Establishment of an Integrated CRISPR/Cas9 Plasmid System for Simple and Efficient Genome Editing in Medaka In Vitro and In Vivo

SIMPLE SUMMARY: The application of CRISPR/Cas9 genome editing in fish is limited to date. An easy-to-use, economical and effective genome editing system is greatly needed. In this study, we established an integrated pCas9-U6sgRNA plasmid system, the sgRNA of which was driven by U6 promoters from different fish species. Taking medaka as an example, our results suggest that pCas9-U6sgRNA driven by endogenous U6 promoter (pCas9-mU6sgRNA) can very effectively mediate gene knock-out in medaka cultured cells, but not by exogenous U6 promoter. The gene editing efficiency of pCas9-mU6sgRNA was up to 93.7% with no detectable off-target. By one-cell embryo microinjection, pCas9-mU6sgRNA can effectively mediate gene knock-out in vivo as well. Furthermore, the gene knock-in at a specific site was efficiently achieved in vitro as well as in vivo through application of pCas9-mU6sgRNA. In conclusion, we have successfully developed a simple, low-cost and effective CRISPR/Cas9 system suitable for medaka gene knock-out and knock-in at a specific site in vitro and in vivo. This study provides an insight into other fish gene manipulation and greatly promotes functional gene studies. ABSTRACT: 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.