Project description:DNA methylation and trimethylated histone H4K20 (H4K20me3) constitute two important epigenetic mechanisms that frequently cooperate in silencing repetitive elements of the mammalian genome. However, it remains elusive how these two modifications crosstalk. Here, we report the specific readout of heterochromatin marks H4K20me3 by the first bromo-adjacent-homology (BAH1) domain of maintenance DNA methyltransferase DNMT1. Engagement of BAH1-H4K20me3 ensures heterochromatin targeting of DNMT1, and cooperates with the previously reported readout of H3K9me3/H3 ubiquitination by the RFTS domain to allosterically stimulate DNMT1’s activity at both global and focal levels. Interplay between RFTS and BAH1 domains profoundly impacts the maintenance of DNA methylation and genomic resistance to radiation damage. Together, our study provides a heterochromatin-regulated model for DNMT1 in which multivalent recognition of repressive histone modifications by DNMT1 directly influence the cellular landscape of DNA methylation and genomic stability.
Project description:Heterochromatin-specific histone modifications frequently coexist with mammalian DNA methylation to orchestrate a repressive chromatin state. However, it remains elusive how these epigenetic modifications crosstalk. Here, we report that the first bromoadjacent homology (BAH1) domain and the replication foci targeting sequence (RFTS) of maintenance DNA methyltransferase DNMT1 function as readers for H4K20me3 and H3K9me3, respectively. Engagements of H4K20me3 by BAH1 and H3K9me3 by RFTS ensure localization of DNMT1 to heterochromatin in cells, and cooperate with the RFTS-ubiquitination readout to allosterically stimulate DNMT1 s methylation activity at both global and focal levels. Strikingly, there is intramolecular crosstalk between the RFTS and BAH1 domains, which profoundly impacts the maintenance of DNA methylation and genomic resistance to radiation damage. Together, our study reveals an all-in-one model for DNMT1 in which repressive histone modifications directly influence the cellular landscape of DNA methylation and genomic stability, a process implicative of the DNMT1-related pathogenesis.
Project description:We report the ChIP-SEQ results of H4K20me3 in BCSCsSETD4 and BCSCsGFP. To explore epigenetic regulation by H4K20me3 in BCSC quiescence, we performed chromatin immunoprecipitation sequencing (ChIP-seq) using BCSCsSETD4 and BCSCsGFP. Quiescent BCSCsSETD4 showed marked enrichment of H4K20me3 modifications relative to BCSCsGFP.
Project description:In human sperm, preserved histones evading histone-to-protamine replacement were observed in certain genes and gene promoters, but also in distal intergenic and repetitive DNA regions. The substantiality of the latter and its putative biological role are still a subject of hot debate. To shed more light on this issue we analyzed H4K20me3, a histone mark regulating heterochromatic and repetitive DNA in somatic cells, which was recently detected in human sperm. Our immunohistochemical and western blot analyses revealed the presence of H4K20me3 in male germ cells at every stage of spermatogenesis and in mature sperms, respectively. By ChIP-sequencing of the motile sperm fractions from three biological replicates we found 4.56% of the sperm genome to be occupied by H4K20me3. By comparing the genome-wide binding sites of H4K20me3 in sperm cells and somatic cells (K562) we found correspondences in 77% of respective peaks. The majority of binding sites (70%) were detected in distal intergenic and intron regions. Intriguingly, H4K20me3 enrichments could be observed in both somatic and sperm cells within satellite repeats and retrotransposons, particularly in long interspersed nuclear repeats (LINEs) and retrotransposons containing long terminal repeats (LTR-retrotransposons). Broad cluster arrangements and strong enrichments in olfactory receptor genes were also characteristic for H4K20me3. This is the first time H4K20me3 is characterized at the genome-wide level in human sperm and compared to somatic cells. Our results reveal that H4K20me3 constitutes the majority of histones preserved in matured human sperm and maintains a somatic-like distribution pattern.
