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Volume 17, Number 11, Issue of June 1, 1997 pp. 4170-4179
Copyright ©1997 Society for Neuroscience

Slow-Channel Transgenic Mice: A Model of Postsynaptic Organellar Degeneration at the Neuromuscular Junction

Received Jan. 14, 1997; revised March 17, 1997; accepted March 21, 1997.

Christopher M. Gomez^{1, 2}, Ricardo Maselli³, Jo Ellen Gundeck¹, Mary Chao³, John W. Day¹, Shiori Tamamizu⁴, Jose A. Lasalde⁴, Mark McNamee⁴, and Robert L. Wollmann⁵

¹ Department of Neurology, ² Institute of Human Genetics, University of Minnesota, Minneapolis, Minnesota 55455, Sections of ³ Neuroscience and ⁴ Molecular and Cellular Biology, University of California, Davis, California, and ⁵ Section of Neuropathology, University of Chicago, Chicago, Illinois 60637

The slow-channel congenital myasthenic syndrome (SCCMS) is a dominantly inherited disorder of neuromuscular transmission characterized by delayed closure of the skeletal muscle acetylcholine receptor (AChR) ion channel and degeneration of the neuromuscular junction. The identification of a series of AChR subunit mutations in the SCCMS supports the hypothesis that the altered kinetics of the endplate currents in this disease are attributable to inherited abnormalities of the AChR. To investigate the role of these mutant AChR subunits in the development of the synaptic degeneration seen in the SCCMS, we have studied the properties of the AChR mutation, L269F, found in a family with SCCMS, using both in vitro and in vivo expression systems. The mutation causes a sixfold increase in the open time of AChRs expressed in vitro, similar to the phenotype of other reported mutants. Transgenic mice expressing this mutant develop a syndrome that is highly reminiscent of the SCCMS. Mice have fatigability of limb muscles, electrophysiological evidence of slow AChR ion channels, and defective neuromuscular transmission. Pathologically, the motor endplates show focal accumulation of calcium and striking ultrastructural changes, including enlargement and degeneration of the subsynaptic mitochondria and nuclei. These findings clearly demonstrate the role of this mutation in the spectrum of abnormalities associated with the SCCMS and point to the subsynaptic organelles as principal targets in this disease. These transgenic mice provide a useful model for the study of excitotoxic synaptic degeneration.

Key words: transgenic mice; neuromuscular junction; slow-channel congenital myasthenic syndrome; acetylcholine receptor; point mutation; calcium overload; excitotoxicity; synaptic degeneration

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