A DELETION IN THE BOVINE MYOSTATIN GENE CAUSES THE DOUBLE-MUSCLED PHENOTYPE IN CATTLE

An exceptional muscle development commonly referred to as 'double-musc led' (Fig. 1) has been seen in several cattle breeds and has attracted considerable attention from beef producers. Double-muscled animals ar e characterized by an increase in muscle mass of about 20%, due to gen eral skeletal-muscle hyperplasia-that is, an increase in the number of muscle fibers rather than in their individual diameter(1). Although t he hereditary nature of the double-muscled condition was recognized ea rly on, the precise mode of inheritance has remained controversial; mo nogenic (dominant and recessive), oligogenic and polygenic models have been proposed(2). In the Belgian Blue cattle breed (BBCB)(4), segrega tion analysis performed both in experimental crosses(3) and in the out bred population suggested an autosomal recessive inheritance. This was confirmed when the muscular hypertrophy (mh) locus was mapped 3.1 cM from microsatellite TCLA44 on the centromeric end of bovine chromosome 2 (ref. 5). We used a positional candidate approach to demonstrate th at a mutation in bovine MSTN, which encodes myostatin, a member of the TGF beta superfamily, is responsible for the double-muscled phenotype . We report an 11-bp deletion in the coding sequence for the bioactive carboxy-terminal domain of the protein causing the muscular hypertrop hy observed in Belgian Blue cattle.