New insights into muscle fiber types in the pig

Comparison of Characteristics of Myosin Heavy Chain-based Fiber and Meat Quality among Four Bovine Skeletal Muscles

Muscle fiber characteristics account for meat quality and muscle fibers are mainly classified into three or more types according to their contractile and metabolic properties. However, the majority of previous studies on bovine skeletal muscle are based on myosin ATPase activity. In the present study, the differences in the characteristics of muscle fibers classified by the expression of myosin heavy chain (MHC) among four bovine skeletal muscles such as longissimus thoracis (LT), psoas major (PM), semimembranosus (SM) and semitendinosus (ST) and their relationships to beef quality were investigated. MHCs 2x, 2a and slow were identified by LC-MS/MS and IIX, IIA and I fiber types were classified. PM, which had the smallest size and highest density of fibers regardless of type, showed the highest myoglobin content, CIE L*, a*, b* and sarcomere length (p<0.05), whereas ST with the highest composition of IIX, showed high shear force and low sarcomere length (p<0.05). The correlation coefficients between muscle fiber characteristics and meat quality showed that type IIX is closely related to poor beef quality and that a high density of small-sized fibers is related to redness and tenderness. Therefore, the differences in meat quality between muscles can be explained by the differences in muscle fiber characteristics, and especially, the muscles with good quality are composed of more small-sized fibers regardless of fiber type.

Promoter analysis and tissue expression of the chicken ASB15 gene

1. This study was conducted to explore the promoter region of the chicken ASB15 gene by detecting the activities of the dual luciferase reporter gene and to assess expression profiles of the ASB15 gene in 10 different tissues from Gushi chickens. 2. Five dual luciferase reporter gene vectors were constructed and transfected into DF1 cells. The activities of recombined plasmids were measured and the core promoter was confirmed by bioinformatic analysis. Total RNA was extracted and the relative expression of the ASB15 gene was examined. 3. Data analysis indicated that the promoter was located from -955 to -212 bp. Results showed that the chicken ASB15 gene was expressed in heart, breast muscle and leg muscle. 4. This study has confirmed the promoter region and the expression profile of the chicken ASB15 gene, which provides a foundation for further exploring its transcriptional regulation and function.

Identification of Rosmarinic Acid-Adducted Sites in Meat Proteins in a Gel Model under Oxidative Stress by Triple TOF MS/MS

Triple TOF MS/MS was used to identify adducts between rosmarinic acid (RosA)-derived quinones and meat proteins in a gel model under oxidative stress. Seventy-five RosA-modified peptides responded to 67 proteins with adduction of RosA. RosA conjugated with different amino acids in proteins, and His, Arg, and Lys adducts with RosA were identified for the first time in meat. A total of 8 peptides containing Cys, 14 peptides containing His, 48 peptides containing Arg, 64 peptides containing Lys, and 5 peptides containing N-termini that which participated in adduction reaction with RosA were identified, respectively. Seventy-seven adduction sites were subdivided into all adducted proteins including 2 N-terminal adduction sites, 3 Cys adduction sites, 4 His adduction sites, 29 Arg adduction sites, and 39 Lys adduction sites. Site occupancy analyses showed that approximately 80.597% of the proteins carried a single RosA-modified site, 14.925% retained two sites, 1.492% contained three sites, and the rest 2.985% had four or more sites. Large-scale triple TOF MS/MS mapping of RosA-adducted sites reveals the adduction regulations of quinone and different amino acids as well as the adduction ratios, which clarify phenol-protein adductions and pave the way for industrial meat processing and preservation.

Expression of GHR and PGC-lα in association with changes of MyHC isof orm types in longissimus muscle of Erhualian and Large White pigs (Sus scrofa) during postnatal growth

Myofibre composition in longissimus dorsi (LD) muscle of Erhualian (EHL) and Large White (LW) pigs was investigated by determining the ratios of mRNA abundances of four myosin heavy chain (MyHC) isoforms (MyHC I, MyHC 2a, MyHC 2x and MyHC 2b) using multiplex RT-PCR. The relationship between expression of growth hormone receptor (GHR) and peroxisome proliferator-activated receptor α coactivator-lα (PGC-lα) mRNAs and changes ofmyofibre type composition during postnatal growth from 3 to 180 days of age were analysed. At 3 days of age, proportions of MyHC I, 2a and 2x fibres were high while only a few MyHC 2b fibres were differentiated. Dramatic changes were observed from day 3 to day 20 with significantly decreased MyHC I, 2a and 2x fibres but abrupt increases in MyHC 2b fibres in both breeds of pigs. Breed difference was exhibited only from day 90, with higher MyHC 2b but less MyHC I and 2a expression in LW pigs. Developmental pattern of GHR mRNA expression in LD muscle coincided with that of MyHC 2b, with LW pigs expressing higher abundance of GHR mRNA. PGC-lα mRNA expression followed distinct patterns in the two breeds of pigs, a higher level of PGC-lα mRNA being expressed in LD muscle of EHL pigs, the breed that possessed more oxidative fibres (MyHC I and MyHC 2a).

Differential expression of skeletal muscle genes following administration of clenbuterol to exercised horses

Background

Clenbuterol, a beta2-adrenergic receptor agonist, is used therapeutically to treat respiratory conditions in the horse. However, by virtue of its mechanism of action it has been suggested that clenbuterol may also have repartitioning affects in horses and as such the potential to affect performance. Clenbuterol decreases the percent fat and increases fat-free mass following high dose administration in combination with intense exercise in horses. In the current study, microarray analysis and real-time PCR were used to study the temporal effects of low and high dose chronic clenbuterol administration on differential gene expression of several skeletal muscle myosin heavy chains, genes involved in lipid metabolism and the β2-adrenergic receptor. The effect of clenbuterol administration on differential gene expression has not been previously reported in the horse, therefore the primary objective of the current study was to describe clenbuterol-induced temporal changes in gene expression following chronic oral administration of clenbuterol at both high and low doses.

