FOXD3 acts as a repressor of repeat elements in a heterochromatin-mediated pathway
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ABSTRACT: Repeat element transcription plays a vital role in early embryonic development. Upregulation of repeats such as MERVL characterises the 2 cell-like population in a mouse embryonic stem cell culture. Repeat element sequences contain binding sites for numerous transcription factors. We identify a the forkhead domain transcription factor FOXD3 as a regulator of repeat element transcription. FOXD3 binds to and recruits the histone methyl transferase Suv39h1 to MERVL and major satellite repeats in mouse embryonic stem cells, consequentially repressing the transcription of these repeats by establishment of the H3K9me3 heterochromatin modification. Notably, depletion of Foxd3 leads to the de-pression of MERVL and major satellite repeats and in turn the activation of a subset of genes expressed in the 2 cell state, shifting the balance between the stem cell and 2 cell-like population in culture. Thus FOXD3 acts as a negative regulator of repeat transcription, ascribing a novel function to this transcription factor.
Project description:Many repetitive DNA elements are packaged in heterochromatin, but depend on occasional transcription to maintain long-term silencing. The factors that promote transcription of repeat elements in heterochromatin are largely unknown. Here, we show that DOT1L, a histone methyltransferase that modifies lysine 79 of histone H3 (H3K79), is required for transcription of major satellite repeats to maintain pericentromeric heterochromatin (PCH), and that this function is essential for preimplantation development. DOT1L is a transcriptional activator at single-copy genes but does not have a known role in repeat element transcription. We show that H3K79me3 is specifically enriched at repetitive elements, that loss of DOT1L compromises pericentromeric major satellite transcription, and that this function depends on interaction between DOT1L and the chromatin remodeler SMARCA5. DOT1L inhibition causes chromosome breaks and cell cycle defects, and leads to embryonic lethality. Together, our findings uncover a vital new role for DOT1L in transcriptional activation of heterochromatic repeats.
Project description:FOXD3 is essential in embryonic stem cells, however the primary molecular mechanism is unclear. Here, we performed BioID to identify proteins collaborating with FOXD3 in protecting embryonic stem cell survival.
Project description:Endogenous retroviruses (ERVs) were usually silenced by various histone modifications on histone H3 variants and respective histone chaperones in embryonic stem cells (ESCs). However, it is still unknown whether chaperones of other histones could repress ERVs. Here, we show that H2A/H2B histone chaperone FACT plays a critical role in silencing ERVs and ERV-derived cryptic promoters in ESCs. Loss of FACT component Ssrp1 activated MERVL whereas the re-introduction of Ssrp1 rescued the phenotype. Additionally, Ssrp1 interacted with MERVL and suppressed cryptic transcription of MERVL-fused genes. Remarkably, Ssrp1 interacted with and recruited H2B deubiquitinase Usp7 to Ssrp1 target genes. Suppression of Usp7 caused similar phenotypes as loss of Ssrp1. Furthermore, Usp7 acted by deubiquitinating H2Bub and thereby repressed the expression of MERVL-fused genes. Taken together, our study uncovers a unique mechanism by which FACT complex silences ERVs and ERV-derived cryptic promoters in ESCs.
