A Cas9-mediated adenosine transient reporter enables enrichment of ABE-targeted cells

Nicholas Brookhouser, Toan Nguyen, Stefan J. Tekel, Kylie Standage-Beier, Xiao Wang, David A. Brafman

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


Background: Adenine base editors (ABE) enable single nucleotide modifications without the need for double-stranded DNA breaks (DSBs) induced by conventional CRIPSR/Cas9-based approaches. However, most approaches that employ ABEs require inefficient downstream technologies to identify desired targeted mutations within large populations of manipulated cells. In this study, we developed a fluorescence-based method, named “Cas9-mediated adenosine transient reporter for editing enrichment” (CasMAs-TREE; herein abbreviated XMAS-TREE), to facilitate the real-time identification of base-edited cell populations. Results: To establish a fluorescent-based assay able to detect ABE activity within a cell in real time, we designed a construct encoding a mCherry fluorescent protein followed by a stop codon (TGA) preceding the coding sequence for a green fluorescent protein (GFP), allowing translational readthrough and expression of GFP after A-to-G conversion of the codon to “TGG.” At several independent loci, we demonstrate that XMAS-TREE can be used for the highly efficient purification of targeted cells. Moreover, we demonstrate that XMAS-TREE can be employed in the context of multiplexed editing strategies to simultaneous modify several genomic loci. In addition, we employ XMAS-TREE to efficiently edit human pluripotent stem cells (hPSCs), a cell type traditionally resistant to genetic modification. Furthermore, we utilize XMAS-TREE to generate clonal isogenic hPSCs at target sites not editable using well-established reporter of transfection (RoT)-based strategies. Conclusion: We established a method to detect adenosine base-editing activity within a cell, which increases the efficiency of editing at multiple genomic locations through an enrichment of edited cells. In the future, XMAS-TREE will greatly accelerate the application of ABEs in biomedical research.

Original languageEnglish (US)
Article number193
JournalBMC Biology
Issue number1
StatePublished - Dec 2020


  • Base editor
  • Genome modification
  • Human pluripotent stem cells
  • Multiplexing

ASJC Scopus subject areas

  • Biotechnology
  • Structural Biology
  • Ecology, Evolution, Behavior and Systematics
  • Physiology
  • General Biochemistry, Genetics and Molecular Biology
  • General Agricultural and Biological Sciences
  • Plant Science
  • Developmental Biology
  • Cell Biology


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