FGF signaling via MAPK is required early and improves Activin A-induced definitive endoderm formation from human embryonic stem cells

► Deep study the FGF signaling role during DE specification in the context of hESCs. ► DE differentiation from hESCs has an early dependence on FGF signaling. ► A serum-free DE protocol is developed based on the findings. ► The DE cells showed potential to differentiate into pancreatic progenitor cells.