DNMT1 regulates the timing of DNA methylation by DNMT3 in an enzymatic activity-dependent manner in mouse embryonic stem cells.

DNA methylation (DNAme; 5-methylcytosine, 5mC) plays an essential role in mammalian development, and the 5mC profile is regulated by a balance of opposing enzymatic activities: DNA methyltransferases (DNMTs) and Ten-eleven translocation dioxygenases (TETs). In mouse embryonic stem cells (ESCs), de novo DNAme by DNMT3 family enzymes, demethylation by the TET-mediated conversion of 5mC to 5-hydroxymethylation (5hmC), and maintenance of the remaining DNAme by DNMT1 are actively repeated throughout cell cycles, dynamically forming a constant 5mC profile. Nevertheless, the detailed mechanism and physiological significance of this active cyclic DNA modification in mouse ESCs remain unclear.

Repression of germline genes by PRC1.6 and SETDB1 in the early embryo precedes DNA methylation-mediated silencing.

Silencing of a subset of germline genes is dependent upon DNA methylation (DNAme) post-implantation. However, these genes are generally hypomethylated in the blastocyst, implicating alternative repressive pathways before implantation. Indeed, in embryonic stem cells (ESCs), an overlapping set of genes, including germline "genome-defence" (GGD) genes, are upregulated following deletion of the H3K9 methyltransferase SETDB1 or subunits of the non-canonical PRC1 complex PRC1.

Maternal DNMT3A-dependent de novo methylation of the paternal genome inhibits gene expression in the early embryo.

De novo DNA methylation (DNAme) during mammalian spermatogenesis yields a densely methylated genome, with the exception of CpG islands (CGIs), which are hypomethylated in sperm. While the paternal genome undergoes widespread DNAme loss before the first S-phase following fertilization, recent mass spectrometry analysis revealed that the zygotic paternal genome is paradoxically also subject to a low level of de novo DNAme. However, the loci involved, and impact on transcription were not addressed.

Precise coordination of cell-ECM adhesion is essential for efficient melanoblast migration during development.

Melanoblasts disperse throughout the skin and populate hair follicles through long-range cell migration. During migration, cells undergo cycles of coordinated attachment and detachment from the extracellular matrix (ECM). Embryonic migration processes that require cell-ECM attachment are dependent on the integrin family of adhesion receptors.

Evolution of imprinting via lineage-specific insertion of retroviral promoters.

Imprinted genes are expressed from a single parental allele, with the other allele often silenced by DNA methylation (DNAme) established in the germline. While species-specific imprinted orthologues have been documented, the molecular mechanisms underlying the evolutionary switch from biallelic to imprinted expression are unknown. During mouse oogenesis, gametic differentially methylated regions (gDMRs) acquire DNAme in a transcription-guided manner.

Talin Autoinhibition Regulates Cell-ECM Adhesion Dynamics and Wound Healing In Vivo.

Cells in multicellular organisms are arranged in complex three-dimensional patterns. This requires both transient and stable adhesions with the extracellular matrix (ECM). Integrin adhesion receptors bind ECM ligands outside the cell and then, by binding the protein talin inside the cell, assemble an adhesion complex connecting to the cytoskeleton.

LTR retrotransposons transcribed in oocytes drive species-specific and heritable changes in DNA methylation.

De novo DNA methylation (DNAme) during mouse oogenesis occurs within transcribed regions enriched for H3K36me3. As many oocyte transcripts originate in long terminal repeats (LTRs), which are heterogeneous even between closely related mammals, we examined whether species-specific LTR-initiated transcription units (LITs) shape the oocyte methylome. Here we identify thousands of syntenic regions in mouse, rat, and human that show divergent DNAme associated with private LITs, many of which initiate in lineage-specific LTR retrotransposons.

Transcription factor ASCL2 is required for development of the glycogen trophoblast cell lineage.

The basic helix-loop-helix (bHLH) transcription factor ASCL2 plays essential roles in diploid multipotent trophoblast progenitors, intestinal stem cells, follicular T-helper cells, as well as during epidermal development and myogenesis. During early development, Ascl2 expression is regulated by genomic imprinting and only the maternally inherited allele is transcriptionally active in trophoblast. The paternal allele-specific silencing of Ascl2 requires expression of the long non-coding RNA Kcnq1ot1 in cis and the deposition of repressive histone marks.

