Generation of Cell Lines Stably Expressing a dCas9-Fusion or sgRNA to Address Dynamics of Long-Term Effects of Epigenetic Editing

Epigenetic modifications play a crucial role in regulating gene expression patterns. Through epigenetic editing approaches, the chromatin structure is modified and the activity of the targeted gene can be reprogrammed without altering the DNA sequence. By using the CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic repeats) platform with nuclease-deactivated dCas9 proteins to direct epigenetic effector domains (EDs) to genomic regulatory regions, the expression of the targeted gene can be modulated. However, the long-term stability of these effects, although demonstrated, remains unpredictable. The versatility and flexibility of (co-)targeting different genes with multiple epigenetic effectors has made the CRISPR/dCas9 platform the most widely used gene modulating technology currently available. Efficient delivery of large dCas9-ED fusion constructs into target cells, however, is challenging. An approach to overcome this limitation is to generate cells that stably express sgRNA(s) or dCas9-ED constructs. The sgRNA(s) or dCas9-ED stable cell lines can be used to study the mechanisms underlying sustained gene expression reprogramming by transiently expressing the other of the two constructs. Here, we describe a detailed protocol for the engineering of cells that stably express CRISPR/dCas9 or sgRNA. Creating a system where one component of the CRISPR/dCas9 is stably expressed while the other is transiently expressed offers a versatile platform for investigating the dynamics of epigenetic reprogramming.