Figure 5. PcG repression of key transcription factors form epigenetic barriers between adult cell types.

(A) Our results suggest that PcG repression of key transcription factors help form the barriers between adult cell types, as depicted by Waddington's epigenetic landscape [41]. Conceptual model based on Fig. 1F. (B) Ectopic expression of endogenously repressed transcription factors overcomes these barriers to convert one cell type to another. For example, expressing Pdx1 in liver cells, where it is PcG repressed, converts them to pancreatic islet cells [21], where it is expressed. Expressing Cebpa in pancreatic islet cells, where it is PcG repressed, converts them to liver cells [22], where it is expressed. Positive autoregulation of transdifferentiation factors would stabilize the newly converted cell identity [7].