Myosin heavy chain expression in human muscle cocultured with mouse spinal cord

Monoclonal antibodies which specifically recognise the neonatal or adult fast (type 2A and 2B) or slow myosin heavy chain (MHC) were used to investigate the myosin composition of human muscle which had regenerated in culture in the presence or absence of embryonic mouse spinal cord tissue. Adult fast MHC was found in an average of 75% of the cultured fibres, irrespective of the time in culture, the source of the muscle, the presence of neurones or modifications to the growth medium. It was not found alone but was always in association with the neonatal and/or slow myosin isoforms. The expression of fast MHC in human muscle therefore differs from that in mouse muscle in this culture system (Ecob-Prince et al. 1986), but is still strong evidence for the development of at least one aspect of an adult phenotype in culture.