ABSTRACT
Human cell line models, including the neuronal precursor line LUHMES, are important for investigating developmental transcriptional dynamics within imprinted regions, particularly the 15q11-q13 Angelman (AS) and Prader-Willi (PWS) syndrome locus. AS results from loss of maternal UBE3A in neurons, where the paternal allele is silenced by a convergent antisense transcript UBE3A-ATS, a lncRNA that terminates at PWAR1 in non-neurons. qRT-PCR analysis confirmed the exclusive and progressive increase in UBE3A-ATS in differentiating LUHMES neurons, validating their use for studying UBE3A silencing. Genome-wide transcriptome analyses revealed changes to 11 834 genes during neuronal differentiation, including the upregulation of most genes within the 15q11-q13 locus. To identify dynamic changes in chromatin loops linked to transcriptional activity, we performed a HiChIP validated by 4C, which identified two neuron-specific CTCF loops between MAGEL2-SNRPN and PWAR1-UBE3A. To determine if allele-specific differentially methylated regions (DMR) may be associated with CTCF loop anchors, whole genome long-read nanopore sequencing was performed. We identified a paternally hypomethylated DMR near the SNRPN upstream loop anchor exclusive to neurons and a paternally hypermethylated DMR near the PWAR1 CTCF anchor exclusive to undifferentiated cells, consistent with increases in neuronal transcription. Additionally, DMRs near CTCF loop anchors were observed in both cell types, indicative of allele-specific differences in chromatin loops regulating imprinted transcription. These results provide an integrated view of the 15q11-q13 epigenetic landscape during LUHMES neuronal differentiation, underscoring the complex interplay of transcription, chromatin looping, and DNA methylation. They also provide insights for future therapeutic approaches for AS and PWS.
ABSTRACT
The discovery of cancer driver mutations is a fundamental goal in cancer research. While many cancer driver mutations have been discovered in the protein-coding genome, research into potential cancer drivers in the non-coding regions showed limited success so far. Here, we present a novel comprehensive framework Dr.Nod for detection of non-coding cis-regulatory candidate driver mutations that are associated with dysregulated gene expression using tissue-matched enhancer-gene annotations. Applying the framework to data from over 1500 tumours across eight tissues revealed a 4.4-fold enrichment of candidate driver mutations in regulatory regions of known cancer driver genes. An overarching conclusion that emerges is that the non-coding driver mutations contribute to cancer by significantly altering transcription factor binding sites, leading to upregulation of tissue-matched oncogenes and down-regulation of tumour-suppressor genes. Interestingly, more than half of the detected cancer-promoting non-coding regulatory driver mutations are over 20 kb distant from the cancer-associated genes they regulate. Our results show the importance of tissue-matched enhancer-gene maps, functional impact of mutations, and complex background mutagenesis model for the prediction of non-coding regulatory drivers. In conclusion, our study demonstrates that non-coding mutations in enhancers play a previously underappreciated role in cancer and dysregulation of clinically relevant target genes.
Subject(s)
Neoplasms , Oncogenes , Regulatory Sequences, Nucleic Acid , Humans , Mutation , Neoplasms/geneticsABSTRACT
Angelman syndrome (AS) is a neurogenetic disorder caused by the loss of ubiquitin ligase E3A (UBE3A) gene expression in the brain. The UBE3A gene is paternally imprinted in brain neurons. Clinical features of AS are primarily due to the loss of maternally expressed UBE3A in the brain. A healthy copy of paternal UBE3A is present in the brain but is silenced by a long non-coding antisense transcript (UBE3A-ATS). Here, we demonstrate that an artificial transcription factor (ATF-S1K) can silence Ube3a-ATS in an adult mouse model of Angelman syndrome (AS) and restore endogenous physiological expression of paternal Ube3a. A single injection of adeno-associated virus (AAV) expressing ATF-S1K (AAV-S1K) into the tail vein enabled whole-brain transduction and restored UBE3A protein in neurons to â¼25% of wild-type protein. The ATF-S1K treatment was highly specific to the target site with no detectable inflammatory response 5 weeks after AAV-S1K administration. AAV-S1K treatment of AS mice showed behavioral rescue in exploratory locomotion, a task involving gross and fine motor abilities, similar to low ambulation and velocity in AS patients. The specificity and tolerability of a single injection of AAV-S1K therapy for AS demonstrate the use of ATFs as a promising translational approach for AS.
