Myosin heavy chain accumulates in dissimilar cell types of the macromere lineage in the sea urchin embryo.

In this study, myosin heavy chain from sea urchin pluteus larvae was characterized by analysis of a 2.5-kb cDNA clone. DNA sequence of 1465 bp demonstrated a 71% similarity in the deduced amino acid sequence to the embryonic rat skeletal muscle sequence. Antibodies generated against a polypeptide encoded by the open reading frame of the cDNA clone specifically identified a 210-kDa myosin protein which accumulated in 8-12 muscle cells differentiating bilateral to the esophagus beginning at early larval stages. This same myosin also accumulated in cells of the endodermal epithelium that comprise the three sphincters of the larval gut. Thus, a gene encoding myosin heavy chain is expressed in dissimilar cell types of the macromere lineage, and the pattern of accumulation in the gut identifies functionally distinct cells of the endodermal epithelium.