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GROWTH AND DEVELOPMENTAL BIOLOGY |
* Key Laboratory of Swine Genetics and Breeding of Ministry of Agriculture & Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, Huazhong Agricultural University, 1 Shizishan Street, Wuhan, Hubei, 430070, P. R. China; and
Unit of Animal Infectious Diseases, National Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, 1 Shizishan Street, Wuhan, Hubei, 430070, P. R. China
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: breed • muscle • pig • proteome • quantitative real-time polymerase chain reaction • two-dimensional gel electrophoresis
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). The indigenous Chinese pig breeds, such as Meishan, are slower growing with relatively greater intramuscular fat content and reddish meat color (White et al., 1995). Given the observed differences between these 2 breeds, they should provide a good basis for the study of molecular mechanisms of breed-specific differences in meat quality.
Previous reports have described the histochemical, physiological, and genetic properties of muscle tissue and examined the meat quality and carcass traits in different pig breeds (White et al., 1995; Lefaucheur et al., 2004; Kim et al., 2008). However, these experiments, based on monitoring the expression of a limited number of genes or proteins, did not completely take into account the complexity and multiplicity of interwoven molecular mechanisms. The proteome analysis based on 2-dimensional gel electrophoresis (2-DE) and mass spectrometry is a method of choice for the quantitative differential display of large numbers of proteins and is a promising and powerful tool in meat science. After the emergence of proteomic technology over the last few years, it has been successfully adopted for the analysis of the porcine skeletal muscle (Lametsch and Bendixen, 2001; Kim et al., 2004, 2007; Sayd et al., 2006). In the present study, we performed proteomic analysis to characterize and compare protein expression profiles in the LM of 2 pig breeds. Our aim was to reveal the differences of breed-related protein expression and muscle fiber types between the indigenous Meishan pig and the Western meat-type breed, Large White, because it might be useful to understand the molecular mechanisms responsible for breed-specific differences in growth performance and meat quality.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Animals and Sampling
Six purebred female pigs (3 Meishan and 3 Large White pigs, 120 d old) provided by Jingpin Pig Station of National Engineering Research Center for Livestock (Huazhong Agricultural University) were used in the present study. The pigs were transported (10 min) to the slaughterhouse (Center of Quality Test and Supervision for Breeding Swine, Wuhan, Ministry of Agriculture), and slaughtered shortly after arrival. The LM were harvested within 20 min after slaughter and immediately frozen in liquid nitrogen, and then kept at –80°C until subsequent analysis (Lametsch et al., 2006; Sayd et al., 2006; Kim et al., 2007). Each muscle sample was extracted once, whereas the subsequent 2-DE analyses of the samples were conducted twice in subsequent order, giving a total of 18 gels (2 breeds, 3 biological replications within breeds, and 3 technical replications).
Extraction of Proteins
Protein samples were prepared from porcine muscle tissues using a modified method (Lametsch and Bendixen, 2001). The frozen LM were each placed in liquid nitrogen and ground thoroughly to a very fine powder with a mortar and pestle. The tissue powder (about 100 mg) was transferred to sterile tubes containing 1 mL of sample preparation buffer {7 M urea, 2 M thiourea, 4% CHAPS, 3-3[(cholamidopropyl)dimethylammonio]-1-propanesulfonate; 1% dithiothreitol (DTT); 2% immobilized pH gradient (IPG) buffer; pH 3 to 10; 10-µL proteinase inhibitor cocktail (BBI, Kitchener, Canada)}, and the mixture was ultrasonicated 6 times (15 s per time). The mixture was then incubated for 60 min at room temperature with occasional vortexing and centrifuged at 20,000 x g for 45 min at 4°C. The supernatant was collected and stored at –80°C until analysis. Protein concentration, determined using the PlusOne 2-D Quant Kit (GE Healthcare Bio-Sciences, Uppsala, Sweden), was 13.6 ± 1.6 mg/mL.
