Abstract
Genetic differences between pluripotent stem cell lines cause variable activity of extracellular signaling pathways, limiting reproducibility of directed differentiation protocols. Here we used human embryonic stem cells (hESCs) to interrogate how exogenous factors modulate endogenous signaling events during specification of foregut endoderm lineages. We find that transforming growth factor β1 (TGF-β1) activates a putative human OTX2/LHX1 gene regulatory network which promotes anterior fate by antagonizing endogenous Wnt signaling. In contrast to Porcupine inhibition, TGF-β1 effects cannot be reversed by exogenous Wnt ligands, suggesting that induction of SHISA proteins and intracellular accumulation of Fzd receptors render TGF-β1-treated cells refractory to Wnt signaling. Subsequently, TGF-β1-mediated inhibition of BMP and Wnt signaling suppresses liver fate and promotes pancreas fate. Furthermore, combined TGF-β1 treatment and Wnt inhibition during pancreatic specification reproducibly and robustly enhance INSULIN+ cell yield across hESC lines. This modification of widely used differentiation protocols will enhance pancreatic β cell yield for cell-based therapeutic applications.