THE ROLE OF LAMIN ASSOCIATED DOMAINS IN GLOBAL CHROMATIN ORGANIZATION AND NUCLEAR ARCHITECTURE

Nuclear structure and scaffolding have been implicated in expression and regulation of the genome (Elcock and Bridger 2010; Fedorova and Zink 2008; Ferrai et al. 2010; Li and Reinberg 2011; Austin and Bellini 2010). Discrete domains of chromatin exist within the nuclear volume, and are suggested to be organized by patterns of gene activity (Zhao, Bodnar, and Spector 2009). The nuclear periphery, which consists of the inner nuclear membrane and associated proteins, forms a sub-nuclear compartment that is mostly associated with transcriptionally repressed chromatin and low gene expression (Guelen et al. 2008). Previous studies from our lab and others have shown that repositioning genes to the nuclear periphery is sufficient to induce transcriptional repression (K L Reddy et al. 2008; Finlan et al. 2008). In addition, a number of studies have provided evidence that many tissue types, including muscle, brain and blood, use the nuclear periphery as a compartment during development to regulate expression of lineage specific genes (Meister et al. 2010; Szczerbal, Foster, and Bridger 2009; Yao et al. 2011; Kosak et al. 2002; Peric-Hupkes et al. 2010). These large regions of chromatin that come in molecular contact with the nuclear periphery are called Lamin Associated Domains (LADs). The studies described in this dissertation have furthered our understanding of maintenance and establishment of LADs as well as the relationship of LADs with the epigenome and other factors that influence three-dimensional chromatin structure. I provide evidence that LAD patterns from DNA adenine methyltransferase identification (DamID)-derived molecular contact maps are reflective of higher order chromatin structure in both ensemble population measure and single cells. Importantly, this work provides the first in situ visualization of chromosome-wide molecular data in a single cell. These data, showing LAD and nonLAD organization, indicate that there is a speicifc and reproducible organization of sub-chromosomal domains. In addition, this work has furthered our understanding of the influence of chromatin state on both LAD and overall chromosome organization—demonstrating that higher-order chromatin structure and epigenetic signatures are closely linked. This work has contributed to the finding that LAD formation can be sequence driven, which was uncovered by examining variable LADs (vLADs) where LAD patterning differs between cell types. Also, examination of LADs across multiple cell types has uncovered genomic characteristics that can define LADs and may have a functional role in the process of genome organizatio

Haploinsufficiency of KMT2D is sufficient to cause Kabuki syndrome and is compatible with life.

To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked DownloadWe present the first patient described with haploinsufficency of KMT2D leading to Kabuki syndrome. Deletion of KMT2D has been thought to be lethal, but here we describe a patient with KMT2D deletion and classical Kabuki syndrome phenotype.Icelandic Research Fund Louma G. Foundation Wellcome Trus

Peripheral blood DNA methylation and neuroanatomical responses to HDACi treatment that rescues neurological deficits in a Kabuki syndrome mouse model

Publisher Copyright: © 2023, The Author(s). © 2023. The Author(s).Background: Recent findings from studies of mouse models of Mendelian disorders of epigenetic machinery strongly support the potential for postnatal therapies to improve neurobehavioral and cognitive deficits. As several of these therapies move into human clinical trials, the search for biomarkers of treatment efficacy is a priority. A potential postnatal treatment of Kabuki syndrome type 1 (KS1), caused by pathogenic variants in KMT2D encoding a histone-lysine methyltransferase, has emerged using a mouse model of KS1 (Kmt2d +/βGeo). In this mouse model, hippocampal memory deficits are ameliorated following treatment with the histone deacetylase inhibitor (HDACi), AR-42. Here, we investigate the effect of both Kmt2d +/βGeo genotype and AR-42 treatment on neuroanatomy and on DNA methylation (DNAm) in peripheral blood. While peripheral blood may not be considered a “primary tissue” with respect to understanding the pathophysiology of neurodevelopmental disorders, it has the potential to serve as an accessible biomarker of disease- and treatment-related changes in the brain. Methods: Half of the KS1 and wildtype mice were treated with 14 days of AR-42. Following treatment, fixed brain samples were imaged using MRI to calculate regional volumes. Blood was assayed for genome-wide DNAm at over 285,000 CpG sites using the Illumina Infinium Mouse Methylation array. DNAm patterns and brain volumes were analyzed in the four groups of animals: wildtype untreated, wildtype AR-42 treated, KS1 untreated and KS1 AR-42 treated. Results: We defined a DNAm signature in the blood of KS1 mice, that overlapped with the human KS1 DNAm signature. We also found a striking 10% decrease in total brain volume in untreated KS1 mice compared to untreated wildtype, which correlated with DNAm levels in a subset KS1 signature sites, suggesting that disease severity may be reflected in blood DNAm. Treatment with AR-42 ameliorated DNAm aberrations in KS1 mice at a small number of signature sites. Conclusions: As this treatment impacts both neurological deficits and blood DNAm in mice, future KS clinical trials in humans could be used to assess blood DNAm as an early biomarker of therapeutic efficacy.Peer reviewe

