A Comparative Study Of Skeletal Muscle Fiber Types In Mongolian Horses During Fetal And Adulthood

Mongolian horse is one of the old horse breeds in the world.As an excellent germplasm resource in Inner Mongolia,it has been living in semi-wild state on the grassland in the long historical evolution.Mongolian horses have excellent sports performance,can quickly run hundreds of kilometers.Muscle fiber has high plasticity and changes with age.The remodeling process of muscle fiber type is essential for the body ’ s life activities,energy homeostasis and fatigue alleviation.Exploring the influence of age factors on the type of Mongolian horse muscle fiber,revealing the principle of Mongolian horse muscle fiber type difference from the genetic point of view,and exploring the mechanism of Mongolian horse muscle fiber type difference in different periods are of great significance for studying Mongolian horse endurance and preventing muscle diseases.In this study,four representative muscle tissues of 4-month-old fetal and 5-year-old adult Mongolian horses,including triceps brachii(anterior limb),splenius(neck),longissimus dorsi(dorsum)and gluteus medius(posterior limb),were selected as a whole to carry out the research.Firstly,the muscle samples of fetal and adult Mongolian horses were stained with HE and immunohistochemistry to observe the phenotypic changes of muscle fibers,and succinate dehydrogenase was used to detect the mitochondrial activity of muscle fibers in two periods.Then,the skeletal muscle samples of Mongolian horses in fetal and adult stages were subjected to transcriptome sequencing to explore the genes and pathways related to the influence of fetal and adult stages on muscle fiber types.The results are as follows :1.The results of HE staining of Mongolian horse muscle fibers showed that the cross-section of single muscle fibers of Mongolian horses in fetal period was nearly spherical,and the nuclei were closely arranged.In adult Mongolian horses,the diameter of single muscle fibers increased significantly,showing irregular shapes,and the nuclei were mostly located at the edge of the cells.Immunohistochemical results showed that the proportion of slow-twitch muscle fibers in adult Mongolian horses was significantly higher than that in fetal Mongolian horses(p<0.01),indicating that the types of skeletal muscle in fetal Mongolian horses and adult Mongolian horses changed.2.Succinate dehydrogenase is one of the mitochondrial marker enzymes,mainly expressed in slow-twitch muscle fibers.In this experiment,it was found that the succinate dehydrogenase activity of Mongolian horses in adulthood was significantly higher than that in fetal Mongolian horses(p < 0.05).3.A total of 250 differentially expressed genes were screened through RNA-seq studies on skeletal muscle of Mongolian horse in fetal and adult stages.Among them,27 genes were significantly up-regulated in Mongolian horse in adult stage,and 17 genes were significantly up-regulated in Mongolian horse in fetal stage.The enrichment analysis of differentially expressed genes showed that the differentially expressed genes were significantly enriched in 26 pathways,of which 11 pathways were annotated in biological processes,8 pathways were annotated in cell composition,and 7 pathways were annotated in molecular function.The differentially expressed genes TNNT1,TNNC1 and ATP2A2 were significantly enriched in the transition between fast and slow fibers pathway,and these differentially expressed genes were also closely related to skeletal muscle contraction,growth and development.The KEGG analysis of the differentially expressed genes showed that there were 10 pathways(P < 0.05)that were significantly enriched,among which AMPK signaling pathway and calcium signaling pathway were involved in the transformation of muscle fiber types.Through transcriptome data analysis,genes with significant changes in the expression levels of ATP2A2,MYOZ2,MYL1,ENO3,MYBPC1,and TMOD4 were screened as candidate genes related to differences in Mongolian horse muscle fiber types,laying a foundation for future research on Mongolian horse endurance and muscle disease prevention in my country theoretical basis.