Generation of myostatin gene-edited blotched snakehead (Channa maculata) using CRISPR/Cas9 system

Blotched snakehead (Channa maculata) is one of the most important freshwater fish in China. Genome editing is of great potential in generating new snakehead strains with valuable economic traits without integration of exogenous genes. Myostatin (Mstn) inhibits the development and growth of skeletal muscle in vertebrates, including teleosts. Mstn mutations induced by genome editing can stimulate muscle growth and development, therefore Mstn is an appropriate candidate to breed the fast-growing snakehead strain. For this study, one orthologous Mstn gene was characterized in C. maculata, designated as CmMstn, which possessed the relatively conserved gene and protein structure. CmMstn had the highest expression level and sexual dimorphism in muscles. Two CRISPR/Cas9 target sites were designed to generate knockout mutants within the mature mRNA sequence of CmMstn located in Exon I and Exon II. 1 nL mixture solution of 200 pg gRNA and 300 pg Cas9 protein was directly microinjected into each snakehead embryonic yolk at 1⁓4 cell stage. Mstn was efficiently edited by CRISPR/Cas9 system in shakehead, and all designed gRNAs effectively worked at their target sites with high mutagenesis efficiencies, from 40.0% to 53.3%. The majority of mutations were frame-shift and resulted in premature termination of transcription and disruption of the molecular function of CmMstn protein. Furthermore, we obtained four founders (F0) of snakehead with the mutated Mstn gene in their primordial germ cells, and nineteen F1 offspring of the F0 mutants mated with wild-type individuals were displayed to carry Mstn null alleles. It is the first application of genome editing technology in blotched snakehead, and CRISPR/Cas9 system successfully edit the primordial germ cells. Our findings will accelerate our understanding of the role of Mstn gene in snakehead growth, and speed up the cultivation of the fast-growing snakehead strain.