Fig. 2: Oocyte-specific hypomethylated genic and intergenic regions.

a The heat map represents the methylation level and CG density at all promoters and genic regions in human sperm, oocytes and 6-week embryos. Genes have been classified into five major groups according to the CG density and methylation patterns at the promoter and genic regions. b The graph represents the methylation level and CG density around PROK1 gene regions. The promoter and genic region of the PROK1 gene exhibit a low CG density. The methylation levels of the PROK1 gene promoter and genic and intergenic regions are low in oocytes, but high in sperm and 6-week human embryos. c Gene expression levels in the 5 groups in oocytes. Purple numbers refer to the number of unexpressed genes. Black numbers refer to the number of expressed genes. The expression levels of the genes in group 2 were significantly lower than in groups 1, 3 and 5, and the expression levels of the genes in group 4 were significantly lower than in groups 1, 3 and 5. All p values of pair-wise comparisons were less than 0.001, and the p value was calculated based on the Mann–Whitney test. d Gene expression in the 5 groups in 6-week human embryos. Purple numbers refer to the number of unexpressed genes. Black numbers refer to the number of expressed genes. The expression levels of the genes in group 1 are significantly lower than in groups 3, 4 and 5, and the expression levels of the genes in group 2 are significantly lower than in groups 3, 4 and 5. All p values of pair-wise comparisons are less than 0.001, and the p value is calculated based on the Mann–Whitney test. e Intergenic methylation levels of genes with highly methylated promoters and genic regions (high: high), promoters with low methylation, but highly methylated genic regions (low: high), and promoters and genic regions with low methylation (low: low) in human sperm, oocytes and 6-week embryos. f The graph represents methylation levels and CG density around GPR25 gene regions. The promoter and genic regions of the GPR25 gene exhibit a high CG density and low methylation levels in sperm, oocytes and 6-week embryos. The methylation level of GPR25 gene intergenic regions is low in oocytes, but high in sperm and 6-week embryos