Abstract
Skeletal muscle, the main source of animal meat products, contains muscle fiber as a key unit. It is well known that transformation takes place between different types of muscle fibers, however, the conversion mechanism is not clear. In a previous study, our lab has demonstrated that there is a decrease in type I muscle fibers and an increase in type IIB muscle fibers in skeletal muscle of myostatin gene-edited Meishan pigs. Very interestingly, we observed the down regulation of miR-208b expression and an increase in expression the predicted target gene Mettl8 (Methyltransferase like 8) in skeletal muscle of MSTN gene-edited Meishan pigs. These results reveal that there is a potential connection between the conversion of skeletal muscle fiber types and miR-208b and Mettl8 expression. In this study, we first explored the expression patterns of miR-208b and Mettl8 in skeletal muscle in Meishan pigs; and then C2C12 cells were used to simulate the development and maturation of muscle fibers. Our results indicated that Myh4 expression level decreased and Myh7 expression level increased following overexpression of miR-208b in C2C12 cells. We therefore speculate that miR-208b can promote the conversion of fast-twitch fibers to slow-twitch fibers. The targeting relationship between Mettl8 and miR-208b was confirmed by results obtained using dual luciferase assay, RT-qPCR, and WB analysis. Following the transfection of Mettl8 siRNA into C2C12 cells, we observed that Mettl8 expression decreased significantly while Myh7 expression increased and Myh4 expression decreased, indicating that Mettl8 promotes the conversion of slow muscle fibers to fast muscle fibers. Additionally, changes in skeletal muscle fiber types are observed in those mice where miR-208b and Mettl8 genes are knocked out. The miR-208b knockout inhibits the formation of slow muscle fibers, and the Mettl8 knockout inhibits the formation of fast muscle fibers. In conclusion, our research results show that miR-208b regulates the conversion of different muscle fiber types by inhibiting Mettl8 expression.
Highlights
Skeletal muscle accounts for 30–40% of body weight in mammals
We have found that Methyltransferase like 8 (Mettl8) and miR-208b were related to each other by multi-omics analysis of MSTN gene-edited Meishan pig skeletal muscle (Xie et al, 2019; Li et al, 2020)
The results showed that Mettl8 expression level in the longissimus dorsi of Meishan pigs is higher on 65 days of embryo development in other growth periods
Summary
Skeletal muscle accounts for 30–40% of body weight in mammals. It is the main source of meat products for meat-producing animals and an important metabolic organ (Doran et al, 2009; Listrat et al, 2016; Abel, 2018). There are four types of skeletal muscle fibers: slow contraction oxidative metabolism type (I), fast contraction oxidative metabolism type (IIA), fast contraction glycolytic metabolism type (IIB), and fast contraction oxidative glycolysis facultative metabolism type (IIX). Different composition of muscle fiber types in skeletal muscle is a key factor that determines meat quality (Choi et al, 2007). A high proportion of slow-oxidized muscle fibers improves meat tenderness, juiciness, and color (Lee et al, 2010)
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