H. Li

Peroxisome Proliferator-Activated Receptor-γ Gene : A Key Regulator of Adipocyte Differentiation in Chickens

The peroxisome proliferator-activated receptors (PPAR) are members of the nuclear hormone receptor superfamily. Peroxisome proliferator-activated receptor-gamma is regarded as a master regulator of adipocyte differentiation in mammals. The current study was designed to investigate the function and regulatory mechanism of PPARgamma in chicken adipogenesis by RNA interference. Preadipocytes were isolated from the abdominal fat tissue of 12-d-old chickens and cultured. Small-interference PPARgamma RNA (siPPARgamma) was synthesized by in vitro transcription and transfected into chicken preadipocytes by using liposomes. The suppressive effect of siPPARgamma was detected by real-time reverse-transcription PCR and reverse-transcription PCR. The results showed that transient transfection with siPPARgamma significantly inhibited differentiation and enhanced proliferation of chicken preadipocytes (P < 0.05). The adipogenesis-associated adipocyte fatty acid-binding protein gene was down-regulated when PPARgamma was silenced. The current work indicates that PPARgamma is a key regulator of chicken preadipocyte differentiation.

Progress of genome wide association study in domestic animals

Domestic animals are invaluable resources for study of the molecular architecture of complex traits. Although the mapping of quantitative trait loci (QTL) responsible for economically important traits in domestic animals has achieved remarkable results in recent decades, not all of the genetic variation in the complex traits has been captured because of the low density of markers used in QTL mapping studies. The genome wide association study (GWAS), which utilizes high-density single-nucleotide polymorphism (SNP), provides a new way to tackle this issue. Encouraging achievements in dissection of the genetic mechanisms of complex diseases in humans have resulted from the use of GWAS. At present, GWAS has been applied to the field of domestic animal breeding and genetics, and some advances have been made. Many genes or markers that affect economic traits of interest in domestic animals have been identified. In this review, advances in the use of GWAS in domestic animals are described.

Comparison of adipose tissue cellularity in chicken lines divergently selected for fatness

After 13 generations of divergent selection for abdominal fatness, 2 chicken lines (a fat line and a lean line) have been established. To clarify the cellular mechanism underlying the differences in fatness between the fat and lean lines, cellularity characteristics of the abdominal adipose tissues were analyzed during the first 7 wk of age by electron microscopy, proliferating cell nuclear antigen staining, and DNA content measurement. The abdominal fat percentage at 7 wk of age in the fat chicken line was 3.8 times that of the lean line, and was accompanied by a 1.3-fold increase in adipocyte diameter and a 2.4-fold increase in adipocyte number. The total cell number of the abdominal fat pad in the fat chicken line was 1.9 times that of the lean line at 7 wk of age. However, no significant difference was observed in the proliferation rate of stroma vascular fraction cells between the 2 chicken lines. These findings suggest that the divergently selected fat and lean chickens have different adipose tissue ontogeny.

A genome-wide scan of selective sweeps in two broiler chicken lines divergently selected for abdominal fat content

BackgroundGenomic regions controlling abdominal fatness (AF) were studied in the Northeast Agricultural University broiler line divergently selected for AF. In this study, the chicken 60KSNP chip and extended haplotype homozygosity (EHH) test were used to detect genome-wide signatures of AF.ResultsA total of 5357 and 5593 core regions were detected in the lean and fat lines, and 51 and 57 reached a significant level (P<0.01), respectively. A number of genes in the significant core regions, including RB1, BBS7, MAOA, MAOB, EHBP1, LRP2BP, LRP1B, MYO7A, MYO9A and PRPSAP1, were detected. These genes may be important for AF deposition in chickens.ConclusionsWe provide a genome-wide map of selection signatures in the chicken genome, and make a contribution to the better understanding the mechanisms of selection for AF content in chickens. The selection for low AF in commercial breeding using this information will accelerate the breeding progress.

