Chicken Intramuscular Fat Deposition Research Articles

Integrative multiomics analysis identifies key genes regulating intramuscular fat deposition during development

Intramuscular fat (IMF) content is an important indicator of livestock and poultry meat quality. Enhancing IMF deposition can significantly improve meat quality. Focusing on the core process of IMF deposition, this study used the Jingxing Yellow (JXY) chickens as a model organism and employed multi-omics approaches, including RNA-sequencing (RNA-seq), Whole-genome bisulfite sequencing (WGBS), and metabolomics, to identify the key genes influencing IMF deposition in chickens during development. The results indicated that the contents of triglycerides (TG) and phospholipids (PLIP) exhibited an upward trend. The TG content did not differ significantly between day 1 (D1) and day 7 (D7), but increased significantly after 35 days (D35) of age. The WGBS results revealed that CpG methylation was the predominant methylation type in the breast muscle tissue of JXY chickens. Integrative analysis of RNA-seq and WGBS identified 50 genes, including PLA2G4F, PALMD, PLSCR5, ARHGEF26, LUM, DCN, TNRC6B, CACNA1C, ROBO1, and MBTPS2, whose methylation levels were significantly negatively correlated with their expression levels. In addition, the combined Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of differentially-expressed metabolites (DEM) and differentially-expressed genes (DEG) converged on the glycerophospholipid metabolism pathway, which was significantly enriched in DEGs such as PLA2G4F, PLA2G15, LPIN1, MBOAT2, DGKH, AGPAT2, and CHKA, as well as DEM like glycerophosphocholine and phosphocholine. Notably, PLA2G4F was identified as a DEG by DNA methylation, suggesting that PLA2G4F could be a key candidate gene influencing IMF deposition during chicken development. These findings are expected to provide a solid theoretical foundation for improving meat quality through targeted genetic and epigenetic interventions.

Dynamic alternations of three-dimensional chromatin architecture contribute to phenotypic characteristics of breast muscle in chicken

Breast muscle growth rate and intramuscular fat (IMF) content show apparent differences between fast-growing broilers and slow-growing indigenous chickens. However, the underlying genetic basis of these phenotypic characteristics remains elusive. In this study, we investigate the dynamic alterations of three-dimensional genome architecture and chromatin accessibility in breast muscle across four key developmental stages from embryo to starter chick in Arbor Acres (AA) broilers and Yufen (YF) indigenous chickens. The limited breed-specifically up-regulated genes (Bup-DEGs) are embedded in breed-specific A compartment, while a majority of the Bup-DEGs involving myogenesis and adipogenesis are regulated by the breed-specific TAD reprogramming. Chromatin loops allow distal accessible regions to interact with myogenic genes, and those loops share an extremely low similarity between chicken with different growth rate. Moreover, AA-specific loop interactions promote the expression of 40 Bup-DEGs, such as IGF1, which contributes to myofiber hypertrophy. YF-specific loop interactions or distal accessible regions lead to increased expression of 5 Bup-DEGs, including PIGO, PEMT, DHCR7, TMEM38B, and DHDH, which contribute to IMF deposition. These results help elucidate the regulation of breast muscle growth and IMF deposition in chickens.

Identification of key differentially methylated genes in regulating muscle development and intramuscular fat deposition in chickens

