Genomic DNA of HEK293T cells or zebrafish embryos was extracted at 50 hpf using a genome DNA extraction kit (Tiangen) following the manufacturer's protocol. In brief, cells or embryos were resuspended in cell lysis solution and incubated at 65 °C for 15 min and 95 °C for 10 min. The genomic region surrounding the CRISPR target site for each gene was PCR amplified and cloned into the pEASY vector (Transgen), which was used for Sanger sequencing (Biomed, Beijing). A total of 200-400 ng PCR products (TakaRa) were subjected to a re-annealing process to enable heteroduplex formation: 95 °C for 10 min, 95 °C to 85 °C ramping at 2 °C/s, 85 °C to 25 °C at 0.3 °C/s and holding at 25 °C for 1 min. After re-annealing, products were treated with SURVEYOR nuclease and SURVEYOR enhancer S (Transgenomic), following the manufacturer's recommended protocol, and analyzed on 10% polyacrylamide gels. Gels were stained with 0.5 μg/ml EtBr in 1× TBE for 20 min, washed in water for 20 min and imaged with a gel-imaging system (Tanon). Quantification was based on relative band intensity.