Cardiac and skeletal myopathy in beta myosin heavy-chain simian virus 40 tsA58 transgenic mice.

The mechanisms regulating cardiac muscle differentiation and development are incompletely understood. To examine the relationships between cardiocyte proliferation and differentiation, we tested the ability of a fragment from the rat beta myosin heavy-chain (MHC beta) gene to correctly target expression of a thermolabile simian virus 40 large tumor antigen allele (tsA58) in the developing mouse. Transgene expression in the heart was observed as early as 10 days postconception and was developmentally regulated in parallel with the endogenous MHC beta gene. Expression was also detected in developing skeletal muscle, although at low levels. Despite the temperature sensitivity of the mutant large tumor antigen protein, a subset of transgenic mice in several lineages developed marked cardiac and skeletal myopathies.