POU5F1 and facioscapulohumeral muscular dystrophy: To directly determine whether the transition between DUX4-fl and DUX4-s expression is developmentally regulated, we generated induced pluripotent stem (iPS) cells from FSHD and control fibroblasts by expression of SOX2, OCT4, and KLF4 transcription factors from Moloney murine leukemia virus vectors [15].