Dear Editor,
With its advantages of simple design and cost-efficiency,the CRISPR/Cas9 technology has been widely adapted for genome editing in different species including zebrafish [1].In zebrafish studies,guide RNA (gRNA) is usually produced via in vitro transcription followed by microinjection with Cas9 mRNA into embryos.The vectors currently used for production of gRNA contain either a T7 or SP6 promoter in vitro or U6 promoter in vivo.Among these,T7 promoter is most popularly used due to its high efficiency and,therefore,limits the gRNA targeting sites to an optimal "GG-N18-NGG" format [2].