Abstract：Myostatin (MSTN) is mainly expressed in skeletal muscle and is involved in regulating the growth and development of skeletal muscle. Mutations in the MSTN gene cause excessive muscle development, resulting in a double-muscle phenotype. In this study, MSTN gene-edited Luxi cattle (Bos taurus) skeletal muscle was used as material to explore the effect of MSTN knockout on bovine muscle phenotype, and to explore the mechanism of MSTN gene regulation of muscle development through the transcriptome. 4 typical skeletal muscles, such as soleus, gastrocnemius, semitendinosus and longissimus dorsi, were taken as materials. The hematoxylin-eosin staining sections of these 4 skeletal muscles were used to observe the effect of MSTN gene knockout on skeletal muscle. qRCR and Western blot were used to detect the mRNA and protein expression of MSTN in these four skeletal muscles. Finally, through transcriptome analysis, the target genes of the mechanism of MSTN knockout on skeletal muscle of Luxi cattle were explored. The results showed that compared with ordinary Luxi cattle, the cross-sectional area of muscle fibers in the skeletal muscle of MSTN gene-edited cattle was significantly increased, and the intermuscular fat was significantly reduced. Transcriptome sequencing results showed that a total of 5 945 differentially expressed genes were identified between the skeletal muscle of MSTN gene-edited cattle and ordinary cattle (FC>1.5, P<0.05), of which the expression was up-regulated in the skeletal muscle of MSTN gene-edited cattle. There were 672 genes and 5 273 down-regulated genes; these differential genes were mainly concentrated in the signaling pathways such as PI3K-Akt, MAPK, p53 and AMPK, and were involved in the developmental processes of muscle satellite cell proliferation and differentiation. Studies have shown that MSTN gene deletion promotes the expression and regulation of genes related to muscle development and differentiation, and increases the cross-sectional area of skeletal muscle fibers, resulting in a muscle hypertrophy phenotype. These results add a little more insight to bovine skeletal muscle research.
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