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Organization
of the Myotendinous Junction is Dependent on the Presence of [alpha]7[beta]1
Integrin |
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Nicolai Miosge,
Christina Klenczar, Rainer Herken, Michael Willem, and Ulrike Mayer |
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Zentrum
Anatomie (NM, CK, RH), Abteilung Histologie, Universität Göttingen,
Göttingen and Max-Planck-Institut für Biochemie (MW, UM), 82152
Martinsried, Germany |
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SUMMARY: The laminin receptor
[alpha]7[beta]1 is enriched at the myotendinous junctions, and mice with
a targeted inactivation of the [alpha]7 gene develop a form of muscular
dystrophy that primarily affects this structure. By ultrastructural analysis
of [alpha]7-deficient mice, in comparison with wild-type and mdx
mice, we attempted to elucidate the role of [alpha]7 integrin for the integrity
and function of the myotendinous junctions. Ultrastructurally, myotendinous
junctions of [alpha]7-deficient myofibers lose their interdigitations and
the myofilaments retract from the sarcolemmal membrane, whereas the lateral
side of the myofibers remains morphologically normal. The basement membrane
at the myotendinous junctions in [alpha]7 -/- mice is significantly broadened,
and immunogold-histochemistry has demonstrated that the laminin [alpha]2
chain is not localized here but, instead, in the matrix of the neighboring
tendon. In contrast, mdx mice have normal myotendinous junctions,
with a matrix protein pattern also found in wild-type mice, however the
lateral sides of the myofibers are severely damaged. These results suggest
that the [alpha]7[beta]1 integrin is a major receptor connecting the muscle
cell to the tendon and helps to organize the myotendinous junction, whereas
the dystrophin-glycoprotein complex is necessary for the lateral integrity
of the muscle cell. |
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