4.1. Cell cultures

Normal human immortalized myoblasts (MB135) derived from the muscle biopsy of a healthy individual with the normal number of D4Z4 repeats and MB135 myoblasts with Doxycycline-inducible DUX4 expression (MB135-DUX4) [2]were a kind gift of Dr.Stephen Tapscott. Cells were cultured at 37 °C, 5% CO2 in the growth medium composed of 60% DMEM (Sigma Aldrich, D5796), 25% 199 Medium (Sigma Aldrich, M4530) and 15% FBS (Life technology, 10270) supplemented with 0.5 ng/ml bFGF (Life technology, PHG0026), 0.2 ug/ml Dexamethasone, 100 units/mL penicillin and 100 μg/ml streptomycin (Thermo Fisher, 15140122).