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.

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.

Project description:Background: Dystrophic epidermolysis bullosa (DEB) is a skin blistering disease caused by mutations in COL7A1, which encodes type VII collagen (C7). There is no cure for DEB, but previous work has shown potential therapeutic benefit in increasing production of even partially functional C7. Genome-wide screens using CRISPR-Cas9 have enabled the identification of genes involved in cancer development, drug resistance, and other genetic diseases, suggesting that they could be used to identify novel drivers of C7 production. Methods: A keratinocyte C7 reporter cell line was created by integrating a tdTomato fluorescent marker into the last exon of the endogenous COL7A1 gene. A genome-wide CRISPR activation (CRISPRa) screen was performed with the C7_tdTomato reporter to identify genes and pathways that increase C7 expression. High tdTomato-expressing cells were sorted and sequenced to identify the single guide RNAs (sgRNAs) that became enriched relative to the starting material. Pathway analysis was performed on the corresponding genes to identify regulators and pathways that influence C7 expression. A targeted drug screen was performed in three different keratinocyte cell lines based on the CRISPRa screen results, and C7 upregulation was evaluated. Results: The C7_tdTomato cell line was validated as an effective reporter cell line for detection of C7 upregulation. The CRISPRa screen identified two genes, DENND4B and TYROBP as top hits based on enrichment in the high fluorescence population and representation with multiple sgRNAs. Pathway analysis of the CRISPRa screen showed enrichment of toll-like receptor and interferon-related upstream regulators and functions related to calcium uptake and immune signaling. Several compounds in the targeted drug screen increased C7 expression in at least one keratinocyte line, but only kaempferol, a plant flavonoid, significantly increased C7 mRNA and protein in a DEB patient line. Conclusions: The novel C7_tdTomato reporter cell line can be used to screen compounds for increased C7 expression. The CRISPRa screen combined with a fluorescent reporter cell line can be used to reveal mechanistic regulators of gene expression and therapeutic targets for rare genetic diseases. Kaempferol has shown promising results in increasing C7 production and should be further evaluated as a potential therapeutic for DEB patients.

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.

Dataset Information

A single-cell transcriptomics CRISPR-activation screen identifies new epigenetic regulators of the zygotic genome activation programm (10X Genomics CRISPRa screen dataset)

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