Chromatin restriction by the nucleosome remodeler Mi-2β and functional interplay with lineage-specific transcription regulators control B-cell differentiation

Chromatin remodeling protein CHD4 regulates axon guidance of spiral ganglion neurons in developing cochlea

The chromodomain helicase binding protein 4 (CHD4) is an ATP-dependent chromatin remodeler. De-novo pathogenic variants of CHD4 cause Sifrim-Hitz-Weiss syndrome (SIHIWES). Patients with SIHIWES show delayed development, intellectual disability, facial dysmorphism, and hearing loss. Many cochlear cell types, including spiral ganglion neurons (SGNs), express CHD4. SGNs are the primary afferent neurons that convey sound information from the cochlea, but the function of CHD4 in SGNs is unknown. We employed the Neurog1(Ngn1) CreERT2 Chd4 conditional knockout animals to delete Chd4 in SGNs. SGNs are classified as type I and type II neurons. SGNs lacking CHD4 showed abnormal fasciculation of type I neurons along with improper pathfinding of type II fibers. CHD4 binding to chromatin from immortalized multipotent otic progenitor-derived neurons was used to identify candidate target genes in SGNs. Gene ontology analysis of CHD4 target genes revealed cellular processes involved in axon guidance, axonal fasciculation, and ephrin receptor signaling pathway. We validated increased Epha4 transcripts in SGNs from Chd4 conditional knockout cochleae. The results suggest that CHD4 attenuates the transcription of axon guidance genes to form the stereotypic pattern of SGN peripheral projections. The results implicate epigenetic changes in circuit wiring by modulating axon guidance molecule expression and provide insights into neurodevelopmental diseases.

Divergent phenotypes in constitutive versus conditional mutant mouse models of Sifrim-Hitz-Weiss syndrome

Chromatin remodellers are among the most important risk genes associated with neurodevelopmental disorders (NDDs), however, their functions during brain development are not fully understood. Here, we focused on Sifrim-Hitz-Weiss Syndrome (SIHIWES)-an intellectual disability disorder caused by mutations in the CHD4 chromodomain helicase gene. We utilized mouse genetics to excise the Chd4 ATPase/helicase domain-either constitutively, or conditionally in the developing telencephalon. Conditional heterozygotes exhibited no change in cortical size and cellular composition, and had only subtle behavioral phenotypes. Telencephalon-specific conditional knockouts had marked reductions in cortical growth, reduced numbers of upper-layer neurons, and exhibited alterations in anxiety and repetitive behaviors. Despite the fact that whole-body heterozygotes exhibited comparable growth defects, they were unaffected in these behaviors, but instead exhibited female-specific alterations in learning and memory. These data reveal unexpected phenotypic divergence arising from differences in the spatiotemporal deployment of loss-of-function manipulations, underscoring the importance of context in chromatin remodeller function during neurodevelopment.

Lineage-specific 3D genome organization is assembled at multiple scales by IKAROS

A generic level of chromatin organization generated by the interplay between cohesin and CTCF suffices to limit promiscuous interactions between regulatory elements, but a lineage-specific chromatin assembly that supersedes these constraints is required to configure the genome to guide gene expression changes that drive faithful lineage progression. Loss-of-function approaches in B cell precursors show that IKAROS assembles interactions across megabase distances in preparation for lymphoid development. Interactions emanating from IKAROS-bound enhancers override CTCF-imposed boundaries to assemble lineage-specific regulatory units built on a backbone of smaller invariant topological domains. Gain of function in epithelial cells confirms IKAROS' ability to reconfigure chromatin architecture at multiple scales. Although the compaction of the Igκ locus required for genome editing represents a function of IKAROS unique to lymphocytes, the more general function to preconfigure the genome to support lineage-specific gene expression and suppress activation of extra-lineage genes provides a paradigm for lineage restriction.

Chromodomain helicase DNA binding protein 4 in cell fate decisions

Loss of spiral ganglion neurons (SGNs) in the cochlea causes hearing loss. Understanding the mechanisms of cell fate transition accelerates efforts that employ directed differentiation and lineage conversion to repopulate lost SGNs. Proposed strategies to regenerate SGNs rely on altering cell fate by activating transcriptional regulatory networks, but repressing networks for alternative cell lineages is also essential. Epigenomic changes during cell fate transitions suggest that CHD4 represses gene expression by altering the chromatin status. Despite limited direct investigations, human genetic studies implicate CHD4 function in the inner ear. The possibility of CHD4 in suppressing alternative cell fates to promote inner ear regeneration is discussed.

