Targeting fidelity of adenine and cytosine base editors in mouse embryos

Nat Commun. 2018 Nov 15;9(1):4804. doi: 10.1038/s41467-018-07322-7.


Base editing directly converts a target base pair into a different base pair in the genome of living cells without introducing double-stranded DNA breaks. While cytosine base editors (CBE) and adenine base editors (ABE) are used to install and correct point mutations in a wide range of organisms, the extent and distribution of off-target edits in mammalian embryos have not been studied in detail. We analyze on-target and proximal off-target editing at 13 loci by a variety of CBEs and ABE in more than 430 alleles generated from mouse zygotic injections using newly generated and published sequencing data. ABE predominantly generates anticipated A•T-to-G•C edits. Among CBEs, SaBE3 and BE4, result in the highest frequencies of anticipated C•G-to-T•A products relative to editing byproducts. Together, these findings highlight the remarkable fidelity of ABE in mouse embryos and identify preferred CBE variants when fidelity in vivo is critical.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenine / metabolism*
  • Alleles
  • Animals
  • Animals, Genetically Modified
  • CRISPR-Associated Protein 9 / genetics
  • CRISPR-Associated Protein 9 / metabolism
  • CRISPR-Cas Systems*
  • Cytosine / metabolism*
  • Embryo, Mammalian
  • Gene Editing / methods*
  • Genetic Loci
  • Mice
  • Microinjections
  • Point Mutation*
  • RNA, Guide, Kinetoplastida / genetics
  • RNA, Guide, Kinetoplastida / metabolism
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Zygote


  • RNA, Guide
  • Cytosine
  • CRISPR-Associated Protein 9
  • Adenine