2-DE
For the first dimension (isoelectric focusing), proteins were solubilized in rehydration solution (7 M urea, 2 M thiourea, 1% DTT, 2% CHAPS, 1% IPG buffer pH 4 to 7, and 0.001% bromophenol blue). The mixtures were then centrifuged at 20,000 x g for 15 min at 20°C, and the supernatants were used for rehydration in IPG strips (GE Healthcare Bio-Sciences). The IPG strips, 18 cm, pH 4 to 7, were rehydrated in 340 mL of this protein solution for 12 h under low voltage (30 V). For analytical gels, 100 µg of protein was loaded on each IPG strip by in-gel rehydration, whereas 800 µg of protein was loaded for preparative gels. The IPG strips were subjected to isoelectric focusing in a Multiphor III (GE Healthcare Bio-Sciences) gel apparatus at 20°C. Voltage (200 V) was applied in the initial step followed by a stepwise increase to 10,000 V, reaching a total of 60 KVh for analytical gels and 90 KVh for preparative gels. Focused IPG strips were equilibrated for 15 min in 6 M urea, 30% glycerol, 2% SDS, 50 mM Tris, pH 8.8, and 1% DTT, and then for an additional 15 min in the same buffer except that DTT was replaced by 4% iodoacetamide. After equilibration, proteins were separated in the second dimension, with the Ettan DALTSix (GE Healthcare Bio-Sciences) apparatus, on 10% SDS-PAGE. The analytical gels were stained with silver staining as described by Mortz et al. (2001), whereas the preparative gels were stained with blue silver (Candiano et al., 2004).
Image and Data Analysis
The 2-DE gels were scanned on an Image Scanner at 300 dots/inch, and spot detection and quantification were performed with Image Master 2D Platinum software Version 6.0 (GE Healthcare Bio-Sciences). Parameters for spot detection were as follows: minimal area 10 pixels; smooth factor 2.0; and saliency 100.0. A reference gel was created from an artificial gel combining all of the spots presenting in different gels into one image. The reference gel was then used for matching of corresponding protein spots between gels. Background subtraction was performed, and the intensity of individual spot was normalized with total intensity. For comparative image analysis, the images were grouped, after which the intensity of the individual spots was analyzed and compared within and between the image groups. The changes in spot patterns revealed by computer-based image analysis were individually inspected and confirmed. Data were expressed as mean ± SEM. The Student’s t-test was used for statistical analysis, and a difference at P < 0.05 was considered statistically significant.
Protein Identification
The protein spots of interest were cut out from the preparative gels using pipet tips and extracted from gels according to the method of Zhang (Zhang et al., 2008). Briefly, the gel pieces were washed 3 times with 200 µL of 25 mM ammonium bicarbonate/50% acetonitrile for 30 min at ambient temperature, shrunken with 50 µL of acetonitrile, and reswollen with 5 µL of 25 mM ammonium bicarbonate containing 10 ng of trypsin at 4°C for 30 min. In-gel tryptic degradation was performed overnight at 37°C, followed by 3 subsequent extractions. The pooled extracts were lyophilized and reconstituted in 2 µL of 0.1% trifluoroacetic acid before matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF/MS) analysis.
Protein identification was performed using MALDI-TOF/MS, as follows. The sample solution with equivalent matrix solution was applied onto the MALDI-TOF target and prepared for MALDI-TOF/MS analysis according to a described previously procedure (Fountoulakis and Langen, 1997). The matrix used was 
-cyano-4-hydroxycinnamic acid. The MALDI-TOF spectra were calibrated using trypsin autodigestive peptide signals and matrix ion signals; MALDI analysis was performed by a fuzzy logic feedback control system (Ultraflex II MALDI TOF/TOF system, Bruker, Germany) equipped with delayed ion extraction. Peptide masses were searched against the NCBI database using the Mascot program (http://www.matrixscience.com). The initial search variables allowed a single trypsin missed cleavage, no restriction on protein mass, carbamidomethyl modification, and peptide mass tolerance of ±1.2 Da. The taxonomic search space was restricted to mammalian. Identities with probability-based Mowse scores >71 (for Mascot) were considered significant.
Quantitative Real-time PCR
Total RNA was prepared from Meishan and Large White LM samples with TRIpure reagent (Bioteke, Beijing, China) according to the instructions of the manufacturer. Strand cDNA was synthesized by reverse transcription of 2 µg of total RNA using Moloney murine leukemia virus reverse transcriptase and oligodT15 (Promega, Madison, WI).
