Polymorphisms in uncoupling protein, melanocortin 3 receptor, melanocortin 4 receptor, and pro-opiomelanocortin genes and association with production traits in a commercial broiler line

Involvement of central opioid and melanocortin receptors in spexin-induced hypophagia following intracerebroventricular injection in neonatal broiler chicks

BACKGROUND

Numerous physiological properties have been documented in the literature pertaining to spexin, such as its role in appetite regulation. Therefore, the present research aimed to assess the impacts of centrally administering spexin and its interaction with opioid and melanocortin receptors on feeding behavior in neonatal broiler chicks. In experiment 1, the chickens were administered intracerebroventricular (ICV) injection of saline and spexin at varying doses of 5, 7.5 and 10 nmol. During the experiment 2, the broilers were subjected to an ICV injection containing saline, β-FNA (µ-opioid receptor antagonist, 5 µg), spexin (10 nmol), and a mixture of β-FNA plus spexin. Experiments 3 to 6 bore resemblance to experiment 2, with the exception that NTI (δ-opioid receptor antagonist, 5 µg), nor-BNI (κ-opioid receptor antagonist, 5 µg), SHU9119 (MC3/MC4 receptor antagonist, 0.5 nmol) and MCL0020 (MC4 receptor antagonist, 0.5 nmol) were administered instead of β-FNA. Then, the birds were promptly placed back into their individual cages and cumulative food intake was assessed at intervals of 30, 60, and 120 min postinjection.

RESULTS

Spexin demonstrated a significant and dose-dependent decrease in food intake when compared to the control group (P < 0.05). Co-injection of β-FNA + spexin diminished spexin-induced hypophagia (P < 0.05) whereas concurrent administration of NTI and nor-BNI with spexin led to an amplification of the decrease in food consumption induced by spexin (P < 0.05). Additionally, anorexigenic impact of spexin was reversed by combined injection of SHU9119 and MCL0020 with spexin (P < 0.05).

CONCLUSION

These observations suggest that both opioid and melanocortin receptors play crucial role in spexin-induced hypophagia.

The role of G protein-coupled receptors and their ligands in animal domestication

The domestication of plants and animals has resulted in one of the most significant cultural and socio-economical transitions in human history. Domestication of animals, including human-supervised reproduction, largely uncoupled particular animal species from their natural, evolutionary history driven by environmental and ecological factors. The primary motivations for domesticating animals were, and still are, producing food and materials (e.g. meat, eggs, honey or milk products, wool, leather products, jewelry and medication products) to support plowing in agriculture or in transportation (e.g. horse, cattle, camel and llama) and to facilitate human activities (for hunting, rescuing, therapeutic aid, guarding behavior and protecting or just as a companion). In recent years, decoded genetic information from more than 40 domesticated animal species have become available; these studies have identified genes and mutations associated with specific physiological and behavioral traits contributing to the complex genetic background of animal domestication. These breeding-altered genomes provide insights into the regulation of different physiological areas, including information on links between e.g. endocrinology and behavior, with important pathophysiological implications (e.g. for obesity and cancer), extending the interest in domestication well beyond the field. Several genes that have undergone selection during domestication and breeding encode specific G protein-coupled receptors, a class of membrane-spanning receptors involved in the regulation of a number of overarching functions such as reproduction, development, body homeostasis, metabolism, stress responses, cognition, learning and memory. Here we summarize the available literature on variations in G protein-coupled receptors and their ligands and how these have contributed to animal domestication.

Mutations in melanocortin-4 receptor: From fish to men

Melanocortin-4 receptor (MC4R), expressed abundantly in the hypothalamus, is a critical regulator of energy homeostasis, including both food intake and energy expenditure. Shortly after the publication in 1997 of the Mc4r knockout phenotypes in mice, including increased food intake and severe obesity, the first mutations in MC4R were reported in humans in 1998. Studies in the subsequent two decades have established MC4R mutation as the most common monogenic form of obesity, especially in early-onset severe obesity. Studies in animals, from fish to mammals, have established the conserved physiological roles of MC4R in all vertebrates in regulating energy balance. Drug targeting MC4R has been recently approved for treating morbid genetic obesity. How the MC4R can be exploited for animal production is highly worthy of active investigation.

