important for the interaction and possible coevolution of leptin with its receptor. We also show for the first time, an authentic avian leptin sequence that activates the JAK-STAT signaling pathway. These newly identified sequences, structures, and tools for avian leptin and its receptor will allow elucidation of the function of these proteins in feral and domestic birds.

Genome-wide interval mapping using SNPs identifies new QTL for growth, body composition and several physiological variables in an F2 intercross between fat and lean chicken lines

BACKGROUND

For decades, genetic improvement based on measuring growth and body composition traits has been successfully applied in the production of meat-type chickens. However, this conventional approach is hindered by antagonistic genetic correlations between some traits and the high cost of measuring body composition traits. Marker-assisted selection should overcome these problems by selecting loci that have effects on either one trait only or on more than one trait but with a favorable genetic correlation. In the present study, identification of such loci was done by genotyping an F2 intercross between fat and lean lines divergently selected for abdominal fatness genotyped with a medium-density genetic map (120 microsatellites and 1302 single nucleotide polymorphisms). Genome scan linkage analyses were performed for growth (body weight at 1, 3, 5, and 7 weeks, and shank length and diameter at 9 weeks), body composition at 9 weeks (abdominal fat weight and percentage, breast muscle weight and percentage, and thigh weight and percentage), and for several physiological measurements at 7 weeks in the fasting state, i.e. body temperature and plasma levels of IGF-I, NEFA and glucose. Interval mapping analyses were performed with the QTLMap software, including single-trait analyses with single and multiple QTL on the same chromosome.

RESULTS

Sixty-seven QTL were detected, most of which had never been described before. Of these 67 QTL, 47 were detected by single-QTL analyses and 20 by multiple-QTL analyses, which underlines the importance of using different statistical models. Close analysis of the genes located in the defined intervals identified several relevant functional candidates, such as ACACA for abdominal fatness, GHSR and GAS1 for breast muscle weight, DCRX and ASPSCR1 for plasma glucose content, and ChEBP for shank diameter.

CONCLUSIONS

The medium-density genetic map enabled us to genotype new regions of the chicken genome (including micro-chromosomes) that influenced the traits investigated. With this marker density, confidence intervals were sufficiently small (14 cM on average) to search for candidate genes. Altogether, this new information provides a valuable starting point for the identification of causative genes responsible for important QTL controlling growth, body composition and metabolic traits in the broiler chicken.

Transcriptional analysis of abdominal fat in genetically fat and lean chickens reveals adipokines, lipogenic genes and a link between hemostasis and leanness

Background

This descriptive study of the abdominal fat transcriptome takes advantage of two experimental lines of meat-type chickens (Gallus domesticus), which were selected over seven generations for a large difference in abdominal (visceral) fatness. At the age of selection (9 wk), the fat line (FL) and lean line (LL) chickens exhibit a 2.5-fold difference in abdominal fat weight, while their feed intake and body weight are similar. These unique avian models were originally created to unravel genetic and endocrine regulation of adiposity and lipogenesis in meat-type chickens. The Del-Mar 14K Chicken Integrated Systems microarray was used for a time-course analysis of gene expression in abdominal fat of FL and LL chickens during juvenile development (1–11 weeks of age).

Results

Microarray analysis of abdominal fat in FL and LL chickens revealed 131 differentially expressed (DE) genes (FDR≤0.05) as the main effect of genotype, 254 DE genes as an interaction of age and genotype and 3,195 DE genes (FDR≤0.01) as the main effect of age. The most notable discoveries in the abdominal fat transcriptome were higher expression of many genes involved in blood coagulation in the LL and up-regulation of numerous adipogenic and lipogenic genes in FL chickens. Many of these DE genes belong to pathways controlling the synthesis, metabolism and transport of lipids or endocrine signaling pathways activated by adipokines, retinoid and thyroid hormones.

Conclusions

The present study provides a dynamic view of differential gene transcription in abdominal fat of chickens genetically selected for fatness (FL) or leanness (LL). Remarkably, the LL chickens over-express a large number of hemostatic genes that could be involved in proteolytic processing of adipokines and endocrine factors, which contribute to their higher lipolysis and export of stored lipids. Some of these changes are already present at 1 week of age before the divergence in fatness. In contrast, the FL chickens have enhanced expression of numerous lipogenic genes mainly after onset of divergence, presumably directed by multiple transcription factors. This transcriptional analysis shows that abdominal fat of the chicken serves a dual function as both an endocrine organ and an active metabolic tissue, which could play a more significant role in lipogenesis than previously thought.

Glucocorticoid-induced changes in gene expression in embryonic anterior pituitary cells

Within the anterior pituitary gland, glucocorticoids such as corticosterone (CORT) provide negative feedback to inhibit adrenocorticotropic hormone secretion and act to regulate production of other hormones including growth hormone (GH). The ontogeny of GH production during chicken embryonic and rat fetal development is controlled by glucocorticoids. The present study was conducted to characterize effects of glucocorticoids on gene expression within embryonic pituitary cells and to identify genes that are rapidly and directly regulated by glucocorticoids. Chicken embryonic pituitary cells were cultured with CORT for 1.5, 3, 6, 12, and 24 h in the absence and presence of cycloheximide (CHX) to inhibit protein synthesis. RNA was analyzed with custom microarrays containing 14,053 chicken cDNAs, and results for selected genes were confirmed by quantitative reverse transcription real-time PCR (qRT-PCR). Levels of GH mRNA were maximally induced by 6 h of CORT treatment, and this response was blocked by CHX. Expression of 396 genes was affected by CORT, and of these, mRNA levels for 46 genes were induced or repressed within 6 h. Pathway analysis of genes regulated by CORT in the absence of CHX revealed networks of genes associated with endocrine system development and cellular development. Eleven genes that were induced within 6 h in the absence and presence of CHX were identified, and eight were confirmed by qRT-PCR. The expression profiles and canonical pathways defined in this study will be useful for future analyses of glucocorticoid action and regulation of pituitary function.

Insulin immuno-neutralization in fed chickens: effects on liver and muscle transcriptome

Chickens mimic an insulin-resistance state by exhibiting several peculiarities with regard to plasma glucose level and its control by insulin. To gain insight into the role of insulin in the control of chicken transcriptome, liver and leg muscle transcriptomes were compared in fed controls and "diabetic" chickens, at 5 h after insulin immuno-neutralization, using 20.7K-chicken oligo-microarrays. At a level of false discovery rate <0.01, 1,573 and 1,225 signals were significantly modified by insulin privation in liver and muscle, respectively. Microarray data agreed reasonably well with qRT-PCR and some protein level measurements. Differentially expressed mRNAs with human ID were classified using Biorag analysis and Ingenuity Pathway Analysis. Multiple metabolic pathways, structural proteins, transporters and proteins of intracellular trafficking, major signaling pathways, and elements of the transcriptional control machinery were largely represented in both tissues. At least 42 mRNAs have already been associated with diabetes, insulin resistance, obesity, energy expenditure, or identified as sensors of metabolism in mice or humans. The contribution of the pathways presently identified to chicken physiology (particularly those not yet related to insulin) needs to be evaluated in future studies. Other challenges include the characterization of "unknown" mRNAs and the identification of the steps or networks, which disturbed tissue transcriptome so extensively, quickly after the turning off of the insulin signal. In conclusion, pleiotropic effects of insulin in chickens are further evidenced; major pathways controlled by insulin in mammals have been conserved despite the presence of unique features of insulin signaling in chicken muscle.

