Fig. 4. TGF-β and Wnt signaling pathways.

This figure summarizes the TGF-β and Wnt signaling pathways, which are mechanistically leveraged to reprogram all cell types. All TGF-β-related signaling follow a mechanism that is suppressed by small molecules that inhibit the TGF-β receptor. In contrast, Wnt signaling is inhibited by β-catenin phosphorylation by GSK-3, but small molecules can be used to inhibit GSK-3, thereby allowing β-catenin to enter into the nucleus to initiate transcription. Expression of TGF-β target genes is therefore suppressed in all cell types during reprogramming, and the target genes of Wnt signaling are transcribed.