Single nucleotide polymorphism in avian uncoupling protein gene is associated with thermoregulation in chicks

Avian uncoupling protein (av-UCP) is a key protein for thermoregulation in poultry. A single nucleotide polymorphism (SNP) in the av-UCP gene has been reported in chickens. The purpose of the current study was to clarify the association between this av-UCP gene mutation and thermoregulation in chickens. Wild and mutant type chicks for the av-UCP gene SNP (g. 1270 of the av-UCP gene exon 3 with C to T substitution and amino acid substitution) were exposed to high ambient temperature. Rectal temperature, radiation temperature on the body surface, and the expression of heat dissipation behavior (wing drooping and panting) during heat exposure were measured. In addition, oxygen consumption rate in the thermoneutral zone in wild and mutant type chicks was measured. Changes in wing temperature during heat exposure in wild-type chicks were lower than those in mutants. The latency of continuous wing drooping during heat exposure in wild-type chicks was shorter than in mutant chicks. It was also found that the SNP in the av-UCP gene caused reduced oxygen consumption. These results suggest that the av-UCP gene mutation affects thermoregulation, especially heat production, in chickens.

Av-UCP single nucleotide polymorphism affects heat production during cold exposure in chicks

OBJECTIVE

Uncoupling protein one (UCP1) is involved in thermogenesis, especially in non-shivering heat production. In chickens, a single nucleotide polymorphism (SNP) of the av-UCP (avian UCP) gene has been reported to be associated with body weight gain and increased abdominal fat. The purpose of this study was to examine the relationship between the av-UCP gene SNP and heat production in chicks.

METHODS

C/C and T/T male chicks (Rhode Island Red) of av-UCP gene SNP (g. 1270, C > T) were exposed to a low temperature environment (16 °C for 15 min) and their physiological responses were compared.

RESULTS

After cold exposure, mean rectal temperatures of C/C chicks were higher than those of T/T chicks. In pectoral muscle, genes expression of av-UCP and carnitine palmitoyltransferase-1 were higher in C/C chicks than T/T chicks. Hypothalamic expression levels of thyrotropin-releasing hormone and proopiomelanocortin genes were higher in C/C chicks than T/T chicks. Expression of hypothalamic corticotropin-releasing hormone, arginine vasotocin, brain-derived neurotrophic factor and neuropeptide Y genes did not differ between C/C and T/T chicks. In addition, plasma free fatty acid levels in C/C chicks were lower than those of T/T chicks.

CONCLUSION

These results suggest that the av-UCP gene SNP affects non-shivering heat production via the hypothalamo-pituitary-thyroid axis and fatty acid metabolism in the chicken.

Pharmacological characterization of three chicken melanocortin-3 receptor mutants

The melanocortin-3 receptor (MC3R) is a G protein-coupled receptor and potentially important in production traits. Three naturally occurring mutations (M54L, G104S, and L151R) in chicken MC3R (cMC3R) were reported previously to be associated with production traits. Here, we inserted the full-length cMC3R coding sequence into pcDNA3.1(+) and generated the 3 mutations by site-directed mutagenesis. The total and cell surface expression of the receptors was measured by flow cytometry. We analyzed the pharmacological characteristics, including binding and cyclic adenosine monophosphate (cAMP) and mitogen-activated protein kinase (MAPK) signaling, using 6 ligands ([Nle⁴, D-Phe⁷]-α-melanocyte stimulating hormone (MSH), α-, β-, γ-, and D-Trp⁸-γ-MSHs, and agouti-related peptide). All mutants had similar total and cell surface expression as the wild-type (WT) cMC3R. M54L had similar pharmacological properties as the WT cMC3R. G104S did not exhibit any specific binding but had minimal response to α-, β-, γ-, and D-Trp⁸-γ-MSH, although it generated 24% WT response when stimulated by NDP-MSH. Although L151R had normal binding, the responses to agonists were reduced to approximately 25% of that of the WT. In MAPK signaling, all 3 mutants showed significantly increased agonist-stimulated phosphorylation of extracellular signal-regulated protein kinases 1/2, indicating the existence of biased signaling at G104S and L151R. In summary, our studies demonstrated that although all 3 mutations are significantly associated with production traits, only G104S and L151R had severe defects in receptor pharmacology. How M54L might cause production trait differences remains to be investigated.

