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(Investigative Ophthalmology and Visual Science. 2006;47:3828-3834.)
© 2006 by The Association for Research in Vision and Ophthalmology, Inc.
DOI:  10.1167/iovs.06-0073
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Identification of Acetylcholine Receptor Subunits Differentially Expressed in Singly and Multiply Innervated Fibers of Extraocular Muscles

Sven Fraterman,1,2 Tejvir S. Khurana,2,3 and Neal A. Rubinstein1,2

1From the Departments of Cell and Developmental Biology and 3Physiology, and the 2Pennsylvania Muscle Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania.

PURPOSE. To identify the acetylcholine receptor (AChR) isoforms among the neuromuscular junctions (NMJs) of singly and multiply innervated fibers (SIFs and MIFs) of rat extraocular muscles (EOMs).

METHODS. EOMs were dissected from adult rats and serially sectioned. Sections were simultaneously stained for acetylcholinesterase and with an antibody to the slow myosin heavy chain to identify NMJ topography and fiber types in the same section. Synapses and subsynaptic regions of SIFs and MIFs were isolated by laser capture microdissection and the AChR subunits identified by RT-PCR.

RESULTS. The en plaque endings of SIFs expressed only the adult {epsilon} subunit, not the fetal {gamma} subunit, of the AChR, whereas the en grappe endings of the MIFs expressed only the {gamma} subunit, and not the {epsilon} subunit. Although the expression of the {epsilon} subunit was confined to the NMJ region of the SIFs, the {gamma} subunit was expressed both synaptically and extrasynaptically within the MIFs. The {gamma} subunit in MIFs correlated with the expression of the myogenic regulatory factor myogenin. Moreover, an unusual neuronal AChR subunit, {alpha}9, was found in the EOMs, but not in the limb muscles.

CONCLUSIONS. The adult {epsilon} and fetal {gamma} subunits of the AChRs are segregated into distinct synapses on distinct fiber types. The maintenance of the fetal subunit in a population of fibers is probably linked to the expression of myogenin and is a unique attribute of the EOM allotype.






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Copyright © 2006 by the Association for Research in Vision and Ophthalmology