Functional genomics in chickens: development of integrated-systems microarrays for transcriptional profiling and discovery of regulatory pathways

The genetic networks that govern the differentiation and growth of major tissues of economic importance in the chicken are largely unknown. Under a functional genomics project, our consortium has generated 30 609 expressed sequence tags (ESTs) and developed several chicken DNA microarrays, which represent the Chicken Metabolic/Somatic (10 K) and Neuroendocrine/Reproductive (8 K) Systems (http://udgenome.ags.udel.edu/cogburn/). One of the major challenges facing functional genomics is the development of mathematical models to reconstruct functional gene networks and regulatory pathways from vast volumes of microarray data. In initial studies with liver-specific microarrays (3.1 K), we have examined gene expression profiles in liver during the peri-hatch transition and during a strong metabolic perturbation—fasting and re-feeding—in divergently selected broiler chickens (fast vs. slow-growth lines). The expression of many genes controlling metabolic pathways is dramatically altered by these perturbations. Our analysis has revealed a large number of clusters of functionally related genes (mainly metabolic enzymes and transcription factors) that control major metabolic pathways. Currently, we are conducting transcriptional profiling studies of multiple tissues during development of two sets of divergently selected broiler chickens (fast vs. slow growing and fat vs. lean lines). Transcriptional profiling across multiple tissues should permit construction of a detailed genetic blueprint that illustrates the developmental events and hierarchy of genes that govern growth and development of chickens. This review will briefly describe the recent acquisition of chicken genomic resources (ESTs and microarrays) and our consortium's efforts to help launch the new era of functional genomics in the chicken.

Transcriptional profiling of hypothalamus during development of adiposity in genetically selected fat and lean chickens

The hypothalamus integrates peripheral signals to regulate food intake, energy metabolism, and ultimately growth rate and body composition in vertebrates. Deviations in hypothalamic regulatory controls can lead to accumulation of excess body fat. Many regulatory genes involved in this process remain unidentified, and comparative studies may be helpful to unravel evolutionarily conserved mechanisms controlling body weight and food intake. In the present study, divergently selected fat (FL) and lean (LL) lines of chickens were used to characterize differences in hypothalamic gene expression in these unique genetic lines that develop differences in adiposity without differences in food intake or body weight. Hypothalamic transcriptional profiles were defined with cDNA microarrays before and during divergence of adiposity between the two lines. Six differentially expressed genes identified in chickens are related to genes associated with control of body fat in transgenic or knockout mice, supporting the importance of these genes across species. We identified differences in expression of nine genes involved in glucose metabolism, suggesting that alterations in hypothalamic glycolysis might contribute to differences in levels of body fat between genotypes. Expression of the sweet taste receptor (TAS1R1), which in mammals is involved in glucose sensing and energy uptake, was also higher in FL chickens, suggesting that early differences in glucose sensing might alter the set point for subsequent body composition. Differences in expression of genes associated with tumor necrosis factor (TNF) signaling were also noted. In summary, we identified alterations in transcriptional and metabolic processes within the hypothalamus that could contribute to excessive accumulation of body fat in FL chickens in the absence of differences in food intake, thereby contributing to the genetic basis for obesity in this avian model.

Transcriptional and pathway analysis in the hypothalamus of newly hatched chicks during fasting and delayed feeding

Background

The hypothalamus plays a central role in regulating appetite and metabolism. However, the gene networks within the hypothalamus that regulate feed intake and metabolism, and the effects of fasting on those pathways are not completely understood in any species. The present experiment evaluated global hypothalamic gene expression in newly hatched chicks using microarray analysis to elucidate genes and pathways regulated by feeding, fasting, and delayed feeding. Ten groups of chicks were sampled over four days post-hatch, including fed, fasted, and 48 h fasted followed by access to feed for 4 h, 24 h, and 48 h. Hypothalamic samples were collected for microarray analysis (n = 4). Expression patterns of selected genes were confirmed by quantitative real-time PCR. Pathway analysis of the microarray results predicted a network of genes involved in neuropeptide or neurotransmitter signaling. To confirm the functionality of this predicted gene network, hypothalamic neurons from fed and fasted chicks were isolated and cultured in the presence of neuropeptide Y, somatostatin, α-melanocyte stimulating hormone, norepinephrine, and L-phospho-serine. Results confirmed functional relationships among members of the predicted gene network. Moreover, the effects observed were dependant upon the nutritional state of the animals (fed vs. fasted).

Results

Differences in gene expression (≥ 1.6 fold) were detected in 1,272 genes between treatments, and of those, 119 genes were significantly (P < 0.05) different. Pathway Miner analysis revealed that six genes (SSTR5, NPY5R, POMC, ADRB2, GRM8, and RLN3) were associated within a gene network. In vitro experiments with primary hypothalamic neurons confirmed that receptor agonists involved in this network regulated expression of other genes in the predicted network, and this regulation within the network was influenced by the nutritional status and age of the chick.

Conclusions

Microarray analysis of the hypothalamus during different nutritional states revealed that many genes are differentially regulated. We found that functional interactions exist among six differentially regulated genes associated within a putative gene network from this experiment. Considering that POMC, an important gene in controlling metabolism, was central to this network, this gene network may play an important role in regulation of feeding and metabolism in birds.

Mapping main, epistatic and sex-specific QTL for body composition in a chicken population divergently selected for low or high growth rate

Background

Delineating the genetic basis of body composition is important to agriculture and medicine. In addition, the incorporation of gene-gene interactions in the statistical model provides further insight into the genetic factors that underlie body composition traits. We used Bayesian model selection to comprehensively map main, epistatic and sex-specific QTL in an F₂ reciprocal intercross between two chicken lines divergently selected for high or low growth rate.

Results

We identified 17 QTL with main effects across 13 chromosomes and several sex-specific and sex-antagonistic QTL for breast meat yield, thigh + drumstick yield and abdominal fatness. Different sets of QTL were found for both breast muscles [Pectoralis (P) major and P. minor], which suggests that they could be controlled by different regulatory mechanisms. Significant interactions of QTL by sex allowed detection of sex-specific and sex-antagonistic QTL for body composition and abdominal fat. We found several female-specific P. major QTL and sex-antagonistic P. minor and abdominal fatness QTL. Also, several QTL on different chromosomes interact with each other to affect body composition and abdominal fatness.

Conclusions

The detection of main effects, epistasis and sex-dimorphic QTL suggest complex genetic regulation of somatic growth. An understanding of such regulatory mechanisms is key to mapping specific genes that underlie QTL controlling somatic growth in an avian model.

Gene expression profiling to identify eggshell proteins involved in physical defense of the chicken egg

BACKGROUND

As uricoletic animals, chickens produce cleidoic eggs, which are self-contained bacteria-resistant biological packages for extra-uterine development of the chick embryo. The eggshell constitutes a natural physical barrier against bacterial penetration if it forms correctly and remains intact. The eggshell's remarkable mechanical properties are due to interactions among mineral components and the organic matrix proteins. The purpose of our study was to identify novel eggshell proteins by examining the transcriptome of the uterus during calcification of the eggshell. An extensive bioinformatic analysis on genes over-expressed in the uterus allowed us to identify novel eggshell proteins that contribute to the egg's natural defenses.

RESULTS

Our 14 K Del-Mar Chicken Integrated Systems microarray was used for transcriptional profiling in the hen's uterus during eggshell deposition. A total of 605 transcripts were over-expressed in the uterus compared with the magnum or white isthmus across a wide range of abundance (1.1- to 79.4-fold difference). The 605 highly-expressed uterine transcripts correspond to 469 unique genes, which encode 437 different proteins. Gene Ontology (GO) analysis was used for interpretation of protein function. The most over-represented GO terms are related to genes encoding ion transport proteins, which provide eggshell mineral precursors. Signal peptide sequence was found for 54 putative proteins secreted by the uterus during eggshell formation. Many functional proteins are involved in calcium binding or biomineralization--prerequisites for interacting with the mineral phase during eggshell fabrication. While another large group of proteins could be involved in proper folding of the eggshell matrix. Many secreted uterine proteins possess antibacterial properties, which would protect the egg against microbial invasion. A final group includes proteases and protease inhibitors that regulate protein activity in the acellular uterine fluid where eggshell formation takes place.