Subject(s)
Angelman Syndrome , Animals , Mice , Angelman Syndrome/genetics , Angelman Syndrome/therapy , Angelman Syndrome/metabolism , Brain/metabolism , Gene Expression Regulation , Transcription Factors/genetics , Phenotype , Ubiquitin-Protein Ligases/geneticsABSTRACT
Precision epigenome editing has gained significant attention as a method to modulate gene expression without altering genetic information. However, a major limiting factor has been that the gene expression changes are often transient, unlike the life-long epigenetic changes that occur frequently in nature. Here, we systematically interrogate the ability of CRISPR/dCas9-based epigenome editors (Epi-dCas9) to engineer persistent epigenetic silencing. We elucidated cis regulatory features that contribute to the differential stability of epigenetic reprogramming, such as the active transcription histone marks H3K36me3 and H3K27ac strongly correlating with resistance to short-term repression and resistance to long-term silencing, respectively. H3K27ac inversely correlates with increased DNA methylation. Interestingly, the dependance on H3K27ac was only observed when a combination of KRAB-dCas9 and targetable DNA methyltransferases (DNMT3A-dCas9 + DNMT3L) was used, but not when KRAB was replaced with the targetable H3K27 histone methyltransferase Ezh2. In addition, programmable Ezh2/DNMT3A + L treatment demonstrated enhanced engineering of localized DNA methylation and was not sensitive to a divergent chromatin state. Our results highlight the importance of local chromatin features for heritability of programmable silencing and the differential response to KRAB- and Ezh2-based epigenetic editing platforms. The information gained in this study provides fundamental insights into understanding contextual cues to more predictably engineer persistent silencing.
Subject(s)
Epigenome , Gene Editing , CRISPR-Cas Systems , Chromatin , DNA Methylation/genetics , Epigenesis, Genetic , Gene Editing/methods , Gene SilencingABSTRACT
Angelman syndrome (AS) is a rare neurodevelopmental disorder characterized by impaired communication skills, ataxia, motor and balance deficits, intellectual disabilities, and seizures. The genetic cause of AS is the neuronal loss of UBE3A expression in the brain. A novel approach, described here, is a stem cell gene therapy which uses lentivector-transduced hematopoietic stem and progenitor cells to deliver functional UBE3A to affected cells. We have demonstrated both the prevention and reversal of AS phenotypes upon transplantation and engraftment of human CD34+ cells transduced with a Ube3a lentivector in a novel immunodeficient Ube3amat-/pat+ IL2rg-/y mouse model of AS. A significant improvement in motor and cognitive behavioral assays as well as normalized delta power measured by electroencephalogram was observed in neonates and adults transplanted with the gene modified cells. Human hematopoietic profiles observed in the lymphoid organs by detection of human immune cells were normal. Expression of UBE3A was detected in the brains of the adult treatment group following immunohistochemical staining illustrating engraftment of the gene-modified cells expressing UBE3A in the brain. As demonstrated with our data, this stem cell gene therapy approach offers a promising treatment strategy for AS, not requiring a critical treatment window.
Subject(s)
Angelman Syndrome/therapy , Genetic Therapy , Intellectual Disability/therapy , Seizures/therapy , Ubiquitin-Protein Ligases/genetics , Angelman Syndrome/genetics , Angelman Syndrome/pathology , Animals , Antigens, CD34/genetics , Ataxia/genetics , Ataxia/pathology , Brain/metabolism , Brain/pathology , Cognitive Dysfunction/genetics , Cognitive Dysfunction/therapy , Disease Models, Animal , Electroencephalography , Gene Expression Regulation/genetics , Genetic Vectors/genetics , Genetic Vectors/therapeutic use , Hematopoietic Stem Cell Transplantation , Humans , Intellectual Disability/genetics , Interleukin-2/genetics , Lentivirus/genetics , Mice , Motor Skills Disorders/genetics , Motor Skills Disorders/pathology , Motor Skills Disorders/therapy , Seizures/geneticsABSTRACT
Angelman syndrome (AS) is a rare genetic neurodevelopmental disorder characterized by intellectual disabilities, motor and balance deficits, impaired communication, and a happy, excitable demeanor with frequent laughter. We sought to elucidate a preclinical outcome measure in male and female rats that addressed communication abnormalities of AS and other neurodevelopmental disorders in which communication is atypical and/or lack of speech is a core feature. We discovered, and herein report for the first time, excessive laughter-like 50 kHz ultrasonic emissions in the Ube3amat-/pat+ rat model of AS, which suggests an excitable, playful demeanor and elevated positive affect, similar to the demeanor of individuals with AS. Also in line with the AS phenotype, Ube3amat-/pat+ rats demonstrated aberrant social interactions with a novel partner, distinctive gait abnormalities, impaired cognition, an underlying LTP deficit, and profound reductions in brain volume. These unique, robust phenotypes provide advantages compared with currently available mouse models and will be highly valuable as outcome measures in the evaluation of therapies for AS.SIGNIFICANCE STATEMENT Angelman syndrome (AS) is a severe neurogenetic disorder for which there is no cure, despite decades of research using mouse models. This study used a recently developed rat model of AS to delineate disease-relevant outcome measures to facilitate therapeutic development. We found the rat to be a strong model of AS, offering several advantages over mouse models by exhibiting numerous AS-relevant phenotypes, including overabundant laughter-like vocalizations, reduced hippocampal LTP, and volumetric anomalies across the brain. These findings are unconfounded by detrimental motor abilities and background strain, issues plaguing mouse models. This rat model represents an important advancement in the field of AS, and the outcome metrics reported herein will be central to the therapeutic pipeline.
