Efficient targeting of FATS at a common fragile site in mice through TALEN-mediated double-hit genome modification.

Transcription activator-like effector nucleases (TALENs) have emerged as a newly developed approach for genome editing. However, its application in targeting specific genomic loci susceptible to DNA damage remains obscure. Here, we report a modified approach for TALENs-based targeting of FATS, a fragile-site gene whose major introns have AT-rich sequence and di-nucleotide repeats. Two pairs of FATS-TALENs were designed to cleave two sites specifically at a coding exon of FATS. After in vitro transcription, the mRNA from FATS-TALEN pairs was microinjected into mouse zygotes. The targeting efficiency of two FATS-TALEN pairs in vivo was more than threefold higher than that of one FATS-TALEN pair. Moreover, large-size DNA deletions were detected, which were heritable and easily detectable by PCR. Our study indicates that the double-hit TALEN approach enhances targeting efficiency in vivo and provides convenience for monitoring germline transmission of mutations by PCR, which will facilitate the functional research on fragile-site genes.