Study On The Level Of Genome Methylation Of Adipose And Muscle Tissues In DLY Pigs

DNA methylation is an important epigenetic modification and has become one of the new research focus because of its important roles in maintaining normal cellular functions, gene imprinting, embryonic development and human oncogenesis. As an agricultural animal and a laboratory model, pig has important economic values and special biological characteristics. Studying on the methylation level among different tissues in whole genome may provide some meaningful data for the methylation study of pig genome and provides new ideas for finding novel functional genes, besides it also offers important reference materials for the molecular genetic mechanism of heterosis. In the present study, the status of methylation was investigated among different tissues, with DNA from outer layer of subcutaneous fat, inner layer of subcutaneous fat, intermuscular fat, greater omentum, lesser omentum, suet oil, longissimus dorsi muscle and psoas major muscle of DLY pigs. The main results are as follow:1. To explore the status of methylation and compare the differences of methylation profile of genomes in eight tissues of pig, the DNA methylation patterns of CCGG sites were screened using 20 selective primer combinations by MSAP (Methylation sensitive amplified polymorphism) technique, and about 7000 bands were amplified altogether. These results indicate that the methylation levels of these tissues are about 14% to 27%. The DNA methylation content in adipose tissues was higher than that in muscle (P<0.01).2. The average levels of methylation of longissimus dorsi muscle, psoas major muscle, outer layer of subcutaneous fat, inner layer of subcutaneous fat, intermuscular fat, greater omentum, lesser omentum and suet oil were about 15.85%, 17.07%, 22.46%, 19.53%, 21.08%, 18.73%, 18.01%, 23.25% respectively. Full-methylation sites were about 6.91%, 7.48%, 9.33%, 8.35%, 9.37%, 8.26%, 7.43% and 10.02% respectively. Hemimethylation sites were about 8.94 %, 9.59%, 13.13%, 11.18%, 11.71%, 10.47%, 10.58% and 13.23% respectively. The results suggest that the hemimethylation sites of the eight tissues were higher than full-methylation sites.3. The least squares means and multiply comparison of methylation in the different sexes, different tissuses shown: the difference of total methylation, full-methylation, hemimethylation in the different sexes weren't significant, but the methylation level in boar was higher than sow. The difference between adipose tissue and muscle tissue as well as the difference among the six adipose tissues were complex. The difference of total methylation, full-methylation and hemimethylation were significant(P<0.05) or extremely significant(P<0.01) respectively. The methylation level of psoas major muscle is slightly higher than longissimus dorsi muscle, but no significant difference was found between the two tissues. It is speculated that the phenomenon of the tissue-specific methylation maybe related to the development of biological function. The methylation of adipose tissue which acts as energy storage and endocrine is particular complex. This difference in methylation may relate to the complex regulation that control of the proliferation and differentiation of fat cells.4. Psoas major muscle has abundance of 2a, 2x fibers and less 2b type fiber compared with the longissimus dorsi muscle, and psoas major muscle has a higher total methylation content, full-methylation content and hemimethylation content, which may be assumed that the higher level of methylation in the psoas major muscle tissues inhibited the expression of MyHC2b. Comparison of the same tissue revealed that the expression of MyHCI is both higher in the psoas major muscle and in the longissimus dorsi muscle of sows than that of boars. To the expression of MyHC2c in the psoas major muscle, boars are significantly higher than sows (P<0.05), this perhaps matter with the higher methylation content of boars, the expression of MyHCI in muscle tissue of boar is inhibited. For how the methylation was involved in muscle development and myogenin gene regulation precisely requires further study to prove.