Project description:It remains unclear how ESCs rapidly establish enhancer regulatory elements to activate lineage-specific genes at the earliest differentiation stages. Previous studies suggest that some tissue-specific enhancers are pre-marked in ESCs with permissive features that support their competence to induce gene expression in response to the binding of lineage transcription factors (TFs). However, the absence of functional assays to identify chromatin regions with the competence to activate gene expression upon TF binding has impeded to better define any pre-marking features and their role on the transcriptional competence of the chromatin. To address this, we leveraged a CRISPR-activation(a) system to systematically interrogate the presence of chromatin regions able to induce the expression of 5 lineage-specific genes that are inactive in human ESCs (hESCs). Multiple CRISPRa screens discovered 42 regions, which we termed Competent Chromatin Regions (CCRs), that can induce the expression of the 5 lineage genes upon CRISPRa targeting. ChIP seq analyses showed that CCRs do not represent primed or active enhancers, since they are not enriched in H3K4me1 or H3K27ac histone modifications. Instead, CCRs exhibit a significant enrichment in POU sequence motifs, along with higher levels of binding by OCT4 and other pluripotent TFs. CCRs have an enriched presence of several repressive and activating chromatin-associated factors, including the DNA demethylation factors TET1 and QSER1 and various HDAC enzymes, which regulate their transcriptional competence. Although CCRs are exclusively found at the topologically associated domains shared with their related genes, we found they do not require an enrichment in pre-established chromatin contacts to exert their function. To assess the extent of our findings, we simulated the earliest stages of lineage differentiation by inducing the expression of the lineage TF FOXA2 in undifferentiated hESCs and we found it preferentially binds to the regions predicted as CCRs. Our results suggest that the factors enriched at CCRs facilitate the binding of lineage TFs and enable ESCs to promptly activate the expression of lineage genes. This study advances our understanding of pluripotency regulation in ESCs by identifying a novel type of regulatory regions that supports their developmental plasticity.

Project description:It remains unclear how ESCs rapidly establish enhancer regulatory elements to activate lineage-specific genes at the earliest differentiation stages. Previous studies suggest that some tissue-specific enhancers are pre-marked in ESCs with permissive features that support their competence to induce gene expression in response to the binding of lineage transcription factors (TFs). However, the absence of functional assays to identify chromatin regions with the competence to activate gene expression upon TF binding has impeded to better define any pre-marking features and their role on the transcriptional competence of the chromatin. To address this, we leveraged a CRISPR-activation(a) system to systematically interrogate the presence of chromatin regions able to induce the expression of 5 lineage-specific genes that are inactive in human ESCs (hESCs). Multiple CRISPRa screens discovered 42 regions, which we termed Competent Chromatin Regions (CCRs), that can induce the expression of the 5 lineage genes upon CRISPRa targeting. ChIP seq analyses showed that CCRs do not represent primed or active enhancers, since they are not enriched in H3K4me1 or H3K27ac histone modifications. Instead, CCRs are characterized by the enriched occupancy of OCT4, NANOG and demethylation factors TET1 and QSER1, which prevent DNA hypermethylation. Although CCRs are exclusively found at the topologically associated domains shared with their related genes, we found they do not require an enrichment in pre-established chromatin contacts to exert their function. To assess the extent of our findings, we simulated the earliest stages of lineage differentiation by inducing the expression of the lineage TF FOXA2 in undifferentiated hESCs and we found it preferentially binds to the regions predicted as CCRs. Our results suggest that the factors enriched at CCRs facilitate the binding of lineage TFs and enable ESCs to promptly activate the expression of lineage genes. This study advances our understanding of pluripotency regulation in ESCs by identifying a novel type of regulatory regions that supports their developmental plasticity.

Project description:Zygotic genome activation (ZGA) is a crucial developmental milestone that remains poorly understood. This first essential transcriptional event in embryonic development coincides with extensive epigenetic reprogramming and is orchestrated, in part, by the interplay of transcriptional and epigenetic regulators. Here, we developed a novel high-throughput screening method that combines pooled CRISPR-activation (CRISPRa) with single-cell transcriptomics and applied this method to systematically probe candidate regulators of ZGA-like transcription. We screened 230 epigenetic and transcriptional factors by upregulating their expression with CRISPRa in mouse embryonic stem cells (ESCs). Through single-cell RNA-sequencing (scRNA-seq), we generated approximately 200,000 single-cell transcriptomes of CRISPRa-perturbed cells, each transduced with a unique short-guide RNA (sgRNA) targeting a specific candidate gene promoter. Using multi-omics factor analysis (MOFA) of the perturbation scRNA-seq profiles, we characterized molecular signatures of ZGA and uncovered 24 factors that promote a ZGA-like response in ESCs, both in the coding and non-coding transcriptome. We further validated nine candidate genes by arrayed CRISPRa analysed by bulk transcriptomics, which demonstrates that the combination of CRISPRa with scRNA-seq is a powerful and valid approach to identify regulators of ZGA-like transcription. Additional cDNA overexpression assays for three top hits, the DNA binding protein Dppa2, the chromatin remodeller Smarca5 and the transcription factor Patz1, confirmed these factors as ZGA-like regulators by alternative methods. Supporting these findings, Dppa2 and Smarca5 knock-out ESCs lose expression of ZGA genes and functional experiments revealed that Smarca5’s regulation of ZGA-like transcription is dependent on Dppa2. Together, our single-cell transcriptomic profiling of CRISPRa-perturbed cells provides comprehensive system-level insights into the molecular mechanisms that orchestrate ZGA.

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Discovery of Competent Chromatin Regions in Human Embryonic Stem Cells [PRO-Seq]

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