Swiech et al. used AAV vectors to mutate target genes in adult mouse brains. This paper is notable for the careful measurement of on-target mutation efficiencies in vivo, including from single cell nuclei, which strongly indicated that about ~65% of transduced brain cells acquired mutations in both alleles of their initial target gene (Mecp2). Off-target effects were apparently low (0-1.6 % rates of mutation at the "top predicted off-target" for each of 3 Dnmt family genes, measured in GFP+ cells). With their AAV vectors, one vector supplies Cas9 production and the other expresses the guide RNA and also GFP; thus fluorescence indicates transduction. They also introduce an AAV vector that coexpresses up to 3 guide RNAs + GFP for multiplexed targeting.
In vivo interrogation of gene function in the mammalian brain using CRISPR-Cas9
Nature Biotechnology. 19 October 2014