Muscle development and intramuscular fat (IMF) deposition are intricate physiological processes characterized by multiple gene expressions and interactions. In this research, the phenotypic variations in the breast muscle of Jingyuan chickens were examined at three different time points: 42, 126, and 180 days old. Differential expression analysis and weighted gene co-expression network analysis (WGCNA) were performed to identify differentially methylated genes (DMGs) responsible for regulating muscle development and IMF deposition. The findings indicate a significant increase in breast muscle weight (BMW), myofiber diameter, and cross-sectional area, as well as IMF content, in correlation with the progressive number of growing days in Jingyuan chickens. The findings also revealed that 380 hypo-methylated and 253 hyper-methylated DMGs were identified between the three groups of breast muscle. Module gene and DMG association analysis identified m6A methylation-mediated multiple DMGs associated with muscle development and fat metabolism. In vitro cell modeling analysis reveals stage-specific differences in the expression of CUBN, MEGF10, BOP1, and BMPR2 during the differentiation of myoblasts and intramuscular preadipocytes. Cycloleucine treatment significantly inhibited the expression levels of CUBN, BOP1, and BMPR2, and promoted the expression of MEGF10. These results suggest that m6A methylation-mediated CUBN, MEGF10, BOP1, and BMPR2 can serve as potential candidate genes for regulating muscle development and IMF deposition, and provide an important theoretical basis for further investigation of the functional mechanism of m6A modification involved in adipogenesis.

RNA sequencing identifies key genes involved in intramuscular fat deposition in chickens at different developmental stages

BackgroundIntramuscular fat (IMF) is an important factor in meat quality, and triglyceride (TG) and Phospholipids (PLIP), as the main components of IMF, are of great significance to the improvement of meat quality.ResultsIn this study, we used 30 RNA sequences generated from the transcriptome of chicken breast muscle tissues at different developmental stages to construct a gene expression matrix to map RNA sequence reads to the chicken genome and identify the transcript of origin. We used weighted gene co-expression network analysis (WGCNA) and identified 27 co-expression modules, 10 of which were related to TG and PLIP. We identified 150 highly-connected hub genes related to TG and PLIP, respectively, which were found to be mainly enriched in the adipocytokine signaling pathway, MAPK signaling pathway, mTOR signaling pathway, FoxO signaling pathway, and TGF-beta signaling pathway. Additionally, using the BioMart database, we identified 134 and 145 candidate genes related to fat development in the TG-related module and PLIP-related module, respectively. Among them, RPS6KB1, BRCA1, CDK1, RPS3, PPARGC1A, ACSL1, NDUFAB1, NDUFA9, ATP5B and PRKAG2 were identified as candidate genes related to fat development and highly-connected hub genes in the module, suggesting that these ten genes may be important candidate genes affecting IMF deposition.ConclusionsRPS6KB1, BRCA1, CDK1, RPS3, PPARGC1A, ACSL1, NDUFAB1, NDUFA9, ATP5B and PRKAG2 may be important candidate genes affecting IMF deposition. The purpose of this study was to identify the co-expressed gene modules related to chicken IMF deposition using WGCNA and determine key genes related to IMF deposition, so as to lay a foundation for further research on the molecular regulation mechanism underlying chicken fat deposition.

Genomic Insights into Molecular Regulation Mechanisms of Intramuscular Fat Deposition in Chicken.

Intramuscular fat (IMF) plays an important role in the tenderness, water-holding capacity, and flavor of chicken meat, which directly affect meat quality. In recent years, regulatory mechanisms underlying IMF deposition and the development of effective molecular markers have been hot topics in poultry genetic breeding. Therefore, this review focuses on the current understanding of regulatory mechanisms underlying IMF deposition in chickens, which were identified by multiple genomic approaches, including genome-wide association studies, whole transcriptome sequencing, proteome sequencing, single-cell RNA sequencing (scRNA-seq), high-throughput chromosome conformation capture (HiC), DNA methylation sequencing, and m6A methylation sequencing. This review comprehensively and systematically describes genetic and epigenetic factors associated with IMF deposition, which provides a fundamental resource for biomarkers of IMF deposition and provides promising applications for genetic improvement of meat quality in chicken.

