Study On Genetic Control Mechanism Of Sheep Muscle Growth

In this study, methods of candidate gene and whole genome microarray were applied to analyze the mechanisms of genetic control mechanism of growth traits in sheep muscle, and the main contents were as the following:I Developmental Changes of Gene Expression of Dlk1,GHR,IGF-l,MSTN and MyoG Genes and Their Association Analysis with Carcass Traits, meat quality in Hu SheepAbstract:In this experiment, Hu sheep was regarded as the researched object and6-month-old Dorset sheep was regarded as the referenced group. Methods of RT-PCR was applied to analyze the expression of Dlkl,GHR,IGF-I,MSTN,MyoG gene in Longissimus Dorsi at different growth stages of Hu sheep,and their association analysis with carcass traits, meat quality in Hu Sheep also been studied. The purpose is to reveal the molecular genetics basis of muscle growth, and provide genetic information for the selection of muscle growth trait, and enriched the genetic resources research of Hu sheep. The results were as follows:1. Developmental Changes of Expression of Dlk1, GHR, IGF-I, MSTN and MyoG Genes in Hu SheepThe expressions of Dlkl, GHR, IGF-I, MSTN and MyoG had a lot of significant differences or extreme significant differences among different growth stages and different genders, which showed that different stages and different genders had important influences on the expressions of the five genes in sheep skeletal muscle. After birth, the expressions of the five genes did not always increase or decrease, the turning points of different genes expression were not at the same time. In terms of6-month-old, the expressions of the five genes in Hu sheep were all higher than that in Dorset sheep, therefore, breed factors might also have some impacts on the different expressions of the five genes, but a further study would be needed for the expressions of the five genes in other growth stages between the two breeds. The results showed that almost every two genes had a significant or an extreme significant positive correlation except the correlation between GHR and MSTN or MyoG.2. The correlation analysis between the5genes expression and Carcass traits in Hu sheepThe expressions of Dlkl, GHR, IGF-I, MSTN had a significant or an extreme significant positive correlation with the Live weight and carcass weight and didn’t have any correlation with the net meat weight in Hu sheep; the expression of MyoG didn’t have any significant correlation with the Live weight, carcass weight and net meat weight in Hu sheep.3. The correlation analysis between5genes expression and meat quality in Hu sheepThe expressions of the5genes all had positive correlation with diameter of muscle fibers and shear force of muscle fibers; in addition, they had a negative correlation with the density of muscle fibers. The expressions of Dlkl, GHR, IGF-I, MSTN had a significant or a extreme significant correlation with diameter of muscle fibers and shear force of muscle fibers, and the expressions of Dlkl、 GHR、IGF-I had a significant or a extreme significant correlation with shear force of muscle fibers. The expression of MyoG didn’t have any correlation with the diameter of muscle fibers, shear force of muscle fibers and density of muscle fibers. Ⅱ Deciphering the regulatory circuitry of ovine skeletal muscle genes from expression data; signaling pathway in Callipyge sheep evidence for the involvement of the TGF-βAbstract:[Background] Recent advances in the analysis of gene expression data enables a detailed picture of the drivers of differences between treatments to be identified, including the identification of key genes that are not differentially expressed. Here we apply these approaches to gene expression data from sheep muscle with a particular focus on the callipyge phenotype. The callipyge mutation in sheep and mutations in the myostatin gene in cattle both lead to significantly increased muscle growth. Although both types of mutations increase the ratio of fast to slow twitch muscle fibers, many other aspects of the phenotypes are very different. Here we have applied new analysis methodologies to compare the identities of putative components of the path from the mutations to the phenotypic outcomes in callipyge sheep and a myostatin mutation in cattle.[Results] The reversed engineering of an Always Correlated gene expression landscape of sheep Longissimus dorsi (LD) muscle is described. Five robust modules including genes encoding muscle, mitochondrial, ribosomal, translation proteins and components of the26S proteosome were identified. We analyzed the callipyge versus normal sheep muscle gene expression data using the Regulatory Impact Factor (RIF2) methodology, which can identify key regulators not differentially expressed between two conditions, but which may be drivers of the phenotypic response. Literature and data-mining of the functions and signaling pathway in relationships of the top candidates supported a role for the TGF-β the processes by which increased DLKl expression in the affected muscles of callipyge sheep leads to increased muscle mass. In addition, plotting the RIF2scores for the callipyge sheep muscle dataset against the RIF2scores for a muscle gene expression data set from cattle with a mutation in the myostatin signaling pathway in both genes further supported a common role for the TGF-β phenotypes. The genes at the intersection of the RIF2analyses of the two datasets included YAP1, which encodes a component Hippo signaling pathway which regulates organ size. This provides the first in vivo evidence for a role for the Hippo signaling pathway in muscle growth in ruminants, supporting recent in vitro evidence for a role in muscle differentiation in the mouse.[Conclusions]The analyses provide new insights into the mechanisms underlying two increased muscle growth phenotypes in ruminants. In particular, they suggest a greater overlap between the mechanisms in callipyge sheep and myostatin cattle, than has previously been anticipated. The results of this study largely enriched the genetic resources research about important functional genes in herbivore of hollow horn ruminant families.