Determination of Polymorphisms in Pituitary Genes of the Native Afghani Naked Neck Chicken

We investigated means to improve the production of the indigenous Naked Neck chicken in Afghanistan. Specifically, we analyzed single nucleotide polymorphisms (SNPs) in the prolactin (PRL) (24 bp indel), growth hormone (GH) (T185G), and pituitary specific transcript factor 1 (PIT-1) (intron 5) genes. Blood samples were collected from 52 birds and genomic DNA was extracted. Polymorphisms in the mentioned loci were analyzed by PCR, allele-specific PCR, and PCR-restriction fragment length polymorphism (RFLP) using TaqI and MspI endonucleases. Cloning followed by DNA sequencing was performed to ascertain the accuracy of the PCR-RFLP analysis for PIT-1.Two alleles were found for the PRL 24 bp indel, GH (T185G), and PIT-1/TaqI, with the following respective allelic frequencies: PRL-In 0.64 and PRL-Del 0.36, GH-T 0.91 and GH-G 0.09, and PIT-1-A 0.64 and PIT-1-B 0.36. Regarding the PIT-1/MspI polymorphism, three novel MspI recognition sites, as well as two reported MspI recognition sites, were detected in intron 5. Moreover, during sequence screening, two novel SNPs were found that generated restriction sites for MseI. Therefore, our results suggest that the PRL indel, GH T185G, and PIT-1/TaqI polymorphisms may be used as selection markers for Afghanistan Naked Neck chickens. Intron 5 of PIT-1 in the Afghani Naked Neck chicken was highly polymorphic compared to the reported Gallus gallus PIT-1 gene (GenBank accession no. NC_006088.4).

Polymorphisms of pro-opiomelanocortin gene and the association with reproduction traits in chickens

Pro-opiomelanocortin (POMC) is a member of prohormone family and has important functions in stress response, skin pigmentation, thermoregulation and reproduction. In this study, the single nucleotide polymorphisms (SNPs) of POMC gene exons were detected by direct sequencing in 317 Zhenning yellow chickens. The sequencing results indicated there were seven mutation sites (g.1140C > T, g.1185 T > C, g.2085 T > C, g.3566A > C, g.3572 G > A, g.3594 G > A and g.3628 G > A) and all of these were synonymous. Furthermore, seven haplotypes were formed and sixteen diplotypes were obtained. The associations between the POMC gene polymorphisms or diplotypes and reproduction traits were also analyzed. The association analysis results indicated that the SNP of g.1140C > T was associated with egg production at 300 d of age (E300), fertilization rate (FR), hatching rate of hatching eggs (HEHR) and hatching rate of fertilized eggs (FEHR; P < 0.05). The SNP of g.3566A>C was associated with FR (P < 0.05), SNP of g.3594G>A was associated with egg weight at 300d of age (EW300; P < 0.05), and SNP of g.3628G>A was associated with HEHR and FEHR (P < 0.01), respectively. Furthermore, chickens with H2H3 diplotype had greater EW300 and FR than those with H1H7 and H3H4 diplotypes (P < 0.05). These results indicate the expression of the POMC gene had significant genotype effects on the reproduction traits of Zhenning yellow chickens, and that the H2H3 diplotype could be used as a potential genetic marker to improve the reproduction traits in chicken breeding.

Mitochondrial metabolism: a driver of energy utilisation and product quality?

High feed efficiency is a very desirable production trait as it positively influences resource utilisation, profitability and environmental considerations, albeit at the possible expense of product quality. The modern broiler is arguably the most illustrative model species as it has been transformed over the past half century into an elite feed converter. Some producers are currently reporting that 42-day-old birds gain 1 kg of wet weight for every 1.35 kg of dry weight consumed. Its large breast muscle is exclusively composed of large, low mitochondrial-content Type IIB fibres, which may contribute to low maintenance costs and high efficiency. In an effort to gain a better understanding of individual variation in chicken feed efficiency, our group has been exploring the biology of the mitochondrion at multiple levels of organisation. The mitochondrion is the organelle where much biochemical energy transformation occurs in the cell. Using Cobb-Vantress industrial birds as our primary experimental resource, we have explored the tissue content, structure and function of the mitochondrion and its relationship to growth, development, efficiency and genetic background. While much remains to be understood, recent highlights include (1) variation in muscle mitochondrial content that is associated with performance phenotypes, (2) altered muscle mitochondrial gene and protein expression in birds differing in feed efficiency, (3) variation in isolated mitochondrial function in birds differing in feed efficiency and (4) evidence for an unexpected role for the mitochondrially localised progesterone receptor in altering bird muscle metabolism. Mitochondrial function is largely conserved across the vertebrates, so the same metabolic principles appear to apply to the major production species, whether monogastric or ruminant. A speculative role for the mitochondria in aspects of meat quality and in influencing postmortem anaerobic metabolism will conclude the manuscript.

