Plant & Animal Genome VI Conference Plant & Animal Genome VI Conference
W20
A visibly distinct muscular hypertrophy (mh) occurs with high frequency in
a number of cattle breeds that have been selected for this trait. The
increase in muscle mass caused by the mh locus is a major component of the
double muscled syndrome that includes a reduction in internal organ size,
general shortening of limb bones, and reduction in fat deposition. There
has been considerable interest in double muscled breeds due to their
increased proficiency of converting feed to lean beef. However, problems
associated with the trait, such as reduction in stress tolerance,
fertility, and calf viability in some double muscled breeds have hindered
exploitation of the desirable carcass composition. Mapping studies in
populations segregating for the mh locus show that it lies near the
centromere of BTA2, between the genes PROC and COL3A1 genes. This is the
same location as myostatin (MSTN), a TGF gene family member that has
dramatic effects on muscle development in mice. Sequencing of MSTN in
double muscled breeds has revealed mutations that are predicted to
interfere with or abolish the function of the protein, indicating that loss
of MSTN function in cattle is the basis of the double muscled condition.
Indeed, knockout mice homozygous for targeted disruption of MSTN display an
extreme increase in muscle mass with significant similarities to that
observed in double muscled cattle, confirming this hypothesis. The fact
that muscular hypertrophy is the result of a loss of function suggests the
exciting possibility that interference with MSTN in other breeds and
livestock species may lead to increased efficiency of meat production.