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The Journal of Neuroscience, December 1, 1998, 18(23):9924-9935

Reexpression of Myogenic Proteins in Mature Electric Organ after Removal of Neural Input

Graciela A. Unguez and Harold H. Zakon

Department of Zoology and Institute for Neuroscience, University of Texas, Austin, Texas 78712

The electric organ (EO) of the weakly electric fish Sternopygus macrurus derives from striated myofibers that fuse and suppress many muscle properties. Mature electrocytes are larger than muscle fibers, do not contain sarcomeres, or express myosin heavy chain (MHC) or tropomyosin. Furthermore, electrocytes express keratin, a protein not expressed in muscle. In S. macrurus the EO is driven continuously at frequencies higher than those of the intermittently active skeletal muscle. The extent to which differences in EO and muscle phenotype are accounted for by activity patterns, or innervation per se, was determined by assessing the expression of MHC, tropomyosin, and keratin 2 and 5 weeks after the elimination of (1) activity patterns by spinal transection or (2) all synaptic input by denervation.

Immunohistochemical analyses showed no changes in muscle fiber phenotypes after either experimental treatment. In contrast, the keratin-positive electrocytes revealed an upregulation of MHC and tropomyosin. Nearly one-third of all electrocytes expressed MHC (35%) and tropomyosin (25%) 2 weeks after spinal transection, whereas approximately two-thirds (61%) expressed MHC 2 weeks after denervation. After 5 weeks of denervation or spinal transection, all electrocytes contained MHC and tropomyosin. Newly formed sarcomere clusters also were observed in denervated electrocytes. The MHC expressed in electrocytes corresponded to that present in a select population of muscle fibers, i.e., type II fibers. Thus, the elimination of electrical activity or all synaptic input resulted in a partial reversal of the electrocyte phenotype to an earlier developmental stage of its myogenic lineage.

Key words: phenotypic conversion; sarcomere formation; electrocytes; sarcomeric proteins; neural influence of electrocyte phenotype; myogenesis

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Copyright © 1998 Society for Neuroscience  0270-6474/98/18239924-12$05.00/0

This article has been cited by other articles:

				J. A. Kim, C. Laney, J. Curry, and G. A. Unguez Expression of myogenic regulatory factors in the muscle-derived electric organ of Sternopygus macrurus J. Exp. Biol., July 1, 2008; 211(13): 2172 - 2184. [Abstract] [Full Text] [PDF]

				H. Cuellar, J. A. Kim, and G. A. Unguez Evidence of post-transcriptional regulation in the maintenance of a partial muscle phenotype by electrogenic cells of S. macrurus FASEB J, December 1, 2006; 20(14): 2540 - 2540. [Abstract] [Full Text] [PDF]

				H. Zakon and G. Unguez Development and regeneration of the electric organ J. Exp. Biol., January 5, 1999; 202(10): 1427 - 1434. [Abstract] [PDF]

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