Behind melanocortin antagonist overexpression in the zebrafish brain: A behavioral and transcriptomic approach

Melanocortin signaling is regulated by the binding of naturally occurring antagonists, agouti-signaling protein (ASIP) and agouti-related protein (AGRP) that compete with melanocortin peptides by binding to melanocortin receptors to regulate energy balance and growth. Using a transgenic model overexpressing ASIP, we studied the involvement of melanocortin system in the feeding behaviour, growth and stress response of zebrafish. Our data demonstrate that ASIP overexpression results in enhanced growth but not obesity. The differential growth is explained by increased food intake and feeding efficiency mediated by a differential sensitivity of the satiety system that seems to involve the cocaine- and amphetamine- related transcript (CART). Stress response was similar in both genotypes. Brain transcriptome of transgenic (ASIP) vs wild type (WT) fish was compared using microarrays. WT females and males exhibited 255 genes differentially expressed (DEG) but this difference was reduced to 31 after ASIP overexpression. Statistical analysis revealed 1122 DEG when considering only fish genotype but 1066 and 981 DEG when comparing ASIP males or females with their WT counterparts, respectively. Interaction between genotype and sex significantly affected the expression of 97 genes. Several neuronal systems involved in the control of food intake were identified which displayed a differential expression according to the genotype of the fish that unravelling the flow of melanocortinergic information through the central pathways that controls the energy balance. The information provided herein will help to elucidate new central systems involved in control of obesity and should be of invaluable use for sustaining fish production systems.

Pharmacologic analyses of four chicken melanocortin-4 receptor mutations

The melanocortin-4 receptor (MC4R) is a critical regulator of mammalian food intake and energy expenditure, with receptor activation resulting in decreased food intake and increased energy expenditure. Recently, studies on role of MC4R in regulation of food intake have been extended to other species, such as chicken. Functional study of mutant MC4Rs is important in proving the causal link between MC4R mutation and production traits. Herein, we cloned chicken MC4R (cMC4R) complementary DNA and generated 4 mutant cMC4Rs (Q18H, G21R, S76L, and L299P) by site-directed mutagenesis and measured their expression by flow cytometry. Pharmacologic characteristics were analyzed with binding and signaling assays using 3 agonists. We showed that G21R had decreased cell surface and total expression (P < 0.05), whereas the other 3 mutants had similar total and cell surface expression levels as wild-type cMC4R. The 4 mutants had either decreased (Q18H, G21R, S76L; P < 0.05) or no (L299P) binding to radiolabeled [Nle(4), D-Phe(7)]-α-melanocyte-stimulating hormone (MSH). In signaling assays, Q18H was constitutively active. Q18H, G21R, and S76L had decreased responses to α-MSH stimulation (P < 0.05). L299P had decreased basal and ligand-stimulated signaling (P < 0.01). Nle(4), D-Phe(7)-MSH was the most potent agonist for cMC4R and therefore would be better suited for further in vivo studies. We conclude that the cloned cMC4R was a functional receptor and provided detailed functional data for these mutations, contributing to a better understanding of cMC4R variants associated with production traits.

A whole genomic scan to detect selection signatures between Berkshire and Korean native pig breeds

Background

Scanning of the genome for selection signatures between breeds may play important role in understanding the underlie causes for observable phenotypic variations. The discovery of high density single nucleotide polymorphisms (SNPs) provide a useful starting point to perform genome–wide scan in pig populations in order to identify loci/candidate genes underlie phenotypic variation in pig breeds and facilitate genetic improvement programs. However, prior to this study genomic region under selection in commercially selected Berkshire and Korean native pig breeds has never been detected using high density SNP markers. To this end, we have genotyped 45 animals using Porcine SNP60 chip to detect selection signatures in the genome of the two breeds by using the F_ST approach.