Results

Steady state clenbuterol concentrations were achieved at approximately 50 h post administration of the first dose for the low dose regimen and at approximately 18–19 days (10 days post administration of 3.2 μg/kg) for the escalating dosing regimen. Following chronic administration of the low dose (0.8 μg/kg BID) of clenbuterol, a total of 114 genes were differentially expressed, however, none of these changes were found to be significant following FDR adjustment of the p-values. A total of 7,093 genes were differentially expressed with 3,623 genes up regulated and 3,470 genes down regulated following chronic high dose administration. Of the genes selected for further study by real-time PCR, down-regulation of genes encoding myosin heavy chains 2 and 7, steroyl CoA desaturase and the β2-adrenergic receptor were noted. For most genes, expression levels returned towards baseline levels following cessation of drug administration.

Conclusion

This study showed no evidence of modified gene expression following chronic low dose administration of clenbuterol to horses. However, following chronic administration of high doses of clenbuterol alterations were noted in transcripts encoding various myosin heavy chains, lipid metabolizing enzymes and the β2-adrenergic receptor.

Dynamics of myosin heavy chain isoform transition in the longissimus muscle of domestic and wild pigs during growth: a comparative study

Dynamics of myofiber differentiation/maturation in porcine skeletal muscle is associated with domestication, breeding and rearing conditions. This study was aimed to comparatively elucidate the age-dependent myosin heavy chain (MyHC) isoform expression and transition pattern in domestic and wild pig (WP) skeletal muscle from birth until adulthood. Domestic pigs (DPs) of Large White breed raised in conventional production system were compared with WPs reared in a large hunting enclosure. Muscle samples for immuno/enzyme histochemistry were taken from the longissimus dorsi muscle within 24 h postmortem at 24 to 48 h, 21 to 23 days, 7 months and ~2 years postpartum. Based on the antibody reactivity to MyHCs (NCL-MHCs, A4.74, BF-F3) and succinate dehydrogenase activity, myofibers were classified into I, I/IIa, IIa, IIx and IIb types. In addition, foetal MyHC expression was determined with the use of F158.4C10 antibody. Maturation of the longissimus dorsi muscle in the WP was characterized by an accelerated transformation of the fast to slow MyHC during the first hours postpartum, followed by differentiation towards oxidative myofibers in which type I, IIa and IIx MyHCs predominated. In the DP, the transformation shifted towards glycolytic myofibers that expressed MyHC-IIb. The expression of foetal MyHC was higher in the DP than in the WP at 1 day of age, and the decline in the foetal MyHC during the first 3 weeks was more rapid in the WP than in the DP denoting an accelerated early postnatal muscle maturation in WP than DP piglets. All foetal MyHC-positive myofibers co-expressed IIa isoform, but not vice versa. The intense myofiber hypertrophy was evident from 3 weeks until 7 months of age. In this period, the myofiber cross-sectional area increased up to 10- and 20-fold in the WP and the DP, respectively. In the DP, the hypertrophy of all myofiber types was more pronounced than in the WP, particularly the hypertrophy of IIx and IIb myofibers. To summarize, the comparison between growing DP with wild ancestors showed that genetic selection and rearing conditions lead to substantial changes in the direction and intensity of postnatal MyHC transformation as evidenced by different proportion of individual myofiber types and differences in their hypertrophic potential.

Integrative analysis of transcriptomics and proteomics of skeletal muscles of the Chinese indigenous Shaziling pig compared with the Yorkshire breed

Background

The Shaziling pig (Sus scrofa) is a well-known indigenous breed in China. One of its main advantages over European breeds is its high meat quality. However, little genetic information is available for the Shaziling pig. To screen for differentially expressed genes and proteins that might be responsible for the meat quality, the longissimus dorsi muscles from Shaziling and Yorkshire pig breeds were investigated using an integrative analysis of transcriptomics and proteomics, involving high-throughput sequencing, the two-dimensional gel electrophoresis, and mass spectrometry.

Results

Sequencing produced 79,320 unigenes by de novo assembly, and 488 differentially expressed genes in the longissimus dorsi muscle of Shaziling pig compared with the Yorkshire breed were identified. Gene Ontology term enrichment of biological functions and Kyoto Encyclopedia of Genes and Genomes analysis showed that the gene products were mainly involved in metabolism, protein binding, and regulation of skeletal muscle development. At the protein level, 23 differentially expressed proteins were identified, which were potentially associated with fatty acid metabolism, the glycolytic pathway, and skeletal muscle growth. Eight differentially expressed genes were confirmed by real-time PCR. These results give an insight into the mechanisms underlying the formation of skeletal muscle in the Shaziling pig.

Conclusions

Certain differentially expressed genes and proteins are involved in fatty acid metabolism, intramuscular fat deposition, and skeletal muscle growth in the Shaziling pig. These results provide candidate genes for improving meat quality and will promote further transcriptomic research in Shaziling pigs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-016-0389-y) contains supplementary material, which is available to authorized users.

Changes in muscle fiber type and expression of mRNA of myosin heavy chain isoforms in porcine muscle during pre- and postnatal development

The purpose of this study is to elucidate developmental changes in muscle fiber type in the pig during pre- and postnatal development. For this purpose, we performed a histochemical analysis for myosin adenosine triphosphatase activity to assess muscle fiber type and determined abundances of messenger RNA (mRNA) of myosin heavy chain (MHC) isoforms. Samples of Longissimus dorsi (LD) muscle were taken from fetuses on day 90 of the fetal stage. Further, samples of LD, Rhomboideus and Biceps femoris (B. femoris) muscles were taken from pigs when they were 1, 12, 26, 45 or 75 days old. Expression of MHC 2b mRNA in the LD and the B. femoris muscles rapidly and considerably increased from the late fetal stage to the early postnatal stage and this increase was associated with the development of type 2b fibers at least in the LD muscle. As shown by the rapid and considerable changes in expression of MHC 2b mRNA, it seems that a certain plasticity of muscle fiber type still remains in this developmental stage.

