CRISPR-mediated editing of cis-regulatory elements in early mouse embryos: a tool for studying pluripotency gene regulation.

In brief Cis-regulatory elements and transcription factor binding motifs play crucial roles in regulating the spatial and temporal patterns of gene expression during development. This study tested the utility of CRISPR/Cas9 as a tool to interrogate the function of transcription factor AP2 gamma motifs in pluripotency gene expression during mouse preimplantation embryo development. Abstract Clustered regularly interspaced short palindromic repeat/CRISPR-associated nuclease 9 (CRISPR/Cas9) is a highly efficient tool that enables the generation of gene knockouts, knock-ins, and single base substitutions in a variety of organisms. Recently, we used CRISPR to examine the activity of cis-regulatory elements (CREs) in mouse preimplantation embryos. However, there is limited information on the feasibility of using CRISPR in preimplantation embryos to interrogate the function of select transcription factor (TF) binding motifs located within critical CREs in pluripotency genes. In the current study we employed CRISPR to disrupt TF AP2 gamma (TFAP2C) binding motifs located within key CREs involved in the regulation of Pou5f1 and Sox2 expression in early embryos. Microinjection of ribonucleoprotein complexes containing Cas9 and single guide RNAs (sgRNAs) targeting TFAP2C motifs located within a distal enhancer and proximal promoter substantially impaired Pou5f1 and Sox2 expression, respectively. Quantification of the editing efficiencies at each targeted CRE revealed that the targeting sgRNA sequences and the number of sgRNAs injected influenced the overall editing rates. Lastly, we investigated whether TFAP2C-induced activation of Sox2 expression in 2-cell embryos required TFAP2C motifs located within the Sox2 proximal promoter. CRISPR-mediated editing of these motifs diminished the activation of Sox2 expression. In summary, these findings indicate that CRISPR/Cas9 is a feasible approach for editing TF motifs in preimplantation embryos and provide evidence that TFAP2C directly contributes to Pou5f1 and Sox2 expression in preimplantation embryos.