Myostatin and follistatin fail to modulate the myogenic differentiation of MDSCs, although the myostatin receptor is expressed. (A-D) Confluent WT MDSCs in myogenic medium were incubated in triplicate on six-well plates for 1 week with recombinant myostatin (B) or follistatin (C) or with no addition (A), and subjected to immunocytochemistry for MHC II (40×). The relative area occupied by the MHC II+ myotubes was estimated by quantitative image analysis (15 fields/well/three wells) (D). Cont, control; Mst, myostatin; Fst, follistatin. No myotubes were formed in confluent Mst KO under any treatment (not shown). (E) Western blot detection in confluent MDSCs from both mice strains of the expression of the ActRIIb and TGF-β1, in two successive passages for each cell line. Myostatin was not detected. MDSCs, muscle-derived stem cells; WT, wild type; Mst KO, myostatin knockout; MHC, myosin heavy chain.