Analysis of Methionine Oxidation in Myosin Isoforms in Porcine Skeletal Muscle by LC-MS/MS Analysis

The purpose of this study was to analyze oxidized methionines in the myosin isoforms of porcine longissimus thoracis, psoas major, and semimembranosus muscles by liquid chromatography (LC) and mass spectrometry (MS). A total of 836 queries matched to four myosin isoforms (myosin-1, -2, -4, and -7) were analyzed and each myosin isoform was identified by its unique peptides (7.3-13.3). Forty-four peptides were observed from all three muscles. Seventeen peptides were unique to the myosin isoform and the others were common peptides expressed in two or more myosin isoforms. Five were identified as oxidized peptides with one or two methionine sulfoxides with 16 amu of mass modification. Methionines on residues 215 (215), 438 (438), 853 (851), 856 (854), 1071 (1069), and 1106 (1104) of myosin-1 (myosin-4) were oxidized by the addition of oxygen. Myosin-2 had two oxidized methionines on residues 215 and 438. No queries matched to myosin-7 were observed as oxidized peptides. LC-MS/MS allows analysis of the oxidation of specific amino acids on specific residue sites, as well as in specific proteins in the food system.

iTRAQ-based quantitative proteomic analysis reveals the distinct early embryo myofiber type characteristics involved in landrace and miniature pig

Background

Pig (Sus scrofa) is a major source of dietary proteins for human consumption and is becoming a valuable model in agricultural and biomedical research. The recently developed isobaric tag for relative and absolute quantitation (iTRAQ) method allows sensitive and accurate protein quantification. Here, we performed the first iTRAQ-based quantitative proteomic analyses of Landrace (LR) and Wuzhishan (WZS) pig longissimus dorsi muscle tissues during early embryonic development.

Results

The iTRAQ-based early embryonic longissimus dorsi muscle study of LR and WZS ranging from 21 to 42 days post coitus (dpc) identified a total of 4431 proteins from17,214 peptides, which were matched with 36,4025 spectra at a false discovery rate of 5 %. In both WZS and LR, the largest amount of differentially expressed proteins (DEPs) were found between 28 and 35 dpc. 252 breed-DEPs were selected by GO analysis, including 8 myofibrillar proteins. Only MYHCI/IIA mRNA were detected due to early embryonic stages, and significantly higher expression of them were found in WZS during these 4 stages. MYHCI was first found in WZS at 28 dpc and expressed in both breeds at later stages, while MYHCII protein was not detected until 35 dpc in both breeds. Thus, 33 myogenic breed-DEPs selected from last two stages were analyzed by STRING, which showed that some myofibrillar proteins (MYH1, TPM4, MYH10, etc.) and functional proteins (CSRP2, CASQ2, OTC, etc.), together with candidate myogenic proteins (H3F3A, HDGFRP2, etc.), probably participate in the regulatory network of myofiber formation.

Conclusion

Our iTRAQ-based early embryonic longissimus dorsi muscle study of LR and WZS provides new data on the in vivo muscle development distinctions during early embryonic development, which contributes to the improved understanding in the regulation mechanism of early myogenesis in agricultural animals.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2464-1) contains supplementary material, which is available to authorized users.

FHL3 differentially regulates the expression of MyHC isoforms through interactions with MyoD and pCREB

In skeletal muscle, muscle fiber types are defined by four adult myosin heavy chain (MyHC) isoforms. Four and a half LIM domain protein 3 (FHL3) regulates myoblasts differentiation and gene expression by acting as a transcriptional co-activator or co-repressor. However, how FHL3 regulates MyHC expression is currently not clear. In this study, we found that FHL3 down-regulated the expression of MyHC 1/slow and up-regulated the expression of MyHC 2a and MyHC 2b, whereas no significant effect was found on MyHC 2x expression. MyoD and phosphorylated cAMP response element binding protein (pCREB) played important roles in the regulation of MyHC 1/slow and MyHC 2a expression by FHL3, respectively. FHL3 could interact with MyoD, CREB and pCREB in vivo. pCREB had stronger interaction with the cyclic AMP-responsive elements (CRE) of the MyHC 2a promoter compared with CREB, and FHL3 significantly affected the binding capacity of pCREB to CRE. We established a model in which FHL3 promotes the expression of MyHC 2a through CREB-mediated transcription and inhibits the expression of MyHC 1/slow by inhibiting MyoD transcription activity during myogenesis. Our data support the notion that FHL3 plays important roles in the regulation of muscle fiber type composition.

MicroRNA Transcriptome Profile Analysis in Porcine Muscle and the Effect of miR-143 on the MYH7 Gene and Protein

