Development of Locus-Directed Editing of the Epigenome from Basic Mechanistic Engineering to First Clinical Applications.

The introduction of CRISPR/Cas systems has resulted in a strong impulse for the field of gene-targeted epigenome/epigenetic reprogramming (EpiEditing), where EpiEditors consisting of a DNA binding part for targeting and an enzymatic part for rewriting of chromatin modifications are applied in cells to alter chromatin modifications at targeted genome loci in a directed manner. Pioneering studies preceding this era indicated causal relationships of chromatin marks instructing gene expression. The accumulating evidence of chromatin reprogramming of a given genomic locus resulting in gene expression changes opened the field for mainstream applications of this technology in basic and clinical research. The growing knowledge on chromatin biology and application of EpiEditing tools, however, also revealed a lack of predictability of the efficiency of EpiEditing in some cases. In this perspective, the dependence of critical parameters such as specificity, effectivity, and sustainability of EpiEditing on experimental settings and conditions including the expression levels and expression times of the EpiEditors, their chromatin binding affinity and specificity, and the crosstalk between EpiEditors and cellular epigenome modifiers are discussed. These considerations highlight the intimate connection between the outcome of epigenome reprogramming and the details of the technical approaches toward EpiEditing, which are the main topic of this volume of Methods in Molecular Biology. Once established in a fully functional "plug-and-play" mode, EpiEditing will allow to better understand gene expression control and to translate such knowledge into therapeutic tools. These expectations are beginning to be met as shown by various in vivo EpiEditing applications published in recent years, several companies aiming to exploit the therapeutic power of EpiEditing and the first clinical trial initiated.

Reader-Effectors as Actuators of Epigenome Editing.

Epigenome editing applications are gaining broader use for targeted transcriptional control as more enzymes with diverse chromatin-modifying functions are being incorporated into fusion proteins. Development of these fusion proteins, called epigenome editors, has outpaced the study of proteins that interact with edited chromatin. One type of protein that acts downstream of chromatin editing is the reader-effector, which bridges epigenetic marks with biological effects like gene regulation. As the name suggests, a reader-effector protein is generally composed of a reader domain and an effector domain. Reader domains directly bind epigenetic marks, while effector domains often recruit protein complexes that mediate transcription, chromatin remodeling, and DNA repair. In this chapter, we discuss the role of reader-effectors in driving the outputs of epigenome editing and highlight instances where abnormal and context-specific reader-effectors might impair the effects of epigenome editing. Lastly, we discuss how engineered reader-effectors may complement the epigenome editing toolbox to achieve robust and reliable gene regulation.

Fine-Tuning the Epigenetic Landscape: Chemical Modulation of Epigenome Editors.

Epigenome editing has emerged as a powerful technique for targeted manipulation of the chromatin and transcriptional landscape, employing designer DNA binding domains fused with effector domains, known as epi-editors. However, the constitutive expression of dCas9-based epi-editors presents challenges, including off-target activity and lack of temporal resolution. Recent advancements of dCas9-based epi-editors have addressed these limitations by introducing innovative switch systems that enable temporal control of their activity. These systems allow precise modulation of gene expression over time and offer a means to deactivate epi-editors, thereby reducing off-target effects associated with prolonged expression. The development of novel dCas9 effectors regulated by exogenous chemical signals has revolutionized temporal control in epigenome editing, significantly expanding the researcher's toolbox. Here, we provide a comprehensive review of the current state of these cutting-edge systems and specifically discuss their advantages and limitations, offering context to better understand their capabilities.

Integrated Methylome and Transcriptome Analysis between Wizened and Normal Flower Buds in Pyrus pyrifolia Cultivar 'Sucui 1'.