Seven altered proteins and 4 myosin heavy chain (MyHC; I, IIa, IIx, and IIb) isoforms were selected to analyze their mRNA expression differences. The gene-specific primers are listed in Table 1. The expression levels of genes were detected by SYBR Green I assay using ABI 7300 real-time PCR thermalcycle instrument (ABI, Norwalk, CT). The quantitative real time-PCR (qRT-PCR) reactions were performed using 0.5 µL of 5 x diluted cDNA, 0.25 µL primers, 12.5-µL Q-PCR mixture (Toyobo, Osaka, Japan), and 11.5 µL of MilliQ water in a reaction volume totaling 25 µL. The specificity of PCR products were confirmed by melting curve analysis. The cDNA from 3 LM samples in each breed was used to detect the relative expression level of the target gene, and all PCR were performed in triplicate. Gene expression levels were quantified relatively to the expression of the GAPDH using Gene Expression Macro software (ABI) by employing an optimized comparative Ct (
Ct) value method. The expression level was calculated as 2^ (–Ct) to compare the relative expression, and SPSS Inc. (Chicago, IL) was used for statistical analysis. The Student’s t-tests were conducted to identify genes differing in expression; P < 0.05 was considered as significant.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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The LM proteins in the molecular mass region from 20 to 90 kDa and the pH range between 4 and 7 were included in the comparative analysis. Most of the proteins were observed between pH 5 and 7. Approximately 500 spots were detected in each gel. Image analysis allowed matching of 300 spots across all 18 gels. Twenty-five protein spots numbered in Figure 1 were significantly different between the 2 breeds and were selected for protein identification. Among the selected 25 protein spots, 15 spots were overexpressed in Large White and 10 spots in Meishan, respectively. The identification and information related to the validity of search results are shown in Table 2. A total of 20 spots were successfully identified by MALDI-TOF/MS and matched to 14 different proteins. Two protein spots (spot 4 and 5) could not be detected in the preparative gels and were therefore not identified, and 3 spots (spot 8, 12, and 25) were not identified due to decreased protein concentration or the lack of porcine protein databases. Among the 20 identified proteins, 10 spots were identified by matching peptide data to porcine protein sequences in the database, whereas the other 10 spots were identified due to interspecies homology to bovine, human, mouse, or rabbit protein sequences. For these protein spots, moderate shifts in molecular weight (MW) and isoelectric point (pI) value compared with the theoretical pI and MW were observed. In addition, 4 [cGPD, PGM1, myosin binding protein H (MyBP-H), albumin] proteins focalized as 2 or 3 different spots. For example, protein spots 9, 10, and 11 were identified as cGPD with the same MW but different pI. Protein spots 19, 20, and 21 all harbor the MyBP-H but different MW and pI.
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Seven differentially expressed proteins (cGPD, ATPase-β, TPI1, PGM1, HSP27, MyBP-H, and ADPR-Actin) identified in the 2-DE experiment were selected and analyzed by qRT-PCR. These proteins were selected for 3 reasons: 1) many proteins had multiple spots in 2-DE gels; 2) their functions were involved in muscle energy metabolism, myofiber regulation, or switching; and 3) their mRNA sequences were available in GenBank. All the mRNA expression patterns of the 7 proteins are shown in Figure 3. Among the selected proteins, 3 proteins (PGM1, MyBP-H, and ADPR-Actin) were highly transcribed in Large White LM (P < 0.05), 2 proteins (cGPD and ATPase-β) were highly transcribed in Meishan pigs (P < 0.05), and 2 proteins (TPI1 and HSP27) tended to express highly in Meishan LM, but not significantly (P > 0.05). The qRT-PCR results indicated that the gene expression patterns of these proteins were in accordance with proteome level changes and validated the 2-DE results for all selected proteins.
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Myosin heavy chain is a more than 220 KDa protein, which cannot enter the 2-DE gel. In postnatal growing pigs, type I (oxidative fiber), IIb (glycolytic fiber), IIa, and IIx (intermediate fiber) MyHC are expressed in skeletal muscle, which are encoded by a distinct gene (Schiaffino and Reggiani, 1994; Lefaucheur et al., 2002).The expression patterns of MyHC isoforms are different among different breeds. So we analyzed the expression levels of 4 MyHC isoforms in pig LM by qRT-PCR using specific primers (Table 1).
