Aggregation of acetylcholine receptors (AChRs) in muscle fibers by nerve-derived agrin plays a key role in the formation of neuromuscular junctions. So far, the effects of agrin on muscle fibers have been studied in culture systems, transgenic animals, and in animals injected with agrin–cDNA constructs. We have applied purified recombinant chick neural and muscle agrin to rat soleus muscle in vivo and obtained the following results. Both neural and muscle agrin bind uniformly to the surface of innervated and denervated muscle fibers along their entire length. Neural agrin causes a dose-dependent appearance of AChR aggregates, which persist ≥7 wk after a single application. Muscle agrin does not cluster AChRs and at 10 times the concentration of neural agrin does not reduce binding or AChR-aggregating activity of neural agrin. Electrical muscle activity affects the stability of agrin binding and the number, size, and spatial distribution of the neural agrin–induced AChR aggregates. Injected agrin is recovered from the muscles together with laminin and both proteins coimmunoprecipitate, indicating that agrin binds to laminin in vivo. Thus, the present approach provides a novel, simple, and efficient method for studying the effects of agrin on muscle under controlled conditions in vivo.
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25 June 2001
Article|
June 25 2001
Effects of Purified Recombinant Neural and Muscle Agrin on Skeletal Muscle Fibers in Vivo
Gabriela Bezakova,
Gabriela Bezakova
aDepartment of Physiology, University of Oslo, 0317 Oslo, Norway
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Johannes P. Helm,
Johannes P. Helm
bDepartment of Anatomy, University of Oslo, 0317 Oslo, Norway
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Maura Francolini,
Maura Francolini
cC.N.R. Center for Cellular and Molecular Pharmacology, Department of Medical Pharmacology, University of Milano, 20129 Milan, Italy
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Terje Lømo
Terje Lømo
aDepartment of Physiology, University of Oslo, 0317 Oslo, Norway
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Gabriela Bezakova
aDepartment of Physiology, University of Oslo, 0317 Oslo, Norway
Johannes P. Helm
bDepartment of Anatomy, University of Oslo, 0317 Oslo, Norway
Maura Francolini
cC.N.R. Center for Cellular and Molecular Pharmacology, Department of Medical Pharmacology, University of Milano, 20129 Milan, Italy
Terje Lømo
aDepartment of Physiology, University of Oslo, 0317 Oslo, Norway
Abbreviations used in this paper: AChR, acetylcholine receptor; EB, extraction buffer; Fl-BuTx, FITC-bungarotoxin; NMJ, neuromuscular junction; PFA, paraformaldehyde; Rh-BuTx, TRITC-α-bungarotoxin; SOL, soleus.
Received:
February 27 2001
Revision Requested:
May 11 2001
Accepted:
May 15 2001
Online ISSN: 1540-8140
Print ISSN: 0021-9525
© 2001 The Rockefeller University Press
2001
The Rockefeller University Press
J Cell Biol (2001) 153 (7): 1441–1452.
Article history
Received:
February 27 2001
Revision Requested:
May 11 2001
Accepted:
May 15 2001
Citation
Gabriela Bezakova, Johannes P. Helm, Maura Francolini, Terje Lømo; Effects of Purified Recombinant Neural and Muscle Agrin on Skeletal Muscle Fibers in Vivo. J Cell Biol 25 June 2001; 153 (7): 1441–1452. doi: https://doi.org/10.1083/jcb.153.7.1441
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