Mapping putative enhancers in mouse oocytes and early embryos reveals TCF3/12 as key folliculogenesis regulators.

Dynamic epigenomic reprogramming occurs during mammalian oocyte maturation and early development. However, the underlying transcription circuitry remains poorly characterized. By mapping cis-regulatory elements using H3K27ac, we identified putative enhancers in mouse oocytes and early embryos distinct from those in adult tissues, enabling global transitions of regulatory landscapes around fertilization and implantation.

Methylome inheritance and enhancer dememorization reset an epigenetic gate safeguarding embryonic programs.

Marked epigenetic reprogramming is essential to convert terminally differentiated gametes to totipotent embryos. It remains puzzling why postfertilization global DNA reprogramming occurs in mammals but not in nonmammalian vertebrates. In zebrafish, global methylome inheritance is however accompanied by extensive enhancer “dememorization” as they become fully methylated.

Evolutionary epigenomic analyses in mammalian early embryos reveal species-specific innovations and conserved principles of imprinting.

While mouse remains the most popular model, the conservation of parental-to-embryonic epigenetic transition across mammals is poorly defined. Through analysis of oocytes and early embryos in human, bovine, porcine, rat, and mouse, we revealed remarkable species-specific innovations as no single animal model fully recapitulates the human epigenetic transition. In rodent oocytes, transcription-dependent DNA methylation allows methylation of maternal imprints but not intergenic paternal imprints.

The landscape of RNA Pol II binding reveals a stepwise transition during ZGA.

Zygotic genome activation (ZGA) is the first transcription event in life. However, it is unclear how RNA polymerase is engaged in initiating ZGA in mammals. Here, by developing small-scale Tn5-assisted chromatin cleavage with sequencing (Stacc-seq), we investigated the landscapes of RNA polymerase II (Pol II) binding in mouse embryos.

Rebooting the Epigenomes during Mammalian Early Embryogenesis.

Upon fertilization, terminally differentiated gametes are transformed to a totipotent zygote, which gives rise to an embryo. How parental epigenetic memories are inherited and reprogrammed to accommodate parental-to-zygotic transition remains a fundamental question in developmental biology, epigenetics, and stem cell biology. With the rapid advancement of ultra-sensitive or single-cell epigenome analysis methods, unusual principles of epigenetic reprogramming begin to be unveiled.

Imprecise DNMT1 activity coupled with neighbor-guided correction enables robust yet flexible epigenetic inheritance.

The epigenome, including DNA methylation, is stably propagated during mitotic division. However, single-cell clonal expansion produces heterogeneous methylomes, thus raising the question of how the DNA methylome remains stable despite constant epigenetic drift. Here, we report that a clonal population of DNA (cytosine-5)-methyltransferase 1 (DNMT1)-only cells produces a heterogeneous methylome, which is robustly propagated on cell expansion and differentiation.

Analysis of Genome Architecture during SCNT Reveals a Role of Cohesin in Impeding Minor ZGA.

Somatic cell nuclear transfer (SCNT) can reprogram a somatic nucleus to a totipotent state. However, the re-organization of 3D chromatin structure in this process remains poorly understood. Using low-input Hi-C, we revealed that, during SCNT, the transferred nucleus first enters a mitotic-like state (premature chromatin condensation).

Resetting histone modifications during human parental-to-zygotic transition.

Histone modifications regulate gene expression and development. To address how they are reprogrammed in human early development, we investigated key histone marks in human oocytes and early embryos. Unlike that in mouse oocytes, the permissive mark trimethylated histone H3 lysine 4 (H3K4me3) largely exhibits canonical patterns at promoters in human oocytes.

Dynamic epigenomic landscapes during early lineage specification in mouse embryos.

In mammals, all somatic development originates from lineage segregation in early embryos. However, the dynamics of transcriptomes and epigenomes acting in concert with initial cell fate commitment remains poorly characterized. Here we report a comprehensive investigation of transcriptomes and base-resolution methylomes for early lineages in peri- and postimplantation mouse embryos.

Isoform Switch of TET1 Regulates DNA Demethylation and Mouse Development.

The methylcytosine oxidase TET proteins play important roles in DNA demethylation and development. However, it remains elusive how exactly they target substrates and execute oxidation. Interestingly, we found that, in mice, the full-length TET1 isoform (TET1e) is restricted to early embryos, embryonic stem cells (ESCs), and primordial germ cells (PGCs).

The landscape of accessible chromatin in mammalian preimplantation embryos.

In mammals, extensive chromatin reorganization is essential for reprogramming terminally committed gametes to a totipotent state during preimplantation development. However, the global chromatin landscape and its dynamics in this period remain unexplored. Here we report a genome-wide map of accessible chromatin in mouse preimplantation embryos using an improved assay for transposase-accessible chromatin with high throughput sequencing (ATAC-seq) approach with CRISPR/Cas9-assisted mitochondrial DNA depletion.