The distribution of myosin heavy chain isoforms among rat extraocular muscle fiber types.
OBJECTIVE
To determine the distribution of myosin heavy chain isoforms in each extraocular muscle (EOM) fiber type.


METHODS
Serial sections of adult rat EOMs were stained with isoform-specific monoclonal antibodies against an array of myosin heavy chains. Immunofluorescent antibody staining of whole adult rat EOMs, examined by confocal microscopy, demonstrated the longitudinal variations of isoforms along individual fibers.


RESULTS
Each global fiber type reacted predominantly with a single isoform-specific antibody and showed no longitudinal variation. Two major orbital fibers were defined, and both contained multiple myosin heavy chains. Both orbital singly and multiply innervated fibers stained proximal and distal to the neuromuscular junction with antibody to embryonic myosin heavy chain, but this isoform was sharply and completely excluded from the domain of the neuromuscular junction. Orbital singly innervated fibers also contained the EOM-specific isoform at the neuromuscular junction. Orbital multiply innervated fibers did not contain the EOM-specific isoform, but additionally contained a slow isoform along their entire length.


CONCLUSIONS
Adult rat EOMs show unique fiber types with arrangements of myosin heavy chain isoforms not seen in other skeletal muscles. Moreover, unique cellular mechanisms must exist to target each isoform to its proper domain along individual orbital fibers.
Rubinstein
N A
NA
Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia 19104, USA. nrubinst@mail.med.upenn.edu
Hoh
J F
JF
D000818:Animals; D000911:Antibodies, Monoclonal; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D018613:Microscopy, Confocal; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000378:metabolism; D009801:Oculomotor Muscles / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats
D000911:Antibodies, Monoclonal; D020033:Protein Isoforms; D018995:Myosin Heavy Chains