Stalling out chromatin machinery-Oncohistone mutation disrupts heterochromatin memory.

In this issue, Sinha et al. use cellular chromatin reporter assays along with CRISPR gene editing to reveal that the histone H3.3K36M oncohistone mutation disrupts epigenetic memory and stability of H3K9me3 domains by blocking transitions into a stably repressed state.

Chemical Epigenetic Regulation of Adeno-Associated Virus Delivered Transgenes.

Adeno-associated virus (AAV) is a powerful gene therapy vector that has been used in several FDA-approved therapies as well as in multiple clinical trials. This vector has high therapeutic versatility with the ability to deliver genetic payloads to a variety of human tissue types, yet there is currently a lack of transgene expression control once the virus is administered. There are also times when transgene expression is too low for the desired therapeutic outcome, necessitating high viral dose administration resulting in possible immunological complications.

Relationship between lysine methyltransferase levels and heterochromatin gene repression in living cells and in silico.

Gene regulation plays essential roles in all multicellular organisms, allowing for different specialized tissue types to be generated from a complex genome. Heterochromatin-driven gene repression, associated with a physical compaction of the genome, is a pathway involving core components that are conserved from yeast to human. Posttranslational modification of chromatin is a critical component of gene regulation.

Characterization of Hepatoma-Derived Growth Factor-Related Protein 2 Interactions with Heterochromatin.

The expression of genetic information is tightly controlled by chromatin regulatory proteins, including those in the heterochromatin gene repression family. Many of these regulatory proteins work together on the chromatin substrate to precisely regulate gene expression during mammalian development, giving rise to many different tissues in higher organisms from a fixed genomic template. Here we identify and characterize the interactions of two related heterochromatin regulatory proteins, heterochromatin protein 1 alpha (HP1α) and M-phase phosphoprotein 8 (MPP8), with hepatoma-derived growth factor-related protein 2 (HRP2).

A simulation model of heterochromatin formation at submolecular detail.

Heterochromatin is a physical state of the chromatin fiber that maintains gene repression during cell development. Although evidence exists on molecular mechanisms involved in heterochromatin formation, a detailed structural mechanism of heterochromatin formation needs a better understanding. We made use of a simple Monte Carlo simulation model with explicit representation of key molecular events to observe molecular self-organization leading to heterochromatin formation.

Bioorthogonal Chemical Epigenetic Modifiers Enable Dose-Dependent CRISPR Targeted Gene Activation in Mammalian Cells.

CRISPR-Cas9 systems have been developed to regulate gene expression by using either fusions to epigenetic regulators or, more recently, through the use of chemically mediated strategies. These approaches have armed researchers with new tools to examine the function of proteins by intricately controlling expression levels of specific genes. Here we present a CRISPR-based chemical approach that uses a new chemical epigenetic modifier (CEM) to hone to a gene targeted with a catalytically inactive Cas9 (dCas9) bridged to an FK506-binding protein (FKBP) in mammalian cells.

A Peptidomimetic Ligand Targeting the Chromodomain of MPP8 Reveals HRP2's Association with the HUSH Complex.

The interpretation of histone post-translational modifications (PTMs), specifically lysine methylation, by specific classes of "reader" proteins marks an important aspect of epigenetic control of gene expression. Methyl-lysine (Kme) readers often regulate gene expression patterns through the recognition of a specific Kme PTM while participating in or recruiting large protein complexes that contain enzymatic or chromatin remodeling activity. Understanding the composition of these Kme-reader-containing protein complexes can serve to further our understanding of the biological roles of Kme readers, while small molecule chemical tools can be valuable reagents in interrogating novel protein-protein interactions.

LSH mediates gene repression through macroH2A deposition.

The human Immunodeficiency Centromeric Instability Facial Anomalies (ICF) 4 syndrome is a severe disease with increased mortality caused by mutation in the LSH gene. Although LSH belongs to a family of chromatin remodeling proteins, it remains unknown how LSH mediates its function on chromatin in vivo. Here, we use chemical-induced proximity to rapidly recruit LSH to an engineered locus and find that LSH specifically induces macroH2A1.