Regulatory role of N6-methyladenosine in intramuscular fat deposition in chicken

Intramuscular fat (IMF) has a pivotal influence on meat quality, with its deposition being a multifaceted physiological interaction of several regulatory factors. N6-methyladenosine (m6A), the preeminent epigenetic alteration among eukaryotic RNA modifications, holds a crucial role in moderating post-transcriptional gene expression. However, there is a dearth of comprehensive understanding regarding the functional machinery of m6A modification in the context of IMF deposition in poultry. Our current study entails an analysis of the disparities in IMF within the breast and leg of 180-day-old Jingyuan chickens. We implemented methylated RNA immunoprecipitation sequencing (MeRIP-seq) and RNA sequencing (RNA-seq) to delve into the distribution of m6A and its putative regulatory frameworks on IMF deposition in chickens. The findings demonstrated a markedly higher IMF content in leg relative to breast (P < 0.01). Furthermore, the expression of METTL14, WTAP, FTO, and ALKBH5 was significantly diminished in comparison to that of breast (P < 0.01). The m6A peaks in the breast and leg primarily populated 3'untranslated regions (3'UTR) and coding sequence (CDS) regions. The leg, when juxtaposed with the breast, manifested 176 differentially methylated genes (DMGs), including 151 hyper-methylated DMGs and 25 hypo-methylated DMGs. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed a pronounced enrichment of DMGs in the biosynthesis of amino acids, peroxisome, Fatty acid biosynthesis, fatty acid elongation, and cell adhesion molecules (CAMs) pathways. Key DMGs, namely ECH1, BCAT1, and CYP1B1 were implicated in the regulation of muscle lipid anabolism. Our study offers substantial insight and forms a robust foundation for further exploration of the functional mechanisms of m6A modification in modulating IMF deposition. This holds profound theoretical importance for improving and leveraging meat quality in indigenous chicken breeds.

Co-expression analysis of long non-coding RNAs and mRNAs involved in intramuscular fat deposition in Muchuan black-bone chicken

ABSTRACT 1. The intramuscular fat (IMF) content in meat products is positively correlated with meat quality, making it an important consumer trait. Long non-coding RNAs (lncRNAs) play central roles in regulating various biological processes, but little is currently known about the mechanisms by which they regulate IMF deposition in chickens. 2. This study sampled the breast muscles of chickens with high (H) and low (L) IMF content and constructed six small RNA libraries. High-throughput sequencing technology was used to profile the breast muscle transcriptome (lncRNA and mRNA) and to identify the differentially expressed lncRNAs (DELs) and mRNAs (DEGs) between the H and L groups. In total, 263 DELs (118 up-regulated and 145 down-regulated lncRNAs) and 443 DEGs (203 up-regulated and 240 down-regulated genes) were identified between the two groups. 3. To analyse the DELs-DEGs interaction network, co-expression analysis was conducted to identify lncRNA-mRNA pairs. In total, 19270 lncRNA/mRNA pairs were identified, including 16 398 significant correlation pairs that presented as positive and 2872 pairs that presented as negative. The lncRNA – mRNA network comprised 263 lncRNA nodes and 440 mRNA nodes. 4. Pathway analysis, using the Kyoto Encyclopedia of Genes and Genomes, indicated pathways associated with fat deposition and lipid metabolism such as the MAPK, PPAR, GnRH, ErbB and calcium signalling pathways, fatty acid elongation and fatty acid metabolism. Overall, the study identified potential candidate lncRNAs, genes and regulatory networks associated with chicken IMF deposition. These findings provide new insights to help clarify the regulatory mechanisms of IMF deposition in chickens which can be used to improve the IMF content in poultry.

Effects of Dietary Vitamin E on Intramuscular Fat Deposition and Transcriptome Profile of the Pectoral Muscle of Broilers.

