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  • 1
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Myosin has been purified from chicken pectoralis muscle at various stages of development, from 10 days' incubation to approximately 10 months after hatching. Embryonic myosin from the earliest stage showed a high level of ATPase activity, similar to that obtained for adult pectoralis myosin. Two-dimensional peptide mapping of partial chymotryptic digests showed, however, that its heavy chain is quite different from that of adult fast myosin. The immunological crossreactivity observed between embryonic myosin and adult fast (pectoralis) myosin is therefore due to shared antigenic determinants rather than the presence of any adult isoforms. In an accompanying paper we will show that embryonic myosin at 10 days' incubation is not a single species, but consists of at least two heavy chain isozymes. The minor fraction binds slow light chains preferentially, and appears to be largely responsible for the observed crossreactivity with slow (ALD) myosin. None of the embryonic myosins is equivalent to the adult forms. Prior to hatching, LC3f is present only in very small amounts (〈5%), and the adult light chain pattern, containing LC1f and LC3f in equimolar amounts, is not generated until after one week post-hatching. At about that time a new heavy chain population is detected, different from either the embryonic heavy chain or the adult heavy chain. The adult heavy chain peptide pattern appears from about three weeks' post-hatching, but a map indistinguishable from that of adult myosin is not observed until about 26 weeks. None of the observed differences in peptide maps can be related to different strains of chicken; pectoralis myosin from adult White Rock gave an identical map to that from White Leghorn. Unexpectedly, posterior latissimus dorsi (PLD) myosin from White Leghorn appears to be different from pectoralis myosin from the same strain, despite the histochemical and immunocytochemical similarity of the two muscles. We conclude that myosin polymorphism is widespread in muscle tissue, and that the expression of myosin isozymes and their subunits is under developmental regulation.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of muscle research and cell motility 13 (1992), S. 654-667 
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Immunogold labelling was used to determine the distribution of myosin isoforms within the A-bands of developing chicken pectoralis muscles. Previous localization studies led to the suggestion that neonatal myosin is preferentially located in the centre of heterogeneous thick filaments that contain either embryonic or adult myosin in addition to neonatal myosin. To further explore the possibility that neonatal myosin may serve to nucleate thick filament assembly, a method was developed to isolate A-segments (arrays of myosin filaments) from myofibrils in the presence of MgATP. A-bands usually dissociate into thick and thin filaments in a relaxing buffer, but the inclusion of an antibody against M-line protein prevented separation of the thick filament array. Well-ordered A-segments, approximately 1.5 μm in length, were prepared from muscles 12, 29, 40 days, and approximately 1 year after hatching. After reaction with monoclonal antibodies specific for neonatal and adult myosins, the A-segments were labelled with gold-conjugated secondary antibodies prior to negative staining. An antibody which cross-reacts with embryonic myosin was used to localize that epitope in A-bands of myofibrils from day 1 and day 3 posthatch muscles. At ages where expression of neonatal myosin was high, extensive gold labelling of A-segments was observed in the electron microscope. However, no preferential distribution of antibodies was observed at any age, independent of whether embryonic or adult myosin was coexpressed with the neonatal myosin, suggesting that neonatal myosin is not segregated to any particular region in the A-bands of developing muscles.
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  • 3
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Chicken pectoralis consists primarily of large white fibres, which react exclusively with antibodies prepared against adult fast myosin. There is, however, a small region of uniformly red fibres which responds to antibodies against adult slow myosin as well as adult fast myosin. The myosin extracted from this red region is also heterogeneous as shown by the presence of both slow and fast light chains. By means of immunoadsorbents, it has been possible to separate the ‘red myosin’ into a ‘fast’ component and a ‘slow’ component. These two fractions have been characterized with respect to their light and heavy chain content by one-dimensional and two-dimensional gel electrophoresis. The myosin heavy chain was reduced to the smaller fragments required for electrophoresis by proteolytic degradation. We conclude from the electrophoretic patterns that the ‘fast’ and ‘slow’ myosin components from the pectoralis red region closely resemble the myosin from the white region of the pectoralis and the myosin from the slow anterior latissimus dorsi (ALD) muscle. The demonstration of a ‘slow myosin’ in adult pectoralis muscle raises the possibility that the crossreactivity of embryonic pectoralis myosin with anti-slow (ALD) myosin antibodies might be due to the presence of such slow components in embryonic chicken muscle. Direct isolation of a slow component from embryonic pectoralis was achieved by immunoadsorption, as described for adult mixed muscle myosin. Analysis of the subunit composition by gel electrophoresis shows an enrichment in adult-type slow light chains, but the heavy chain pattern is quite distinct from that of adult slow heavy chain. These studies suggest that several myosin isozymes exist in embryonic chicken pectoralis, but that none is identical to those myosins found in the different fibres of the adult pectoralis muscle.
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