Expression of alpha-cardiac and alpha-skeletal actin mRNAs in relation to innervation in regenerating and non-regenerating rat skeletal muscles.

The expression of alpha-cardiac and alpha-skeletal actin mRNA in regenerating muscle was examined. Changes in mRNA levels were analyzed in autografted extensor digitorum longus (EDL) muscles in rats using alpha-isoform specific synthetic oligonucleotides and beta-actin cDNA as probes. After autografting, the expression of alpha-cardiac actin mRNA was induced; concomitantly that of alpha-skeletal actin mRNA was reduced. The pattern of alpha-actin mRNA expression appeared to be similar to that seen in embryonic skeletal muscle. In order to evaluate the effects of innervation on alpha-actin mRNA expression in regenerating muscle, nerveless, standard, and nerve-intact autografted muscles were examined. More complete innervation facilitated the recovery of alpha-skeletal actin mRNA to control levels, but had little effect on the amount of alpha-cardiac actin mRNA. We found that regenerating muscle shows that embryonic pattern of alpha-actin mRNAs in the early stage and concluded that the recovery of alpha-skeletal actin mRNA expression to the adult pattern is influenced by innervation, while alpha-cardiac actin mRNA expression is nerve independent.