Figure 7.

Localization of Δ30 and Δ34 proteins is distinct at early developmental stages in animals expressing only truncated MHC. Three stages of embryogenesis are represented: A–D, 1.5-fold; E–H, twofold; and I–L, threefold. Like wild-type, embryos expressing only a Δ30 construct have well-defined stripes of myosin staining at the 1.5-fold stage (arrowheads in A and B), the time at which movement commences in wild type. A full-length chimeric protein expressed in the double mutant shows the same pattern (D). Later in development, animals expressing only Δ30 often show regions of expanded stain, indicating aberrant accumulations of Δ30 MHC within or near the contractile apparatus (arrows in F, I, and J). Expression of a single full-length construct can also result in abnormal, irregularly shaped accumulations (L, arrow) or stray filamentous staining (L, arrowhead) in later developmental stages. In contrast, a Δ34 construct in double mutant animals shows delayed localization of the protein in early stages of muscle cell organization. At the 1.5-fold stage, embryos expressing only BHtagΔ34 have no prominent bands (C). Instead, staining appears dotted or broken (arrowhead), and diffuse staining outside the contractile apparatus is strong. These animals arrest elongation at the twofold stage, but the localization of truncated myosin changes as development continues. In younger arrested animals (G), the bands of staining grow stronger compared with diffuse staining in the cell body. Older arrested animals (K) show strong localization of the protein to bands, in some places showing the four bands per quadrant characteristic of wild type (arrowheads), despite the aberrant shape of the animals. Δ30 expressed from transgene stEx148 was stained with antibody 5.6. The three tagged constructs, BHtagΔ30 stEx153, BHtagΔ34 stEx120, and chimera4.tag stEx118, were stained with anti-HA. The transgenic double mutant embryos from the strain unc-54(e190); myo-3(st386)/eDf1; stEx120 were recognized by their failure to stain with the MHC A head-specific antibody 5–14. Bar, 5 μm.