Results

In the comparison of Berkshire and KNP breeds using the FDIST approach, a total of 1108 outlier loci (3.48%) were significantly different from zero at 99% confidence level with 870 of the outlier SNPs displaying high level of genetic differentiation (F_ST ≥0.490). The identified candidate genes were involved in a wide array of biological processes and molecular functions. Results revealed that 19 candidate genes were enriched in phosphate metabolism (GO: 0006796; ADCK1, ACYP1, CAMK2D, CDK13, CDK13, ERN1, GALK2, INPP1; MAK, MAP2K5, MAP3K1, MAPK14, P14KB, PIK3C3, PRKC1, PTPRK, RNASEL, THBS1, BRAF, VRK1). We have identified a set of candidate genes under selection and have known to be involved in growth, size and pork quality (CART, AGL, CF7L2, MAP2K5, DLK1, GLI3, CA3 and MC3R), ear morphology and size (HMGA2 and SOX5) stress response (ATF2, MSRB3, TMTC3 and SCAF8) and immune response ( HCST and RYR1).

Conclusions

Some of the genes may be used to facilitate genetic improvement programs. Our results also provide insights for better understanding of the process and influence of breed development on the pattern of genetic variations.

Electronic supplementary material

The online version of this article (doi:10.1186/2055-0391-56-23) contains supplementary material, which is available to authorized users.

Association of single nucleotide polymorphism of GHSR and TGFB2 genes with growth and body composition traits in sire and dam lines of a broiler chicken

Growth hormone secretagogue receptor (GHSR) modulates many physiological processes by binding to its ligand, as well as transforming growth factor-beta 2 (TGFB2) regulates cell growth and development in animals and, therefore, are candidate genes for performance in chickens. In the current study, single nucleotide polymorphisms of GHSR C3286 > T and TGFB2 T(-640) > C were genotyped in sire and dam lines of a broiler chicken to evaluate the association with the growth and body composition traits. Least squares means analysis showed that the GHSR C3286 > T SNP was significantly (P < 0.01) associated with growth (DFI and ADG) and body composition traits (AFW and %AFW). In addition, the TGFB2 T(-640) > C SNP was associated with ADG (P < 0.05) and DFI and body composition traits (DW, LBW, BAKWT, %BMW, %HNDWT and %CW) (P < 0.01). Significant associations of the single nucleotide polymorphisms (SNPs) on the traits reported in the present study might be the distinct usage of codons in avian, or relating to an enhancer element and modulating the expression of the gene in chicken. The data indicated that these SNPs could be valuable genetic elements for selection of chickens for better performance in the population.

Population genomic analyses based on 1 million SNPs in commercial egg layers

Identifying signatures of selection can provide valuable insight about the genes or genomic regions that are or have been under selective pressure, which can lead to a better understanding of genotype-phenotype relationships. A common strategy for selection signature detection is to compare samples from several populations and search for genomic regions with outstanding genetic differentiation. Wright's fixation index, F_ST, is a useful index for evaluation of genetic differentiation between populations. The aim of this study was to detect selective signatures between different chicken groups based on SNP-wise F_ST calculation. A total of 96 individuals of three commercial layer breeds and 14 non-commercial fancy breeds were genotyped with three different 600K SNP-chips. After filtering a total of 1 million SNPs were available for F_ST calculation. Averages of F_ST values were calculated for overlapping windows. Comparisons of these were then conducted between commercial egg layers and non-commercial fancy breeds, as well as between white egg layers and brown egg layers. Comparing non-commercial and commercial breeds resulted in the detection of 630 selective signatures, while 656 selective signatures were detected in the comparison between the commercial egg-layer breeds. Annotation of selection signature regions revealed various genes corresponding to productions traits, for which layer breeds were selected. Among them were NCOA1, SREBF2 and RALGAPA1 associated with reproductive traits, broodiness and egg production. Furthermore, several of the detected genes were associated with growth and carcass traits, including POMC, PRKAB2, SPP1, IGF2, CAPN1, TGFb2 and IGFBP2. Our approach demonstrates that including different populations with a specific breeding history can provide a unique opportunity for a better understanding of farm animal selection.

