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S Khanna, AP Merriam, P Leahy, FH Andrade, JD Porter; Diversity of Muscle Tissue Class Signatures by Genome-Wide Profiling: Is Extraocular Muscle a Separate Class? . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1454.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: DNA microarray data established that rodent extraocular muscle (EOM) is a distinct skeletal muscle type. To see if EOM is a novel class among established muscle types, we evaluated EOM gene expression patterns relative to leg, cardiac (C), and smooth (Sm) muscle. Methods: DNA microarray, using Affymetrix U34A arrays (8,800 gene probes) with selected rat muscle groups, was used to compare profiles of the full range of muscle tissue phenotypes: EOM, leg (skeletal), C, and Sm. Muscle type expression clusters were determined on the basis of both exclusivity of gene expression (present only in a specific muscle class) and preferential expression (significantly elevated in a specific class). Results: Expression analysis most clearly defined two major groups: Sm exclusively expressed 96 genes and preferentially expressed 219 genes, while the striated muscles as a group (EOM, C, leg) were defined by exclusive expression of 121 genes and preferential expression of 153 genes. Among striated muscles, C (26 exclusive; 62 preferential) and skeletal (EOM and leg; 31 exclusive; 55 preferential) formed two distinct clusters. Subdivision of the skeletal muscle group yielded a weakly defined leg group (2 exclusive; 13 preferential) and a modest EOM-specific pattern (10 exclusive; 20 preferential). Finally, using the full probe set and comparing the expression patterns of only EOM vs. leg muscle, we confirmed prior findings of substantial EOM identity, as 126 genes showed increased and 76 decreased expression in EOM relative to leg. Conclusions: EOM is a distinct type of skeletal muscle. Prior head-to-head comparisons between other skeletal muscles show only modest, fiber type-related, differences, while EOM has a robust identity in comparison with skeletal muscle alone. As anticipated, analyses of expression profiles of striated vs. Sm and skeletal vs. C were consistent with fundamental structural/functional differences in muscle tissue classes. The EOM expression signature, while clearly divergent from other skeletal muscles, was not sufficiently novel to define a new, distinctive class of muscle tissue.
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