Project description:Transcription factor/enhancer interactions determine cell specific gene expression. Here, we followed enhancers during differentiations of embryonic stem (ESCs) to epiblast like cells (EpiLCs). There were highly dynamic changes in histone lysine 27 acetylation at enhancer sites throughout the genome. These sites were enriched for a Foxd3 binding motif, a forkhead transcription factor essential in early embryonic development. Surprisingly, Foxd3 occupied largely mutually exclusive sites in the ESCs versus EpiLCs. Foxd3 bound to nucleosome occupied regions, simultaneously evicting the histones while inhibiting full gene expression through the recruitment of histone deacetylases. Knockout of Foxd3 resulted in hyperacetylation and transcriptional upregulation of neighboring genes, many of which were further upregulated at later stages of differentiation. These data show that Foxd3 primes enhancer sites during pregastrulation by removing nucleosomes, yet suppresses neighboring histone hyperacetylation. Such a mechanism may be common to many transcription factors that prepare enhancers for later gene activation during development. ChIP-seq of H3K4me1, H3K27ac, H3K27me3, p300, H3K4me3, RNA Pol2 and Oct4 in four pluripotent states: embryonic stem cells (ESCs) day 1 ESC differentiation, Epi-like stem cells (EpiLCs), and epiblast stem cells (EpiSCs); ChIP-seq of 3XFlag tagged Foxd3 in ESCs and EpiLCs; ChIP-seq of H3K4me1, H3K27ac, H3K27me3, p300 and H3K4me3 in Foxd3 conditional knockout cells (tamoxifen-inducible) -/+ 36h Tamoxifen treatemnt. ChIP seq of Flag-Foxd3 (third replicate), ChIP-seq of HDAC1 and Brg1 in WT and Foxd3 KO cells and MNase-ChIP-seq of H3K4me1
Project description:Transcription factor/enhancer interactions determine cell specific gene expression. Here, we followed enhancers during differentiations of embryonic stem (ESCs) to epiblast like cells (EpiLCs). There were highly dynamic changes in histone lysine 27 acetylation at enhancer sites throughout the genome. These sites were enriched for a Foxd3 binding motif, a forkhead transcription factor essential in early embryonic development. Surprisingly, Foxd3 occupied largely mutually exclusive sites in the ESCs versus EpiLCs. Foxd3 bound to nucleosome occupied regions, simultaneously evicting the histones while inhibiting full gene expression through the recruitment of histone deacetylases. Knockout of Foxd3 resulted in hyperacetylation and transcriptional upregulation of neighboring genes, many of which were further upregulated at later stages of differentiation. These data show that Foxd3 primes enhancer sites during pregastrulation by removing nucleosomes, yet suppresses neighboring histone hyperacetylation. Such a mechanism may be common to many transcription factors that prepare enhancers for later gene activation during development. Total RNA obtained Foxd3 knockout embryonic stem cells (ESCs) and epiblast-like cells (EpiLCs) (treated with 1uM tamoxifen for 36h to induce knockout) compared to wild-type controls
Project description:Repetitive sequences, transposable elements and silent tissue-specific genes in C. elegans are differentially enriched for di- and tri-methyl H3 lysine 9 (H3K9). SET-25 (SUV39h1/h2) catalyzes H3K9me3, while MET-2 (SetDB1) deposits only H3K9me1/me2. RNA-seq and genome-wide H3K9 methylation mapping in met-2 and set-25 single mutants showed that H3K9me2-mediated repression of satellite repeats by MET-2 correlates with germline integrity. Aberrant transcription of repeats and DNA transposons generates R-loops, loss of fertility and hydroxyurea hypersensitivity. In a genome-wide synthetic lethal screen, we identified the BRCA1 complex and factors implicated in the degradation of nuclear RNA as essential for germline integrity in met-2 mutants. Highly additive with met-2, the loss of the BRCA1 complex triggers satellite repeat transcription, generating R-loops on transcribed repeats. Supporting direct causality between satellite repeat transcription and BRCA1-mediated genome integrity, the targeted induction of MSAT1 transcripts at endogenous sites leads to damage-induced loss of fertility in wild-type C. elegans.
Project description:Repetitive sequences, transposable elements and silent tissue-specific genes in C. elegans are differentially enriched for di- and tri-methyl H3 lysine 9 (H3K9). SET-25 (SUV39h1/h2) catalyzes H3K9me3, while MET-2 (SetDB1) deposits only H3K9me1/me2. RNA-seq and genome-wide H3K9 methylation mapping in met-2 and set-25 single mutants showed that H3K9me2-mediated repression of satellite repeats by MET-2 correlates with germline integrity. Aberrant transcription of repeats and DNA transposons generates R-loops, loss of fertility and hydroxyurea hypersensitivity. In a genome-wide synthetic lethal screen, we identified the BRCA1 complex and factors implicated in the degradation of nuclear RNA as essential for germline integrity in met-2 mutants. Highly additive with met-2, the loss of the BRCA1 complex triggers satellite repeat transcription, generating R-loops on transcribed repeats. Supporting direct causality between satellite repeat transcription and BRCA1-mediated genome integrity, the targeted induction of MSAT1 transcripts at endogenous sites leads to damage-induced loss of fertility in wild-type C. elegans.
