Expression of fos and jun genes in human skeletal muscle after exercise

It is believed that the induction of the fos and jun gene family of transcription factors might be at the origin of genetic events leading to the differential regulation of muscle-specific genes. We have investigated the effect of a 30-min running bout in untrained subjects on the expression of the mRNAs of all members of the fos and jun gene families, including c-fos, fosB, fosBdel, fra-1, and fra-2 as well as c-jun, junB, and junD. While the fos family members were transiently upregulated 10- to 20-fold (an exception being fra-2) the induction of the jun family members was up to 3-fold only. The induction of c-fos could also be demonstrated at the protein level. Both c-fos and c-jun mRNAs were coinduced in muscle fiber nuclei. The induction was not restricted to a particular fiber type, as expected from established muscle fiber recruitment schemes, but followed a "patchy" pattern confined to certain regions of the muscle. The signals leading to the expression of these immediate early genes are therefore unclear.