Comparison of CRISPR/Cas9 and TALENs on editing an integrated EGFP gene in the genome of HEK293FT cells

Zuyong He, Chris Proudfoot, C. Bruce A. Whitelaw, Simon G. Lillico

Genome editors such as CRISPR/Cas9 and TALENs are at the forefront of research into methodologies for targeted modification of the mammalian genome. To date few comparative studies have been carried out to investigate the difference of genome editing characteristics between CRISPR/Cas9 and TALENs. While the CRISPR/Cas9 system has overtaken TALENs as the tool of choice for most research groups working in this field, we hypothesized that there could be certain applications whereby the application of TALENs would have specific benefits. Here we compare CRISPR/Cas9 and TALEN as tools for introducing site-specific editing events at an integrated EGFP gene in the genome of HEK293FT cells. Guide RNAs and TALEN pairs were designed to target two loci within the EGFP gene. We found that paired Cas9 nucleases induced targeted genomic deletion more efficiently and precisely than two TALEN pairs. However, when concurrently supplied with a plasmid template spanning the two DNA double-strand breaks (DSBs) within EGFP, TALENs stimulated homology directed repair (HDR) more efficiently than CRISPR/Cas9 and caused fewer targeted genomic deletions. Our data suggest that the choice of genome editing tool should be determined by the desired genome editing outcome. Such a rational approach is likely to benefit research outputs for groups working in fields as diverse as modification of cell lines, to animal models for disease studies, or gene therapy strategies.