When normalized to GAPDH, the total MyHC mRNA levels (I+IIa+IIb+IIx) were not significantly influenced by breed (P > 0.05), suggesting that the 4 MyHC isoforms were in equilibrium. The normalized expression of type I was greater in Meishan LM compared with the Large White, but without reaching statistical significance (P > 0.05). However, expressions of other 3 types were different drastically between 2 breeds. In Meishan pigs, a marked decrease in type IIb (P < 0.01) was exhibited, but type IIa (P < 0.05), IIx (P < 0.05), and I+IIa (P < 0.01) were increased. In particular, the mRNA level of type IIa in the Meishan pigs was nearly 2 times greater than that in the Large White pigs, whereas in Large White pigs, type IIb accounted for nearly 50% of the MyHC transcripts (Table 3).
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Skeletal muscle fibers are important factors influencing meat quality. Many reports have examined the relationship between muscle fiber type and meat quality (Kim et al., 2008). Breed probably accounts for most of the genetic factors affecting the muscle fiber composition of a certain muscle. Previous research have confirmed that the distribution of type II fibers was different in breeds through MyCH composition analysis by immunohistochemistry, qRT-PCR, or semiquantitative RT-PCR and indicated that the MyHC composition at the mRNA level was in agreement with the protein level (Lefaucheur et al., 2004; Wimmers et al., 2008). In the present study, we analyzed the mRNA levels of MyHC types using qRT-PCR. The results showed that type I fiber expression was low in the Meishan and Large White pigs and not significantly affected by breed. However, type IIb fiber was highly expressed in the Large White breed. Type I+IIa and IIx expression was greater in the Meishan pigs than in the Large White. The percentage of MyHC IIb was an important feature because it contributed to an increase in muscle mass, whereas the presence of oxidative fibers (type I and IIa fibers) was positively related to the color characteristics, better water-holding capacity, and better tenderness of meat (Wimmers et al., 2008). Furthermore, oxidative fibers are rich in mitochondria, which are related to the relative capacity of muscle tissue to oxidize fatty acids. The increased muscle fat content, reduced muscle growth rate, and better meat quality in Meishan pigs may be related to the increased expression of oxidative muscle fibers. Our data also suggest that the differential expression of muscle fiber types was in accordance with previous research (Lefaucheur et al., 2004; Yang et al., 2005; Wimmers et al., 2008).
Metabolism-Related Proteins
Four proteins differentially expressed between 2 breeds were involved in energy metabolism. Changes of enzyme concentration would lead to the corresponding changes of the production of energetic molecules, which were closely related to muscle growth.
Three enzymes, namely, TPI1, PGM1, and cGPD, were involved in shifts in the main pathway of glycolysis. The TPI1 and PGM1 were highly expressed in Large White pigs. The TPI1 enzyme is an essential housekeeping enzyme in all living cells and tissues, catalyzing the interconversion of dihydroxyacetone phosphate and D-glyceraldehyde 3-phosphate (Hollan et al., 1995), which is well characterized by increased glycolytic metabolism. The PGM1 enzyme catalyzes the interconversion of glucose-1-phosphate and glucose-6-phosphate, whose activity is increased by phosphorylation and reduced in oxidative fibers of skeletal muscle (Hemmer et al., 1993). The increased TPI1 and PGM1 expression in Large White pigs indicated that Large White LM relied more on glycolytic metabolism, using more carbohydrates and less lipids as fuel than Meishan, and implying that the Large White LM had relatively greater glycogen. Glycogen enrichment in Large White LM suggested that this breed carried more glycolytic-type muscle fibers (type IIb). Our results supported the hypothesis that the intensive selection for lean muscle growth in Western pig breeds induced a shift in muscle metabolism toward a more glycolytic and less oxidative fiber type (Lefaucheur et al., 2004). Moreover, the results of MyCH analysis in Meishan and Large White LM on mRNA levels also demonstrated this shift in fiber types. Therefore, the TPI1 and PGM1 increased in Large White LM muscle, which were consistent with a reduced proportion of oxidative fibers compared with Meishan pigs.
