Fig. 5

Overview of DNA methylation dynamics during teleost embryogenesis. (A) mCG dynamics in medaka, zebrafish, and medaka-zebrafish hybrids at the whole genome level (genome browser snapshots), hox clusters (HOX), Cancer Testis Antigen promoters (CTA), and phylotypic enhancers (PHYLO) in gametes, ZGA blastula embryos, and during the phylotypic period. Early teleost embryogenesis, as observed in medaka, zebrafish, and medaka-zebrafish hybrids, is characterised by maternal adoption of a paternal-like mCG methylome state prior to ZGA onset. Organogenesis stages (phylotypic period) are characterised by CTA promoter hypermethylation (hypermC), and phylotypic (organogenesis) enhancer demethylation (hypomC). Both processes, while highly conserved between medaka and zebrafish, are not carried out to the same extent in medaka-zebrafish hybrid embryos. (B) mCH dynamics at TGCT tandem repeats in medaka, zebrafish, and medaka-zebrafish hybrid embryos in gametes, ZGA blastula embryos, and during the phylotypic period. TGCT methylation is present in both maternal and paternal zebrafish germline genomes, whereas in medaka and medaka-zebrafish hybrid embryos this type of methylation can be found only in the maternal genome. Notably, zebrafish and medaka differ in their sperm packaging mechanisms with zebrafish employing histones, and medaka protamines, to package their sperm.