Vitamin E is an essential micronutrient for animals. The aim of this study was to determine the effect of vitamin E on intramuscular fat (IMF) deposition and the transcriptome profile of the pectoral muscle in broiler chickens. Arbor Acres chickens were divided into five treatment groups fed a basal diet supplemented with 0, 20, 50, 75, and 100 IU/kg dietary DL-α-tocopheryl acetate (vitamin E), respectively. Body weight, carcass performance, and IMF content were recorded. Transcriptome profiles of the pectoral muscles of 35-day-old chickens in the control and treatment groups (100 IU/kg of vitamin E) were obtained by RNA sequencing. The results showed that diets supplemented with 100 IU/kg of vitamin E significantly increased IMF deposition in chickens on day 35. In total, 159 differentially expressed genes (DEGs), including 57 up-regulated and 102 down-regulated genes, were identified in the treatment (100 IU/kg vitamin E) group compared to the control group. These DEGs were significantly enriched in 13 Gene Ontology terms involved in muscle development and lipid metabolism; three signaling pathways, including the mitogen-activated protein kinase and FoxO signaling pathways, which play key roles in muscular and lipid metabolism; 28 biofunctional categories associated with skeletal and muscular system development; 17 lipid metabolism functional categories; and three lipid metabolism and muscle development-related networks. The DEGs, pathways, functional categories, and networks identified in this study provide new insights into the regulatory roles of vitamin E on IMF deposition in broilers. Therefore, diets supplemented with 100 IU/kg of vitamin E will be more beneficial to broiler production.

A selected population study reveals the biochemical mechanism of intramuscular fat deposition in chicken meat

BackgroundIncreasing intramuscular fat (IMF) is an important strategy to improve meat quality, but the regulation mechanism of IMF deposition needs to be systematically clarified.ResultsA total of 520 chickens from a selected line with improved IMF content and a control line were used to investigate the biochemical mechanism of IMF deposition in chickens. The results showed that the increased IMF would improve the flavor and tenderness quality of chicken meat. IMF content was mainly determined both by measuring triglyceride (TG) and phospholipid (PLIP) in muscle tissue, but only TG content was found to be decisive for IMF deposition. Furthermore, the increase in major fatty acid (FA) components in IMF is mainly derived from TGs (including C16:0, C16:1, C18:1n9c, and C18:2n6c, etc.), and the inhibition of certain very-long-chain FAs would help to IMF/TG deposition.ConclusionsOur study elucidated the underlying biochemical mechanism of IMF deposition in chicken: Prevalent accumulation of long-chain FAs and inhibitions of medium-chain FAs and very long chain FA would jointly result in the increase of TGs with the FA biosynthesis and cellular uptake ways. Our findings will guide the production of high-quality chicken meat.

Screening and functional validation of lipid metabolism-related lncRNA-46546 based on the transcriptome analysis of early embryonic muscle tissue in chicken.

The study was conducted to screen differentially expressed long noncoding RNA (lncRNA) in chickens by high-throughput sequencing and explore its mechanism of action on intramuscular fat deposition. Herein, Rose crown and Cbb broiler chicken embryo breast and leg muscle lncRNA and mRNA expression profiles were constructed by RNA sequencing. A total of 96 and 42 differentially expressed lncRNAs were obtained in Rose crown vs Cobb broiler chicken breast and leg muscle, respectively. lncRNA-ENSGALT00000046546, with high interspecific variability and a potential regulatory role in lipid metabolism, and its predicted downstream target gene 1-acylglycerol-3-phosphate-O-acyltransferase 2 (AGPAT2), were selected for further study on the preadipocytes. lncRNA-46546 overexpression in chicken preadipocyte 2 cells significantly increased (p<0.01) the expression levels of AGPAT2 and its downstream genes diacylglycerol acyltransferase 1 and diacylglycerol acyltransferase 2 and those of the fat metabolism-related genes peroxisome proliferator-activated receptor γ, CCAAT/enhancer binding protein α, fatty acid synthase, sterol regulatory element-binding transcription factor 1, and fatty acid binding protein 4. The lipid droplet concentration was higher in the overexpression group than in the control cells, and the triglyceride content in cells and medium was also significantly increased (p<0.01). This study preliminarily concludes that lncRNA-46546 may promote intramuscular fat deposition in chickens, laying a foundation for the study of lncRNAs in chicken early embryonic development and fat deposition.

