Analysis of DNA methylation in diploid and triploid of Crassostrea angulata

DNA methylation is an important epigenetic mechanism. It can induce changes in the biological phenotype by altering gene expression and the gene expression networks involved, thereby leading to the process of adaptive evolution. At present, epigenetic studies of polyploid genomes have been carried out in multiple aquatic animals, but epigenetic research on the polyploid genome of Crassostrea angulata has not been reported yet. In order to explore the methylation status of genomic DNA in different tissues of diploid and triploid C. angulata, the experiment used the fluorescence-labeled methylation sensitive amplification polymorphism (F-MSAP) technology to compare and analyze genomic DNA methylation in four tissues of C. angulata (mantle, gill, gonad, and adductor). The results showed that a total 1 388 to 3 871 methylation sensitive sites were detected. The full methylation levels of the mantle, gill, gonad, and adductor muscle of diploids were 11.75%, 12.84%, 12.22%, and 12.51%, respectively. The hemimethylation levels were 9.30%, 7.60%, 9.82%, and 8.61%, respectively. The total methylation levels were 21.05%, 20.44%, 22.04%, and 21.12%, respectively. The full methylation levels of the mantle, gill, gonad, and adductor muscle of triploids were 11.26%, 11.34%, 15.06%, and 30.28%, respectively. The hemimethylation levels were 10.47%, 7.31%, 7.49%, and 3.28%, respectively. The total methylation levels were 21.73%, 18.65%, 22.55%, and 33.56%, respectively. There were extremely significant epigenetic differences between the tissues. The full methylation level was higher than the hemimethylation level, and full methylation was the main methylation mode. The total methylation level of triploids increased by 0.51%-12.44% compared with diploids, and the epigenetic differences between diploids and triploids were extremely significant. The research shows that the mantle, gill, gonad, and adductor muscle tissues of C. angulata have different degrees of methylation levels. Methylation changes have occurred in triploid C. angulata, and these changes may affect the way of gene expression. This study can provide reference materials for the epigenetic research of polyploid C. angulata.