CONCLUSIONS

Our original study provides the first detailed description of the chicken uterus transcriptome during formation of the eggshell. We have discovered a cache of about 600 functional genes and identified a large number of encoded proteins secreted into uterine fluid for fabrication of the eggshell and chemical protection of the egg. Some of these uterine genes could prove useful as biological markers for genetic improvement of phenotypic traits (i.e., egg and eggshell quality).

Regulation of ANKRD9 expression by lipid metabolic perturbations

Fatty acid oxidation (FAO) defects cause abnormal lipid accumulation in various tissues, which provides an opportunity to uncover novel genes that are involved in lipid metabolism. During a gene expression study in the riboflavin deficient induced FAO disorder in the chicken, we discovered the dramatic increase in mRNA levels of an uncharacterized gene, ANKRD9. No functions have been ascribed to ANKRD9 and its orthologs, although their sequences are well conserved among vertebrates. To provide insight into the function of ANKRD9, the expression of ANKRD9 mRNA in lipidperturbed paradigms was examined. The hepatic mRNA level of ANKRD9 was repressed by thyroid hormone (T(3)) and fasting, elevated by re-feeding upon fasting. However, ANKRD9 mRNA level is reduced in response to apoptosis. Transient transfection assay with green fluorescent protein tagged- ANKRD9 showed that this protein is localized within the cytoplasm. These findings point to the possibility that ANKRD9 is involved in intracellular lipid accumulation. [BMB reports 2009; 42(9): 568-573].

QTL for several metabolic traits map to loci controlling growth and body composition in an F2 intercross between high- and low-growth chicken lines

Quantitative trait loci (QTL) for metabolic and body composition traits were mapped at 7 and 9 wk, respectively, in an F2 intercross between high-growth and low-growth chicken lines. These lines also diverged for abdominal fat percentage (AFP) and plasma insulin-like growth factor-I (IGF-I), insulin, and glucose levels. Genotypings were performed with 129 microsatellite markers covering 21 chromosomes. A total of 21 QTL with genomewide level of significance were detected by single-trait analyses for body weight (BW), breast muscle weight (BMW) and percentage (BMP), AF weight (AFW) and percentage (AFP), shank length (ShL) and diameter (ShD), fasting plasma glucose level (Gluc), and body temperature (Tb). Other suggestive QTL were identified for these parameters and for plasma IGF-I and nonesterified fatty acid levels. QTL controlling adiposity and Gluc were colocalized on GGA3 and GGA5 and QTL for BW, ShL and ShD, adiposity, and Tb on GGA4. Multitrait analyses revealed two QTL controlling Gluc and AFP on GGA5 and Gluc and Tb on GGA26. Significant effects of the reciprocal cross were observed on BW, ShD, BMW, and Gluc, which may result from mtDNA and/or maternal effects. Most QTL regions for Gluc and adiposity harbor genes for which alleles have been associated with increased susceptibility to diabetes and/or obesity in humans. Identification of genes responsible for these metabolic QTL will increase our understanding of the constitutive “hyperglycemia” found in chickens. Furthermore, a comparative approach could provide new information on the genetic causes of diabetes and obesity in humans.

A comprehensive analysis of QTL for abdominal fat and breast muscle weights on chicken chromosome 5 using a multivariate approach

Quantitative trait loci (QTL) influencing the weight of abdominal fat (AF) and of breast muscle (BM) were detected on chicken chromosome 5 (GGA5) using two successive F(2) crosses between two divergently selected 'Fat' and 'Lean' INRA broiler lines. Based on these results, the aim of the present study was to identify the number, location and effects of these putative QTL by performing multitrait and multi-QTL analyses of the whole available data set. Data concerned 1186 F(2) offspring produced by 10 F(1) sires and 85 F(1) dams. AF and BM traits were measured on F(2) animals at slaughter, at 8 (first cross) or 9 (second cross) weeks of age. The F(0), F(1) and F(2) birds were genotyped for 11 microsatellite markers evenly spaced along GGA5. Before QTL detection, phenotypes were adjusted for the fixed effects of sex, F(2) design, hatching group within the design, and for body weight as a covariable. Univariate analyses confirmed the QTL segregation for AF and BM on GGA5 in male offspring, but not in female offspring. Analyses of male offspring data using multitrait and linked-QTL models led us to conclude the presence of two QTL on the distal part of GGA5, each controlling one trait. Linked QTL models were applied after correction of phenotypic values for the effects of these distal QTL. Several QTL for AF and BM were then discovered in the central region of GGA5, splitting one large QTL region for AF into several distinct QTL. Neither the 'Fat' nor the 'Lean' line appeared to be fixed for any QTL genotype. These results have important implications for prospective fine mapping studies and for the identification of underlying genes and causal mutations.

Effects of BDNF, T3, and corticosterone on expression of the hypothalamic obesity gene network in vivo and in vitro

Hypothalamic neuropeptides, neurotrophins, and systemic hormones modulate food intake and body composition. Although advances toward elucidating these interactions have been made, many aspects of the underlying mechanisms remain vague. Hypothalami from fat and lean chicken lines were assessed for differential expression of anabolic/orexigenic and catabolic/anorexigenic genes. Effects of triiodothyronine (T(3)), corticosterone (Cort), and brain-derived neurotrophic factor (BDNF) on expression of anabolic/orexigenic and catabolic/anorexigenic genes were tested in cultures of hypothalamic neurons. From this, we found that BDNF increased and T(3) decreased gene expression for BDNF, leptin receptor (LEPR), pro-opiomelanocortin (POMC), thyrotropin releasing hormone (TRH), and agouti-related protein (AGRP). Thyroid hormone levels were manipulated during development to show that T(3) inhibited BDNF, TRH, and BDNF receptor gene expression. Delivery of T(3), Cort, T(3) plus Cort, or vehicle in vivo continuously for 72 h indicated that Cort and T(3) have overlapping roles in regulating TRH, LEPR, and POMC gene expression and that Cort and T(3) regulate BDNF, neuropeptide Y, and AGRP in opposite directions. Collectively, these findings suggest that interactions between the neuropeptide BDNF and the hormones T(3) and/or Cort may constitute a homeostatic mechanism that links hypothalamic energy regulation controlling body composition.

Insulin immuno-neutralization in chicken: effects on insulin signaling and gene expression in liver and muscle

In order to evaluate the role of insulin in chicken, an insulin immuno-neutralization was performed. Fed chickens received 1 or 3 i.v. injections of anti-insulin serum (2-h intervals), while fed or fasted controls received normal serum. Measurements included insulin signaling cascade (at 1 h in liver and muscle), metabolic or endocrine plasma parameters (at 1 and 5 h), and qRT-PCR analysis (at 5 h) of 23 genes involved in endocrine regulation, metabolisms, and transcription. Most plasma parameters and food intake were altered by insulin privation as early as 1 h and largely at 5 h. The initial steps of insulin signaling pathways including insulin receptor (IR), IR substrate-1 (IRS-1), and Src homology collagen and downstream elements: phosphatidylinositol 3-kinase (PI3K), Akt, GSK3, ERK2, and S6 ribosomal protein) were accordingly turned off in the liver. In the muscle, IR, IRS-1 tyrosine phosphorylation, and PI3K activity remained unchanged, whereas several subsequent steps were altered by insulin privation. In both tissues, AMPK was not altered. In the liver, insulin privation decreased Egr1, PPAR gamma, SREBP1, THRSP alpha (spot 14), D2-deiodinase, glucokinase (GK), and fatty acid synthase (whereas D3-deiodinase and IGF-binding protein 1 transcripts were up-regulated. Liver SREBP1 and GK and plasma IGFBP1 proteins were accordingly down- and up-regulated. In the muscle, PPAR beta delta and atrogin-1 mRNA increased and Egr1 mRNA decreased. Changes in messengers were partly mimicked by fasting. Thus, insulin signaling in muscle is peculiar in chicken and is strictly dependent on insulin in fed status. The 'diabetic' status induced by insulin immuno-neutralization is accompanied by impairments of glucagon secretion, thyroid axis, and expression of several genes involved in regulatory pathways or metabolisms, evidencing pleiotropic effects of insulin in fed chicken.

