Although CRISPR/Cas9 has been used in gene manipulation of several fish species in vivo, its application in fish cultured cells is still challenged and limited. In this study, we established an integrated CRISPR/Cas9 plasmid system and evaluated its efficiency of gene knock-out or knock-in at a specific site in medaka (Oryzias latipes) in vitro and in vivo. By using the enhanced green fluorescent protein reporter plasmid pGNtsf1, we demonstrate that pCas9-U6sgRNA driven by endogenous U6 promoter (pCas9-mU6sgRNA) mediated very high gene editing efficiency in medaka cultured cells, but not by exogenous U6 promoters. After optimizing the conditions, the gene editing efficiencies of eight sites targeting for four endogenous genes were calculated, and the highest was up to 94% with no detectable off-target. By one-cell embryo microinjection, pCas9-mU6sgRNA also mediated efficient gene knock-out in vivo. Furthermore, pCas9-mU6sgRNA efficiently mediated gene knock-in at a specific site in medaka cultured cells as well as embryos. Collectively, our study demonstrates that the genetic relationship of U6 promoter is critical to gene editing efficiency in medaka cultured cells, and a simple and efficient system for medaka genome editing in vitro and in vivo has been established. This study provides an insight into other fish genome editing and promotes gene functional analysis.
Keywords: CRISPR/Cas9; U6 promoter; fish cultured cells; knock-in; knock-out; medaka.