Missense Mutation in Human CHD4 Causes Ventricular Noncompaction by Repressing ADAMTS1

BACKGROUND

Left ventricular noncompaction (LVNC) is a prevalent cardiomyopathy associated with excessive trabeculation and thin compact myocardium. Patients with LVNC are vulnerable to cardiac dysfunction and at high risk of sudden death. Although sporadic and inherited mutations in cardiac genes are implicated in LVNC, understanding of the mechanisms responsible for human LVNC is limited.

METHODS

We screened the complete exome sequence database of the Pediatrics Cardiac Genomics Consortium and identified a cohort with a de novo CHD4 (chromodomain helicase DNA-binding protein 4) proband, CHD4M202I, with congenital heart defects. We engineered a humanized mouse model of CHD4M202I (mouse CHD4M195I). Histological analysis, immunohistochemistry, flow cytometry, transmission electron microscopy, and echocardiography were used to analyze cardiac anatomy and function. Ex vivo culture, immunopurification coupled with mass spectrometry, transcriptional profiling, and chromatin immunoprecipitation were performed to deduce the mechanism of CHD4M195I-mediated ventricular wall defects.

RESULTS

CHD4M195I/M195I mice developed biventricular hypertrabeculation and noncompaction and died at birth. Proliferation of cardiomyocytes was significantly increased in CHD4M195I hearts, and the excessive trabeculation was associated with accumulation of ECM (extracellular matrix) proteins and a reduction of ADAMTS1 (ADAM metallopeptidase with thrombospondin type 1 motif 1), an ECM protease. We rescued the hyperproliferation and hypertrabeculation defects in CHD4M195I hearts by administration of ADAMTS1. Mechanistically, the CHD4M195I protein showed augmented affinity to endocardial BRG1 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily A, member 4). This enhanced affinity resulted in the failure of derepression of Adamts1 transcription such that ADAMTS1-mediated trabeculation termination was impaired.

CONCLUSIONS

Our study reveals how a single mutation in the chromatin remodeler CHD4, in mice or humans, modulates ventricular chamber maturation and that cardiac defects associated with the missense mutation CHD4M195I can be attenuated by the administration of ADAMTS1.

The epigenetic factor CHD4 contributes to metastasis by regulating the EZH2/β-catenin axis and acts as a therapeutic target in ovarian cancer

BACKGROUND

The overall survival rate of patients with advanced ovarian cancer (OC) has remained static for several decades. Advanced ovarian cancer is known for its poor prognosis due to extensive metastasis. Epigenetic alterations contribute to tumour progression and therefore are of interest for potential therapeutic strategies.

METHODS

Following our previous study, we identified that CHD4, a chromatin remodelling factor, plays a strong role in ovarian cancer cell metastasis. We investigated the clinical significance of CHD4 through TCGA and GEO database analyses and explored the effect of CHD4 expression modulation and romidepsin treatment on the biological behaviour of ovarian cancer through CCK-8 and transwell assays. Bioluminescence imaging of tumours in xenografted mice was applied to determine the therapeutic effect of romidepsin. GSEA and western blotting were used to screen the regulatory mechanism of CHD4.

RESULTS

In ovarian cancer patient specimens, high CHD4 expression was associated with a poor prognosis. Loss of function of CHD4 in ovarian cancer cells induced suppression of migration and invasion. Mechanistically, CHD4 knockdown suppressed the expression of EZH2 and the nuclear accumulation of β-catenin. CHD4 also suppressed the metastasis of ovarian cancer cells and prevented disease progression in a mouse model. To inhibit the functions of CHD4 that are mediated by histone deacetylase, we evaluated the effect of the HDAC1/2 selective inhibitor romidepsin. Our findings indicated that treatment with romidepsin suppressed the progression of metastases in vitro and in vivo.

CONCLUSIONS

Collectively, our results uncovered an oncogenic function of CHD4 in ovarian cancer and provide a rationale for clinical trials of romidepsin in ovarian cancer patients.

CHD4 orchestrates the symphony of T and B lymphocytes development and a good mediator in preventing from autoimmune disease

Chromodomain helicase DNA binding protein 4 (CHD4) is an ATPase subunit of the nucleosome remodeling and deacetylation complex. It has been implicated in gene transcription, DNA damage repair, maintenance of genome stability, and chromatin assembly. Meanwhile, it is highly related to cell cycle progression and the proceeding of malignancy. Most of the previous studies were focused on the function of CHD4 with tumor cells, cancer stem cells, and cancer cells multidrug resistance. Recently, some researchers have explored the CHD4 functions on the development and differentiation of adaptive immune cells, such as T and B lymphocytes. In this review, we will discuss details of CHD4 in lymphocyte differentiation and development, as well as the critical role of CHD4 in the pathogenesis of the autoimmune disease.

