Project description:Maternal imprinting at the Xist gene is essential to achieve paternal allele-specific imprinted X chromosome inactivation (XCI) in female mammals. However, the mechanism underlying the Xist imprinting is unclear. Here we show that the Xist gene is coated with H3K27me3 in mouse oocytes, which persists through preimplantation development. Ectopic removal of H3K27me3 induces maternal Xist expression and maternal XCI, indicating that maternal H3K27me3 is the imprinting mark of Xist.
Project description:Genomic imprinting is essential for mammalian development. Recent studies have revealed that maternal histone H3 lysine 27 tri-methylation (H3K27me3) can mediate DNA methylation-independent genomic imprinting. However, the regulatory mechanisms and functions of this new imprinting mechanism are largely unknown. Here we demonstrate that maternal Eed, an essential component of the Polycomb group complex 2 (PRC2), is required for establishing H3K27me3 imprinting. We found that all H3K27me3 imprinted genes, including Xist, lose their imprinted expression in Eed maternal KO (matKO) embryos, resulting in male-biased lethality. Surprisingly, although maternal X chromosome inactivation (XmCI) occurs in Eed matKO embryos at preimplantation due to loss of Xist imprinting, it is resolved at peri-implantation. Ultimately, both X chromosomes are reactivated in the embryonic cell lineage prior to random XCI, and only a single X chromosome undergoes random XCI in the extra-embryonic cell lineage. Thus, our study not only demonstrates an essential role of Eed in H3K27me3 imprinting establishment but also reveals a unique XCI dynamics in the absence of Xist imprinting.
Project description:Genomic imprinting regulates parental origin-dependent mono-allelic gene expression. It is mediated by either germline differential methylation of DNA (canonical imprinting) or oocyte-derived H3K27me3 (non-canonical imprinting) in mice. Depletion of Eed, an essential component of Polycomb repressive complex 2, results in genome-wide loss of H3K27me3 in oocytes, which causes loss of non-canonical imprinting (LOI) in embryos. Although Eed maternal KO (matKO) embryos show partial lethality after implantation, it is unknown whether LOI itself contributes to the developmental phenotypes of these embryos, which makes it unclear whether non-canonical imprinting is developmentally relevant. Here, by combinatorial matKO of Xist, a non-canonical imprinted gene whose LOI causes aberrant transient maternal X chromosome inactivation (XCI) at preimplantation, we show that prevention of the transient maternal XCI greatly restores the development of Eed matKO embryos. Moreover, we find that the placentae of Eed matKO embryos are remarkably enlarged in a manner independent of Xist LOI. Heterozygous deletion screening of individual autosomal non-canonical imprinted genes suggests that LOI of the Sfmbt2 miRNA cluster-chromosome 2 miRNA cluster (C2MC), solute carrier family 38 member 4 (Slc38a4), and Gm32885 contributes to the placental enlargement. Taken together, our study provides evidence that Xist imprinting sustains embryonic development and autosomal non-canonical imprinting restrains placental overgrowth.
Project description:Polycomb repressive complexes 1 and 2 (PRC1/2) maintain transcriptional silencing of developmental genes largely by catalyzing mono-ubiquitination of histone H2A at lysine 119 (H2AK119ub1) and trimethylation of histone H3 at lysine 27 (H3K27me3), respectively. How Polycomb domains are reprogrammed during mammalian preimplantation development remains largely unclear. Here we show that, although H2AK119ub1 and H3K27me3 are highly colocalized in gametes, they undergo differential reprogramming dynamics following fertilization. H3K27me3 maintains thousands of maternally biased domains up to the blastocyst stage, whereas maternally biased H2AK119ub1 distribution in zygotes is largely equalized at the two-cell stage. Notably, while maternal PRC2 depletion has a limited effect on global H2AK119ub1 in early embryos, it disrupts allelic H2AK119ub1 at H3K27me3 imprinting loci including Xist. By contrast, acute H2AK119ub1 depletion in zygotes does not affect H3K27me3 imprinting maintenance, at least by the four-cell stage. Importantly, loss of H2AK119ub1, but not H3K27me3, causes premature activation of developmental genes during zygotic genome activation (ZGA) and subsequent embryonic arrest. Thus, our study reveals distinct dynamics and functions of H3K27me3 and H2AK119ub1 in mouse preimplantation embryos.