Functional genomics of the chicken--a model organism

Since the sequencing of the genome and the development of high-throughput tools for the exploration of functional elements of the genome, the chicken has reached model organism status. Functional genomics focuses on understanding the function and regulation of genes and gene products on a global or genome-wide scale. Systems biology attempts to integrate functional information derived from multiple high-content data sets into a holistic view of all biological processes within a cell or organism. Generation of a large collection ( approximately 600K) of chicken expressed sequence tags, representing most tissues and developmental stages, has enabled the construction of high-density microarrays for transcriptional profiling. Comprehensive analysis of this large expressed sequence tag collection and a set of approximately 20K full-length cDNA sequences indicate that the transcriptome of the chicken represents approximately 20,000 genes. Furthermore, comparative analyses of these sequences have facilitated functional annotation of the genome and the creation of several bioinformatic resources for the chicken. Recently, about 20 papers have been published on transcriptional profiling with DNA microarrays in chicken tissues under various conditions. Proteomics is another powerful high-throughput tool currently used for examining the dynamics of protein expression in chicken tissues and fluids. Computational analyses of the chicken genome are providing new insight into the evolution of gene families in birds and other organisms. Abundant functional genomic resources now support large-scale analyses in the chicken and will facilitate identification of transcriptional mechanisms, gene networks, and metabolic or regulatory pathways that will ultimately determine the phenotype of the bird. New technologies such as marker-assisted selection, transgenics, and RNA interference offer the opportunity to modify the phenotype of the chicken to fit defined production goals. This review focuses on functional genomics in the chicken and provides a road map for large-scale exploration of the chicken genome.

Manipulation of thyroid status and/or GH injection alters hepatic gene expression in the juvenile chicken

Both thyroid hormone (T3) and growth hormone (GH) are important regulators of somatic growth in birds and mammals. Although T3-mediated gene transcription is well known, the molecular basis of T3 interaction with GH on growth and development of birds remains unknown. In earlier studies, we discovered that exogenous GH alone increased accumulation of visceral fat in young chickens, while the combination of GH injections and dietary T3 worked synergistically to deplete body fat. In the present study, cDNA microarray and quantitative RT-PCR analyses enabled us to examine hepatic gene expression in young chickens after chronic manipulation of thyroid status and GH injection alone or in combination with T3. Thyroid status modulates expression of common and unique sets of genes involved in a wide range of molecular functions (i.e., energy metabolism, storage and transport, signal transduction, protein turnover and drug detoxification). Hepatic expression of 35 genes was altered by hypothyroidism (e.g., ADFP, ANGPTL3, GSTalpha, CAT, PPARG, HMGCL, GHR, IGF1, STAT3, THRSPalpha), whereas hyperthyroidism affected expression of another cluster of 13 genes (e.g., IGFBP1, KHK, LDHB, BAIA2L1, SULT1B, TRIAD3). Several genes were identified which have not been previously ascribed as T3 responsive (e.g., DEFB9, EPS8L2, ARHGAP1, LASS2, INHBC). Exogenous GH altered expression of 17 genes (e.g., CCAR1, CYP2C45, GYS2, ENOB, HK1, FABP1, SQLE, SOCS2, UPG2). The T3+GH treatment depleted the greatest amount of body fat, where 34 differentially expressed genes were unique to this group (e.g., C/EBP, CDC42EP1, SYDE2, PCK2, PIK4CA, TH1L, GPT2, BHMT). The marked reduction in body fat brought about by the T3+GH synergism could involve modulation of hormone signaling via altered activity of the Ras superfamily of molecular switches, which control diverse biological processes. In conclusion, this study provides the first global analysis of endocrine (T3 and GH) regulation of hepatic gene transcription in the chicken.

Functional Annotation of Genomic Data with Metabolic Inference

Metabolomics is an appealing new approach in systems biology aimed at enabling an improved understanding of the dynamic biochemical composition of living systems. Biological systems are remarkably complex. Importantly, metabolites are the end products of cellular regulatory processes, and their concentrations reflect the ultimate response of a biological system to genetic or environmental changes. In this article, we describe the components of lipid metabolomics and then use them to investigate the metabolic basis for increased abdominal adiposity in 2 strains of divergently selected chickens. Lipid metabolomics were chosen due to the availability of well-developed analytical platforms and the pervasive physiological importance of lipids in metabolism. The analysis suggests that metabolic shifts that result in increased abdominal adiposity are not universal and vary with genetic background. Metabolomics can be used to reverse engineer selection programs through superior metabolic descriptions that can then be associated with specific gene networks and transcriptional profiles.

Avian apolipoprotein A-V binds to LDL receptor gene family members

Apolipoprotein A-V (apoA-V) affects plasma triglyceride (TG) levels; however, the properties of apoA-V that mediate its action(s) are still incompletely understood. It is unclear how apoA-V, whose plasma concentration is extremely low, can affect the pronounced TG differences observed in individuals with various apoA-V dysfunctions. To gain novel insights into apoA-V biology, we expanded our previous studies in the chicken to this apolipoprotein. First, we characterized the first avian apoA-V, revealing its expression not only in liver and small intestine but also in brain, kidney, and ovarian follicles and showing its presence in the circulation. Second, we demonstrate directly that galline apoA-V binds to the major LDL receptor family member (LR) of the laying hen and that this interaction does not depend on the association of the apolipoprotein with lipid or lipoproteins. We propose that a direct interaction with LRs may represent a novel, additional mechanism for the modulation of TG levels by apoA-V.

Chicken genomics resource: sequencing and annotation of 35,407 ESTs from single and multiple tissue cDNA libraries and CAP3 assembly of a chicken gene index

Its accessibility, unique evolutionary position, and recently assembled genome sequence have advanced the chicken to the forefront of comparative genomics and developmental biology research as a model organism. Several chicken expressed sequence tag (EST) projects have placed the chicken in 10th place for accrued ESTs among all organisms in GenBank. We have completed the single-pass 5′-end sequencing of 37,557 chicken cDNA clones from several single and multiple tissue cDNA libraries and have entered 35,407 EST sequences into GenBank. Our chicken EST sequences and those found in public databases (on July 1, 2004) provided a total of 517,727 public chicken ESTs and mRNAs. These sequences were used in the CAP3 assembly of a chicken gene index composed of 40,850 contigs and 79,192 unassembled singlets. The CAP3 contigs show a 96.7% match to the chicken genome sequence. The University of Delaware (UD) EST collection (43,928 clones) was assembled into 19,237 nonredundant sequences (13,495 contigs and 5,742 unassembled singlets). The UD collection contains 6,223 unique sequences that are not found in other public EST collections but show a 76% match to the chicken genome sequence. Our chicken contig and singlet sequences were annotated according to the highest BlastX and/or BlastN hits. The UD CAP3 contig assemblies and singlets are searchable by nucleotide sequence or key word ( http://cogburn.dbi.udel.edu ), and the cDNA clones are readily available for distribution from the chick EST website and clone repository ( http://www.chickest.udel.edu ). The present paper describes the construction and normalization of single and multiple tissue chicken cDNA libraries, high-throughput EST sequencing from these libraries, the CAP3 assembly of a chicken gene index from all public ESTs, and the identification of several nonredundant chicken gene sets for production of custom DNA microarrays.