Associations of polymorphisms in GHRL, GHSR, and IGF1R genes with feed efficiency in chickens

The ghrelin (GHRL), ghrelin receptor (GHSR), and insulin-like growth factor 1 receptor (IGF1R) genes have crucial effects on body weight (BW), body weight gain (BWG), feed intake (FI), and feed conversion ratio (FCR) in many species. However, few studies on associations of GHRL, GHSR, and IGF1R with BWG, FI, and FCR have been reported in chickens. In this study, 16 SNPs in GHRL, GHSR, and IGF1R genes were genotyped by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The objective of this study was to examine the associations of GHRL, GHSR, and IGF1R genes polymorphisms with BW at 49 days (BW49) and 70 days (BW70) of age, BWG, FI, and FCR in the interval in two yellow meat-type populations with a total of 724 birds. The results showed that rs15675067 of GHRL was significantly associated with BW70, BWG, and FCR (P < 0.05). For GHSR, rs16675844 had significant effects on FI and FCR (P < 0.01), and that rs14678932 showed significant association with BWG and FI (P < 0.05). Rs14011780 of IGF1R was strongly associated with BW49, BW70, and FCR (P < 0.05). Furthermore, haplotypes based on three SNPs of rs14986828, rs15675067, and rs15675065 in GHRL were significantly associated with BW70 and FCR (P < 0.05). Meanwhile, a three-SNP haplotype comprising rs14011783, rs14011780, and rs14011776 in IGF1R showed significant effects on BW49, BW70, and FCR (P < 0.05). Therefore, it was concluded that the identified SNPs and analyzed haplotypes in this study might be useful for broiler breeding programs.

Genome-wide patterns of genetic variation in two domestic chickens

Domestic chickens are excellent models for investigating the genetic basis of phenotypic diversity, as numerous phenotypic changes in physiology, morphology, and behavior in chickens have been artificially selected. Genomic study is required to study genome-wide patterns of DNA variation for dissecting the genetic basis of phenotypic traits. We sequenced the genomes of the Silkie and the Taiwanese native chicken L2 at ∼23- and 25-fold average coverage depth, respectively, using Illumina sequencing. The reads were mapped onto the chicken reference genome (including 5.1% Ns) to 92.32% genome coverage for the two breeds. Using a stringent filter, we identified ∼7.6 million single-nucleotide polymorphisms (SNPs) and 8,839 copy number variations (CNVs) in the mapped regions; 42% of the SNPs have not found in other chickens before. Among the 68,906 SNPs annotated in the chicken sequence assembly, 27,852 were nonsynonymous SNPs located in 13,537 genes. We also identified hundreds of shared and divergent structural and copy number variants in intronic and intergenic regions and in coding regions in the two breeds. Functional enrichments of identified genetic variants were discussed. Radical nsSNP-containing immunity genes were enriched in the QTL regions associated with some economic traits for both breeds. Moreover, genetic changes involved in selective sweeps were detected. From the selective sweeps identified in our two breeds, several genes associated with growth, appetite, and metabolic regulation were identified. Our study provides a framework for genetic and genomic research of domestic chickens and facilitates the domestic chicken as an avian model for genomic, biomedical, and evolutionary studies.

Three novel SNPs in the coding region of the bovine MC3R gene and their associations with growth traits

The involvement of melanocortin-3 receptor (MC3R) is well recognized in the regulation of feeding efficiency, body weight, and energy homeostasis. The objective of this study was to investigate the associations between MC3R gene polymorphisms and growth traits. Three novel SNPs (c.24C→T, c.220T→A, c.734G→C) and five haplotypes were identified in 234 Xiangxi cattle. The associations between MC3R gene polymorphisms and growth traits indicated that the individuals with TT and AT genotypes maintained higher body weight than those with the AA genotype at the c.220T→A locus (P < 0.05). The animals with GG and CG genotypes had higher heart girth and body weight than those with the CC genotype at c.734G→C (P < 0.05). The animals with H3H3 and H2H3 haplotype combinations had higher body weight than those with other haplotype combinations (P < 0.05). The results suggest that these SNPs in the MC3R gene might be useful genetic markers for marker-assisted selection and cattle breeding.

