NODAL and teratoma: Thus, these data show that the differentiation strategy of modulating prodifferentiation and antiproliferative signals by stimulating the Activin A/Nodal or BMP signaling pathways or inhibiting the MEK/ERK and PI3K/Act signaling pathways during the time window from 5 to 10 days of ES cell differentiation may be effective for significantly reducing of the number of cells that initiate teratoma development (Figure 7).