Porcine skeletal muscle fibres are classified based on their different physiological and biochemical properties. Muscle fibre phenotype is regulated by several independent signalling pathways, including the mitogen-activated protein kinase (MAPK), nuclear factor of activated T cells (NFAT), myocyte enhancer factor 2 (MEF2) and peroxisome proliferator-activated receptor (PPAR) signalling pathways. MicroRNAs are non-coding small RNAs that regulate many biological processes. However, their function in muscle fibre type regulation remains unclear. The aim of our study was to identify miRNAs that regulate muscle fibre type during porcine growth to help understand the miRNA regulation mechanism of fibre differentiation. We performed Solexa/Illumina deep sequencing for the microRNAome during 3 muscle growth stages (63, 98 and 161 d). In this study, 271 mature miRNAs and 243 pre-miRNAs were identified. We detected 472 novel miRNAs in the muscle samples. Among the mature miRNAs, there are 23 highest expression miRNAs (over 10,000 RPM), account for 85.3% of the total counts of mature miRNAs., including 10 (43.5%) muscle-related miRNAs (ssc-miR-133a-3p, ssc-miR-486, ssc-miR-1, ssc-miR-143-3p, ssc-miR-30a-5p, ssc-miR-181a, ssc-miR-148a-3p, ssc-miR-92a, ssc-miR-21, ssc-miR-126-5p). Particularly, both ssc-miR-1 and ssc-miR-133 belong to the MyomiRs, which control muscle myosin content, myofibre identity and muscle performance. The involvement of these miRNAs in muscle fibre phenotype provides new insight into the mechanism of muscle fibre regulation underlying muscle development. Furthermore, we performed cell transfection experiment. Overexpression/inhibition of ssc-miR-143-3p in porcine skeletal muscle satellite cell induced an/a increase/reduction of the slow muscle fibre gene and protein (MYH7), indicating that miR-143 activity regulated muscle fibre differentiate in skeletal muscle. And it regulate MYH7 through the HDAC4-MEF2 pathway.

Differential expression of lipid metabolism-related genes and myosin heavy chain isoform genes in pig muscle tissue leading to different meat quality

The aim of this study was to investigate the variations in meat quality, lipid metabolism-related genes, myosin heavy chain (MyHC) isoform genes and peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) gene mRNA expressions in longissimus dorsi muscle (LM) of two different pig breeds. Six Rongchang and six Landrace barrows were slaughtered at 161 days of age. Subsequently, meat quality traits and gene expression levels in LM were observed. Results showed that Rongchang pigs not only exhibited greater pH, CIE a*24 h and intramuscular fat content but also exhibited lower body weight, carcass weight, dressing percentage, LM area and CIE b*24 h compared with Landrace pigs (P<0.05). Meanwhile, the mRNA expression levels of the lipogenesis (peroxisome proliferator-activated receptor gamma, acetyl-CoA carboxylase and fatty acid synthase) and fatty acid uptake (lipoprotein lipase)-related genes were greater in the Rongchang (P<0.05), whereas the lipolysis (adipose triglyceride lipase and hormone sensitive lipase) and fatty acid oxidation (carnitine palmitoyltransferase-1B)-related genes were better expressed in the Landrace. Moreover, compared with the Landrace, the mRNA expression levels of MyHCI, MyHCIIa and MyHCIIx were greater, whereas the mRNA expression levels of MyHCIIb were lower in the Rongchang pigs (P<0.05). In addition, the mRNA expression levels of PGC-1α were greater in Rongchang pigs than in the Landrace (P<0.05), which can partly explain the differences in MyHC isoform gene expressions between Rongchang and Landrace pigs. Although the small number of samples does not allow to obtain a definitive conclusion, we can suggest that Rongchang pigs possess better meat quality, and the underlying molecular mechanisms responsible for the better meat quality in fatty pigs may be partly due to the higher mRNA expression levels of lipogenesis and fatty acid uptake-related genes, as well as the oxidative and intermediate muscle fibers, and due to the lower mRNA expression levels of lipolysis and fatty acid oxidation-related genes, as well as the glycolytic muscle fibers.

Effect of porcine Akirin2 on skeletal myosin heavy chain isoform expression

Akirin2 plays an important role in skeletal myogenesis. In this study, we found that porcine Akirin2 (pAkirin2) mRNA level was significantly higher in fast extensor digitorum longus (EDL) and longissimus lumborum (LL) muscles than in slow soleus (SOL) muscle of pigs. Overexpression of pAkirin2 increased the number of myosin heavy chain (MHC)-positive cells, indicating that pAkirin2 promoted myoblast differentiation. We also found that overexpression of pAkirin2 increased the mRNA expressions of MHCI and MHCIIa and decreased the mRNA expression of MHCIIb. Myocyte enhancer factor 2 (MEF2) and nuclear factor of activated T cells (NFAT) are the major downstream effectors of calcineurin. Here we also observed that the mRNA expressions of MEF2C and NFATc1 were notably elevated by pAkirin2 overexpression. Together, our data indicate that the role of pAkirin2 in modulating MHCI and MHCIIa expressions may be achieved through calcineurin/NFATc1 signaling pathway.

Dietary resveratrol supplementation improves meat quality of finishing pigs through changing muscle fiber characteristics and antioxidative status

This study investigated the effects of resveratrol (0, 300, 600 mg/kg) on meat quality, muscle fiber characteristics and antioxidative capacity of finishing pigs. The results showed that resveratrol not only increased m. longissimus dorsi (LM) pH(24 h), a*, crude protein and myoglobin content but also decreased L*(24 h), shear force, drip loss, glycolytic potential, as well as backfat depth, LM lactate dehydrogenase activity and mRNA level. Meanwhile, LM total antioxidative capacity, glutathione peroxidase activity and its mRNA level were increased by resveratrol, while malonaldehyde content was decreased. In addition, resveratrol increased myosin heavy chain (MyHC)IIa mRNA level and decreased MyHCIIb mRNA level, along with decreased myofiber cross-sectional area. In conclusion, these results suggest that resveratrol is an effective feed additive to improve pork quality, and the underlying mechanism may be partly due to the changed muscle fiber characteristics and antioxidative capacity induced by resveratrol.

