Nishiyama, J. et al. Neuron https://doi.org/10.1016/j.neuron.2017.10.004 (2017).

CRISPR–Cas9-mediated genome editing can occur via either nonhomologous end joining or homology-directed repair (HDR); the latter is preferable in the brain, as HDR introduces fewer errors. However, HDR in postmitotic neurons has been inefficient thus far, which has made the technology difficult to use in the adult brain. Nishiyama et al. now show that they can achieve efficient genome editing in the brains of mice at various ages by delivering the guide RNA and the HDR template through infection with adeno-associated viruses (AAVs). The source for Cas9 can either be a transgene or an AAV as well. The researchers apply the technology to introduce tags such as HA or mEGFP into postmitotic neurons with high fidelity.