Krüppel-like factor KLF9 inhibits chicken intramuscular preadipocyte differentiation

ABSTRACT 1. Poultry meat quality is affected by many factors, among which intramuscular fat (IMF) is predominant. IMF content affects tenderness, juiciness and flavour of meat. Krüppel-like transcriptional factors (KLFs) are important regulators of adipocyte differentiation. However, little is known about the KLF9 gene associated with poultry IMF deposition, especially intramuscular adipocyte differentiation. 2. Previous work has shown that chicken KLF9 was differentially expressed during adipogenesis of intramuscular preadipocytes differentiation. In this study, the function of KLF9 in chicken intramuscular preadipocytes differentiation was investigated. 3. In the chicken preadipocyte differentiation model, KLF9 expression showed a major increase with adipogenic induction. Overexpression of KLF9 down-regulated the expression of the adipogenic marker gene AP2, and impaired triglyceride accumulation. Knockdown of KLF9 in chicken intramuscular preadipocytes increased the expression of PPARG, CEBPA and AP2. In addition, it was proposed that KLF9 may regulate adipogenesis via lncRNAs NONGGAT002209.2, NONGGAT003346.2, NONGGAT000436.2 and NONGGAT006302.2 in chicken. 4. The data supported a novel role of KLF9 in regulating chicken intramuscular preadipocyte differentiation. Such findings may contribute to a more thorough understanding of chicken IMF deposition and the improvement of poultry meat quality.

Gga-miRNA-18b-3p Inhibits Intramuscular Adipocytes Differentiation in Chicken by Targeting the ACOT13 Gene.

Intramuscular fat (IMF) is the most important evaluating indicator of chicken meat quality, the content of which is positively correlated with tenderness, flavor, and succulence of the meat. Chicken IMF deposition process is regulated by many factors, including genetic, nutrition, and environment. Although large number of omics’ studies focused on the IMF deposition process, the molecular mechanism of chicken IMF deposition is still poorly understood. In order to study the role of miRNAs in chicken intramuscular adipogenesis, the intramuscular adipocyte differentiation model (IMF-preadipocytes and IMF-adipocytes) was established and subject to miRNA-Seq. A total of 117 differentially expressed miRNAs between two groups were obtained. Target genes prediction and functional enrichment analysis revealed that eight pathways involved in lipid metabolism related processes, such as fatty acid metabolism and fatty acid elongation. Meanwhile a putative miRNA, gga-miR-18b-3p, was identified be served a function in the intramuscular adipocyte differentiation. Luciferase assay suggested that the gga-miR-18b-3p targeted to the 3′UTR of ACOT13. Subsequent functional experiments demonstrated that gga-miR-18b-3p acted as an inhibitor of intramuscular adipocyte differentiation by targeting ACOT13. Our findings laid a new theoretical foundation for the study of lipid metabolism, and also provided a potential target to improve the meat quality in the poultry industry.

LncRNA IMFNCR Promotes Intramuscular Adipocyte Differentiation by Sponging miR-128-3p and miR-27b-3p.

Poultry meat quality is affected by many factors, among which intramuscular fat (IMF) is predominant. IMF content affects the tenderness, juiciness, and flavor of chicken. An increasing number of studies are focusing on the functions of lncRNAs in adipocyte differentiation. However, little is known about lncRNAs associated with intramuscular adipocyte differentiation. In the present study, we focused on an up-regulated lncRNA during intramuscular adipogenetic differentiation, which we named intramuscular fat-associated long non-coding RNA (IMFNCR). IMFNCR promotes intramuscular adipocyte differentiation. In-depth analyses showed that IMFNCR acts as a molecular sponge for miR-128-3p and miR-27b-3p and that PPARG is a direct target of miR-128-3p and miR-27b-3p in chicken. High-fat and high-protein diet inhibited chicken IMFNCR level in vivo. Moreover, IMFNCR level was positively correlated with PPARG mRNA level in chicken breast muscle tissues, a vital corollary to ceRNA function. Altogether, our research showed that IMFNCR acts as a ceRNA to sequester miR-128-3p and miR-27b-3p, leading to heightened PPARG expression, and thus promotes intramuscular adipocyte differentiation. Taken together, our findings may contribute to a more thorough understanding of chicken IMF deposition and the improvement of poultry meat quality.

