Highly efficient in vivo C-to-T base editing in Atlantic salmon (Salmo salar) – A step towards aquaculture precision breeding

Abstract

The salmon industry has the potential to provide nutritious food to the expanding world population. However, the industry faces several sustainability challenges related to environmental impact and fish welfare. Genome editing presents a promising approach for precision breeding, where small, targeted changes to the fish genome may facilitate the introduction of advantageous traits like disease resistance, delayed maturation, or enhanced growth. This study presents the first application of base editing in an aquaculture fish species. By co-injecting cytidine base editor AncBE4max mRNA and gRNA targeting the pigmentation gene solute carrier family 45 member 2 in Atlantic salmon embryos, we were able to induce a specific C-to-T conversion, thereby introducing a premature stop codon and achieving an albino phenotype. High-throughput sequencing revealed an average of 50–66% correct conversion of the target base depending on the base editor mRNA concentration and up to 89% in a single individual. Our results suggest that AncBE4max provides a simple and efficient approach to making precise single nucleotide edits in the Atlantic salmon genome. Additionally, we used conventional CRISPR/Cas9 combined with oligonucleotide templates to insert point mutations at various positions up- and downstream of the Cas9 cleavage site, demonstrating that the insertion efficiency was affected by the position of the mutation. The application of genome editing tools that allow for precise changes in this species is a step towards aquaculture precision breeding and the introduction of traits promoting a more sustainable industry.