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© The Rockefeller University Press, 0021-9525/1997//1047 $5.00
The Journal of Cell Biology, Volume 136, Number 5, , 1997 1047-1058

Article

Laminin-induced Clustering of Dystroglycan on Embryonic Muscle Cells: Comparison with Agrin-induced Clustering



Monroe W. Cohen*, Christian Jacobson{ddagger}, Peter D. Yurchenco§, Glenn E. Morris||, and Salvatore Carbonetto{ddagger}

* Department of Physiology, McGill University, Montreal, Quebec, Canada H3G1Y6; {ddagger} Centre for Research in Neuroscience, McGill University, Montreal General Hospital Research Institute, Montreal, Quebec, Canada H3G 1A4; § Department of Pathology, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854; and || MRIC Biotechnology Group, The North East Wales Institute, Plas Coch, Mold Road, Wrexam, United Kingdom LL11 2AW

The effect of laminin on the distribution of dystroglycan (DG) and other surface proteins was examined by fluorescent staining in cultures of muscle cells derived from Xenopus embryos. Western blotting confirmed that previously characterized antibodies are reactive in Xenopus. In control cultures, {alpha}DG, βDG, and laminin binding sites were distributed as microclusters (<1 µm2 in area) over the entire dorsal surface of the muscle cells. Treatment with laminin induced the formation of macroclusters (1–20 µm2), accompanied by a corresponding decline in the density of the microclusters. With 6 nM laminin, clustering was apparent within 150 min and near maximal within 1 d. Laminin was effective at 30 pM, the lowest concentration tested. The laminin fragment E3, which competes with laminin for binding to {alpha}DG, inhibited laminin-induced clustering but did not itself cluster DG, thereby indicating that other portions of the laminin molecule in addition to its {alpha}DG binding domain are required for its clustering activity. Laminin-induced clusters also contained dystrophin, but unlike agrin-induced clusters, they did not contain acetylcholine receptors, utrophin, or phosphotyrosine, and their formation was not inhibited by a tyrosine kinase inhibitor. The results reinforce the notion that unclustered DG is mobile on the surface of embryonic muscle cells and suggest that this mobile DG can be trapped by at least two different sets of molecular interactions. Laminin self binding may be the basis for the laminin-induced clustering.

Abbreviations used in this paper: AChR, acetylcholine receptor; DAP, dystrophin associated protein; DG, dystroglycan; LBS, laminin binding sites; PY, phosphotyrosine; ROI, region of interest.

D. McDonald, M. Ignatova, and T. Inoue provided excellent technical assistance. We thank K.P. Campbell for the generous gift of anti-{alpha}DG antibody.

Please address all correspondence to M.W. Cohen, Department of Physiology, McGill University, 3655 Drummond Street, Montreal, Quebec, Canada H3G1Y6. Tel.: (514) 398-4342; Fax: (514) 398-7452.


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