Project description:RNA interference is required for post-transcriptional silencing, but also has additional roles in transcriptional silencing of centromeres and genome stability. However, these roles have been difficult to detect in mammals. Strikingly, we found that Dicer-deficient embryonic stem cells have strong proliferation and chromosome segregation defects as well as increased transcription of centromeric satellite repeats, which triggers the interferon response. We conducted a CRISPR-Cas9 genetic screen to restore viability and identified transcriptional activators, histone H3K9 methyltransferases, and chromosome segregation factors as suppressors, resembling Dicer suppressors identified in independent screens in fission yeast. The strongest suppressors were mutations in the transcriptional co-activator Brd4, which reversed the strand-specific transcription of major satellite repeats suppressing the interferon response, and in the histone acetyltransferase Elp3. We show that identical mutations in the second bromodomain of Brd4 rescue Dicer-dependent silencing and chromosome segregation defects in both mammalian cells and fission yeast. This remarkable conservation demonstrates that RNA interference has an ancient role in transcriptional silencing of satellite repeats, which is essential for cell cycle progression and proper chromosome segregation. Our results have pharmacological implications for cancer and autoimmune diseases characterized by unregulated transcription of satellite repeats.
Project description:Centromeric repetitive DNA sequences are highly variable during evolution, which are the hub for genome stability in almost all the eukaryotic organisms. However, how centromeric repeat sequences diverge rapidly among closely related species and populations, and how polyploidy contributed to the diversity of centromere among co-evolved subgenomes are largely unknown. Here, we applied the Brachypodium system to investigate the track of centromere evolution within this taxa, and their adaptation to alloploidization process. Subgenome divergent centromeric satellite repeat were discovered in tetraploid B. hybridum, and this divergent was originated form their two diploid progenitors. Furthermore, differential sequences influence the association sites with CENH3 nucleosomes on the monomer satellite repeats, and positioning of CENH3 nucleosomes on the satellite DNA are stable in each subgenome after alloploidization. Only minor intrasubgenomic variations were observed on these satellite repeats from diploid to tetraploid in B. hybridum, and no evident intersubgenomic transfer of centromeric satellite repeats after alloploidization. Pan-genome analysis reveals that the general principle of centromere dynamic within the populations in Brachypodium genomes with different polyploidy level. Our results provide an unprecedented information regarding the genomic and functional diversity of centromeric repeat DNA during evolution.
Project description:Following implantation, mouse epiblast cells transit from a naïve to a primed state in which they are competent for both somatic and primordial germ cell (PGC) specification. Using mouse embryonic stem cells (mESC) as an in vitro model to study the transcriptional regulatory principles orchestrating peri-implantation development, here we show that the transcription factor Foxd3 is necessary for the exit from naïve pluripotency and the progression to a primed pluripotent state. During this transition, Foxd3 acts as a repressor that dismantles a significant fraction of the naïve pluripotency expression program through the decommissioning of active enhancers associated with key naïve pluripotency and early germline genes. Subsequently, Foxd3 needs to be silenced in primed pluripotent cells to allow the reactivation of relevant genes required for proper PGC specification. Our findings uncover a wave of activation-deactivation of Foxd3 as a crucial step for the exit from naïve pluripotency and subsequent PGC specification. Genome-wide binding profiles for Foxd3 were investigated in mouse embryonic stem cells (mESC). A mESC line (FH-Foxd3 mESC line) expressing exogenous Foxd3 tagged with Flag and HA epitope (FH-Foxd3) at nearly endogenous levels was generated. ChIPs were performed against FH-Foxd3 using anti-HA or anti-Flag antibodies.