On day 3, the medium was changed to RPMI 1640/B27− medium supplemented with 5 µM IWP4 (Stemgent, Beltsville, MD, USA). On day 5, the medium was changed again to RPMI 1640/B27− medium to remove the Wnt-signaling inhibitor. The cells were then maintained in RPMI 1640/B27− ...