Project description:Using proteome arrays and mass spectrometry, we find that the histone chaperone DAXX interacts with crotonylated histones. We show that histone crotonylation and gene expression changes promoted by the short-chain fatty acid crotonate depend on DAXX.
Project description:A multitude of histone chaperones is required to protect histones from their biosynthesis to DNA deposition. They cooperate through the formation of co-chaperone complexes, but the crosstalk between nucleosome assembly pathways is unclear. Using explorative interactomics approaches, we map the organization of the histone H3-H4 chaperones network and define the interplay between histone chaperones systems. We identify and validate a panel of novel histone (PTM) dependent complexes. We show DAXX acts separately from the rest of the network, recruiting heterochromatin factors and promoting lysine 9 tri-methylated new histone H3.3 prior to deposition onto DNA. With its functionality, DAXX provides a molecular mechanism for de novo heterochromatin assembly.
Project description:Objective: Daxx is a protein with multiple functions and is essential for embryonic development. Daxx knockout embryos fail to develop properly and exhibit lethal phenotype around E6.5. One of the important functions is as a histone chaperone for the histone H3 variant, H3.3. Daxx interacts with Atrx to form a protein complex that deposits H3.3 into heterochromatic regions of the genome, including centromeres, telomeres and repeat loci. Here, we investigated how histone chaperone function of Daxx contributes to the embryonic development. Methods: We developed two Daxx mutant alleles in the mouse germline which abolish the interactions between Daxx and Atrx (DaxxY130A), Daxx and H3.3 (DaxxS226A). We set up mating between either heterozygous DaxxY130A or heterozygous DaxxS226A individually and looked for the viability of homozygous mutants at different development stages. We also performed bulk RNA-seq on tissues from the two mutant embryos and analyzed the changes in gene expression and transposable elements (TE). Results: We found that the interaction between Daxx and Atrx is dispensable for viability in both the pre- and post-natal setting as homozygous Daxx-Y130A mutants are both viable and fertile. The loss of the Atrx interaction, however, does cause dysregulated expression of both endogenous retroviruses and nearby protein coding genes. On the contrary, the interaction between Daxx and H3.3 is not required for embryonic development but is essential for postnatal viability. Transcriptome analysis of embryonic tissues demonstrates that this interaction is important for silencing endogenous retroviruses and for maintaining proper hematopoiesis. Conclusions: The histone chaperone function of Daxx is dispensable for embryonic development but important for hematopoiesis, which is independent of the interaction with Atrx. Moreover, both the interactions with Atrx and with H3.3 is important for regulation of ERV expression. Overall, these results clearly demonstrate that Daxx and H3.3 have both Atrx-dependent and independent functions, advancing our understanding of this epigenetic regulatory complex.
Project description:DAXX, a H3.3 histone chaperone known for its role in heterochromatin maintenance, has been understudied in the context of gene expression regulation. In this study, we generated Daxx knockout myogenic cells and observed a significant loss of myogenic markers expression and impaired differentiation. Transcriptome analysis revealed broad dysregulations in Daxx KO cells, including loss of myogenic identity and a concurrent upregulation of genes involved in DNA replication and telomere maintenance. Chromatin immunoprecipitation followed by sequencing demonstrated a marked reduction in H3.3 deposition, particularly in intronic and intergenic regions. Further analysis indicated that loss of DAXX leads to decreased H3K27ac at myogenic loci and a shift in repressive histone marks, which led to impaired gene expression. Intriguingly, double knockout of Daxx and Hira resulted in distinct transcriptomic alterations, demonstrating that DAXX and HIRA have both overlapping and unique roles in H3.3 incorporation. Our work also suggests the presence of additional histone chaperone complexes in maintaining chromatin integrity in myoblasts. Our findings establish DAXX as a critical regulator of myogenic gene expression and muscle cell identity through a distinct mechanism from that of HIRA and highlighted an unanticipated plasticity in the deposition loci for DAXX and HIRA in myoblasts.
