alpha-Actin proteins and gene transcripts are colocalized in embryonic mouse muscle

The alpha-actins are among the earliest muscle-specific mRNAs to appear in developing cardiac and skeletal muscle. To determine if there is coexpression of the alpha-actin proteins at early stages of myogenesis, we have used an alpha-actin-specific polyclonal antibody and in situ hybridization with specific cRNA probes to cardiac and skeletal alpha-actin transcripts on serial slides of mouse embryo sections. As soon as we can detect alpha-actin mRNAs in embryonic striated muscle, we also detect the protein suggesting that alpha-actin transcripts are translated very rapidly after transcription during myogenesis. In skeletal muscle, this colocalization of alpha-actin mRNA and protein was observed both in the myotomes of somites and in developing muscles in the limbs. In cardiac muscle, alpha-actin transcripts and proteins are abundantly expressed as soon as a cardiac tube forms.