alpha-Cardiac actin is the major sarcomeric isoform expressed in embryonic avian skeletal muscle.

A primer extension assay that is diagnostic for the messenger RNA's (mRNA's) transcribed from the beta-cytoplasmic, alpha-cardiac, and alpha-skeletal actin genes of the chicken was used to measure the mRNA levels for these actin isoforms. Measurements were made in chicken breast muscle during myogenesis in vivo and in vitro. alpha-Cardiac actin mRNA accounts for more than 90 percent of the sarcomeric actin transcripts expressed in avian embryonic breast muscle. Five weeks after hatching, alpha-skeletal actin mRNA is the only detectable sarcomeric actin transcript.