Distinct Myosin Heavy Chain Isoform Transitions in Developing Slow and Fast Cat Hindlimb MusclesUnguez G.A. · Talmadge R.J. · Roy R.R. · Dalponte D. · Edgerton V.R.
aDepartment of Physiological Science and bBrain Research Institute, University of California, Los Angeles, Calif., and cDepartment of Human Nutrition, Foods and Exercise, Virginia Polytech Institute, Blacksburg, Va., USA
The expression of myosin heavy chain (MHC) isoforms leading to adult fiber phenotypes in the tibialis anterior (TA) and soleus muscles of the cat were investigated from embryonic day 35 to 1 year after birth. Electrophoresis and immunoblotting of myofibrils demonstrated the expression of 5 different MHC isoforms, i.e. I, IIa, IIx, embryonic, and neonatal, during development. Based on electrophoresis, the adult-like MHC composition of the soleus and TA were not observed until postnatal day 40 (P40) and 120 (P120), respectively. In contrast, immunohistochemical analyses revealed that the adult-like fiber phenotype composition was attained much later (P120) in the soleus. The existence of multiple MHC isoforms in individual fibers suggested that transitions occurred until P120 in both muscles. Adult type I fibers were first observed at P1. Adult IIA fibers were first observed at P30 in the TA and P40 in the soleus. IIX fibers were not identified until P40 in the TA. The transition to the predominantly slow phenotype of the soleus involved a gradual loss of embryonic and fast isoforms accompanied by an accumulation of slow MHC. In contrast, the expression of slow and fast MHC in the fast TA muscle was relatively unchanged throughout development. These results show that the establishment of a given MHC-based fiber phenotype varies significantly between slow and fast muscles in the kitten.
Roland R. Roy, PhD
Brain Research Institute, UCLA Box 951761
1320 Gonda Neuroscience and Genetics Building
Los Angeles, CA 90095-1761 (USA)
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Accepted after revision: October 13, 1999
Number of Print Pages : 15
Number of Figures : 10, Number of Tables : 2, Number of References : 42
Cells Tissues Organs (in vivo, in vitro)
Founded 1945 as Acta Anatomica
Vol. 167, No. 2-3, Year 2000 (Cover Date: 2000)Formerly Acta Anatomica
Journal Editor: H.-W. Denker, Essen; A.W. English, Atlanta, Ga.
ISSN: 1422–6405 (print), 1422–6421 (Online)
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