Comprehensive nucleosome interactome screen establishes fundamental principles of nucleosome binding.

Nuclear proteins bind chromatin to execute and regulate genome-templated processes. While studies of individual nucleosome interactions have suggested that an acidic patch on the nucleosome disk may be a common site for recruitment to chromatin, the pervasiveness of acidic patch binding and whether other nucleosome binding hot-spots exist remain unclear. Here, we use nucleosome affinity proteomics with a library of nucleosomes that disrupts all exposed histone surfaces to comprehensively assess how proteins recognize nucleosomes.

Epigenetic Control of a Local Chromatin Landscape.

Proper regulation of the chromatin landscape is essential for maintaining eukaryotic cell identity and diverse cellular processes. The importance of the epigenome comes, in part, from the ability to influence gene expression through patterns in DNA methylation, histone tail modification, and chromatin architecture. Decades of research have associated this process of chromatin regulation and gene expression with human diseased states.

Histone hyperacetylation disrupts core gene regulatory architecture in rhabdomyosarcoma.

Core regulatory transcription factors (CR TFs) orchestrate the placement of super-enhancers (SEs) to activate transcription of cell-identity specifying gene networks, and are critical in promoting cancer. Here, we define the core regulatory circuitry of rhabdomyosarcoma and identify critical CR TF dependencies. These CR TFs build SEs that have the highest levels of histone acetylation, yet paradoxically the same SEs also harbor the greatest amounts of histone deacetylases.

Dose-dependent activation of gene expression is achieved using CRISPR and small molecules that recruit endogenous chromatin machinery.

Gene expression can be activated or suppressed using CRISPR--Cas9 systems. However, tools that enable dose-dependent activation of gene expression without the use of exogenous transcription regulatory proteins are lacking. Here we describe chemical epigenetic modifiers (CEMs) designed to activate the expression of target genes by recruiting components of the endogenous chromatin-activating machinery, eliminating the need for exogenous transcriptional activators.

Ring finger protein 121 is a potent regulator of adeno-associated viral genome transcription.

Adeno-associated viruses (AAV) are Dependoparvoviruses that have shown promise as recombinant vectors for gene therapy. While infectious pathways of AAV are well studied, gaps remain in our understanding of host factors affecting vector genome expression. Here, we map the role of ring finger protein 121 (RNF121), an E3 ubiquitin ligase, as a key regulator of AAV genome transcription.

Contribution of promoter DNA sequence to heterochromatin formation velocity and memory of gene repression in mouse embryo fibroblasts.

Durable gene silencing through the formation of compact heterochromatin domains plays a critical role during mammalian development in establishing defined tissues capable of retaining cellular identity. Hallmarks of heterochromatin gene repression are the binding of heterochromatin protein 1 (HP1), trimethylation of lysine 9 on histone H3 (H3K9me3) and the methylation of cytosine residues of DNA. HP1 binds directly to the H3K9me3 histone modification, and while DNA methyltransferases have been found in complex with histone methyltransferases and HP1, there remains much to be known about the relationship between DNA sequence and HP1 in differentiated mammalian cells.

Chemical screen for epigenetic barriers to single allele activation of Oct4.

Here we utilized the chromatin in vivo assay (CiA) mouse platform to directly examine the epigenetic barriers impeding the activation of the CiA:Oct4 allele in mouse embryonic fibroblasts (MEF)s when stimulated with a transcription factor. The CiA:Oct4 allele contains an engineered EGFP reporter replacing one copy of the Oct4 gene, with an upstream Gal4 array in the promoter that allows recruitment of chromatin modifying machinery. We stimulated gene activation of the CiA:Oct4 allele by binding a transcriptional activator to the Gal4 array.

Pathway-Based High-Throughput Chemical Screen Identifies Compounds That Decouple Heterochromatin Transformations.

