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. Author manuscript; available in PMC: 2009 Jun 11.
Published in final edited form as: Curr Opin Cell Biol. 2007 Dec 3;19(6):634–645. doi: 10.1016/j.ceb.2007.09.015

Figure 1.

Figure 1

The decision to proliferate or differentiate. Pdx1+ progenitor cells face a binary decision to either self-renew to expand the progenitor pool, or to undergo cell cycle arrest and begin the differentiation process. Progenitor cells that receive the Notch signal pathway via downstream effector Hes1 represses not only genes specific to differentiation but also the cell cycle arrest mediator, p57, thereby allowing the progenitor cells to continue to self-renew. Cells that do not receive the Notch signal upregulate p57 and exit the cell cycle to allow the differentiation process. The quiescent state of differentiated cell type is maintained by accumulation of cell cycle inhibitor p27.