MOLECULAR DEFINITION OF AN ALLELIC SERIES OF MUTATIONS DISRUPTING THEMYOSTATIN FUNCTION AND CAUSING DOUBLE-MUSCLING IN CATTLE

We have determined the entire myostatin coding sequence for 32 double- muscled cattle sampled from ten European cattle breeds. Seven DNA sequ ence polymorphisms were identified, of which five would be predicted t o disrupt the function of the protein, one is a conservative amino aci d substitution, and one a silent DNA sequence variant. Four additional DNA sequence poly morphisms were identified in myostatin intronic seq uences. In all but two breeds, all double-muscled animals were either homozygous or compound heterozygotes for one of the five loss-of-funct ion mutations. The absence of obvious loss-of-function mutations in th e coding sequence of the two remaining breeds points either towards ad ditional mutations in unexplored segments of the gene, or rewards locu s heterogeneity of double-muscling.