Characterization of miRNA transcriptome profiles related to breast muscle development and intramuscular fat deposition in chickens.

Studies of the miRNA expression profiles associated with the postnatal late development of skeletal muscle and IMF deposition are lacking in chicken. Here, we evaluated the patterns of muscle fiber growth and IMF deposition in breast muscle in the Chinese domestic breed called Gushi chicken, where we constructed four small RNA libraries from breast muscle tissues at 6, 14, 22, and 30 weeks. A total of 388 known miRNAs and 31 novel miRNAs were identified based on four small RNA libraries. Comparative analysis identified 92 significant differentially expressed (SDE) miRNAs based on six combinations. KEGG pathway analysis for the SDE miRNAs showed that metabolic pathways such as glycolysis and biosynthesis of amino acids were significantly enriched before 22 weeks, and pathways such as biosynthesis of unsaturated fatty acids and fatty acid elongation were significantly enriched after 22 weeks. This trend was consistent with the patterns of breast muscle fiber growth and IMF deposition in Gushi chickens. We also constructed miRNA-mRNA interaction networks related to breast muscle development and IMF deposition. The results showed that miRNAs such as gga-miR-1a-3p, and gga-miR-133a-5p may play important roles in breast muscle development, and miRNAs such as gga-miR-103-3p, and gga-miR-138-2-3p may have key roles in IMF deposition. This study determined the dynamic miRNA transcriptome in breast muscle tissue for the first time in Gushi chickens. The results provide a valuable resource for investigating the post-transcriptional regulation mechanisms during postnatal late development of breast muscle and IMF deposition and for evaluating the muscular disease.

Integrated Analysis of MiRNA and Genes Associated with Meat Quality Reveals that Gga-MiR-140-5p Affects Intramuscular Fat Deposition in Chickens

Background/Aims: Poultry meat quality is affected by many factors, among which intramuscular fat (IMF) is predominant. IMF content affects the tenderness, juiciness, and favor of chicken. An increasing number of studies are focusing on the functions of microRNAs (miRNAs) during the adipogenic process. However, little is known about miRNAs associated with poultry IMF deposition, especially intramuscular adipocyte differentiation. Methods: The IMF content of two physiological stages was measured, and miRNA-Seq and RNA-Seq data were integrated and analyzed. A chicken intramuscular adipocyte cell differentiation model was constructed. A luciferase reporter assay, miRNA overexpression, and Oil Red O staining were used to confirm the targets of gga-miR-140-5p. Results: Our results showed that late-laying-period hens, which had a higher IMF content, exhibited lower global expression levels of miRNAs than juvenile hens. A total of 104 differentially expressed (DE) miRNAs were identified between the two groups. Integrated analysis of differentially expressed genes and DE miRNAs identified a total of 378 miRNA-mRNA pairs. Functional enrichment analysis revealed that these intersecting genes are involved in ubiquitin-mediated proteolysis, the peroxisome proliferator-activated receptor signaling pathway, glycerophospholipid metabolism, and fatty acid elongation and degradation pathways. Furthermore, we demonstrated that gga-miR-140-5p promoted intramuscular adipocyte differentiation via targeting retinoid X receptor gamma. Conclusion: Our findings may contribute to a more thorough understanding of chicken IMF deposition and the improvement of poultry meat quality.