Project description:Genome wide chromatin maps have shown that spreading repressive histone modifications such as H3K9me3 and H4K20me3 are present on pericentromeric and telomeric repeats and on the inactive X chromosome where H3K27me3 or H3K9me3 alternately modify megabasepair sized domains. However, only a few regions along an autosome of which Homeobox gene clusters are notable examples, have been shown to display spreading of repressive histone modifications. Here we present a ChIP-Chip map of repressive and active histone modifications along mouse Chr.17 in embryonic, fibroblast cells. Our results show that the majority of H3K27me3 modifications form BLOCs rather than focal peaks. H3K27me3 BLOCs modify silent genes of all types and their flanking intergenic regions, indicating a negative correlation between H3K27me3 and transcription. However, non-transcribed gene-poor regions also lacked H3K27me3. We therefore performed a low resolution analysis of whole mouse Chr.17 which revealed that H3K27me3 specifically marks megabasepair sized domains that are enriched for genes, SINEs and active histone modifications. These genic H3K27me3 domains alternate with similar sized gene-poor domains that are deficient in active histone modifications, but enriched for LINE and LTR transposons as well as H3K9me3 and H4K20me3. Thus, a mouse autosome can be seen to contain alternating chromatin bands that predominantly separate genes from one retrotransposons class, which could offer unique chromatin compartments for the specific regulation of genes or the silencing of transposons. Keywords: Chip-chip, chromosome 17 wide unbiased mapping unbiased mapping of several histone modifications on chromosome 17 in two independent MEF cell lines
Project description:Cellular senescence is a stable proliferation arrest and tumor suppressor mechanism. Abundance of histone modification, H4K20me3, has been reported to increase in senescent cells. Generally, H4K20me3 promotes formation of compacted transcriptionally silent constitutive heterochromatin, but its specific role in senescence is unknown. Here, we show that in senescent cells H4K20me3 is enriched at specific families of gene repeats (ZNFs, Olfactory Receptors, Protocadherins), and DNA sequences contained within senescence-associated heterochromatin (senescence-associated heterochromatin (SAHF)). Furthermore, in senescent cells, but not proliferating cells, H4K20me3 is also markedly enriched at bodies of repressed genes, including proliferation-promoting genes. Ectopic expression of SUV420H2, responsible for deposition of H4K20me3, reinforces senescence-associated proliferation arrest, and slows proliferation of transformed cells and tumorigenesis in vivo. These results indicate a dedicated role for H4K20me3 in control of nuclear organization and gene expression in senescent cells and stable senescence-associated proliferation arrest and tumor suppression.
Project description:Chromosome 1 pericentric heterochromatin rearrangements : potent drivers of nuclear architecture perturbations and gene deregulation in human B cell lymphoma Epigenetic perturbations are increasingly described in cancer cells where they are thought to contribute to deregulated gene expression and genome instability. Here, we report the first evidence, that a distinct category of chromosomal translocation observed in human tumours â those targeting 1q12 satellite DNA - can directly mediate such perturbations by promoting the formation of aberrant heterochromatic foci (aHCF). By detailed investigations of a 1q12 translocation to chromosome 2p, in a case of human B cell lymphoma, aberrant aHCF were shown to be localised to the nuclear periphery and to arise as a consequence of long range âpairingâ between the translocated 1q12 and chromosome 2 centromeric regions. Remarkably, adjacent 2p sequences showed increased levels of repressive histone modifications, including H4K20me3 and H3K9me3, and were bound by HP1. aHCF were associated to aberrant spatial localisation and deregulated expression of a novel 2p gene (GMCL1) that was found to have prognostic impact in B cell lymphoma. Thus constitutive heterochromatin rearrangements can contribute to tumourigenesis by perturbing gene expression by via long range epigenetic mechanisms. The formation of aberrant heterochromatic foci, coupled to abnormal enrichment of adjacent 2p sequences in repressive heterochromatin marks (H4K20me3, H3K9me3 and HP1), delayed replication and repositioning of the rearranged chromosome 2 to the nuclear periphery, could be associated to altered gene expression of at least those genes brought into close proximity to heterochromatin. To assess this question, global gene expression profiling was performed in the lymphoma B cells presenting the aberrant heterochromatin foci (CH1), treated or not with the histone deacetylase inhibitor, trichostatin A.
Project description:Genome wide chromatin maps have shown that spreading repressive histone modifications such as H3K9me3 and H4K20me3 are present on pericentromeric and telomeric repeats and on the inactive X chromosome where H3K27me3 or H3K9me3 alternately modify megabasepair sized domains. However, only a few regions along an autosome of which Homeobox gene clusters are notable examples, have been shown to display spreading of repressive histone modifications. Here we present a ChIP-Chip map of repressive and active histone modifications along mouse Chr.17 in embryonic, fibroblast cells. Our results show that the majority of H3K27me3 modifications form BLOCs rather than focal peaks. H3K27me3 BLOCs modify silent genes of all types and their flanking intergenic regions, indicating a negative correlation between H3K27me3 and transcription. However, non-transcribed gene-poor regions also lacked H3K27me3. We therefore performed a low resolution analysis of whole mouse Chr.17 which revealed that H3K27me3 specifically marks megabasepair sized domains that are enriched for genes, SINEs and active histone modifications. These genic H3K27me3 domains alternate with similar sized gene-poor domains that are deficient in active histone modifications, but enriched for LINE and LTR transposons as well as H3K9me3 and H4K20me3. Thus, a mouse autosome can be seen to contain alternating chromatin bands that predominantly separate genes from one retrotransposons class, which could offer unique chromatin compartments for the specific regulation of genes or the silencing of transposons. Keywords: Chip-chip, chromosome 17 wide unbiased mapping
Project description:Heterochromatin, which is a densely packed chromatin state that is transcriptionally silent, is a critical regulator of gene expression. However, it is unclear how the repressive histone modification, H4K20me3, or the histone methyltransferase, SUV420H2, regulate embryonic stem (ES) cell fate by patterning the epigenetic landscape. Here, we observed a near complete genome-wide loss of H4K20me3 in SUV420H2 depleted ES cells, suggesting that SUV420H enzymes are paramount for establishing global H4K20me3 domains. We also found that SUV0420H2-bound regions are enriched with repetitive DNA elements. Together, these findings describe a novel role for SUV420H2 in regulating the chromatin landscape of ES cells.