Tissue- and time-directed electroporation of CAS9 protein-gRNA complexes <i>in vivo</i> yields efficient multigene knockout for studying gene function in regeneration.

Abstract

A rapid method for temporally and spatially controlled CRISPR-mediated gene knockout in vertebrates will be an important tool to screen for genes involved in complex biological phenomena like regeneration. Here we show that <i>in vivo</i> injection of CAS9 protein-guide RNA (gRNA) complexes into the spinal cord lumen of the axolotl and subsequent electroporation leads to comprehensive knockout of <i>Sox2</i> gene expression in SOX2⁺ neural stem cells with corresponding functional phenotypes from the gene knockout. This is particularly surprising considering the known prevalence of RNase activity in cerebral spinal fluid, which apparently the CAS9 protein protects against. The penetrance/efficiency of gene knockout in the protein-based system is far higher than corresponding electroporation of plasmid-based CRISPR systems. We further show that simultaneous delivery of CAS9-gRNA complexes directed against <i>Sox2</i> and <i>GFP</i> yields efficient knockout of both genes in <i>GFP</i>-reporter animals. Finally, we show that this method can also be applied to other tissues such as skin and limb mesenchyme. This efficient delivery method opens up the possibility for rapid <i>in vivo</i> genetic screens during axolotl regeneration and can in principle be applied to other vertebrate tissue systems.