Project description:Polycomb repressive complexes 1 and 2 (PRC1/2) maintain transcriptional silencing of developmental genes largely by catalyzing mono-ubiquitination of histone H2A at lysine 119 (H2AK119ub1) and trimethylation of histone H3 at lysine 27 (H3K27me3), respectively. How Polycomb domains are reprogrammed during mammalian preimplantation development remains largely unclear. Here we show that, although H2AK119ub1 and H3K27me3 are highly colocalized in gametes, they undergo differential reprogramming dynamics following fertilization. H3K27me3 maintains thousands of maternally biased domains up to the blastocyst stage, whereas maternally biased H2AK119ub1 distribution in zygotes is largely equalized at the two-cell stage. Notably, while maternal PRC2 depletion has a limited effect on global H2AK119ub1 in early embryos, it disrupts allelic H2AK119ub1 at H3K27me3 imprinting loci including Xist. By contrast, acute H2AK119ub1 depletion in zygotes does not affect H3K27me3 imprinting maintenance, at least by the four-cell stage. Importantly, loss of H2AK119ub1, but not H3K27me3, causes premature activation of developmental genes during zygotic genome activation (ZGA) and subsequent embryonic arrest. Thus, our study reveals distinct dynamics and functions of H3K27me3 and H2AK119ub1 in mouse preimplantation embryos.
Project description:Genomic imprinting is an epigenetic mechanism by which genes are expressed in a parental-origin-dependent manner. We recently discovered that, like DNA methylation, oocyte-inherited H3K27me3 can also serve as an imprinting mark in mouse pre-implantation embryos. In this study, we found H3K27me3 is strongly biased toward the maternal allele with some associated with DNA methylation-independent paternally expressed genes (PEGs) in human morulae. The H3K27me3 domains largely overlap with DNA partially methylated domains (PMDs), and occupy developmental gene promoters. Thus, our study not only reveals the H3K27me3 landscape but also establishes a correlation between maternal-biased H3K27me3 and PEGs in human morulae.
Project description:Polycomb repressive complexes 1 and 2 (PRC1/2) maintain transcriptional silencing of developmental genes largely by catalyzing mono-ubiquitination of histone H2A at lysine 119 (H2AK119ub1) and trimethylation of histone H3 at lysine 27 (H3K27me3), respectively. How Polycomb domains are reprogrammed during mammalian preimplantation development remains largely unclear. Here we show that, although H2AK119ub1 and H3K27me3 are highly colocalized in gametes, they undergo differential reprogramming dynamics following fertilization. H3K27me3 maintains thousands of maternally biased domains up to the blastocyst stage, whereas maternally biased H2AK119ub1 distribution in zygotes is largely equalized at the two-cell stage. Notably, while maternal PRC2 depletion has a limited effect on global H2AK119ub1 in early embryos, it disrupts allelic H2AK119ub1 at H3K27me3 imprinting loci including Xist. By contrast, acute H2AK119ub1 depletion in zygotes does not affect H3K27me3 imprinting maintenance, at least by the four-cell stage. Importantly, loss of H2AK119ub1, but not H3K27me3, causes premature activation of developmental genes during zygotic genome activation (ZGA) and subsequent embryonic arrest. Thus, our study reveals distinct dynamics and functions of H3K27me3 and H2AK119ub1 in mouse preimplantation embryos.
Project description:Faithful maintenance of genomic imprinting is essential for mammalian development. While germline DNA methylation-dependent (canonical) imprinting is relatively stable during development, the recently discovered oocyte-derived H3K27me3-mediated noncanonical imprinting is mostly transient in early embryos with only a few genes maintain imprinted expression in the extraembryonic lineage. How these few noncanonical imprinted genes maintain their extraembryonic-specific imprinting is unknown. Here we report that maintenance of extraembryonic-specific noncanonical imprinting requires maternal allele-specific de novo DNA methylation (secondary differentially methylation regions; DMRs) at implantation. The secondary DMRs are located at the gene promoters with paternal allele-specific H3K4me3 preformed during preimplantation development. Importantly, genetic ablation of Eed and DNA methyltransferases revealed that both maternal H3K27me3 and zygotic Dnmt3a/3b are required for establishing secondary DMRs and for maintaining noncanonical imprinting. Thus, our study not only reveals the mechanism underlying maintenance of noncanonical imprinting, but also sheds light on how histone modifications in oocytes and preimplantation embryos may shape the secondary DMRs in post-implantation embryos.