doi:10.1369/jhc.4A6609.2005
Volume 53 (11): 1383-1390, 2005 Copyright ©The Histochemical Society, Inc. Myosin Heavy Chain Isoforms in Equine Gluteus Medius Muscle : Comparison of mRNA and Protein Expression Profiles
Department of Pathobiology, Division of Anatomy and Physiology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands Correspondence to: Karin Eizema, Utrecht University, Faculty of Veterinary Medicine, Division of Anatomy and Physiology, PO Box 80.158, NL-3508 TD Utrecht, The Netherlands. E-mail: c.g.h.eizema{at}vet.uu.nl The major structural protein in skeletal muscle, myosin heavy chain (MyHC), is primarily transcriptionally controlled. We compared the expression of MyHC isoforms on the mRNA and protein level in biopsies from the m. gluteus medius from adult untrained horses. In transverse sections, the majority of fibers showed qualitatively identical mRNA and protein expression patterns. However, coexpression of 2a and 2d/x MyHCs was substantially more common at the protein than at the mRNA level, suggesting a fine-tuning of these two genes in normal muscle not subjected to any training protocol. Because transverse sections give a limited sampling of mRNA expression in the case of uneven distribution of transcripts in a muscle fiber, we also analyzed longitudinal sections. We present, for the first time, evidence that expression of MyHC mRNA and protein was equal along the length of the fiber. Hence, mRNA expression is not regulated by differential expression of isoforms by separate myonuclei. It is concluded that the number of protein hybrid fibers in equine gluteus medius muscle is controlled by alteration of the transcription pattern uniformly along the fiber, rather than by simultaneous transcription of genes. The differences with the results in muscle of small animals and humans are discussed. (J Histochem Cytochem 53:13831390, 2005)
Key Words: horse fiber type hybrid fiber in situ hybridization immunohistochemistry myosin heavy chain
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