Silkworm mutagenesis using a ribonucleoprotein-based CRISPR/Cas12a system.

The development of highly efficient genome editing tools has revolutionized developmental biology and genetic studies in silkworm. Although methods based on CRISPR/Cas9 are currently popular, the Cas12a system has emerged as a promising option. However, it has not yet been applied to target the silkworm genome in vivo, and its activity in silkworm has not yet been characterized. In this study, we established a ribonucleoprotein-based CRISPR/Cas12a system, and compared it to the CRISPR/Cas9 system using 19 crRNA and 17 sgRNAs to target three different genes in vivo. Although Cas12a generates mutants less efficiently than Cas9, we used it successfully to generate transmissible indels, and demonstrated its application by targeting the FibH and mp genes to produce mutants with the expected phenotypes. We also assessed the influence of temperature (37 °C vs. 25 °C) on Cas12a activity, and demonstrated that the effects are target dependent. In summary, we have established a ribonucleoprotein-based CRISPR/Cas12a system in silkworm that offers a practical alternative to CRISPR/Cas9 and extends the genome editing tool box available for silkworm research.