Role of ATP-dependent chromatin remodelers in hematopoietic stem and progenitor cell maintenance

PURPOSE OF REVIEW

ATP-dependent chromatin remodeling factors utilize energy from ATP hydrolysis to modulate DNA-histone structures and regulate gene transcription. They are essential during hematopoiesis and for hematopoietic stem and progenitor cell (HSPC) function. This review discusses the recently unveiled roles of these chromatin remodelers in HSPC regulation, with an emphasis on the mechanism of chromodomain helicase DNA-binding (CHD) family members.

RECENT FINDINGS

Recent studies of ATP-dependent chromatin remodelers have revealed that individual CHD family members engage in distinct mechanisms in regulating HSPC cell fate. For example, CHD8 is required for HSPC survival by restricting both P53 transcriptional activity and protein stability in steady state hematopoiesis while the related CHD7 physically interacts with RUNX family transcription factor 1 (RUNX1) and suppresses RUNX1-induced expansion of HSPCs during blood development. Moreover, other CHD subfamily members such as CHD1/CHD2 and CHD3/CHD4, as well as the switch/sucrose non-fermentable, imitation SWI, and SWI2/SNF2 related (SWR) families of chromatin modulators, have also been found important for HSPC maintenance by distinct mechanisms.

SUMMARY

The expanding knowledge of ATP-dependent chromatin remodelers in hematopoiesis illustrates their respective critical roles in HSPC maintenance including the regulation of HSPC differentiation, survival, and self-renewal. Further studies are warranted to elucidate how different chromatin remodeling complexes are integrated in various HSPC cell fate decisions during steady-state and stress hematopoiesis.

CHD4 is recruited by GATA4 and NKX2-5 to repress noncardiac gene programs in the developing heart

The nucleosome remodeling and deacetylase (NuRD) complex is one of the central chromatin remodeling complexes that mediates gene repression. NuRD is essential for numerous developmental events, including heart development. Clinical and genetic studies have provided direct evidence for the role of chromodomain helicase DNA-binding protein 4 (CHD4), the catalytic component of NuRD, in congenital heart disease (CHD), including atrial and ventricular septal defects. Furthermore, it has been demonstrated that CHD4 is essential for mammalian cardiomyocyte formation and function. A key unresolved question is how CHD4/NuRD is localized to specific cardiac target genes, as neither CHD4 nor NuRD can directly bind DNA. Here, we coupled a bioinformatics-based approach with mass spectrometry analyses to demonstrate that CHD4 interacts with the core cardiac transcription factors GATA4, NKX2-5, and TBX5 during embryonic heart development. Using transcriptomics and genome-wide occupancy data, we characterized the genomic landscape of GATA4, NKX2-5, and TBX5 repression and defined the direct cardiac gene targets of the GATA4-CHD4, NKX2-5-CHD4, and TBX5-CHD4 complexes. These data were used to identify putative cis-regulatory elements controlled by these complexes. We genetically interrogated two of these silencers in vivo: Acta1 and Myh11 We show that deletion of these silencers leads to inappropriate skeletal and smooth muscle gene misexpression, respectively, in the embryonic heart. These results delineate how CHD4/NuRD is localized to specific cardiac loci and explicates how mutations in the broadly expressed CHD4 protein lead to cardiac-specific disease states.

Clinical and Serological Features and Pregnancy Outcomes in Women with Polymyositis/Dermatomyositis: A Case-based Review

We encountered a 30-year-old woman who developed dermatomyositis during pregnancy and was positive for anti-Mi-2 antibodies. She was successfully treated with prednisolone and tacrolimus and delivered a healthy child. We reviewed the cases of idiopathic inflammatory myositis (IIM) that developed during pregnancy that were published after the year 2000 to elucidate the profile of myositis-specific antibodies (MSAs) in them and to evaluate their obstetric outcomes. In cases with IIM that developed during pregnancy, anti-Mi-2, anti-TIF1-g, anti-Jo-1, and anti-EJ antibodies was detected in one case each. The obstetric outcomes of the IIM-complicated pregnancies were poor, especially when complicated with active maternal myositis. Further studies focusing on the possible causal relationships between MSAs and cases with IIM that developed during pregnancy are needed. For better obstetric outcomes, appropriate suppression of the maternal disease activity using immunosuppressants and vigilance regarding the patient's requirement of Caesarean section is important.

