Abstract. The thick filaments of the nematode, Caenorhabditis elegans, arising predominantly from the body-wall muscles, contain two myosin isoforms and paramyosin as their major proteins. The two myosins are located in distinct regions of the surfaces, while paramyosin is located within the backbones of the filaments. Tubular structures constitute the cores of the polar regions, and electron-dense material is present in the cores of the central regions To biochemically detect minor associated proteins, a new procedure for the isolation of thick filaments of high purity and structural preservation has been developed. The final step, glycerol gradient centrifugation, yielded fractions that are contaminated by, at most, 1-2 % with actin, tropomyosin, or ribosome-associated proteins on the basis of Coomassie Blue staining and electron microscopy. Silver staining and radioautography of gel electrophoretograms of unlabeled and 35S-labeled proteins, respectively, revealed at least 10 additional bands that cosedimented with thick filaments in glycerol gradients. Core structures prepared from wild-type thick filaments contained at least six of these thick filament-associated protein bands. The six proteins also cosedimented with thick filaments purified by gradient centrifugation from CB190 mutants lacking myosin heavy chain B and from CB1214 mutants lacking paramyosin. For these reasons, we propose that the six associated proteins are potential candidates for putative components of core structures in the thick filaments of body-wall muscles of C elegans. M YOSIN-CONTAINING filaments have been a major focus of research for over 30 years (11). The demonstration that myosin was contained in one set of filaments was critical to the foundation of the sliding-filament theory of muscle contraction (15). The isolation of natural filaments containing myosin and the formation of synthetic filaments from purified myosin were key confirmations of the theory and raised the important question as to whether the intrinsic self-assembly of myosin molecules explained the formation of thick filaments in vivo (14).The discovery that additional, nonmyosin proteins are components of natural thick filaments in both vertebrate and invertebrate muscles suggests that the assembly of these filaments may be more complex than simple self-assembly of myosin. For example, recent studies of rabbit skeletal muscles indicate that epitopes of the C, H, and X proteins are localized at very specific and distinct positions near the surface of specific thick filaments (1). Studies of various invertebrate muscles show that paramyosin is a major protein component of the backbones of the thick filaments (30). In other invertebrate muscles, paramyosin may be present only as a relatively minor protein (3,12,25). The diversity of nonmyosin protein components of thick filaments, their locations, and their relative amounts supports the alternative hypothesis that the assembly of thick filaments, in general, may require a sequence of specific reactions involving bot...

We describe multiple human cardiac and skeletal muscle spectrin isoforms. Cardiac muscle expresses five erythroid alpha,beta spectrin-reactive isoforms with estimated MR's of 280, 274, 270, 255, and 246 kD, respectively. At least one nonerythroid alpha-spectrin of MR 284 kD is expressed in heart. While skeletal muscle shares the 280, 270, and 246 kD erythroid spectrins, it expresses an immunologically distinct 284 kD nonerythroid alpha-spectrin isoform. The 255 kD erythroid beta-spectrin isoform is specific for cardiac tissue. By immunocytochemistry, both erythroid beta- and nonerythroid alpha-spectrins are localized to costameres, the plasma membrane, and the neuromuscular junctional region.

Myotonic dystrophy (DM) is an autosomal dominant disorder which affects skeletal muscle, heart, eye lens, brain, and endocrine functions. The disease‐causing mutations are expansions of the triplet repeat CTG in the 3′ untranslated region of a locus which encodes a serine/threonine protein kinase that represents a new family of protein kinases. A monoclonal antibody to a recombinant DM protein kinase (mAb DM‐1) reacts specifically with the 64 kDa isoform of DM protein kinase in type I fibers in skeletal muscle, the fiber type which characteristically atrophies in the disease. Within type I fibers of normal muscle the isoform may be localized with mAb DM‐1 to the triad region. In the DM disease state, the enzyme is redistributed to the pathologically characteristic peripheral sarcoplasmic masses. In markedly affected human distal myotonic muscle, the levels of the 64 kDa DM kinase isoform are elevated relative to slow skeletal myosin heavy chain. These results suggest that, consistent with the dominant clinical phenotype, the localization and accumulation of the 64 kDa isoform are altered in the heterozygous disease state. © 1996 Wiley‐Liss, Inc.

Myotonic dystrophy (DM) is an autosomal dominant disorder which affects skeletal muscle, heart, eye lens, brain, and endocrine functions. The disease-causing mutations are expansions of the triplet repeat CTG in the 3' untranslated region of a locus which encodes a serine/threonine protein kinase that represents a new family of protein kinases. A monoclonal antibody to a recombinant DM protein kinase (mAb DM-1) reacts specifically with the 64 kDa isoform of DM protein kinase in type I fibers in skeletal muscle, the fiber type which characteristically atrophies in the disease. Within type I fibers of normal muscle the isoform may be localized with mAb DM-1 to the triad region. In the DM disease state, the enzyme is redistributed to the pathologically characteristic peripheral sarcoplasmic masses. In markedly affected human distal myotonic muscle, the levels of the 64 kDa DM kinase isoform are elevated relative to slow skeletal myosin heavy chain. These results suggest that, consistent with the dominant clinical phenotype, the localization and accumulation of the 64 kDa isoform are altered in the heterozygous disease state.

No abstract