Comparison Of Muscle Fiber Types In Jinhua And Landrace Pigs And The Effect Of ERK Gene On Muscle Fiber Transition

One of the main factors determining pig growth rate and meat quality is the composition of skeletal muscle fibers. In postnatal growing pigs, skeletal muscles consist of four fiber types (type I, II a, II x and II b) which are characterized by the expression of myosin heavy-chain (MyHC) gene isoforms. The specific purpose was to investigate the variations in meat quality, muscle fiber type and enzyme activity between local Jinhua and exotic Landrace pigs at the different age point (30,90,150 and 180 days of age), as well as the same BW of 64 kg, respectively. We compared differentialy expressed muscle fiber types such as types I andâ…¡A (oxidative), typeâ…¡B (glycolytic), as well as typeâ…¡X (intermediate) fibers in longissimus dorsi (LD) using real-time RT-PCR. Furthermore, the metabolic enzyme activities of lactate dehydrogenase (LDH), succinic dehydrogenase (SDH) and malate dehydrogenase (MDH) were used as markers of glycolytic and oxidative capacities, respectively. Takeing advantage of the global microarray technology. ERK gene were identified as differently expression between Jinhua and Landrace pigs. The effect of ERK on muscle fiber transition and muscle fiber metabolism were studied by using real-time PCR, gene overexpression and western blotting techniques. Results are as follwiong:1. Comparison of carcass quality and meat quality between Jinhua pigs and Landrace pigsMeat quality and carcass traits were compared between Jinhua and Landrace pigs at the same age (180 days of age), as well as the same BW of 64 kg, respectively. At the same age, Jinhua pigs exhibited significantly higher intramuscular fat content and back fat thickness than those in Landrace pigs (P< 0.01). but body weight as well as the LD muscle area were significantly lower than those of Landrace. Water holding capacity, measured as the drip loss, and color parameters were significantly different between breeds (P< 0.01), Jinhua pigs showed lower drip loss and redness. Other meat qualities such as pH 45min did not differ significantly between the breeds.At the same BW of 64 kg, our results also suggest that Jinhua pigs exhibited a higher intramuscular fat content and back fat thickness, but lower LD muscle area and drip loss than those in Landrace (P< 0.01). Other meat qualities such as pH 45min, color parameters did not differ significantly between the two breeds. These results showed that Jinhua pigs and Landrace had great differences in meat quality, Jinhua pigs had better meat quality than Landraces.2. Comparisons of different muscles metabolic enzymes and muscle fiber types in Jinhua and Landrace PigsWe analyzed the expression levels of MyHC isform types I,â…¡A,â…¡X andâ…¡B and the activites of LDH, SDH and MDH in pig LD muscle by real-time RT-PCR using specific primers. As expected, strong differences were observed for all f(?) MyHC fiber types between breeds in LD. Interestinglly, the two breeds either at the same age or the same BW had the same trend. In LD muscle, the mRNA level of oxidative fiber type (types I) were higher in Jinhua pigs compared to that of Landrace (P< 0.01). However, glycolytic fiber type (typeâ…¡B) was highly expressed in the LD muscle of Landrace compared to that of Jinhua (P< 0.01). We also analyzed the activites of LDH, SDH and MDH which used as markers of glycolytic and oxidative capacities in LD and soleus muscles. The results showed that the two breeds either at the same age or the same BW had the same trend (P< 0.05). Further more, we studied the relationships between muscle fiber type and pork quality using Pearson's bivariate correlation analysis. The MyHC I,â…¡A gene expression had significant positive relation to backfat thichness and intramuscular fat content significant negative relation to body weight, LD muscle area and drip loss. Contrastly, MyHC II B gene expression had significant negative relation to backfat thichness and intramuscular fat content,significant positive relation to body weight, LD muscle area and drip loss. These results suggested that the elevated expression of the oxidative fibers and higher activities of oxidative enzymes in Jinhua pigs were related to meat quality as indicated by a higher intramuscular fat and lower drip loss. Based on these results, we concluded that muscle fiber composition and postmortem muscle metabolism can explain in parts the variation of meat quality in Jinhua and Landrace pigs.3. Study on the effect and the regulation mechanism of ERK on the muscle fiber transition and energy metabolism.In former study, transcriptional analysis of longissimus dorsi muscle between Jinhua and Landrac pigs was performed by microarray and quantitative real-time PCR techniques. ERK was identified and described as an inportan factor in muscle fiber transition and energy metabolism. In vivo gene overexpression system of rat muscle electroporation was successfully established. Using the ERK gene force expression technique to explore the effect and the molecular mechanism of ERK on the muscle fiber transition and energy metabolism. The results show that increased the gene expression of ERK by gene force expression system enhanced the MyHC II A,â…¡X,â…¡B and LDH genes expression, meanwhile, decreased MyHC I, SDH, MDH and PGC-1 a genes expression. These results revealed that ERK could play an important role in muscle fiber transition.