Heterochromatin protein 1 (HP1) facilitates the formation of repressive heterochromatin domains by recruiting histone lysine methyltransferase enzymes to chromatin, resulting in increased levels of histone H3K9me3. To identify chemical inhibitors of the HP1-heterochromatin gene repression pathway, we combined a cell-based assay that utilized chemical-mediated recruitment of HP1 to an endogenous active gene with high-throughput flow cytometry. Here we characterized small molecule inhibitors that block HP1-mediated heterochromatin formation.

Deferiprone: Pan-selective Histone Lysine Demethylase Inhibition Activity and Structure Activity Relationship Study.

Deferiprone (DFP) is a hydroxypyridinone-derived iron chelator currently in clinical use for iron chelation therapy. DFP has also been known to elicit antiproliferative activities, yet the mechanism of this effect has remained elusive. We herein report that DFP chelates the Fe ion at the active sites of selected iron-dependent histone lysine demethylases (KDMs), resulting in pan inhibition of a subfamily of KDMs.

Nucleosome Turnover Regulates Histone Methylation Patterns over the Genome.

Recent studies have indicated that nucleosome turnover is rapid, occurring several times per cell cycle. To access the effect of nucleosome turnover on the epigenetic landscape, we investigated H3K79 methylation, which is produced by a single methyltransferase (Dot1l) with no known demethylase. Using chemical-induced proximity (CIP), we find that the valency of H3K79 methylation (mono-, di-, and tri-) is determined by nucleosome turnover rates.

Repressing Gene Transcription by Redirecting Cellular Machinery with Chemical Epigenetic Modifiers.

Regulation of chromatin compaction is an important process that governs gene expression in higher eukaryotes. Although chromatin compaction and gene expression regulation are commonly disrupted in many diseases, a locus-specific, endogenous, and reversible method to study and control these mechanisms of action has been lacking. To address this issue, we have developed and characterized novel gene-regulating bifunctional molecules.

Cavitation Enhancement Increases the Efficiency and Consistency of Chromatin Fragmentation from Fixed Cells for Downstream Quantitative Applications.

One of the most sensitive, time-consuming, and variable steps of chromatin immunoprecipitation (ChIP) is chromatin sonication. Traditionally, this process can take hours to properly sonicate enough chromatin for multiple ChIP assays. Further, the length of sheared DNA is often inconsistent.

Targeted Gene Repression Using Novel Bifunctional Molecules to Harness Endogenous Histone Deacetylation Activity.

Epigenome editing is a powerful method for life science research and could give rise to new therapies for diseases initiated or maintained by epigenetic dysregulation, including several types of cancers and autoimmune disorders. In addition, much is still unknown about the mechanisms by which histone-modifying proteins work in concert to properly regulate gene expression. To investigate and manipulate complex epigenetic interactions in live cells, we have developed a small molecule platform for specifically inducing gene repression and histone deacetylation at a reporter gene.

Report and Application of a Tool Compound Data Set.

Small molecule tool compounds have enabled profound advances in life science research. These chemicals are potent, cell active, and selective, and, thus, are suitable for interrogating biological processes. For these chemicals to be useful they must be correctly characterized and researchers must be aware of them.

Tethering of Lsh at the Oct4 locus promotes gene repression associated with epigenetic changes.

Lsh is a chromatin remodeling factor that regulates DNA methylation and chromatin function in mammals. The dynamics of these chromatin changes and whether they are directly controlled by Lsh remain unclear. To understand the molecular mechanisms of Lsh chromatin controlled regulation of gene expression, we established a tethering system that recruits a Gal4-Lsh fusion protein to an engineered Oct4 locus through Gal4 binding sites in murine embryonic stem (ES) cells.

Epigenetic roots of immunologic disease and new methods for examining chromatin regulatory pathways.

The ability to accurately quantitate and experimentally examine epigenetic modifications across the human genome has exploded in the past decade. This has given rise to a wealth of new information concerning the contributions of epigenetic regulatory networks to the pathogenesis of human disease. In particular, immunological disorders have strong developmental roots in chromatin regulatory pathways.