Subject(s)
Angelman Syndrome/genetics , Disease Models, Animal , Laughter/physiology , Microcephaly/genetics , Ubiquitin-Protein Ligases/genetics , Vocalization, Animal/physiology , Angelman Syndrome/metabolism , Angelman Syndrome/psychology , Animals , Brain/metabolism , Female , Gene Deletion , Laughter/psychology , Male , Microcephaly/metabolism , Microcephaly/psychology , Organ Culture Techniques , Protein Biosynthesis/physiology , Rats , Rats, Sprague-Dawley , Rats, Transgenic , Reflex, Startle/physiology , Social Behavior , Ubiquitin-Protein Ligases/deficiencyABSTRACT
Epigenome editing refers to the generation of precise chromatin alterations and their effects on gene expression and cell biology. Until recently, much of the efforts in epigenome editing were limited to tissue culture models of disease. However, the convergence of techniques from different fields including mammalian genetics, virology, and CRISPR engineering is advancing epigenome editing into a new era. Researchers are increasingly embracing the use of multicellular model organisms to test the role of specific chromatin alterations in development and disease. The challenge of successful live-animal epigenomic editing will depend on a well-informed foundation of the current methodologies for cell-specific delivery and editing accuracy. Here we review the opportunities for basic research and therapeutic applications.
Subject(s)
Epigenome , Epigenomics/methods , Gene Editing/methods , Animals , Cell Transplantation/methods , Clustered Regularly Interspaced Short Palindromic Repeats , Dependovirus/genetics , Mice, Transgenic , Zinc Fingers/geneticsABSTRACT
BACKGROUND: LRIG1, the founding member of the LRIG (leucine-rich repeat and immunoglobulin-like domain) family of transmembrane proteins, is a negative regulator of receptor tyrosine kinases and a tumour suppressor. Decreased LRIG1 expression is consistently observed in cancer, across diverse tumour types, and is linked to poor patient prognosis. However, mechanisms by which LRIG1 is repressed are not fully understood. Silencing of LRIG1 through promoter CpG island methylation has been reported in colorectal and cervical cancer but studies in breast cancer remain limited. METHODS: In silico analysis of human breast cancer patient data were used to demonstrate a correlation between DNA methylation and LRIG1 silencing in basal/triple-negative breast cancer, and its impact on patient survival. LRIG1 gene expression, protein abundance, and methylation enrichment were examined by quantitative reverse-transcription PCR, immunoblotting, and methylation immunoprecipitation, respectively, in breast cancer cell lines in vitro. We examined the impact of global demethylation on LRIG1 expression and methylation enrichment using 5-aza-2'-deoxycytidine. We also examined the effects of targeted demethylation of the LRIG1 CpG island, and transcriptional activation of LRIG1 expression, using the RNA guided deadCas9 transactivation system. RESULTS: Across breast cancer subtypes, LRIG1 expression is lowest in the basal/triple-negative subtype so we investigated whether differential methylation may contribute to this. Indeed, we find that LRIG1 CpG island methylation is most prominent in basal/triple-negative cell lines and patient samples. Use of the global demethylating agent 5-aza-2'-deoxycytidine decreases methylation leading to increased LRIG1 transcript expression in basal/triple-negative cell lines, while having no effect on LRIG1 expression in luminal/ER-positive cell lines. Using a CRISPR/deadCas9 (dCas9)-based targeting approach, we demonstrate that TET1-mediated demethylation (Tet1-dCas9) along with VP64-mediated transcriptional activation (VP64-dCas9) at the CpG island, increased endogenous LRIG1 expression in basal/triple-negative breast cancer cells, without transcriptional upregulation at predicted off-target sites. Activation of LRIG1 by the dCas9 transactivation system significantly increased LRIG1 protein abundance, reduced site-specific methylation, and reduced cancer cell viability. Our findings suggest that CRISPR-mediated targeted activation may be a feasible way to restore LRIG1 expression in cancer. CONCLUSIONS: Our study contributes novel insight into mechanisms which repress LRIG1 in triple-negative breast cancer and demonstrates for the first time that targeted de-repression of LRIG1 in cancer cells is possible. Understanding the epigenetic mechanisms associated with repression of tumour suppressor genes holds potential for the advancement of therapeutic approaches.
