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© The Rockefeller University Press, 0021-9525/1998//1279 $5.00
The Journal of Cell Biology, Volume 142, Number 5, , 1998 1279-1287


Articles

{gamma}-Sarcoglycan Deficiency Leads to Muscle Membrane Defects and Apoptosis Independent of Dystrophin



Andrew A. Hack*, Chantal T. Ly{ddagger}, Fang Jiang{ddagger}, Cynthia J. Clendenin{ddagger}, Kirsten S. Sigrist{ddagger}, Robert L. Wollmann§, and Elizabeth M. McNally{ddagger}

* Department of Molecular Genetics and Cell Biology, {ddagger} Department of Medicine, Section of Cardiology, and § Department of Pathology, University of Chicago, Chicago, Illinois 60637

{gamma}-Sarcoglycan is a transmembrane, dystrophin-associated protein expressed in skeletal and cardiac muscle. The murine {gamma}-sarcoglycan gene was disrupted using homologous recombination. Mice lacking {gamma}-sarcoglycan showed pronounced dystrophic muscle changes in early life. By 20 wk of age, these mice developed cardiomyopathy and died prematurely. The loss of {gamma}-sarcoglycan produced secondary reduction of β- and {delta}-sarcoglycan with partial retention of {alpha}- and {varepsilon}-sarcoglycan, suggesting that β-, {gamma}-, and {delta}-sarcoglycan function as a unit. Importantly, mice lacking {gamma}-sarco- glycan showed normal dystrophin content and local- ization, demonstrating that myofiber degeneration occurred independently of dystrophin alteration. Furthermore, β-dystroglycan and laminin were left intact, implying that the dystrophin–dystroglycan–laminin mechanical link was unaffected by sarcoglycan deficiency. Apoptotic myonuclei were abundant in skeletal muscle lacking {gamma}-sarcoglycan, suggesting that programmed cell death contributes to myofiber degeneration. Vital staining with Evans blue dye revealed that muscle lacking {gamma}-sarcoglycan developed membrane disruptions like those seen in dystrophin-deficient muscle. Our data demonstrate that sarcoglycan loss was sufficient, and that dystrophin loss was not necessary to cause membrane defects and apoptosis. As a common molecular feature in a variety of muscular dystrophies, sarcoglycan loss is a likely mediator of pathology.

Key Words: muscular dystrophy • sarcolemma • dystrophin • extracellular matrix • apoptosis



Abbreviations used in this paper: DMD, Duchenne muscular dystrophy; LGMD, limb girdle muscular dystrophy; CK, creatine kinase; EBD, Evans blue dye; DGC, dystrophin-glycoprotein complex; ECM, extracellular matrix.

A.A. Hack is supported by the Medical Scientist Training Program and the Training Program in Development Biology. E.M. McNally is supported by the National Institues of Health, Muscular Dystrophy Association, Heart Research Foundation, and a Research Resources award from the Howard Hughes Medical Institute to the University of Chicago Biological Sciences Division.

Address all correspondence to Elizabeth M. McNally, M.D., Ph.D., Department of Medicine, Section of Cardiology, 5841 S. Maryland Ave., MC 6088, The University of Chicago, Chicago, IL 60637. Tel.: (773) 702-2672. Fax: (773) 702-2681. E-mail: emcnally{at}medicine.bsd.uchicago.edu



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