Regulation of Neural Specification from Human Embryonic Stem Cells by BMP and FGF

Inhibition of bone morphogenetic protein (BMP) signaling is required for vertebrate neural induction, and fibroblast growth factors (FGFs) may affect neural induction through phosphorylation at the linker region of Smad1, thus regulating BMP signaling. Here we show that human embryonic stem cells efficiently convert to neuroepithelial cells in the absence of BMP antagonists, or even when exposed to high concentrations of exogenous BMP4. Molecular and functional analyses revealed multiple levels of endogenous BMP signaling inhibition that may account for the efficient neural differentiation. Blocking FGF signaling inhibited neural induction, but did not alter the phosphorylation of the linker region of Smad1, suggesting that FGF enhances human neural specification independently of BMP signaling.