Subject(s)
DNA Methylation , Membrane Glycoproteins , Triple Negative Breast Neoplasms , Cell Line, Tumor , CpG Islands/genetics , Decitabine/pharmacology , Female , Gene Expression Regulation, Neoplastic , Gene Silencing , Humans , Membrane Glycoproteins/genetics , Membrane Glycoproteins/metabolism , Mixed Function Oxygenases/genetics , Mixed Function Oxygenases/metabolism , Promoter Regions, Genetic , Proto-Oncogene Proteins/genetics , Triple Negative Breast Neoplasms/geneticsABSTRACT
A significant number of X-linked genes escape from X chromosome inactivation and are associated with a distinct epigenetic signature. One epigenetic modification that strongly correlates with X-escape is reduced DNA methylation in promoter regions. Here, we created an artificial escape by editing DNA methylation on the promoter of CDKL5, a gene causative for an infantile epilepsy, from the silenced X-chromosomal allele in human neuronal-like cells. We identify that a fusion of the catalytic domain of TET1 to dCas9 targeted to the CDKL5 promoter using three guide RNAs causes significant reactivation of the inactive allele in combination with removal of methyl groups from CpG dinucleotides. Strikingly, we demonstrate that co-expression of TET1 and a VP64 transactivator have a synergistic effect on the reactivation of the inactive allele to levels >60% of the active allele. We further used a multi-omics assessment to determine potential off-targets on the transcriptome and methylome. We find that synergistic delivery of dCas9 effectors is highly selective for the target site. Our findings further elucidate a causal role for reduced DNA methylation associated with escape from X chromosome inactivation. Understanding the epigenetics associated with escape from X chromosome inactivation has potential for those suffering from X-linked disorders.
Subject(s)
Chromosomes, Human, X/chemistry , Epigenesis, Genetic , Promoter Regions, Genetic , Protein Serine-Threonine Kinases/genetics , RNA, Messenger/genetics , X Chromosome Inactivation , Alleles , CRISPR-Associated Protein 9/genetics , CRISPR-Associated Protein 9/metabolism , Catalytic Domain , Cell Line, Tumor , Chromosomes, Human, X/metabolism , CpG Islands , Gene Editing , Gene Silencing , Humans , Mixed Function Oxygenases/genetics , Mixed Function Oxygenases/metabolism , Neurons/cytology , Neurons/metabolism , Protein Serine-Threonine Kinases/metabolism , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins/metabolism , RNA, Guide, Kinetoplastida/genetics , RNA, Guide, Kinetoplastida/metabolism , RNA, Messenger/metabolism , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Trans-Activators/genetics , Trans-Activators/metabolismABSTRACT
Ubiquitin E3 ligase 3A (UBE3A) encodes an E3 ubiquitin ligase whose loss from the maternal allele causes the neurodevelopmental disorder Angelman syndrome (AS). Previous studies of UBE3A function have not examined full Ube3a deletion in mouse, the complexity of imprinted gene networks in brain nor the molecular basis of systems-level cognitive dysfunctions in AS. We therefore utilized a systems biology approach to elucidate how UBE3A loss impacts the early postnatal brain in a novel CRISPR/Cas9-engineered rat Angelman model of a complete Ube3a deletion. Strand-specific transcriptome analysis of offspring from maternally or paternally inherited Ube3a deletions revealed the expected parental expression patterns of Ube3a sense and antisense transcripts by postnatal day 2 (P2) in hypothalamus and day 9 (P9) in cortex, compared to wild-type littermates. The dependency of genome-wide effects on parent-of-origin, Ube3a genotype and time (P2 and P9) was investigated through transcriptome (RNA sequencing of cortex and hypothalamus) and methylome (whole-genome bisulfite sequencing of hypothalamus). Weighted gene co-expression and co-methylation network analyses identified co-regulated networks in maternally inherited Ube3a deletion offspring enriched in postnatal developmental processes including Wnt signaling, synaptic regulation, neuronal and glial functions, epigenetic regulation, ubiquitin, circadian entrainment and splicing. Furthermore, we showed that loss of the paternal Ube3a antisense transcript resulted in both unique and overlapping dysregulated gene pathways with maternal loss, predominantly at the level of differential methylation. Together, these results provide a holistic examination of the molecular impacts of UBE3A loss in brain, supporting the existence of interactive epigenetic networks between maternal and paternal transcripts at the Ube3a locus.
