Genetic obesity and the muscle satellite cell.

The nuclear content of skeletal muscles from lean and obese (ob/ob) male mice was investigated. Four lean and four ob/ob mice were examined at 2, 3, 5, 8, and 16 weeks of age. Differences in body weight between the two phenotypes were significant after 5 weeks of age. For all ages in the soleus and after 3 weeks of age in the gastrocnemius, muscle wet weight and length were less in ob/ob mice than in lean mice. Age did not influence the incidence of myonuclei in fiber cross sections for either muscle. Compared to lean mice the incidence of myonuclei per fiber cross section was significantly lower for ob/ob mice in the soleus muscle but not in the gastrocnemius muscle. The incidence of satellite cells in fiber cross sections and the percentage of nuclei within the basal lamina that were satellite cell nuclei decreased as age increased. Muscle fibers of ob/ob mice contained fewer myonuclei either because of shorter muscle length (gastrocnemius), or because of the combined effect of shorter muscle length and fewer myonuclei per unit length (soleus). The lower apparent number of myonuclei in the muscles of ob/ob mice was associated with a lower apparent number of satellite cells.