24 well plates (3×104cells/well) in proliferation medium and
then the next day switched to myogenic differentiation medium (DMEM supplemented
with 2% FBS and 1% PS). Three days after plating, immunocytochemical staining
for fast myosin heavy chain (MyHCf) was performed. The cells were fixed in cold
methanol (−20°C) for 5 minutes, blocked with 10% donkey serum
(Jackson ImmunoResearch, 017-000-121) for 1 hour, and then incubated with a
mouse anti-MyHCf (Sigma-Aldrich, M4276, 1:250) antibody for 2 hours at RT. The
primary antibody was detected with an Alexa 594-conjugated anti-mouse IgG
antibody (Invitrogen, A21203, 1:500;) for 30 minutes. The nuclei were revealed
by 4, 6-diamidino-2-phenylindole (DAPI, D9542, 100ng/ml, Sigma-Aldrich)
staining. The percentage of differentiated myotubes was quantified as the number
of nuclei in MyHCf positive myotubes relative to the total number of nuclei.