DNA methylation differences between male and female gonads of the oyster reveal the role of epigenetics in sex determination

DNA methylation involved in sex determination mechanism by regulating gene expression related to sex determination networks are common in vertebrates. However, the mechanism linking epigenetics in invertebrates and sex determination has remained elusive. Here, methylome of the male and female gonads in the oyster Crassostrea gigas were conducted to explore the role of epigenetics in invertebrate sex determination. Comparative analysis of gonadal DNA methylation of females and males revealed that male gonads displayed a higher level of DNA methylation and a greater number of hypermethylated genes. Luxury genes presented hypomethylation, while housekeeping genes got hypermethylation. Genes in the conserved signaling pathways, rather than the key master genes in the sex determination pathway, were the major targets of substantial DNA methylation modification. The negative correlation of expression and promoter methylation in the diacylglycerol kinase delta gene (Dgkd) - a ubiquitously expressed gene - indicated DNA methylation may fine turn the expression of Dgkd and be involved in the process of sex determination. Dgkd can be used as an epigenetic marker to distinguish male C. gigas based on the different methylation regions in the promoter region. The results suggest that DNA methylation mechanisms played potential functional impacts in the sex determination in oysters, which is helpful to deepen the understanding of sex determination in invertebrate.