Immunocytochemical localization of two myosins within the same muslce cells in Caenorhabditis elegans.

Nematodes synthesize two major classes of myosin heavy chains. These heavy chains associate to form only homodimeric myosin molecules, and these myosin homodimers are anti-genically different from one another (Schachat, Garcea and Epstein, 1978). The two myosins may be designated unc-54 myosin, since this species is altered in mutants of the unc-54 locus, and non-unc-54 myosin, since this class is not affected in unc-54 mutants. We present here experiments in which specific anti-myosin IgG and anti-unc-54 myosin IgG are used to locate the two myosins within the same body-wall muscle cells of Caenorhabditis elegans. These results are necessary for further evaluation of the possible functions of the two myosin homodimers in the thick filaments of these muscles.Myosin can be localized to all body-wall and pharyngeal muscle cells using anti-myosin antibody. In longitudinal sections of body-wall muscle, the staining with anti-myosin coincides with the birefringence of A bands that contain thick filaments. Anti-unc-54 myosin stains all body-wall A bands uniformly but does not react with the pharynx. This result demonstrates that unc-54 is located exclusively in body-wall muscle cells of the wild-type strain N2. Non-unc-54 myosin is localized with anti-myosin in all body-wall muscle cells of the unc-54 null mutant E190, as expected; however, unc-54 myosin could not be detected by anti-unc-54 myosin antibody in this mutant.Since we can localize unc-54 myosin and non-unc-54 myosin in all body-wall muscle cells of wild-type and E190, respectively, we conclude that the two myosins must be present in the same muscle cells. In addition, since unc-54 myosin is located in all body-wall A bands, at least some sarcomeres must contain both myosins. This conclusion is consistent with the observations of Garcea, Schachat and Epstein (1978) that wild-type and E190 synthesize similar amounts of non-unc-54 myosin. Within the limits of resolution of our methods, unc-54 myosin is distributed throughout body-wall A bands. We conclude, therefore, that the majority of thick filaments within these A bands must contain unc-54 myosin along their entire length. Possible roles for unc-54 and non-unc-54 myosins in the assembly and organization of thick filaments are discussed.