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www.clinicalomics.com November/December 2017 Clinical OMICs 3 (continued on next page) News Repair Rather than Replace Feng Zhang-Led Team Develops New CRISPR Version that Targets and Edits RNA By Alex Philippidis A new version of the gene-editing tool CRISPR (clus- tered regularly interspaced short palindromic repeats) has been developed by a research team led by Feng Zhang, Ph.D., which says its ability to target and edit RNA pres- ents several advantages over its familiar DNA-editing counterpart. Zhang, of the Broad Institute of MIT and Harvard, an orig- inal innovator of CRISPR/Cas9 technology, and colleagues, said this new CRISPR—which uses a version of the Cas13 enzyme—would enable transient edits that can be more eas- ily reversed. That would thus allow the potential for tempo- ral control over editing outcomes, as well as avoid the ethical issues that have arisen around DNA germline editing. The researchers closely characterized new subfamilies of Cas, uncovering an active version of Cas13, called Cas13b. They designed a version of Cas13b and fused it with the ADAR protein, resulting in a platform they called RNA Editing for Programmable A to I Replacement (REPAIR). "REPAIR presents a promising RNA-editing platform with broad applicability for research, therapeutics, and biotechnology," the researchers wrote in "RNA editing with CRISPR-Cas13," published today in the journal Sci- ence. "The temporary nature of REPAIR-mediated edits will likely be useful for treating diseases caused by temporary changes in cell state, such as local inflammation, and could also be used to treat disease by modifying the function of proteins involved in disease-related signal transduction. "REPAIR provides a new approach for treating genetic disease or mimicking protective alleles, and establishes RNA editing as a useful tool for modifying genetic func- tion," Zhang and colleagues concluded. Likely Many More Molecules The discovery of CRISPR/Cas13 "points out that there are likely many more molecules in the CRISPR kingdom that should be evaluated for their natural capability as supe- rior tools for editing—in this case, RNA," said Stanley Qi, Ph.D., of Stanford University, speaking exclusively to Clinical OMICs. Qi developed the dCas9 technology for non-editing genome engineering, including CRISPR interference (CRIS- PRi) for sequence-specific transcription regulation; and dCas9 for genome imaging in living cells. He is an assis- tant professor in the department of bioengineering, depart- ment of chemical & systems biology, a faculty member of the interdisciplinary research institute Stanford ChEM-H (Chemistry, Engineering & Medicine for Human Health), and an editorial board member of The CRISPR Journal, an international, multidisciplinary peer-reviewed journal to be launched in 2018 by Clinical OMICs publisher Mary Ann Liebert, Inc. "Undoubtedly, the new discoveries provide useful and powerful tools for RNA editing, when fused with ADAR enzymes. But it also inspires further questions—such as what are the structural and biochemical features that makes one Cas13 better than another? Ultimately, the ability to design synthetic molecules as Cas9 or Cas13 should be the dreams of bioengineers," Qi added. One example cited by the researchers of how helpful REPAIR editing could prove against disease is that it would allow the re-coding of some serine, threonine, and tyrosine residues targeted by kinases: "Phosphorylation of these res- idues in disease-relevant proteins affects disease progres- sion for many disorders including Alzheimer 's disease and multiple neurodegenerative conditions." Another potential application of REPAIR would be to tran- The new CRISPR, using a version of the Cas13 enzyme, would enable transient edits that are more easily reversed. vchal / Getty Images