Base editors (BEs) composed of a cytidine deaminase fused to CRISPR-Cas9 convert cytidine to uridine, leading to single-base-pair substitutions in eukaryotic cells. We delivered BE mRNA or ribonucleoproteins targeting the Dmd or Tyr gene via electroporation or microinjection into mouse zygotes. F0 mice showed nonsense mutations with an efficiency of 44-57% and allelic frequencies of up to 100%, demonstrating an efficient method to generate mice with targeted point mutations.

Adenine base editors (ABEs) composed of an engineered adenine deaminase and the Streptococcus pyogenes Cas9 nickase enable adenine-to-guanine (A-to-G) single-nucleotide substitutions in a guide RNA (gRNA)-dependent manner. Here we demonstrate application of this technology in mouse embryos and adult mice. We also show that long gRNAs enable adenine editing at positions one or two bases upstream of the window that is accessible with standard single guide RNAs (sgRNAs). We introduced the Himalayan point mutation in the Tyr gene by microinjecting ABE mRNA and an extended gRNA into mouse embryos, obtaining Tyr mutant mice with an albino phenotype. Furthermore, we delivered the split ABE gene, using trans-splicing adeno-associated viral vectors, to muscle cells in a mouse model of Duchenne muscular dystrophy to correct a nonsense mutation in the Dmd gene, demonstrating the therapeutic potential of base editing in adult animals.

No abstract

Plant organelles including mitochondria and chloroplasts contain their own genomes, which encode many genes essential for respiration and photosynthesis, respectively. Gene editing in plant organelles, an unmet need for plant genetics and biotechnology, has been hampered by the lack of appropriate tools for targeting DNA in these organelles. In this study, we developed a Golden Gate cloning system1, composed of 16 expression plasmids (8 for the delivery of the resulting protein to mitochondria and the other 8 for delivery to chloroplasts) and 424 transcription activator-like effector subarray plasmids, to assemble DddA-derived cytosine base editor (DdCBE)2 plasmids and used the resulting DdCBEs to efficiently promote point mutagenesis in mitochondria and chloroplasts. Our DdCBEs induced base editing in lettuce or rapeseed calli at frequencies of up to 25% (mitochondria) and 38% (chloroplasts). We also showed DNA-free base editing in chloroplasts by delivering DdCBE mRNA to lettuce protoplasts to avoid off-target mutations caused by DdCBE-encoding plasmids. Furthermore, we generated lettuce calli and plantlets with edit frequencies of up to 99%, which were resistant to streptomycin or spectinomycin, by introducing a point mutation in the chloroplast 16S rRNA gene.

DddA-derived cytosine base editors (DdCBEs), composed of the split interbacterial toxin DddAtox, transcription activator-like effector (TALE), and uracil glycosylase inhibitor (UGI), enable targeted C-to-T base conversions in mitochondrial DNA (mtDNA). Here, we demonstrate highly efficient mtDNA editing in mouse embryos using custom-designed DdCBEs. We target the mitochondrial gene, MT-ND5 (ND5), which encodes a subunit of NADH dehydrogenase that catalyzes NADH dehydration and electron transfer to ubiquinone, to obtain several mtDNA mutations, including m.G12918A associated with human mitochondrial diseases and m.C12336T that incorporates a premature stop codon, creating mitochondrial disease models in mice and demonstrating a potential for the treatment of mitochondrial disorders.