Hiroshi Asahara

Conditional knockout mice are valuable tools for examining the functions of targeted genes in a time‐ and space‐specific manner. Here, we generated gene‐edited mice by using the Tol2 transposon to introduce guide RNA (gRNA) into fertilized eggs obtained by crossing LSL (loxP‐stop‐loxP)‐CRISPR‐associated 9 (Cas9) mice, which express Cas9 in a Cre‐dependent manner, with CAG‐CreER mice. Transposase mRNA and plasmid DNA, which contained a gRNA sequence for the gene encoding tyrosinase flanked by the transposase recognition sequence, were injected together into fertilized eggs. As a result, the transcribed gRNA cleaved the target genome in a Cas9‐dependent manner. Using this method, it is possible to generate conditional genome‐edited mice more easily in a shorter period of time.