Uncovering the embryonic development-related proteome and metabolome signatures in breast muscle and intramuscular fat of fast-and slow-growing chickens

BackgroundSkeletal muscle development is closely linked to meat production and its quality. This study is the first to quantify the proteomes and metabolomes of breast muscle in two distinct chicken breeds at embryonic day 12 (ED 12), ED 17, post-hatch D 1 and D 14 using mass spectrometry-based approaches.ResultsResults found that intramuscular fat (IMF) accumulation increased from ED 17 to D 1 and that was exactly the opposite of when most obvious growth of muscle occurred (ED 12 - ED 17 and D 1 - D 14). For slow-growing Beijing-You chickens, Ingenuity Pathway Analysis of 77–99 differential abundance (DA) proteins and 63–72 metabolites, indicated significant enrichment of molecules and pathways related to protein processing and PPAR signaling. For fast-growing Cobb chickens, analysis of 68–95 DA proteins and 56–59 metabolites demonstrated that molecules and pathways related to ATP production were significantly enriched after ED12. For IMF, several rate-limiting enzymes for beta-oxidation of fatty acid (ACADL, ACAD9, HADHA and HADHB) were identified as candidate biomarkers for IMF deposition in both breeds.ConclusionsThis study found that ED 17 - D 1 was the earliest period for IMF accumulation. Pathways related to protein processing and PPAR signaling were enriched to support high capacity of embryonic IMF accumulation in Beijing-You. Pathways related to ATP production were enriched to support the fast muscle growth in Cobb. The beta-oxidation of fatty acid is identified as the key pathway regulating chicken IMF deposition at early stages.

Lower Expression of SLC27A1 Enhances Intramuscular Fat Deposition in Chicken via Down-Regulated Fatty Acid Oxidation Mediated by CPT1A.

Intramuscular fat (IMF) is recognized as the predominant factor affecting meat quality due to its positive correlation with tenderness, juiciness, and flavor. Chicken IMF deposition depends on the balance among lipid synthesis, transport, uptake, and subsequent metabolism, involving a lot of genes and pathways, however, its precise molecular mechanisms remain poorly understood. In the present study, the breast muscle tissue of female Wenchang chickens (WC) (higher IMF content, 1.24 in D120 and 1.62 in D180) and female White Recessive Rock chickens (WRR; lower IMF content, 0.53 in D120 and 0.90 in D180) were subjected to RNA-sequencing (RNA-seq) analysis. Results showed that many genes related to lipid catabolism, such as SLC27A1, LPL, ABCA1, and CPT1A were down-regulated in WC chickens, and these genes were involved in the PPAR signaling pathway and formed an IPA® network related to lipid metabolism. Furthermore, SLC27A1 was more down-regulated in WRR.D180.B than in WRR.D120.B. Decreased cellular triglyceride (TG) and up-regulated CPT1A were observed in the SLC27A1 overexpression QM-7 cells, and increased cellular triglyceride (TG) and down-regulated CPT1A were observed in the SLC27A1 knockdown QM-7 cells. These results suggest that lower lipid catabolism exists in WC chickens but not in WRR chickens, and lower expression of SLC27A1 facilitate IMF deposition in chicken via down-regulated fatty acid oxidation mediated by CPT1A. These findings indicate that reduced lipid catabolism, rather than increased lipid anabolism, contributes to chicken IMF deposition.

Protein Profiles for Muscle Development and Intramuscular Fat Accumulation at Different Post-Hatching Ages in Chickens.