THE ROLE OF LAMIN ASSOCIATED DOMAINS IN GLOBAL CHROMATIN ORGANIZATION AND NUCLEAR ARCHITECTURE

Nuclear structure and scaffolding have been implicated in expression and regulation of the genome (Elcock and Bridger 2010; Fedorova and Zink 2008; Ferrai et al. 2010; Li and Reinberg 2011; Austin and Bellini 2010). Discrete domains of chromatin exist within the nuclear volume, and are suggested to be organized by patterns of gene activity (Zhao, Bodnar, and Spector 2009). The nuclear periphery, which consists of the inner nuclear membrane and associated proteins, forms a sub-nuclear compartment that is mostly associated with transcriptionally repressed chromatin and low gene expression (Guelen et al. 2008). Previous studies from our lab and others have shown that repositioning genes to the nuclear periphery is sufficient to induce transcriptional repression (K L Reddy et al. 2008; Finlan et al. 2008). In addition, a number of studies have provided evidence that many tissue types, including muscle, brain and blood, use the nuclear periphery as a compartment during development to regulate expression of lineage specific genes (Meister et al. 2010; Szczerbal, Foster, and Bridger 2009; Yao et al. 2011; Kosak et al. 2002; Peric-Hupkes et al. 2010). These large regions of chromatin that come in molecular contact with the nuclear periphery are called Lamin Associated Domains (LADs). The studies described in this dissertation have furthered our understanding of maintenance and establishment of LADs as well as the relationship of LADs with the epigenome and other factors that influence three-dimensional chromatin structure. I provide evidence that LAD patterns from DNA adenine methyltransferase identification (DamID)-derived molecular contact maps are reflective of higher order chromatin structure in both ensemble population measure and single cells. Importantly, this work provides the first in situ visualization of chromosome-wide molecular data in a single cell. These data, showing LAD and nonLAD organization, indicate that there is a speicifc and reproducible organization of sub-chromosomal domains. In addition, this work has furthered our understanding of the influence of chromatin state on both LAD and overall chromosome organization—demonstrating that higher-order chromatin structure and epigenetic signatures are closely linked. This work has contributed to the finding that LAD formation can be sequence driven, which was uncovered by examining variable LADs (vLADs) where LAD patterning differs between cell types. Also, examination of LADs across multiple cell types has uncovered genomic characteristics that can define LADs and may have a functional role in the process of genome organizatio

Leveraging the Mendelian disorders of the epigenetic machinery to systematically map functional epigenetic variation.

To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked DownloadAlthough each Mendelian Disorder of the Epigenetic Machinery (MDEM) has a different causative gene, there are shared disease manifestations. We hypothesize that this phenotypic convergence is a consequence of shared epigenetic alterations. To identify such shared alterations, we interrogate chromatin (ATAC-seq) and expression (RNA-seq) states in B cells from three MDEM mouse models (Kabuki [KS] type 1 and 2 and Rubinstein-Taybi type 1 [RT1] syndromes). We develop a new approach for the overlap analysis and find extensive overlap primarily localized in gene promoters. We show that disruption of chromatin accessibility at promoters often disrupts downstream gene expression, and identify 587 loci and 264 genes with shared disruption across all three MDEMs. Subtle expression alterations of multiple, IgA-relevant genes, collectively contribute to IgA deficiency in KS1 and RT1, but not in KS2. We propose that the joint study of MDEMs offers a principled approach for systematically mapping functional epigenetic variation in mammals. Keywords: IgA deficiency; Mendelian; chromatin; computational biology; computational methods; epigenetics; genetics; genomics; histone machinery; mouse; systems biology.Louma G Foundation Icelandic Research Fund Icelandic Technology Development Fund Johns Hopkins University Maryland Genetics, Epidemiology and Medicine (MD-GEM) training program - Burroughs-Wellcome Fund United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Institute of General Medical Sciences (NIGMS

A Lamina-Associated Domain Border Governs Nuclear Lamina Interactions, Transcription, and Recombination of the Tcrb Locus

