| As the main breed of Mongolian traditional endurance horse racing in Inner Mongolia,Mongolian horses have the advantages of the greatest stamina and strong disease resistance,and can often achieve good results in ultra-long-distance endurance races.This is not only based on the good innate endurance potential of Mongolian horses but also affected by traditional Mongolian training before racing.It is a traditional endurance training method that combines aerobic endurance training and strict diet control.Achieve the effect of controlling body fat and improving the horse’s endurance sports performance.Equine skeletal muscle is the main locomotive organ,and its strong contractility and rich distribution of mitochondria can provide long-lasting and strong power for horses during exercise.The composition of different types of muscle fibers in skeletal muscles allows the skeletal muscles of the horse’s whole body to respond to different types of exercises.The adaptive transition between muscle fibers will be affected by the duration and intensity of exercise.Therefore,the determination of the muscle fiber composition of horse skeletal muscle and its changes during training will be beneficial to the study on the source of endurance quality of Mongolian horses,and provide a scientific basis for the study on Mongolian traditional horse training to improve horse endurance sports performance.The following main results were obtained through the research:1.The results of the comparison of the proportion of fast and slow muscle fibers in the skeletal muscles of the four main moving parts of Mongolian horses show that: the proportion of slow muscle fibers: splenius of the neck(60.83%)> triceps of the forelimb arm(60.50%)> longissimus dorsi of the back(14.33%)> hindlimb gluteus medius(8.87%),the proportion of fast-twitch fibers: hindlimb gluteus medius(91.13%)> back longissimus dorsi(85.67%)> forelimb triceps(79.50%)> muscle neck splenius(39.17%).Moreover,the ratio of slow muscle fibers in the four parts of Mongolian horses is higher than that of thoroughbred horses of the same age and sex.The results of energy metabolism enzyme activity detection of the splenius muscle with the highest proportion of slow-twitch fibers and the gluteus medius muscle with the highest proportion of fast-twitch fibers showed that the splenius had higher oxidase activity than the gluteus medius,and the gluteus medius had higher glycolytic activity.enzymatic activity.The whole-transcriptome sequencing results of the slow muscle representing the skeletal muscle splenius and the fast muscle representing the skeletal muscle gluteus medius showed that the high expression genes of the slow muscle were mainly enriched in the functional items related to muscle contraction,and the high expression genes of the fast muscle were mainly enriched in the energy metabolism Related functional entries,in which it was found that the slow muscle inhibitory factor SOX6 was significantly overexpressed in Mongolian horse fast muscle and had a higher level of exon skipping events,and showed a strong association with eca-miR-499,LOC102147674 and circ-EIF4G3 expression correlation and excellent binding sites.2.After 28 days of horse-hanging training on six Mongolian horses,the transformation of fast-twitch fibers to slow-twitch fibers occurred in different degrees in the gluteus medius.The average proportion of slow-twitch fibers increased significantly by 5.86%.The activity of metabolic enzymes was significantly increased from 74.89 U/g to 325.22 U/g.By observing the changes in the transcript levels of gluteus medius samples before and after training,it was found that the fast-twitch-specific expressed genes such as ACTN3,CASQ1,MYL1,MYOM2,and TNNI2 related to muscle contraction were downregulated along with the decrease in glycolytic activity during the horse-hanging process.In the enrichment results,the glycolysis pathway and the protein balance pathway are involved in the expression changes of genes,showing the trend of energy changes during the fasting process with the decrease of glycogen energy supply and the increase of protein consumption,and the slow muscle-specific expression of eca-miR-499-5p The adaptive changes of MYL1,MYOM2,and PI3K-Akt signaling pathway genes that have binding sites with them may be involved in the above-mentioned changes in muscle fiber transformation and energy metabolism.3.Six Mongolian horses under the same conditions underwent a 28-day dietary restriction experiment.The proportion of fast and slow muscle fibers in the gluteus medius of the horses changed to varying degrees but did not show the same trend of change.Only the glycolytic metabolic enzymes of skeletal muscle were significantly downregulated.The data observed by whole-transcriptome sequencing showed that the changes at the transcript level were consistent with the constant changes in energy metabolism during fasting,indicating that dietary restriction during traditional endurance training may affect the consumption of skeletal muscle protein.The results of functional annotation of noncoding RNA are also consistent with functional changes at the overall transcript level.The differentially expressed lnc RNAs are different from most of the differentially expressed m RNAs,miRNAs,and circ RNAs that are down-regulated.More differentially expressed lnc RNAs are up-regulated,and the functional annotation results of their target genes Focusing on the items related to the muscle system,lnc RNAs whose expression changes after feeding restriction may be involved in the adaptive changes of skeletal muscle during the dietary restriction experiment.4.After the identification of the dual luciferase reporter assay,the target binding sites between the slow muscle-specific expressed gene eca-miR-499 and its target genes SOX6,MYOM2,MSTRG.16465.1 and circ-URI1 were determined.According to the expression specificity of the muscle fiber-specific expressed SOX6 and MYOM2,and the potential ce RNA mechanism of MSTRG.16465.1 and circ-URI1.We constructed a molecular regulation model that affects the fast and slow muscle fiber typing and conversion of horse skeletal muscle,with eca-miR-499-5p as the core. |
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