Relationship between abdominal fat content and avian uncoupling protein gene expression in skeletal muscle of Japanese quail Coturnix japonica

1. The genetic architecture of the avian uncoupling protein (avUCP) was investigated and the relationship between avUCP gene expression and the amount of abdominal fat of Japanese quail was determined by quantitative real-time PCR. 2. The Japanese quail avUCP gene consists of six exons and five introns. Sequences of nucleotides and amino acids were 94·6% and 86·0% identical to those of the chicken avUCP gene, and phylogenetic analysis showed that the Japanese quail avUCP gene consists of the same clusters as the chicken and turkey avUCP. 3. Expression of the avUCP gene was significantly higher in the Pectoralis major (1·28 ± 0·24) than in the Biceps femoris (0·63 ± 0·14). 4. A positive correlation coefficient between the avUCP gene expression in the Pectoralis major and Biceps femoris was observed (r = 0·79, P = 0·02), whereas a negative correlation coefficient was observed between the abdominal fat percentage (AFP) and gene expression in both the Pectoralis major (r = -0·82, P = 0·01) and Biceps femoris (r = -0·61, P = 0·11). 5. The avUCP gene was associated with the accumulation of abdominal fat in Japanese quail and it was concluded that modulation of avUCP gene expression could be utilised to control abdominal fat accumulation in poultry.

Molecular cloning and SNP association analysis of chicken PMCH gene

The pre-melanin-concentrating hormone (PMCH) gene is an important gene functionally concerning the regulations of body fat content, feeding behavior and energy balance. In this study, the full-length cDNA of chicken PMCH gene was amplified by SMART RACE method. The single nucleotide polymorphisms (SNPs) in the PMCH gene were screened by comparative sequence analysis. The obtained non-synonymous coding SNPs (ncSNPs) were designed for genotyping firstly. Its effects on growth, carcass characteristics and meat quality traits were investigated employing the F2 resource population of Gushi chicken crossed with Anak broiler by AluI CRS-PCR-RFLP. Our results indicated that the cDNA of chicken PMCH shared 67.25 and 66.47% homology with that of human and bovine PMCH, respectively. The deduced amino acid sequence of chicken PMCH (163 amino acids) were 52.07 and 50.89% identical to those of human and bovine PMCH, respectively. The PMCH protein sequence is predicted to have several functional domains, including pro-MCH, CSP, IL7, XPGI and some low complexity sequence. It has 8 phosphorylation sites and no signal peptide sequence. gga-miR-18a, gga-miR-18b, gga-miR-499 microRNA targeting site was predicted in the 3' untranslated region of chicken PMCH mRNA. In addition, a total of seven SNPs including an ncSNP and a synonymous coding SNP, were identified in the PMCH gene. The ncSNP c.81 A>T was found to be in moderate polymorphic state (polymorphic index=0.365), and the frequencies for genotype AA, AB and BB were 0.3648, 0.4682 and 0.1670, respectively. Significant associations between the locus and shear force of breast and leg were observed. This polymorphic site may serve as a useful target for the marker assisted selection of the growth and meat quality traits in chicken.

Effects of single and combined genotypes of MC4R and POU1F1 genes on two production traits in Langshan chicken

The objective of this study was to analyze the effects of single and combined genotypes of MC4R and POU1F1 genes in Chinese well-known indigenous chicken (Langshan chicken) population. Genetic variants within MC4R gene and POU1F1 gene were screened through PCR-SSCP and DNA sequencing methods. A C/T mutation at nt 944 in MC4R gene (NC_006089.2:g. 944C>T) and a G/A mutation at nt 3109 in POU1F1 gene (NC_006088.2:g. 3109 G>A) were identified. Associations between the mutations of the two genes with two production traits were analyzed. The results showed that, at MC4R locus, individuals with BB and AB genotypes had highly significantly higher body weight at 16 weeks (p < 0.01) than did those with the AA genotype. And, individuals within AA and AB genotypes had significantly higher egg numbers at 300 days (p < 0.05). At POU1F1 locus, individuals with CD genotype had higher body weight at 16 weeks and egg numbers at 300 days (p < 0.05). Furthermore, combined genotypes from these two loci were found to be associated with egg numbers at 300 days (p < 0.05). The individuals within combined genotype AB/CD had higher egg production. Therefore, variations identified within the MC4R and POU1F1genes are suitable for future use in identifying chickens with the genetic potential of higher body weight and reproductive traits, at least in the population of Langshan chickens.

