Temporal Expression of Myosin Heavy Chain Gene during Ascidian Embryogenesis

A muscle‐specic monoclonal antibody, termed Mu‐2, recognizes a single 220‐kd polypeptide which first appears in early tailbud‐stage embryos of the ascidian Halocynthia roretzi (17). In the present investigation, a cDNA library was prepared from poly(A)+ RNA isolated from tailbud embryos. The resulting cDNAs were inserted into the expression vector γgt11, and the library was screened with the Mu‐2. One of positive clones, containing an insert about 1.6‐kb in length, was selected and subcloned. Partial sequence analyses at the 5′ terminus and at the 3′ terminus of the 1.6‐kb cDNA allowed the amino acid sequence. The deduced sequence showed extensive homology to the rodent myosin heavy chain protein. Using an antisense RNA probe generated from the cDNA, Northern blot hybridization was carried out to measure the level of the myosin heavy chain gene transcripts during normal embryogenesis. These transcripts were not detected at pregastruia stages, after which they accumulated rapidly.