Analysis of Myosin Heavy Chain Isoforms from Longissimus Thoracis Muscle of Hanwoo Steer by Electrophoresis and LC-MS/MS

The purpose of this study was to analyze myosin heavy chain (MHC) isoforms in bovine longissimus thoracis (LT) muscle by liquid chromatography (LC) and mass spectrometry (MS). LT muscles taken from Hanwoo (Korean native cattle) steer (n=3) used to separate myosin bands by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The peptide queries were obtained from the myosin bands by LC-MS/MS analysis following in-gel digestion with trypsin. A total of 33 and 43 queries were identified as common and unique peptides, respectively, of MHC isoforms (individual ions scores >43 indicate identity or extensive homology, p<0.05). MHC-1 (IIx), -2 (IIa), -4 (IIb), and -7 (slow/I) were identified based on the Mowse score (5118, 3951, 2526, and 2541 for MHC-1, -2, -4, and -7, respectively). However, more analysis is needed to confirm the expression of MHC-4 in bovine LT muscle because any query identified as a unique peptide of MHC-4 was not found. The queries that were identified as unique peptides could be used as peptide markers to confirm MHC-1 (14 queries), -2 (8 queries), and -7 (21 queries) in bovine LT muscle; no query identified as a unique peptide of MHC-4 was found. LC-MS/MS analysis is a useful approach to study MHC isoforms at the protein level.

Effects of ractopamine administration and castration method on muscle fiber characteristics and sensory quality of the longissimus muscle in two Piétrain pig genotypes

Single and combined effects of ractopamine supplementation (RAC, 7.5 vs. 0 ppm), castration method (surgical castration: SC vs. immuno-castration: IM) and genotype (genotype A: GA vs. GB containing 25% or 50% Piétrain) were determined on longissimus muscle (LM) fiber traits and quality of pork (n=512). RAC increased fiber IIX cross-sectional area (P=0.009) and decreased glycolytic potential (P=0.02) and pork tenderness (P<0.001). Fiber traits indicated that LM of IM pigs was more oxidative (P<0.05) and meat had slightly higher (P=0.04) off-flavor score and WBSF than SC. LM from GB pigs was paler (P<0.05) and had greater (P<0.05) glycolytic potential, IIX fiber cross sectional area and pork off-flavor than GA. RAC supplementation, castration method and genotype or their combination affected some fiber traits and some quality parameters but differences reported were small indicating these treatments or their combination could be used without major prejudice to meat quality.

Effect of L-lysine on expression of selected genes, serum concentration of amino acids, muscle growth and performance of growing pigs

Lysine (Lys) is the first limiting amino acid (AA) in most feed formulations for pigs and most abundant, along with leucine, in muscle proteins. An experiment was conducted with 17 pigs (17.7 ± 0.05 kg initial BW) to identify a role of dietary Lys in the control of protein synthesis in pigs. Fourteen pigs were randomly assigned to one of the two wheat-based dietary treatments: Lys-deficient, 3.0 g/kg (DEF) and Lys-adequate, 10.8 g/kg (ADE). Samples from jejunum mucosa, liver, Longissumus and Semitendinosus muscles, and blood were collected. The other three pigs were sacrificed at the beginning of the trial to measure basal carcass composition. Weight gain, gain:feed ratio, Lys intake and loin eye area were greater in ADE than in DEF pigs (p < 0.01). Muscle-related carcass characteristics were better, and myosin heavy chain IIb expression (MyHC IIb) in Semitendinosus was higher in ADE than in DEF pigs. Expression of AA transporters CAT-1 was lower (p < 0.05), serum Lys was higher and serum Val was lower in pigs fed the ADE diet. The higher muscularity, MyHC IIb expression in Semitendinosus muscle and Lys serum of pigs fed the ADE diet suggest that Lys increases growth rate not only by functioning as protein construction unit but also as potential control of the protein synthesis process.

Cloning and transcriptional activity analysis of the porcine cofilin 2 gene promoter

Cofilins (CFL), including CFL1 and CFL2, are members of the family of actin-binding proteins in eukaryote. CFL2 is predominantly expressed in mammalian skeletal muscle and heart and is important to muscle fiber formation and muscular regeneration. To study transcriptional regulation of porcine CFL2, a 2.5 kb upstream sequence starting from the major CFL2 transcriptional start site was cloned by genome walking. Twelve DNA fragments of the 5' flank region of the porcine CFL2 gene were further isolated from porcine genomic DNA via PCR and inserted into the luciferase reporter vector pGL4.10 to make 12 CFL2 reporter constructs. All reporter vectors were transfected into C2C12, NIH3T3, or Hela cells and their relative luciferase activity measured after 48 h, respectively. Bioinformatics analysis suggested that there were two TATA-boxes at the -508 bp and -453 bp, as well as a GC-box and a CAAT-box in this sequence. Additional transcription factor binding sites including SP1, AP1, AP2, and GATA-1 sites were also predicted. The transcriptional activity of pGL4.10-1554 (1502 bp to +51 bp) was the strongest, and the promoter's active region was mapped to a region from -1502 bp to -1317 bp. Our data provide a foundation for future studies into transcriptional regulation of CFL2.

Effect of dietary zinc and ractopamine hydrochloride on pork chop muscle fiber type distribution, tenderness, and color characteristics