Here, cytosine methylation in the whole genome of pear flower buds was mapped at a single-base resolution. There was 19.4% methylation across all sequenced C sites in the Pyrus pyrifolia cultivar 'Sucui 1' flower bud genome. Meantime, the CG, CHG, and CHH sequence contexts (where H = A, T or C) exhibited 47.4%, 33.3%, and 11.9% methylation, respectively. Methylation in different gene regions was revealed through combining methylome and transcriptome analysis, which presented various transcription trends. Genes with methylated promoters exhibited lower expression levels than genes with non-methylated promoters, while body-methylated genes displayed an obvious negative correlation with their transcription levels. The methylation profiles of auxin- and cytokinin-related genes were estimated. And some of them proved to be hypomethylated, with increased transcription levels, in wizened buds. More specifically, the expression of the genes PRXP73, CYP749A22, and CYP82A3 was upregulated as a result of methylation changes in their promoters. Finally, auxin and cytokinin concentrations were higher in wizened flower buds than in normal buds. The exogenous application of paclobutrazol (PP333) in the field influenced the DNA methylation status of some genes and changed their expression level, reducing the proportion of wizened flower buds in a concentration-dependent manner. Overall, our results demonstrated the relationship between DNA methylation and gene expression in wizened flower buds of P. pyrifolia cultivar 'Sucui 1', which was associated with changes in auxin and cytokinin concentrations.

Direct neuronal reprogramming of mouse astrocytes is associated with multiscale epigenome remodeling and requires Yy1.

Direct neuronal reprogramming is a promising approach to regenerate neurons from local glial cells. However, mechanisms of epigenome remodeling and co-factors facilitating this process are unclear. In this study, we combined single-cell multiomics with genome-wide profiling of three-dimensional nuclear architecture and DNA methylation in mouse astrocyte-to-neuron reprogramming mediated by Neurogenin2 (Ngn2) and its phosphorylation-resistant form (PmutNgn2), respectively. We show that Ngn2 drives multilayered chromatin remodeling at dynamic enhancer-gene interaction sites. PmutNgn2 leads to higher reprogramming efficiency and enhances epigenetic remodeling associated with neuronal maturation. However, the differences in binding sites or downstream gene activation cannot fully explain this effect. Instead, we identified Yy1, a transcriptional co-factor recruited by direct interaction with Ngn2 to its target sites. Upon deletion of Yy1, activation of neuronal enhancers, genes and ultimately reprogramming are impaired without affecting Ngn2 binding. Thus, our work highlights the key role of interactors of proneural factors in direct neuronal reprogramming.

MIMOSA: a resource consisting of improved methylome prediction models increases power to identify DNA methylation-phenotype associations.

Although DNA methylation (DNAm) has been implicated in the pathogenesis of numerous complex diseases, from cancer to cardiovascular disease to autoimmune disease, the exact methylation sites that play key roles in these processes remain elusive. One strategy to identify putative causal CpG sites and enhance disease etiology understanding is to conduct methylome-wide association studies (MWASs), in which predicted DNA methylation that is associated with complex diseases can be identified. However, current MWAS models are primarily trained using the data from single studies, thereby limiting the methylation prediction accuracy and the power of subsequent association studies. Here, we introduce a new resource, MWAS Imputing Methylome Obliging Summary-level mQTLs and Associated LD matrices (MIMOSA), a set of models that substantially improve the prediction accuracy of DNA methylation and subsequent MWAS power through the use of a large summary-level mQTL dataset provided by the Genetics of DNA Methylation Consortium (GoDMC). Through the analyses of GWAS (genome-wide association study) summary statistics for 28 complex traits and diseases, we demonstrate that MIMOSA considerably increases the accuracy of DNA methylation prediction in whole blood, crafts fruitful prediction models for low heritability CpG sites, and determines markedly more CpG site-phenotype associations than preceding methods. Finally, we use MIMOSA to conduct a case study on high cholesterol, pinpointing 146 putatively causal CpG sites.

Genome-Scale Multimodal Analysis of Cell-Free DNA Whole-Methylome Sequencing for Noninvasive Esophageal Cancer Detection.

