Figure 1. Landmark events on the path to induced pluripotency.

It is thought that expression of the four reprogramming factors Oct4 (O), Klf4 (K), Sox2 (S), and cMyc (M) triggers a cascade of events within two to three weeks that leads to the iPS cell state. Stable and clonally expandable pre-iPS cells can also be generated as a by-product of this process and can enter the fully re-programmed state upon addition of indicated molecules.