Expression of myosin heavy chain gene in the sea urchin: coregulation with muscle actin transcription in early development.

A fragment of a Strongylocentrotus purpuratus (Sp) myosin heavy chain (MHC) gene was isolated from a genomic recombinant DNA library by cross-reaction with a cloned Drosophila melanogaster (Dm) MHC probe. A portion of a 227-nucleotide Sp coding sequence that is included in this fragment predicts a peptide very closely homologous with a region of the Dm sequence. The MHC gene sequence is present in a single copy per haploid Sp genome, and the gene is utilized in adult as well as embryonic muscle. The quantity of MHC transcript was measured in embryos of various stages by single-strand RNA probe excess titration. Transcripts are not observed until postgastrular stages, after which they accumulate rapidly. The time course of accumulation closely parallels that measured earlier for muscle actin message.