PURPOSE: Simultaneous profiling of cell-free DNA (cfDNA) methylation and fragmentation features to improve the performance of cfDNA-based cancer detection is technically challenging. We developed a method to comprehensively analyze multimodal cfDNA genomic features for more sensitive esophageal squamous cell carcinoma (ESCC) detection. MATERIALS AND METHODS: Enzymatic conversion-mediated whole-methylome sequencing was applied to plasma cfDNA samples extracted from 168 patients with ESCC and 251 noncancer controls. ESCC characteristic cfDNA methylation, fragmentation, and copy number signatures were analyzed both across the genome and at accessible cis-regulatory DNA elements. To distinguish ESCC from noncancer samples, a first-layer classifier was developed for each feature type, the prediction results of which were incorporated to construct the second-layer ensemble model. RESULTS: ESCC plasma genome displayed global hypomethylation, altered fragmentation size, and chromosomal copy number alteration. Methylation and fragmentation changes at cancer tissue-specific accessible cis-regulatory DNA elements were also observed in ESCC plasma. By integrating multimodal genomic features for ESCC detection, the ensemble model showed improved performance over individual modalities. In the training cohort with a specificity of 99.2%, the detection sensitivity was 81.0% for all stages and 70.0% for stage 0-II. Consistent performance was observed in the test cohort with a specificity of 98.4%, an all-stage sensitivity of 79.8%, and a stage 0-II sensitivity of 69.0%. The performance of the classifier was associated with the disease stage, irrespective of clinical covariates. CONCLUSION: This study comprehensively profiles the epigenomic landscape of ESCC plasma and provides a novel noninvasive and sensitive ESCC detection approach with genome-scale multimodal analysis.

Designing Epigenome Editors: Considerations of Biochemical and Locus Specificities.

The advent of locus-specific protein recruitment technologies has enabled a new class of studies in chromatin biology. Epigenome editors (EEs) enable biochemical modifications of chromatin at almost any specific endogenous locus. Their locus-specificity unlocks unique information including the functional roles of distinct modifications at specific genomic loci. Given the growing interest in using these tools for biological and translational studies, there are many specific design considerations depending on the scientific question or clinical need. Here, we present and discuss important design considerations and challenges regarding the biochemical and locus specificities of epigenome editors. These include how to: account for the complex biochemical diversity of chromatin; control for potential interdependency of epigenome editors and their resultant modifications; avoid sequestration effects; quantify the locus specificity of epigenome editors; and improve locus-specificity by considering concentration, affinity, avidity, and sequestration effects.

Protocol for Efficient Generation of Chimeric Antigen Receptor T Cells with Multiplexed Gene Silencing by Epigenome Editing.

Multiplex gene regulation enables the controlled and simultaneous alteration of the expression levels of multiple genes and is generally pursued to precisely alter complex cellular pathways with a single intervention. Thus far, this has been typically exploited in combination with genome editing tools (i.e., base-/prime-editing, designer nucleases) to enable simultaneous genetic alterations and modulate complex physiologic cellular pathways. In the field of cancer immunotherapy, multiplex genome editing has been used to simultaneously inactivate three genes (i.e., TRAC, B2M, and PDCD1) and generate universal chimeric antigen receptor (CAR) T cells resistant to the inhibitory activity of the PD-1 ligand. However, the intrinsic risk of genomic aberrations driven by such tools poses concerns because of the generation of multiple single-strand or double-strand DNA breaks followed by DNA repair. Modulating gene expression without DNA damage using epigenome editing promises a safer and efficient approach to alter gene expression. This method enables for simultaneous activation and/or repression of target genes, offering superior fine-tuning capabilities with reduced off-targeting effects and potential reversibility as compared to genome editing. Here we describe a detailed protocol for achieving multiplexed and sustainable gene silencing in CAR T cells. In an exemplary approach, we use designer epigenome modifiers (DEMs) for the simultaneous inactivation of two T cell inhibitory genes, PDCD1 and LAG3 to generate CAR T cells with increased resistance to tumor-induced exhaustion.

Protocol for Allele-Specific Epigenome Editing Using CRISPR/dCas9.

