Studies Test Abilities of CRISPR-Cas9 Systems to Hit their Targets

As CRISPR/Cas comes of age, synthetic RNA-guided transcription factors are the stars of two independent studies published in Nature Methods today. 

The first, from Duke University’s Charles Gersbach, Ph.D., and his colleagues present a Cas9-based transactivator targeted to DNA sequences by guide RNA molecules. In their paper, Dr. Gersbach et al. show that coexpression of this transactivator plus combinations of guide RNAs in human cells “induced specific expression of endogenous target genes, demonstrating a simple and versatile approach for RNA-guided gene activation,” they write.

Separately, J. Keith Joung, M.D., Ph.D., and his colleagues at Massachusetts General Hospital show that single or multiple short guide RNAs (gRNAs) can direct dCas9 fused to a VP64 transcriptional activation domain to increase expression of endogenous human genes. “This proof-of-principle work shows that [CRISPR]-Cas systems can target heterologous effector domains to endogenous sites in human cells,” Dr. Joung et al. write.

CRISPR RNA-guided nuclease—or RGNs—are not without their potential pitfalls, however. In June, MGH’s Dr. Joung and colleagues reported having found that CRISPR-associated RGNs readily produce off-target alterations. 

“RNA-guided gene activation by CRISPRCas9-based transcription factors” and “CRISPR RNA-guided activation of endogenous human genes” appeared online in Nature Methods July 25.