Muscle development and growth influences the efficiency of poultry meat production, and is closely related to deposition of intramuscular fat (IMF), which is crucial in meat quality. To clarify the molecular mechanisms underlying muscle development and IMF deposition in chickens, protein expression profiles were examined in the breast muscle of Beijing-You chickens at ages 1, 56, 98 and 140 days, using isobaric tags for relative and absolute quantification (iTRAQ). Two hundred and four of 494 proteins were expressed differentially. The expression profile at day 1 differed greatly from those at day 56, 98 and 140. KEGG pathway analysis of differential protein expression from pair-wise comparisons (day 1 vs. 56; 56 vs. 98; 98 vs. 140), showed that the fatty acid degradation pathway was more active during the stage from day 1 to 56 than at other periods. This was consistent with the change in IMF content, which was highest at day 1 and declined dramatically thereafter. When muscle growth was most rapid (days 56–98), pathways involved in muscle development were dominant, including hypertrophic cardiomyopathy, dilated cardiomyopathy, cardiac muscle contraction, tight junctions and focal adhesion. In contrast with hatchlings, the fatty acid degradation pathway was downregulated from day 98 to 140, which was consistent with the period for IMF deposition following rapid muscle growth. Changes in some key specific proteins, including fast skeletal muscle troponin T isoform, aldehyde dehydrogenase 1A1 and apolipoprotein A1, were verified by Western blotting, and could be potential biomarkers for IMF deposition in chickens. Protein–protein interaction networks showed that ribosome-related functional modules were clustered in all three stages. However, the functional module involved in the metabolic pathway was only clustered in the first stage (day 1 vs. 56). This study improves our understanding of the molecular mechanisms underlying muscle development and IMF deposition in chickens.

Gene expression and enzyme activity of lipoprotein lipase correlate with intramuscular fat content in Guangxi san-huang and Arbor Acres chickens.

Lipoprotein lipase (LPL) is a key enzyme in lipid metabolism. This study investigated LPL gene expression, LPL enzyme activity, and the correlation of each with intramuscular fat (IMF) in Chinese Guangxi san-huang (GXSH) and Arbor Acres (AA) chickens. The results showed that age and breed had significant effects on LPL expression and enzyme activity. Correlation analyses showed significant positive correlations between LPL expression levels and IMF contents in the breast and thigh tissues of both GXSH (r = 0.712, P = 0.001; r = 0.792, P < 0.001, respectively) and AA (r = 0.644, P < 0.001; r = 0.545, P < 0.001, respectively) chickens. The results also indicated a significant positive correlation between LPL enzyme activity and IMF contents in the breast and thigh tissues of both GXSH (r = 0.615, P = 0.001; r = 0.685, P < 0.001, respectively) and AA (r = 0.600, P = 0.001; r = 0.528, P = 0.003, respectively) chickens. The results indicated that the LPL gene was significantly correlated with IMF in these two breeds. The results presented here could contribute to knowledge of LPL mRNA developmental expression patterns and enzyme activity, and it could facilitate further research on the molecular mechanisms underlying IMF deposition in chickens.

Expression profiles of key transcription factors involved in lipid metabolism in Beijing-You chickens

Intramuscular fat (IMF) is a crucial factor for the meat quality of chickens. With the aim of studying the molecular mechanisms underlying IMF deposition in chickens, the expression profiles of five candidate transcription factors involved in lipid metabolism in several tissues were examined in Beijing-You (BJY) chickens at five ages (0, 4, 8, 14 and 20wk). Results showed that accumulation of IMF in breast (IMFbr), thigh (IMFth) and abdominal fat weight increased significantly (P<0.01) after 8wk. Accumulation of both IMFbr and IMFth from 8 to 14wk exceeded that from 14 to 20wk; IMFth was 4–7 times of IMFbr. As for the expression profiles of key transcription factors: 1) expression of C/EBPα and PPARγ in abdominal fat was significantly higher than that in breast and thigh muscles at all ages. The expression of C/EBPα was positively correlated with PPARγ in both breast and thigh muscles, which indicated that both C/EBPα and PPARγ promoted fat deposition and might act through a unified pathway; 2) the expression of SREBP-1 in 0, 4, and 8wk in thigh muscle was significantly higher than that in breast; 3) expression of C/EBPβ at 4 and 8wk was significantly higher than that at 14 and 20wk; and it was positively correlated with IMFth and IMFbr from 0 to 8wk; 4) expression of PPARα in breast and thigh muscles was significantly higher than that in abdominal fat. Taken together, all five transcription factors studied play roles in lipid metabolism in chickens with C/EBPα and PPARγ being important effectors.