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Maternal SMARCA5 is required for major ZGA in mouse [NOME-seq]

ABSTRACT: Zygotic genome activation in mice happens in two waves, a minor wave in the 1 cell embryo, and a major wave at the two-cell stage, both accompanied by global transcriptional and epigenetic reprogramming. However, the orchestration of these reprogramming events by maternal factors deposited in the oocyte is not yet entirely understood. We and others have recently shown that epigenetic modifiers such as SMARCA5 (the main ATPase in ISWI complexes), can initiate the ZGA transcriptional programme in vitro. So far, the role of SMARCA5 in ZGA in vivo has not been addressed, as constitutive knock-out mice lacking SMARCA5 are not viable. We have overcome this issue by using the targeted protein-depletion system Trim-Away. Degradation of SMARCA5 in early zygotes in combination with single cell multi-omics methods allow us to investigate its role in transcription, DNA methylation and chromatin accessibility during ZGA, as well as the wider impact of the lack of maternal SMARCA5 on embryonic development. We show that in absence of SMARCA5, major ZGA transcription is downregulated, whereas maternal and other genes are upregulated. Our results show that the global accessibility at the two-cell stage is higher than in a wild-type context, and that major ZGA gene promoters are not following that global trend but remain less accessible in SMARCA5 depleted embryos. Moreover, while the accessibility of repeat elements like MERVL increases, so does the methylation level in these regions, suggesting that SMARCA5 might indirectly influence more than just the chromatin accessibility during these stages.

ORGANISM(S): Mus musculus

PROVIDER: GSE248179 | GEO | 2024/09/18

REPOSITORIES: GEO

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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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Maternal SMARCA5 is required for major ZGA in mouse [NOME-seq]

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