Worm Breeder's Gazette 7(2): 21
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
In order to examine the role of MHCA in Sup-3 suppression (see accompanying report), we hope to determine the composition of thick filaments in particular mutants by binding monoclonal antibodies to isolated filaments. As a preliminary study, we have studied ultrastructure of thick filaments from several paramyosin mutants. We have found that the 1.5 x 0.032 micron cigar-shaped filaments present in the paramyosin null mutant, unc-15(e1214)(ref. 1) are also found in unc-15(e73) strains. In addition, the unc-15(e73) mutant contains 3.7 x 0.022 m filaments with tassle-like ends (wild type filaments are 10 to 14 m x 0.022 m). The tassles probably represent protruding myosin heads and are similar to those found on the cigar- shaped filaments. Both cigar-shaped and longer tassled filaments contain myosin because both structures bind myosin heavy chain specific antibodies. We have not been able to determine whether any of the structures observed correspond to the hollow filaments observed in unc-15(e73) animals. The somewhat elongated and tassled filaments found in unc-15(e73) animals might account for their superior locomotion in comparison to unc-15(e1214) animals. Perhaps the defective paramyosin is being incorporated into the tassled filaments of unc-15(e73) and, perhaps, these structures might be aberrant intermediates of thick filament assembly. The possibility exists that these are abortive intermediates because animals containing the temperature-sensitive unc- 15(e1402) allele do not recover after late temperature shifts (2). However, the inability to recover from temperature shifting could be due to other requirements for muscle development. The sup-3 mutation appears to allow defective paramyosin to assemble into thick filaments of normal appearance and length in sup-3(e1407) 3) animals. This result is consistent with the observation of thick filaments of normal appearance in cross sections of sup-3(e1407) 3) animals. In addition to normal length filaments, the suppressed strain also contained the 3.7 m-long filaments as well as a few 1.5 m-long cigar-shaped filaments.