Summary

Genetic differences between pluripotent stem cell lines causes variable activity of extra-cellular signaling pathways, which limits the reproducibility of directed differentiation protocols. Here we used human embryonic stem cells (hESCs) to interrogate how exogenously provided factors modulate endogenous signaling events during specification of foregut endoderm lineages. We find that TGF-β1 activates an OTX2 / LHX1 gene regulatory network that promotes anterior fate by antagonizing endogenous Wnt signaling. In contrast to Porcupine inhibition, the effects of TGF-β1 cannot be reversed by exogenous Wnt ligands, suggesting that induction of SHISA proteins and intracellular accumulation of Fzd receptors make TGF-β1 treated cells refractory to Wnt signaling. Subsequently, TGF-β1-mediated inhibition of Bmp- and Wnt-signaling suppresses liver- and promotes pancreas fate. However, pancreas differentiation is delayed by TGF-β1-induced CYP26A1 expression and inhibition of RA signaling. Our study thus identifies multiple mechanisms of crosstalk between major developmental signaling pathways during foregut patterning.