Another glycolytic enzyme, cGPD, is essential for mitochondrial oxidation of glycolytic NADH. The cGPD enzyme, together with its mitochondrial isoform, constitute the glycerol-3-phosphate dehydrogenase shuttle and catalyze the conversion of the glycolytic intermediary dihydroxyacetone phosphate into glycerol-3-phosphate, to which fatty acids are esterified to form triglycerides (Fell and Small, 1986). The central role of cGPD in the triglyceride synthesis makes this enzyme a useful marker of late adipogenesis extensively used in mammals (Salazar-Olivo et al., 1995). In our research, 3 spots were identified as cGPD, 2 (spot 10 and 11) of which were upregulated in Meishan LM and the other one (spot 9) was upregulated in Large White LM. However, the cGPD proteins have different pI, probably due to posttranslational modifications. Meanwhile, the cGPD protein in mRNA level was also highly expressed in Meishan pigs. The upregulation of cGPD protein may indicate increased mitochondrial oxidation of cytosolic NADH in Meishan LM. This is in agreement with the increased intramusclar fat and the increased ability of the Meishan pig to accumulate fat.
Besides these glycolytic metabolism proteins, ATPase-β, an oxidative metabolism-related protein, was elevated in Meishan LM. The ATPase enzyme is involved in oxidative energy metabolism in mitochondria and has an essential role in cellular function (Izquierdo, 2006). The ATPase-β is the catalytic part of the ATP synthase complex and catalyzes the rate-limiting step of ATP formation in eukaryotic cells (Izquierdo, 2006). The greater expression of ATPase-β in Meishan LM indicated that the Meishan breed possess a greater oxidative capacity than the Large White breed. In skeletal muscle, the greater fat content was more oxidative (Hocquette et al., 1998). Previous research also indicated that ATPase was concerned with muscle growth (Lefaucheur et al., 2002; Lin and Hsu, 2005). These reports combined with our results suggested that ATPase-β has an important role in muscle fat content and muscle growth ability of the pig.
Myofibrillar Regulatory Proteins
Myofibril filaments are responsible for generating the physical movement of muscles (Piec et al., 2005), which consist of 2 types, thick and thin. The thick filaments consist primarily of the protein myosin, held in place by titin filaments, whereas thin filaments consist primarily of the protein actin, coiled with nebulin filaments. Our differential proteomic analysis indicated that many myofibril regulatory proteins were differentially expressed in LM between the 2 breeds. The MyBP-H protein is an important regulatory protein of the thick filament mainly found in fast skeletal muscle (Clark et al., 2002; Bouley et al., 2005), which was upregulated in Large White LM. Its strong affinity for myosin suggested possible roles in myofibril assembly and in the regulation of contraction. Thus, MyBP-H has significant effects on length, thickness, and lateral alignment of myosin filaments (Clark et al., 2002). So this increased content in Large White LM could be correlated with the greater proportion of type IIb fibers. In slow-twitch muscle, myosin light chain (MLC) isoforms, represented by MLC1sa and MLC1sb, were mainly expressed (Bouley et al., 2005). In our research, MLC1sa and MLC1sb were upregulated in Meishan LM. Previous research using proteome analysis reported that MLC1sa had increased expression in early pig postnatal LM (Kim et al., 2007). Moreover, other research indicated that MLC1sa and MLC1sb were significantly downregulated in double-muscled muscle (Bouley et al., 2005). These reports correspond to our present results about high expression of MLC1sa and MLC1sb in Meishan. All of above analyses showed that the expression of the MLC slow-twitch isoforms showed a fiber type-specific manner in porcine muscle.
Three identified proteins hold important muscle contractile functions: ACTA1, ADPR-Actin, CapZ-β. The ACTA1 protein corresponds to the monomeric form of actin filaments. The abundance of ACTA1 was significantly increased in Meishan LM, which might indicate an increased need of material to promote myofibril assembly. The F-actin capping protein is a heterodimer, associated with the and β subunits. The CapZ-β specifically binds to the barbed ends of actin filaments, blocks the exchange of actin monomers, and anchors the thin filaments to the Z-line (McGregor et al., 2004). It has a critical role in both cell signaling and the regulation of actin in myofilament contractility and is a key factor in maintaining thin filament uniform length. The upregulation of CapZ-β in Large White LM may explain, in part, the increased ability of muscle accretion in Large White pigs.