A total of 320 finishing pigs (PIC 327 × 1050; initially 98 kg) were used to determine the effects of adding Zn to diets containing ractopamine HCl (RAC) on muscle fiber type distribution, fresh chop color, and cooked meat characteristics. Dietary treatments were fed for approximately 35 d and consisted of a corn-soybean meal-based negative control (CON), a positive control diet with 10 mg/kg of RAC (RAC+), and the RAC+ diet plus 75, 150, or 225 mg/kg added Zn from either ZnO or Availa-Zn. Loins randomly selected from each treatment (n = 20) were evaluated using contrasts: CON vs. RAC+, interaction of Zn level × source, Zn level linear and quadratic polynomials, and Zn source. There were no Zn source effects or Zn source × level interactions throughout the study (P > 0.10). Pigs fed RAC+ had increased (P < 0.02) percentage type IIX and a tendency for increased (P = 0.10) percent type IIB muscle fibers. Increasing added Zn decreased (linear, P = 0.01) percentage type IIA and tended to increase (P = 0.09) IIX muscle fibers. On d 1, 2, 3, 4, and 5 of display, pork chops from pigs fed the RAC+ treatment had greater (P < 0.03) L* values compared to the CON. On d 0 and 3 of display, increasing added Zn tended to decrease (quadratic, P = 0.10) L* values and decreased (quadratic, P < 0.03) L* values on d 1, 2, 4, and 5. Pigs fed RAC+ had decreased (P < 0.05) a* values on d 1 and 4 of display and tended to have decreased (P < 0.10) a* values on d 0 and 2 compared to CON pork chops. Pork chops from the RAC+ treatment had a tendency for increased (P < 0.08) oxymyoglobin percentage compared to CON pork chops on d 1, 2, 4, and 5. On d 0, as dietary Zn increased in RAC+ diets, there was a decrease (linear, P < 0.01) in the formation of pork chop surface oxymyoglobin percentage. Metmyoglobin reducing ability (MRA) of pork chops on d 5 was decreased in the RAC+ group. Chops from pigs fed added Zn had increased (quadratic, P < 0.03) MRA on d 3 and 5 of the display period. There was a trend for increased (linear, P = 0.07) cooking loss with increasing Zn in RAC diets and treatments did not affect tenderness as measured by Warner-Bratzler shear force (P > 0.07). In conclusion, RAC+ diets produced chops that were lighter and less red but maintained a greater percentage of surface oxymyoglobin throughout a 5-d simulated retail display. Ractopamine reduced MRA at the end of the display period, but supplementing Zn to RAC diets restored MRA to near CON treatment levels at the end of the display period.

Expression of MyHC genes, composition of muscle fiber type and their association with intramuscular fat, tenderness in skeletal muscle of Simmental hybrids

In adult bovine skeletal muscle, it expressed four isoforms of Myosin heavy chain (MyHC) gene, MyHC-I, MyHC-IIa, MyHC-IIb, and MyHC-IIx that are translated into different structural protein myofibrils, and then further form different types of muscle fiber. In the studies, our objective is to reveal the expression patterns of MyHC genes in longissimus dorsi (Ld), semitendinosus (Se) and soleus (Sol) of Simmental hybrids cattle, and their association with intramuscular fat (IMF) content and meat shearing force (MSF). The muscle tissue of Ld, Se and Sol were collected from 6, 12 and 36-month old Simmental hybrids respectively, then the expression levels of MyHCs were examined by real-time PCR, at the same time, IMF, MSF and muscle type were measured with chemical assessment, shearing force measurer and immunostaining respectively. Our results showed that t Ld, Se, and Sol expressed MyHC-I, MyHC-IIa and MyHC-IIx isoforms but not MyHC-IIb, furthermore MyHC-I, MyHC-IIa and MyHC-IIx had different expression patterns in different skeletal muscle. The expression of MyHC-I in Se and Sol, MyHC-IIa in Ld, Se, and Sol, and MyHC-IIx in Sol was decreased with increasing age. The highest expression of MyHC-I in Ld, and MyHC-IIx in Ld and Se was observed in 12-month-old animals. The percentage of type-IIa fiber approximately occupied 70-80 % among various muscle fiber of Ld, Se and Sol. The percentage of different type fiber was not related to IMF content and MSF, but the expression levels of MyHC-I and MyHC-IIa were negatively related to IMF content (r = -0.724, and -0.681, respectively) and MSF (r = -0.672, and -0.641, respectively). The expression level of MyHC-IIx was also negatively related to MSF (r = -0.655). In conclusion, MyHC gene might be considered as a negative factor in genetic selection of IMF content and MSF.

Age-related changes in the features of porcine adult stem cells isolated from adipose tissue and skeletal muscle

A better understanding of the control of body fat distribution and muscle development is of the upmost importance for both human and animal physiology. This requires a better knowledge of the features and physiology of adult stem cells in adipose tissue and skeletal muscle. Thus the objective of the current study was to determine the type and proportion of these cells in growing and adult pigs. The different cell subsets of stromal vascular cells isolated from these tissues were characterized by flow cytometry using cell surface markers (CD11b, CD14, CD31, CD34, CD45, CD56, and CD90). Adipose and muscle cells were predominantly positive for the CD34, CD56, and CD90 markers. The proportion of positive cells changed with age especially in intermuscular adipose tissue and skeletal muscle where the percentage of CD90(+) cells markedly increased in adult animals. Further analysis using coimmunostaining indicates that eight populations with proportions ranging from 12 to 30% were identified in at least one tissue at 7 days of age, i.e., CD90(+)/CD34(+), CD90(+)/CD34(-), CD90(+)/CD56(+), CD90(+)/CD56(-), CD90(-)/CD56(+), CD56(+)/CD34(+), CD56(+)/CD34(-), and CD56(-)/CD34(+). Adipose tissues appeared to be a less heterogeneous tissue than skeletal muscle with two main populations (CD90(+)/CD34(-) and CD90(+)/CD56(-)) compared with five or more in muscle during the studied period. In culture, cells from adipose tissue and muscle differentiated into mature adipocytes in adipogenic medium. In myogenic conditions, only cells from muscle could form mature myofibers. Further studies are now needed to better understand the plasticity of those cell populations throughout life.

