Transcriptional analysis of mouse skeletal myofiber diversity and adaptation to endurance exercise.

Vertebrate skeletal myofibers are heterogeneous with respect to their metabolic, contractile and morphological properties. To better understand skeletal myofiber diversity and plasticity at the transcriptional level, we carried out a whole-genome gene expression analysis of skeletal muscles composed primarily of slow/oxidative fibers (soleus) and fast fibers (extensor digitorum longus, EDL). We also followed gene expression changes in plantaris muscles from mice undergoing voluntary wheel running, a protocol that triggers transformation of glycolytic fibers into oxidative ones. Microarray analysis identified 70 genes differentially expressed by 3-fold or greater in soleus vs. EDL muscles and 15 genes up-regulated in exercised vs. sedentary plantaris muscles. A subset of these results were verified by northern blot and/or real-time RT-PCR analyses. Our results expand knowledge of the differences among various types of skeletal myofibers and their adaptation to exercise at the transcriptional level.