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Haploinsufficiency, but not defective paternal 5mC oxidation, accounts for the developmental defects of maternal Tet3 knockouts

ABSTRACT: DNA demethylation of paternal genome in zygotes takes place in various mammals including mice and human. Recent studies have revealed that this is achieved through Tet3-mediated iterative oxidation of 5-methylcytosine (5mC) coupled with replication-dependent dilution. Tet3-mediated paternal DNA demethylation is believed to be required for mouse development given that Tet3 heterozygous embryos, derived by fertilizing Tet3 knockout (KO) oocytes with wild-type (WT) sperms, exhibit 5mC oxidation defects and embryonic sublethality, Here we demonstrate that the sublethality phenotype of the maternal KO mice is caused by haploinsufficiency of Tet3, but not by defective paternal 5mC oxidation. We found that Tet3 heterozygous mice derived from crosses of heterozygous father or mother with WT mice also exhibit sublethality phenotype similarly to Tet3 maternal KO mice. Importantly, embryos reconstituted with WT paternal nuclei that bypassed 5mC oxidation develop to term and grow to adulthood normally. Genome-scale DNA methylation analysis of the maternal KO zygotes and blastocysts demonstrated that hypermethylation caused by the depletion of maternal Tet3 is largely diminished by the blastocyst stage. Our study thus not only demonstrates that Tet3-mediated paternal 5mC oxidation is dispensable for mouse development but also suggests the existence of a compensation mechanism in preimplantation embryos that can compensate for the defective 5mC oxidation in zygotes.

ORGANISM(S): Mus musculus

PROVIDER: GSE62719 | GEO | 2015/02/28

SECONDARY ACCESSION(S): PRJNA264894

REPOSITORIES: GEO

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Project description:Fertilization triggers a global erasure of 5-methylcytosine from paternal DNA as part of extensive epigenetic reprogramming during the transition from gametic specialization to totipotency. This active removal has been shown to involve oxidation by TET3, but the targeting of this pathway and the wider context of demethylation remain poorly understood. We optimized a novel technique for whole-genome bisulfite sequencing and applied it to wild-type and TET3-deficient zygotes, using SNPs to access paternal alleles. As the great majority of sperm-contributed methylation lies outside the CpG islands (CGIs) and promoters analysed to date, these genome-wide methylation profiles allow paternal methylation trajectories in the zygote to be comprehensively examined for the first time. This global view revealed that in addition to pervasive loss of methylation from intergenic sequences and most repetitive elements, gene bodies constitute a major target of zygotic demethylation. Methylation loss is associated with zygotic genome activation, and at gene bodies is also linked to increased transcriptional noise in the early embryo. Our data maps the primary contribution of oxidative demethylation to a subset of gene bodies and single-copy intergenic sequences, and implicates the action of redundant pathways at many loci. We further uncover a novel function for TET3 in protection from de novo methylation at CGIs and promoters. This work adds new breadth to our understanding of the molecular events involved in reprogramming gametic identity following fertilization. Three independent collections of zygotes were performed for each genotype (control and TET3 deletion), giving a total of 225 control and 237 TET3 deletion zygotes, of which 120 and 129 were derived from 129S2/SvHsd studs for control and TET3 samples, respectively. Zygotes were pooled and whole-genome bisulfite libraries were prepared using a post-bisulfite adaptor tagging strategy optimized from (Miura et al. Nucleic Acids Research 2012, 40:e136)

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Haploinsufficiency, but not defective paternal 5mC oxidation, accounts for the developmental defects of maternal Tet3 knockouts

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