豫西黑猪不同屠宰体重肌纤维组织学及成肌调控基因发育性变化

【目的】试验旨在揭示豫西黑猪背最长肌肌纤维组织学、肌纤维类型和成肌调控相关基因发育性变化及其相互之间的关系。【方法】选取平均体重约为60、75、90、105和120 kg共5个体重阶段的豫西黑猪,每个体重屠宰3头,共15头,公母随机。采用HE染色和免疫荧光染色分析快慢肌类型组成和纤维组织学特性,利用实时荧光定量PCR方法测定成肌调控相关基因生肌决定因子（myogenic differentiation,MyoD）、配对盒7（paired-box 7,Pax7）、肌肉生长抑制素（myostatin,MSTN）、肌细胞生成素（myogenin,MyoG）、肌细胞增强因子2C （myocyte enhancer factor 2C,MEF2C）和肌纤维肌球蛋白重链（myosin heavy chain,MyHC）亚型的mRNA表达量。【结果】随着豫西黑猪体重的增加,肌纤维密度整体呈下降趋势,在75 kg时极显著高于其他体重阶段（P<0.01）,肌纤维面积和肌纤维直径整体呈上升趋势;慢肌面积占比在60和105 kg时显著或极显著低于其他体重阶段（P<0.05;P<0.01）,快慢肌所占面积总百分比在90 kg时极显著低于其他体重阶段（P<0.01）。实时荧光定量PCR检测结果发现,MyHCⅠ基因mRNA表达量在75和105 kg时极显著高于其他体重阶段（P<0.01）,MyHCⅡA基因mRNA表达量整体呈下降趋势,MyHCⅡX基因mRNA表达量在60 kg时达到最高,而MyHCⅡB基因mRNA表达量在75 kg时极显著低于其他体重阶段（P<0.01）;MyoD、Pax7、MSTN、MyoG、MEF2C基因mRNA表达量分别于60、75、90、120、120 kg时达到最大值。相关性分析结果表明,除MSTN基因外,MyoG、MyoD、Pax7和MEF2C基因均与肌纤维形态和MyHC基因各亚型之间有显著或极显著的相关性（P<0.05;P<0.01）;通过对120 kg的豫西黑猪和杜洛克猪比较发现,两者间肌纤维直径、肌纤维面积、肌纤维密度,以及MyHC和相关成肌调控基因mRNA表达量均有极显著差异（P<0.01）。【结论】在豫西黑猪60~120 kg生长阶段,肌纤维面积、肌纤维直径整体呈上升趋势,肌纤维密度呈下降趋势;在肌肉发育过程中,纤维类型组成的变化主要是Ⅰ、ⅡA、ⅡX型肌纤维向ⅡB型肌纤维的转化;与杜洛克猪相比,豫西黑猪肌纤维面积和肌纤维直径较大,肌纤维密度较低,MyHCⅠ与MyHCⅡA基因mRNA表达量较高。

Developmental Changes of Muscle Fiber Histology and Myogenic Regulatory Genes with Different Slaughter Weights in Yuxi Black Pigs

【Objective】 The aim of this study was to reveal the developmental changes of muscle fiber histology, muscle fiber type and myoblast-related regulatory genes of longissimus dorsi muscle in Yuxi Black pigs and their relationship.【Method】 The average weight with 60, 75, 90, 105 and 120 kg Yuxi Black pigs were selected, each weight slaughtered 3 pigs, a total of 15 pigs, and the male and female randomly selected.HE staining and immunofluorescence staining were used to determine the composition of fast and slow muscle types and fibrous histological characteristics, and the mRNA expressions of myogenic differentiation (MyoD), paired-box 7 (Pax7), myostatin (MSTN), myogenin (MyoG), myocyte enhancer factor 2C (MEF2C) and myosin heavy chain (MyHC) subtypes were measured by Real-time quantitative PCR.【Result】 With the increase of weight in Yuxi Black pigs, the overall muscle fiber density showed a downward trend, which was extremely significantly higher than that of other groups at 75 kg (P<0.01), and the area and diameter of muscle fibers showed an overall upward trend.At 60 and 105 kg, the percentage of slow muscles area were significantly or extremely significantly lower than other weight stages (P<0.05 or P<0.01), and the total percentage of the area occupied by the fast and slow muscles were extremely significantly lower than that of other weight stages at 90 kg (P<0.01).Real-time quantitative PCR results found that the mRNA expression of MyHCⅠ gene at 75 and 105 kg was extremely significantly higher than other body weight (P<0.01), the mRNA expression of MyHCⅡA gene as a whole showed a downward trend, the mRNA expression of MyHCⅡX gene at 60 kg reached the highest, and the mRNA expression of MyHCⅡB gene at 75 kg was extremely significantly lower than other body weight (P<0.01).The mRNA expression of MyoD, Pax7, MSTN, MyoG and MEF2C genes reached their maximum values at 60, 75, 90, 120 and 120 kg, respectively.The correlation analysis results showed that in addition to MSTN gene, MyoG, MyoD, Pax7 and MEF2C genes had significant or extremely significant correlations with muscle fiber morphology and MyHC gene subtypes (P<0.05 or P<0.01).Through the comparison of 120 kg of Yuxi Black pigs and Duroc pigs, it was found that the diameter, area, density of muscle fiber, and the mRNA expression of MyHC gene and related muscle-forming regulatory genes between the two were extremely significant differences (P<0.01).【Conclusion】 During the growth stage of 60 to 120 kg in Yuxi Black pigs, the area and diameter of muscle fiber increased and the density of muscle fiber decreased, and the change of muscle fiber type composition was mainly the transformation of types Ⅰ, ⅡA and ⅡX muscle fiber to type ⅡB muscle fiber.Compared with Duroc pigs, the area and diameter of muscle fiber in Yuxi Black pigs were larger, the density of muscle fiber was lower, and the mRNA expression of MyHCⅠ and MyHCⅡA genes were higher.