Subject(s)
Genomic Imprinting , Ubiquitin-Protein Ligases/genetics , Angelman Syndrome/genetics , Angelman Syndrome/metabolism , Animals , Brain/metabolism , Cerebral Cortex/metabolism , Epigenesis, Genetic , Female , Gene Expression , Gene Expression Profiling/methods , Gene Regulatory Networks/genetics , Hypothalamus/metabolism , Neuroglia/metabolism , Neurons/metabolism , Rats , Rats, Sprague-Dawley , Synapses/genetics , Synapses/metabolism , Systems Biology , Transcriptome , Ubiquitin-Protein Ligases/metabolism , Wnt Signaling PathwayABSTRACT
DNA methylation is an important epigenetic modification involved in gene regulation and transposable element silencing. Changes in DNA methylation can be heritable and, thus, can lead to the formation of stable epialleles. A well-characterized example of a stable epiallele in plants is fwa, which consists of the loss of DNA cytosine methylation (5mC) in the promoter of the FLOWERING WAGENINGEN (FWA) gene, causing up-regulation of FWA and a heritable late-flowering phenotype. Here we demonstrate that a fusion between the catalytic domain of the human demethylase TEN-ELEVEN TRANSLOCATION1 (TET1cd) and an artificial zinc finger (ZF) designed to target the FWA promoter can cause highly efficient targeted demethylation, FWA up-regulation, and a heritable late-flowering phenotype. Additional ZF-TET1cd fusions designed to target methylated regions of the CACTA1 transposon also caused targeted demethylation and changes in expression. Finally, we have developed a CRISPR/dCas9-based targeted demethylation system using the TET1cd and a modified SunTag system. Similar to the ZF-TET1cd fusions, the SunTag-TET1cd system is able to target demethylation and activate gene expression when directed to the FWA or CACTA1 loci. Our study provides tools for targeted removal of 5mC at specific loci in the genome with high specificity and minimal off-target effects. These tools provide the opportunity to develop new epialleles for traits of interest, and to reactivate expression of previously silenced genes, transgenes, or transposons.
Subject(s)
Arabidopsis/genetics , DNA Methylation , Genome, Plant , Mixed Function Oxygenases/chemistry , Proto-Oncogene Proteins/chemistry , Arabidopsis Proteins/metabolism , Catalytic Domain , DNA Transposable Elements , DNA, Plant/chemistry , Epigenesis, Genetic , Flowers , Gene Expression Regulation, Plant , Gene Silencing , Homeodomain Proteins/metabolism , Humans , Mutation , Promoter Regions, Genetic , Transcription Factors/metabolism , Zinc FingersABSTRACT
Specific applications of CRISPR/Cas genome editing systems benefit from chemical modifications of the sgRNA. Herein we describe a versatile and efficient strategy for functionalization of the 3'-end of a sgRNA. An exemplary collection of six chemically modified sgRNAs was prepared containing crosslinkers, a fluorophore and biotin. Modification of the sgRNA 3'-end was broadly tolerated by Streptococcus pyogenes Cas9 in an inâ vitro DNA cleavage assay. The 3'-biotinylated sgRNA was used as an affinity reagent to identify IGF2BP1, YB1 and hnRNPâ K as sgRNA-binding proteins present in HEK293T cells. Overall, the modification strategy presented here has the potential to expand on current applications of CRISPR/Cas systems.