The discovery and adaptation of CRISPR/Cas systema for epigenome editing has allowed for a straightforward design of targeting modules that can direct epigenome editors to virtually any genomic site. This advancement in DNA-targeting technology brings allele-specific epigenome editing into reach, a "super-specific" variation of epigenome editing whose goal is an alteration of chromatin marks at only one selected allele of the genomic target locus. This technology could be useful for the treatment of diseases caused by a mutant allele with a dominant effect, because allele-specific epigenome editing allows the specific silencing of the mutated allele leaving the healthy counterpart expressed. Moreover, it may allow the direct correction of aberrant imprints in imprinting disorders where editing of DNA methylation is required exclusively in a single allele. Here, we describe a basic protocol for the design and application of allele-specific epigenome editing systems using allele-specific DNA methylation at the NARF gene in HEK293 cells as an example. An sgRNA/dCas9 unit is used for allele-specific binding to the target locus containing a SNP in the seed region of the sgRNA or the PAM region. The dCas9 protein is connected to a SunTag allowing to recruit up to 10 DNMT3A/3L units fused to a single-chain Fv fragment, which specifically binds to the SunTag peptide sequence. The plasmids expressing dCas9-10x SunTag, scFv-DNMT3A/3L, and sgRNA, each of them co-expressing a fluorophore, are introduced into cells by co-transfection. Cells containing all three plasmids are enriched by FACS, cultivated, and later the genomic DNA and RNA can be retrieved for DNA methylation and gene expression analysis.

Generation of Whole-Genome Bisulfite Sequencing Libraries for Comprehensive DNA Methylome Analysis.

Whole-genome bisulfite sequencing (WGBS) enables the detection of DNA methylation at a single base-pair resolution. The treatment of DNA with sodium bisulfite allows the discrimination of methylated and unmethylated cytosines, but the power of this technology can be limited by the input amounts of DNA and the length of DNA fragments due to DNA damage caused by the desulfonation process. Here, we describe a WGBS library preparation protocol that minimizes the loss and damage of DNA, generating high-quality libraries amplified with fewer polymerase chain reaction (PCR) cycles, and hence data with fewer PCR duplicates, from lower amounts of input material. Briefly, genomic DNA is sheared, end-repaired, 3'-adenylated, and ligated to adaptors with fewer clean-up steps in between, minimizing DNA loss. The adapter-ligated DNA is then treated with sodium bisulfite and amplified with a few PCR cycles to reach the yield needed for sequencing.

Analysis of Methylome of Different Forms of Basal Cell Hyperplasia and Squamous Cell Metaplasia of Bronchial Epithelium.

Squamous cell lung cancer (SCLC) occurs as a result of dysregenerative changes in the bronchial epithelium: basal cell hyperplasia (BCH), squamous cell metaplasia (SM), and dysplasia. We previously suggested that combinations of precancerous changes detected in the small bronchi of patients with SCLC may reflect various "scenarios" of the precancerous process: isolated BCH→stopping at the stage of hyperplasia, BCH+SM→progression of hyperplasia into metaplasia, SM+dysplasia→progression of metaplasia into dysplasia. In this study, DNA methylome of various forms of precancerous changes in the bronchial epithelium of SCLC patients was analyzed using the genome-wide bisulfite sequencing. In BCH combined with SM, in contrast to isolated BCH, differentially methylated regions were identified in genes of the pathogenetically significant MET signaling pathway (RNMT, HPN). Differentially methylated regions affecting genes involved in inflammation regulation (IL-23, IL-23R, IL12B, IL12RB1, and FIS1) were detected in SM combined with dysplasia in comparison with SM combined with BCH. The revealed changes in DNA methylation may underlie various "scenarios" of the precancerous process in the bronchial epithelium.

Integrated analysis of DNA methylome and transcriptome revealing epigenetic regulation of CRIR1-promoted cold tolerance.

BACKGROUND: DNA methylation contributes to the epigenetic regulation of nuclear gene expression, and is associated with plant growth, development, and stress responses. Compelling evidence has emerged that long non-coding RNA (lncRNA) regulates DNA methylation. Previous genetic and physiological evidence indicates that lncRNA-CRIR1 plays a positive role in the responses of cassava plants to cold stress. However, it is unclear whether global DNA methylation changes with CRIR1-promoted cold tolerance. RESULTS: In this study, a comprehensive comparative analysis of DNA methylation and transcriptome profiles was performed to reveal the gene expression and epigenetic dynamics after CRIR1 overexpression. Compared with the wild-type plants, CRIR1-overexpressing plants present gained DNA methylation in over 37,000 genomic regions and lost DNA methylation in about 16,000 genomic regions, indicating a global decrease in DNA methylation after CRIR1 overexpression. Declining DNA methylation is not correlated with decreased/increased expression of the DNA methylase/demethylase genes, but is associated with increased transcripts of a few transcription factors, chlorophyll metabolism and photosynthesis-related genes, which could contribute to the CRIR1-promoted cold tolerance. CONCLUSIONS: In summary, a first set of transcriptome and epigenome data was integrated in this study to reveal the gene expression and epigenetic dynamics after CRIR1 overexpression, with the identification of several TFs, chlorophyll metabolism and photosynthesis-related genes that may be involved in CRIR1-promoted cold tolerance. Therefore, our study has provided valuable data for the systematic study of molecular insights for plant cold stress response.

