Human extraocular muscles: unique pattern of myosin heavy chain expression during myotube formation.
OBJECTIVE
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 frozen sections.


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 MyHC alpha-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 myogenesis.
Pedrosa-Domellöf
F
F
Department of Integrative Medical Biology, Umeå University, Sweden. fatima.pedrosa-domellof@anatomy.umu.se
Holmgren
Y
Y
Lucas
C A
CA
Hoh
J F
JF
Thornell
L E
LE
D002454:Cell Differentiation; D004591:Electrophoresis, Polyacrylamide Gel; D005865:Gestational Age; D006801:Humans; D007124:Immunoenzyme Techniques; D018482:Muscle, Skeletal / Q000196:embryology / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000096:biosynthesis*; D009801:Oculomotor Muscles / Q000196:embryology* / Q000378:metabolism*
D018995:Myosin Heavy Chains