Physiol. Res. 49: 617-633, 2000

Regulation of Myosin Expression in Developing and Regenerating Extrafusal and Intrafusal Muscle Fibers with Special Emphasis on the Role of Thyroid Hormones


Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic

Received January 24, 2000
Accepted April 14, 2000

Expression of the muscle phenotype is the result of interaction between intrinsic and extrinsic factors, the latter including innervation, mechanical influences and hormonal signals. This minireview summarizes some of the current knowledge regarding the regulation of myosin heavy chain (MHC) isoform transitions during muscle development and regeneration. It describes the role of genetic factors, neural and mechanical influences and it focuses on the contribution of thyroid hormones to the differentiation of muscle fiber phenotypes as shown by the regulation of the expression of MHC isoforms and development of myofibrillar ATPase activity. Finally, it shortly summarizes results regarding the differentiation of MHC isoforms in regenerated muscle fibers of the graft after heterochronous isotransplantation in rats with different thyroid status.

Key words
Myosin heavy chains · Myofibrillar proteins · Muscle cell lineages · Muscle innervation · Thyroid hormones ·
Muscle fiber types · Muscle spindles

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Dr. T. Soukup, Institute of Physiology, Czech Academy of Sciences, Vídeòská 1083, CZ-142 20 Prague, Czech Republic, Fax: +420 2 475 2488, E-mail:

© 2000 by the Institute of Physiology, Czech Academy of Sciences