Summary: Tcrb locus V(D)J recombination is regulated by positioning at the nuclear periphery. Here, we used DamID to profile Tcrb locus interactions with the nuclear lamina at high resolution. We identified a lamina-associated domain (LAD) border composed of several CTCF-binding elements that segregates active non-LAD from inactive LAD regions of the locus. Deletion of the LAD border causes an enhancer-dependent spread of histone H3 lysine 27 acetylation from the active recombination center into recombination center-proximal LAD chromatin. This is associated with a disruption to nuclear lamina association, increased chromatin looping to the recombination center, and increased transcription and recombination of recombination center-proximal gene segments. Our results show that a LAD and LAD border are critical components of Tcrb locus gene regulation and suggest that LAD borders may generally function to constrain the activity of nearby enhancers. : Chen et al. identify a Tcrb locus lamina-associated domain border that constrains the activity of the Tcrb enhancer. Deletion of the border causes enhancer-dependent loss of nuclear lamina association, spreading of H3K27 acetylation, and elevated transcription and VDJ recombination of gene segments in affected chromatin. Keywords: T cell receptor β, Tcrb, V(D)J recombination, nuclear lamina, lamina-associated domain, LAD border, DamID, CTC

Precocious chondrocyte differentiation disrupts skeletal growth in Kabuki syndrome mice.

To access publisher's full text version of this article click on the hyperlink belowKabuki syndrome 1 (KS1) is a Mendelian disorder of the epigenetic machinery caused by mutations in the gene encoding KMT2D, which methylates lysine 4 on histone H3 (H3K4). KS1 is characterized by intellectual disability, postnatal growth retardation, and distinct craniofacial dysmorphisms. A mouse model (Kmt2d+/βGeo) exhibits features of the human disorder and has provided insight into other phenotypes; however, the mechanistic basis of skeletal abnormalities and growth retardation remains elusive. Using high-resolution micro-CT, we show that Kmt2d+/βGeo mice have shortened long bones and ventral bowing of skulls. In vivo expansion of growth plates within skulls and long bones suggests disrupted endochondral ossification as a common disease mechanism. Stable chondrocyte cell lines harboring inactivating mutations in Kmt2d exhibit precocious differentiation, further supporting this mechanism. A known inducer of chondrogenesis, SOX9, and its targets show markedly increased expression in Kmt2d-/- chondrocytes. By transcriptome profiling, we identify Shox2 as a putative KMT2D target. We propose that decreased KMT2D-mediated H3K4me3 at Shox2 releases Sox9 inhibition and thereby leads to enhanced chondrogenesis, providing a potentially novel and plausible explanation for precocious chondrocyte differentiation. Our findings provide insight into the pathogenesis of growth retardation in KS1 and suggest therapeutic approaches for this and related disorders.Wellcome Trust Baltimore Center for Musculoskeletal Science 2015 Pilot and Feasibility Award William and Ella Owens Medical Research Foundation Johns Hopkins School of Medicine Clinician Scientist Award Hartwell Foundation Individual Biomedical Research Award United States Department of Health & Human Services National Institutes of Health (NIH) - USA Louma G. Foundatio

Author Correction: Deficiency of TET3 leads to a genome-wide DNA hypermethylation episignature in human whole blood (npj Genomic Medicine, (2021), 6, 1, (92), 10.1038/s41525-021-00256-y):Deficiency of TET3 leads to a genome-wide DNA hypermethylation episignature in human whole blood (npj Genomic Medicine, (2021), 6, 1, (92), 10.1038/s41525-021-00256-y)

In this article the author name Siddharth Banka was incorrectly written as Sidharth Banka. The original article has been corrected

Deficiency of TET3 leads to a genome-wide DNA hypermethylation episignature in human whole blood

TET3 encodes an essential dioxygenase involved in epigenetic regulation through DNA demethylation. TET3 deficiency, or Beck-Fahrner syndrome (BEFAHRS; MIM: 618798), is a recently described neurodevelopmental disorder of the DNA demethylation machinery with a nonspecific phenotype resembling other chromatin-modifying disorders, but inconsistent variant types and inheritance patterns pose diagnostic challenges. Given TET3’s direct role in regulating 5-methylcytosine and recent identification of syndrome-specific DNA methylation profiles, we analyzed genome-wide DNA methylation in whole blood of TET3-deficient individuals and identified an episignature that distinguishes affected and unaffected individuals and those with mono-allelic and bi-allelic pathogenic variants. Validation and testing of the episignature correctly categorized known TET3 variants and determined pathogenicity of variants of uncertain significance. Clinical utility was demonstrated when the episignature alone identified an affected individual from over 1000 undiagnosed cases and was confirmed upon distinguishing TET3-deficient individuals from those with 46 other disorders. The TET3-deficient signature - and the signature resulting from activating mutations in DNMT1 which normally opposes TET3 - are characterized by hypermethylation, which for BEFAHRS involves CpG sites that may be biologically relevant. This work expands the role of epi-phenotyping in molecular diagnosis and reveals genome-wide DNA methylation profiling as a quantitative, functional readout for characterization of this new biochemical category of disease