Chromodomain helicase DNA-binding 4 (CHD4) regulates early B cell identity and V(D)J recombination

B lymphocytes develop from uncommitted precursors into immunoglobulin (antibody)-producing B cells, a major arm of adaptive immunity. Progression of early progenitors to antibody-expressing cells in the bone marrow is orchestrated by the temporal regulation of different gene programs at discrete developmental stages. A major question concerns how B cells control the accessibility of these genes to transcription factors. Research has implicated nucleosome remodeling ATPases as mediators of chromatin accessibility. Here, we describe studies of chromodomain helicase DNA-binding 4 (CHD4; also known as Mi-2β) in early B cell development. CHD4 comprises multiple domains that function in nucleosome mobilization and histone binding. CHD4 is a key component of Nucleosome Remodeling and Deacetylase, or NuRD (Mi-2) complexes, which assemble with other proteins that mediate transcriptional repression. We review data demonstrating that CHD4 is necessary for B lineage identity: early B lineage progression, proliferation in response to interleukin-7, responses to DNA damage, and cell survival in vivo. CHD4-NuRD is also required for the Ig heavy-chain repertoire by promoting utilization of distal variable (V_H ) gene segments in V(D)J recombination. In conclusion, the regulation of chromatin accessibility by CHD4 is essential for production of antibodies by B cells, which in turn mediate humoral immune responses to pathogens and disease.

Sentinels of chromatin: chromodomain helicase DNA-binding proteins in development and disease

Chromatin is highly dynamic, undergoing continuous global changes in its structure and type of histone and DNA modifications governed by processes such as transcription, repair, replication, and recombination. Members of the chromodomain helicase DNA-binding (CHD) family of enzymes are ATP-dependent chromatin remodelers that are intimately involved in the regulation of chromatin dynamics, altering nucleosomal structure and DNA accessibility. Genetic studies in yeast, fruit flies, zebrafish, and mice underscore essential roles of CHD enzymes in regulating cellular fate and identity, as well as proper embryonic development. With the advent of next-generation sequencing, evidence is emerging that these enzymes are subjected to frequent DNA copy number alterations or mutations and show aberrant expression in malignancies and other human diseases. As such, they might prove to be valuable biomarkers or targets for therapeutic intervention.

The chromatin remodeler CHD8 governs hematopoietic stem/progenitor survival by regulating ATM-mediated P53 protein stability

The Chd8 gene encodes a member of the chromodomain helicase DNA-binding (CHD) family of SNF2H-like adenosine triphosphate (ATP)-dependent chromatin remodeler, the mutations of which define a subtype of autism spectrum disorders. Increasing evidence from recent studies indicates that ATP-dependent chromatin-remodeling genes are involved in the control of crucial gene-expression programs in hematopoietic stem/progenitor cell (HSPC) regulation. In this study, we identified CHD8 as a specific and essential regulator of normal hematopoiesis. Loss of Chd8 leads to severe anemia, pancytopenia, bone marrow failure, and engraftment failure related to a drastic depletion of HSPCs. CHD8 forms a complex with ATM and its deficiency increases chromatin accessibility and drives genomic instability in HSPCs causing an activation of ATM kinase that further stabilizes P53 protein by phosphorylation and leads to increased HSPC apoptosis. Deletion of P53 rescues the apoptotic defects of HSPCs and restores overall hematopoiesis in Chd8-/- mice. Our findings demonstrate that chromatin organization by CHD8 is uniquely necessary for the maintenance of hematopoiesis by integrating the ATM-P53-mediated survival of HSPCs.

Chromatin Remodeling in the Brain-a NuRDevelopmental Odyssey

During brain development, the genome must be repeatedly reconfigured in order to facilitate neuronal and glial differentiation. A host of chromatin remodeling complexes facilitates this process. At the genetic level, the non-redundancy of these complexes suggests that neurodevelopment may require a lexicon of remodelers with different specificities and activities. Here, we focus on the nucleosome remodeling and deacetylase (NuRD) complex. We review NuRD biochemistry, genetics, and functions in neural progenitors and neurons.

Established and emergent roles for Ikaros transcription factors in lymphoid cell development and function

Ikaros zinc finger transcription factors are important regulators of the gene programs underlying the development of hematopoietic cell lineages. The family consists of five members: Ikaros, Helios, Aiolos, Eos, and Pegasus, which engage in both homo- and heterotypic intrafamilial interactions to exert diverse functional effects. Pioneering studies focused on the role of these factors in early lymphoid development, as their absence resulted in severe defects in lymphocyte populations. More recent work has now begun to define nuanced, stage-specific roles for Ikaros family members in the differentiation and function of mature T, B, and innate lymphoid cell populations including natural killer (NK) cells. The precise transcriptional mechanisms by which these factors function, both independently and collaboratively, is an area of active investigation. However, several key themes appear to be emerging regarding the pathways influenced by Ikaros family members, including the end-to-end regulation of cytokine signaling. Here, we review roles for Ikaros factors in lymphoid cell development, differentiation, and function, including a discussion of the current understanding of the transcriptional mechanisms they employ and considerations for the future study of this important transcription factor family.

