Enhancements of the CRISPR-Cas System in the Silkworm Bombyx mori

The silkworm (Bombyx mori) is a lepidopteran model insect that has been utilized for basic research and industrial applications. In this species, transcription activator-like effector nucleases (TALENs) have been found to function efficiently, and we previously developed a TALEN-mediated genome editing system for knockout and knock-in experiments using plasmids and single-stranded oligodeoxynucleotides (ssODNs) as donors. By contrast, clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9)-mediated genome editing, especially for gene integration, remains limited. In this study, we attempted to improve CRISPR-Cas systems to expand the utility of genome editing in the silkworm. Codon optimization of Cas9 improved genome editing efficiency, and single-guide RNA utilization also resulted in a higher genome editing efficiency than crRNA/tracrRNA when Cas9 messenger RNA (mRNA) was used. CRISPR-Cas12a-mediated genome editing and targeted sequence integration using ssODNs were both successfully performed. Overall, our study provides a robust technical platform that can facilitate basic and applied silkworm studies.