Fine-Mapping Quantitative Trait Loci for Body Weight and Abdominal Fat Traits: Effects of Marker Density and Sample Size

Highly significant QTL for BW and abdominal fat traits on chicken chromosome 1 were reported previously in a unique F2 population. The objective of this study was to confirm and refine the QTL locations. Compared with the previous experiment, this study added 8 new families, including all the animals in the pedigree, and genotyped 9 more microsatellite markers, including 6 novel ones. Linkage analyses were performed. The results of the linkage analyses showed that the confidence intervals for BW and abdominal fat percentage were narrowed sharply to a small interval spanning 5.5 and 3.7 Mb, respectively. The results of the present study showed that using more markers and individuals could decrease the confidence interval of QTL effectively. In the current QTL region, by combining the biological knowledge of genes and the results of a microarray analysis that was performed in divergently selected lean and fat lines, several genes stood out as potential candidate genes.

Selection signature analysis implicates the PC1/PCSK1 region for chicken abdominal fat content

We conducted a selection signature analysis using the chicken 60k SNP chip in two chicken lines that had been divergently selected for abdominal fat content (AFC) for 11 generations. The selection signature analysis used multiple signals of selection, including long-range allele frequency differences between the lean and fat lines, long-range heterozygosity changes, linkage disequilibrium, haplotype frequencies, and extended haplotype homozygosity. Multiple signals of selection identified ten signatures on chromosomes 1, 2, 4, 5, 11, 15, 20, 26 and Z. The 0.73 Mb PC1/PCSK1 region of the Z chromosome at 55.43-56.16 Mb was the most heavily selected region. This region had 26 SNP markers and seven genes, Mar-03, SLC12A2, FBN2, ERAP1, CAST, PC1/PCSK1 and ELL2, where PC1/PCSK1 are the chicken/human names for the same gene. The lean and fat lines had two main haplotypes with completely opposite SNP alleles for the 26 SNP markers and were virtually line-specific, and had a recombinant haplotype with nearly equal frequency (0.193 and 0.196) in both lines. Other haplotypes in this region had negligible frequencies. Nine other regions with selection signatures were PAH-IGF1, TRPC4, GJD4-CCNY, NDST4, NOVA1, GALNT9, the ESRP2-GALR1 region with five genes, the SYCP2-CADH4 with six genes, and the TULP1-KIF21B with 14 genes. Genome-wide association analysis showed that nearly all regions with evidence of selection signature had SNP effects with genome-wide significance (P<10–6) on abdominal fat weight and percentage. The results of this study provide specific gene targets for the control of chicken AFC and a potential model of AFC in human obesity.

A POLYMORPHISM IN THE 3-FLANKING REGION OF INSULIN- LIKE GROWTH FACTOR BINDING PROTEIN 2 GENE ASSOCIATED WITH ABDOMINAL FAT IN CHICKENS

Insulin-like growth factor binding protein 2 (IGFBP2) is the predominant insulin-like growth factor binding protein in serum of different species. It binds insulin-like growth factors and plays an important role in growth and fat metabolism. The current study was designed to investigate the associations of IGFBP2 gene 3-flanking region polymorphisms with chicken fatness traits. The random populations (5 distinct populations: Arbor Acres broiler, Hyline Brown layer, Shiqiza, BeijingYou, and Baier), the Northeast Agricultural University broiler lines divergently selected for abdominal fat content (NEAUHLF), and the the Northeast Agricultural University F(2) (NEAU F(2)) resource population were used in the current study. Body weight and body composition traits were measured in NEAUHLF and NEAU F(2) populations. A SNP of 1196C > A in the 3-flanking region of the IGFBP2 gene was detected, and the PCR-single strand conformation polymorphism method was then used to genotype all of the individuals derived from the above populations. There was a highly significant difference (P < 0.01) in the allele frequency among the 5 distinct populations. The IG-FBP2 polymorphism was significantly associated with abdominal fat weight and percentage of abdominal fat (P < 0.05) in NEAUHLF and NEAU F(2) populations. The research suggests that the IGFBP2 gene could be a candidate locus or linked to a major gene that affects fatness traits in chickens.

