Satellite cell activation and populations on single muscle-fiber cultures from adult zebrafish (Danio rerio).

Satellite cells (SC), stem cells in skeletal muscle, are mitotically quiescent in adult mammals until activated for growth or regeneration. In mouse muscle, SC are activated by nitric oxide (NO), hepatocyte growth factor (HGF) and the mechanically induced NO-HGF signaling cascade. Here, the SC population on fibers from the adult, ectothermic zebrafish and SC responsiveness to activating stimuli were assessed using the model system of isolated fibers cultured at 27°C and 21°C. SC were identified by immunostaining for the HGF receptor, c-met, and activation was determined using bromodeoxyuridine uptake in culture or in vivo. In dose-response studies, SC activation was increased by treatment with the NO-donor drug isosorbide dinitrate (1mM) or HGF (10 ng/mL) to maximum activation at lower and higher concentrations, respectively, than in previous studies of mouse fibers. HGF-induced activation was blocked by anti-c-met antibody, and reduced by culture at 21°C. The effect of cyclical stretch (3 hr at 4 cycles per min) increased activation and was blocked by NOS inhibition and reduced by culture at 21°C. The number of c-met+ SC/fiber increased rapidly (by 3 hr) after stretching. The character of signaling in SC activation on zebrafish fibers, in particular temperature-dependent responses to HGF and stretch gives new insights into the influence of ectothermy on regulation of muscle growth in teleosts and suggests use of the single-fiber model system to explore the basis of fiber hyperplasia and the conservation of regulatory pathways between species. [ABSTRACT FROM AUTHOR]