Figure 3. How Myc and cell cycle regulatory controls intersect with different stages of reprogramming.

Cells subject to reprogramming cues undergo a three step process as they transition towards iPSCs. The initial step involves Myc which causes global changes in genes expression, including repression of differentiation genes, without induction of pluripotency genes (see Sridharan et al., 2009; Zhao and Daley et al., 2008; Mahereli et al., 2008; Judson et al., 2009; Silva et al., 2008; Mikkelesen et al., 2008). Other reprogramming factors, possibly in combination with Myc (Huangfu et al., 2008), then drive the formation of partially reprogrammed cells (PRCs) and then fully reprogrammed iPSCs. Roles for Myc have also been defined in the maintenance of iPSCs and other pluripotent cell types, some of which are directly related to cell cycle control (Cartwright et al., 2005; Wang et al., 2008; Judson et al., 2009; Hanna et al., 2009). Possible points at which Myc could be involved, but for which there are no solid data, are indicated by broken arrows. For example, it is likely that for reprogramming cells need to be constantly kept cycling by Myc.