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Fig. 1 Maternal dnmt1 is essential for embryonic DNA methylation and development.(A) Schematic of DNA methylation landscapes in zebrafish (red) and mammals (blue) during early development. mCG, methylated CG. (B) Schematic of dnmt1 mKD via OMIS, zKD, and zKO. Three main developmental stages were examined in this study, including the 256-cell (pre-ZGA), dome, and shield (post-ZGA) stages. ZGA begins around 3 hpf. zKO embryos (dnmt1−/−) could survive until 120 hpf. (C) Violin plots showing average DNA methylation levels across the genome at different developmental stages of control (blue) and dnmt1 mKD embryos (red), zKD embryos (red), and zKO (red) embryos/larvae. (D) Survival curve of control (blue line), dnmt1 mKD embryos (red line), and dnmt1 mKD embryos rescued with either dnmt1 mismatch mRNAs [mKD; WT overexpressed embryos (WT OE), green dashed line] or catalytically mutant dnmt1 mismatch mRNAs (mKD; Mut OE, orange dashed line). Log-rank test was used to calculate P value. (E) Representative images of embryo phenotypes in control, dnmt1 mKD embryos, and dnmt1 mKD embryos rescued with either dnmt1 mismatch mRNAs (WT OE) or catalytically inactive mutant dnmt1 mismatch mRNAs (Mut OE) across different developmental stages. The numbers and ratios of embryos with a particular phenotype in each group are also shown. Scale bar, 250 μm. (F) Immunostaining of 5mC (green) in control and dnmt1 mKD oocytes, 256-cell, and dome embryos, as well as dnmt1 mKD embryos rescued by either dnmt1 mismatch mRNA (WT OE) or catalytically inactive mutant dnmt1 mismatch mRNA (Mut OE). DNA was stained with 4′,6-diamidino-2-phenylindole (DAPI) (blue). Scale bars, 50 μm. (G) Violin plot showing the global DNA methylation levels at the 256-cell and dome stages in control (Ctrl, blue), dnmt1 mKD (red), dnmt1 mismatch mRNA rescued (WT OE, green), and catalytically inactive mutant dnmt1 mismatch mRNA rescued embryos (Mut OE, yellow)