Key result
Muscle denervation prematurely upregulates Myf-5 and MRF4 mRNA while later increasing MyoD and myogenin during regeneration.
Denervation differentially upregulates myogenic regulatory factors during muscle regeneration, suggesting distinct roles in regulatory control of muscle gene expression.
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Denervation timing modulates myogenic factor expression in regenerating muscle; hypothesis-generating for distinct regulatory roles, no clinical implications yet.
Given the importance of the myogenic regulatory factors (MRFs) for myoblast differentiation during development, the aims of this work were to clarify the spatial and temporal expression pattern of the four MRF mRNAs during soleus regeneration in mouse after cardiotoxin injury, using in situ hybridization, and to investigate the influence of innervation on the expression of each MRF during a complete degeneration/regeneration process. For this, we performed cardiotoxin injury-induced regeneration experiments on denervated soleus muscle. Myf-5, MyoD, and MRF4 mRNAs were detected in satellite cell-derived myoblasts in the first stages of muscle regeneration analyzed (2--3 days P-I). The Myf-5 transcript level dramatically decreased in young multinucleated myotubes, whereas MyoD and MRF4 transcripts were expressed persistently throughout the regeneration process. Myogenin mRNA was transiently expressed in forming myotubes. These results are discussed with regard to the potential relationships between MyoD and MRF4 in the satellite cell differentiation pathway. Muscle denervation precociously (at 8 days P-I) upregulated both the Myf-5 and the MRF4 mRNA levels, whereas the increase of both MyoD and myogenin mRNA levels was observed later, in the late stages of regeneration (30 days P-I). This significant accumulation of each differentially upregulated MRF during soleus regeneration after denervation suggests that each myogenic factor might have a distinct role in the regulatory control of muscle gene expression. This role is discussed in relation to the expression of the nerve-regulated genes, such as the nAChR subunit gene family. (J Histochem Cytochem 49:887-899, 2001)
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Launay et al. (2001) studied Muscle regeneration after cardiotoxin injury. Muscle denervation vs. Normal innervation was evaluated on Spatial and temporal expression pattern of MRF mRNAs. Muscle denervation precociously upregulated Myf-5 and MRF4 mRNA levels at 8 days post-injury, while increasing MyoD and myogenin mRNA levels later at 30 days post-injury during soleus regeneration.
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