Double-Muscled Phenotype in Mutant Sheep Directed by the CRISPRCas9 System

Abstract

Myostatin (MSTN) is a well-known negative regulator of muscle growth. The double-muscled sheep caused by natural loss-of-function mutations of MSTN have very strong skeletal muscle. In this study, our results demonstrate the successful generation of MSTN mutant sheep via specific targeting of an exon 1 site using Cas9 technology. The MSTN-knockout sheep in our study had increased muscle significantly just like double-muscled phenotype. Our study suggests that the direct injection of Cas9: sgRNA into zygotes could be widely used to create gene knockouts in large domestic animals. Notably, on the basis of our findings, sheep can be added to the growing list of species for which genome editing is now practical. The generation of MSTN mutant sheep has implications for the genetic improvement of local sheep varieties, and also for the usage of sheep as a model for large animal medical research.