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Fatima Pedrosa Domellof, Jing-Xia Liu; A novel type of multiple innervation and a complex relation between desmin and innervation in human extraocular muscles. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3437.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the relation between the location of motor endplates and the lack of desmin previously found in a subgroup of muscle fibers containing myosin heavy chain slow tonic (MyHCsto) in human extraocular muscles (EOMs).
Nine EOMs collected from 6 healthy subjects (42, 47, 64, 68, 81, 82 years old) were processed for immunohistochemistry with antibodies against desmin, MyHC isoforms and markers of endplates and axons.
A novel type of multiple innervation was found in the human EOMs, in addition to the other well-known types of endplates, i.e. i) “en plaque” endplates found in all muscle fibers, ii) “en grappe” endplates found in multiply innervated fibers containing MyHCsto and iii) palisade endings found close to the tendon. This novel type of multiple innervation consisted of several typical large “en plaque” motor endplates present along approximately 500-microns long segments of individual muscle fibers. These multiply innervated muscle fibers lacked MyHCslow and fast2A, and were therefore classified as muscle fibers containing MyHCeom. Desmin was generally absent in a segment of any fiber type in the vicinity of its typical, single “en plaque” motor endplate. It was also absent from MyHCsto muscle fibers containing “en grappe” endplates. Desmin was either absent or present in muscle fibers containing the novel multiple “en plaque” endplates. Finally, desmin was present in the slow tonic muscle fibers receiving palisade endings.
Our data indicate that an additional type of multiply innervated fiber type lacking MyHCslow and fast2A, exists in the human EOMs. Furthermore, the cytoskeletal organization of the muscle fibers at the endplates in the human EOMs differs fundamentally from those of limb muscles, where desmin is concentrated in the folds of the neuromuscular junction and postulated to have an important role in cell signalling.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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