An atlas of the tomato epigenome reveals that KRYPTONITE shapes TAD-like boundaries through the control of H3K9ac distribution.

In recent years, the exploration of genome three-dimensional (3D) conformation has yielded profound insights into the regulation of gene expression and cellular functions in both animals and plants. While animals exhibit a characteristic genome topology defined by topologically associating domains (TADs), plants display similar features with a more diverse conformation across species. Employing advanced high-throughput sequencing and microscopy techniques, we investigated the landscape of 26 histone modifications and RNA polymerase II distribution in tomato (Solanum lycopersicum). Our study unveiled a rich and nuanced epigenetic landscape, shedding light on distinct chromatin states associated with heterochromatin formation and gene silencing. Moreover, we elucidated the intricate interplay between these chromatin states and the overall topology of the genome. Employing a genetic approach, we delved into the role of the histone modification H3K9ac in genome topology. Notably, our investigation revealed that the ectopic deposition of this chromatin mark triggered a reorganization of the 3D chromatin structure, defining different TAD-like borders. Our work emphasizes the critical role of H3K9ac in shaping the topology of the tomato genome, providing valuable insights into the epigenetic landscape of this agriculturally significant crop species.

Epigenetic disease markers in primary sclerosing cholangitis and primary biliary cholangitis-methylomics of cholestatic liver disease.

BACKGROUND: The epigenome, the set of modifications to DNA and associated molecules that control gene expression, cellular identity, and function, plays a major role in mediating cellular responses to outside factors. Thus, evaluation of the epigenetic state can provide insights into cellular adaptions occurring over the course of disease. METHODS: We performed epigenome-wide association studies of primary sclerosing cholangitis (PSC) and primary biliary cholangitis (PBC) using the Illumina MethylationEPIC Bead Chip. RESULTS: We found evidence of increased epigenetic age acceleration and differences in predicted immune cell composition in patients with PSC and PBC. Epigenetic profiles demonstrated differences in predicted protein levels including increased levels of tumor necrosis factor receptor superfamily member 1B in patients with cirrhotic compared to noncirrhotic PSC and PBC. Epigenome-wide association studies of PSC discovered strongly associated 5'-C-phosphate-G-3' sites in genes including vacuole membrane protein 1 and SOCS3, and epigenome-wide association studies of PBC found strong 5'-C-phosphate-G-3' associations in genes including NOD-like receptor family CARD domain containing 5, human leukocyte antigen-E, and PSMB8. Analyses identified disease-associated canonical pathways and upstream regulators involved with immune signaling and activation of macrophages and T-cells. A comparison of PSC and PBC data found relatively little overlap at the 5'-C-phosphate-G-3' and gene levels with slightly more overlap at the level of pathways and upstream regulators. CONCLUSIONS: This study provides insights into methylation profiles of patients that support current concepts of disease mechanisms and provide novel data to inspire future research. Studies to corroborate our findings and expand into other -omics layers will be invaluable to further our understanding of these rare diseases with the goal to improve and individualize prognosis and treatment.

Noninvasive Lung Cancer Subtype Classification Using Tumor-Derived Signatures and cfDNA Methylome.

