Myostatin(Mstn) gene is a new member of the TGF-β superfamily, which is expressed specifically in skeletal muscle and functions as a negative regulator of skeletal muscle growth. Myostatin gene may represent an ideal target for manipulating muscle mass because it is a single gene, the absence of which results in increased muscle mass, and a natural knockout is already present in the existing double-muscled cattle population, suggesting that manipulation of this gene should not interfere with other growth systems and result in abnormal pathology.