Molecular therapy : the journal of the American Society of Gene Therapy
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Exome and deep sequencing of cells treated with a panel of lentiviral guide RNA demonstrate that both on- and off-target editing proceed in a time-dependent manner. Thus, methods to temporally control Cas9 activity would be beneficial. To address this need, we describe a "self-inactivating CRISPR (SiC)" system consisting of a single guide RNA that deactivates the Streptococcus pyogenes Cas9 nuclease in a doxycycline-dependent manner. ⋯ This tool facilitates diverse applications including (1) the timed regulation of genetic knockouts in hard-to-transfect cells using lentivirus, including human leukocytes for the identification of glycogenes regulating leukocyte-endothelial cell adhesion; (2) genome-wide lentiviral sgRNA (single guide RNA) library applications where Cas9 activity is ablated after allowing pre-determined editing times. Thus, stable knockout cell pools are created for functional screens; and (3) temporal control of Cas9-mediated editing of myeloid and lymphoid cells in vivo, both in mouse peripheral blood and bone marrow. Overall, SiC enables temporal control of gene editing and may be applied in diverse application including studies that aim to reduce off-target genome editing.
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Dravet syndrome (DS) is a severe epileptic encephalopathy caused mainly by heterozygous loss-of-function mutations of the SCN1A gene, indicating haploinsufficiency as the pathogenic mechanism. Here we tested whether catalytically dead Cas9 (dCas9)-mediated Scn1a gene activation can rescue Scn1a haploinsufficiency in a mouse DS model and restore physiological levels of its gene product, the Nav1.1 voltage-gated sodium channel. We screened single guide RNAs (sgRNAs) for their ability to stimulate Scn1a transcription in association with the dCas9 activation system. ⋯ To test the therapeutic potential of this approach, we delivered the Scn1a-dCas9 activation system to DS pups using adeno-associated viruses. Parvalbumin interneurons recovered their firing ability, and febrile seizures were significantly attenuated. Our results pave the way for exploiting dCas9-based gene activation as an effective and targeted approach to DS and other disorders resulting from altered gene dosage.