FIGURE 1

Generation of iPS cells by retroviral transfection of four transcription factors: several groups used the depicted strategy to generate pluripotent stem cells from terminally differentiated somatic cells. As shown in the figure, mice carrying Nanog-GFP or Oct4-GFP were first generated. Embryonic or somatic fibroblast cells were isolated from these mice and cultured in vitro. When transfected with the four transcription factors, Oct4/Sox2/cMyc/Klf4, some of the differentiated fibroblast cells can be reprogrammed back to the embryonic state and thus start to express Nanog or Oct4 in conjunction with GFP. GFP can then be used as a selection marker to purify the single cell colonies which were expanded into iPS cell clones. These selected iPS cells were characterized for their ES-like properties via different methods, such as the expression of ES cell marker genes, their epigenetic properties and their developmental potentials. The results showed that the four transcription factors could indeed reprogram terminally differentiated cells into pluripotent stem cells.