Fig. 1

Graphical representation of key events during postnatal skeletal muscle growth (a) and indication of different types of cell nuclei within mature muscle tissue (b) a In mice, skeletal muscle post-natal development is comprised of 2 main growth periods. Until 3 weeks of age (left panel), satellite cells proliferate, followed by the incorporation of newly generated myonuclei into myofibres, resulting in hyperplasia. The rate of proliferation and fusion gradually declines during this period. After 3 weeks of age (right panel), the proliferation of satellite cells ceases and there is no additional incorporation of myonuclei into the myofibres. Past 3 weeks of age, muscle growth therefore results from hypertrophy only. By 3 weeks of postnatal age, the neuromuscular junction (NMJ) and innervation have matured and the vascular system and the extra-cellular matrix (ECM) are considered developed. b Longitudinal section of adult mouse limb muscle stained with haematoxylin and eosin. Histology shows that the bulk of the mature myofibre is occupied by sarcoplasm filled with contractile proteins, with muscle nuclei located at the surface of the myofibre. The interface with the interstitial connective tissue shows a blood vessel and various cell types within the extracellular matrix