Development and application of an integrated allele-specific pipeline for methylomic and epigenomic analysis (MEA).

Background: Allele-specific transcriptional regulation, including of imprinted genes, is essential for normal mammalian development. While the regulatory regions controlling imprinted genes are associated with DNA methylation (DNAme) and specific histone modifications, the interplay between transcription and these epigenetic marks at allelic resolution is typically not investigated genome-wide due to a lack of bioinformatic packages that can process and integrate multiple epigenomic datasets with allelic resolution. In addition, existing ad-hoc software only consider SNVs for allele-specific read discovery.

Maternal DNA Methylation Regulates Early Trophoblast Development.

Critical roles for DNA methylation in embryonic development are well established, but less is known about its roles during trophoblast development, the extraembryonic lineage that gives rise to the placenta. We dissected the role of DNA methylation in trophoblast development by performing mRNA and DNA methylation profiling of Dnmt3a/3b mutants. We find that oocyte-derived methylation plays a major role in regulating trophoblast development but that imprinting of the key placental regulator Ascl2 is only partially responsible for these effects.

Impact of flanking chromosomal sequences on localization and silencing by the human non-coding RNA XIST.

Background: X-chromosome inactivation is a striking example of epigenetic silencing in which expression of the long non-coding RNA XIST initiates the heterochromatinization and silencing of one of the pair of X chromosomes in mammalian females. To understand how the RNA can establish silencing across millions of basepairs of DNA we have modelled the process by inducing expression of XIST from nine different locations in human HT1080 cells.

Results: Localization of XIST, depletion of Cot-1 RNA, perinuclear localization, and ubiquitination of H2A occurs at all sites examined, while recruitment of H3K9me3 was not observed.

Setdb1 is required for germline development and silencing of H3K9me3-marked endogenous retroviruses in primordial germ cells.

Transcription of endogenous retroviruses (ERVs) is inhibited by de novo DNA methylation during gametogenesis, a process initiated after birth in oocytes and at approximately embryonic day 15.5 (E15.5) in prospermatogonia.

Tissue-specific alternative polyadenylation at the imprinted gene Mest regulates allelic usage at Copg2.

The gene Mest (also known as Peg1) is regulated by genomic imprinting in the mouse and only the paternal allele is active for transcription. MEST is similarly imprinted in humans, where it is a candidate for the growth retardation Silver-Russell syndrome. The MEST protein belongs to an ancient family of hydrolases but its function is still unknown.

An extended domain of Kcnq1ot1 silencing revealed by an imprinted fluorescent reporter.

The distal region of mouse chromosome 7 contains two imprinted domains separated by a relatively gene-poor interval. We have previously described a transgenic mouse line called Tel7KI, which contains a green fluorescent protein (GFP) reporter inserted 2.6 kb upstream of the Ins2 gene at the proximal end of this interval.

Partial loss of Ascl2 function affects all three layers of the mature placenta and causes intrauterine growth restriction.

Several imprinted genes have been implicated in the regulation of placental function and embryonic growth. On distal mouse chromosome 7, two clusters of imprinted genes, each regulated by its own imprinting center (IC), are separated by a poorly characterized region of 280kb (the IC1-IC2 interval). We previously generated a mouse line in which this IC1-IC2 interval has been deleted (Del(7AI) allele) and found that maternal inheritance of this allele results in low birth weights in newborns.

Rescue of placental phenotype in a mechanistic model of Beckwith-Wiedemann syndrome.

Background: Several imprinted genes have been implicated in the process of placentation. The distal region of mouse chromosome 7 (Chr 7) contains at least ten imprinted genes, several of which are expressed from the maternal homologue in the placenta. The corresponding paternal alleles of these genes are silenced in cis by an incompletely understood mechanism involving the formation of a repressive nuclear compartment mediated by the long non-coding RNA Kcnq1ot1 initiated from imprinting centre 2 (IC2).

The interval between Ins2 and Ascl2 is dispensable for imprinting centre function in the murine Beckwith-Wiedemann region.

Imprinted genes are commonly clustered in domains across the mammalian genome, suggesting a degree of coregulation via long-range coordination of their monoallelic transcription. The distal end of mouse chromosome 7 (Chr 7) contains two clusters of imprinted genes within a approximately 1 Mb domain. This region is conserved on human 11p15.