Project description:Endogenous retroviruses (ERVs) comprise a significant portion of mammalian genomes. Although specific ERV loci feature regulatory roles for host gene expression, most ERV integrations are transcriptionally repressed by Setdb1 mediated H3K9me3 and DNA methylation. However, the protein network which regulates the deposition of these chromatin modifications is still incompletely understood. Here, we performed a genome-wide sgRNA screen for genes involved in ERV silencing and identified the GHKL ATPase protein Morc3 as a top-scoring hit. Morc3 knock-out cells display de-repression, reduced H3K9me3, and increased chromatin accessibility of distinct ERV families. We found that the Morc3 ATPase cycle and Morc3 SUMOylation are important for ERV chromatin regulation. Proteomic analysis revealed that Morc3 mutant proteins fail to interact with the histone H3.3 chaperone Daxx. This interaction depends on Morc3 SUMOylation and Daxx SUMO binding. Notably, in Morc3 ko cells, we observed strongly reduced histone H3.3 on Morc3 binding sites. Thus, our data demonstrate Morc3 as a critical regulator of Daxx-mediated histone H3.3 incorporation to ERV regions. This dataset comprises several experiments addressing different questions: 1. ChIP-MS experiment to determine the protein interaction context of Morc3 using a Morc3-3xFLAG knock-in ES cell line compared to wild type ES cells (Experiment 20200408). 2. ChIP-MS experiments to investigate changes in the protein interaction context of the Morc3 mutant rescue cell lines. Comparison of Morc3 knock-out cell lines with re-expression of Morc3-CW-3xFLAG mutant (Ref. #3111), Morc3-ATP-binding-3xFLAG and Morc3-SUMOylation-3xFLAG mutants (Ref. #3635), and Morc3-deltaN-3xFLAG mutant (Ref. #5174) compared to wt Morc3-3XFLAG rescue. 3. ChIP-MS experiment to determine if the interaction between Morc3 and Daxx is mediated through this C-terminal SIM, comparing Daxx knock-out cell lines with re-expression of wild type 3xFLAG-Daxx protein or 3xFLAG-Daxx ∆SIM, which lacks the C-terminal SIM domain. (Ref. #3301)
Project description:A multitude of histone chaperones are required to support histones from their biosynthesis until DNA deposition. They cooperate through the formation of histone co-chaperone complexes, but the crosstalk between nucleosome assembly pathways remains enigmatic. Using exploratory interactomics, we define the interplay between histone H3–H4 chaperones in the histone chaperone network. We identify several novel histone dependent complexes and predict the structure of the ASF1 and SPT2 co-chaperone complex, expanding the role of ASF1 in histone dynamics. We show that DAXX provides a unique functionality to the histone chaperone network, recruiting histone methyltransferases to promote H3K9me3 catalysis on new histone H3.3–H4 prior to deposition onto DNA. Hereby, DAXX provides a molecular mechanism for de novo H3K9me3 deposition and heterochromatin assembly. Collectively, our findings provide a framework for understanding how cells orchestrate histone supply and employ targeted deposition of modified histones to underpin specialized chromatin states.
Project description:A multitude of histone chaperones are required to support histones from their biosynthesis until DNA deposition. They cooperate through the formation of histone co-chaperone complexes, but the crosstalk between nucleosome assembly pathways remains enigmatic. Using exploratory interactomics, we define the interplay between histone H3–H4 chaperones in the histone chaperone network. We identify several novel histone dependent complexes and predict the structure of the ASF1 and SPT2 co-chaperone complex, expanding the role of ASF1 in histone dynamics. We show that DAXX provides a unique functionality to the histone chaperone network, recruiting histone methyltransferases to promote H3K9me3 catalysis on new histone H3.3–H4 prior to deposition onto DNA. Hereby, DAXX provides a molecular mechanism for de novo H3K9me3 deposition and heterochromatin assembly. Collectively, our findings provide a framework for understanding how cells orchestrate histone supply and employ targeted deposition of modified histones to underpin specialized chromatin states.
Project description:Neuroendocrine tumors (NETs) often harbor loss-of-function mutations in Daxx gene. Daxx interacts with several partners to regulate cellular processes and gene expression. We used microarrays to detail the global gene expression change in Daxx knockout MEFs and identified up-regulated genes during this process.
Project description:The histone variant H3.3 is incorporated in a replication-independent manner at heterochromatic regions by the ATRX-DAXX histone chaperone complex. Here, we present a high-resolution x-ray crystal structure of an interaction surface between ATRX and DAXX. We used single amino acid substitutions in DAXX that abrogate formation of the complex to explore ATRX-dependent and -independent functions of DAXX. We found that the repression of specific murine endogenous retroviruses is dependent on DAXX, but not on ATRX. In support, we reveal the existence of two biochemically distinct DAXX-containing complexes: The ATRX-DAXX complex involved in gene repression and telomere chromatin structure, and a DAXX-SETDB1-KAP1-HDAC1 complex that represses endogenous retroviruses independently of ATRX and H3.3 incorporation into chromatin. We found that histone H3.3 stabilizes DAXX protein levels and affects DAXX-regulated genes independently of its incorporation into nucleosomes. Our findings represent the first description of a nucleosome-independent function for the H3.3 histone variant.