J. Biol. Chem., Vol. 260, Issue 18, 9957-9960, 08, 1985
Myosin heavy chain in avian muscular dystrophy corresponds to the neonatal isozyme
G Huszar, L Vigue and J Haines
We have previously demonstrated, based on comparison of homologous amino
acid sequences and of two-dimensional CNBr peptide gel patterns, that the
myosin heavy chain in pectoralis muscles of Storrs, Connecticut dystrophic
chickens is different from that of their normal controls (Huszar, G.,
Vigue, L., De-Lucia, J. Elzinga, M., and Haines, J. (1985) J. Biol. Chem.
260, 7429-7434). Others have shown, however, that genomic banks and mRNA
complements of the control and dystrophic birds are not different. In the
present studies, we have examined the hypothesis that the "dystrophic"
myosin heavy chain is not a novel gene product, but is a developmental
isozyme which is expressed in pectoralis muscles of adult chickens due to
the dystrophic process. Two- dimensional maps of myosin heavy chain CNBr
peptides were prepared from breast muscles of 17-day in ovo (embryonic),
25-day posthatch (neonatal), and adult birds of the Storrs dystrophic and
of two control strains. Also, myosin and actomyosin ATPase enzymatic
activities of the various preparations were determined in the pH range of
5.5 to 9.0. Analysis of the peptide maps demonstrates that the embyronic,
neonatal, and control adult myosin heavy chain isozymes are distinctly
different gene products with only minute variations between the respective
developmental isozymes in dystrophic and control muscles. However, the
pectoralis myosin heavy chain of adult dystrophic birds, which is a
homogeneous isozyme population by amino acid sequences and gel patterns,
corresponds to that of the neonatal-type myosin heavy chain. The ATPase
properties of the embryonic, neonatal, or adult pectoralis myosins and
actomyosins were not different, whether the level of specific activity or
the pattern of pH activation is considered. Since the mobility of neonatal
chicks (primarily neonatal-type isozymes) is not restricted, the
differences in myosin heavy chain structures are part of the syndrome, but
not the cause of avian muscular dystrophy.
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