Dogs (Canis familiaris) serve as human companions and are raised to herd livestock, aid hunters, guard homes, perform police and rescue work, and guide the blind. Dogs exhibit close similarities to humans in terms of metabolic, physiological, and anatomical characteristics, and thus are ideal genetic and clinical models to study human diseases (Tsai et al., 2007). Gene target technology is a powerful tool to create new strains of animals with favorable traits. However, thus far, gene-target dogs have not been developed due to their unique species-specific reproductive characteristics, which limits the applications of dogs especially in the field of biomedical research. Recently, clustered regularly interspaced short palindromic repeats (CRISPRs)/CRISPR-associated (Cas) 9 system was applied to edit specific genes with a high efficiency (Cong et al., 2013; Mali et al., 2013). Here we attempt to explore the feasibility of producing gene knockout (KO) dogs by using this technology. Beagle dog, the most widely used breed in biomedical research, was used as our animal model. Myostatin (MSTN) was chosen as the first gene of interest. MSTN is a negative regulator of skeletal muscle mass (McPherron et al., 1997). Spontaneous mutations of MSTN cause muscle hypertrophy in many species, including dogs (Mosher et al., 2007), without causing severe adverse consequences.