Gene expression profiling during cellular differentiation in the embryonic pituitary gland using cDNA microarrays

The anterior pituitary is comprised of five major hormone-secreting cell types that differentiate during embryonic development in a temporally distinct manner. Microarrays containing 5,128 unique cDNAs expressed in the chicken neuroendocrine system were produced and used to identify genes with potential involvement in the onset of thyroid-stimulating hormone beta-subunit (TSHbeta), growth hormone (GH), and prolactin (PRL) mRNA during embryonic development. We identified 352 cDNAs that were differentially expressed (P < or = 0.05) on embryonic day 10 (e10), e12, e14, or e17, the period of thyrotroph, somatotroph, and lactotroph differentiation. Self-organizing maps were used to identify genes that may function to initiate hormone gene transcription. Consistent with cellular ontogeny, TSHbeta mRNA increased steadily between e10 and e17, GH mRNA increased between e12 and e17, and PRL mRNA did not increase until e17. Expression of 141 genes increased in a manner similar to TSHbeta mRNA, and 64 genes decreased between e10 and e17. Although genes with these expression profiles are likely involved in development of the pituitary gland as a whole, some of these could be specifically associated with thyrotroph differentiation. Similarly, the expression profiles of 69 and 61 genes indicate a potential involvement in the induction of GH and PRL mRNA, respectively. Quantitative real-time RT-PCR was used to confirm microarray results for 31 genes. This is the first study to evaluate changes in anterior pituitary gene expression during embryonic development of any species using microarrays, and numerous transcription factors and signaling molecules not previously implicated in pituitary development were identified.

Duplicated Spot 14 genes in the chicken: characterization and identification of polymorphisms associated with abdominal fat traits

In mammals, thyroid hormone responsive Spot 14 (THRSP) is a small acidic protein that is predominately expressed in lipogenic tissue (i.e., liver, abdominal fat and the mammary gland). This gene has been postulated to play a role in lipogenesis, since it responds to thyroid hormone stimulation, high glucose levels and it is localized to a chromosomal region implicated in obesity. In this paper, we report the identification and characterization of duplicated polymorphic paralogs of Spot 14 in the chicken, THRSPalpha and THRSPbeta. Despite low similarity in amino acid (aa) sequence between chickens and mammals, other properties of Spot 14 (i.e., pI, subcellular localization, transcriptional control and functional domains) appear to be highly conserved. Furthermore, a synteny group of THRSP and its flanking genes [NADH dehydrogenase (NDUFC2) and glucosyltransferase (ALG8)] appears to be conserved among chickens, humans, mice and rats. Polymorphic alleles, involving a variable number of tandem repeats (VNTR), were discovered in the putative protein coding region of the duplicated chicken THRSPalpha (9 bp) and THRSPbeta (6 or 12 bp) genes. Our study shows that the THRSPalpha locus is associated with abdominal fat traits in a broilerxLeghorn resource population.

Systems-wide chicken DNA microarrays, gene expression profiling, and discovery of functional genes

The goal of our current consortium project is to launch a new era--functional genomics of poultry--by providing genomic resources [expressed sequence tags (EST) and DNA microarrays] and by examining global gene expression in target tissues of chickens. DNA microarray analysis has been a fruitful strategy for the identification of functional genes in several model organisms (i.e., human, rodents, fruit fly, etc.). We have constructed and normalized five tissue-specific or multiple-tissue chicken cDNA libraries [liver, fat, breast, and leg muscle/epiphyseal growth plate, pituitary/hypothalamus/pineal, and reproductive tract (oviduct/ovary/testes)] for high-throughput DNA sequencing of EST. DNA sequence clustering was used to build contigs of overlapping sequence and to identify unique, non-redundant EST clones (unigenes), which permitted printing of systems-wide chicken DNA microarrays. One of the most promising genetic resources for gene exploration and functional gene mapping is provided by two sets of experimental lines of broiler-type chickens developed at INRA, France, by divergent selection for extremes in growth traits (fast-growing versus slow-growing; fatness versus leanness at a similar growth rate). We are using DNA microarrays for global gene expression profiling to identify candidate genes and to map growth, metabolic, and regulatory pathways that control important production traits. Candidate genes will be used for functional gene mapping and QTL analysis of F2 progeny from intercrosses made between divergent genetic lines (fat x lean lines; fast-growing x slow-growing lines). Using our first chicken liver microarray, we have already identified several interesting differentially expressed genes in commercial broilers and in divergently selected broiler lines. Many of these candidate genes are involved in the lipogenic pathway and are controlled in part by the thyrotropic axis. Thus, genome-wide transcriptional profiling is a powerful tool used to visualize the cascade of genetic circuits that govern complex biological responses. Global gene expression profiling and QTL scans should enable us to functionally map the genetic pathways that control growth, development, and metabolism of chickens. This emerging technology will have broad applications for poultry breeding programs (i.e., use of molecular markers) and for future production systems (i.e., the health and welfare of birds and the quality of poultry products).

Insulin-like growth factors and body growth in chickens divergently selected for high or low growth rate

Insulin-like growth factors (IGFs) stimulate growth rate in a number of animal species and are likely to contribute to genetic variations of growth potential. The present study was designed to link levels of IGF-I and IGF-II mRNA and peptides with growth rate in divergently selected genotypes of chickens with high (HG) or low (LG) growth rates. Circulating IGF-I and -II and hepatic mRNA levels were measured under ad libitum feeding conditions from 1 to 12 weeks of age, and at 6 weeks of age under three different nutritional conditions (fed, fasted for 16 or 48 h, re-fed for 4 or 24 h after a 48-h fast). IGF binding proteins (IGFBPs) were also measured. Circulating IGFs increased with age and were higher in HG chickens from 1 to 6 weeks. They decreased with fasting and only IGF-II was fully restored after 24 h of re-feeding, while IGF-I remained low. A significant decrease in steady state IGF-I mRNA levels was also observed with fasting. Across the nutritional study, hepatic IGF-I mRNAs were significantly higher in HG chickens. Variations of IGF-II mRNA levels with nutritional state or genotype exhibited a similar trend. IGFBP (28, 34 and 40 kDa) levels increased with age, while only faint differences were observed between genotypes. IGFBP-28 transiently increased with fasting and was inversely related to blood glucose and insulin levels, suggesting that it is equivalent to mammalian IGFBP-1. In HG chickens, IGFBP-28 and IGFBP-34 levels decreased markedly following re-feeding. Therefore, high and low growth rates were respectively associated with high and low IGF-I and -II levels, supporting the hypothesis of a stimulatory role for both IGFs during post-hatching growth of chickens.

Characterization of unique truncated prolactin receptor transcripts, corresponding to the intracellular domain, in the testis of the sexually mature chicken

We have examined expression of the chicken PRL receptor (cPRLR) gene in different tissues of the chicken by Northern blot analysis. Most tissues examined (ovary, testis, oviduct, kidney, and fat) possess a prominent full-length (4.6-kb) cPRLR transcript. A larger (11.7-kb) transcript is also detected in ovary, oviduct, testis, and kidney after longer exposure. A unique pattern of cPRLR expression was found in the testis of sexually mature chickens, which have an unusually high abundance of three small transcripts (1.2, 1.7, and 2 kb) in addition to the 4.6-kb transcript found in other tissues. Three domain-specific complementary DNA (cDNA) probes were constructed that correspond to the first and second ligand-binding regions in the extracellular domain and the transmembrane-intracellular domain. With these probes, Northern blot analysis of polyadenylated RNA prepared from the testes of a mature (22-week-old) chicken indicates that the highly abundant (1.2- and 1.7-kb) and less abundant (2.0-kb) cPRLR transcripts in testis hybridize only to the intracellular domain probe. Two types of truncated testis-specific cPRLR transcripts were identified using 5'-RACE (rapid amplification of cDNA ends) analysis of polyadenylated RNA from the testis of a 22-week-old chicken. The predominant truncated cDNA sequence contains the highly conserved box 1 motif [(+)box 1 cDNA] and diverges (at nucleotide 1396) from that of the cPRLR cDNA, just downstream of the transmembrane domain. The other truncated cDNA lacks the box 1 motif [(-)box 1 cDNA], which is replaced by 39 bases that could encode a hydrophobic N-terminus with a putative 5'-untranslated region of 131 bases. Young chickens predominately express the full-length cPRLR messenger RNA (4.6 kb) in the testis. At the onset of sexual maturity, there is a dramatic increase in abundance of the testis-specific (+)box 1 transcript, whereas expression of the full-length cPRLR is depressed. The presence of truncated [(+) or (-)box 1] cPRLR transcripts in the sexually mature chicken testis suggests a complex mechanism of PRL action on gonadal function.