Accurate diagnosis of lung cancer is important for treatment decision-making. Tumor biopsy and histologic examination are the standard for determining histologic lung cancer subtypes. Liquid biopsy, particularly cell-free DNA (cfDNA), has recently shown promising results in cancer detection and classification. In this study, we investigate the potential of cfDNA methylome for the noninvasive classification of lung cancer histologic subtypes. We focused on the two most prevalent lung cancer subtypes, lung adenocarcinoma and lung squamous cell carcinoma. Using a fragment-based marker discovery approach, we identified robust subtype-specific methylation markers from tumor samples. These markers were successfully validated in independent cohorts and associated with subtype-specific transcriptional activity. Leveraging these markers, we constructed a subtype classification model using cfDNA methylation profiles, achieving an AUC of 0.808 in cross-validation and an AUC of 0.747 in the independent validation. Tumor copy-number alterations inferred from cfDNA methylome analysis revealed potential for treatment selection. In summary, our study demonstrates the potential of cfDNA methylome analysis for noninvasive lung cancer subtyping, offering insights for cancer monitoring and early detection. SIGNIFICANCE: This study explores the use of cfDNA methylomes for the classification of lung cancer subtypes, vital for effective treatment. By identifying specific methylation markers in tumor tissues, we developed a robust classification model achieving high accuracy for noninvasive subtype detection. This cfDNA methylome approach offers promising avenues for early detection and monitoring.

DNA methylation and stroke prognosis: an epigenome-wide association study.

BACKGROUND AND AIMS: Stroke is the leading cause of adult-onset disability. Although clinical factors influence stroke outcome, there is a significant variability among individuals that may be attributed to genetics and epigenetics, including DNA methylation (DNAm). We aimed to study the association between DNAm and stroke prognosis. METHODS AND RESULTS: To that aim, we conducted a two-phase study (discovery-replication and meta-analysis) in Caucasian patients with ischemic stroke from two independent centers (BasicMar [discovery, N = 316] and St. Pau [replication, N = 92]). Functional outcome was assessed using the modified Rankin Scale (mRS) at three months after stroke, being poor outcome defined as mRS > 2. DNAm was determined using the 450K and EPIC BeadChips in whole-blood samples collected within the first 24 h. We searched for differentially methylated positions (DMPs) in 370,344 CpGs, and candidates below p-value < 10-5 were subsequently tested in the replication cohort. We then meta-analyzed DMP results from both cohorts and used them to identify differentially methylated regions (DMRs). After doing the epigenome-wide association study, we found 29 DMPs at p-value < 10-5 and one of them was replicated: cg24391982, annotated to thrombospondin-2 (THBS2) gene (p-valuediscovery = 1.54·10-6; p-valuereplication = 9.17·10-4; p-valuemeta-analysis = 6.39·10-9). Besides, four DMRs were identified in patients with poor outcome annotated to zinc finger protein 57 homolog (ZFP57), Arachidonate 12-Lipoxygenase 12S Type (ALOX12), ABI Family Member 3 (ABI3) and Allantoicase (ALLC) genes (p-value < 1·10-9 in all cases). DISCUSSION: Patients with poor outcome showed a DMP at THBS2 and four DMRs annotated to ZFP57, ALOX12, ABI3 and ALLC genes. This suggests an association between stroke outcome and DNAm, which may help identify new stroke recovery mechanisms.

Pregnancy induced hypertension and umbilical cord blood DNA methylation in newborns: an epigenome-wide DNA methylation study.

OBJECTIVIES: Pregnancy induced hypertension (PIH) syndrome is a disease that unique to pregnant women and is associated with elevated risk of offspring cardiovascular diseases (CVDs) and neurodevelopmental disorders in their kids. Previous research on cord blood utilizing the Human Methylation BeadChip or EPIC array revealed that PIH is associated with specific DNA methylation site. Here, we investigate the whole genome DNA methylation landscape of cord blood from newborns of PIH mother. METHODS: Whole-genome bisulfite sequencing (WGBS) was used to examine the changes in whole genome DNA methylation in the umbilical cord blood of three healthy (NC) and four PIH individuals. Using methylKit, we discovered Hypo- and hyper- differentially methylated probes (DMPs) or methylated regions (DMRs) in the PIH patients' cord blood DNA. Pathway enrichments were assessed using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment assays. DMPs or DMRs relevant to the immunological, neurological, and circulatory systems were also employed for enrichment assay, Metascape analysis and PPI network analysis. RESULTS: 520 hyper- and 224 hypo-DMPs, and 374 hyper- and 186 hypo-DMRs between NC and PIH group, respectively. Both DMPs and DMRs have enhanced pathways for cardiovascular, neurological system, and immune system development. Further investigation of DMPs or DMRs related to immunological, neurological, and circulatory system development revealed that TBK1 served as a hub gene for all three developmental pathways. CONCLUSION: PIH-associated DMPs or DMRs in umbilical cord blood DNA may play a role in immunological, neurological, and circulatory system development. Abnormal DNA methylation in the immune system may also contribute to the development of CVDs and neurodevelopment disorders.

