LOCALIZATION OF MYOGENIN, C-FOS, C-JUN, AND MUSCLE-SPECIFIC GENE MESSENGER-RNAS IN REGENERATING RAT SKELETAL-MUSCLE

It has been suggested that myogenin is an important factor for the differentiation of myoblasts and that its function in myogenesis is regulated by proto-on-cogenes in in vitro experiments. We have characterized the spatial and temporal expression patterns of myogenin, c-fos, c-jun, and muscle creatine kinase mRNAs during the skeletal muscle regeneration process using in situ hybridization histochemistry. Myogenin transcripts are first detected in the myonuclei/nuclei of satellite cells at 6 h after induction of regeneration. Myogenin mRNA is expressed in desmin-positive myoblasts, yet no muscle creatine kinase mRNA is detected in this cell type. Both the muscle creatine kinase and myogenin mRNAs are expressed in the newly formed myotubes, but not at earlier stages. Transcripts for c-fos and c-jun mRNAs are expressed first in the myonuclei/nuclei of satellite cells at 3 h post-trauma. c-jun mRNA is expressed in both myoblasts and myotubes, while c-fos mRNA was not detected in these cells. These results suggest that myogenin plays important roles in the regeneration of injured muscle and that c-jun and c-fos may have different roles in this process.