Engineering a photoactivatable A-to-I RNA base editor for gene therapy in vivo.

Tunable and reversible regulation of exogenous and endogenous gene expression would be useful for improving the safety and efficacy of gene therapy. Current chemically inducible systems are limited by the rapid diffusion and extended metabolism of small molecules, and associated side effects. Here we develop a photoactivatable RNA adenosine base editor (PA-rABE) by harnessing a compact Cas13 variant and a split ADAR2 deaminase fused with the Magnets system, which is activated through blue-light-induced dimerization. PA-rABE achieves highly efficient editing on endogenous RNA with minimal bystander editing and off-target effects. By editing a phosphorylation site of the endogenous CTNNB1 gene, PA-rABE stabilizes the β-catenin protein and activates Wnt signaling in vivo. Using adeno-associated virus vectors to deliver PA-rABE along with an hF9 variant containing a premature termination codon, we show amelioration of clotting defects in hemophilia B mice upon illumination. In summary, PA-rABE offers a controlled RNA base-editing technology for diverse biomedical applications, enabling reversible and spatiotemporally specific modulation.