Critical factors for cardiac reprogramming.

Cellular reprogramming achieved by somatic nuclear transfer or cell fusion has long been recognized.1 The potency of specific transcription factors as cell fate determinants was first demonstrated by the discovery of MyoD, a master regulator for skeletal muscle differentiation, and by the subsequent identification of several genes as lineageconverting transcription factors in blood cells.2,3 These pioneering works led to the landmark study by the Yamanaka laboratory that demonstrated the generation of induced pluripotent stem cells from fibroblasts by transducing four stem cell-enriched transcription factors, Oct4, Sox2, Klf4, and c-Myc.4,5 Numerous subsequent improvements in techniques and additional factors have increased the efficiency and robustness of the technology, and such enhancements continue, as do analyses of the similarities and differences of induced pluripotent stem cells to embryonic stem cells. Increasingly efficient differentiation protocols now permit us to make significant quantities of many individual cell types from induced pluripotent stem cells.