Characteristics Of Meat Production Traits And Skeletal Muscle Fiber Types Of MSTN Gene Editing Pigs

Meat production trait has always been an important goal of modern pig genetic improvement.Focusing on the aims of improving meat production and meat quality,a number of key factors that can be used for the genetic improvement of porcine meat production have been located and identified.Myostatin（MSTN）is a myocytokine encoded by MSTN gene,which can inhibit the growth of skeletal muscle.At present,several MSTN gene editing pigs,which has improved the meat production in a number of pig populations,have been created by the gene editing technologies.However,there are few studies on the muscle fibre characteristics of multiple skeletal muscle types in the whole body of MSTN gene modified pigs.There is also a lack of specific research on the regulation of MSTN gene on the multiple porcinr skeletal muscles.The genetic mechanism of improving meat production of pigs after MSTN gene modification has not been clarified.In this study,16MSTN edited white pigs and wild-type white pigs were selected as the research objects.The skeletal muscle tissues of 11 parts of the experimental pigs,including psoas major,semitendinosus,biceps femoris,trapezius cervicalis,gluteus superficialis,latissimus dorsi,rectus abdominis,transverse abdominal muscle,soleus muscle,gastrocnemius muscle and supraspinatus muscle,were collected and evaluated.The carcass and meat quality of MSTN^-/+and wild-type big white pigs,the diameter and cross-sectional area of muscle fibers in multiple skeletal muscle tissue were refined,and the characteristics of muscle fiber types were analyzed as well.The results show that:a)After MSTN gene modification,the expression level of MSTN gene changed in different extent from multiple skeletal muscle tissues.There was no significant difference between MSTN and WT in the expression levels of MSTN in trapezius cervicis,psoas major,gastrocnemius and transverse abdominal muscles.The expression levels of MSTN in the other 7 skeletal muscle tissues were up-regulated differentially.b)Compared with wild type pigs,the eye muscle area and carcass lean rate of MSTN^-/+pigs were significantly and extremely significantly increased,separately.The drip loss was 86%higher than that of wild type pigs,which was significantly higher than that of wild type pigs.The Intramuscular fat was 55%lower than that of wild type pigs,which was significantly higher than that of wild type pigs,while p H₁was significantly higher than that of wild type pig.c)The mean diameter of gluteus superficialis muscle of MSTN^-/+pig was significantly larger than that of wild pig（p<0.05）.The diameter of semitendinosus muscle,soleus muscle,latissimus dorsi muscle,gluteus superficialis muscle,rectus abdominis muscle,supraspinatus muscle and psoas major muscle was significantly larger than that of wild type pig（p<0.01）.There was no significant difference of the diameter of muscle fiber from four muscle tissues,including transverse abdominal muscle,latissimus dorsi muscle, gastrocnemius muscle and biceps femoris muscle.The diameter of trapezius cervicalis muscle of MSTN^-/+pig was reduced by 20%,compared with the wild types.d)The effect of MSTN gene editing event on cross section of each skeletal muscle fibers from different anatomical location was also different.The cross-sectional area of skeletal muscle in multiple parts of MSTN^-/+pigs was up-regulated,such as semitendinosus,soleus,rectus abdominis,supraspinatus,gluteus superficialis and psoas major,were significantly larger than those of wild type pigs,while that of the trapezius muscle fiber was decreased,compared with that of wild type pig.There was no significant difference in cross-sectional area of muscle fibers in latissimus dorsi,transversus abdominis,gastrocnemius,and biceps femoris.e)Changes in the proportion of My HCs in skeletal muscle sites where muscle fiber hypertrophy occurs are not consistent.The expression of MYH2 or MYH7encoding oxidized muscle fibers was down-regulated in soleus muscle,psoas muscle and latissimus dorsi muscle,and the expression of MYH1 or MYH7encoding fermented muscle fibers was up-regulated.While the biceps femoris also showed up-regulation of MYH4 expression and down-regulation of MYH2 and MYH7 expression levels,there was no hypertrophy of muscle fibers.semitendinosus is mainly reflected in the up-regulation of MYH1 and MYH4 gene expression levels.My HCs expression abundance of supraspinatus muscle did not change significantly.We found that the expression of MSTN gene in different skeletal muscle tissues showed different trends after MSTN gene modification.The diameter and cross-sectional area of myofibers from most muscle tissues increased accompanied with the up-regulation of MSTN gene expression.However,the distribution of My HCs in the hypertrophied skeletal muscle after MSTN gene editing,was not the same.In conclusion,MSTN gene editing events affects the increase of muscle fiber area and the conversion of muscle fiber types of different skeletal muscle tissues specifically.