A comparative study of the central effects of melanocortin peptides on food intake in broiler and layer chicks

Broiler chicks eat more food than layer chicks. However, the causes of the difference in food intake in the neonatal period between these strains are not clear. In this study, we examined the involvement of proopiomelanocortin (POMC)-derived melanocortin peptides α-, β- and γ-melanocyte-stimulating hormones (MSHs) in the difference in food intake between broiler and layer chicks. First, we compared the hypothalamic mRNA levels of POMC between these strains and found that there was no significant difference in these levels between broiler and layer chicks. Next, we examined the effects of central administration of MSHs on food intake in these strains. Central administration of α-MSH significantly suppressed food intake in both strains. Central administration of β-MSH significantly suppressed food intake in layer chicks, but not in broiler chicks, while central administration of γ-MSH did not influence food intake in either strain. It is therefore likely that the absence of the anorexigenic effect of β-MSH might be related to the increased food intake in broiler chicks.

Polymorphisms of the pro-opiomelanocortin and agouti-related protein genes and their association with chicken production traits

Pro-opiomelanocortin (POMC) and agouti-related protein (AGRP) are hypothalamic neuropeptides that play a central role in the regulation of food intake and energy expenditure and for this reason the variations in the POMC and AGRP genes in chicken were examined by screening the DNA pools. Two silent cSNPs mutations in POMC gene and one silent cSNP mutation in AGRP gene were identified. PCR-restriction fragment length polymorphism (RFLP) was used to test the cSNPs c. C495T in the POMC and c. C9T in the AGRP gene in the F2 resource population of Gushi chicken crossed with Anak broiler. The association analysis on the polymorphisms of POMC, AGRP gene and production traits showed that the c. C495T mutation in the POMC gene was significantly linked to the pelvis breadth at 4 weeks of age (P = 0.035), body weight at 2 weeks of age (P = 0.013) and was highly significantly linked to the chest depth at 12 weeks of age (P = 0.006). The c. T9T genotype in the AGRP gene was associated with a low breast muscle water loss rate (P = 0.025), increased chest width at 12 weeks of age (P = 0.005) and body weight at 2 weeks of age (P = 0.036), a high slaughter rate (P = 0.049) and semi-evisceration weight (P = 0.019). These findings may have important implications for the molecular aspects of chicken breeding.

The polymorphisms of bovine melanocortin-3 receptor pseudogene

Mammalian melanocortin-3 receptor (MC3R) plays an important role in the central control of energy homeostasis, and several functional polymorphisms of mc3r have been detected. Interestingly, the bovine mc3r was a pseudogene, and its polymorphisms and function remain to be investigated. Single-strand conformation polymorphism (SSCP) showed 5, 2 and 3 genotypes in fragment F1, F2 and F3 of mc3r in seven cattle breeds, respectively. All genotypes revealed novel sequences. Three SNPs 657G>T, 756C>T, 822T>C were detected in fragment F1, five SNPs 1091T>C, 1133T>C, 1144C>T, 1259T>C and 1319G>A were detected in fragment F2, and two SNPs 1687G>A, 1860C>T were detected in F3. The SNPs in fragment F1 and F2 were located at exon 2. The five SNPs in fragment F2 demonstrated a tight linkage disequilibrium status. Variation detected here might have an impact on the function of bovine mc3r pseudogene.

[Genetic analysis of epistatic effects between ApoB and UCP on abdominal fat trait in chicken]

It has been found that epistasis for selective response plays an indispensible role in animal genetics and breeding. In this study, the polymorphisms of T123G in apoliprotein B (ApoB) and C1197A in uncoupling protein (UCP) among individuals from the 8th to the 10th generation populations of the Northeast Agricultural University broiler lines divergently selected for abdominal fat content (NEAUHFL) were detected, and genetic analysis of the epistatic effects between the two SNPs on abdominal fat percentage (AFP) was performed using Natural and Orthogonal InterActions (NOIA) model. According to these assays, we concluded that at least one out of four epistatic components between these two SNPs was significantly associated with AFP (Plt;0.05) in fat lines from the 8th to the 10th generations of NEAUHFL; on the contrary, none was significantly associated with AFP (P>0.05) in lean lines. Our results suggested that epistatic interactions among QTLs and functional SNPs in candidate genes affecting fat traits might lead to differences in growth patterns of fat traits between lean and fat chicken lines.