Mutants altering coordinate synthesis of specific myosins during nematode muscle development.

Mutations in the unc-52 gene on linkage group II retard the construction of body-wall muscle sarcomeres during larval development in the nematode Caenorhabditis elegans. Unc-52 mutants show decreased accumulation of myosin heavy chains relative to other polypeptides during larval development, correlating with the structural retardation. Pulse radiolabeling experiments show that decreased synthesis of specific body-wall myosin heavy chains that are encoded by the unc-54 gene on linkage group I is responsible for the defective myosin accumulation. In the wild type, a constant ratio of the synthesis of the unc-54-coded myosin B to myosin A, about 2:1, is maintained during the larval stages in which the synthesis of both myosins increases exponentially and rapid sarcomere growth and addition ensues. During the first 26 hr of larval development, before any structural or behavioral effects of unc-52 mutations are apparent, the synthesis of myosin heavy chains is also normal. By 38 hr, decreased synthesis of myosin B is detected in the unc-52 mutant SU200, when sarcomere growth slows considerably. The effects of mutation in the unc-52 locus are trans acting upon the synthesis of unc-54-coded myosin in a specific set of muscle cells during a defined period of larval development.