Approximately 50% of the protein content of the muscle fiber is made up of the contractile machinery, mostly consisting of myosin complexes of the thick filaments and actin strings of the thin filaments (Doran et al., 2007). Previous proteomics research in meat quality always overemphasized the significance of metabolism. Admittedly, metabolism mechanism is crucial in meat quality, but the contractile machinery-related proteins are important too. Our results showed that there were several myofibrillar proteins with considerable differences between the 2 breeds. It may contribute to understanding the molecular mechanisms responsible for breed specificity.
Defense and Stress-Related Proteins
In response to stress, cells rapidly produce a series of proteins known as heat shock proteins (HSP). These HSP, also called stress proteins, are considered to be molecular chaperones that play a universal physiological role in maintaining cellular homeostasis (Liu and Steinacker, 2001). Heat shock proteins have been shown to respond in muscle diseases and after exercise. But different HSP have different functions in muscle. For example, HSP27 shows abundant constitutive expression in skeletal muscle and plays a key role in organizing and protecting the myofibril structure (Sugiyama et al., 2000), whereas Hsp70 is a highly conserved and essential protein against stress, which contributes to the remodeling response of skeletal muscle tissue, including muscle regeneration and contraction (Duguez et al., 2003). In our research, HSP27 and HSP70 displayed relatively greater expression in Large White LM. Previous proteome or transcriptome studies in ovine and swine muscle also demonstrated that HSP27 or HSP70 protein increased in glycolytic-type muscle fibers (Hamelin et al., 2006, 2007; Kim et al., 2007). These were in agreement with the results that the increased glycolytic metabolism in Large White was associated with upregulation of HSP27 and HSP70. The different functions that have been described for the 2 HSP indicated that they may have an important role in postnatal muscle growth of different breeds.
Miscellaneous
Serum albumin and SGN4 were both overexpressed in Large White LM; SGN4 is one subunit of COP9 signalosome complex, which is a phosphorylase that controls eukaryotic protein degradation via the ubiquitin proteasome system (Oron et al., 2002) and is involved in the regulation of channel proteins or carrier proteins. Although SGN4 might play a role in muscle growth and protein degradation, the precise functions in skeletal muscle remain uncertain and are worth further research.
Albumin represents the major plasma protein that exhibits a high degree of multifunctionality. Previous proteome research reported that it was differently expressed in skeletal muscle on different conditions, such as ovine muscle hypertrophy (Hamelin et al., 2006), postmortem proteolysis in pig LM (Hwang et al., 2005), and aging in rat skeletal muscle (Piec et al., 2005). However, these authors did not provide a rational explanation for the role of albumin in muscle or they assumed it was a result of contamination from blood. Indeed, in skeletal muscle, albumin serves as a temporary AA storage site, maintains osmotic pressure, and acts as a transporter for free fatty acids (Ellmerer et al., 2000). In agreement with earlier research results (Heilig and Pette, 1988), our proteomics approach showed that albumin was upregulated in Large White LM. The increase of albumin may result from the great ability to synthesize proteins within muscle in Large White.
In conclusion, we have used mass spectrometry-based proteomics technology and qRT-PCR for the biochemical analysis of LM between Large White and Meishan pigs. This was the first proteomics-based investigation of different pig breeds in total LM protein, and the 14 identified proteins included energy metabolic enzymes, myofibrillar proteins, and HSP. Proteins or enzymes play important roles in muscle growth and metabolism; thus, the differences in proteins may be related to the genetic architecture underlying muscle growth potential. Furthermore, the MyHC composition of LM in Meishan and Large White pigs was analyzed by qRT-PCR. The mRNA levels of I+IIa and IIx fibers were elevated in the Meishan pigs, whereas the IIb fiber expression was greater in the Large White pigs. These results may provide valuable information for understanding the molecular mechanisms responsible for breed-specific differences in growth performance and meat quality. Further investigations are needed to evaluate whether the different expression levels of energy metabolic and myofibril contractile-related proteins in 2 pig breeds are associated with muscle growth and meat quality.
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Footnotes |
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2 Corresponding author: yongjx81{at}webmail.hzau.edu.cn
Received for publication December 7, 2008. Accepted for publication April 21, 2009.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
