Fig. 2. Immunoblots of muscle extracts from sedentary and exercising desMEF2-lacZ mice. (A) Expression of the lacZ transgene was detected only in soleus muscles of sedentary animals (0 days), but was up-regulated by running (3–14 days) in muscles recruited for this locomotor activity (soleus, plantaris, W. vastus but not EDL). Each lane was loaded with muscle extracts prepared from a pool of five animals (10 muscles) and comparable recovery and transfer of each sample was assessed by anti-tubulin antibody. (B) Up-regulation of desMEF2-lacZ transgene expression in plantaris muscle by running (3–14 days) occurs without detectable changes in the abundance of major MEF2 isoforms or of the activated (phosphorylated) form of p38 MAPK.