Porcine skeletal muscle differentially expressed gene ATP5B: molecular characterization, expression patterns, and association analysis with meat quality traits

The 2-DE/MS-based proteomics approach was used to investigate the differences of porcine skeletal muscle, and ATP5B was identified as one differential expression protein. In the present study, ATP5B gene was further cloned by RT-PCR, the sequence was analyzed using the bioinformatics method, and the mRNA expression was detected by qRT-PCR. Sequence analysis showed that the porcine ATP5B gene contains an ORF encoding 528-amino-acid residues with 49 and 166 nucleotides in the 5' and 3' UTRs, respectively. The mRNA of ATP5B was widely expressed in all 14 tissues tested, but especially highly expressed in parorchis and fat. The expression pattern of ATP5B was similar in Large White and Meishan breeds, showing that the expression was upregulated by 3 days after birth and downregulated during postnatal development of skeletal muscle. Comparing the two breeds, the mRNA abundance of ATP5B in Large White was more highly expressed than in Meishan at all developmental stages (P < 0.05). Moreover, a synonymous mutation, G75A in exon 8, was identified and association analysis with the traits of meat quality showed that it was significantly associated with the RLF, FMP, IFR, IMF, and IMW (P < 0.05). These results suggested that ATP5B probably plays a key role in porcine skeletal muscle development and may provide further insight into the molecular mechanisms responsible for breed-specific differences in meat quality.

Effects of dietary l-arginine supplementation to gilts during early gestation on foetal survival, growth and myofiber formation

The effects of l-arginine on porcine foetal development and myogenesis were determined. Twenty Swiss Large White gilts were randomly allocated to either the control (C) or l-arginine treatment (A). In addition to the standard gestation diet, A-sows received 26 g l-arginine daily from days 14 to 28 of gestation. At day 75 of pregnancy, sows were sacrificed and the number and weight of foetuses were recorded. From each litter, the lightest, heaviest and the ones with an average foetal weight (FtW) were selected. Primary (P), secondary (S) and total myofiber number as well as S/P ratio were determined in the semitendinosus (ST) and rhomboideus (RH) muscles. In A-sows, the number of viable foetuses (13.0 v. 9.3) and total FtW (4925 v. 3729 g) was greater (P ⩽ 0.04) than in C-sows. Compared to C-sow foetuses, the ST of A-sow foetuses had 7% more (17 699 v. 16 477; P = 0.04) P myofibers and the S/P ratio in both muscles was lower (ST = 20.3 v. 21.5; RH = 24.1 v. 27.1; P ⩽ 0.07). Regardless of the maternal diet, the S myofiber number and the S/P ratio in both muscles were greater (P ⩽ 0.01) in foetuses with a high FtW compared to low FtW. These data suggest that l-arginine supplemented to gilts during early gestation enhanced foetal survival and in the ST positively affected the primary phase of myofiber formation.

Characteristics of impala (Aepyceros melampus) skeletal muscles

The aim of this study was to determine citrate synthase (CS), phosphofructokinase (PFK) activities and myosin heavy chain (MHC) isoform contents in four muscle groups (semimembranosus (S), deltoideus (D), longissimus lumborum (LL), and psoas major (PM)) of impala (n=6). All four muscle groups expressed predominantly MHC IIa (means of 55±22-93±12%). MHC IIx was only expressed in D. In D, positive correlations were found between MHC I and age (r=0.93; P<0.05) and the weight of the animals (r=0.94; P<0.01). PFK (means of 175±179-374±181), CS (means of 100±23-126±38 μmol/min/gdw) and MHC content indicated that energy provision in the impala is produced to a large extent via oxidative pathways and fibre types vary with animal characteristics.

In vitro characterization of proliferation and differentiation of pig satellite cells

Skeletal muscle contains various muscle fiber types exhibiting different contractile properties based on the myosin heavy chain (MyHC) isoform profile. Muscle fiber type composition is highly variable and influences growth performance and meat quality, but underlying mechanisms regulating fiber type composition remain poorly understood. The aim of the present work was to develop a model based on muscle satellite cell culture to further investigate the regulation of adult MyHC isoforms expression in pig skeletal muscle. Satellite cells were harvested from the mostly fast-twitch glycolytic longissimus (LM) and predominantly slow-twitch oxidative rhomboideus (RM) muscles of 6-week-old piglets. Satellite cells were allowed to proliferate up to 80% confluence, reached after 7 day of proliferation (D7), and then induced to differentiate. Kinetics of proliferation and differentiation were similar between muscles and more than 95% of the cells were myogenic (desmin positive) at D7 with a fusion index reaching 65 ± 9% after 4 day of differentiation. One-dimensional SDS polyacrylamide gel electrophoresis revealed that satellite cells from both muscles only expressed the embryonic and fetal MyHC isoforms in culture, without any of the adult MyHC isoforms that were expressed in vivo. Interestingly, triiodothyronine (T3) induced de novo expression of adult fast and α-cardiac MyHC in vitro making our culture system a valuable tool to study de novo expression of adult MyHC isoforms and its regulation by intrinsic and/or extrinsic factors.

An atlas of DNA methylomes in porcine adipose and muscle tissues

It is evident that epigenetic factors, especially DNA methylation, have essential roles in obesity development. Here, using pig as a model, we investigate the systematic association between DNA methylation and obesity. We sample eight variant adipose and two distinct skeletal muscle tissues from three pig breeds living within comparable environments but displaying distinct fat level. We generate 1,381 Gb of sequence data from 180 methylated DNA immunoprecipitation libraries, and provide a genome-wide DNA methylation map as well as a gene expression map for adipose and muscle studies. The analysis shows global similarity and difference among breeds, sexes and anatomic locations, and identifies the differentially methylated regions. The differentially methylated regions in promoters are highly associated with obesity development via expression repression of both known obesity-related genes and novel genes. This comprehensive map provides a solid basis for exploring epigenetic mechanisms of adipose deposition and muscle growth.

