Ephrin - A 5 promotes bovine muscle progenitor cell migration before mitotic activation 1

Satellite cells are the resident stem cell population of adult skeletal muscle tissue that is responsible for growth and regeneration. The cells typically congregate near the tips of the muscle fi bers and in close proximity to the neural muscular junction (NMJ). Ephrin-A5 is a chemotactic molecule that participates in the correct positioning and formation of the NMJ. The objective of the experiment was to examine the effects of ephrin-A5 signaling on bovine satellite cell (BSC) biology. Primary cultures of BSC demonstrate changes in velocity with time in culture that is unique to the Paired box protein 7 (Pax7):Myogenic factor 5 (Myf5) subpopulation. Treatment of the BSC with ephrin-A5 causes a reduction (P < 0.05) in velocity with a concomitant increase (P < 0.05) in directed migration. The chemoattractant properties of ephrin-A5 occur before myogenic differentiation 1 (MyoD) expression in the myogenic precursors and are abrogated after their differentiation to committed myoblasts. Ephrin-A5 induced migration appears to require components of the Ras homolog gene family member A (RhoA) and Rho-associated protein kinase (ROCK) signaling machinery. Supplementation of culture media with a chemical ROCK inhibitor suppressed (P < 0.05) ephrin-A5 initiated BSC migration. These results contrast with treatment of BSC with hepatocyte growth factor (HGF), a key modulator of myogenic and motogenic activity. Treatment of BSC with HGF had no effect on cell motility or migration immediately after culture establishment. Twenty-four hours after culture establishment, BSC demonstrated an increase (P < 0.05) in transwell migration toward HGF. These results document that temporal and spatial gradients of chemokines and growth factors participate in the localization of BSC within the niche.