Project description:5-methylcytosine is a major epigenetic modification sometimes called "the fifth nucleotide". However, our knowledge of how offspring inherit the DNA methylome from parents is limited. We generated nine single-base resolution DNA methylomes including zebrafish gametes and early embryos. The oocyte methylome is significantly hypo-methylated compared to sperm. Strikingly, the paternal DNA methylation pattern is maintained throughout early embryogenesis. The maternal DNA methylation pattern is maintained until the 16-cell stage. Then, the oocyte methylome is gradually discarded through cell division, and progressively reprogrammed to a pattern similar to that of the sperm methylome. The passive demethylation rate and the de novo methylation rate are similar in the maternal DNA. By the midblastula stage, the embryo?s methylome is virtually identical to the sperm methylome. Moreover, inheritance of the sperm methylome facilitates the epigenetic regulation of embryogenesis. Therefore, besides DNA sequences, sperm DNA methylome is also inherited in zebrafish early embryos.
Project description:5-methylcytosine is a major epigenetic modification sometimes called "the fifth nucleotide". However, our knowledge of how offspring inherit the DNA methylome from parents is limited. We generated nine single-base resolution DNA methylomes including zebrafish gametes and early embryos. The oocyte methylome is significantly hypo-methylated compared to sperm. Strikingly, the paternal DNA methylation pattern is maintained throughout early embryogenesis. The maternal DNA methylation pattern is maintained until the 16-cell stage. Then, the oocyte methylome is gradually discarded through cell division, and progressively reprogrammed to a pattern similar to that of the sperm methylome. The passive demethylation rate and the de novo methylation rate are similar in the maternal DNA. By the midblastula stage, the embryo?s methylome is virtually identical to the sperm methylome. Moreover, inheritance of the sperm methylome facilitates the epigenetic regulation of embryogenesis. Therefore, besides DNA sequences, sperm DNA methylome is also inherited in zebrafish early embryos. hMeDIP-seq is performed in sperm,2-cell,16-cell,1k-cell and a input control sample 4 new samples are added to GSE44075. RNA-seq is performed in sperm, egg,1k-cell, germring samples .hMeDIP-seq is performed in sperm,2-cell,16-cell,1k-cell and a input control sample 10 new samples are added to GSE44075. Bisulfite-seq is performed for nine samples : sperm, egg,16-cell,32-cell,64-cell,128-cell,1k-cell , Germring and testis. TAB-seq is performed for one sample , 32-cell.
Project description:Unlike that of mammals, the total DNA methylome of many cold-blooded vertebrates is globally inherited from gametes to early embryos. In zebrafish, this is however accompanied by sweeping “dememorization” of enhancers prior to fertilization for sperm and just after fertilization for oocyte, as they undergo full methylation and are not demethylated again until phylotypic stage. The significance of both global methylome inheritance and enhancer dememorization in early embryos remains largely unknown. Adding to the puzzles, the zygotic mutant zebrafish of dnmt1, the major DNA methylation maintenance methyltransferase, surprisingly can develop to term. To solve the role of DNA methylation in early development, we generated zebrafish embryos derived from dnmt1-knocking down oocytes using a recently developed method OMIS (Oocyte Microinjection in situ), which successfully eliminated DNA methylation before zygotic genome activation. dnmt1-deficient embryos failed to initiate epiboly and died around gastrulation. This is in part caused by activation of immune response and p53-regulated apoptosis, likely triggered by the derepression of transposable elements. Single cell RNA-seq further revealed defective differentiation in these mutants. DNA methylation is also required for the establishment of repressive histone marks H3K27me3 and H2AK119ub. Strikingly, the loss of DNA methylation leads to extensive derepression of somatic genes and enhancers, which acquire ectopic H3K27ac, accessible chromatin, and H3K4me3. These somatic enhancers are preferentially CG-rich and are bound by CG-containing TFs. By contrast, embryonic enhancers are generally CG-poor, methylation-insensitive, and are bound by CG-less TFs. Hence, the global DNA methylome inheritance is essential for vertebrate early development, and enhancer dememorization resets an epigenetic gate that separates embryonic and somatic programs.