Ontogeny of growth hormone receptor gene expression in tissue of growth-selected strains of broiler chickens

The purpose of this study was to determine the relationship between genetic selection for growth traits and tissue expression of the chicken growth hormone receptor (cGHR) gene. Two different populations of broiler chickens were studied. One population consisted of strain (S) 80, selected for 14 generations for high 9-week body weight (BW), and its progenitor, S90 (a 1950's strain). The second population consisted of S21, selected for 10 generations for high 4-week BW and low abdominal fat, and its progenitor S20 (a 1970's strain). Tissue (liver, fat, breast and leg muscle) and blood samples were collected from six birds/strain at 2-week intervals between 1 and 11 weeks of age. An RNase protection assay was developed to measure mRNA levels of full-length cGHR (3.2 and 4.3 kb) transcripts and chicken glyceraldehyde 3-phosphate dehydrogenase (for normalization) in total RNA prepared from tissue. Analysis of the area-under-curve (AUC) was used for strain comparisons of certain developmental profiles (BW, plasma hormones and tissue cGHR mRNA). The BW AUC showed that the growth rates are different (P < 0.05) among the four strains (S21 > S20 > S80 > S90). Both slow-growing strains (S90 and S80) had a higher (P < 0.05) plasma GH AUC than the two fast-growing strains (S20 and S21). The plasma T3 AUC was highest (P < 0.05) in S90 due to maintenance of higher T3 levels after 3 weeks of age. At 11 weeks of age, hepatic and plasma GH-binding activities were positively related to growth rate (S21 > S20 > S80 > S90). However, the developmental increase in cGHR mRNA in liver and fat was similar among these different populations of growth-selected broiler chickens. Steady-state levels of cGHR mRNA increased in a developmental manner in the liver (5-fold at 9 weeks of age) and abdominal fat (4.5-fold at 11 weeks of age) of all strains. In contrast, there was no developmental increase or strain difference in cGHR mRNA levels in breast and leg muscle. There is a discrepancy between GH-binding activity in liver and plasma, which is different among strains, and steady-state levels of tissue cGHR mRNA which are similar among strains. These observations suggest that the cGHR is under translational or post-translational regulation which would determine the amount of cGHR protein available for GH binding.

Molecular cloning and sequence analysis of chicken type I deiodinase cDNA: expression in normal and dwarf broiler chickens

A cDNA encoding the chicken type I iodothyronine deiodinase (cDI-1) was isolated and sequenced from a cDNA library prepared from ConA-activated chicken splenic T-lymphocytes. The coding region of cDI-1 cDNA is composed of 738 basepairs (bp) which encodes a 246 amino acid protein. The predicted amino acid sequence of cDI-1 indicates only 60% identity to several mammalian type I deiodinases. The cDI-1 cDNA contains a codon for a highly conserved selenocysteine residue (Cys124). Northern blot analysis of total RNA prepared from different tissues of a 3-week-old broiler chicken shows a single transcript (2 kb) in liver and kidney. The abundance of hepatic cDI-1 transcripts in growth hormone receptor (GHR)-deficient dwarf chicken was similar to normal chickens despite lower levels of plasma T3 (37% lower) and elevated levels of T4 (21% higher) in dwarf chickens. This finding suggests that regulation of hepatic cDI-1 mRNA is GH-independent in the post-hatch chicken.

Growth hormone down-regulates growth hormone receptor mRNA in chickens but developmental increases in growth hormone receptor mRNA occur independently of growth hormone action

The purpose of this study was to determine the role of growth hormone (GH) in regulating expression of the chicken GH receptor (cGHR) gene by comparing the levels of cGHR mRNA in livers of normal chickens with that of GHR-deficient dwarf chickens. Since the sex-linked dwarf chicken lacks a functional cGHR, there are no genes activated as a result of GH action. Examination of the early developmental profile of hepatic cGHR mRNA in normal and dwarf chickens should yield information on the relative contribution of developmental and hormonal factors to the regulation of cGHR gene expression. Using a sensitive RNase protection assay, we found that the abundance of the major cGHR transcripts (4.3, 3.2 and 0.8 kb) in normal chickens increases about 2-fold between 1 and 7 weeks of age. Due to a splice site mutation in the dwarf chicken, the two larger transcripts encoding the full-length cGHR are not expressed. However, the expression of the truncated cGHR transcript (0.8 kb) in dwarf chickens increases about 5-fold between 1 and 7 weeks of age which suggests that the cGHR gene is overexpressed when not down-regulated by GH. Furthermore, a single promoter, appears to control expression of cGHR transcripts in liver since primer extension analysis revealed the same 5'-end in both full-length and 0.8 kb transcripts. These observations suggest that even though developmental increases in cGHR gene expression occur independently of GH action, GH, either directly or indirectly, down-regulates expression of the cGHR gene in normal chickens.

Cryptic peptides of prepro-TRH antagonize TRH-induced GH secretion in chickens at extrapituitary sites

Complete processing of the TRH precursor in the rat hypothalamus generates TRH and a number of other "cryptic' peptides that flank the TRH progenitor sequences. Two of these peptides, P4 (Ser-Phe-Pro-Trp-Met-Glu-Ser-Asp-Val-Thr; present between amino acids 160 and 169 of rat prepro-TRH) and P5 (Phe-Ile-Asp-Pro-Gly-Leu-Gln-Arg-Ser-Trp- Glu-Glu-Lys-Glu-Gly-Glu-Gly-Val-Leu-Met-Pro-Glu; present between amino acids 178 and 199 of rat prepro-TRH), have recently been shown to modulate TRH-induced GH and thyrotrophin release from rat pituitary glands. The possibility that these peptides might modulate GH secretion in chickens was examined, since TRH is a physiological GH-releasing factor in birds. The administration of P4 and P5 (at doses of 10 and 100 micrograms/kg) consistently lowered basal plasma GH concentrations 30 and 60 min after a bolus i.v. injection. Pretreatment with P4 and P5 similarly suppressed the GH response to systemic TRH challenge. The GH-releasing activity of maximally stimulatory doses of TRH was also reduced by concomitant injections of either P4 (100 micrograms/kg) or P5 (100 micrograms/kg), which blocked the GH-releasing activity of submaximally effective doses of TRH. In marked contrast, neither P4 nor P5 significantly affected basal or TRH-induced GH release from chicken pituitary glands incubated in vitro. These results demonstrate novel actions of P4 and P5 on hypothalamic-pituitary function and, for the first time, indicate extrapituitary sites of action for these cryptic peptides in modulating anterior pituitary function.

