Project description:Nucleosome occupancy is fundamental for establishing chromatin architecture. However, little is known about the relationship between nucleosome dynamics and initial cell lineage specification. Here, we determine the mechanisms that control global nucleosome dynamics during embryonic stem (ES) cell differentiation into endoderm. Both nucleosome depletion and de novo occupation occur during the differentiation process, with higher overall nucleosome density after differentiation. The variant histone H2A.Z and the winged helix transcription factor Foxa2 both act to regulate nucleosome depletion and gene activation, thus promoting ES cell differentiation, whereas DNA methylation promotes nucleosome occupation and suppresses gene expression. Nucleosome depletion during ES cell differentiation is dependent on Nap1l1-coupled SWI/SNF and INO80 chromatin remodeling complexes. Thus, both epigenetic and genetic regulators cooperate to control nucleosome dynamics during ES cell fate decisions.
Project description:We determine the mechanisms that control global nucleosome dynamics during embryonic stem (ES) cell differentiation into endoderm. Three cell types (ES, pEHP, and EHP) were assayed for RNA expression levels.
Project description:Nucleosome is the basic structural unit of chromatin, and its dynamics plays critical roles in the regulation of genome functions. However, how the nucleosome structure is regulated by histone variants in vivo is still largely uncharacterized. Here, by employing Micrococcal nuclease (MNase) digestion of crosslinked chromatin followed by chromatin immunoprecipitation (ChIP) and paired-end sequencing (MNase-X-ChIP-seq), we mapped genome-wide unwrapping states of nucleosomes containing histone variant H2A.Z in mouse embryonic stem (ES) cells. We found that H2A.Z is enriched with unwrapped nucleosomes. Interestingly, the function of +1 H2A.Z nucleosome in transcriptional regulation is correlated with the unwrapping states. We further showed that H2A.Z nucleosomes adjacent the CTCF binding sites (CBS) may adopt an open conformation. We confirmed the unwrapping state of H2A.Z nucleosomes under native condition by re-ChIP of H2A.Z after CTCF CUT&RUN in mouse ES cells. Importantly, we found that depletion of H2A.Z results in increased CTCF binding, indicating dynamic competition between the unwrapped H2A.Z nucleosomal intermediates and CTCF at the CBS. Taken together, our results showed that histone variant H2A.Z regulates transcription and CTCF binding through modulating the nucleosome unwrapping.
Project description:The histone variant H2A.Z is one of the most evolutionally conserved histone variants. Here, we identified a cancer-associated mutation in H2A.Z and evaluate the mutation. Structural and biochemical in vitro analyses showed that the H2A.Z mutation destabilizes nucleosome containing it. Then we applied the genetic complementation analysis to analyze cellular functions of the H2A.Z mutant. Although the H2A.Z mutant is deposited into nucleosome and rescues the lethality of H2A.Z DKO cells, the mutant does not complement mitotic defects of H2A.Z DKO cells, suggesting that stability of H2A.Z nucleosome is required for proper mitotic progression. Importantly, the H2A.Z mutant led to mitotic defects even in the presence of a larger pool of wild-type H2A.Z. Thus, it is implicated that the cancer-associated mutation appeared in an allele of the H2A.Z isoform genes would be involved in carcinogenesis through causing mitotic defects.
Project description:The site-specific chromatin incorporation of eukaryotic histone variant H2A.Z is driven by the multi-component chromatin remodeling complex SWR1/SRCAP/ p400. The budding yeast SWR1 complex replaces the H2A-H2B dimer in the canonical nucleosome with the H2A.Z-H2B dimer, but the mechanism governing the directionality of H2A-to-H2A.Z exchange remains elusive. Here, we use single-molecule force spectroscopy to dissect the disassembly/ reassembly of H2A-nucleosome and H2A.Z-nucleosome. We find that the N-terminal 1-135 residues of yeast SWR1-complex-protein-2 (previously termed Swc2-Z) facilitate the disassembly of nucleosomes containing H2A but not H2A.Z. The Swc2-mediated nucleosome disassembly/reassembly requires the inherently unstable H2A-nucleosome, whose instability is conferred by three H2A α2-helix residues Gly47, Pro49 and Ile63 as they selectively weaken the structural rigidity of H2A-H2B dimer. It also requires Swc2-ZN (residues 1-37) that directly anchors to H2A-nucleosome and functions in the SWR1-catalyzed H2A.Z replacement in vitro and yeast H2A.Z deposition in vivo. Our findings providecrucial insights into how SWR1 complex discriminates between the H2A-nucleosome and H2A.Z-nucleosome, establishing a simple paradigm for the governace of unidirectional H2A.Z exchange.