Black wildebeest skeletal muscle exhibits high oxidative capacity and a high proportion of type IIx fibres

The aim of the study was to investigate the skeletal muscle characteristics of black wildebeest (Connochaetes gnou) in terms of fibre type and metabolism. Samples were obtained post mortem from the vastus lateralis and longissimus lumborum muscles and analysed for myosin heavy chain (MHC) content. Citrate synthase (CS), 3-hydroxyacyl co A dehydrogenase (3HAD), phosphofructokinase (PFK), lactate dehydrogenase (LDH) and creatine kinase (CK) activities were measured spectrophotometrically to represent the major metabolic pathways in these muscles. Both muscles had less than 20% MHC I, whereas MHC IIa and MHC IIx were expressed in excess of 50% in the vastus lateralis and longissimus lumborum muscles, respectively. Overall fibre size was 2675±1034 μm(2), which is small compared with other species. Oxidative capacity (CS and 3HAD) in both muscles was high and did not differ from one another, but the longissimus lumborum had significantly (P<0.05) higher PFK, LDH and CK activities. No relationships were observed between fibre type and the oxidative and oxygen-independent metabolic capacity as measured by specific enzyme activities. This study confirms the presence of both fast-twitch fibres and high oxidative capacity in black wildebeest, indicating an animal that can run very fast but is also fatigue resistant.

Changes in muscle composition during the development of diving ability in the Australian fur seal

During development the Australian fur seal transitions from a terrestrial, maternally dependent pup to an adult marine predator. Adult seals have adaptations that allow them to voluntarily dive at depth for long periods, including increased bradycardic control, increased myoglobin levels and haematocrit. To establish whether the profile of skeletal muscle also changes in line with the development of diving ability, biopsy samples were collected from the trapezius muscle of pups, juveniles and adults. The proportions of different fibre types and their oxidative capacity were determined. Only oxidative fibre types (Type I and IIa) were identified, with a significant change in proportions from pup to adult. There was no change in oxidative capacity of Type I and IIa fibres between pups and juveniles but there was a two-fold increase between juveniles and adults. Myoglobin expression increased between pups and juveniles, suggesting improved oxygen delivery, but with no increase in oxidative capacity, oxygen utilisation within the muscle may still be limited. Adult muscle had the highest oxidative capacity, suggesting that fibres are able to effectively utilise available oxygen during prolonged dives. Elevated levels of total creatine in the muscles of juveniles may act as an energy buffer when fibres are transitioning from a fast to slow fibre type.

The influence of the PRKAG3 mutation on glycogen, enzyme activities and fibre types in different skeletal muscles of exercise trained pigs

BACKGROUND

AMP-activated protein kinase (AMPK) plays an important role in the regulation of glucose and lipid metabolism in skeletal muscle. Many pigs of Hampshire origin have a naturally occurring dominant mutation in the AMPK γ3 subunit. Pigs carrying this PRKAG3 (R225Q) mutation have, compared to non-carriers, higher muscle glycogen levels and increased oxidative capacity in m. longissimus dorsi, containing mainly type II glycolytic fibres. These metabolic changes resemble those seen when muscles adapt to an increased physical activity level. The aim was to stimulate AMPK by exercise training and study the influence of the PRKAG3 mutation on metabolic and fibre characteristics not only in m. longissimus dorsi, but also in other muscles with different functions.

METHODS

Eight pigs, with the PRKAG3 mutation, and eight pigs without the mutation were exercise trained on a treadmill. One week after the training period muscle samples were obtained after euthanisation from m. biceps femoris, m. longissimus dorsi, m. masseter and m. semitendinosus. Glycogen content was analysed in all these muscles. Enzyme activities were analysed on m. biceps femoris, m. longissimus dorsi, and m. semitendinosus to evaluate the capacity for phosphorylation of glucose and the oxidative and glycolytic capacity. Fibre types were identified with the myosin ATPase method and in m. biceps femoris and m. longissimus dorsi, immunohistochemical methods were also used.

RESULTS

The carriers of the PRKAG3 mutation had compared to the non-carriers higher muscle glycogen content, increased capacity for phosphorylation of glucose, increased oxidative and decreased glycolytic capacity in m. longissimus dorsi and increased phosphorylase activity in m. biceps femoris and m. longissimus dorsi. No differences between genotypes were seen when fibre type composition was evaluated with the myosin ATPase method. Immunohistochemical methods showed that the carriers compared to the non-carriers had a higher percentage of type II fibres stained with the antibody identifying type IIA and IIX fibres in m. longissimus dorsi and a lower percentage of type IIB fibres in both m. biceps femoris and m. longissimus dorsi. In these muscles the relative area of type IIB fibres was lower in carriers than in non-carriers.

CONCLUSIONS

In exercise-trained pigs, the PRKAG3 mutation influences muscle characteristics and promotes an oxidative phenotype to a varying degree among muscles with different functions.

Fiber type and metabolic characteristics of lion (Panthera leo), caracal (Caracal caracal) and human skeletal muscle

Lion (Panthera leo) and caracal (Caracal caracal) skeletal muscle samples from Vastus lateralis, Longissimus dorsi and Gluteus medius were analyzed for fiber type and citrate synthase (CS; EC 2.3.3.1), 3-hydroxyacyl Co A dehydrogenase (3HAD; EC 1.1.1.35), phosphofructokinase-1 (PFK; EC 2.7.1.11), creatine kinase (CK; EC 2.7.3.2), phosphorylase (PHOS; EC 2.4.1.1) and lactate dehydrogenase (LDH; EC 1.1.1.27) activities and compared to human runners, the latter also serving as validation of methodology. Both felids had predominantly type IIx fibers (range 50-80%), whereas human muscle had more types I and IIa. Oxidative capacity of both felids (CS: 5-9 μmol/min/g ww and 3HAD: 1.4-2.6 μmol/min/g ww) was lower than humans, whereas the glycolytic capacity was elevated. LDH activity of caracal (346 ± 81) was higher than lion (227 ± 62 μmol/min/g ww), with human being the lowest (55 ± 17). CK and PHOS activities were also higher in caracal and lion compared to human, but PFK was lower in both felid species. The current data and past research are illustrated graphically showing a strong relationship between type II fibers and sprinting ability in various species. These data on caracal and lion muscles confirm their sprinting behavior.