13-P043 Unraveling the complex mechanisms of spatial and temporal Sonic hedgehog expression in the limb

Activin A/TGFb, FGF, Wnt and BMP signalling are crucial for the self-renewal and early differentiation of human embryonic stem cells (hESCs). However, the mechanism of how they coordinate to regulate these two processes is unclear. To address this question, we treated hESCs with graded concentrations of these growth factors and their inhibitors separately and in combination and carried out comprehensive analysis on marker gene expression. We found that the expression of pluripotency marker genes and key lineage determination genes change in a highly coordinated manner depending on the combination and the dosage of growth factors. Similar to mESCs, inhibition of ERK1/2 reduced differentiation in hESCs. hESCs can maintain long-term selfrenew in the presence of ERK1/2 inhibitor in a chemically defined medium. Our results suggest that ERK1/2 signalling enhances hESCs differentiation. We propose a model that the balancing action between Activin A/TGFb, FGF, Wnt and BMP signalling determines hESC self-renewal or lineage choices.