(E) Immunoblots of phosphorylated Smad2 (P-Smad2), total Smad2, MYC, PMEPA1, OTX2 and β-actin were performed on extracts from cell cultures of PDX4, PDX3 and PDX7 treated by either DMSO (vehicle), LY364947, SB431542, blocking antibody against ActivinB (Ab α-ActB), Follistatin, PBS or ActivinB for 24 hours. 