Functional interactions between Mi-2β and AP1 complexes control response and recovery from skin barrier disruption

Keratinocytes respond to environmental signals by eliciting induction of genes that preserve skin's integrity. Here we show that the transcriptional response to stress signaling is supported by short-lived epigenetic changes. Comparison of chromatin accessibility and transcriptional changes induced by barrier disruption or by loss of the nucleosome remodeler Mi-2β identified their striking convergence in mouse and human keratinocytes. Mi-2β directly repressed genes induced by barrier disruption by restricting AP1-enriched promoter-distal sites, occupied by Mi-2β and JUNB at steady state and by c-JUN after Mi-2β depletion or stress signaling. Barrier disruption led to a modest reduction in Mi-2β expression and a further selective reduction of Mi-2β localization at stress response genes, possibly through competition with activated c-JUN. Consistent with a repressive role at stress response genes, genetic ablation of Mi-2β did not prevent reestablishment of barrier integrity but was required for return to homeostasis. Thus, a competition between Mi-2β-repressive and activating AP1 complexes may permit rapid transcriptional response to and resolution from stress signaling.

Chd4 choreographs self-antigen expression for central immune tolerance

Autoreactive T cells are eliminated in the thymus to prevent autoimmunity by promiscuous expression of tissue-restricted self-antigens in medullary thymic epithelial cells. This expression is dependent on the transcription factor Fezf2, as well as the transcriptional regulator Aire, but the entire picture of the transcriptional program has been obscure. Here, we found that the chromatin remodeler Chd4, also called Mi-2β, plays a key role in the self-antigen expression in medullary thymic epithelial cells. To maximize the diversity of self-antigen expression, Fezf2 and Aire utilized completely distinct transcriptional mechanisms, both of which were under the control of Chd4. Chd4 organized the promoter regions of Fezf2-dependent genes, while contributing to the Aire-mediated induction of self-antigens via super-enhancers. Mice deficient in Chd4 specifically in thymic epithelial cells exhibited autoimmune phenotypes, including T cell infiltration. Thus, Chd4 plays a critical role in integrating Fezf2- and Aire-mediated gene induction to establish central immune tolerance.

The chromatin remodeling enzyme Chd4 regulates genome architecture in the mouse brain

The development and function of the brain require tight control of gene expression. Genome architecture is thought to play a critical regulatory role in gene expression, but the mechanisms governing genome architecture in the brain in vivo remain poorly understood. Here, we report that conditional knockout of the chromatin remodeling enzyme Chd4 in granule neurons of the mouse cerebellum increases accessibility of gene regulatory sites genome-wide in vivo. Conditional knockout of Chd4 promotes recruitment of the architectural protein complex cohesin preferentially to gene enhancers in granule neurons in vivo. Importantly, in vivo profiling of genome architecture reveals that conditional knockout of Chd4 strengthens interactions among developmentally repressed contact domains as well as genomic loops in a manner that tightly correlates with increased accessibility, enhancer activity, and cohesin occupancy at these sites. Collectively, our findings define a role for chromatin remodeling in the control of genome architecture organization in the mammalian brain.

The Methyl-CpG-Binding Domain 2 and 3 Proteins and Formation of the Nucleosome Remodeling and Deacetylase Complex

The Nucleosome Remodeling and Deacetylase (NuRD) complex uniquely combines both deacetylase and remodeling enzymatic activities in a single macromolecular complex. The methyl-CpG-binding domain 2 and 3 (MBD2 and MBD3) proteins provide a critical structural link between the deacetylase and remodeling components, while MBD2 endows the complex with the ability to selectively recognize methylated DNA. Hence, NuRD combines three major arms of epigenetic gene regulation. Research over the past few decades has revealed much of the structural basis driving formation of this complex and started to uncover the functional roles of NuRD in epigenetic gene regulation. However, we have yet to fully understand the molecular and biophysical basis for methylation-dependent chromatin remodeling and transcription regulation by NuRD. In this review, we discuss the structural information currently available for the complex, the role MBD2 and MBD3 play in forming and recruiting the complex to methylated DNA, and the biological functions of NuRD.