Subject(s)
Biotin/chemistry , CRISPR-Associated Protein 9/genetics , CRISPR-Cas Systems , DNA/chemistry , Gene Editing/methods , RNA, Guide, Kinetoplastida/chemistry , Binding Sites , Biotinylation , CRISPR-Associated Protein 9/metabolism , Cross-Linking Reagents/chemistry , DNA/metabolism , DNA Cleavage , Fluorescent Dyes/chemistry , Gene Expression , HEK293 Cells , Heterogeneous-Nuclear Ribonucleoprotein K/genetics , Heterogeneous-Nuclear Ribonucleoprotein K/metabolism , Humans , Models, Molecular , Nucleic Acid Conformation , Protein Binding , RNA, Guide, Kinetoplastida/genetics , RNA, Guide, Kinetoplastida/metabolism , RNA-Binding Proteins/genetics , RNA-Binding Proteins/metabolism , Y-Box-Binding Protein 1/genetics , Y-Box-Binding Protein 1/metabolismABSTRACT
RNA-directed DNA methylation in Arabidopsis thaliana depends on the upstream synthesis of 24-nucleotide small interfering RNAs (siRNAs) by RNA POLYMERASE IV (Pol IV) and downstream synthesis of non-coding transcripts by Pol V. Pol V transcripts are thought to interact with siRNAs which then recruit DOMAINS REARRANGED METHYLTRANSFERASE 2 (DRM2) to methylate DNA. The SU(VAR)3-9 homologues SUVH2 and SUVH9 act in this downstream step but the mechanism of their action is unknown. Here we show that genome-wide Pol V association with chromatin redundantly requires SUVH2 and SUVH9. Although SUVH2 and SUVH9 resemble histone methyltransferases, a crystal structure reveals that SUVH9 lacks a peptide-substrate binding cleft and lacks a properly formed S-adenosyl methionine (SAM)-binding pocket necessary for normal catalysis, consistent with a lack of methyltransferase activity for these proteins. SUVH2 and SUVH9 both contain SRA (SET- and RING-ASSOCIATED) domains capable of binding methylated DNA, suggesting that they function to recruit Pol V through DNA methylation. Consistent with this model, mutation of DNA METHYLTRANSFERASE 1 (MET1) causes loss of DNA methylation, a nearly complete loss of Pol V at its normal locations, and redistribution of Pol V to sites that become hypermethylated. Furthermore, tethering SUVH9 [corrected] with a zinc finger to an unmethylated site is sufficient to recruit Pol V and establish DNA methylation and gene silencing. These results indicate that Pol V is recruited to DNA methylation through the methyl-DNA binding SUVH2 and SUVH9 proteins, and our mechanistic findings suggest a means for selectively targeting regions of plant genomes for epigenetic silencing.
Subject(s)
Arabidopsis Proteins/chemistry , Arabidopsis Proteins/metabolism , Arabidopsis , DNA Methylation , DNA-Directed RNA Polymerases/metabolism , Histone-Lysine N-Methyltransferase/chemistry , Histone-Lysine N-Methyltransferase/metabolism , Arabidopsis/enzymology , Arabidopsis/genetics , Arabidopsis Proteins/genetics , Binding Sites/genetics , Biocatalysis , Chromatin/chemistry , Chromatin/genetics , Chromatin/metabolism , Crystallography, X-Ray , DNA (Cytosine-5-)-Methyltransferases/genetics , DNA (Cytosine-5-)-Methyltransferases/metabolism , DNA Methylation/genetics , DNA-Binding Proteins/chemistry , DNA-Binding Proteins/metabolism , Flowers/growth & development , Gene Expression Regulation, Plant , Gene Silencing , Genome, Plant/genetics , Models, Molecular , Mutation/genetics , Phenotype , Protein Structure, Tertiary , Protein Transport , RNA, Plant/biosynthesis , RNA, Plant/genetics , RNA, Plant/metabolism , RNA, Small Interfering/biosynthesis , RNA, Small Interfering/genetics , RNA, Small Interfering/metabolism , Transcription, Genetic , Zinc FingersABSTRACT
Distinct epigenomic profiles of histone marks have been associated with gene expression, but questions regarding the causal relationship remain. Here we investigated the activity of a broad collection of genomically targeted epigenetic regulators that could write epigenetic marks associated with a repressed chromatin state (G9A, SUV39H1, Krüppel-associated box (KRAB), DNMT3A as well as the first targetable versions of Ezh2 and Friend of GATA-1 (FOG1)). dCas9 fusions produced target gene repression over a range of 0- to 10-fold that varied by locus and cell type. dCpf1 fusions were unable to repress gene expression. The most persistent gene repression required the action of several effector domains; however, KRAB-dCas9 did not contribute to persistence in contrast to previous reports. A 'direct tethering' strategy attaching the Ezh2 methyltransferase enzyme to dCas9, as well as a 'recruitment' strategy attaching the N-terminal 45 residues of FOG1 to dCas9 to recruit the endogenous nucleosome remodeling and deacetylase complex, were both successful in targeted deposition of H3K27me3. Surprisingly, however, repression was not correlated with deposition of either H3K9me3 or H3K27me3. Our results suggest that so-called repressive histone modifications are not sufficient for gene repression. The easily programmable dCas9 toolkit allowed precise control of epigenetic information and dissection of the relationship between the epigenome and gene regulation.
