Easy-to-Use CRISPR-Cas9 Genome Editing in the Cultured Pacific Abalone (Haliotis discus hannai)

The Pacific abalone is an important aquaculture shellfish and serves as an important model in basic biology study. However, the study of abalone is limited by lack of highly efficient and easy-to-use gene-editing tools. In this paper, we demonstrate efficient gene knockout in Pacific abalone using CRISPR-Cas9. We developed a highly effective microinjection method by nesting fertilized eggs in a low-concentration agarose gel. We identified the cilia developmental gene beta-tubulin and light-sensitive transmembrane protein r-opsin as target genes and designed highly specific sgRNAs for modifying their genomic sequences. Sanger sequencing of the genomic regions of beta-tubulin and r-opsin genes from injected larvae identified various genomic long-fragment deletions. In situ hybridization showed gene expression patterns of beta-tubulin and r-opsin were significantly altered in the mosaic mutants. Knocking out beta-tubulin in abalone embryos efficiently affected cilia development. Scanning electron microscopy and swimming behavior assay showed defecting cilia and decreased motility. Moreover, knocking out of r-opsin in abalone embryos effectively affected the expression and development of eyespots. Overall, this work developed an easy-to-use mosaic gene knockout protocol for abalone, which will allow researchers to utilize CRISPR-Cas9 approaches to study unexploited abalone biology and will lead to novel breeding methods for this aquaculture species.