Rows of similar colors represent studies that used similar strategies for reprogramming.
This timeline summarizes the key strategies and techniques used to develop i PS cells in the first five years after Yamanaka et al.'s 2006 breakthrough.
(4)A small subset of the transfected cells become i PS cells and generate ES-like colonies.
i PSCs are typically derived by introducing products of specific sets of pluripotency-associated genes, or "reprogramming factors", into a given cell type.
i PSC derivation is typically a slow and inefficient process, taking 1–2 weeks for mouse cells and 3–4 weeks for human cells, with efficiencies around 0.01%–0.1%.
However, considerable advances have been made in improving the efficiency and the time it takes to obtain i PSCs.
Additional genes, however, including certain members of the Klf family (Klf1, Klf2, Klf4, and Klf5), the Myc family (c-myc, L-myc, and N-myc), Nanog, and LIN28, have been identified to increase the induction efficiency.
The table at right summarizes the key strategies and techniques used to develop i PS cells in the first five years after Yamanaka et al.'s 2006 breakthrough.
While this combination is most conventional in producing i PSCs, each of the factors can be functionally replaced by related transcription factors, mi RNAs, small molecules, or even non-related genes such as lineage specifiers.Upon introduction of reprogramming factors, cells begin to form colonies that resemble pluripotent stem cells, which can be isolated based on their morphology, conditions that select for their growth, or through expression of surface markers or reporter genes.Induced pluripotent stem cells were first generated by Shinya Yamanaka's team at Kyoto University, Japan, in 2006.However, since the generation of embryonic stem cells involves destruction (or at least manipulation) of the pre-implantation stage embryo, there has been much controversy surrounding their use.Further, because embryonic stem cells can only be derived from embryos, it has so far not been feasible to create patient-matched embryonic stem cell lines.