Subject(s)
Chromatin/chemistry , Endonucleases/genetics , Epigenomics/methods , Gene Silencing , Histones/genetics , Chromatin/metabolism , DNA (Cytosine-5-)-Methyltransferases/genetics , DNA (Cytosine-5-)-Methyltransferases/metabolism , DNA Methyltransferase 3A , Endonucleases/metabolism , Gene Editing , HCT116 Cells , HEK293 Cells , Histocompatibility Antigens/genetics , Histocompatibility Antigens/metabolism , Histone-Lysine N-Methyltransferase/genetics , Histone-Lysine N-Methyltransferase/metabolism , Histones/metabolism , Humans , Methylation , Methyltransferases/genetics , Methyltransferases/metabolism , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , Promoter Regions, Genetic , RNA, Messenger/genetics , RNA, Messenger/metabolism , Receptor, ErbB-2/genetics , Receptor, ErbB-2/metabolism , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Repressor Proteins/genetics , Repressor Proteins/metabolism , Transcription Factors/genetics , Transcription Factors/metabolismABSTRACT
A specific double-stranded DNA sensing system is of great interest for diagnostic and other biomedical applications. Zinc finger domains, which recognize double-stranded DNA, can be engineered to form custom DNA-binding proteins for the recognition of specific DNA sequences. As a proof of concept, a sequence-enabled reassembly of a TEM-1 ß-lactamase system (SEER-LAC) was previously demonstrated to develop zinc finger protein (ZFP) arrays for the detection of a double-stranded bacterial DNA sequence. Here, we implemented the SEER-LAC system to demonstrate the direct detection of pathogen-specific DNA sequences present in E. coli O157:H7 on a lab-on-a-chip. ZFPs custom-designed to detect Shiga toxin in E. coli O157:H7 were immobilized on a cyclic olefin copolymer (COC) chip, which can function as a non-PCR based molecular diagnostic device. Pathogen-specific double-stranded DNA was directly detected by using engineered ZFPs immobilized on the COC chip with high specificity, providing a detection limit of 10 fmol of target DNA in a colorimetric assay. Therefore, in this study, we demonstrated the great potential of ZFP arrays on the COC chip for further development of a simple and novel lab-on-a-chip technology for the detection of pathogens.
Subject(s)
DNA, Bacterial/isolation & purification , DNA-Binding Proteins/chemistry , Escherichia coli O157/isolation & purification , Immobilized Proteins/chemistry , Zinc Fingers , Escherichia coli O157/genetics , Lab-On-A-Chip Devices , Polymers , Protein Engineering , Sensitivity and SpecificityABSTRACT
Genome-wide association studies (GWAS) have identified single nucleotide polymorphisms (SNPs) associated with increased risk for colorectal cancer (CRC). A molecular understanding of the functional consequences of this genetic variation is complicated because most GWAS SNPs are located in non-coding regions. We used epigenomic information to identify H3K27Ac peaks in HCT116 colon cancer cells that harbor SNPs associated with an increased risk for CRC. Employing CRISPR/Cas9 nucleases, we deleted a CRC risk-associated H3K27Ac peak from HCT116 cells and observed large-scale changes in gene expression, resulting in decreased expression of many nearby genes. As a comparison, we showed that deletion of a robust H3K27Ac peak not associated with CRC had minimal effects on the transcriptome. Interestingly, although there is no H3K27Ac peak in HEK293 cells in the E7 region, deletion of this region in HEK293 cells decreased expression of several of the same genes that were downregulated in HCT116 cells, including the MYC oncogene. Accordingly, deletion of E7 causes changes in cell culture assays in HCT116 and HEK293 cells. In summary, we show that effects on the transcriptome upon deletion of a distal regulatory element cannot be predicted by the size or presence of an H3K27Ac peak.
