Project description:Histone chaperones prevent promiscuous histone interactions before chromatin assembly. They guarantee faithful deposition of canonical histones and functionally specialized histone variants into chromatin in a spatial- and temporally-restricted manner. Here, we identify the binding partners of the primate-specific and H3.3-related histone variant H3.Y using several quantitative mass spectrometry approaches, and biochemical and cell biological assays. We find the HIRA, but not the DAXX/ATRX, complex to specifically recognize H3.Y, explaining its presence in transcriptionally active euchromatic regions. Accordingly, H3.Y nucleosomes are enriched in the transcription-promoting FACT complex and depleted of repressive posttranslational histone modifications. H3.Y mutational gain-of-function analyses screens reveal an unexpected combinatorial amino acid sequence requirement for histone H3.3 interaction with DAXX but not HIRA, and for H3.3 recruitment to PML nuclear bodies. We demonstrate the importance and necessity of specific H3.3 core region and C-terminal amino acids in discriminating between distinct chaperone complexes. Further, ChIP-seq experiments reveal that in contrast to euchromatic HIRA-dependent deposition sites, human DAXX/ATRX-dependent regions of histone H3 variant incorporation are enriched in heterochromatic H3K9me3 and simple repeat sequences. These data demonstrate that H3.Y's unique amino acids allow a functional distinction between HIRA and DAXX binding and its consequent deposition into open chromatin.
Project description:The lymphoid and myeloid lineages are in equilibrium during steady-state hematopoiesis. Tilting hematopoiesis towards innate immunity has been linked to inflammation and may predispose to myeloproliferative disease. Although epigenetic players have been implicated in the control of hematopoiesis and pathogenesis of blood neoplasms, the role of chromatin-based mechanisms in regulating the lymphoid/myeloid balance remains only partially understood. Here, we show that loss of the H3.3 chaperone Daxx causes myeloid skewing, neutrophilia and pyoderma gangrenosum-like lesions, a human skin disease of unknown etiology. Daxx deficiency leads to chromatin opening at intergenic regions, including TERRA target sites, deregulation of repeat elements and activation of anti-viral defense pathways. Finally, the other main H3.3 chaperone, Hira, is dispensable for normal hematopoiesis but supports expansion of Daxx-deficient neutrophils. These results define a role for Daxx in proper selection of lymphoid versus myeloid lineages, linked to control of repeat elements and anti-inflammatory responses.
Project description:The lymphoid and myeloid lineages are in equilibrium during steady-state hematopoiesis. Tilting hematopoiesis towards innate immunity has been linked to inflammation and may predispose to myeloproliferative disease. Although epigenetic players have been implicated in the control of hematopoiesis and pathogenesis of blood neoplasms, the role of chromatin-based mechanisms in regulating the lymphoid/myeloid balance remains only partially understood. Here, we show that loss of the H3.3 chaperone Daxx causes myeloid skewing, neutrophilia and pyoderma gangrenosum-like lesions, a human skin disease of unknown etiology. Daxx deficiency leads to chromatin opening at intergenic regions, including TERRA target sites, deregulation of repeat elements and activation of anti-viral defense pathways. Finally, the other main H3.3 chaperone, Hira, is dispensable for normal hematopoiesis but supports expansion of Daxx-deficient neutrophils. These results define a role for Daxx in proper selection of lymphoid versus myeloid lineages, linked to control of repeat elements and anti-inflammatory responses.
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: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.
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:Defective silencing of retroviral elements has been linked to inflamm-aging, cancer and auto-immune diseases. However, the underlying mechanisms are only partially understood. Here, we implicate the histone H3.3 chaperone Daxx, a retrotransposable element (RTE) repressor inactivated in myeloid leukemia and other neoplasms, in protection from inflammatory disease. Loss of Daxx has profound effects on chromatin landscapes and histone marks of hematopoietic progenitors, leading to engagement of a Pu.1-dependent transcriptional program for myelopoiesis at the expense of B-cell differentiation. This causes neutrophilia and inflammation, predisposing mice to development of an autoinflammatory skin disease. These molecular and phenotypic perturbations are in part reverted in animals lacking both Pu.1 and Daxx. However, hematopoietic progenitors in these mice also show unique chromatin and transcriptome alterations, suggesting synergistic interaction between the two pathways. Overall, our findings implicate RTE silencing in hematopoiesis and reveal a potential functional relationship between the H3.3 loading machinery and the pioneer transcription factor Pu.1.
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:DAXX and ATRX are tumor suppressor proteins that form a complex with histone H3.3 chaperone and are frequently mutated in cancers with the alternative lengthening of telomeres (ALT), such as pediatric glioblastoma. Rapid loss of function of either DAXX or ATRX are not by themselves sufficient to induce the ALT phenotype. However, cells lacking DAXX or ATRX can be readily selected for ALT-like features. Here, we show that a key feature of ALT selected DAXX and ATRX null glioblastoma cells is the attenuation of p53 function. RNA-seq analysis of DAXX or ATRX null U87 glioblastoma cells with ALT-like features revealed that p53 pathway is among perturbed. ALT-selected DAXX and ATRX-null cells had aberrant response to DNA damaging agent etoposide. Both DAXX and ATRX-null ALT cells showed a loss of p53 binding at a subset of response elements. Complementation of DAXX null cells with wt DAXX rescued p53 binding and transcription, while the tumor associated mutation L130R, that disrupts ATRX binding, was incapable of rescuing p53 chromatin binding. We show that histone H3.3 binding is reduced in DAXX-null cells especially at subtelomeric p53 binding sites and telomere repeats. These findings indicate that DAXX and ATRX function to enable p53 chromatin binding through modulation of histone H3.3 binding, especially at sub-telomeric sites.