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. Author manuscript; available in PMC: 2011 Oct 1.
Published in final edited form as: Trends Cell Biol. 2010 Aug 31;20(10):609–617. doi: 10.1016/j.tcb.2010.08.003

Figure 1. Cell fusion experiments showing the importance of DNA methylation as an epigenetic barrier for reprogramming.

Figure 1

Figure 1

(a) Human fibroblasts can be fused with mouse muscle cells to generate heterokaryons and the plethora of muscle transcription factors can induce the expression of human muscle genes that were repressed in fibroblasts. On the other hand, the fusion of HeLa human cancer cells with murine muscle cells cannot induce human muscle genes unless treated with the demethylating drug 5-Azacytidine prior to cell fusion [4, 5]. (TF): transcription factor.

(b) Human fibroblasts can also be fused with murine ES cells to generate heterokaryons and the factors present in the ES cells can reprogram the human Oct4 and Nanog promoters, causing DNA demethylation and gene expression. On the other hand, this reprogramming cannot occur when the mouse putative DNA demethylase, AID is silenced by RNAi [60].