Subject(s)
Gene Expression Regulation, Neoplastic , Histones/metabolism , Transcriptome , Acetylation , Cell Proliferation , Colorectal Neoplasms/genetics , Colorectal Neoplasms/metabolism , Enhancer Elements, Genetic , Genome-Wide Association Study , HCT116 Cells , HEK293 Cells , Humans , Papillomavirus E7 Proteins/genetics , Polymorphism, Single Nucleotide , Protein Processing, Post-Translational , Sequence DeletionABSTRACT
Dyskeratosis Congenita (DC) is a heritable multi-system disorder caused by abnormally short telomeres. Clinically diagnosed by the mucocutaneous symptoms, DC patients are at high risk for bone marrow failure, pulmonary fibrosis, and multiple types of cancers. We have recapitulated the most common DC-causing mutation in the shelterin component TIN2 by introducing a TIN2-R282H mutation into cultured telomerase-positive human cells via a knock-in approach. The resulting heterozygous TIN2-R282H mutation does not perturb occupancy of other shelterin components on telomeres, result in activation of telomeric DNA damage signaling or exhibit other characteristics indicative of a telomere deprotection defect. Using a novel assay that monitors the frequency and extension rate of telomerase activity at individual telomeres, we show instead that telomerase elongates telomeres at a reduced frequency in TIN2-R282H heterozygous cells; this recruitment defect is further corroborated by examining the effect of this mutation on telomerase-telomere co-localization. These observations suggest a direct role for TIN2 in mediating telomere length through telomerase, separable from its role in telomere protection.
Subject(s)
Telomerase/metabolism , Telomere Shortening/genetics , Telomere-Binding Proteins/genetics , Telomere/metabolism , Aminopeptidases/metabolism , Cell Line, Tumor , DNA Repair/genetics , Dipeptidyl-Peptidases and Tripeptidyl-Peptidases/metabolism , Dyskeratosis Congenita/genetics , Gene Knock-In Techniques , HCT116 Cells , Humans , Mutation/genetics , Serine Proteases/metabolism , Shelterin Complex , Telomere Homeostasis/genetics , Telomeric Repeat Binding Protein 1/genetics , Tripeptidyl-Peptidase 1ABSTRACT
Angelman syndrome (AS) is a neurological genetic disorder caused by loss of expression of the maternal copy of UBE3A in the brain. Due to brain-specific genetic imprinting at this locus, the paternal UBE3A is silenced by a long antisense transcript. Inhibition of the antisense transcript could lead to unsilencing of paternal UBE3A, thus providing a therapeutic approach for AS. However, widespread delivery of gene regulators to the brain remains challenging. Here, we report an engineered zinc finger-based artificial transcription factor (ATF) that, when injected i.p. or s.c., crossed the blood-brain barrier and increased Ube3a expression in the brain of an adult mouse model of AS. The factor displayed widespread distribution throughout the brain. Immunohistochemistry of both the hippocampus and cerebellum revealed an increase in Ube3a upon treatment. An ATF containing an alternative DNA-binding domain did not activate Ube3a. We believe this to be the first report of an injectable engineered zinc finger protein that can cause widespread activation of an endogenous gene in the brain. These observations have important implications for the study and treatment of AS and other neurological disorders.
Subject(s)
Angelman Syndrome/genetics , Angelman Syndrome/metabolism , Brain/metabolism , Gene Expression Regulation , Transcription Factors/metabolism , Ubiquitin-Protein Ligases/genetics , Animals , Blood-Brain Barrier/metabolism , Disease Models, Animal , Gene Expression , Genes, Reporter , Genetic Loci , Mice , Transcription Factors/administration & dosage , Zinc FingersABSTRACT
Clustered regularly interspaced short palindromic repeat (CRISPR) RNA-guided nucleases have gathered considerable excitement as a tool for genome engineering. However, questions remain about the specificity of target site recognition. Cleavage specificity is typically evaluated by low throughput assays (T7 endonuclease I assay, target amplification followed by high-throughput sequencing), which are limited to a subset of potential off-target sites. Here, we used ChIP-seq to examine genome-wide CRISPR binding specificity at gRNA-specific and gRNA-independent sites for two guide RNAs. RNA-guided Cas9 binding was highly specific to the target site while off-target binding occurred at much lower intensities. Cas9-bound regions were highly enriched in NGG sites, a sequence required for target site recognition by Streptococcus pyogenes Cas9. To determine the relationship between Cas9 binding and endonuclease activity, we applied targeted sequence capture, which allowed us to survey 1200 genomic loci simultaneously including potential off-target sites identified by ChIP-seq and by computational prediction. A high frequency of indels was observed at both target sites and one off-target site, while no cleavage activity could be detected at other ChIP-bound regions. Our results confirm the high-specificity of CRISPR endonucleases and demonstrate that sequence capture can be used as a high-throughput genome-wide approach to identify off-target activity.