Human Molecular Genetics Advance Access originally published online on March 10, 2006
Human Molecular Genetics 2006 15(8):1279-1289; doi:10.1093/hmg/ddl045
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Aberrant neuromuscular junctions and delayed terminal muscle fiber maturation in 
-dystroglycanopathies
1Division of Clinical Genetics, Department of Medical Genetics and 2Department of Pediatrics, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan, 3Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi 470-1192, Japan, 4National Institute of Neuroscience, National Center of Neurology and Psychiatry, Kodaira, Tokyo 187-8502, Japan, 5Division of Clinical Research, Nagasaki Medical Center of Neurology, Kawatanamachi, Nagasaki 859-3615, Japan, 6Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology, Tatsunokuchi, Ishikawa 923-1292, Japan and 7Department of Clinical Genetics, The Tokyo Metropolitan Institute of Medical Science, Bunkyo-ku, Tokyo 113-8613, Japan
* To whom correspondence should be addressed. Tel: +81 668793380; Fax: +81 668793389; Email: toda{at}clgene.med.osaka-u.ac.jp
Received October 15, 2005; Accepted February 28, 2006
Recent studies have revealed an association between post-translational modification of 
-dystroglycan (-DG) and certain congenital muscular dystrophies known as secondary -dystroglycanopathies (-DGpathies). Fukuyama-type congenital muscular dystrophy (FCMD) is classified as a secondary -DGpathy because the responsible gene, fukutin, is a putative glycosyltransferase for -DG. To investigate the pathophysiology of secondary -DGpathies, we profiled gene expression in skeletal muscle from FCMD patients. cDNA microarray analysis and quantitative real-time polymerase chain reaction showed that expression of developmentally regulated genes, including myosin heavy chain (MYH) and myogenic transcription factors (MRF4, myogenin and MyoD), in FCMD muscle fibers is inconsistent with dystrophy and active muscle regeneration, instead more of implicating maturational arrest. FCMD skeletal muscle contained mainly immature type 2C fibers positive for immature-type MYH. These characteristics are distinct from Duchenne muscular dystrophy, suggesting that another mechanism in addition to dystrophy accounts for the FCMD skeletal muscle lesion. Immunohistochemical analysis revealed morphologically aberrant neuromuscular junctions (NMJs) lacking MRF4 co-localization. Hypoglycosylated -DG indicated a lack of aggregation, and acetylcholine receptor (AChR) clustering was compromised in FCMD and the myodystrophy mouse, another model of secondary -DGpathy. Electron microscopy showed aberrant NMJs and neural terminals, as well as myotubes with maturational defects. Functional analysis of NMJs of -DGpathy showed decreased miniature endplate potential and higher sensitivities to d-Tubocurarine, suggesting aberrant or collapsed formation of NMJs. Because -DG aggregation and subsequent clustering of AChR are crucial for NMJ formation, hypoglycosylation of -DG results in aberrant NMJ formation and delayed muscle terminal maturation in secondary -DGpathies. Although severe necrotic degeneration or wasting of skeletal muscle fibers is the main cause of congenital muscular dystrophies, maturational delay of muscle fibers also underlies the etiology of secondary -DGpathies.