Engineered Methionine Adenosyltransferase Cascades for Metabolic Labeling of Individual DNA Methylomes in Live Cells.

Methylation, a widely occurring natural modification serving diverse regulatory and structural functions, is carried out by a myriad of S-adenosyl-l-methionine (AdoMet)-dependent methyltransferases (MTases). The AdoMet cofactor is produced from l-methionine (Met) and ATP by a family of multimeric methionine adenosyltransferases (MAT). To advance mechanistic and functional studies, strategies for repurposing the MAT and MTase reactions to accept extended versions of the transferable group from the corresponding precursors have been exploited. Here, we used structure-guided engineering of mouse MAT2A to enable biocatalytic production of an extended AdoMet analogue, Ado-6-azide, from a synthetic methionine analogue, S-(6-azidohex-2-ynyl)-l-homocysteine (N3-Met). Three engineered MAT2A variants showed catalytic proficiency with the extended analogues and supported DNA derivatization in cascade reactions with M.TaqI and an engineered variant of mouse DNMT1 both in the absence and presence of competing Met. We then installed two of the engineered variants as MAT2A-DNMT1 cascades in mouse embryonic stem cells by using CRISPR-Cas genome editing. The resulting cell lines maintained normal viability and DNA methylation levels and showed Dnmt1-dependent DNA modification with extended azide tags upon exposure to N3-Met in the presence of physiological levels of Met. This for the first time demonstrates a genetically stable system for biosynthetic production of an extended AdoMet analogue, which enables mild metabolic labeling of a DNMT-specific methylome in live mammalian cells.

Methylome analysis in girls with idiopathic central precocious puberty.

BACKGROUND: Genetic and environmental factors are implicated in many developmental processes. Recent evidence, however, has suggested that epigenetic changes may also influence the onset of puberty or the susceptibility to a wide range of diseases later in life. The present study aims to investigate changes in genomic DNA methylation profiles associated with pubertal onset analyzing human peripheral blood leukocytes from three different groups of subjects: 19 girls with central precocious puberty (CPP), 14 healthy prepubertal girls matched by age and 13 healthy pubertal girls matched by pubertal stage. For this purpose, the comparisons were performed between pre- and pubertal controls to identify changes in normal pubertal transition and CPP versus pre- and pubertal controls. RESULTS: Analysis of methylation changes associated with normal pubertal transition identified 1006 differentially methylated CpG sites, 86% of them were found to be hypermethylated in prepubertal controls. Some of these CpG sites reside in genes associated with the age of menarche or transcription factors involved in the process of pubertal development. Analysis of methylome profiles in CPP patients showed 65% and 55% hypomethylated CpG sites compared with prepubertal and pubertal controls, respectively. In addition, interestingly, our results revealed the presence of 43 differentially methylated genes coding for zinc finger (ZNF) proteins. Gene ontology and IPA analysis performed in the three groups studied revealed significant enrichment of them in some pathways related to neuronal communication (semaphorin and gustation pathways), estrogens action, some cancers (particularly breast and ovarian) or metabolism (particularly sirtuin). CONCLUSIONS: The different methylation profiles of girls with normal and precocious puberty indicate that regulation of the pubertal process in humans is associated with specific epigenetic changes. Differentially methylated genes include ZNF genes that may play a role in developmental control. In addition, our data highlight changes in the methylation status of genes involved in signaling pathways that determine the migration and function of GnRH neurons and the onset of metabolic and neoplastic diseases that may be associated with CPP in later life.