Phase-separated DropCRISPRa platform for efficient gene activation in mammalian cells and mice

Liquid-liquid phase separation (LLPS) plays a critical role in regulating gene transcription via the formation of transcriptional condensates. However, LLPS has not been reported to be engineered as a tool to activate endogenous gene expression in mammalian cells or in vivo. Here, we developed a droplet-forming CRISPR (clustered regularly interspaced short palindromic repeats) gene activation system (DropCRISPRa) to activate transcription with high efficiency via combining the CRISPR-SunTag system with FETIDR-AD fusion proteins, which contain an N-terminal intrinsically disordered region (IDR) of a FET protein (FUS or TAF15) and a transcription activation domain (AD, VP64/P65/VPR). In this system, the FETIDR-AD fusion protein formed phase separation condensates at the target sites, which could recruit endogenous BRD4 and RNA polymerase II with an S2 phosphorylated C-terminal domain (CTD) to enhance transcription elongation. IDR-FUS9Y>S and IDR-FUSG156E, two mutants with deficient and aberrant phase separation respectively, confirmed that appropriate phase separation was required for efficient gene activation. Further, the DropCRISPRa system was compatible with a broad set of CRISPR-associated (Cas) proteins and ADs, including dLbCas12a, dAsCas12a, dSpCas9 and the miniature dUnCas12f1, and VP64, P65 and VPR. Finally, the DropCRISPRa system could activate target genes in mice. Therefore, this study provides a robust tool to activate gene expression for foundational research and potential therapeutics.