CRISPR-Cas9 technologies have dramatically increased the ease of targeting DNA sequences in the genomes of living systems. Fusion of chromatin-modifying domains to the nuclease-deactivated dCas9 has enabled targeted epigenome editing in both cultured cells and animal models. However, delivering large dCas9 fusion proteins to target cells and tissues is an obstacle to widespread adoption of these tools for in vivo studies. Here we describe the generation and characterization of two conditional transgenic mouse lines for epigenome editing, Rosa26:LSL-dCas9-p300 for gene activation and Rosa26:LSL-dCas9-KRAB for gene repression. By targeting gRNAs to transcriptional start sites or distal enhancer elements, we demonstrate regulation of target genes and corresponding changes to epigenetic states and downstream phenotypes in the brain and liver in vivo , and in T cells and fibroblasts ex vivo . These mouse lines are convenient and valuable tools for facile, temporally controlled, and tissue-restricted epigenome editing and manipulation of gene expression in vivo .

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