DNA methylation related genes in the oyster genome. (A) Conserved domain organization of the DNMT1, DNMT2 and DNMT3 proteins among oyster Crassostrea gigas, honeybee Apis mellifera and human Homo sapiens. Honeybees have two DNMT1 genes (DNMT1A and DNMT1B), and the DNMT1A protein is presented. Human have three DNMT3 genes (DNMT3A, DNMT3B and DNMT3L), and the DNMT3A protein is presented. (B) Expression levels of the oyster DNMTs and MBD2/3 genes in different developmental stages and adult organs, denoted by reads per kilobase of transcript per million mapped reads (RPKM). Numbers after sample names indicate the orders in development, with smaller numbers representing earlier stages in development.