Fig. 4.

Satellite cell activation process is regulated through nitric oxide (NO)-mediated hepatocyte growth factor (HGF) release from the extra-cellular matrix (ECM). (A) Transverse cross-section through a mouse extensor digitorum longus muscle stained with antibodies against laminin (red) marking the basal lamina of individual myofibres. Quiescent Pax7⁺ (green) satellite cells are seen beneath the basal lamina. (B) Recently formed satellite cell doublet marked through Pax7 expression (green) on the surface of a mature adult myofibre. DAPI (blue) stains all the nuclei present in A and B. (C) Schematic showing how the regulation of satellite cell proliferation is regulated through NO production within the damaged myofibre, causing the activation of matrix metalloproteinases, the breakdown of the surrounding ECM and the subsequent release of bound HGF. HGF induces satellite cell progeny proliferation, thus regulating the regeneration response to injury.