Six myosin heavy chain isoforms are expressed during chick breast muscle development

Two major embryonic myosin heavy chains are expressed in embryonic chick breast muscle until the first week after hatching. Of these, one is already detected in the 8-day-old embryo. The other appears on day 12. Two putative slow embryonic isoforms represent minor components transiently expressed between days 8 and 12. A neonatal heavy chain is expressed at low concentrations on day 8 and increases with development. It is the only isoform two weeks after hatching, and is ultimately replaced by the fast myosin heavy chain in the adult muscle.