Comparison of gene expression in normal and growth hormone receptor-deficient dwarf chickens reveals a novel growth hormone regulated gene

Because of a dysfunctional growth hormone (GH) receptor there is an absence of GH-dependent gene expression in the sex-linked dwarf chicken. Therefore, a comparison of mRNAs expressed in normal and dwarf chickens should lead to the identification of mRNAs that are regulated by GH action. We have compared gene expression in normal and dwarf chickens using the mRNA differential display technique. A combination of three anchored oligo dT primers and 15 random decamers were used to detect at least 75 differentially expressed mRNAs. One of these, designated GHRG-1, hybridizes to a 0.9 kb transcript found only in liver and in normal chickens shows a pattern of developmental expression which parallels the plasma GH profile. A GHRG-1 cDNA clone was isolated that encodes a 120 amino acid peptide with no homology to any known gene. Sequence of the promoter from a genomic clone shows a region with strong similarity to the GH response element identified in the serine protease inhibitor gene, Spi 2.1. These results suggest that GHRG-1 is a novel GH regulated gene.

Chronic intravenous infusion of chicken growth hormone increases body fat content of young broiler chickens

The purpose of this study was to determine the effects of programmed intravenous infusion of chicken growth hormone (cGH) on growth and metabolism of young broiler chickens (4-7 weeks of age). Four-week-old broiler cockerels, fitted with indwelling jugular catheters, were randomly assigned to three treatment groups (6 birds/group): pulsatile infusion of buffer (phosphate buffer, pH 7.4)[PB-P] at 3 hr intervals, pulsatile infusion of cGH (15 micrograms/kg at 3 hr intervals)[GH-P], or continuous infusion of cGH (120 micrograms/kg-day)[GH-C]. Birds were bled 5 min before (0-min) and 5 min post-infusion (relative to the pulses of PB and cGH) at 5, 6, and 7 weeks of age. Pulsatile infusion of cGH increased (P < 0.05) feed consumption by 24% and reduced (P < 0.05) feed efficiency by 14% without affecting body weight (BW) gain. The relative weights (%BW) of liver, abdominal fat, and bursa of Fabricius were not affected by the pattern of cGH infusion. However, the body fat content of cGH-infused chickens was increased (P < 0.05) by 13% (GH-C) and 17% (GH-P), while body protein and water contents were slightly reduced. Body ash content was not affected by pattern of cGH infusion. When compared with the PB-P controls, the GH-P treatment depressed (P < 0.05) hepatic GH-binding activity by 52% without affecting plasma insulin-like growth factor-I (IGF-I) levels. Continuous infusion of cGH increased (P < 0.05) plasma IGF-I by 16%, thyroxine (T4) by 31%, and glucagon levels by 55%, although plasma GH levels were only 47% higher than those of the PB-P group. However, the GH-P treatment was only half as effective as the GH-C pattern in elevating plasma levels of T4 and glucagon. This study shows that programmed intravenous infusion of cGH increases deposition of body fat in young rapidly-growing broiler chickens.

Dysfunctional growth hormone receptor in a strain of sex-linked dwarf chicken: evidence for a mutation in the intracellular domain

The sex-linked dwarf (dwdw) chicken represents a valuable animal model for studying GH insensitivity and the consequence of mutations in the GH receptor (GHR) gene. We have recently reported undetectable hepatic GH-binding activity and an aberrantly sized transcript in a strain of dwdw chickens obtained from Arbor Acre Farms, Inc. (Glastonbury, CT, USA). Southern blot analysis of the chicken GHR (cGHR) gene revealed a restriction-fragment length polymorphism in HindIII and EcoRI digests of genomic DNA in this strain of dwdw chicken. In order to localize the molecular mutation, we analysed the gene structure and determined the complete sequence of the 3' untranslated region (3' UTR) of the normal cGHR. With the use of this information, we located a large deletion in the 3' end of the cGHR gene of the Connecticut (CT) strain of dwdw chicken. This deletion (1773 bp) contained 27 highly conserved amino acids of the 3' end of the coding region, the in-frame stop codon, a less frequently used poly(A) signal that is normally found 445 bp downstream of the stop codon, and a large portion of the 3' UTR. Because of this deletion, 27 novel amino acids were substituted and the open reading frame was extended for an additional 26 amino acids before reaching the transcriptional termination site. The predicted amino acid sequence of the novel carboxyl-terminus of the dwdw cGHR is largely hydrophobic with a polylysine tail, whereas the carboxyl-terminus of the wild-type (DwDw) cGHR is composed of hydrophilic amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Endocrine and metabolic responses of intact and hypophysectomized turkey poults given a daily injection of chicken growth hormone

Female turkey poults were hypophysectomized at 4-5 weeks of age. Beginning at 6 weeks of age, 20 hypophysectomized and 20 intact birds received a daily intramuscular injection of natural chicken growth hormone (cGH, 100 micrograms/kg body weight) or vehicle for 12 days. Blood samples were taken from each bird just before injection and 4 hr post-injection at 6 and 12 days of treatment. Hypophysectomy reduced the growth rate of turkey poults to 75% of that of intact controls, significantly reduced carcass protein and ash percentages, and significantly lower plasma concentrations of GH, insulin-like growth factor-I, triiodothyronine, thyroxine, insulin, glucose, triglycerides, and non-esterified fatty acids. Hypophysectomy was without effect on liver GH receptor binding activity, but increased liver 5'-monodeiodinase activity. Daily cGH injection had no effect on the average daily gain of either hypophysectomized or intact poults when compared to vehicle-injected controls over 12 days of treatment. Daily cGH administration increased plasma insulin-like growth factor-I levels in intact and hypophysectomized turkeys, and increased plasma triiodothyronine, insulin, glucose, and triglyceride concentrations in hypophysectomized birds, but not in intact birds. Responses of young turkeys to hypophysectomy and GH replacement were consistent with the known metabolic role of GH in other species, but the influence of GH on growth appears to be of less importance in poultry than in mammals.

Pulsatile infusion of growth hormone-releasing factor depresses growth of young broiler chickens

This study was conducted to determine the effects of programmed intravenous infusion of growth hormone-releasing factor (GRF) on the growth and metabolism of young broiler chickens (4-7 weeks of age). Twelve 4-week-old chickens, fitted with jugular catheters, were randomly assigned to three treatment groups (four birds/group): pulsed infusion of saline [SAL-P] at 3 hr intervals, pulsed infusion of GRF1-44 (5 micrograms/kg at 3 hr intervals)[GRF-P], or continuous infusion of GRF (40 micrograms/kg-day)[GRF-C]. The GRF-P treatment depressed (P < 0.05) average daily gain by 32%, average daily feed consumption by 24%, and final body weight by 17% when compared with the SAL-P group. Pulsatile infusion of GRF (GRF-P) reduced (P < 0.05) abdominal fat weight by 39% and body fat content by 28% when compared to the SAL-P group. Plasma GH levels were elevated (P < 0.05) 2.1-fold in the GRF-P group at 15 min-post-infusion, while GH levels in the GRF-C group were maintained about 70% higher than those in the SAL-P group. Plasma levels of insulin-like growth factor-I (IGF-I) were consistently lower in the GRF-P group at all ages. There were no significant differences in plasma levels of triiodothyronine (T3), thyroxine (T4), insulin, or glucose among treatment groups. This study shows that pulsatile infusion of GRF, designed to enhance plasma GH levels, does not improve growth rate, feed efficiency, or body composition of young broiler chickens.