Tissue expression characterization of chicken adipocyte fatty acid-binding protein and its expression difference between fat and lean birds in abdominal fat tissue.

Fatty acid-binding proteins are considered to be the carriers for the transportation of intracellular fatty acids and play an important role in the development of fatness traits. Adipocyte fatty acid-binding protein (A-FABP) is one of the family members. The current study was designed to analyze the tissue expression characterization of chicken A-FABP and its expression difference between the fat and lean males in abdominal fat tissue to reveal the possible relationship between the expression of A-FABP and abdominal fat tissue development and growth in chicken. First, fusion protein glutathione S-transferase/A-FABP was induced and purified, and then the antiserum containing specific polyclonal antibodies was obtained by immunizing healthy female rabbits using the purified fusion protein. Second, tissue expression characterization of A-FABP was investigated by Western blot. Finally, A-FABP expression difference in abdominal fat tissue between the fat and lean males was investigated by real-time reverse transcription-PCR and Western blot methods. The results showed that A-FABP expressed specifically in abdominal fat tissue and the mRNA expression level of A-FABP in fat males was lower than that of lean males at 2, 3, 4, 6, 7, 9, and 10 wk of age (P<0.05), and the protein expression level of fat males was lower than that of lean males at 6 and 10 wk of age (P<0.05). These results suggested that chicken A-FABP might affect abdominal fat deposition through changing its expression level, and the possible mechanism may be that a high expression level of A-FABP induced the high lipolytic rate and led to the decreased abdominal fat mass accordingly.

Identification of differentially expressed proteins in adipose tissue of divergently selected broilers

Reducing fat has been a major goal for the broiler industry. To gain insight into the molecular mechanisms underlying the regulation of fat deposition in chickens, a 2-dimensional electrophoresis-based proteomic approach was used to analyze the differentially expressed proteins in abdominal adipose tissues of Northeast Agricultural University broiler lines divergently selected for abdominal fat content (NEAUHLF). A total of 20 differentially expressed protein spots were found in abdominal adipose tissue between fat and lean broilers at 7 wk of age. Among them, 12 protein spots were upregulated and 8 protein spots were downregulated in fat birds compared with those in lean birds. These 20 protein spots were then identified by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry and matched to 15 proteins by searching against the NCBInr and SWISS-PROT databases, including adipocyte fatty acid-binding protein, apolipoprotein A-I, long-chain acyl-coenzyme A dehydrogenase, heat shock protein beta 1, glutathione S-transferase theta 1, glutathione S-transferase class alpha, guanine nucleotide-binding protein beta polypeptide 1, syntaxin 2, vimentin, cofilin 2, otokeratin, telomerase catalytic subunit, and 3 hypothetical proteins. These proteins are mainly related to lipid metabolism, chaperone, redox, signal transduction, transport, and cytoskeleton. The results, from the point of view of protein expression, establish the groundwork for further studies of the basic genetic control of growth and development of broiler adipose tissue.

Variation at the insulin-like growth factor 1 gene and its association with body weight traits in the chicken.

The insulin-like growth factor 1 (IGF1) is essential for normal embryonic and postnatal growth in mammals. In this study, a total of 342 F(2) individuals, derived from Broiler crossing to Baier layer (Northeast Agricultural University Resource Population, NEAURP), were used to investigate the associations of haplotypes in the chicken IGF1 (cIGF1) gene with body weight traits. Primers for the 5-flanking, exon 3 and 3-flanking regions of cIGF1 were designed according to chicken genome database. Single nucleotide polymorphisms (SNPs) between parental lines were detected by sequencing, and PCR restriction fragment length polymorphism (PCR-RFLP) and PCR single-stranded-conformation polymorphism (PCR-SSCP) methods were used to genotype the SNPs in the population. Haplotypes were constructed with the three SNPs detected. The association analysis showed that haplotypes based on three cIGF1 polymorphisms (c.-366A>C, c.528G>A and c.*1024C>T) were associated with body weight traits, suggesting that cIGF1 or a tightly linked gene had effects on body weight in the chicken.