Exogenous DNA can be a template to precisely edit a cell’s genome. However, the delivery of in vitro-produced DNA to target cells can be inefficient, and low abundance of template DNA may underlie the low rate of precise editing. One potential tool to produce template DNA inside cells is a retron, a bacterial retroelement involved in phage defense. However, little effort has been directed at optimizing retrons to produce designed sequences. Here, we identify modifications to the retron non-coding RNA (ncRNA) that result in more abundant reverse-transcribed DNA (RT-DNA). By testing architectures of the retron operon that enable efficient reverse transcription, we find that gains in DNA production are portable from prokaryotic to eukaryotic cells and result in more efficient genome editing. Finally, we show that retron RT-DNA can be used to precisely edit cultured human cells. These experiments provide a general framework to produce DNA using retrons for genome modification.
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Custom code to process or analyze data from this study is available on GitHub at https://github.com/Shipman-Lab/retron_architectures.
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This work was supported by funding from the Simons Foundation Autism Research Initiative (SFARI) Bridge to Independence Award Program, the Pew Biomedical Scholars Program and a UCSF Program for Breakthrough Biomedical Research New Frontiers Research Award. S.L.S. acknowledges additional funding support from NIH/NIGMS (1DP2GM140917-01) and the L.K. Whittier Foundation. S.C.L. was supported by a Berkeley Fellowship for Graduate Study. K.D.C. was supported by an NSF Graduate Research Fellowship (2019247827) and a UCSF Discovery Fellowship. S.K.L. was supported by an NSF Graduate Research Fellowship (2034836). We thank K. Claiborn for editorial assistance.
S.L.S., S.C.L. and K.D.C. are inventors on patent applications related to the technologies described in this work.
Peer review information Nature Chemical Biology thanks Channabasavaiah Gurumurthy and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
a. Schematic of the sequencing prep pipeline for RT-DNA. b. Representative image of a PAGE analysis showing the addition of nucleotides to the 3’ end of a single-stranded DNA, controlled by reaction time. The experiment was repeated twice with similar results. c. Alternate analysis of the RT-DNA for the a1/a2 length library, using a TdT-based sequencing preparation. Related to Fig. 2.
a. Representative image of a PAGE analysis of Eco1 and Eco2 RT-DNA isolated from yeast. The ladder is shown at a different exposure to the left of the gel image. The experiment was repeated twice with similar results. b. Enrichment of the Eco1 RT-DNA/plasmid template when uninduced compared to a dead RT construct. Closed circles show each of three biological replicates, with red for the dead RT version and black for the live RT. c. Identical analysis as in b, but for Eco1 in HEK293T cells. Related to Fig. 3.
a-c. Percent of cells precisely edited, quantified by multiplexed sequencing, for the wt (black) and extended (green) recombineering constructs for three additional loci in E coli. Related to Fig. 4a–d.
a. Percent of ADE2 loci with imprecise edits or sequencing errors at 24 and 48 hours. Closed circles show each of three biological replicates, with black for the wt a1/a2 length and green for the extended a1/a2 (two extended versions, v1 and v2). Induction conditions are shown below the graph for the RT and Cas9. b. Breakdown of the data in a. by type of edit/error. c. Imprecise edits and sequencing errors found in all data sets, ranked by frequency. Above the graph are the wt ADE2 locus and intended precise edit. On the Y axis are the imprecise edits and sequencing errors found. X axis represents count of each sequence in all data sets. Related to Fig. 4h.
a-d. Percent of cells precisely edited, quantified by multiplexed sequencing, for the wt (black) and extended (green) recombineering constructs for four additional loci in S. cerevisiae at 24 and 48 hours. Cultures edited at the LYP1 E27X site were not viable beyond 24 hours. e-h. Percent of imprecise edits or sequencing errors for the loci in a-d. Related to Fig. 4e–h.
a-f. Percent of cells imprecisely edited (indels), quantified by multiplexed sequencing, in the presence of the ncRNA/gRNA plasmid and either Cas9 alone or Cas9 and Eco1 RT (as indicated below). Individual circles represent each of three biological replicates. Related to Fig. 5.
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Lopez, S.C., Crawford, K.D., Lear, S.K. et al. Precise genome editing across kingdoms of life using retron-derived DNA. Nat Chem Biol 18, 199–206 (2022). https://doi.org/10.1038/s41589-021-00927-y