Project description:The incorporation of histone variant H2A.Z, a conserved H2A variant, into nucleosomes creates specialized chromatin domains that regulate DNA-templated processes, including transcription. H2A.Z-containing nucleosomes may poise gene regulatory regions for transcription, but mechanistic details are lacking. In Saccharomyces cerevisiae, the diverging H2A.Z C-terminus is thought to provide the H2A.Z exclusive functions. To elucidate the roles of this H2A.Z C-terminus genome wide, we made use of derivatives where the C-terminus was replaced with the corresponding region of H2A (ZA protein), or the H2A region plus a transcriptional activating peptide, with the idea of regenerating the H2A.Z-dependent regulation globally. An assessment of the genome-wide distribution of these H2A.Z derivatives shows that the H2A.Z C-terminal region is crucial for both maintaining the occupation level of H2A.Z and the proper positioning of the targeted nucleosomes. Interestingly, the specific contribution on incorporation efficiency vs nucleosome positioning varies enormously, depending on loci analyzed. For the ZA protein, positioning changes most importantly near origins of replication and snoRNA gene promoters, while incorporation is affected on all other sites. Furthermore, the role of H2A.Z in global transcription regulation also depends on its C-terminal region. Remarkably however, the latter mostly involves genes without a H2A.Z nucleosome in the promoter.
Project description:Histone variant H2A.Z-containing nucleosomes are incorporated at most eukaryotic promoters. This incorporation is mediated by the conserved SWR1 complex, which replaces histone H2A in canonical nucleosomes with H2A.Z in an ATP-dependent manner. Here, we show that promoter-proximal nucleosomes are highly heterogeneous for H2A.Z in Saccharomyces cerevisiae, with substantial representation of nucleosomes containing one, two, or no H2A.Z molecules. SWR1-catalyzed H2A.Z replacement in vitro occurs in a stepwise and unidirectional fashion, one H2A.Z-H2B dimer at a time, producing heterotypic nucleosomes as intermediates and homotypic H2A.Z nucleosomes as end products. The ATPase activity of SWR1 is specifically stimulated by H2A-containing nucleosomes without ensuing histone H2A eviction. Remarkably, further addition of free H2A.Z-H2B dimer leads to hyperstimulation of ATPase activity, eviction of nucleosomal H2A-H2B and deposition of H2A.Z-H2B. These results suggest that the combination of H2A-containing nucleosome and free H2A.Z-H2B dimer acting as both effector and substrate for SWR1 governs the specificity and outcome of the replacement reaction. Total nucleosomes from MNase-treated nuclear extracts were fractionated by sequential immunoprecipitation into homotypic H2A/H2A (AA), heterotypic H2A/H2A.Z (AZ), and homotypic H2A.Z/H2A.Z (ZZ) nucleosomes.
Project description:The histone variant H2A.Z is a genome-wide signature of nucleosomes proximal to eukaryotic regulatory DNA. While the multi-subunit SWR1 chromatin remodeling complex is known to catalyze ATP-dependent deposition of H2A.Z, the mechanism of recruitment to S. cerevisiae promoters has been unclear. A sensitive assay for competitive binding of di-nucleosome substrates revealed that SWR1 preferentially binds long nucleosome-free DNA adjoining core particles, allowing discrimination of gene promoters over gene bodies. We traced the critical DNA binding component of SWR1 to the conserved Swc2/YL1 subunit, whose activity is required for both SWR1 binding and H2A.Z incorporation in vivo. Histone acetylation by NuA4 enhances SWR1 binding, but the interaction with nucleosome-free DNA is the major determinant. ‘Hierarchical cooperation’ between high affinity DNA- and low affinity histone modification-binding factors may reconcile the large disparity in affinities for chromatin substrates, and unify classical control by DNA-binding factors with post-translational histone modifications and ATP-dependent nucleosome mobility. Swr1 TAP IF of various mutants
Project description:To investigate the incorporation dynamics of histone variant H2A.Z, we determined its genomic localization at single nucleosome resolution, as well as the localization of its chromatin remodelers Swr1 and Ino80. We find that Swr1 binding alone is a poor predictor of H2A.Z occupancy levels, and that normal Swr1 and Ino80 localization are actually dependent on H2A.Z. Additionally, we find that H2A.Z’s bimodal incorporation on either side of the NDR is not a general feature of TSS, but is specifically a marker for bidirectional transcription, such that the upstream flanking -1 H2A.Z-containing nucleosome is more appropriately considered as a +1 H2A.Z nucleosome for antisense transcription.