Study On Molecular Difference Of Both IGF1 And MEF2A Genes In Skeletal Muscle Of Laying Hens And Broilers During Embryonic Period

Under the artificial selection of high intensity,there were obvious separation of characters in commercial layers and broilers.Especially in skeletal muscle development: the development speed of skeletal muscle in commercial layers and broilers is extremely different.The development of skeletal muscle in the embryonic stage of poultry is of great significance to the later muscle production.Because the number of muscle fibers that closely related to the poultry’s production and quality of the muscles after birth is basically fixed in the embryonic period,and there are basically only hypertrophy and growth of muscle fibers after birth.The study is about the phenotypic differences of skeletal muscle development in the embryonic stage of the laying hens and broilers.Meanwhile,we exploered the potential genetic mechanisms leading to these phenotypic differences.It can provide an important theoretical basis for the breeding direction of the future local chicken species and improvement of variety characters.Meanwhile,it can also provide a molecular basis for promoting skeletal muscle development in avian embryos.In this experiment,the white feather broiler,Roman egg laying hens and Daheng broiler were selected for object of study.We compared the developmental characteristics of skeletal muscle of 3 chicken breeds at different embryonic stages,and explored the expression patterns and differences of two candidate genes that have specific SNP loci in laying hens and broilers in the leg muscle and the pectoral muscle of the 3 chicken breeds.We tentatively explored potential molecular regulation mechanisms and possible epigenetic regulatory mechanisms that lead to differences in gene expression patterns.The results of the test are as follows:(1)The changes of the weight of the leg muscle and the pectoral muscle in the whole embryo period were all white feather broiler > Daheng broiler > Roman egg laying hens.The white feather broiler and Roman egg laying hens showed significant variety difference(P < 0.05).(2)The results of tissue section showed that the differentiation time of the pectoral muscle and leg muscle in white feather broilers was earlier than that in Roman egg laying hens.In addition,the differentiation time of leg muscle was earlier than that of the pectoral muscle.(3)IGF1 gene had different expression patterns in leg muscles and pectoral muscles of three chicken breeds at the whole embryo stage.It had similar changes in the leg muscles and the pectoral muscles of two broiler breeds: in the leg muscles,they showed the same change rule that of descending – ascending– descending;in the pectoral muscles,they showed the same change rule that of descending.We compared the expression difference of IGF1 gene both the leg muscles and pectoral muscles of 3 chicken breeds during the whole embryo stage.It was found that there was no significant difference in embryo age both 11.5 days and 17.5 days of embryo age,but the significant variety differences were found in other embryo ages(P < 0.05).(4)The polymorphism of the SNP locus in the promoter region of the IGF1 gene 2000 bp was analyzed.Three SNP locis were detected,which were G1679 C,C1601T and C1448 T respectively.The GG genotypes of SNP1 and CC genotypes of SNP2 and SNP3 were dominant in white feather broilers.The CC genotypes of SNP1 and TT genotype of SNP2 and SNP3 does not exist in two highly selected varieties,while all of them had high frequency in the local breeding varieties.We preliminarily speculate that the variation of these 3 SNP locis may affect the expression of IGF1 downstream genes.(5)MEF2A gene had different expression patterns in leg muscles and pectoral muscles of three chicken breeds at the whole embryo stage.The expression level of MEF2 A gene showed significant breed difference in the pectoral muscle at the whole embryo stage,except at 12 days of embryo age(P < 0.05).In leg muscle,the expression level of MEF2 A gene showed significant breed difference at the whole embryo stage(P < 0.05).(6)The degree of methylation of the CpG island of the 592 bp long that located in the upstream of the MEF2 A gene transcription site(-339 bp to-931bp)was analyzed.The results showed that the change of the methylation level of MEF2 A gene in the pectoral muscles of three chicken breeds was negatively correlated with the change of the expression level,and the only white feather broiler with the change rule of methylation level in the leg muscles was negatively correlated with the change of the expression level.The difference of the methylation level of MEF2 A gene in the pectoral muscles of the three breeds was negatively correlated with the difference of the expression level: the expression of the chicken with high methylation level was lower.The expression of MEF2 A in the pectoral muscles of three chicken breeds and the leg muscles of white feathered chicken may be regulated by the methylation level of the CpG island in the promoter region,and the reason for the difference in the expression of the MEF2 A gene in the pectoral muscles of the three breeds may be caused by the different degree of methylation in the promoter region of the CpG island.