Abstract
Purpose:
To determine whether the lack of desmin reported in the slow tonic muscle fibers of human extraocular muscles (EOMS) is related to the presence of slow tonic myosin heavy chain (MyHC) or multiple innervation or a feature specific to extraocular muscles and to determine whether the EOMs are affected in a model of desmin muscle dystrophy.
Methods:
Immunohistochemistry was used to investigate the presence of desmin in i) chicken anterior latissimus dorsi (ALD), a muscle rich in slow tonic muscle fibers, ii) muscle spindles, whose muscle fibers contain MyHC slow tonic and are multiply innervated and iii) EOMs of rabbit, rat and zebra fish. The morphology, muscle fiber size and muscle fiber integrity was evaluated in the EOMs of desmin knockout mice and compared to that of wild type controls.<br />
Results:
Chicken ALD and muscle spindle fibers were labeled with antibodies against desmin in similar patterns to those seen in control skeletal muscle fibers. Muscle fibers containing slow tonic MyHC in the EOMs of the different animals studied showed absence or very low levels of expression of desmin, as previously observed in the human EOMs. The EOMs of the desmin KO mice showed no obvious signs of muscle dystrophy, in contrast to other highly used skeletal muscles. More animals are under evaluation.
Conclusions:
The very low levels of expression or lack of desmin in the slow tonic muscle fibers was a feature typical for the EOMs across species and not related to the presence of multiple innervation or slow tonic MyHC, in other muscles. Preliminary data indicate that the EOMs remain apparently unaffected in desmin muscle dystrophy.<br />