Overexpression of a truncated growth hormone receptor in the sex-linked dwarf chicken: evidence for a splice mutation

Sex-linked dwarfism in chickens is a form of GH resistance that resembles the Laron syndrome in humans. The dwarfism found in chickens is due to a mutant gene (dw) carried on the sex chromosome. The homozygous dwarf (dwdw) chicken is characterized by reductions in stature and plasma insulin-like growth factor-I (IGF-I) levels. Despite the absence of hepatic GH-binding activity, Southern blot analysis shows that there is no gross structural change in the gene for the GH receptor (GHR) in this strain of dwdw chicken. GH-dependent IGF-I production can be restored in cultured dwdw hepatocytes after transfection and transient expression of a chicken GHR (cGHR) cDNA, indicating that other factors that participate in GH-mediated IGF-I synthesis are intact. Northern blot analysis of liver, muscle, fat, and pituitary RNA from normal (DwDw) chickens shows a major transcript of 4.3 kilobases (kb) and three minor transcripts (0.8, 1.7, and 3.2 kb), which correspond to the cGHR. In contrast, the 0.8-kb transcript is the major cGHR transcript expressed in these tissues from dwdw chickens. Northern blot analysis with domain-specific probes shows that the 0.8-kb transcript in DwDw and dwdw liver contains only a small portion of the extracellular domain of the cGHR. A cDNA clone encoding this transcript has been isolated from a liver library prepared from a normal chicken.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Abnormal growth hormone receptor gene expression in the sex-linked dwarf chicken

Sex-linked dwarfism is a recessive mutation that causes a reduction in body weight gain and long bone growth of chickens. We examined the effect of the dwarfing gene on body weight, hepatic GH-binding activity, and the structure and expression of the growth hormone receptor (GHR) gene in two different lines of sex-linked dwarf (SLD) broiler chickens. Liver samples from one line of dwarf chicken were obtained from Arbor Acres Farm, Inc. (Glastonbury, CT) and fertile eggs from the second line of SLD were obtained from the University of Georgia. In the GA line, the average body weight of homozygous (dwdw) males at 11 weeks of age was 43% lower than that of normal (DwDw) males, while heterozygous (Dwdw) males were only 9% below normal. In the CT line, hepatic GH-binding activity of 35-week-old chickens was high (20% specific binding) in normal (DwDw) males and undetectable in liver membranes prepared from dwdw males. At 11 weeks of age, hepatic GH-binding activity of Dwdw males (3.9% specific binding) in the GA line was reduced by 44% and that of dwdw males was almost undetectable (0.34% specific binding) when compared to the average of normal GA males (7.1% specific binding). Southern and Northern blot analyses revealed different abnormalities in the GHR gene from the two separate lines of SLD. A restriction fragment length polymorphism in DNA and an aberrantly sized transcript (mRNA) were detected in the CT line of SLD chickens.(ABSTRACT TRUNCATED AT 250 WORDS)

Response of young broiler chickens to chronic injection of recombinant-derived human insulin-like growth factor-I

The purpose of this study was to determine if exogenous insulin-like growth factor-I (IGF-I) would improve growth rate or body composition of young broiler chickens. Broiler cockerels were given a daily intramuscular (im) injection of sodium acetate buffer (buffer control), 100 or 200 micrograms recombinant-derived human IGF-I (rhIGF-I) per kg body weight from 11 to 24 days of age. Exogenous IGF-I did not affect the average daily gain, average daily feed consumption, or the gain-to-feed ratio of broiler chickens. Although daily injection of 200 micrograms/kg of rhIGF-I reduced (P less than 0.05) body ash content, there was no significant effect of IGF-I treatment on either body fat or protein content. Plasma GH levels were depressed (P less than 0.05) by chronic treatment with rhIGF-I. In contrast, plasma levels of T3 and T4 were not affected by rhIGF-I treatment. The half-life of rhIGF-I in plasma was determined at 25 days of age in naive control or chronically-injected chickens after a single intravenous dose of 50 micrograms rhIGF-I/kg. We found a single compartment, first-order disappearance pattern of rhIGF-I from chicken plasma. The half-life (t1/2) of rhIGF-I in plasma was similar (t1/2 = 32.5 min) for naive controls (injected once) or chronically-treated chickens which had received a daily injection of rhIGF-I (100 or 200 micrograms/kg) for 14 d. These data indicate that daily injection of IGF-I cannot be used to enhance growth performance or body composition of broiler chickens when given during the early growth period. The depression of plasma GH levels in rhIGF-I-injected chickens supports a negative-feedback role of IGF-I on pituitary GH secretion.

Molecular cloning of the chicken growth hormone receptor complementary deoxyribonucleic acid: mutation of the gene in sex-linked dwarf chickens

A novel complementary DNA (cDNA) encoding the chicken GH receptor was isolated from a chicken liver cDNA library, using polymerase chain reaction with primers derived from highly conserved sequences of the mammalian GH receptor. The nucleotide sequence predicts a mature protein of 592 amino acids and a 16 amino acid signal peptide that are partially homologous to the sequence reported for the rabbit (53%), rat (58%), and human (50%) GH receptors. Despite this low level of homology, a number of structural features of the GH receptor are conserved, including 7 cysteine residues in the extracellular domain and 5 in the intracellular region. Three transcripts of approximately 4.7, 4.0, and 1.0 kilobases are present on Northern blots of total RNA prepared from the livers of 35-week-old male chickens. Expression of the GH receptor was also detected in a wide range of tissues. The chicken GH receptor cDNA was then used as a probe in Southern and Northern blot analyses of DNA and RNA prepared from livers of sex-linked dwarf chickens, which have undetectable levels of hepatic GH-binding activity, in addition to other endocrine abnormalities. A restriction fragment length polymorphism was found in DNA, and an aberrantly-sized transcript was found in hepatic RNA of the dwarf chicken. These results indicate that a mutation in the GH receptor gene is responsible for the phenotype of the sex-linked dwarf chicken. This type of dwarfism resembles Laron-type dwarfism in humans, where a defect in the GH receptor gene has recently been identified. These receptor-deficient chickens should serve as a unique model system for studying the role of the GH receptor in growth and development.

Measurement of developmental changes in plasma insulin-like growth factor-I levels of broiler chickens by radioreceptor assay and radioimmunoassay

The main purpose of this study was to examine the relationship between insulin-like growth factor-I (IGF-I) and growth hormone (GH) during embryonic and posthatching development of broiler chickens. Two heterologous assays were validated for measurement of IGF-I in chicken and turkey plasma. A radioreceptor assay (RRA), utilizing microsomal membranes prepared from human placenta, was modified and validated for measurement of IGF peptide (mainly IGF-I). A double-antibody radioimmunoassay (RIA) was validated for measurement of immunoreactive IGF-I levels in chicken and turkey plasma. In both assay systems, recombinant-derived human IGF-I was used for standards and trace hormone. Hypophysectomy in turkey poults reduced plasma levels of IGF (RRA) by 35% and IGF-I (RIA) by 59% as compared to intact control turkeys. In Experiment 1, 14 chicken embryos were bled at 15, 17, 19, and 21 days of incubation and at 1 week of age to determine plasma levels of IGF-I and GH. Plasma IGF levels (RRA) remained constant during late incubation, but increased significantly (P less than 0.05) at 1 week of age. Plasma IGF-I levels (RIA) declined 2 days before hatching; however, plasma levels of IGF-I were sharply elevated (P less than 0.05) at 1 week of age. Plasma GH concentrations were low in embryos and were greatly elevated (P less than 0.05) at hatching (21 days of incubation) and at 1 week of age. In Experiment 2, 12 different broiler cockerels were weighed and then bled by cardiac puncture each week from hatching (1 day of age) to 7 weeks of age. The plasma profiles of IGF, IGF-I, GH, triiodothyronine (T3), and thyroxine (T4) were each compared to relative growth rate by analysis of covariance. Plasma IGF and IGF-I levels increased progressively from 0 to 3 weeks of age and were maintained in a plateau from 3 to 7 weeks of age. Plasma GH levels reached a peak at 4 weeks of age, but declined sharply thereafter, while IGF and IGF-I levels remained elevated. Plasma T3 concentrations were progressively increased and reached peak concentrations at 3 weeks of age, while plasma T4 levels increased only at 6 and 7 weeks of age. There was a high correlation (P less than 0.01) between relative growth rate and age-related changes in plasma levels of IGF (r = 0.96), IGF-I (r = 0.97), and T3 (r = 0.94); however, there was no correlation between relative growth rate and changes in plasma GH or T4.(ABSTRACT TRUNCATED AT 400 WORDS)