Compact CRISPR/Cas9 systems that can be packaged into an adeno-associated virus show promise for gene therapy. However, the requirement of protospacer adjacent motifs (PAMs) restricts the target scope. To expand this repertoire, we revisited and optimized a small Cas9 orthologue derived from Streptococcus pasteurianus for efficient genome editing in vivo. We found that SpaCas9 enables potent targeting of 5'-NNGYRA-3' PAMs, which are distinct from those recognized by currently used small Cas9s; the Spa-CBE and Spa-ABE systems efficiently generated robust C-to-T and A-to-G conversions both in vitro and in vivo. In addition, by exploiting natural variation in the PAM-interacting domain, we engineered three SpaCas9... More
Compact CRISPR/Cas9 systems that can be packaged into an adeno-associated virus show promise for gene therapy. However, the requirement of protospacer adjacent motifs (PAMs) restricts the target scope. To expand this repertoire, we revisited and optimized a small Cas9 orthologue derived from Streptococcus pasteurianus for efficient genome editing in vivo. We found that SpaCas9 enables potent targeting of 5'-NNGYRA-3' PAMs, which are distinct from those recognized by currently used small Cas9s; the Spa-CBE and Spa-ABE systems efficiently generated robust C-to-T and A-to-G conversions both in vitro and in vivo. In addition, by exploiting natural variation in the PAM-interacting domain, we engineered three SpaCas9 variants to further expand the targeting scope of compact Cas9 systems. Moreover, mutant mice with efficient disruption of the Tyr gene were successfully generated by microinjection of SpaCas9 mRNA and the corresponding sgRNA into zygotes. Notably, all-in-one AAV delivery of SpaCas9 targeting the Pcsk9 gene in adult mouse liver produced efficient genome editing events and reduced its serum cholesterol. Thus, with distinct PAMs and a small size, SpaCas9 will broaden the CRISPR/Cas9 toolsets for efficient gene modifications and therapeutic applications.
