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Fatima Pedrosa–Domellöf, Ylva Holmgren, Christine Angela Lucas, Joseph Foon Yoon Hoh, Lars-Eric Thornell; Human Extraocular Muscles: Unique Pattern of Myosin Heavy Chain Expression during Myotube Formation. Invest. Ophthalmol. Vis. Sci. 2000;41(7):1608-1616.
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purpose. To study the myosin heavy chain composition of the human extraocular
muscles (EOMs) during development.
methods. EOMs from human fetuses of 8 to 22 weeks of gestation were studied with
immunocytochemistry and gel electrophoresis. Antibodies specific
against nine isoforms of myosin heavy chain (MyHC) were used in serial
results. The developing EOMs had a delayed time course of myotube formation and
a unique composition and distribution of MyHCs compared with human limb
skeletal muscle. The primary myotubes coexpressed two developmental
isoforms of MyHCI from the earliest stages. The third developmental
MyHCI delineated the future orbital layer at 10 to 12 weeks of
gestation. MyHC-slow tonic also appeared early, whereas MyHCα
-cardiac and MyHC-extraocular, important components of adult EOM,
were never detected at the gestational ages studied.
conclusions. The developmental features of the EOMs differed significantly from
those reported for limb muscles of the corresponding ages. It is clear
that the knowledge of limb muscle development does not fully apply to
more specialized muscles, such as the eye muscles. The extreme
complexity displayed by the EOMs probably reflects their distinct
embryonic origin, innervation, and regulatory program of
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